EPA/600/2-87/040
May 1987
STABILIZATION OF SEWAGE SLUDGE BY
TWO-PHASE ANAEROBIC DIGESTION
by
S. Ghosh
M. P. Henry
A. Sajjad
Institute of Gas Technology
Chicago, Illinois 60616
Cooperative Agreement No. CR 809982
Project Officers
Harry E. Bostian
B. Vincent Salotto
Joseph B. Farrell
Wastewater Research Division
Water Engineering Research Laboratory
Cincinnati, Ohio 45268
U.S. Envfrohmentaf Protection Agency
WATER ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
REPRODUCEDBY
U.S. DEPARTMENTOF COMMERCE
NATIONAL TECHNICAL
INFORMATION SERVICE
SPRINGFIELD, VA 22161
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DISCLAIMER
The information in this document has been funded wholly or in part by the
United States Environmental Protection Agency under assistance agreement
number CR 809982 to the Institute of Gas Technology. It has been subject to
the Agency's peer and administrative review, and it has been approved for
publication as an EPA document. Mention of trade names or commercial products
does not constitute endorsement or recommendation for use.
ii
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FOREWORD
The U.S. Environmental Protection Agency is charged by Congress with
protecting the Nation's land, air, and water systems. Under a mandate of
national environmental laws, the agency strives to formulate and implement
actions leading to a compatible balance between human activities and the
ability of natural systems to support and nurture life. The Clean Water Act,
the Safe Drinking Water Act, and the Toxic Substances Control. Act are three of
the major congressional laws that provide the framework for restoring and
maintaining the integrity of our Nation's water, for preserving and enhancing
the water we drink, and for protecting the environment from toxic substances.
These laws direct EPA to perform research to define our environmental
problems, measure the impacts, and search for solutions.
;,;•) The Water Engineering Research Laboratory is that component of EPA's
^ Research and Development program concerned with preventing, treating, and
|v managing municipal and industrial wastewater discharges; establishing
,^ practices to control and remove contaminants from drinking water and to
?~ prevent its deterioration during storage and distribution; and assessing the
_A nature and controllability of releases of toxic substances to the air, water,
4 and land from manufacturing processes and subsequent product uses. This
^r publication is one of the products of that research and provides a
communication link between the researcher and the user community.
The research described in this report was concerned with evaluation of
alternative approaches to anaerobic digestion, a process commonly used on the
residual stream from wastewater treatment. The principal approach studied was
that of separating the acid and methane forming phases by using two digestion
vessels rather than one. The effects of varying temperature and other
operating parameters, and of adding enzymes to the process, were also
investigated.
Francis T. Mayo, Director
Water Engineering Research Laboratory
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ABSTRACT
Laboratory research was conducted to study the performance characteris-
tics of separate acid- and methane-phase anaerobic sludge digesters and the
overall two-phase systems under mesophilic and therraophilic fermentation
conditions at several levels of hydraulic flow-through and organic loading
rates, culture pH, and feed solids consistency. Chicago municipal wastewater
sludges were used as digester feeds. The sludges were chemically and
biochemically characterized, and theoretical digestion efficiencies and
anaerobic biodegradability factors were determined. Performances of single-
stage and two-phase systems using continuous-flow, continuously-stirred tank
reactor (CFCSTR) digesters were studied under a variety of comparable
operating conditions. The effects of three important variables (pH, hydraulic
residence time, and temperature) on acid-phase sludge digestion were
determined based on the results of digestion runs conducted according to a
factorial experimental design. In a more applied part of the research, novel
upflow digesters which were mixed by indigenous gas production and had high
solids retention times were used in lieu of the CFCSTR digesters to develop an
advanced two-phase system. The study also included investigation of the
effects of cellulase-cellobiase pretreatment of the two-phase process sludge
feed and of lipase treatment of the acid-phase digester on liquefaction,
acidification, and gasification efficiencies.
The CFCSTR two-phase process performed better than CFCSTR single-stage
digestion under all operating conditions. The performance of the two-phase
process was further enhanced by using the upflow digesters and cellulase-
cellobiase pretreatment of the feed sludge in combination with direct lipase
treatment of the acid-phase culture.
This report was submitted in fulfillment of Cooperative Agreement No.
CR 809982 by the Institute of Gas Technology under the sponsorship of the U.S.
Environmental Protection Agency. This report covers the period October 1,
1982, to November 30, 1985, and work was completed as of November 30, 1985.
IV
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CONTENTS
Abstract
Figures viil
Tables x
Abbreviations and Symbols xx
Acknowledgment xxi
1. Introduction 1
Project objectives... 2
2. Results and Conclusions • • •• 4
Kinetic analyses of single-stage and two-phase
digestion • 4
Chemical characteristics of digester feeds 5
Theoretical efficiencies and chemical and biochemical
reactivities of digester feeds 5
Single-stage CFCSTR digestion 6
CFCSTR two-phase digestion 7
Process comparison: CFCSTR single-stage versus CFCSTR
two-phase 9
Characteristics of thermophilic digestion 10
Effects of pH, HRT, and temperature on acid-phase
digestion. 11
Optimum operating conditions for two-phase digestion 12
Advanced mesophilic two-phase digestion with novel
upflow reactors *• •• 12
Advanced thermophilic two-phase digestion with novel
upflow reactors 13
Thermo-thermo-thermo three-stage digestion 13
Meso-meso two-phase CFCSTR digestion of enzyme-treated
sludge • 14
3. Recommendations. 15
4. Background « 16
Utility of anaerobic digestion 16
Conventional sludge digestion processes 17
Disadvantages and limitations of conventional digestion.. 19
Process improvement needs and approaches. 20
Two-phase anaerobic digestion 21
5. Experimental Plan. • 44
Digester feeds - 44
Digestion systems 44
Digestion runs 44
6. Materials and Methods 50
Process feeds. 50
Apparatus for digestion systems..... 53
Chemical analyses.. • • 61
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CONTENTS (Continued)
Anaerobic digestibility potential test 74
Enzymatic pretreatment of sludge. 75
System start-up and operation 76
7. Chemical Characterization of Process Feeds... 90
Chemical characterization of unprocessed raw sludges 90
Chemical characterization of digester feed sludge 90
8. Stability of Digester Feeds 106
9. Theoretical Gas and Methane Yields of Digester Feed Sludge.... 108
Theoretical yields based on elemental analysis.. 108
Theoretical methane yields based on theoretical
sludge COD 108
Theoretical methane yields based on analytical COD 110
Theoretical methane yields based on calorific value 110
10. Biodegradability of Digester Feed Sludge 116
11. Performance of Single-Stage CFCSTR Digesters 120
Experimental runs 120
Single-stage CFCSTR process performance 120
Comparison of CPL conversions under mesophilic
conditions 129
Comparison of CPL conversions under thermophilic
conditions 129
Mass balances 13U
12. Performance of CFCSTR Two-Phase Digestion Systems 131
Experimental runs 131
Performance of meso-meso systems 131
Performance of meso-thermo systems.... 137
Performance of thermo-thermo systems 141
Comparison of meso—meso, meso-thermo, and thermo—thermo
two-phase systems 141
13. Process Comparison: CFCSTR Single-Stage Versus CFCSTR
Two-Phase 149
Process comparison at a 15-day HRT 149
Process comparison at a 7-day HRT 152
Process comparison at a 3-day HRT 152
Characteristics of thermophilic digestion 155
14. Performance of Acid-Phase Runs: Parametric-Effect Studies.... 163
Experimental runs 163
Mesophilic acid-phase runs. 163
Thermophilic acid-phase runs 171
Effect of temperature on acid-phase digestion 178
Analysis of variance and statistical inference 181
15. Advanced Two-Phase Digestion Tests: Applied Studies 186
Two-phase process improvement with novel upflow
reactors 186
Thermo-thermo-thermo upflow three-stage digestion 203
Final thermo-thermo upflow two-phase run. 204
vi
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CONTENTS (Continued)
Two-phase process improvement with enzyme treatment
of digester feed 208
References 214
Appendices
A. Feed Slurry Analyses 221
B. Effluent Analyses for Single-Stage CFCSTR Digesters 231
C. Effluent Analyses for Two-Phase CFCSTR Digestion Systems 251
D. Effluent Analyses for Parametric-Effect Acid-Phase Digesters.. 283
E. Effluent Analyses for Advanced Two-Phase Digestion Systems.... 313
F. Feed Sludge Lots and Batches Used During Steady-State
Digestion Runs. 331
G. Comparison of Calculation of Volatile Solids by MOP-16
Formula With Material Balance Method 333
VI1
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FIGURES
Number Page
1 Two-phase anaerobic digestion process concept 22
2 Physical model of the two-phase anaerobic digestion process.... 24
3 Efficiency of acidogenic conversion of a soluble carbohydrate
substrate by complete-mix and high-SRT novel digesters....... 25
4 Efficiency of acidogenic conversion of municipal sludge
volatile solids by complete-mix and high-SRT novel
digesters 26
5 Operating characteristics of a complete-mix acid-phase digester
charged with 70 g VS/L sewage sludge 30
6 Operating characteristics of a complete-mix methane digester
charged with effluents from an acid-phase digester operated
with 70 g VS/L sewage sludge at a 2-day HRT 31
7 Operating characteristics of a single-stage complete-mix
conventional digester charged with 70 g VS/L sewage sludge... 32
8 Leach-bed two-phase anaerobic digestion 41
9 Schematic diagram of CFCSTR two-phase anaerobic digestion
system 58
10 Schematic diagram of two-phase upflow digestion system for
applied studies 60
11 Effect of feeding frequency on specific growth rates in a
CFCSTR digester operated at a 15-day HRT 79
12 Effect of feeding frequency on specific growth rates in a
CFCSTR digester operated at a 2-day HRT 80
13 Correlation between carbon and volatile solids concentrations
of raw and digested sewage sludges. 88
14 Total digester gas and methane yields from anaerobic
digestibility potential (ADP) test conducted at 35°C
with Lot 16, Batch 1 Hanover Park sludge 117
viii
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FIGURES (Continued)
Number
15 Comparison of organic reduction efficiencies of CFCSTR
single-stage and two-phase anaerobic digestion systems 151
16 Effect of pH on mesophilic acid-phase digestion of Hanover
Park sludge at an HRT of about 2.2 days and a loading
rate of about 23 kg VS/m3-day 16b
17 Effect of pH on thermophilic acid-phase digestion of Hanover
Park sewage sludge at an HRT of about 2.1 days and a
loading rate of about 25 kg VS/m3-day 177
18 Operating conditions of the thermo-thermo two-phase system
fed with a mixture of Downers Grove primary and Stickney
activated sludge 205
19 Methane yield and production rate from the thermo-thermo
two-phase system fed with a mixture of Downers Grove
primary and Stickney activated sludges 2(Jb
20 Methane content and effluent volatile acids of the
thermo-therrao two-phase system fed with a mixture of
Downers Grove primary and Stickney activated sludges 207
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TABLES
Number Page
1 STEADY-STATE PERFORMANCE OF CONVENTIONAL SINGLE-STAGE
MESOPHILIC (35°C) DIGESTION OF SEWAGE SLUDGE IN
CFCSTR REACTORS 20
2 ESTIMATED KINETIC CONSTANTS FOR MESOPHILIC (37°C)
ACIDOGENIC AND METHANOGENIC CULTURES GROWN ON SOLUBLE
AND PARTICULATE SUBSTRATES 28
3 COMPARISON OF THEORETICAL PERFORMANCES OF CFCSTR
SINGLE-STAGE AND TWO-PHASE DIGESTION OF SEWAGE SLUDGE 33
4 HIGH-RATE AND TWO-PHASE MESOPHILIC (35°C) DIGESTION
OF SOFT-DRINK BOTTLING WASTE 36
5 PERFORMANCE OF AN ADVANCED TWO-PHASE UPFLOW MESOPHILIC
(35°C) DIGESTION SYSTEM AT AN HRT OF 5.9 DAYS WITH A
5.8 WT % TS-CONTENT FEED 39
6 COMPARISON OF HYPOTHETICAL CONVENTIONAL AND TWO-PHASE
UPFLOW MESOPHILIC DIGESTION SYSTEMS TO STABILIZE AND GASIFY
91 METRIC TONS/DAY OF SLUDGE AT AN HRT OF 5.5 DAYS 40
7 DESIGN OPERATING CONDITIONS FOR PROCESS COMPARISON
DIGESTION RUNS CONDUCTED WITH CFCSTR DIGESTERS 46
8 DESIGN OPERATING CONDITIONS FOR PARAMETRIC-EFFECTS
CFCSTR ACID-PHASE DIGESTION RUNS 48
9 STEADY-STATE OPERATING CONDITIONS FOR ADVANCED STUDIES FOR
MESOPHILIC (BOTH PHASES) TWO-PHASE DIGESTION RUNS 49
10 COLLECTION, PROCESSING, AND SOLIDS ANALYSES OF VACUUM-
FILTERED ACTIVATED SLUDGE CAKE FROM STICKNEY 52
11 COLLECTION, PROCESSING, AND SOLIDS ANALYSES OF
DOWNERS GROVE PRIMARY SLUDGE 53
12 LIST OF CFCSTR DIGESTERS USED FOR SINGLE-STAGE DIGESTION
RUNS FOR PROCESS COMPARISON STUDIES 54
13 LIST OF CFCSTR DIGESTERS USED FOR TWO-PHASE DIGESTION
RUNS FOR PROCESS COMPARISON STUDIES. 55
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TABLES (Continued)
Number Page
14 LIST OF DIGESTERS USED FOR CFCSTR PARAMETRIC-EFFECTS
ACID-PHASE DIGESTION RUNS .................................... 56
15 LIST OF DIGESTERS USED FOR ADVANCED TWO-PHASE DIGESTION
RUNS .................... ..................................... 57
16 SAMPLE COLLECTION AND PROCESSING PROTOCOL ...................... 62
17 EFFECT OF SAMPLE PREPARATION ON TOTAL COD DETERMINATIONS
OF FEED AND EFFLUENT SLURRIES FROM CFCSTR MESOPHILIC
AND THERMOPHILIC ACID-PHASE DIGESTERS OPERATED WITH
HANOVER PARK SLUDGE .......................................... 64
18 LIST OF PHYSICAL AND CHEMICAL ANALYSES/MEASURERMENTS,
METHOD OF DETERMINATION, AND THE INTENDED USE OF THE
RESULTING DATA ....... . ....................................... 66
19 TOTAL CARBOHYDRATE CONCENTRATIONS IN HANOVER PARK SLUDGE
AS DETERMINED BY THE ANTHRONE AND THE PHENOL-SULFURIC
ACID METHODS ............................................ ..... 70
20 RECOVERIES OF COMMON LIPIDS BY THE SOXHLET, ASM, AND
O'ROURKE METHODS ............................................. 73
21 RECOVERIES OF SLUDGE LIPIDS AND MOTOR OIL BY THE
SOXHLET, ASM, AND O'ROURKE METHODS .................. . ........ 74
22 ROUTINE PROCESS MONITORING SCHEDULE ....................... ..... 82
23 STEADY-STATE CRITERIA .............. ...... ......... . ............ 83
24 REDUCED OPERATING AND PERFORMANCE PARAMETERS ................... 84
25 VOLATILE SOLIDS AND CARBON CONTENTS OF RAW AND
DIGESTED SEWAGE SLUDGES .......... ............................ 89
26 COLLECTION, PROCESSING, AND SOLIDS ANALYSES OF
HANOVER PARK RAW SLUDGE ........................... . .......... 91
27 COLLECTION, PROCESSING, AND SOLIDS ANALYSES OF
DOWNERS GROVE RAW PRIMARY SLUDGE ............................. 94
xi
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TABLES (Continued)
Number page
28 COLLECTION, PROCESSING, AND SOLIDS ANALYSES OF
STICKNEY RAW ACTIVATED SLUDGE 94
29 CHEMICAL CHARACTERISTICS OF UNPROCESSED RAW SLUDGES 95
30 SOLIDS ANALYSES OF DIGESTER FEED SLURRIES 96
31 DIRECT MEASUREMENTS OF TOTAL, SUSPENDED AND DISSOLVED
SOLIDS CONTENTS OF DIGESTER FEED SLURRIES 97
32 ELEMENTAL ANALYSES AND CALORIFIC VALUES OF DIGESTER FEED
SLURRIES PREPARED FROM HANOVER PARK SLUDGE 99
33 CHEMICAL OXYGEN DEMAND ANALYSES FOR DIGESTER SLURRIES 100
34 AMMONIA AND ORGANIC NITROGEN CONTENTS OF DIGESTER
FEED SLURRIES 102
35 ACID-BASE CHARACTERISTICS OF DIGESTER FEED SLURRIES 103
36 CRUDE PROTEIN, TOTAL CARBOHYDRATE, AND LIPIDS ANALYSES OF
DIGESTER FEED SLURRIES PREPARED FROM HANOVER PARK SLUDGE 105
37 TIME PROFILES OF SOLIDS AND VOLATILE ACIDS ANALYSES OF
DIGESTER FEED SLURRY WHICH WAS PUMPED CONTINUALLY
FROM THE REFRIGERATED (4°C) FEED RESERVOIR TO THE
ANAEROBIC DIGESTER 107
38 THEORETICAL GAS AND METHANE YIELDS OF HANOVER PARK SLUDGE
BASED ON ELEMENTAL ANALYSES 109
39 THEORETICAL METHANE YIELDS OF HANOVER PARK SLUDGE BASED
ON THEORETICAL CARBONACEOUS COD Ill
40 THEORETICAL METHANE YIELDS OF HANOVER PARK SLUDGE BASED
ON ANALYTICAL CARBONACEOUS COD'S 112
41 THEORETICAL METHANE YIELD OF HANOVER PARK SLUDGE BASED
ON CALORIFIC VALUE 112
42 SUMMARY OF THEORETICAL METHANE YIELDS FOR HANOVER PARK
SLUDGE 113
xii
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TABLES (Continued)
Number
43 DEPENDENCE OF POTENTIAL METHANE YIELD OF HANOVER PARK SLUDGE
ON PROTEIN, CARBOHYDRATE, AND LIPID CONTENTS 115
44 GAS AND METHANE PRODUCTIONS FROM MESOPHILIC ANAEROBIC
DIGESTIBILITY POTENTIAL TEST CONDUCTED WITH LOT 16
BATCH 1 HANOVER PARK SLUDGE 118
45 VOLATILE SOLIDS REDUCTION AND MASS BALANCES FOR THE
MESOPHILIC ADP TEST CONDUCTED WITH HANOVER PARK
ACTIVATED-PRIMARY SLUDGE 119
46 ACTUAL OPERATING CONDITIONS FOR SINGLE-STAGE CFCSTR
DIGESTERS FED WITH HANOVER PARK SLUDGE 121
47 EFFECT OF HRT ON STEADY-STATE GAS PRODUCTIONS FROM
MESOPHILIC CFCSTR SINGLE-STAGE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE 122
48 EFFECT OF HRT ON THE QUALITY OF STEADY-STATE EFFLUENTS
FROM MESOPHILIC CFCSTR SINGLE-STAGE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE 123
49 EFFECT OF HRT ON STEADY-STATE ORGANIC REDUCTION EFFICIENCIES
OF MESOPHILIC CFCSTR SINGLE-STAGE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE 124
50 EFFECT OF HRT ON STEADY-STATE GAS PRODUCTIONS FROM
THERMOPHILIC CFCSTR SINGLE-STAGE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE 125
51 EFFECT OF HRT ON THE QUALITY OF STEADY-STATE EFFLUENTS FROM
THERMOPHILIC CFCSTR SINGLE-STAGE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE 126
52 EFFECT OF HRT ON STEADY-STATE ORGANIC REDUCTION EFFICIENCIES
OF THERMOPHILIC CFCSTR SINGLE-STAGE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE 127
53 COMPARISON OF STEADY-STATE PERFORMANCES OF MESOPHILIC AND
THERMOPHILIC CFCSTR SINGLE-STAGE DIGESTERS OPERATED WITH
HANOVER PARK SLUDGE 128
xiii
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TABLES (Continued)
Number
54 ACTUAL STEADY-STATE OPERATING CONDITIONS FOR PROCESS
COMPARISON CFCSTR TWO-PHASE DIGESTION SYSTEMS OPERATED
WITH HANOVER PARK SLUDGE 132
55 EFFECT OF HRT ON STEADY-STATE GAS PRODUCTIONS FROM MESO-MESO
CFCSTR TWO-PHASE DIGESTION OF HANOVER PARK SLUDGE 133
56 EFFECT OF HRT ON THE QUALITY OF STEADY-STATE EFFLUENTS FROM
MESO-MESO CFCSTR TWO-PHASE SYSTEMS OPERATED WITH
HANOVER PARK SLUDGE 134
57 EFFECT OF HRT ON STEADY-STATE ORGANIC REDUCTION EFFICIENCIES
OF MESO-MESO CFCSTR TWO-PHASE SYSTEMS OPERATED WITH
HANOVER PARK SLUDGE 135
58 EFFECT OF HRT ON GAS PRODUCTIONS FROM STEADY-STATE
MESO-THERMO CFCSTR TWO-PHASE SYSTEMS OPERATED WITH
HANOVER PARK SLUDGE 138
59 EFFECT OF HRT ON STEADY-STATE EFFLUENT QUALITIES OF
MESO-THERMO CFCSTR TWO-PHASE SYSTEMS OPERATED WITH
HANOVER PARK SLUDGE -. 139
60 EFFECT OF HRT ON STEADY-STATE ORGANIC REDUCTION EFFICIENCIES
OF MESO-THERMO CFCSTR TWO-PHASE SYSTEMS OPERATED WITH
HANOVER PARK SLUDGE 140
61 EFFECT OF HRT ON STEADY-STATE GAS PRODUCTIONS FROM CFCSTR
THERMO-THERMO TWO-PHASE SYSTEMS OPERATED WITH
HANOVER PARK SLUDGE 142
62 EFFECT OF HRT ON STEADY-STATE EFFLUENT QUALITIES OF
THERMO-THERMO CFCSTR TWO-PHASE SYSTEMS OPERATED WITH
HANOVER PARK SLUDGE 143
63 COMPARISON OF STEADY-STATE PERFORMANCE OF MESO-MESO AND
MESO-THERMO CFCSTR TWO-PHASE DIGESTION SYSTEMS OPERATED
AT A 15-DAY HRT WITH HANOVER PARK SLUDGE 144
64 COMPARISON OF STEADY-STATE PERFORMANCE OF CFCSTR MESO-MESO,
MESO-THERMO, AND THERMO-THERMO TWO-PHASE DIGESTION
SYSTEMS OPERATED AT A 7-DAY HRT WITH HANOVER PARK SLUDGE 146
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TABLES (Continued)
Number Page
65 COMPARISON OF STEADY-STATE SYSTEM PERFORMANCES OF MESO-MESO
AND THERMO-THERMO CFCSTR TWO-PHASE DIGESTION SYSTEMS
OPERATED AT A 3-DAY HRT WITH CHICAGO SLUDGE 147
66 COMPARISON OF STEADY-STATE PERFORMANCES OF CFCSTR SINGLE-STAGE
AND TWO-PHASE DIGESTION SYSTEMS OPERATED AT ABOUT A 15-DAY
SYSTEM HRT WITH HANOVER PARK SLUDGE 150
67 COMPARISON OF STEADY-STATE PERFORMANCES OF CFCSTR SINGLE-STAGE
AND TWO-PHASE DIGESTION SYSTEMS OPERATED AT ABOUT A 7-DAY
HRT WITH HANOVER PARK SLUDGE 153
68 COMPARISON OF STEADY-STATE PERFORMANCES OF CFCSTR SINGLE-STAGE
AND TWO-PHASE DIGESTION SYSTEMS OPERATED AT ABOUT A 3-DAY
HRT WITH HANOVER PARK SLUDGE 154
69 STEADY-STATE EFFLUENT VOLATILE ACIDS CONCENTRATIONS IN
MESOPHILIC AND THERMOPHILIC CFCSTR ACID-PHASE DIGESTERS
OPERATED WITH HANOVER PARK SLUDGE AT ABOUT A 2-DAY HRT 156
70 STEADY-STATE EFFLUENT VOLATILE ACIDS CONCENTRATIONS IN
MESOPHILIC AND THERMOPHILIC CFCSTR METHANE-PHASE DIGESTERS
OF TWO-PHASE SYSTEMS FED WITH HANOVER PARK SLUDGE 157
71 STEADY-STATE VOLATILE ACIDS CONCENTRATIONS IN MESOPHILIC
AND THERMOPHILIC SINGLE-STAGE CFCSTR DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE 158
72 COMPARISON OF STEADY-STATE METHANE YIELDS AND EFFLUENT
VOLATILE ACIDS CONCENTRATION FROM MESOPHILIC AND
THERMOPHILIC CFCSTR ACID-PHASE DIGESTION OF HANOVER PARK
SLUDGE OPERATED AT ABOUT A 2-DAY HRT 160
73 STEADY-STATE EFFLUENT VOLATILE ACIDS CONCENTRATIONS IN
MESOPHILIC AND THERMOPHILIC SINGLE-STAGE CFCSTR DIGESTERS
OPERATED WITH THE CELLULOSE FRACTION OF MUNICIPAL SOLID
WASTE AT A 7-DAY HRT 161
74 PROTEIN, CARBOHYDRATE, AND LIPID CONVERSIONS AT STEADY-STATE
IN THERMOPHILIC CFCSTR METHANE-PHASE DIGESTERS FED WITH
HANOVER PARK SEWAGE SLUDGE 161
xv
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TABLES (Continued)
Number
75 ACTUAL STEADY-STATE OPERATING CONDITIONS FOR PARAMETRIC-
EFFECTS CFCSTR ACID-PHASE DIGESTERS FED WITH HANOVER
PARK SLUDGE 164
76 EFFECT OF pH ON STEADY-STATE GAS PRODUCTIONS FROM
MESOPHILIC CFCSTR ACID-PHASE DIGESTERS OPERATED WITH
HANOVER PARK SLUDGE AT ABOUT A 2-DAY HRT 165
77 EFFECT OF pH ON STEADY-STATE EFFLUENT QUALITIES OF
MESOPHILIC CFCSTR ACID-PHASE DIGESTERS OPERATED WITH
HANOVER PARK SLUDGE AT ABOUT A 2-DAY HRT 166
78 EFFECT OF pH ON STEADY-STATE ORGANIC REDUCTION EFFICIENCIES
OF MESOPHILIC CFCSTR ACID-PHASE DIGESTERS OPERATED WITH
HANOVER PARK SLUDGE AT ABOUT A 2-DAY HRT 167
79 EFFECT OF pH ON STEADY-STAE GAS PRODUCTIONS FROM MESOPHILIC
CFCSTR ACID-PHASE DIGESTERS OPERATED WITH HANOVER PARK
SLUDGE AT ABOUT A 1.3-DAY HRT 169
80 EFFECT OF pH ON STEADY-STATE EFFLUENT QUALITIES OF MESOPHILIC
CFCSTR ACID-PHASE DIGESTERS OPERATED WITH HANOVER PARK
SLUDGE AT ABOUT A 1.3-DAY HRT 170
81 EFFECT OF pH ON STEADY-STATE ORGANIC REDUCTION EFFICIENCIES
OF MESOPHILIC CFCSTR DIGESTERS OPERATED WITH HANOVER PARK
SLUDGE AT ABOUT 1.3-DAY HRT 171
82 COMPARISON OF STEADY-STATE PERFORMANCES OF MESOPHILIC AND
THERMOPHILIC ACID-PHASE DIGESTERS OPERATED WITH HANOVER .
PARK SLUDGE AT pH 7 172
83 COMPARISON OF STEADY-STATE PERFORMANCES OF MESOPHILIC AND
THERMOPHILIC ACID-PHASE DIGESTERS OPERATED WITH HANOVER
PARK SLUDGE AT pH 5 173
84 EFFECT OF pH ON STEADY-STATE GAS PRODUCTIONS FROM
THERMOPHILIC CFCSTR ACID-PHASE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE AT ABOUT A 2-DAY HRT 174
xv i
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TABLES (Continued)
Number
85 EFFECT OF pH STEADY-STATE EFFLUENT QUALITIES OF THERMOPHILIC
CFCSTR ACID-PHASE DIGESTERS OPERATED WITH HANOVER PARK
SLUDGE AT ABOUT A 2-DAY HRT 175
86 EFFECT OF pH STEADY-STATE ORGANIC REDUCTION EFFICIENCIES
OF THERMOPHILIC CFCSTR ACID-PHASE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE AT ABOUT A 2-DAY HRT... 176
87 EFFECT OF pH ON STEADY-STATE GAS PRODUCTIONS FROM
THERMOPHILIC CFCSTR ACID-PHASE DIGESTERS OPERATED WITH
HANOVER PARK SLUDGE AT ABOUT A 1.3-DAY HRT 179
88 EFFECT OF pH ON STEADY-STATE EFFLUENT QUALITIES OF
THERMOPHILIC CFCSTR ACID-PHASE DIGESTERS OPERATED WITH
HANOVER PARK SLUDGE AT ABOUT A 1.3-DAY HRT 180
89 EFFECT OF pH ON STEADY-STATE ORGANIC REDUCTION EFFICIENCIES
OF THERMOPHILIC CFCSTR DIGESTERS OPERATED WITH HANOVER
PARK SLUDGE AT ABOUT A 1.3-DAY HRT 181
90 RESULTS OF ANALYSIS OF VARIANCE (ANOVA) OF ACID-PHASE
DIGESTION STEADY-STATE DATA TO ASSESS THE EFFECTS OF THE
CONTROL VARIABLES OF CULTURE TEMPERATURE, pH, AND HRT
ON REDUCTIONS OF CARBOHYDRATES, PROTEIN, AND LIPIDS 183
91 RESULTS OF ANALYSIS OF VARIANCE (ANOVA) OF ACID-PHASE
DIGESTION STEADY-STATE DATA TO ASSESS THE EFFECTS OF THE
CONTROL VARIABLES OF CULTURE TEMPERATURE, pH AND HYDRAULIC
RESIDENCE TIME (HRT) ON TOTAL GAS YIELD, GAS PRODUCTION
RATE AND METHANE CONTENT 184
92 STEADY-STATE OPERATING CONDITIONS FOR ADVANCED UPFLOW
TWO-PHASE DIGESTION RUNS CONDUCTED WITH HANOVER PARK
SLUDGE 188
93 COMPARISON OF STEADY-STATE GAS PRODUCTIONS FROM MESO-MESO
UPFLOW TWO-PHASE, MESO-MESO CFCSTR TWO-PHASE AND MESOPHILIC
CFCSTR SINGLE-STAGE SYSTEMS OPERATED WITH HANOVER PARK
SLUDGE AT ABOUT A 7-DAY HRT 189
xvii
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TABLES (Continued)
Number Page
94 COMPARISON OF STEADY-STATE EFFLUENT QUALITIES OF MESO-MESO
UPFLOW TWO-PHASE, MESO-MESO CFCSTR TWO-PHASE AND
MESOPHILIC SINGLE-STAGE SYSTEMS OPERATED WITH HANOVER PARK
SLUDGE AT ABOUT A 7-DAY HRT 190
95 STEADY-STATE pH, ORP, AND VOLATILE ACIDS AND ETHANOL
CONCENTRATION PROFILES IN MESO-MESO UPFLOW TWO-PHASE
DIGESTERS OPERATED WITH HANOVER PARK SLUDGE AT ABOUT
A 7-DAY HRT 192
96 COMPARISON OF STEADY-STATE ORGANIC REDUCTION EFFICIENCIES
OF MESO-MESO UPFLOW TWO-PHASE, MESO-MESO CFCSTR TWO-PHASE
AND MESOPHILIC SINGLE-STAGE SYSTEMS, OPERATED WITH
HANOVER PARK SLUDGE AT ABOUT A 7-DAY HRT 193
97 COMPARISON OF STEADY-STATE GAS PRODUCTIONS FROM MESOPHILIC
ACID-PHASE DIGESTION OF HANOVER PARK SLUDGE WITH AND
WITHOUT METHANE-PHASE EFFLUENT RECYCLE 194
98 COMPARISON OF VOLATILE ACIDS PRODUCTION RATES FROM
MESOPHILIC AND THERMOPHILIC UPFLOW ACID-PHASE DIGESTION
OF HANOVER PARK SLUDGE WITH AND WITHOUT -METHANE-PHASE
EFFLUENT RECYCLE 196
99 COMPARISON OF GAS PRODUCTIONS FROM MESOPHILIC AND
THERMOPHILIC UPFLOW ACID-PHASE DIGESTION OF HANOVER
PARK SLUDGE 197
100 COMPARISON OF EFFLUENT QUALITIES FROM MESOPHILIC AND
THERMOPHILIC UPFLOW ACID-PHASE DIGESTION OF HANOVER PARK
SLUDGE WITHOUT METHANE-PHASE EFFLUENT RECYCLE 198
101 COMPARISON OF GAS PRODUCTIONS FROM MESO-THERMO AND
THERMO-THERMO UPFLOW TWO-PHASE AND THERMO-THERMO
THREE-STAGE DIGESTION SYSTEMS OPERATED WITH HANOVER
PARK SLUDGE 199
102 COMPARISON OF EFFLUENT QUALITIES FROM MESO-THER>D AND
THERMO-THERMO UPFLOW TWO-PHASE AND THERMO-THERMO
THREE-STAGE DIGESTION SYSTEMS OPERATED WITH HANOVER
PARK SLUDGE 201
xviii
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TABLES (Continued)
Number
103 SOLIDS, pH, ORP, AND VOLATILE ACIDS CONCENTRATION PROFILES
IN THERMOPHILIC UPFLOW METHANE-PHASE DIGESTER OPERATED
IN TANDEM WITH THERMOPHILIC UPFLOW ACID-PHASE DIGESTER 202
104 EFFECT OF CELLULASE-CELLOBIASE PRETREATMENT ON VOLATILE ACIDS
AND GAS PRODUCTION DURING INCUBATION FROM MIXED DOWNERS
GROVE PRIMARY AND STICKNEY ACTIVATED DIGESTER FEED
SLUDGES 209
105 EFFECT OF CELLULASE-CELLOBIASE AND LIPASE TREATMENT ON
STEADY-STATE GAS PRODUCTIONS FROM MESO-MESO CFCSTR
TWO-PHASE SYSTEMS OPERATED WITH MIXED DOWNERS GROVE
PRIMARY AND STICKNEY ACTIVATED SLUDGES AT AN HRT
OF ABOUT 3 DAYS 210
106 EFFECT OF CELLULASE-CELLOBIASE AND LIPASE TREATMENT ON
STEADY-STATE EFFLUENT QUALITIES OF MESO-MESO CFCSTR
TWO-PHASE SYSTEMS OPERATED WITH MIXED DOWNERS GROVE
PRIMARY AND STICKNEY ACTIVATED SLUDGES AT ABOUT A
3-DAY HRT 211
107 EFFECT OF CELLULASE-CELLOBIASE AND LIPASE TREATMENT ON
STEADY-STATE ORGANIC REDUCTION EFFICIENCIES OF MESO-MESO
CFCSTR TWO-PHASE SYSTEMS OPERATED WITH MIXED DOWNERS
GROVE PRIMARY AND STICKNEY ACTIVATED SLUDGES AT ABOUT A
3-DAY HRT 212
xix
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ABBREVIATIONS AND SYMBOLS
ABBREVIATIONS
SNG
UASB
CFCSTR
Me so
Thermo
Meso-meso
Meso-thermo
Thermo-thermo
A-P
M-P
HRT
SCF
SCM
VA
TVA
TS
VS
FS
TSS
VSS
FSS
COD
CPL
ECPL
VSR
ANOVA
ORP
SYMBOLS
a
P
substitute natural gas
upflow anaerobic sludge blanket
continuous-flow continuously-stirred tank reactor
digester operated at a mesophilic (35°C) temperature
digester operated at a thermophilic (55°C) temperature
two-phase system with mesophilic acid- and methane-phase
digesters
two-phase system with mesophilic acid-phase and thermophilic
methane-phase digesters
two-phase system with thermophilic acid- and methane-phase
digesters
acid-phase digester
methane-phase digester
hydraulic residence time
standard cubic feet (dry) at 60°F and 30-in. Hg
standard cubic meter (dry) at 15.55°C and 762 mm Hg
volatile acids
total volatile acids as acetic
total solids
volatile solids
fixed solids
total suspended solids
volatile suspended solids
fixed suspended solids
chemical oxygen demand
carbohydrates, protein, and lipids
sum of carbohydrates, protein, and lipids
volatile solids reduction
analysis of variance
oxidation reduction potential
level of significance
specific growth rate
saturation coefficient
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ACKNOWLEDGMENT
The authors gratefully acknowledge the following persons for their
contributions to this project.
The sludge feeds used in this work were provided by Mr. Lance Blythe,
Hanover Park Sewage Treatment Plant, Metropolitan Sanitary District of Greater
Chicago (MSDGC), Hanover Park, Illinois; Mr. Robert O'Malley, West-Southwest
Sewage Treatment Plant, MSDGC, Chicago, Illinois; and Ms. Jan Lasina, Downers
Grove Sanitary District, Downers Grove, Illinois. Enzymes used for the feed
pretreatment studies were provided by Ms. Karen E. Yacovelli, Novo Labora-
tories, Inc., Wilton, Conneticut.
Several staff members of the Office of Research and Development, U.S.
EPA, provided advice and guidance during the course of the work. Dr. Joseph
Farrell was instrumental during the development and revision of the
experimental plan, and Dr. James Heidman and Mr. R. V. Villiers provided
insight into the interpretation of the analytical results. Dr. Lewis Rossraan
provided the computer program used to conduct the ANOVA tests on the
parametric-effect digestion data and helped tp interpret the ANOVA results.
The efforts of the EPA Project Officers, Dr. H. E. Bostian and Mr. B. V.
Salotto, who reviewed the experimental work and suggested improvements, and
the interest expressed by Mr. James Basilico, throughout the project are
greatly appreciated.
Dr. F. G. Pohland, Professor of Civil Engineering, Georgia Institute of
Technology, and Dr. Paul H. Smith, Professor of Microbiology, University of
Florida, consultants for IGT on this project, reviewed the experimental work
and made helpful suggestions.
Several IGT staff members also contributed to the work. Messrs. L.
Hoffman, R. Schlusser, J. Jensen, and T. Sumlin installed and maintained much
of the digestion equipment, and Dr. S. Chao, Mr. A. Janos, Mr. N. Petrulis,
Mr. J. Marsh, and Ms. J. Mensinger helped to conduct some of the chemical
analyses.
xxi
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SECTION 1
INTRODUCTION
Anaerobic digestion is an important aspect of biotechnology because of
its applicability to waste treatment, energy conversion, and production of
chemicals. In addition, the digestion process can be coupled to appropriate
thermal and electrochemical processes to produce electric power, methanol,
hydrocarbons, and other useful products.
The conventional digestion system using the single-stage continual-flow,
continuously-stirred tank reactor (CFCSTR) digester is perhaps the most
commonly used in commercial sludge stabilization. The single-stage CFCSTR
process has several disadvantages, however, including the requirement of
large, capital-intensive digestion tanks and process instability because of
imbalances between the symbiotic fermentation steps of acid formation by
acidogenic bacteria (acidogens) and acid-gasification by the more sensitive
and slow-growing methane bacteria (methanogens).
A review of the anaerobic digestion literature indicates that an advanced
digestion mode in which the acid-production and acid-gasification phases are
conducted separately has several advantages over single-stage digestion.
Among the principal benefits of this two-phase digestion process are reduced
plant capital and operating costs, enhanced stabilization and gasification
rates and efficiencies, increased net energy production, and improved process
stability and reliability at higher system loadings-and shorter hydraulic
residence times (HRT's). Although several two-phase digestion studies have
been conducted with soluble synthetic substrates and wastes to support some of
the claimed benefits of two-phase digestion, there is a paucity of information
on process behavior with such particulate feeds as sewage sludge.
First, it is necessary to demonstrate that two-phase digestion of sludge
is superior to single-stage digestion under identical operating conditions.
The relative advantages (if any) of two-phase digestion over the single-stage
process could be a function of such basic operating parameters as HRT,
fermentation temperature, and pH; these should be studied. Next, the effects
of these important variables on acid- and methane-phase digestion stages need
to be delineated. The efficiencies of the conversion of the major organic
components of sewage sludge — carbohydrates, proteins, and lipids — by two-
phase and conventional digestion at appropriate ranges of HRT and digestion
temperature should be compared to establish the superiority of one or the
other process. Overall, it is necessary to quantify the benefits of two-phase
digestion in terms of gains in conversion rates and efficiencies relative to
the baseline performance of single-stage digestion. This project was
undertaken to develop this fundamental information by conducting parallel two-
phase and single-stage digestion studies, with each process using the same
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reactor design to obtain a valid comparison. Although several reactor designs
are available to conduct anaerobic digestion, the commonly used CFCSTR reactor
was selected for the process comparison experiments.
Once the superiority of the two-phase process is demonstrated — an
important initial goal — it is also necessary to investigate means of
improving this process further to maximize solids stabilization as well as the
volumetric gas formation rate at system HRT's that are lower than those of the
CFCSTR digesters. Two obvious approaches to accomplishing these goals are
1) to use reactor designs that provide solid residence times (SRT's) that are
higher than those of the CFCSTR, and 2) to enhance the reactivity (or
biodegradability) of the feed sludge by cost-effective enzyme or chemical
treatment. Accordingly, the second part of this research project was
concerned with 1) the application of novel upflow digesters that are known to
exhibit better performances than those of CFCSTR digesters, and 2) cellulase
and lipase treatment of the raw sludge to increase the digestibilities of
these two major sludge components.
PROJECT OBJECTIVES
The overall objective of this research was to conduct fundamental and
applied studies to demonstrate the application of an advanced digestion
process (two-phase digestion) to stabilize and gasify sewage sludges at higher
overall rates and efficiencies than are achieved by conventional high-rate
digestion.
The research was directed toward developing a better understanding of the
fundamental engineering aspects of the acid-forming and methane-forming phases
of the overall anaerobic digestion process and investigating selected two-
phase process configurations for further development by pilot-plant-scale
application later at a selected sewage treatment plant. To address these
objectives, the program was divided into two parts:- Fundamental studies and
applied studies. Specific objectives for each part of the program are
described below.
Specific Objectives
Fundamental Studies—
The specific objectives of the Fundamental Studies were to conduct bench-
scale anaerobic digestion experiments and —
• To compare two-phase and conventional single-stage, high-rate anaerobic
digestion processes at mesophilic and thermophilic culture temperatures
at selected HRT's
• To develop basic information on the effects of key operating variables on
acid-phase digester performance with a selected sewage sludge.
Applied Studies—
The specific objectives of the Applied Studies were —
2
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To conduct a bench-scale investigation of an advanced two-phase digestion
mode using novel upflow acid- and methane-phase digesters and interphase
culture recycling to identify the best two-phase digestion process
configuration for pilot-scale testing later in a sewage treatment plant
To study the effect of sludge pretreatment by selected cellulase and
lipase enzyme systems on two-phase process performance at a short
hydraulic residence time.
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SECTION 2
RESULTS AND CONCLUSIONS
Several important aspects of single-stage and two-phase anaerobic diges-
tion were investigated during this research. The results of the experimental
work showed that under comparable operating conditions, the two-phase sludge
digestion process was more stable and exhibited higher conversion efficiencies
and rates than single-stage digestion. Theoretical and kinetic analyses of
single-stage and two-phase processes supported these experimental observa-
tions. The performance of the two-phase digestion process could be improved
considerably by the use of high-SRT upflow reactors in lieu of CFCSTR
digesters, or by pretreatment of the digester feed by a commercial cellulase-
cellobiase system and direct lipase treatment of the acid-phase digester. It
was observed that, although sludge liquefaction and acidification were
enhanced at a higher digester temperature, the thermophilic acetogens and
methanogens were inhibited by certain unidentified products of protein and
lipid degradation.
Only 59% of the sludge volatile solids were anaerobically biodegradable,
and complete conversion of the biodegradable material was achieved by two-
phase digestion.
The following are specific results and conclusions from work on the
specific research topics listed below.
KINETIC ANALYSES OF SINGLE-STAGE AND TWO-PHASE DIGESTION
1. Kinetic analysis based on the available information indicated that, in
theory, the rate of production of volatile acids in single-stage CFCSTR
anaerobic digesters is higher than the rate of conversion of volatile
acids unless the digester is operated at a fairly high HRT — usually
20 days or higher. Single-stage digestion at lower HRT's leads to an
imbalance between volatile acids production and volatile acids
conversion, resulting in acids accumulation and inhibition of acidogenic
and/or methanogenic fermentation(s). Also digester operation at unduly
high HRT's is tantamount to maintenance of the acidogenic bacteria in the
stationary or the endogenous growth phases, which leads to the decelera-
tion of the substrate hydrolysis and acidification processes* Two-phase
fermentation, which provides for separate culturing of the kinetically
dissimilar digester organisms, has the advantages of maximizing the rates
of volatile solids degradation and volatile acids formation and minimiz-
ing volatile acids conversion (methanogenesis) in the acid-phase
digester. Methanogenesis, on the other hand, is maximized and the acid
formation rate is minimized in the methane digester. Thus, in two-phase
fermentation, both groups of digester organisms could be maintained in
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the exponential growth phase and the probability of unbalanced
acidogenic-methanogenic fermentation and its inhibition is minimized.
The two-phase process thus should afford higher sludge stabilization
rates and efficiencies at lower HRT's and higher loading rates than are
feasible with single-stage digestion.
CHEMICAL CHARACTERISTICS OF DIGESTER FEEDS
1. About 80-95 wt % of total solids (TS) content of the Chicago sludge used
for the digestion studies was insoluble particulate matter with the
balance being soluble material. On the average, about 8 wt % of the TS
was soluble inorganics, 21 wt % (of TS) was insoluble inorganics (fixed
solids), 7 wt % (of TS) was soluble organics, and 64 wt % (of TS) was
insoluble organics. The total COD of the sludge solids averaged 1.5 g
COD/g VS. About 93% of the sludge COD was due to particulate organic
matter. Of the total nitrogenous matter, 85-91% was particulate protein-
aceous material. The average protein, carbohydrate, and lipid contents
of the feed sludge lots were about 33 wt %, 24%, and 27 wt % of the VS,
respectively. On the average, about 83 wt % of organics could be
accounted for by proteins, lipids, and carbohydrates. The chemical
characteristics of the feed indicated that the success of the digestion
process would be dictated to a large extent by the ability of the
digester culture to hydrolyze proteins and lipids and metabolize the
hydrolysis products to produce acetate or other methanogenic substrates.
2. Decomposition of the feed sludge during storage and delivery to the
digester could be minimized by refrigerated storage. It was observed
that certain indicator chemical characteristics of the digester feed
slurry remained virtually unchanged and stable during refrigerated
storage at 2° to 4°C, as indicated by a time-series analysis of the feed
reservoir contents for TS, VS, and individual volatile acids during a
worst-case storage period of 8 days.
THEORETICAL EFFICIENCIES AND CHEMICAL AND BIOCHEMICAL REACTIVITIES OF DIGESTER
FEEDS
1. The theoretical total gas (biogas) and methane yields of the Hanover Park
wastewater sludge, as estimated from the elemental analysis, theoretical
carbonaceous COD, and calorific value, were within a few percentage
points of each other. The total biogas and methane yields of this feed
sludge were 0.50 and 0.79 SCM/kg VS reacted (8.0 and 12.6 SCF/lb VS
reacted), respectively. In contrast to these observations, the analyti-
cal COD's (in terms of kg of measured total and carbonaceous COD's per kg
of sludge VS) of the different sludge lots collected at various times of
the year were significantly different from each other; consequently,
theoretical methane yields of different lots based on measured carbonace-
ous COD's differed from each other by as much as about 38%. The
analytical carbonaceous COD content and the analytical COD-based methane
yields of the Hanover Park sludge were related to the sum total of the
masses of total carbohydrate, crude protein, and lipids in the sludge
(SCPL). It was found that the theoretical methane yield varied directly
as the SCPL of the sludge.
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2. Comparison of the elemental-composition-based and analytical (directly
measured) COD's of the raw sludge showed that about 59% of the sludge
volatile solids (VS) was chemically oxidizable under the COD test
conditions.
3. Results of long-term batch anaerobic digestibility potential (ADP) tests
indicated maximum expected biogas and methane yields of 0.46 and
0.32 SCM/kg VS added (7.3 and 5.1 SCF/lb VS added) from mesophilic diges-
tion of the Hanover Park wastewater sludge. These gas yields provided a
VS reduction of 48%. Results of the ADP test showed that about 80 wt %
of the sludge VS was rapidly biodegradable and about 20 wt % was
relatively recalcitrant to mesophilic (35°C) anaerobic digestion.
4. A comparison of the theoretical and the ADP methane yields indicated that
about 58% of the sludge VS was anaerobically biodegradable under meso-
philic (35°C) conditions. This biodegradability factor compared well
with the observation that about 59% of the sludge carbonaceous VS was
chemically oxidizable. Thus, it appeared that the chemical oxidizability
of the carbonaceous VS could be a good measure of anaerobic biodegrad-
ability.
5. There was a high degree of correlation between influent and effluent VS
and total carbon concentrations; VS reductions calculated on the bases of
mass-flow of gaseous carbon out and mass-flow of feed carbon in seemed to
be more accurate than those calculated by other methods.
SINGLE-STAGE CFCSTR DIGESTION
1. A comparison of the performances of mesophilic single-stage CFCSTR runs
conducted at 15, 7, and 3-day HRT's indicated that optimum process
performance would be expected at an HRT of 7 days.
2. With single-stage CFCSTR digesters, the best thermophilic performance was
obtained at an HRT of 15 days. Gas and methane yields and organic
reductions decreased and volatile acids accumulation increased as the
digester HRT was decreased from 15 to 7 to 3 days. Inhibitory levels of
volatile acids were observed at the 7 and 3-day HRT's.
3. There was clear evidence of the occurrence of unbalanced acidogenic-
methanogenic fermentations in the single-stage CFCSTR processes at the
3-day HRT under the mesophilic"and thermophilic conditions.
4. Comparison of steady-state performances of single-stage CFCSTR mesophilic
and thermophilic runs under the comparable HRT and loading rate condi-
tions showed that higher methane yields and production rates were
obtained at the thermophilic temperature at all operating conditions
tested (HRT's of about 15, 7, and 3 days and loading rates of about 2,7,
and 15 kg VS/m3-day).
5. The highest thermophilic methane yield and methane production rate of
0.28 SCM/kg VS added (4.5 SCF/lb VS added) and 1.8 vol/vo1-day,
respectively, observed in the single-stage CFCSTR systems were 24% and
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12% higher than the highest observed single-stage CFCSTR mesophilic
methane yield and methane production rate.
6. Volatile acids concentrations of the single-stage CFCSTR thermophilic
digester effluents were in all cases higher than those of the single-
stage CFCSTR mesophilic digester effluents, suggesting that higher
degrees of hydrolysis and acidification occurred during thermophilic
operation.
7. Even though the volatile acids concentrations were high in the
thermophilic CFCSTR, the pH levels remained high due to higher
alkalinities and ammonia nitrogen concentrations in the thermophilic
CFCSTR than in the mesophilic CFCSTR.
8. Although the single-stage thermophilic digesters effected enhanced
hydrolysis and acid production, gasification of the volatile acids was
not similarly enhanced, with the result that high concentrations of
unconverted acids accumulated and emanated with the thermophilic
effluents.
9. During single-stage CFCSTR digestion, carbohydrate conversion was highest
(44%) during mesophilic operation at the lowest HRT (3 days); in
contrast, the highest carbohydrate conversion (25%) during thermophilic
operation was observed at the highest HRT (15 days). Thermophilic
carbohydrate reductions in single-stage CFCSTR's were lower than those at
the mesophilic temperature at all test HRT's.
10. Crude protein reductions in thermophilic single-stage CFCSTR digesters at
15 and 7-day HRT's were about double those in the mesophilic single-stage
CFCSTR digesters; however, thermophilic and mesophilic protein
conversions were comparable at the lowest HRT.
11. During single-stage CFCSTR digestion, lipid reductions at the thermo-
philic temperature were higher than those at the mesophilic temperature
at all HRT's.
CFCSTR TWO-PHASE DIGESTION
Acid-Phase Digestion
1. The mesophilic and thermophilic acid-phase digesters exhibited enhanced
volatile acids production and gas-formation rates as the HRT was
decreased from 2 to 0.9 days and the loading rate was increased from 2 to
15 kg VS/m3-day.
2. The "natural" pH of the mesophilic and thermophilic acid-phase digesters
stabilized at about 6.6.
3. There was no evidence of hydrogen accumulation in the head gases except
during mesophilic operation at an HRT of 0.9 days. These observations
(coupled with the fact that all acid-phase runs exhibited high methane-
content gases) indicated that the rate of hydrogen utilization by the
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syntrophic — and carbon dioxide-reducing — methane bacteria exceeded the
rate of hydrogen production during oxidation of the sludge hydrolysates.
4. It was apparent that the wash-out (or critical) HRT of the syntrophic
methane formers was less than 1 day.
5. Gases from the mesophilic and thermophilic acid digesters contained more
nitrogen than those of the methane digester, suggesting that substrate
oxidation during acidogenesis was coupled to nitrogen oxides reduction
(denitrification).
6. The ICPL [sum total of the masses of total carbohydrate (C), crude
protein (P), and lipids (L)] reductions in the mesophilic acid digester
were higher than those in the mesophilic methane digester at all HRT's
and loading-rates, indicating that liquefaction of organics was
predominant in the acid digester. Conversely, ZCPL reductions in the
mesophilic acid digesters were lower than those in the thermophilic
methane digester, suggesting continued and enhanced liquefaction of the
organics under the thermophilic conditions of the latter digester.
7. Carbohydrate and lipid reductions in the mesophilic acid-phase digester
decreased as the HRT was decreased from 2 to 0.9 days.
8. Acetate was the predominant volatile acid in the mesophilic and thermo-
philic acid digesters, followed by propionic and isovaleric/butyric.
Methane-Phase Digestion
1. Total gas and methane yields and the gas-phase methane content decreased,
and their production rates and acids accumulation increased as the HRT of
the mesophilic methane digester was decreased from 13 to 5 to 2 days.
2. Surprisingly, both gas and methane yields and production rates, and
volatile acids accumulations, increased as the HRT of the thermophilic
methane digester was reduced from 13 to 5.5 days; however, all these
performance parameters exhibited lower values as the HRT was decreased
from 5.5 to 2 days. Thus, a methane digester HRT of 5.5 days seemed to
be optimum for thermophilic methanogenesis.
3. About 86% of the meso-meso two-phase system methane production was
derived from the raesophilic methane digester when the ratio of the
methane digester HRT to the system HRT was 0.87; this percentage dropped
as the HRT ratio was decreased. Thermophilic methane digesters fed with
mesophilic acid digester effluents showed the same trend as above, but
exhibited a lower proportion of system methane production when operated
in series with a thermophilic acid digester.
4. The methane contents and bicarbonate alkalinities of both the mesophilic
and thermophilic methane digesters were considerably higher than those of
the acid digesters. The bicarbonate alkalinity increased significantly
during methane fermentation; enhancement of the bicarbonate alkalinity
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had the effect of scrubbing the gas-phase C0£, thereby enhancing the gas-
phase methane content of the methane digester.
5. For a given HRT and loading-rate, the thermophilic methane digester
exhibited much higher acids accumulation and ammonia-nitrogen concentra-
tion than the mesophilic methane digester. Accumulation of propionate
was higher than that of any other volatile acids.
Overall System Performance
1. The results of meso-meso, tneso-therrao, and thermo-thermo two-phase
digestion studies showed that, for 15-day and 3-day system HRT's, the
meso-meso operations were better than the meso-thermo or thermo-thermo
operations in terms of gas and methane productions and VS and organic
reductions. For a 7-day HRT, the meso-thermo two-phase system was better
than the meso-meso or the thermo-thermo operation in terms of methane
yield and VS reduction.
2. The meso-thermo and thermo-thermo two-phase processes had much higher
effluent volatile acids concentrations than the meso-meso two-phase
process.
3. Although liquefaction and acidification were enhanced under thermophilic
conditions, the gasification reactions were not similarly enhanced.
PROCESS COMPARISON: CFCSTR SINGLE-STAGE VERSUS CFCSTR TWO-PHASE
Process Comparison at a 15-Day System HRT
1. Both the raeso-thermo and the meso-meso two-phase processes were superior
to the mesophilic or thermophilic single-stage digestion in all respects.
2. The meso-meso two-phase run exhibited the best performance; it afforded
the highest methane yield of 0.41 SCM/kg VS added, a VS reduction of 54%,
and a ECPL conversion efficiency of 57%, indicating complete conversion
of biodegradable organics. By comparison, the best single-stage methane
yield and VS reduction were 0.28 SCM/kg VS added and 39%, respectively.
The above meso-meso two-phase methane yield was 82% of the theoretical
methane yield, which was based on 100% recovery of the feed carbon in the
digester gases.
Process Comparison at a 7-Day System HRT
1. The meso-thermo two-phase system exhibited better performance than the
meso-meso and the thermo-thermo two-phase and the single-stage mesophilic
and thermophilic digestion processes in terms of gas and methane yields,
methane content of gas, and VS (total and biodegradable) and ECPL
reductions; however, the volatile acids concentration in the effluent of
the meso-thermo system was higher than those of the other systems. The
next best performance was exhibited by the meso-meso two-phase process;
the effluent acids concentration of this process was one-tenth of the
concentration of the meso-thermo effluent.
9
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2. The performance of the thermo-therrao two-phase process was worse than
those of the meso-thermo and raeso-meso two-phase processes.
3. The methane-phase gas production declined sharply when it was charged
with therraophilic acid-digester effluent, indicating that thermophilic
metabolites could have retarded the acetogenic and/or methanogenic
bacteria.
4. Two-phase digestion effected higher lipid and carbohydrate degradations
than single-stage digestion. Protein and lipid conversions were enhanced
under thermophilic conditions. Carbohydrate reduction was enhanced under
mesophilic conditions. The lipid degradation efficiency was higher than
those of proteins and carbohydrates.
Process Comparison at a 3-Day System HRT
1. The thermo-thermo and the meso-meso two-phase systems exhibited higher
methane yields and production rates and VS and organic reductions than
the mesophilic and thermophilic single-stage digesters. However, at the
3-day HRT, the meso-meso two-phase system was better than the thermo-
thermo process.
2. Volatile acids accumulations (2000-3200 mg/L) in the single-stage
digesters were double those of the two-phase systems showing that,
whereas unbalanced digestion occurred in the former process at a 3-day
HRT, a more balanced acidogenic-methanogenic fermentation was experienced
in the latter fermentation mode.
3. At a 3-day system HRT, the methane yield of the meso-meso two-phase
process was 102% higher than that of single-stage mesophilic digestion;
this positive methane yield differential at the 3-day HRT was higher than
those observed at the 7 and the 15-day HRT's. -Thus, the benefits of two-
phase fermentation were more evident at the lowest HRT.
CHARACTERISTICS OF THERMOPHILIC DIGESTION
1. Volatile acids gasification efficiency at the thermophilic temperature
was lower than that under mesophilic digestion conditions.
2. Under thermophilic conditions, the efficiencies of volatile acids
conversion by two-phase digestion was higher than those by single-stage
digestion.
3. Relative to mesophilic (35°C) digestion conditions, the thermophilic
(55°C) digestion temperature enhanced the hydrolysis of sludge particles
and acidification of the hydrolysate but retarded acetogenic conversions
of propionate, branch-chain fatty acids, and caproate and methanogenic
conversions of acetate and hydrogen and C02.
4. Thermophilic degradation products of proteins and lipids seemed to be
inhibitory to thermophilic acetogens and methanogens.
10
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5. For comparable operating conditions, buffer capacities of the methane-
phase digesters of the two-phase systems were higher than those of the
single-stage digesters, and this positive alkalinity differential
increased as the system HRT decreased from 15 to 7 to 3 days. The two-
phase process was thus more stable than the single-stage digester, and
the relative stability of the former process increased as the system HRT
decreased.
EFFECTS OF pH, HRT, AND TEMPERATURE ON ACID-PHASE DIGESTION
Mesophilic Acid-Phase Runs; pH and HRT Effects
1. The optimum pH for mesophilic acidogenesis of the Hanover Park sludge was
between 5.5 and 6.2; gas and acid productions were maximized within this
range. At an HRT of 2 days, protein, lipid and ECPL reductions were
higher at pH 5 than at pH 7; carbohydrate reductions at these two pH's
were about the same. At an HRT of 1.3, pH 7 effected a higher degree of
acidogenesis than pH 5. The worst acid-phase performance was obtained at
an HRT of 1.3 days and a pH of 5, which was a combination of a low HRT
and a low pH. There was hydrogen in the digester gas at an HRT of
1.3 days and a pH of 5.
2. At pH 7, the efficiency of acidogenesis was higher at an HRT of 2 days
than at 1.3 days. At pH 5, methane yield and production rate were higher
at an HRT of 1.3 days than at an HRT of 2 days, whereas acids productions
at these two HRT's were about the same.
Thermophilic Acid-Phase Runs; pH and HRT Effects
1. Optimum thermophilic acid-digester performance was obtained at a pH of 6.
2. Carbohydrate, protein, lipids and ICPL reductions, and gas and volatile
acids productions, were higher at pH 7 than at pH 5.
3. At pH's 7 and 5, gas and volatile acids productions were higher at an HRT
of 2 days than at an HRT of 1.3 days.
4. As with mesophilic acid-phase digestion, the worst thermophilic acid-
phase digester performance was observed at the lowest HRT of 1.3 days and
at the lowest pH of 5.
Temperature Effects
1. Gas and methane yields and production rates from the thermophilic acid
digesters were lower than those from the mesophilic acid digester under
all test operating conditions; however, the reverse was true for volatile
acids production. These observations indicated that the activities of
the syntrophic methane formers were probably inhibited under thermophilic
conditions.
11
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Statistical Inference from Analysis of Variance (ANOVA) of the Factorial
Experiment
1. The culture pH had a strong influence on the conversion of VS and the
major organic components of carbohydrate, protein, and lipids; these
conversions increased as the pH was increased to the optimum value.
2. Increases in culture temperatures and HRT tended to increase carbohydrate
conversion; however, the effect of each variable could not be separated
because of large temperature-HRT interaction.
3. Increase in acid-digester HRT tended to increase protein and lipid
reductions.
4. The digester HRT, temperature, and culture pH each independently
influenced (and increased) acid-digester gas yield; the gas yield
decreased as the HRT and culture temperature increased, and it increased
as the culture pH was increased.
5. Overall, enhanced hydrolysis and acidification were achieved at the
thermophilic temperature and at a pH of about 6.
OPTIMUM OPERATING CONDITIONS FOR TWO-PHASE DIGESTION
1. Based on the process comparison and parametric-effect acid-phase
digestion studies, the following operating conditions were regarded
optimum for two-phase anaerobic digestion of Hanover Park sludge:
• A culture temperature of 35°C
• A system HRT of 7 days (a 2-day HRT for acid digester and a 5-day
HRT for methane digester)
• A feed VS concentration of 50 g/L
• A pH of about 6.6 for the acid digester, obtainable without pH
control
o A pH of 7 or higher for the methane digester.
ADVANCED MESOPHILIC TWO-PHASE DIGESTION WITH NOVEL UPFLOW REACTORS
1. Methane yield from the mesophilic upflow two-phase system was 17% higher
than that from the CFCSTR two-phase system with both systems operated at
an HRT of 7 days and a system loading rate of about 7 kg/nr-day; this
increase in methane yield reflected the reactor effect.
2. Volatile acids production in the upflow acid-phase digester was about
three times that of the CFCSTR acid digester. There was no evidence of
acetogenesis occurring in the acid digester.
12
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3. The upflow two-phase digestion system exhibited higher VS, protein,
carbohydrate, and lipid reduction than the CFCSTR two-phase digestion
process.
4. Acetate and the higher volatile acids were readily converted within the
bottom one-half of the culture depth of the upflow methane digester.
Acetogenesis, acetate conversion, and syntrophic methane fermentation
were the predominant reactions in the methane digester.
5. Recycling of the upflow methane digester effluents to the upflow acid
digester enhanced methane and nitrogen gas yields and production rates
and the volatile acids formation rate, indicating that this recycling had
the effect of enhancing sludge hydrolysis and acidification.
ADVANCED THERMOPHILIC TWO-PHASE DIGESTION WITH NOVEL UPFLOW REACTORS
1. During meso-thermo upflow two-phase digestion of Hanover Park sludge, the
thermophilic methane-phase digester produced more acids than the
mesophilic acid digester, and system gas yield was low under these
conditions. Two-phase system performance did not improve when the upflow
acid digester temperature was changed from 35°C to 55°C.
2. There was little evidence of acetogenic and methanogenic activities in
the upflow methane digester.
3. The inhibitory effects of thermophilic metabolities on aceto-
methanogenesis were more severe on the high-SRT upflow methane digester
than on the CFCSTR methane digesters. The reason for this enhanced
inhibition could be that the high-SRT upflow digester contained a larger
reservoir of inhibitor-producing substances than the CFCSTR digester,
which experiences continual flushing of the inhibitors.
THERMO-THERMO-THERMO THREE-STAGE DIGESTION
1. A three-stage system consisting of an upflow acid digester, an upflow
methane digester, and a CFCSTR methane digester performed better than the
meso-thermo or the thermo-thermo upflow two-phase systems primarily
because the CFCSTR methane digester exhibited considerably higher
gasification efficiency than the upflow methane digester.
2. It was observed that a thermophilic temperature of 60°C was detrimental
to methane fermentation of thermophilic acid-digester effluents; gas
production practically ceased at 60°C.
3. Considerably improved performance of a thermo-thermo upflow two-phase
system could be obtained when a prolonged enrichment and acclimation
period was used, and when a mixed Downers Grove primary/Stickney
activated sludge was substituted for the Hanover Park sludge*
Apparently, the degree of thermophilic inhibition could depend on the
nature and source of the raw sludge.
13
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MESO-MESO TWO-PHASE CFCSTR DIGESTION OF ENZYME-TREATED SLUDGE
1. Cellulase-cellobiase treatment of the feed sludge and lipase treatment of
the acid-phase digester increased the methane yield from the mesophilic
CFCSTR two-phase system by about 23% over that obtained from digestion of
the untreated raw sludge; this increase was significant at the system HRT
of 3 days used to evaluate the effect of enzyme treatment.
2. Carbohydrate reductions by the acid-phase digester and the overall two-
phase system were 50% and 64%, respectively, with cellulase-cellobiase
treatment compared with the corresponding reductions of 16% and 50%
obtained without enzyme treatment, indicating that the commercial enzyme
system was effective in hydrolyzing sludge carbohydrates.
3. Lipid reductions by the methane-phase digester and the overall two-phase
process were 36% and 39%, respectively, with lipase treatment compared
with the corresponding reductions of 9% and 27% obtained without such
treatment, indicating that the commercial lipase was effective in
hydrolyzing the sludge lipids.
4. Two-phase system effluents contained lower volatile acids concentrations
when the system feed sludge was enzyme-treated than those obtained
without any enzyme treatment. This performance, considered together with
the observed enhancement of methane content, yield, and production rate
achieved by enzyme treatment, seemed to indicate that enzyme treatment of
sludge had beneficial effects on the acidogenic, acetogenic, and
methanogenic organisms.
14
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SECTION 3
RECOMMENDATIONS
The process-comparison studies of this project demonstrated that the two-
phase digestion process can exhibit performances that are superior to those of
the single-stage digestion process under a comparable set of operating
conditions. These studies should be repeated with larger scale pilot systems,
but under one set of selected operating conditions and with CFCSTR digesters
and concentrated sludge feeds.
In this research the best system performance was exhibited by a two-phase
system that utilized high-SRT novel upflow digesters. It is recommended that
engineering studies be undertaken to investigate the flow regimes, solids-
retention characteristics, etc., of digesters of unconventional design.
Considerable work remains to be done to develop the structural details of
efficient digestion reactors.
This research indicated that the biochemical steps of acetogenesis and
aceticlastic and syntrophic methane fermentation could be severely retarded
during thermophilic fermentation of sewage sludge. It is recommended that a
separate investigation of the causative factors underlying this problem be
initiated.
The effect of temperature on acid and methane fermentation should be
studied in more detail than was accomplished in this project.
Stabilization (reduction) of volatile solids is an important criterion
for evaluating digester performance in a municipal wastewater treatment
plant. Volatile solids reduction calculation, which is needed for this
evaluation, is commonly based on an outmoded procedure. Unrealistic and
inaccurate results are obtained when determinations of residual sludge mass
for ultimate disposal are based on such calculation methods as the one
outlined in the Water Pollution Control Federation (WPCR) Manual of Practice
(MOP) No. 16. There is a need to develop a better, more accurate method for
the determination of volatile solids reduction during anaerobic digestion.
15
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SECTION 4
BACKGROUND
UTILITY OF ANAEROBIC DIGESTION
Waste Treatment Application
One of the widely used unit processes in sewage and industrial wastewater
treatment is anaerobic digestion. During its more than 100 years of commer-
cial application, anaerobic digestion has proved to be a cost-effective
disposal process because of the following characteristics:
• The capability to stabilize large volumes of dilute organic slurries
(sludge) at relatively low cost
• The capability to generate medium-Btu fuel gas from low-grade feed carbon
• Low tnicrobial cell mass production
• The capability to produce stable and odor-free solid residues of good
fertilizing value
• A high kill rate of pathogenic organisms and viruses.
Anaerobic digestion is preferred to alternative biological and thermo-
chemical sludge stabilization methods that are energy-intensive and have
unfavorable environmental impacts. Increased application of this process to
waste stabilization is expected, both to conserve energy and to help meet new
and stringent pollution abatement standards.
Sludge treatment and disposal are among the most difficult problems in
wastewater treatment and represent as much as 25% to 30% of the capital and
operating costs of a sewage treatment plant.^'^ Also, published data indi-
cate that about 40% of the total cost of sludge handling and disposal is
incurred in operating the digestion system. »' Any improvement of the con-
ventional sludge digestion process could thus result in substantial savings in
waste disposal costs.
Energy-Production Application; Methane From Wastes
One attractive feature of anaerobic digestion is its ability to convert
organic (and inorganic) carbon in the feeds to a product gas stream high in
methane, which has a high demand as a clean fuel. This aspect of the process
has prompted several investigators to advocate its application for the simul-
taneous stabilization and gasification of municipal, industrial, and agricul-
16
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tural wastes. There was an upsurge of interest in applying anaerobic diges-
tion for methane (substitute natural gas or SNG) production from biomass and
waste since the advent of the "energy crisis" in the early 1970's. The impact
of SNG from waste alone could be significant. For example, it is estimated
that in a city of 1 million people, 0.3 to 0.6 million SCM/day of SNG may be
obtained by digesting municipal sludge and refuse alone. This quantity of SNG
could satisfy 5% to 15% of the community's natural gas demand.
Nationwide, about 180 million metric tons of municipal refuse, 80 million
metric tons of industrial waste, 3 billion metric tons of agricultural wastes,
and 6 million metric tons of sludge solids are currently produced annually.
These wastes represent a renewable source of nonfossil carbon which, instead
of causing enormous land, air, and water pollution problems, could be
converted by anaerobic digestion to produce substantial amounts of
supplemental SNG.
Energy-Production Application; Methane From Biomass
Because of the ability of anaerobic digestion to generate fuel gases
(methane and hydrogen), an entirely new line of digestion process application
is developing for small- and large-scale conversion of biomass and other high-
moisture organic feedstocks to SNG.-'"8 Several authors have pointed out the
potential of biomass as a plentiful source of renewable energy for both the
developing and developed countries. It is recognized that biomass and waste
could supply up to 15% of U.S. energy needs by the end of this century via
gasification or other conversion schemes,-* and that anaerobic digestion will
play a major role in producing gaseous fuels from biomass. »' The feasibility
of SNG production by anaerobic digestion has already been demonstrated for
such biomass species as grass, algae, marine giant kelp, and water
hyacinth.9-16 The energy-production application of anaerobic digestion may in
time exceed its classical waste treatment application in terms of plant
capacity and investment.
Chemical Production
Considerable work has been done to demonstrate that certain novel
configurations of the anaerobic digestion process can be employed to produce
organic acids from biomass and wastes in reasonable yields with the residue
from the acid-production process converted to generate methane. '»* Since
the prices of the organic acids are about one order of magnitude higher than
that of methane on a mass basis, the economics of the digestion process
improve significantly with such dual applications.
CONVENTIONAL SLUDGE DIGESTION PROCESSES
Originating from the rather crude septic-tank system and the Imhoff tank,
the anaerobic digestion process has evolved through a series of modifications
into the high-rate digestion process now employed by many waste-treatment
plants. The most widely used process designs are the so-called "standard-
rate" (or low-rate) and "high-rate" digestion systems.
17
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Standard-Rate Digestion
Standard-rate digesters are unmixed, covered tanks with hydraulic
residence times (HRT's) of 30 to 60 days. These digesters are fed inter-
mittently at organic loading rates of 0.5 to 1.6 kg VS/m^-day.^ A state of
stratification exists in these tanks, and contact between influent organics
and the digesting organisms is limited. Consequently, standard-rate digestion
is frequently a diffusion-controlled process.
High-Rate Digestion
High-rate digestion differs from the standard-rate process in that con-
tinuous or more frequent feeding and mixing of the raw and digesting sludge
are used. Mass transfer, therefore, is theoretically not a limiting factor in
high-rate digestion kinetics. This allows process operation at reduced HRT's
of 15 days or less; loading rates of 1.6 to 3.2 kg VS/m^-day for high-rate
digester designs are common.
Anaerobic Contact Process
An advanced high-rate digestion system is the anaerobic contact process
which is comprised of a high-rate digester, a degasser (optional) and an
anaerobic settler. Effluent from the mixed high-rate digester is settled in
the settler and a fraction of the settler underflow is recycled to the high-
rate digester to maintain a higher biological population. As a result of cell
mass recycling, lower hydraulic residence times (9 to 12 days) are possible in
the contact process. However, the anaerobic contact process is more suitable
for dilute wastes; it is seldom used to stabilize municipal sewage sludge.
Two-Stage Digestion
Standard-rate digesters are single-stage systems that provide for diges-
tion, supernatant separation and sludge concentration, and even digested
sludge storage, all in the same tank. 9»20 Aside from the slower kinetics,
standard-rate digesters suffer from the disadvantage that valuable heated
digester space has to be provided for supernatant separation and storage.
Also, the supernatant withdrawn from standard-rate digesters is high in bio-
chemical oxygen demand (BOD) and suspended solids, probably because hindered
settling conditions prevail in these tanks.^ These difficulties are overcome
in the "stage-digestion" system in which the fermentation process is
accomplished separately from supernatant separation, sludge concentration, and
storage. In a common configuration of the stage-digester system, the first
digestion tank is mixed and is maintained at the optimum digestion tempera-
ture. The second tank receives digested sludge from the first tank and holds
it in a quiescent condition to permit a better solid-liquid separation and a
polishing treatment of the supernatant liquor. *»22 fhe "secondary stage" is
often a covered, unheated tank where the digestion process initiated in the
first tank continues to "technical completion" at a much slower rate. In
some systems an uncovered third tank may also be provided for winter and/or
operational storage.
18
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DISADVANTAGES AND LIMITATIONS OF CONVENTIONAL DIGESTION
It is well known that the overall anaerobic digestion process is mediated
by at least three different dominant groups of anaerobes — acidogenic,
acetogenic, and methanogenic organisms — that are responsible for liquefac-
tion, acetate formation, and methane production. These microbial groups are
different from each other in terms of physiology, metabolic characteristics,
growth kinetics, environmental requirements, and sensitivity to physical and
chemical environmental stresses and toxicity. The conventional digestion
process provides for the culturing of these diverse groups of organisms under
the same environmental conditions, and no attempt is made to optimize the
separate microbial phases. The single-stage conventional digesters harboring
mixed microbial phases are designed to accommodate the rate-limiting bio-
chemical step which is frequently that of the methanogenic population. This
design philosophy has led to the use of high HRT's, low flowthrough rates,
large digestion tanks, and high capital and operating and maintenance costs.
Digester operation at low flow rates results in low gas and methane production
rates and causes the relatively fast-growing acidogenic organisms to operate
at lower growth rates associated with the declining or the stationary growth
phases. In addition, considerable difficulties are encountered in mixing
large digestion tanks. Lack of adequate or "complete" mixing gives rise to
scum formation, sludge deposits, and accumulated incrustations, all of which
have the ultimate effect of reducing the active or effective volume of the
digester. It has been reported that up to 60% of the digester volume could be
"dead" space.
A serious limitation of the conventional single-stage digestion is the
occurrence of unbalanced acidogenic and methanogenic fermentations in response
to process operation at high organic loading rates. This is illustrated by
the data in Table l.^3 The data presented in this table show that as the
loading rate on the mesophilic sludge digester was increased, methane yield
and methane content of the digester gases decreased"while the digester vola-
tile acids concentration increased. Stable and balanced acidogenic and
methanogenic fermentations occurred up to a loading rate of about 1.9 kg
VS/m -day as indicated by the high methane yields, low residual VA's and high
VS stabilization efficiencies. At higher loadings, liquefaction and acidifi-
cation predominated over methane formation as indicated by the high VA
concentrations, lower methane yields and concentrations, and low VS reduction
efficiencies. Occurrence of high acids concentration had the effect of
inhibiting the methanogenic bacteria.
The above observations indicate that single-stage digesters have an upper
limit for the loading rate which is maintained in commercial digesters by
increasing the HRT and utilizing dilute feed slurries or both. Low HRT's and
high loading rates which decrease digester size and capital and operating
costs and increase net energy production (due to lower heating requirement)
cannot be applied to the single-stage CFCSTR digester because these operating
conditions lead to unbalanced acidogenic and methanogenic fermentations
resulting in dominant acidogenic activity, volatile acids accumulation, and
inhibition of methane fermentation.
19
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TABLE 1. STEADY-STATE PERFORMANCE OF CONVENTIONAL SINGLE-STAGE MESOPHILIC
(35°C) DIGESTION OF SEWAGE SLUDGE IN CFCSTR REACTORS
Loading rate,
kg VS/m3-day
1.28 (0.08)*
1.44 (0.09)
1.92 (0.12)
5.45 (0.34)
9.13 (0.57)
Methane content
of digester
mol %
72.7
69.5
70.1
57.7
51.1
Methane yield,
SCM/kg VS
added
0.300
0.310
0.290
0.076
0.047
Digester
volatile
acids, mg/L
100
80
100
1370
3220
VS
stabilization
efficiency, %
41.3
45.5
42.7
15.5
11.6
Numbers in parentheses are the loading rates in Ib VS/ft3-day.
PROCESS IMPROVEMENT NEEDS AND APPROACHES
In view of the important role of anaerobic digestion in sewage sludge
stabilization and energy conversion from various types of organic materials,
it is necessary to develop an innovative and alternative anaerobic digestion
technology that is capable of efficient and rapid-rate conversion of sub-
strates and of exhibiting higher net energy production efficiency. The
conventional digestion processes are not capable of meeting these needs.
Innovative digestion systems necessarily incorporate advanced reactor
designs and fermentation modes that permit process operation with concentrated
feeds at lower HRT's and higher loading rates than are possible with the
conventional high-rate process configurations. Achievement of these
objectives, of course, means reduction in capital and operating costs and
enhanced net energy (surplus methane) production.
Several approaches could be used to improve the anaerobic digestion
process. One approach is to develop and apply novel digestion reactors that
retain substrate and microbial solids for residence times significantly higher
than the HRT. For biochemical processes that are mediated by several micro-
bial phases, a staged fermentation system, referred to as "two-phase"
digestion, that permits separate optimization of the dominant microbial
reactions, is expected to exhibit superior performance. Thus, a unified
approach to process improvement would involve separate optimization of the
Net energy production efficiency = (Energy value of digester methane —
External thermal and electrical energies)/(Energy value of digester
methane).
20
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liquefaction-acidification and methanation phases with an appropriate novel
reactor design selected for each fermentation phase.2 »-*
Novel Process Concepts
Various approaches can be envisioned to enhance the efficiency, kinetics,
and stability of the anaerobic digestion process. Chemical or enzymatic
hydrolysis of the particulate feed and utilization of genetically improved
microorganisms, for example, could improve the process, but these methods do
not seem to be cost-effective or practical at this time. Engineering
approaches including application of advanced operating or fermentation modes
and utilization of novel reactors are feasible and merit development for
digestion process improvement in the near term. Thus, a two-part approach, as
outlined below, is needed:
• First, the kinetically dissimilar reaction steps of the overall digestion
steps must be optimized in isolated environments or reactor stages
because this is not achieved in single-stage mixed-phase digesters, as
indicated by the data in Table 1.
o Second, novel digestion reactor designs that provide high substrate and
microbial solids retention times (SRT's), must be developed and applied.
TWO-PHASE ANAEROBIC DIGESTION
The Phase-Optimization Concept
There is ample evidence in the literature indicating that the environ-
mental requirements and the growth kinetic characteristics of acidogenic and
acetogenic-methanogenic bacteria are very different from each other.17»19,26-35
Optimization of the above kinetically dissimilar microbial phases in separate
digesters has many advantages which include enhanced net energy production,
increased process stability, maximized substrate conversion, decreased
digester size and plant capital and operating costs, and production of a
higher methane-content gas. Phase separation can be achieved by inhibition of
methane formers,3*' dialysis separation, or kinetic control. Phase
separation by kinetic control of nonmethanogenic and acetogenic-methanogenic
bacterial growth by adjustment of HRT and reactor loading rate is the simplest
and has been applied by several researchers since it was first demonstrated by
Pohland and Ghosh.19 In the two-stage two-phase approach, hydrolysis and
acidogenesis are dominant in the first-stage digester and aceticlastic
methanogenesis is the predominant reaction in the second-stage digester
(Figure 1). Methane fermentation by carbon dioxide reduction, which is
mediated by hydrogenotrophic methanogens and is faster than the aceticlastic
reaction and is recognized to be the primary source of methane in anaerobic
digestion, is not dominant in the lower-HRT acid-phase digester.
Acetogenesis, which is the process of oxidation of higher fatty acids to
acetate, is supposedly a slow reaction because of the unfavorable free energy
of reaction, and may not be an important conversion step in the first-stage
digester. For highly biodegradable liquid substrates which could be rapidly
converted by fermentative pathways to acids and molecular hydrogen, acetogen-
esis may not occur in the first-stage digester and may thus be shifted to the
21
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second stage. On the other hand, some acetogenesis may occur in the first-
stage digester when it is charged with particulate substrates. Acetogenic
conversion could also occur in the first-stage digester when higher HRT's or
SRT's are used to promote hydrolysis at a higher efficiency.
Phase Separation with CFCSTR Bioreactors
Commercial high-rate digesters are intermittently or continuously mixed
by compressed digester gas, mechanical agitation, or recirculation of the
digester contents. The first proposed two-phase digestion process configura-
tion consisted of two conventional CFCSTR reactors operated in series.
Anaerobic settlers can be installed in tandem with each digester to permit
densification and recycling of settled effluent solids to increase microbial
and substrate solids retention times (SRTm and SRTS). Figure 2 represents a
physical model of the two-phase anaerobic digestion process utilizing
complete-mix digesters and anaerobic solid-liquid separators. The purpose of
the solid-liquid separator, according to classical concepts, is to produce a
concentrated stream of microbial mass and to selectively retain the microbial
solids within the digestion system longer than the HRT. In this way, the
microbial solids residence time (SRTm) is higher than the HRT, and the
efficiency of the digestion process is enhanced commensurate with the value of
the ratio of SRTffi to HRT.
Application of Novel Biodigesters
With few exceptions, solids-liquid separation is difficult with most
anaerobic digester effluents, and separate settling of the effluent solids as
shown in Figure 2 is not practical. Novel reactor designs which combine
solids retention with digestion, and are equivalent in performance to the
classical digester-separator combination shown in Figure 2, have been deve-
loped and applied successfully during the last two decades. In these
digesters the microbial and substrate solids residence times are considerably
higher than the HRT, and these reactor characteristics provide the following
dual benefits:
• For a given HRT, the high-SRT novel digester exhibits a higher substrate
conversion efficiency than that of a complete-mix digester.
• The critical or wash-out HRT of a novel digester is considerably lower
than that of a complete-mix digester, which means that the former
digester can provide a selected conversion efficiency at a much lower HRT
than that of the latter.
The benefits of acidogenic conversion of soluble and particulate sub-
strates in high-SRT digesters are illustrated in Figures 3 and 4. In these
examples, the novel digester was assumed to have a microbial or a substrate
solids residence time that was double the HRT. The growth kinetic constants
(maximum specific growth rate, y, and saturation constant, K, for the soluble
carbohydrate and the sewage sludge volatile solids substrates are shown on
Figures 3 and 4; these kinetic constants and the biokinetic models on which
these curves of Figures 3 and 4 were based on work presented in an earlier
paper.38 Inspection of Figure 3 shows that a high-SRT novel digester can
23
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FEED-
re
GAS
ACID
REACTOR
SOLIDS RECYCLE
RECYCLE FOR INTERPHASE NEUTRALIZATION
EFFLUENT
WASTE
SOLIDS
Figure 2. Physical model of the two-phase anaerobic digestion process.
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~2L
UJ 70
i ,j
W 1
O
»-« 60
U_
UJ 50
2 4°
CO 30
o:
LU
> 20
z
o 10
n
^ — — — • ~^——~~
FEED = 5 g/L /^ X^"^
^- 1.25 h-' / /
K = 23 mg/L
_
HIGH-SRT NOVEL
DIGESTER
(SRTm = 2 HRT)
w
-
-
i i
' /
1
COMPLETE-MIX
DIGESTER
(HRT = SRT)
i t
i
0
10 20 30 40
HYDRAULIC RESIDENCE TIME,
50
60
m i n
A85040277H
Figure 3. Efficiency of acidogenic conversion of a soluble carbohydrate
substrate (glucose) by complete-mix and high-SRT novel digesters.
-------
to
NOVEL
DIGESTER
> 80-
NOVEL
DIGESTER
(SRTm =
2 HRT)
COMPLETE-MIX
DIGESTER
(HRT = SRT)
8 30
40 g/L
0.16 h"1
5 10 15 20 25
HYDRAULIC RESIDENCE TIME, h
A85040278H
Figure 4. Efficiency of acidogenic conversion of municipal sludge volatile
solids by complete-raix and high-SRT novel digesters.
-------
exhibit the same conversion efficiency as that of a complete-mix reactor, but
at one-half the HRT of the latter digester; this superior performance of the
novel digester in converting the soluble feed is due to enhanced retention of
the microbial solids. Novel digesters would exhibit similar improvement in
performance when charged with particulate feeds because of microbial solids
retention. However, like microbial solids, substrate solids are also retained
longer than the HRT, and an additional increase in efficiency over that
effected by microbial solids retention alone is realized by use of the high-
SRT novel digesters. Thus, as indicated in Figure 4, a complete-mix
conventional digester requires an HRT of about 28 hours to exhibit an 80%
conversion efficiency with sludge VS; a novel digester in which the SRTm and
SRTS are twice the HRT, the same conversion efficiency can be achieved at an
HRT of about 8 hours.
High SRT novel digesters that utilize suspended-growth cultures and
combine digestion with solids retention within the same vessel, and are
primarily suitable for soluble feeds, include the Dorr-Oliver Claridigester,
the Tower digester developed by the University of Sydney, Australia, and the
Baffle-Flow digester developed by Prof. McCarty of Stanford University. In
still other novel reactor designs, microbial solids are retained by immobil-
izing the cells on to static or moving media. The UASB Biothane and the Dorr-
Oliver Anitron digesters and the biodisc reactor are examples of cell reten-
tion by immobilization on moving media (e.g., "granules" for UASB and sand for
the Anitron digesters). By comparison, the Celrobic and the Bacardi downflow
anaerobic filters retain solids by fixation of cells on static media used to
pack the digestion vessel. A system that is of hybrid design and utilizes
both the suspended-growth and the fixed-film cultures has also been applied
successfully in laboratory scale. A more detailed discussion on the design
and operating characteristics of the above "novel" digesters can be found in a
recent publication.
All the novel digesters discussed above are suitable for low suspended-
solids content soluble feeds. Novel digesters that are expected to provide
high SRT's and are suitable for particulate feeds include the Pfulg-Enerbio
digester,2* the ENEA plug-flow digester, and the upflow digester with solid
deflectors.23
Advantages of Two-Phase Digestion Based on Kinetic Considerations
The application of kinetic control to separate the acid-forming and
methane-forming phases of anaerobic digestion of soluble substrates was first
demonstrated by Pohland and Ghosh,19»2° and later by Ghosh et al,28 Ghosh and
Klass,38»39 Heerties and van der Meer,^° Smith et al.,41 Cohen et &1»t and
Ghosh and Henry.3^
Pohland and Ghosh,19»26 and Ghosh and Klass38 studied the kinetic
characteristics of acid-forming and methane-forming organisms derived from a
digested sewage sludge inoculum and reported the kinetic constants for the
acidogenic and raethanogenic mixed cultures (Table 2). Kinetic rate constants
for acidogenic and methanogenic bacteria were assumed based on previous
experiences and results for two-phase and combined-phase systems fed with
70 g/L (of volatile solids) in sewage sludge. These assumed constants were
27
-------
TABLE 2. ESTIMATED KINETIC CONSTANTS FOR MESOPHILIC (37°C) ACIDOGENIC AND
METHANOGENIC CULTURES GROWN ON SOLUBLE AND PARTICULATE SUBSTRATES
Kinetic constant
tss
00 Maximum specific
gjowth rate,
(li), day
Saturation
constant,
(K), mg/L
Acid
grown
Batch
cultures
7.2
400 as
glucose
formers
on glucose
Continuous
culture
30.0
23 as
glucose
Acid formers
grown on
sewage sludge
Continuous
culture
3.84
26.0
as VS
Methane
Mixed volatile
acids substrates
from glucose
(Continuous culture)
3.4
600
as acetate
formers
Acetate substrate
(semicontinuous
culture)
0.49
4200
as acetate
Cell yield
coefficient
0.15
0.17
0.4
0.28
-------
used to generate theoretical performance curves for acid-, methane-, and
combined-phase digesters indicated in Figures 5 through 7.
Examination of the data in Table 2 shows that the values of the kinetic
constants depend to a significant extent on the nature of the substrate and
the culturing mode. It is reasonable to expect, therefore, that considerable
improvement in individual culture kinetics may be achieved by optimizing the
growth environment for each class of digesting bacteria. Thus, by separate
culturing of the acidogenic and methanogenic organisms, it is possible to
maximize volatile solids conversion (hydrolysis) and volatile acids production
(acidification) rates in the acid-phase digester, as shown in Figure 5. For
the operating conditions indicated in Figure 5, volatile acids (acetate)
conversion to methane (methanogenesis) cannot occur in the acid digester below
a critical HRT of about 2.3 days, and the volatile acids conversion rate is
lower than its production rate at higher HRT's. Conversely, volatile acids
conversion rate (methanogenesis) is maximized in the separate methane
digester, and is much higher than volatile acids production rates at all HRT's
(Figure 6); these characteristics of the separate methane digester lead to
increased process stability and insurance against unbalanced acidogenic-
methanogenic fermentation, which could occur in a single-stage digestion
process at low HRT's as shown in Figure 7.
In contrast to the operating characteristics of the separate methane
digester of a two-phase digestion process, volatile acids production rate is
higher than volatile acids conversion rate in a single-stage CFCSTR conven-
tional digester unless it is operated at a high HRT of about 22 days or higher
for the example process depicted in Figure 7. Single-stage digester operation
at lower HRT's means 1) unbalanced acidogenic-methanogenic fermentation and
the consequent accumulation of volatile acids which in turn leads to
inhibition of the methane formers, and 2) maintenance of the hydrolytic and
acidogenic bacteria at low growth rates and in the stationary or endogenous
growth phases which could be significantly deleterious to the overall
conversion process.
A comparison of the theoretical performances of the two-phase and single-
stage CFCSTR processes whose operating characteristics are depicted in
Figures 5 through 7 shows that the two-phase process could be operated at a
much higher loading rate and a much lower HRT than those of the single-stage
process, and yet would provide a 79% increase in methane production rate with
both processes exhibiting about the same methane yield (Table 3).
In developing the above theoretical treatment, kinetic models applying to
acetate-utilizing methanogens, which are predominant and rate-limiting in
sludge-fed methane digesters, were utilized. In addition, substrate
inhibition of methanogenesis was not considered since it was assumed that
residual volatile acids concentration in the single-stage and the methane
digester of the two-phase system would be maintained at non-inhibitory levels
by appropriate selection of digester HRT and the loading rate. Kinetic models
utilized to develop the theoretical basis for superior performance of the two-
phase anaerobic digestion relative to the single-stage process, were reported
in earlier publications.26,28,29,38,43 Two-phase process performance observed
29
-------
u>
o
90
80 -
O D 70
(!)
60
O— 50
O 3
\ 0
§_l 40
H 0)
B - 3°
QLJ
Oh-
Q.Q:
20
10
0
VOLATILE SOLIDS
CONVERSION RATE
VOLATILE ACIDS
PRODUCTION RATE
I /VOLATILE ACIDS
1 /CONVERSION RATE
123456789101112
HYDRAULIC RESIDENCE TIME (HRT), days
A85050323H
Figure 5. Operating characteristic of a complete-mix acid-phase digester
charged with sewage sludge having a volatile solids concentration of
70 g/L (kinetic constants assumed were \i = 3.84 day"* and K = 26 g/L for
acid formers, and \i = 0.49 day"^ and K = 4.2 g/L for methane formers).
-------
16
.
O 0
I-.-D
CO I
Qd <5
UJ L
> D
Z-P
O —
O 3
\ 0
H D)
O
QUJ
Oh-
Ql<
O.Q:
"o
CO
\
u.
o
CO
9
UJ
UJ
12h
10
8
6
4
o
EFFLUENT
iVOLATILE
UCIDS
VOLATILE ACIDS (VA)
'ERSION RATE
TWO-PHASE SYSTEM
METHANE YIELD
VOLATILE ACIDS
PRODUCTION RATE
4000
_
0)
E
CO
3000 O
i— i
o
UJ
2000
O
1000
1234567891011
HYDRAULIC RESIDENCE TIME (HRT), days
0
12
UJ
u.
u_
LU
A85050322H
Figure 6. Operating characteristics of a complete-mix methane digester
charged with effluents from an acid-phase digester which is operated with a
sludge volatile solids concentration of 70 g/L (see Figure 4.5) at an HRT
of 2 days (kinetic constants assumed were p = 3.84 day"* and K = 26 g/L
for acid formers, and y = 0.60 day"* and K = 3 g/L for methane formers).
-------
OJ
EFFLUENT
VOLATILE
ACIDS
4000
- 1000
2 4 6 8 10 12 14 16 18 20 22
HYDRAULIC RESIDENCE TIME (HRT), days
0)
E
-3000
Q
n
O
2000 u
_j
O
UJ
u_
u.
UJ
24
A85050321H
Figure 7. Operating characteristics of a single-stage complete-mix
conventional digester charged with sewage sludge having aA volatile solids
concentration of 70 g/L (kinetic constants assumed were y 3.84 day"^ and
36 g/L for acid formers, and \i = 0.49 day
methane formers).
-1
and K = 6 g/L for
-------
TABLE 3. COMPARISON OF THEORETICAL PERFORMANCES OF CFCSTR SINGLE-STAGE
AND TWO-PHASE DIGESTION OF SEWAGE SLUDGE
CFCSTR Two-phase digestion
CFCSTR
single-stage
Acid-phase Methane-phase System
Sludge VS concentration,
g/L
HRT, days
Loading rate, kg
VS/m3-day
Methane production
rate, SCM/m^-day
Methane yield, SCM/kg
VS added
Residual VA in methane
digester, mg/L
70
2
35.0
10
7.0
3.0
0.385
600
70
12
5.8
2.5
0.385
70
22
3.2
1.4
0.365
610
Kinetic constants assumed in developing the performances are reported in
Figures 5 through 7. It was assumed that gas from" the single-stage
digester has a methane content of 60 raol % and that gas from the acid
digester has 70 mol % methane. It was further assumed that 90% of the
volatile acids is converted to gas in the two-phase system compared with
85% for the single-stage digester.
in this project were generally in agreement with the type of projections that
can be made from these models and are presented in Table 3.
The performance of a two-phase system is expected to be superior to that
of a single-stage system irrespective of the reactor type used as the
digestion vessel. The theoretical development presented in the foregoing
paragraphs was based on the application of CFCSTR digesters. But similar
development is possible for other novel high-SRT bioreactors. For example, it
could be shown that a two-phase system consisting of a UASB acid digester and
a UASB methane digester exhibits superior performance relative to a single-
stage UASB system.
33
-------
Historical Development of the Two-Phase Concept
9 o
Babbit and Baumann" were probably the first to suggest that separation
of the anaerobic digestion process into "two or more stages" may have the
advantage of overcoming the inhibitory effects of the intermediate products
(for example, volatile acids) in the early stages (hydrolysis and acidifica-
tion) of digestion. The first experimental work on two-phase digestion was
conducted by Hammer and Borchardt, ^ and Schauraburgh and Kirsch. 6 These
researchers attempted to separate the acid and methane phases by dialysis
membranes, selected inactivation of the acid- or methane-formers by
appropriate inhibitors. »° The complexity and operational difficulties of
these techniques with acidogenic and methanogenic organisms, however, make
them unattractive and impractical. Since the cited work, little interest has
been expressed in these methods for separating the microbial phases of
anaerobic digestion.
Phase Separation by Kinetic Control
A much simpler and more practical technique to separate and maintain
dominant microbial phases is that studied by Ghosh and Pohland. This
technique, termed "kinetic control, relies on the principles of population
dynamics and enrichment of the acidogenic and methanogenic phases in separate
digesters by simple operational adjustment of the reactor dilution rate or the
organic loading rate and cell mass recycle ratios. The objectives of these
adjustments are to exceed the maximum specific growth rate of the acetate-
utilizing methane formers by the allowable growth rate in the first reactor
(acid digester), and to promote maximized conversion of the biodegradable
substrates in the first phase to volatile acids and other intermediates
acceptable to the acetogenic bacteria and the methane formers. Considerable
work has been done to accomplish phase separation by kinetic control since
Pohland and Ghosh reported the results of their phase separation studies in
1971. Various configurations of two-phase digestion have been developed for
the digestion of liquid, "semi-solid," and "solid" substrates which are
briefly described in the following sections.
Two-Phase Digestion of Soluble Substrates
The application of kinetic control to separate the acidogenic and
methanogenic phases of anaerobic fermentation of soluble substrates was first
demonstrated by Pohland and Ghosh,19'26 and later by Heertjes and van der
Meer,47 Smith et al.,^1 Cohen et al., and others. Ghosh and Pohland^5 also
presented kinetic models describing the velocities of production as well as
the concentrations and yields of product acids and gases from two-phase diges-
tion of soluble substrates. A comparative study of the kinetic characteris-
tics of the acidogenic and methanogenic organisms was also presented.
Various reactor designs, differing from the completely mixed digesters
used by Pohland and Ghosh, were studied by other researchers. Cohen et al.
experimented with a two-phase system consisting of a completely mixed acid-
phase reactor and a plug-flow type upflow methane digester with a built-in
settler to conduct anaerobic digestion of glucose. The cell yield coefficient
in the acid-phase digester at 30°C was 0.11, compared with a yield coefficient
34
-------
of 0.17 at 37°C reported by Ghosh and Pohland.29»45 Ethanol, acetate, propio-
nate, butyrate, formate, lactate, carbon dioxide and hydrogen were the main
products of acidogenesis. Butyrate was produced in the largest concentra-
tions, followed by acetate. The acidogenic reaction products were gasified in
the upflow methane digester to produce head gases having 84.3 mol % methane
and 15.7 mol % carbon dioxide.
Ghosh47 and Ghosh and Henry^ operated a CFCSTR acid-phase and an upflow
packed-bed methane digester with real soft-drink bottling waste, and deraon-
•strated that a two-phase digestion process could be operated at about seven
times the loading rate and one-half the HRT of the conventional process and
still obtain the same methane production as, and a slightly higher COD reduc-
tion than, the conventional process (Table 4). An important advantage of the
two-phase process was that gases from the methane phase had a significantly
higher methane content than those of the conventional digester. It was
projected that two-phase operation would allow the total digester volume (and
associated capital and operating costs) to be reduced by 67% and the net
energy production to be increased by more than 73% relative to those of the
conventional process. Also, while the conventional high-rate digester failed
at an HRT of 10 days and a feed COD concentration of 26,000 mg/L, the two-
phase process exhibited stable and efficient performance at a system HRT of
7.4 days and a feed COD concentration up to 45,000 mg/L.
The two-phase digestion process has been proven in both pilot- and full-
scale operation at overall loading rates up to 12 kg COD/m^-day and HRT's down
to 13 hours, affording the same or higher methane yields as achieved at one-
tenth the loading rate and ten times the HRT needed for stable operation of a
single-stage high-rate digester. °»4" The commercial process (known as the
Anodek process in Europe) utilized a,CSTR acid-phase digester operated in
tandem with a UASB methane digester. '
Heertjes and van der Meer^ also conducted two-phase digestion of
saccharose and sodium acetate in an upflow digester with an internal settler
built at the top (effluent end) of this digester. High conversion efficien-
cies were obtained at 3- to 6-hour residence times and a relatively low
loading (1.92 kg TOC/m^-day). A two-reactor two-phase system exhibited
increased stability at higher loadings up to 11.84 kg TOC/m^-day.
Smith et al.^1 operated a packed-bed mesophilic (37°C) upflow methane
digester ("anaerobic filter") with solids-free acidic substrates derived from
animal wastes. Satisfactory acid-phase digestion could not be developed with
this waste. Methane digester gas production rates from 0.24 to a high value
of 2.77 volume/digester volume-day were observed at hydraulic retention times
of 1.1 to 40.5 days.
Pipyn et al.-*° investigated anaerobic digestion of distillery wastewaters
(~10,000 mg/L COD) in a two-phase pilot plant consisting of a 36-m3 CFCSTR
acid-phase digester and a 5-m upflow methane-phase digester. The acid-phase
was operated at 42°±2°C at an HRT of 16 to 72 hours, while the methane-phase
digester was maintained at 39°±2°C and an HRT of 14 hours. Overall COD and
BOD reductions of 84% and 92% were obtained. The methane digester gases had a
methane content of 75±3 mol %.
35
-------
TABLE 4. HIGH-RATE AND TWO-PHASE MESOPHILIC (35°C)
DIGESTION OF SOFT-DRINK BOTTLING WASTE
Loading, kg VS/m -day
HRT, days
Methane yield, SCM/kg VS added
Methane content, mol %
Conventional
high rate
0.64
15
0.64
61.1
Acid
phase
16.0
2.2
0.06
0.2
Two-phase
Methane
phase
6.4*
5.2*
0.59
70.5
Overall
4.8
7.4
0.61
63.1
Gas production rate,
SCM/m3-day
Digestion efficiencies, %
VS reduction
COD reduction
Digester volume for 9090 kg/day
TS load, 1000 m3
Net energy production
106 kcal/day
Percent of total production
0.4
72
84
5.6
11.7
37
1.03
0.6
3.68
1.2
2.90
64
96
1.8
20.2
62
Loading and HRT of the upflow filter methane digester were calculated on the
basis of the gross volume of the packed bed.
Two-Phase Digestion of Semi-Solid Substrates
28
=38
Ghosh et al. ° and Ghosh and KlassJ° first demonstrated the feasibility
of separating the acid and methane phases of anaerobic digestion of a
particulate feed (activated sludge) by kinetic control. Satisfactory acid-
phase digestion occurred at hydraulic retention times of 10 to 24 hours and
high loadings of 32 to 80 kg VS/m3-day. Acidogenesis occurred at an
oxidation-reduction potential (Ec) of -240 mV and a pH of 5.7, compared to
-400 mV and 7.0 for methane formers. Kinetic constants were determined for
both phases of activated sludge digestion. Methanogenesis was the rate-
controlling step of the overall digestion process. The methane digester gases
contained 70 mol % methane. One important finding from this work was that
36
-------
high reactor loadings are required to maximize acid production rate per unit
reactor volume and to minimize acid digester retention time. °»->u Two-phase
mesophilic digestion of 1.7 to 2.5 wt % VS-content Chicago activated sludge
exhibited an average methane yield of 0.27 SCM/kg VS added and a VS reduction
of 40%28 at an overall HRT of 6.9 to 7.7 days compared with 0.22 SCM/kg VS
added and 34% observed during conventional digestion of this sludge at an HRT
of 14 days. The methane content of conventional digester gases was 60 mol %
compared with 70 mol % in the head gases of the methane-phase digester.
Eastman and Ferguson27 conducted acid-phase digestion of primary sewage
sludge at HRT's of 9 to 72 hours, and concluded that hydrolysis of the solid
sludge particles was the rate-limiting step of the overall acidogenic phase.
Lipids were not biodegraded, and 50% of the non-lipid COD of primary sludge
was solubilized. Acidogenic sludge was difficult to settle. Hydrogen
evolution occurred at the minimum detention time of 9 hours. Volatile acid
production and distribution of acid species in the effluent appeared to be
influenced by the reactor pH. Brown-'* indicated that hydrolysis of particu-
late substrate was favored at an acidic pH (pH 6), and methane fermentation of
the acid-digestion products was better at an alkaline pH (pH 7.5). Detailed
investigation of the pH effect, however, was not conducted to delineate the pH
optima. The methane digester gases contained 80 mol percent methane.
Norrman and Frostell52 conducted mesophilic (33°C) two-phase digestion of
a semi-solid synthetic feed (blended dog food) in a laboratory system
comprised of a completely mixed acid-phase digester and a packed-bed upflow
methane digester. The acid digester was followed by a 500-mL gravity settler,
the supernatant from which was fed to the packed-bed methane digester. Acid
digester pH was low (pH 4). Solid-liquid separation was a problem with the
acid-digester effluent. The overall system was operated at HRT's of 2.7 to
12.1 days and low loadings of 0.42 to 2.24 kg VS/m3-day. A long starting time
was required for the anaerobic filter. The methane digester gases contained
65 to 80 raol % methane. Like Norrman and Frostell,' Therkelsen and Carlson-33
also investigated the two-phase digestion characteristics of dog food, but at
a thermophilic temperature of 50°C. The performances of completely mixed and
plug flow acid digesters were compared. Surprisingly, lactate was the major
acidic product. The pH of the acid digester was also low (pH 4) and grease
and organic nitrogen were not reduced significantly. One interesting
observation was that acid production in a plug-flow acid digester was much
higher than that in the complete-mix reactor. At the test loadings (5.9 to
9.9 kg VS/m3-day) and HRT's (4.3 to 7.5 days), two-phase thermophilic
digestion of dog food was slightly better than thermophilic conventional
digestion.
Keenan54 conducted two-phase digestion of simulated solid waste (Purina
Dog Chow) at 22° and 48°C. The acid-phase digester had relatively long HRT's
of 4.5 and 6 days; the methane digester had a HRT of 10 days. Acid digester
gases contained mainly C02 and a small amount of hydrogen. Gases from the
methane digester had 80 mol percent methane. The acid digester effluent had
13,000 to 14,000 mg/L of volatile acids. There was no significant difference
in acid conversion efficiencies at 22° and 48°C. The two-phase process
exhibited higher stability than the conventional mixed-phase high-rate
process.
37
-------
In contrast to the two-reactor systems studied by most researchers,
Johnson-*-* found evidence of separation of the acidogenic and methanogenic
phases during anaerobic fermentation of pig excrement and biomass leachate in
a four-stage system. The two-phase multi-stage process was superior to
conventional high-rate digestion.
Two-Phase Digestion of Semi-Solid Feeds With Novel Upflow Bioreactors
A review of the literature on digestion of such particulate feeds as
sewage sludge, municipal solid waste, manure, and various biomass species
showed that mesophilic digestion of these feeds is generally conducted at an
HRT higher than 10 days and at loading rates lower than 3.2 kg VS/m3-day.?3'56
Best methane yields and methane production rates are less than 0.42 std m /kg
VS added and 1.9 vol/culture vol-day, respectively. These performances were
significantly exceeded during digestion of sewage sludge in an advanced two-
phase system comprised of custom-designed and unmixed upflow digesters
operated in series to optimize the liquefying-acidification and acetogenesis-
raethanation reactions. The system was operated in a continuous mode for
about 16 months and exhibited a progressively increasing methane yield at
HRT's of less than 6 days. With continuing culture enrichment and improve-
ments in reactor design, the methane yield increased from 0.31 to 0.43 SCM/kg
VS added, and then to 0.48 SCM/kg VS added (Table 5). This methane yield was
about 77% of the theoretical methane yield achievable with this sewage sludge
and is the highest methane yield reported for sludge at this HRT. Operation
of the novel process configuration was very stable and superior to that of
conventional single-stage digestion in terms of methane yield, gas production
rate, and net energy production. Considerations of the volatile suspended
solids (VSS) and particulate (or solid-phase) COD inputs to and outputs from
the acid- and methane-phase digesters showed a liquefaction efficiency between
46 and 55% in the first-stage digester compared with a liquefaction efficiency
between 0 and 10% only for the methane digester. 3 Acetogenesis and
methanogenesis predominated in the second-stage digester. Whereas little
methane fermentation occurred in the acid-phase digester at an HRT of 1.1
days, methane production increased 20-fold when the first-stage HRT was
increased to 1.3 daysj acetate was the major volatile acid at the lower HRT,
but propionate predominated at the higher HRT.
As shown in Table 6, a 91 metric ton/day hypothetical two-phase upflow
digestion plant requires about 60% of the digester volume needed for a
conventional single-stage system, and exhibits a VS reduction three times that
of the latter process. These performances translate to substantial savings in
capital and operating costs. The single-stage conventional process is a net
energy consumer for a low-HRT operation. By comparison, about 83% of the
digester methane is available as surplus bio-fuel if a two-phase upflow
digestion process is used.
Two-Phase Digestion of Solid Feeds
The two-phase digestion systems described above are suitable for semi-
solid feeds; the above process configurations may not be applied to gasify and
stabilize solid feeds unless they are diluted to form slurries. This dilution
approach, although commonly employed, is not attractive for many reasons. A
38
-------
TABLE 5. PERFORMANCE OF AN ADVANCED TWO-PHASE UPFLOW MESOPHILIC (35°C)
DIGESTION SYSTEM AT AN HRT OF 5.9 DAYS (1.3 Days for Acid Phase and
4.6 Days for Methane Phase) WITH A 5.8 wt % TS-CONTENT FEED
Operating conditions/performance Acid phase Methane phase System
Run duration, number of HRT's
Loading rate, kg VS/nr-day
35
28.8
10
7.8
8
6.2
Gas production
Methane yield, SCM/kg VS added 0.06 0.42 0.48
Methane content, raol % 59.2 70.1 68.4
Methane production rate, SCM/m3-day 1.77 3.27 2.96
Effluent characteristics
pH 6.6 7.2 7.2
Volatile acids, mg/L
Acetic 643 77 77
Propionic 2251 48 48
Isobutyric 123 0 0
n-Butyric 141 0 0
Isovaleric 266 0 0
n-Valeric 79 0 0
Caproic 000
Total as acetic 2827 118 118
Ethanol, mg/L 000
special process configuration — leach-bed two-phase digestion — is more
suitable for "dry" or high-solids-content feeds, is simpler than slurry-phase
digestion, and is conducted without dilution of the feed, without mixing, and
even under ambient conditions. Leach-bed solid-phase anaerobic fermentation
is particularly attractive for such low-moisture organic feeds as municipal
and industrial solid wastes, sludge cakes, manure, agricultural and forestry
residues, farm wastes, and other similar organic biomass and wastes.
The leach-bed two—phase digestion process overcomes the difficulties of
the so-called dry digestion by inducing rapid bio-leaching of the solid feed
by application of an acidogenic culture, and promoting continued and
accelerated liquefaction and acidification of the bed by recirculation of the
reactivated culture (Figure 8). This fermentation approach employs active
control of all phases of the overall digestion process. Liquefaction products
from the acidogenic leach-bed are moved to an acid-recovery process or are
diverted to a separate methane-phase digester for gasification of the volatile
acids with recycling of the methane-phase effluent to the leach-bed to
39
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TABLE 6. COMPARISON OF HYPOTHETICAL CONVENTIONAL AND TWO-PHASE UPFLOW
MESOPHILIC (35°C) DIGESTION SYSTEMS TO STABILIZE AND GASIFY
91 METRIC TONS/DAY (Dry Solids Basis) OF SLUDGE AT AN HRT OF 5.5 DAYS
Conventional
Operation and performance
Feed VS, wt %
' o
Loading rate, kg VS/nr-day
Methane yield, SCM/kg VS added
Methane production rate, SCM/nr* vol-day
VS reduction to gas, %
Gross methane production, 10 std m^/day
Estimated operating energy requirement, 10^ kcal/day
Feed sludge heating
Mixing
Pumping
Heating, ventilation, lighting, other
Total
Net energy production, 10^ kcal/day
Digester volume, 1000 in-*
2.2
4.0
0.13
0.5
24
6.8
61.2
1.5
0.5
2.0
65.2
4.8
13.6
Two-stage
upflow
3 7
•J • /
6.6
0.48
2.8
75
26.6
38.6
0
0.8
1.3
40.7
196.6
8.3
conserve the nutrients indigenous to the solid substrate and thus to eliminate
or reduce the need for external nutrient addition.
The leach-bed two-phase digestion process is superior to the traditional
slurry-culture single-stage digestion process because —
• It is able to handle "dry" or high-solids-containing feeds.
• A minimum of feed processing (e.g., shredding, grinding and separation)
and feed pretreatment (e.g., chemical or enzymatic) are necessary.
• Feed slurrification is not necessary.
• Intensive mechanical mixing is not required.
• Addition of external nutrients is eliminated or minimized.
• The process can be applied for in-situ bioconversion of waste deposits
(e.g., landfills) and the ultimate disposal of the final residues.
40
-------
GASES
FEED
SOLID BED
RECYCLE
CONTROLLED
ENVIRONMENT
ACID
RECOVERY
I
t
PRODUCT ORGANIC ACIDS
r
CH4
CO 2
METHANE
FERMENTER
A84050465H
Figure 8. Leach-bed two-phase anaerobic digestion.
-------
• Fermentation can be conducted in simple containment vessels.
• There are fewer fermenter volume and energy requirements, compared with
the conventional dilute-slurry fermentation processes.
Investigation with a small pilot-scale system consisting of a 126-L
refuse-derived feed (RDF)-filled mesophilic (35°C) leach bed and a mesophilic
12.5-L methane-phase anaerobic filter exhibited a volatile acids yield of 23%
(0.23 g acids/g VS) and a methane yield of 0.31 SCM/kg VS added, indicating
complete conversion of the biodegradable fraction of refuse.-^ For batch
operation, gasification was virtually completed in about three months. The
leach-bed two-phase digestion process can be operated in the sequential-batch,
fed-batch, or the semi-continuous fermentation mode. Leach-bed two-chase
digestion of municipal landfill is known as the LanFilgas® process.
Benefits of Two-Phase Digestion
Based on data reported in the literature, it appears that two-phase
anaerobic fermentation has the potential of fulfilling the need for a short-
residence-time and high-efficiency bioraass/waste-to-methane conversion
process. Acid-phase digestion can be conducted at HRT's as low as 3 to
6 hours for soluble organics and 9 to 48 hours for particulate organic
material. The overall two-phase system can be operated at HRT's of 2 to
7 days depending on the feed — a substantial improvement over conventional
high-rate digestion conducted at HRT's of about 12 to 20 days.
In addition, two-phase digestion has several other demonstrated and
potential benefits as follows:
o The capacity of maintaining an optimum environment for each group of
digester organisms, thus optimizing the overall "digestion process.
• A substantial reduction in total reactor volume and consequent savings in
capital and operating costs.
o Improved mixing in smaller low-residence-time digesters.
• Possibility of auto-mixing by the high-rate of gas production.
• Higher rates of solids stabilization and methane production.
• Much higher methane content (up to 85 raol %) of the final product gas.
• Decreased heat requirements and increased net energy production.
• Suitability for incorporation into existing treatment plants with minimum
capital investment.
• Reduction of the nitrogen content of the system effluent by simultaneous
liquefaction and denitrification of waste feeds in the acid digester.
42
-------
• Increased process stability because the sensitive methane bacteria are
separated and are not subjected to environmental shocks of sudden acid
production and dropping pH.
It is expected that the cost of operating a two-phase digestion system
would be significantly lower than that of conventional single-stage digestion
because of reduced operating energy requirements, lower residue disposal
costs, and lower annualized plant capital cost.
43
-------
SECTION 5
EXPERIMENTAL PLAN
DIGESTER FEEDS
Since many municipal digesters receive both primary and activated
sludges, it was decided that the digestion experiments of this project should
be conducted with mixtures of these two sludges to be collected from the
Chicago metropolitan area. Another factor that was considered important was
the source of the collected sludge. It was reasoned that sludges collected
from both large and small sewage treatment plants should be tested.
Accordingly, mixed primary-activated, primary, and activated sludges were
collected from a suburban and a City-of-Chicago plant of the Metropolitan
Sanitary District of Greater Chicago (MSDGC) system and from a plant of a
suburban (Downers Grove) sanitary district.
DIGESTION SYSTEMS
Consistent with the objectives of this research, it was necessary to
utilize two types of digestion apparatus — two-phase and single-stage
digestion systems. Two-phase systems for the fundamental studies comprised
CFCSTR acid- and methane-phase digesters, whereas novel upflow and CFCSTR
digesters were used to conduct the two-phase runs for the Applied Studies.
The choice of the digester type for the fundamental studies allowed for
direct comparison of single-stage and two-phase digestion and a delineation of
the effect of the fermentation mode on system performance. Similarly, by
cross comparison of two-phase digestion runs with CFCSTR and upflow digesters
employed in the fundamental and applied studies, it was possible to assess the
effect of reactor design.
DIGESTION RUNS
A total of 27 single-stage and two-phase digestion runs were conducted to
accomplish the objectives of Process-Comparison, Parametric-Effects acid-
phase, and Applied-Studies digestion runs. Runs were conducted with single-
stage (SS) and two-phase (TP) digestion systems at mesophilic (M) and thermo-
philic (T) temperatures at various HRT's, feed VS concentrations, and pH's,
and with and without enzyme treatment of the raw sludge.
A rational numbering system which identifies the digester type, digester
HRT, temperature, and culture pH for a particular run was used. The first
letters of a run number indicate the digester type (e.g., SS for single-stage,
AP for acid-phase, MP for methane phase, TP for two-phase system with CFCSTR
digesters, UTP for two-phase system with upflow digesters). The first letters
44
-------
of run number are followed by the digester HRT in days which in turn is
followed by the letter(s) M, T, M-M, M-T or T-T denoting single-stage meso-
philic (meso) or thermophilic (thermo) temperature, or meso-meso, meso-thermo,
or thermo-thertno acid-methane phase temperature combinations of a two-phase
system. The digits following the temperature notation indicate the target
culture pH to be attained by addition of acid or alkali. A run number with
(E) at the end indicates that the feed sludge in this run was treated with
cellulose and lipase. As an illustration, Run No. TP3M-M(E) indicates a
CFCSTR two-phase run at a system HRT of 3 days with a mesophilic acid-phase
digester operated in series with a mesophilic methane digester with enzyme
treatment of the feed sludge.
Fundamental Studies
Process-Comparison Studies—
A number of digestion runs were planned as shown in Table 7 to conduct
comparative studies of single-stage high-rate and two-phase digestion pro-
cesses under the same conditions of temperature, HRT, loading rates, and feed
VS concentrations. Single-stage digestion runs were planned at fermentation
temperatures of 35°C and 55°C and at HRT's of 15, 7, and 3 days with parallel
two-phase runs conducted at these same target HRT's. The experimental design
thus provided for the pairing of single-stage and two-phase runs based on HRT,
and digestion temperature. All digesters of the mesophilic pairs were
operated at 35°C. The single-stage and methane-phase (MP) digesters of the
thermophilic pairs had a target temperature of 55°C. The acid-phase (AP)
digesters of the thermophilic two-phase systems were to have temperatures of
35° or 55°C depending on the system HRT. As shown in Table 7, a mesophilic
temperature of 35°C was chosen for the acid digester when the system HRT of
the thermophilic two-phase system was high (15 days). For a low system HRT
(3 days) both digesters of the thermophilic two-phase- process had a target
temperature of 55°C. It was reasoned that owing to faster kinetics, a
thermophilic temperature could be more appropriate than a mesophilic
temperature when the system HRT is decidedly low. For the intermediate HRT of
7 days, two thermophilic two-phase runs were planned, one with the acid-phase
digester 35°C and the other at 55°C. Thus, the thermophilic two-phase systems
in reality were meso-thermo (35°C AP-55°C MP) or thermo-thermo (55°C AP-55°C
MP) processes.
The above experimental design was expected to provide the following
information:
• Effects of HRT and temperature on single-stage and two-phase digestion
• Benefits, if any, of two-phase digestion over the single-stage process in
terms of gas and methane productions and rates and efficiencies of
conversions of VS, total carbohydrate, lipids, and proteins.
45
-------
TABLE 7. DESIGN OPERATING CONDITIONS FOR PROCESS COMPARISON DIGESTION RUN.S CONDUCTED
WITH CFCSTR DIGESTERS
Single-stage digestion runs
Run no.
Digester no.
Culture temperature, °C
HRT, days
Organic loading rate,
kg VS/m3-day
Feed VS concentration, g/L
Two-phase digestion runs
Run no.
Digester nos.
Culture temperatures, °C
HRT, days
Acid-phase
Methane-phase
System
System organic loading rate,
kg VS/mi -day
Feed VS concentration, g/L
SS15M
331
35
15
2.1
31.5
TP15M-M
332-333
35-35
2
13
15
2.1
31.5
SS7M
331
35
7
7.1
50.0
TP7M-M
334-333
35-35
2
5
7
7.1
50.0
SS3M
331
35
3
16.7
50.0
TP3M-M
334-333
35-35
0.8
2.2
3.0
16.7
50.0
SS15T
337
55
15
2.1
31.5
TP15M-M
334-337
35-55
2
13
15
2.1
31.5
SS7T
331
55
7
7.1
50.0
TP7M-T TP7T-T
334-331 335-331
35-55 55-55
2 2
5 5
7 7
7.1 7.1
50.0 50.0
SS3T
335
35
3
16.7
50.0
TP3T-T
335-331
55-55
0.8
2.2
3.0
16.7
50.0
The first number is that of the acid-phase and the second number is that of the methane-phase.
* The first temperature is that of acid-phase culture and the second temperature is that of the
methane-phase culture.
-------
Parametric-Effects Acid-Phase Runs—
A total of 12 CFCSTR acid-phase digestion runs were planned at two
temperatures, four pH's and two HRT's (Table 8) to delineate the effects of
these operating parameters on acid digestion of sewage sludge. The factorial
experimental design follows a three-criteria classification in which a
selected variate (e.g., total volatile acid concentration, protein reduction,
or gas yield, etc.) is influenced by three treatment variables: digestion
temperature, pH, and HRT. The effects of the treatment variables on digester
performance as measured by a selected variate (e.g., organic component
reduction, volatile acid production) may be evaluated by performing the
analysis of variance (ANOVA) test using steady-state values of the variate.
Applied Studies
Advanced Two-Phase Digestion—
Several two-phase experiments were planned with upflow acid and methane
digesters maintained at mesophilic and thermophilic temperatures and without
and with recycling of the methane digester effluents to the acid phase — it
was reasoned that this effluent recycling would moderate the acid digester pH
and supply hydrogen utilizing methanogens which, by removing electrons, would
enhance hydrolysis and acidification. Screening studies were planned at meso-
meso, meso-thermo, and thermo-thermo acid- and methane-phase temperature
conditions to be able to select the best reactor temperature combination. It
was decided that this advanced two-phase process would be operated at an HRT
and pH deemed best from the results of the Fundamental Studies. This
experimental design was expected to aid in the selection of optimum operating
conditions for the two-phase process. At least one steady-state run was
planned at the optimum operating conditions (Table 9).
Enhancement of Sludge Reactivity by Enzyme Treatment—
It is well known that the volumetric rate of anaerobic digestion
increases at lower HRT's; however, a decrease in stabilization efficiency is
also experienced as the rate of conversion increases. One way to enhance the
conversion efficiency at the lower HRT is to increase the reactivities of
certain organic components by enzymatic treatment. As mentioned before,
cellulase and lipase treatments of the raw sludge were considered to this end
in view of the success of this approach in another EPA-sponsored project. The
applied studies included a 3-day HRT CFCSTR run that would be conducted with
enzyme treatment of the feed sludge (Table 9).
-------
TABLE 8. DESIGN OPERATING CONDITIONS FOR PARAMETRIC-EFFECTS CFCSTR ACID-PHASE DIGESTION RUNS
oo
Mesophilic acid-phase runs
Run no.
Digester no.
Culture temperature, °C
Culture pH
HRT, days
Organic loading rate,
kg VS/m3-day
Feed volatile solids concentration, g/L
Therraophilic acid-phase runs
Run no.
Digester no.
Culture temperature, °C
Culture, pH
Culture temperature, °C
HRT, days
Organic loading rate,
kg VS/m3-day
Feed VS concentration, g/L
AP2M7
334
35
7
2
25.0
50.0
AP217
335
55
, 7.0
55
2.0
25.0
50.0
AP2M6
334
35
6
2
25.0
50.0
AP2T6
335
55
6.0
55
2.0
25.0
50.0
AP2M5.5
334
35
5.5
2
25.0
50.0
AP2T5.5
335
55
5.5
55
2.0
25.0
50.0
AP2M5
334
35
5
2
25.0
50.0
AP2T5
335
55
5.0
55
2.0
25.0
50.0
AP1.3M7
334
35
7
1.3
38.5
50.0
AP1.3T7
335
55
7.0
55
1.3
38.5
50.0
AP1.3M5
334
35
5
1.3
38.5
50.0
AP1.3T5
335
55
5.0
55
1.3
38.5
50.0
-------
TABLE 9. STEADY-STATE OPERATING CONDITIONS FOR ADVANCED STUDIES
FOR MESOPHILIC (BOTH PHASES) TWO-PHASE DIGESTION RUNS
Run no.
Digester no.(s)
Culture mode
Feed pretreatraent
HRT, days
Acid-phase
Methane-phase
System
o
Loading rate, kg VS/m -day
Feed volatile solids concentration, g/L
UTP7M-M
338-339
Upflow
None
2
5
7
7.1
50.0
TP3M-M(E)
334-333
CFCSTR
Enzymatic
0.8
2.2
3.0
16.7
50.0
-------
SECTION 6
MATERIALS AND METHODS
PROCESS FEEDS
Mixed primary-activated municipal sludges were used as digester feeds in
this project. These mixed sludges were either obtained directly from a
treatment plant or were prepared by mixing activated and primary sludges
collected separately. Raw sludges were obtained from several sources and were
processed by various methods, as described in the following sections, to
prepare feedstocks for freezer storage. Digester feed slurries were prepared
from these homogenized batches of feedstocks.
Sources of Raw Sludge
Raw wastewater sludges were collected from several water pollution
control plants in the Greater Chicago area to conduct the digestion
experiments. Raw primary, raw activated, and raw mixed primary-activated
sludges were collected from wastewater treatment plants located in Hanover
Park, Chicago, and Downers Grove, Illinois.
The fundamental studies digestion runs were conducted with mixed primary-
activated sludges collected from the Hanover Park wastewater treatment plant
of the Metropolitan Sanitary District of Greater Chicago (MSDGC). The Hanover
Park plant is located in a northwest suburb of Chicago, and has a wastewater
flow rate of about 35,000 nrVday (9.2 mgd). About 5% of the plant flow is
from industrial discharges. The collected sludge contained about 60% primary
sludge and 40% activated sludge.
The applied studies were conducted with raw sludges from wastewater
treatment plants in Hanover Park and Downers Grove, and with vacuum-filtered
activated sludge cake from the West-Southwest (Stickney) wastewater treatment
plant of the MSDGC. The Stickney plant has a raw sewage flow of about
820 MGD; about 50% of this flow is of industrial origin. Vacuum-filtered
activated sludge cakes having TS contents between 12 and 14 wt % were
collected. The Downers Grove plant has a wastewater flow rate of about
42,000 m3/day, and 10%-15% of the flow is of industrial origin. Raw primary
sludge having a solids content between 3.5 and 5 wt % was collected from this
plant.
Collection and Processing of Hanover Park Raw Sludge
Raw municipal sludge that could be collected from the Hanover Park waste-
water treatment plant was dilute in solids content and was not suitable for
use as digester feed directly. This sludge had to be concentrated before
50
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digester feed could be prepared. Four different processing methods, described
below, were used to concentrate the Hanover Park sludge*
Method 1. Freezing and Thawing in 200-Liter Drums—
The raw sludge was collected in large lots of several 200-liter drums
from the Hanover Park plant. The collected sludge was trucked immediately to
a freezer warehouse and stored at -26°C. Several drums of the frozen sludge
from a lot were retrieved at a time from the cold storage and brought to IGT
for thawing and solid-liquid separation upon completion of the thawing
process. The liquid portion (supernatant) was decanted and discarded, and the
concentrated bottom sludges from all the drums were fed to a 0.6-nr-capacity
double-ribbon blender and homogenized to prepare a single batch. While
blending was in progress, sludge was withdrawn from a bottom port in the
blender to fill up 10-liter plastic storage bags. Small aliquots taken from
each bag were mixed in a container to produce a composite sample for total
solids (TS), volatile solids (VS), and other analyses. The 10-liter sludge
containers were stored in the refrigerated warehouse or in an IGT freezer;
these containers were thawed, as needed, and the concentrated sludge was
diluted and blended with tap water to prepare digester feed sludge of a
selected consistency. The feed slurry was stored in a refrigerator. It was
charged directly to the digester for manual (and once-a-day) feeding. For
continuous feeding, the feed sludge was stored in a refrigerated in a
continuously mixed feed reservoir, and this sludge was delivered to the
digester with a timer-operated pump.
Method 2. Freezing and Thawing in 10-Liter Bags—
Method 2 was used in a few cases when digester feed sludge was needed
quickly. In this method, the collected lot of raw dilute sludge was brought
to IGT, and several drums were blended in the 0.6-m^-capacity blender. The
blended sludge was transferred to 10-liter plastic bags, which were then
placed in an in-house freezer. The bags were then thawed; water was drained
out of the bag during the thawing, leaving concentrated sludge in the bag.
The contents of the bag(s) were homogenized to produce a batch of thick
sludge.
Method 3. Concentration by Laboratory Centrifuge—
In Method 3, a laboratory centrifuge (Sorvall® Model RC-5B) was used to
concentrate small lots of raw sludge. Centrifugation was done for 10 minutes
at 7000 rpra, and the centrifuged pellets were blended to prepare a
concentrated batch of sludge. Since only 3 liters of sludge could be
processed at a time by the laboratory centrifuge, this method was used when
feed sludge was needed quickly.
Method 4. Concentration by Pilot Centrifuge—
Considering the tedious and time-consuming nature of sludge concentration
by freezing and thawing, an alternative sludge concentration procedure
involving the use of a pilot centrifuge was tried during the second year of
the project. The dilute raw sludge was concentrated by a Model 309 Alfa-Laval
51
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pilot centrifuge with a rated capacity of 4-40 liters/min. The centrifuge was
fed continuously with an air-operated drum pump at flow rates considerably
below 40 liters/min. Many problems, including centrifuge-motor burn out, pipe
clogging, etc., were experienced. In addition, the solids capture in the
centrifuged cakes was low. It was felt that considerable amounts of
biodegradable solids were probably lost in the discarded supernatant. The
solids content of the centrifuged cake was about 8.5 wt % TS without any
polymer treatment of the dilute sludge. Only one lot of sludge was processed
by this method.
Nineteen lots of Hanover Park raw sludge, totaling about 30,000 liters
were collected, during the project. The sludge lots were processed in 1 to 15
batches. The processing method for each batch is described in the next
section. The raw sludge had TS contents between 2 and 3.5 wt % and VS
contents between 68 and 76 wt % of TS. By comparison, the concentrated sludge
had VS concentrations between 60 and 79 wt % of TS.
Collection and Processing of Stickney and Downers Grove Sludges
Since the processing of the mixed activated-primary sludge from Hanover
Park was difficult, digester feed sludge was prepared by mixing concentrated
activated and primary sludges. Activated sludge (AS) cakes were collected
from the wastewater treatment plant of Chicago Metropolitan Sanitary District
in Stickney, IL. These sludge cakes had a TS concentration of about 14 wt %
(Table 10), so there was no need for sludge concentration. The collected
sludge cakes were diluted and blended in a commercial-size double-ribbon
blender at IGT, and the blended sludges were transferred to 10-liter plastic
bags for storage at -26°C.
TABLE 10. COLLECTION, PROCESSING, AND SOLIDS ANALYSES OF
VACUUM-FILTERED ACTIVATED SLUDGE CAKE FROM STICKNEY
Date Lot Quantity, TS, VS, wt 5
collected no. kg wt % of TS
9/84 20 221 13.67 65.68
11/84 21 314 13.67 66.55
Raw primary sludges (PS) were collected from the Downers Grove wastewater
plant; these sludges had TS contents between 3.5 and 5 wt % (Table 11). The
VS concentration of the Stickney activated sludge was between 65% and 67% of
TS. By comparison, the VS concentration of the Downers Grove sludge varied
between 75% and 80% of TS. The activated and primary sludges were mixed in
the ratio of about 73% activated to 27% primary sludge on a dry TS basis —
similar to the AS/PS ratio of 75:25 for the Hanover Park sludge — to provide
52
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TABLE 11. COLLECTION, PROCESSING, AND SOLIDS ANALYSES OF
DOWNERS GROVE PRIMARY SLUDGE
Date
collected
10/84
12/84
12/84
12/84
Lot
no.
22
23
24
25
Quantity,
liters
49
58
15
18
TS,
wt %
4.90
3.78
4.63
4.34
VS, wt %
of TS
79.67
75.86
77.82
76.71
about a 7 wt % TS-content digester feed sludge. The digester feed sludge was
prepared in this manner to provide a VS concentration similar to that of the
Hanover Park sludge (68% to 70% of TS).
APPARATUS FOR DIGESTION SYSTEMS
Eight digestion systems were used to conduct the Fundamental and Advanced
Studies digestion runs. The digester dimensions and volumes are described in
Tables 12 through 15. Details of the digester systems and ancillary equipment
are described below.
Digestion Systems for Fundamental Studies
Six digesters were used to conduct the CFCSTR single-stage and two-phase
process-comparison runs (Tables 12 and 13) and the CFCSTR acid-phase
parametric-effects runs (Table 14). These runs were part of the fundamental
studies. All the digesters were cylindrical in shape and fabricated of
Plexiglas with removable headplates. Various ports were provided for feed
slurry delivery, effluent removal, and sampling of the liquid and gaseous
digester effluents. Each digester was provided with equipment for culture
agitation, temperature control, and gas collection. Automatic feed systems
were installed on the single-stage and acid-phase digesters to permit inter-
mittent feeding under conditions approximating continuous flow. In addition,
automatic pH controllers were installed on the two separate acid-phase
digesters to control culture pH's. A schematic diagram of a CFCSTR two-phase
digestion system is presented in Figure 9; the design of the single-stage and
parametric-effect acid-phase digesters was similar to that shown in Figure 9
except that these systems had no methane-phase digester.
Each digester was mixed with three-blade propellers mounted on a
stainless-steel shaft, which passed through a custom-made shaft-seal housing
mounted on the center of the digester headplate. The shaft was driven at
53
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TABLE 12. LIST OF CFCSTR DIGESTERS USED FOR SINGLE-STAGE
DIGESTION RUNS FOR PROCESS COMPARISON STUDIES
Run no.
Digester
no.
Digester
height,
cm
Digester
diameter,
era
Total
volume,
L
Culture
volume,
L
Mesophilic (35°C)
SS15M
SS7M
SS3M
Thermophilic (55°C)
331
331
331
38
38
38
29
29
29
25.5
25.5
25.5
20.0
15.0
15.0
SS15T
SS7T
SS3T
337 38
331 38
335 25
29
29
19
25.5
25.5
7.2
20.0
15.0
5.2
about 120 rpm by a variable speed motor. Four vertical baffles were attached
90° apart on the inside wall of the digester to minimize vortexing.
Digester temperature was sensed by a thermistor probe installed in an
oil-filled thermowell, which extended through the digester headplate into the
culture. The temperature was maintained by a proportional controller
connected to heating tapes or pads wrapped around the outside of the digester.
The controller maintained the culture temperature to within 0.5°C of the
setpoint.
Gas production in each digester was measured with automatic gas burets,
which continuously collected and wasted small volumes of gas (about 50 mL) as
it was produced by the digester. Gas collection and wasting cycles were
totalized by electro-mechanical digital counters. Gas productions were
determined to an accuracy of 3% or less, as determined by periodic
calibrations.
Each automated feed system consisted of a refrigerated and mixed 19-liter
feed reservoir, a timer-operated progressive cavity pump and associated piping
and valves (Figure 9). The feed reservoir was maintained at 3° to 5°C to
minimize biological degradation of the feed slurry. A pneumatically operated
pinch valve was installed between the pump and the digester to prevent
backflow of the culture through the pump. The autofeed system delivered feed
slurry to the digester at regular intervals (12 to 60 times per day) to
approximate continuous-flow conditions.
54
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TABLE 13. LIST OF CFCSTR DIGESTERS USED FOR TWO-PHASE DIGESTION
RUNS FOR PROCESS COMPARISON STUDIES
Run no.
Meso-meso
TP15M-M
TP7M-M
TP3M-K
Meso-thermo
TP15M-T
TP7M-T
Thermo-thermo
TP7T-T
TP3T-T
Acid-phase
Methane-phase
System
Acid-phase
Me thane-phas e
System
Acid-phase
Methane-phase
System
Acid-phase
Methane-phase
System
Acid-phase
Methane-phase
System
Acid-phase
Methane-phase
System
Acid-phase
Methane-phase
System
Digester
no.
332
333
334
333
334
333
334
337
334
331
335
331
335
331
Digester
height,
cm
25
38
25
38
25
38
25
38
25
38
25
38
25
38
Digester
diameter,
cm
19
29
19
29
19
29
19
29
19
29
19
29
19
29
Total
volume ,
L
7.2
25.5
32.7
7.2
25.5
32.7
7.2
25.5
32.7
7.2
25.5
32.7
7.2
25.5
32.7
7.2
25.5
32.7
7.2
25.5
32.7
Culture
volume,
L
3.0
20.0
23.0
5.2
13.5
18.7
5.2
12.3
17.5
3.2
20.0
23.2
5.2
15.0
20.2
5.2
15.0
20.2
5.2
15.0
20.2
55
-------
TABLE 14. LIST OF DIGESTERS USED FOR CFCSTR PARAMETRIC-EFFECTS
ACID-PHASE DIGESTION RUNS
Run no .
Mesophilic
AP2M7
AP2M6
AP2M5.5
AP2M5
AP1.3M7
AP1.3M5
Thermophilic
AP2T7
AP2T6
AP2T5.5
AP2T5
AP1.3T7
AP1.3T5
Digester
no.
334
334
334
334
334
334
335
335
335
335
335
335
Digester
height,
cm
25
25
25
25
25
25
25
25
25
25
25
25
Digester
diameter,
cm
19
19
19
19
19
19
19
19
19
19
19
19
Total
volume,
L
7.2
7.2
7.2
7.2
7.2
7.2
7.2
7.2
7.2
7.2
7.2
7.2
Culture
volume,
L
6.0
5.2
5.2
5.2
5.2
5.2
6.0
5.2
5.2
5.2
5.2
5.2
Effluents from the automatically-fed single-stage and parametric-effects
acid-phase digesters were wasted continuously through gravity overflow pipes
to collection vessels. The overflows were U-shaped in design to prevent the
loss of product gases with the effluent. Effluents from the acid-phase
digester of the two-phase system were delivered to their associated methane-
phase digester by gravity overflows or by timer-operated peristaltic pumps.
The pH control systems for the parametric-effects acid-phase digesters
consisted of an automatic pH controller with analog pH meter (Cole-Parmer
Model No. 5997), an in-line pH probe, and a peristaltic pump and storage
vessel for delivery of the pH control solution to the culture. The pH probe
was mounted through the headplate and extended about 2.5 cm deep into the
culture. The peristaltic pump was activated by the controller to deliver the
pH control solution to the digester whenever the culture pH deviated more than
about 0.1 pH units from the setpoint. A 2.5-N solution of NaOH was used to
control the culture to pH 7; 2.5-N HC1 was used for control to pH 6 and below.
56
-------
TABLE 15. LIST OF DIGESTERS USED FOR ADVANCED TWO-PHASE DIGESTION RUNS
Run no.
CPCSTR two-phase system operated
with enzyme-treated sludge
TP3M-M(E)
i
Upflow two-phase system
UTP7M-M
Digester
no.
Acid-phase 334
Methane-phase 333
System —
Acid-phase* 338
Methane-Phaset 339
System —
Digester
height,
Culture mode cm
CFCSTR 25
CFCSTR 38
— —
Upflow
Hybrid upflow/ 71
complete-mix
Digester Total
diameter, volume,
cm L
19 7.2
29 25.5
32.7
8.5
19 21.5
30.0
Culture
volume ,
L
5.2
12.9
16.1
7.0
19.0
26.0
The acid-phase digester was rectangular In shape with a trapezoidal bottom with a height, width, and length of 22, 11, and 34 cm,
respectively.
' The methane-phase digester was cylindrical In shape with a small Inverted pyramid at the bottom, 20 cm square and 9 cm high.
-------
AUTOMATIC GAS BURET
AUTOMATIC GAS BURET
00
M
REFRIGERATED
FEED RESERVOIR
M ELECTRIC MOTOR
P PUMP
SV SOLENOID VALVE
He HELIUM TANK
V PINCH VALVE
COMPLETE-MIX COMPLETE-MIX
ACID-PHASE METHANE-PHASE
DIGESTER DIGESTER
T TIMER
HP HEATING PAD/TAPE
TC TEMPERATURE CONTROLLER
C DIGITAL COUNTER
Figure 9. Schematic diagram of CFCSTR two-phase
anaerobic digestion system.
EFFLUENT
COLLECTION
A8306I068
-------
j)igestion Systems for Advanced Studies
Four digesters comprising two separate two-phase systems were used to
conduct the advanced studies digestion runs (Table 15). One of the two-phase
systems (Digester Nos. 333 and 334) was operated as a CFCSTR system receiving
enzyme-treated sludge, and the other (Digester Nos. 338 and 339) was operated
as an upflow system. Systems for culture agitation, temperature control, gas
collection, feed slurry delivery, and effluent removal were similar to those
described previously for the fundamental studies runs, except as noted below.
A lipase dosing system was installed on the acid-phase digester (Digester
No. 334) of the two-phase system operated with enzyme-treated sludge feed.
The dosing system consisted of a timer-operated peristaltic pump and an enzyme
storage vessel. The rate and frequency of delivery of the lipase solution to
the acid-phase digester was controlled by varying the settings of the timer.
A schematic of the upflow two-phase system is depicted in Figure 10. The
upflow acid-phase digester (Digester No. 338) consisted of a rectangular tank
separated into two compartments by a central vertical baffle. The digester
feed slurry was pumped into the left compartment through a vertical feed pipe
that extended through the bottom of the digester about halfway up into the
culture. A small deflector located just above the feed pipe directed the
slurry toward the bottom of the compartment. Feed solids then flowed upward
toward the culture surface in the left compartment, over the central baffle,
and into the right compartment. Additional baffles (not pictured) were
installed in the right compartment to keep floating scum away from the
overflow effluent port and to promote sedimentation and retention of feed
solids within the digester. The bottom of each compartment sloped toward the
center of the digester to permit storage of settled solids. Two pipes with
ball valves were installed at the bottom of the digester on either side of the
central baffle and were connected to a pump to permit delivery of the stored
sludge to the methane-phase digester. Sludge could be withdrawn from either
compartment by opening one of the ball valves and closing the other. The rate
of sludge withdrawal from the bottom of the acid-phase digester was controlled
by a timer that operated the pump. Temperature control was provided by hot
water, which was recirculated from a water bath through a jacket around the
outside of the digester.
The upflow methane-phase digester (Digester No. 339) consisted of a
cylindrical tank with a truncated, inverted pyramid-shaped bottom, a feed pipe
and solids deflector, and three sets of alternating static baffles and
turbine-type impellors. Effluents from the acid-phase digester were pumped
into the bottom of the methane-phase digester through a vertical pipe which
extended about one-third up into the culture. The solids in the incoming feed
were directed toward the bottom of the digester by an inverted cup-shaped
deflector that allowed the liquid portion of the feed to flow upward toward
the culture surface. Three ring-shaped horizontal baffles were attached at
the 9, 13, and 17-liter levels of the digester. In addition, three sets of
turbine-type impellors were attached to a low-speed (9.8 rpm) central rotating
shaft. This pattern of alternating static baffles and impellors was designed
to produce a circuitous flow pattern within the digester while also providing
areas of local mixing. Effluent ports with U-shaped overflows were installed
59
-------
AUTOMATIC GASJURET
1
AUTOMATIC GAS BURET
REFRIGERATED
FEED RESERVOIR
UPFLOW
ACID-PHASE
DIGESTER
UPFLOW
METHANE-PHASE
DIGESTER
EFFLUENT
COLLECTION
M ELECTRIC MOTOR
P PUMP
SV SOLENOID VALVE
He HELIUM TANK
V PINCH VALVE
T TIMER
HP HEATING PAD/TAPE
TC TEMPERATURE CONTROLLER
C DIGITAL COUNTER
A8306I069
Figure 10. Schematic diagram of two-phase upflow digestion
system for applied studies.
-------
at the side of the digester to permit operation at culture volumes of 15 to
19 liters.
CHEMICAL ANALYSES
Sample Collection and Preparation
Sample Collection—
Sample collection was carried out in strict accordance with the sample
collection procedures outlined in Part 105, APHA Standard Methods (15th
Edition)58 or in ASTM Part 26, (1982) manuals.5^ xwo types of samples, gas
and liquid, were collected. Gas samples were collected directly from the
digester head space in well-purged disposable plastic syringes and analyzed
immediately by gas chromatography. Liquid samples were collected during
sludge processing operations and from digester feed reservoirs and effluents.
As specified in Table 16, three types of liquid samples were collected:
grab, grab composite, and time composite.
Grab Samples—Grab samples were spot or catch samples representing
physical and/or chemical characteristics at the time of sampling and the
location of sample collection.
Grab Composite Samples: Processed Feed—
Several constant-volume grab samples were collected from each large batch
of blended feed sludge, which was withdrawn from a large blender to fill 10 or
20-liter containers for refrigerated storage. The grab samples were collected
every time a sludge container was filled. These samples were mixed and
homogenized to produce a grab composite for solids a'nalyses.
Grab Composite Samples; Feed and Effluent Slurries—Daily grab samples
from digester feed reservoirs and effluent were collected, composited, and
processed to characterize feed and effluent quality during steady-state
segments of the digestion runs.
Time Composite Samples; Effluents—Grab samples were composited from
digester effluents accumulated over a 24-hour period.
Sample Preparation—
Sample preparation was not required for gas samples; these were analyzed
immediately after collection. The liquid samples were homogenized for
representativeness of the final aliquots withdrawn for analysis. Wherever
possible, sample preparation procedures as outlined in the APHA or ASTM
Standard Methods were followed.
In the case of the COD and ammonia and organic nitrogen analyses, sample
preparation procedures were modified to improve the accuracy and precision of
these analytical determinations. These modifications were necessary due to
the heterogeneous nature and high solids contents of the slurries.
61
-------
TABLE 16. SAMPLE COLLECTION AND PROCESSING PROTOCOL
Determination
Carbon (total)
Hydrogen
Nitrogen, ammonia
Nitrogen, organic
Sulfur (total)
Phosphorus
Ash
Heating value
Total solids
Volatile solids
Fixed solids
PH
Alkalinities
(total and
bicarbonate)
Volatile acids
COD (total and
filtrate)
Lipids
Carbohydrates
(total)
Sample
Influent
Effluent
Influent
Effluent
Influent
Effluent
Influent
Effluent
Influent
Effluent
Influent
Effluent
Influent
Effluent
Influent
Effluent
Influent
Effluent
Influent
Effluent
Influent
Effluent
Influent
Effluent
Influent
Effluent
Influent
Effluent
Influent
Effluent
Influent
Effluent
Influent
Effluent
source
(feed)
(feed)
(feed)
(feed)
(feed)
(feed)
(feed)
(feed)
(feed)
(feed)
(feed)
(feed)
(feed)
(feed)
(feed)
(feed)
(feed)
Sample type
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
Grab
Grab
Grab
Grab
Grab
Grab
Grab,
Grab,
Grab,
Grab,
Grab,
Grab,
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
grab
composite
composite.
composite
composite,
composite
composite,
composite
composite,
composite
composite,
composite
composite,
composite
composite,
composite
composite,
composite
composite,
composite
composite,
composite
composite,
composite
composite,
composite
composite,
composite
compos! te ,
time
time
time
time
time
time
time
time
time
time
time
time
time
time
composite
composite
composite
composite
composite
composite
composite
composite
composite
composite
composite
composite
composite
composite
Sample preservation
(if not analyzed Immediately)
Seal and freeze
Seal and freeze
Seal and freeze
Seal and freeze
pH <2 with H2S04, seal
pH <2 with H2S04, seal
pH <2 with H2S04, seal
pH <2 with H2S04, seal
Seal and freeze
Seal and freeze
Seal and freeze
Seal and freeze
Seal and freeze
Seal and freeze
Seal and freeze
Seal and freeze
Seal and freeze
Seal and freeze
Seal and freeze
Seal and freeze
Seal and freeze
Seal and freeze
__
—
1.5 mL 20% H3P04/10 ml
refrigerate at 4*C
1.5 mL 20Z H3P04/10 ml
refrigerate at 4°C
pH <2 with H2S04, seal
pH <2 with H2S04, seal
Seal and freeze
Seal and freeze
Seal and freeze
Seal and freeze
and freeze
and freeze
and freeze
and freeze
sample;
sample;
and freeze
and freeze
Gas composition
Head space
Grab
62
-------
Total COD analyses were conducted with feed and effluent slurries from
two of the CFCSTR parametric-effect acid-phase runs using APHA Standard
Methods and modified sample preparation procedures to compare the precision of
the two methods (Table 17). Analyses of the samples were conducted in an
identical manner with regard to reagent volumes and reflux time and differed
only in the preparation method.
Preparation and dilution of samples by the APHA method (Method 1)
consisted of the following steps:
• The collected sample (about 500 mL) was homogenized for about 1 minute in
a Waring blender.
• 5.0 mL of blended and mixed sample were transferred to a volumetric flask
with a 5.0-mL wide-tip pipet and diluted to 500.0 mL with distilled water
to prepare a 1:100 diluted sample.
• 10-mL aliquots of the mixed and diluted sample were added to each COD
flask with a 10.0 mL wide-tip pipet.
Sample preparation and dilution by the modified method (Method 2)
consisted of the following steps:
• The collected sample was homogenized as in Method 1.
• About 25 g of blended and mixed sample was weighed and diluted with
25.0 mL distilled water to prepare a dilution of known proportion.
• Four 5-mL aliquots of this diluted and mixed sample were diluted to
500.0 mL in a 500.0 mL volumetric flask; the pipets were flushed into the
flask with distilled water after the transfer of each aliquot.
• Two 5.0-mL aliquots of this diluted and mixed sample were pipeted into
each replicate COD flask; each aliquot was flushed with distilled water
into the COD flask after transfer.
The standard deviations of the COD's conducted by the modified sample
preparation method were substantially lower than those conducted by the APHA
sample preparation method, for both' feed and effluent slurries. The data
indicated that the precision of total COD's on samples prepared by the
modified method was superior to that obtained with samples prepared by the
APHA method. Accordingly, all of the total COD analyses were conducted with
samples prepared by the modified method. Samples analyzed for ammonia and
organic nitrogen were also prepared by this method.
Sample Handling, Identification, Preservation, and Storage
Liquid samples were collected in clean glass and plastic bottles that
were rinsed out two or three times with the fluid being sampled. Before
collecting samples from tubings or pipes, the lines were flushed out
sufficiently by draining the digester or reservoir contents to ensure
collection of representative samples. Each sample bottle was marked with an
63
-------
TABLE 17. EFFECT OF SAMPLE PREPARATION ON TOTAL COD DETERMINATIONS OF FEED AND EFFLUENT SLURRIES
FROM CFSTR MESOPHILIC AND THERMOPHILIC ACID-PHASE DIGESTERS OPERATED WITH HANOVER PARK SLUDGE
Run AP2T7
Run AP2M7
Feed slurry
Effluent slurry
Feed slurry
Effluent slurry
Sample preparation method
Total COD, mg/L
APHA* Modifiedt APHA Modified
APHA Modified APHA Modified
Replicate
Replicate
Replicate
Replicate
Replicate
Average
1
2
3
4
5
Standard deviation
Coefficient of
variation, %
103
127
139
123
18
,054
,302
,426
—
—
,260
,520
15.0
77,655
78,994
80,780
79,887
80,333
79,530
1,239
1.6
101,322
99,590
51,094
—
—
84,002
28,512
33.9
68,842
69,706
71,152
74,387
76,235
72,064
3,145
4.4
69
107
97
91
19
,820
,384
,858
—
— -
,507
,830
21.7
81,972
86,164
86,630
95,945
84,767
87,096
5,269
6.0
99,590
113,446
64,950
—
~--~
92,662
24,979
27.0
88,268
82,298
82,298
84,430
__
84,323
2,815
3.3
* The APHA sample preparation consisted of preparing a 1:100 dilution of the sample; 10.0-mL aliquots of the diluted
and mixed sample were added to each replicate flask with a 10-mL wide-tip pipet.
* The modified sample preparation consisted of diluting a known weight of sample (about 25 grams) with 25.0-mL of
water; two 5.0-mL aliquots of this diluted and mixed sample were added to a 500.0-mL volumetric flask with a
5.0-mL wide-tip pipet, and two 5.0 ml aliquots of this mixed and diluted sample were added to each replicate
flask. Each aliquot was washed with water directly into the flask after pipeting.
-------
identification number; a label containing information on date, time, location
of sample, and the name of the sample collector was securely attached.
All samples were analyzed for the intended data as soon as they were
collected, if possible. Temperature, pH, alkalinity, and gas composition
determinations were performed immediately after collection of the sample. In
cases where the analysis could not be performed immediately, the sample was
preserved by procedures prescribed in APHA (15th Edition)58 and ASTM (1982)
Standard Methods.
Feed Analyses
Processed sludge feed lots were analyzed for total solids (TS), volatile
solids (VS), and fixed solids (FS). Digester feed slurry samples collected
during steady state were analyzed for pH, TS, VS, and FS, total and
bicarbonate alkallnities, ammonia and organic nitrogen, lipids, carbohydrates,
and crude protein. Several fresh slurry samples were also analyzed for total
and volatile suspended solids and total and filtrate COD, elemental content,
and heating value. An anaerobic biogasification potential (ABP) test was also
conducted on one Hanover Park feed sample to estimate the biodegradability of
the feed sludge.
Effluent Analyses
Digester performances were monitored by daily measurement of gas
production; effluent pH was determined at least three times per week. Gas
composition and volatile acids concentrations were analyzed at least once per
week during nonsteady-state segments and two or three times per week during
steady-state segments. Steady-state effluent samples were analyzed for TS,
VS, and FS, total and bicarbonate alkalinities, ammonia and organic nitrogen,
lipids, carbohydrates, and crude protein. In a few cases, effluents were also
analyzed for total and volumetric suspended solids, 'total and filtrate COD,
elemental contents, and heating value*
Analytical Procedures
A number of physical and chemical analyses were performed to evaluate
digester performance, monitor the progress of digestion runs, and characterize
digester feeds and effluents. Details of these analytical methods are
presented in Table 18.
Information derived from results of the physical and chemical analyses
was used for the following purposes:
• To determine the empirical formula of the feed, and to estimate
theoretical and biodegradable gas and methane yield potentials
• To monitor acid- and methane-phase culture development, population
transitions in response to changes in operating conditions, and the
condition of the culture during runs
65
-------
TABLE 18. LIST OF PHYSICAL AND CHEMICAL ANALYSES/MEASUREMENTS, METHOD
OF DETERMINATION, AND THE INTENDED USE OF THE RESULTING DATA
Measurement /Ana lysis
Sample
Method
Intended Use
Temperature
Digester culture APHA Std. Methods (15th ed.) Part 212
Digester gas Same as above
Culture monitoring and maintenance; evaluate temperature
effect on digestion.
Reduce gas volumes to those at the standard temperature of
60*F,
Liquid flow rate
Gas pressure
C, H, N, S, Ash,
Heating Value, and t*
TS, VS, Fixed solids
Total and volatile
suspended solid1?
PH
Total and bicarbonate
alkalinity
Digester influent
and eftluent
Digester gas
Digester gas
Digester teed and
effluent
Sane as above
Digester leed
and effluent
Same as above
Same as above
Independent determination of liquid
volume in calibrated containers and ttme
by certified timers
Measured in a gas collector calibrated
according to ASTM Fart 26, Designation
0-1071-7HO, Article 12 (1982)
ASTM 19H2 edition Part 26 <_\9o2)
Designation D-J631-77
ASTM 1982 edition. Part 26, Designation
D-317B, 3179, 3177, 3174. and AVHA
Std. Methods (l*)th ed.) Part 424
APHA Std. Methods (15th ed.) Part 209-G
Determine residence times; use to perform mass balances.
Calculate total gas yield and methane yield and
determine process efficiency*
Reduce gas volumes to those at the standard pressure of
30-1n. Hg.
Estimate empirical formulas and theoretical gas and methane
yields; elemental balances; use in estimating carbon and
energy recoveries in gas; nutrient availability and
limitations.
Determine gas and methane yields; solids balances; estimate
sludge concentration and SRT; determine solids reduction
efficiencies.
Culture monitoring, maintenance, and status; use In carbon
balance.
Organic-N Same as above
Anmonia-N Same as above
Volatile Acids Digester feed and
effluent
Digester culture
COD (total and filtrate) Digester feed and
effluent
Lipids Same as above
Crude protein Same as above
Carbohydrate Same as above
Centrlfu£atlnn method (described, In test) Determine suspended solids retention and llqulfactlon.
APHA Std. Methods (15th ed.) Part 423 Culture monitoring and maintenance; evaluate pH effect.
Ttttat alkalinity as per APHA Std.
Methods (15th ed.) Part 403-4; bicarbonate
alkalinity by calculation
AI'IIA Std. Methods (15th rd.) Part 420-A
APHA Std. Methods (15th ed.) Part 417-D
Modified APHA Std. Methods (15th ed.);
procedure mpditlcatlon described in text
Same as above
APHA Std. Methods (15th ed.) Part 508-A
(,'as production
C>as composition
C02. «2. »2>
Digester gas
Same as above
APHA Std. Methods (15th ed.) Part
Organic nitrogen X 6.25
American Society for Microbiology, Manual
of Methods for General Microbiology (1981)
Same as gas volume
APHA Standard Methods (15th ed.) Part 511-B
Estimate crude protein and protein digestion efficiency.
Monitor nitrogen availability; use in nitrogen balance.
Estimate feed-to-acid and acid-to-gas conversion
efficiencies.
Monitor digestion status.
Evaluate feed hydrolysis and acidification efficiencies;
estimate aclds-to-methane conversion efficiency*
Evaluate llpld conversion efficiency.
Evaluate protein digestion efficiency.
Evaluate carbohydrate conversion efficiency.
Determine gas and methane yields and production rates;
utilize to conduct mass balance.
Monitor culture status; determine methane yields; utilize
In mass balances
-------
• To identify steady-state operation and evaluate steady-state digester
performances and efficiencies in accordance with project objectives
• To evaluate conversion efficiencies of various feed components, and to
perform mass balances
• To determine substrate conversion and product formation efficiencies
during steady-state segments of the digestion runs.
Standard Test Procedures
As indicated in Table 18, measurement methods and test procedures used
throughout this project were as specified in APHA Standard Methods, ASTM, or
other accepted analytical manuals, with the exceptions of the volatile fatty
acids (VFA) and suspended solids determination. Descriptions of these
modified procedures are provided below.
Evaluation and Selection of Alternative Analytical Procedures
Volatile Fatty Acids—
Gas chromatography was used to determine VFA concentrations in feed and
digested sludges. The chromatographic technique was preferred to the elution
chromatographic and distillation methods because, using this technique, the
individual volatile acids could be separated and measured with greater
accuracy and precision. Information on the concentrations of individual
volatile acids was necessary for proper monitoring of digester performance;
the gas chromatographic technique described here provided this required
information. Also, the gas chromatographic method was less time-consuming and
was convenient when a large number of samples had to be analyzed quickly.
Most investigators in the anaerobic fermentation field utilize gas chromato-
graphic techniques similar to the one described here to obtain volatile fatty
acids concentration data. °~6^
A Hewlett Packard Model 5840A Reporting Gas Chromatograph equipped with a
hydrogen-air flame ionization detector, a programmable digital processor to
control the various aspects of GC analysis (for example, temperatures,
detector operation, integration of peak areas, component identification,
chromatogram plotting, retention times, run programming, etc.), and an
automatic liquid sampler were used. The glass column, 1.8 m x 4 mm in
diameter, was packed with acid-washed Chromosorb 101, as suggested by All Tech
Associates and John Mansville Corp. •* Similar column packings are used by
other investigators.60"62 The injection port was maintained at 200°C, while
the column was operated at 190°C. Detector temperature was set at 250°C. The
nitrogen carrier gas was supplied at a flow rate of about 25 mL/min. Hydrogen
gas pressure and flow rate were maintained at 18 psig and 25 mL/min, while air
pressure and flow rate were set at 28 psig and 240 mL/min, respectively.
A 10-mL sample of the feed or digester effluent was acidified to a pH of
about 1.7 with 1.5 mL of 20% H^o^; it was then centrifuged for 15 minutes at
15,000 rpm to separate a clear liquid fraction, which was transferred to a
2-mL clean glass vial. The glass vial was sealed with a Teflon-faced rubber
67
-------
septum and then placed in an automatic sampler tray. A 1-yL sample was
withdrawn from the bottle and injected into the chromatographic column by the
automated injection system.
The injector was programmed for automatic washing to the 10-yL syringe
with portions of the sample four times before the sample was withdrawn for
injection and analysis. This operation was followed by eight additional
purgings to ensure expulsion of air. The column was periodically injected
with acidified water samples between sample injections. A standard VFA
solution containing a mixture of individual volatile acids of known concentra-
tion was chromatographed in the same manner as the unknown. Unknown fatty
acids concentrations were calculated by comparing areas under chromatogram
peaks obtained for individual VFA's in the unknown and standard samples.
Individual VFA concentrations are expressed in terms of equivalent acetic acid
concentration.
Suspended Solids—
Analysis of feed and effluent suspended solids by the APHA Standard
Methods procedure (Parts 209-D and 209-G, 15th Edition)5** was problematic due
to the high concentration (20 to 40 g/L) of suspended solids in the samples.
To avoid clogging the filters with solids particles, it was necessary to use
very small sample volumes (less than 5 mL). The difficulty in accurately
measuring the small sample volumes resulted in widely dispersed replicate data
for each determination. A centrifugation procedure was then developed for the
determination of total and volatile suspended solids to overcome the
limitations of the APHA filtration method.
Suspended solids determinations by the centrifugation method were
conducted in triplicate and consisted of the following steps:
• Known weights of sample (about 20 g) were transferred to 50-mL centrifuge
tubes.
• The tubes were centrifuged for 20 minutes at 20,000 rpm to separate the
sample into solids pellets and clean supernate fractions.
• The clean supernate was drained off, taking care to minimize loss of
floating solids particles; distilled water was then added to each tube,
and the pellets were resuspended with a small magnet.
• The centrifugation and suspension steps were repeated twice more.
• The suspended solids were transferred to crucibles and dried and ashed at
103° and 550°C, respectively, to determine total and volatile suspended
solids of the plug.
• The supernate collected after each centrifuge operation was analyzed for
total and volatile suspended solids contents per APHA Standard Methods,
Parts 209-D and 209-G.
68
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• Suspended solids concentrations for each sample were reported as the sums
of the TSS and VSS contents of the solids pellet and supernate fractions.
Carbohydrates—
Since the APHA Standard Methods do not include a carbohydrate analysis
procedure for sewage sludge, and because there is no consensus among
researchers as to which method of the many published techniques is suitable
for this material, considerable work was done to select a suitable analytical
procedure to determine the "total carbohydrate" contents of feed and digested
sludges. As discussed below, determination of total carbohydrates in sludge
is difficult because of the complex composition of this generic material, the
heterogeneity of sludges, and the limitation of the analytical methods in
detecting various types of sugars.
Carbohydrates can be classified as monosaccharides, oligosaccharides, and
high-molecular-weight polysaccharides such as starch, glycogen, cellulose,
hemicellulose, pectins, xylans, mannans, etc. In addition, sewage sludge
contains a variety of carbohydrates that have their origin in microbial cells;
this is particularly true of activated sludge. Cells contain nucleic acids
that, upon degradation, yield deoxyribose and ribose. Microbial cell walls
contain other complex polysaccharides (for example, capsular polysaccharides,
lipopolysaccharide) containing amino sugars, and other monosaccharides.
Most commonly used analytical methods for determination of "total
carbohydrate" are derived or adapted from the Molisch test."6 This method
involves heating the sample with concentrated sulfuric acid and a "color
developer" which is usually an aromatic amine or a phenol. The reactions
include —
• Hydrolysis of polysaccharides to monosaccharides
• Dehydration and transformation of the monosaccharide to form furfural (in
the case of pentose sugars) or hydroxy methyl-furfural (in the case of
hexose sugars)
• Complexation of the hydrolysis products with the color developer to form
a colored compound, the concentration of which is measured
spectrophotometrically.
Samples such as sewage sludge and digested sludge contain particulate
polysaccharides of various compositions, and the result of total carbohydrate
analysis depends to a large extent on the details of the hydrolysis
procedure. The degree of hydrolysis and the nature of the hydrolysis products
depend on the type of acid used, the acid concentration, pH, hydrolysis time
and temperature, and other factors. For example, complete hydrolysis of
cellulose yields glucose, whereas partial hydrolysis yields the disaccharide,
cellulobiose. Hydrolysis of hemicellulose, on the other hand, produces D-
xylose and D-glucoronic acids. The reactivities of these different compounds
with the color developer are quite different. Also, it has been pointed out
that certain hydrolysis products such as amino sugars, trioses, tetroses, and
other carbohydrates that do not form furfural or furfural derivatives hardly
69
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react with the coloring agent."' Separate specific assays are, therefore,
required to ascertain the concentrations of carbohydrates that do not yield
furfurals upon hydrolysis. It is apparent that no single analytical method or
color-forming agent can accurately measure the various types of carbohydrates
that are present in biological suspensions and sewage sludges.
Among the myriad of color developers such as indole, orcinol, carbazole,
cysteine, trypotophan, ct-naphthol, anthrone and phenol used for colorimetric
determination of total carbohydrates, the last two compounds have been
particularly useful and are utilized in the so-called anthrone and phenol-
sulfuric-acid methods.6" These two methods were investigated to select the
better method for this project.
Analysis of the Hanover Park sludge with the anthrone and phenol-sulfuric
acid methods indicated that a much higher concentration is obtained by the
latter procedure (Table 19). One reason for the lower carbohydrate analysis
by the anthrone method is that the anthrone reagent exhibits weak reactions
with pentoses and heptoses, for example, and much stronger reactions with
hexoses.68 The phenol reagent, on the other hand, reacts equally well with
all sugars. It was determined from HPLC analysis that the concentration of
five carbon sugars was much higher than that of the hexoses, which could cause
the anthrone analysis to be considerably lower than that obtained by the
phenol-sulfuric acid procedure. Also, the total carbohydrate contents
obtained by the anthrone procedure were much lower than those reported in the
literature.69'71
TABLE 19. TOTAL CARBOHYDRATE CONCENTRATIONS IN HANOVER PARK SLUDGE AS
DETERMINED BY THE ANTHRONE AND THE PHENOL-SULFURIC ACID METHODS
Anthrone
Phenol sulfuric
Total carbohydrate concentration
Analytical
methods
mg/L
Average
wt %
of TS
Average
wt %
of VS
Average
8,000
8,100
13,900
14,400
13,700
14,440
8,050
14,100
11.1
11.3
19.4
20.0
19.1
20.0
11.2
19.6
15.9
16.1
27,
28
27,
28.7
16.0
28.1
Lipids—
Considerable work was done to select a suitable procedure to determine
lipid contents of feed and digested sludges. Lipids are a diverse group of
70
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high-molecular-weight carbon-oxygen-hydrogen compounds that are insoluble in
water but soluble in such organic solvents as benzene, ethers (diethyl ether,
petroleum ether, etc.), chloroform, acetone, pentane, hexane, freon
(dichlorodifluoromethane, CCl2F2)f or mixtures thereof. Simple llpids include
fats (glycerides and triglycerides, which are products of a combination of
fatty acids and the trihydroxyalcohol, glycerol), waxes (esters of fatty acids
and alcohol rather than glycerol), oils (low- to high-molecular-weight
hydrocarbons ranging from gasoline to heavy oil to lubricating oils), esters
of long-chain fatty acids (calcium or magnesium soaps), etc. Compound lipids
have a more complex structure and include phospholipids (for example,
lecithins and cephalins, frequently combined with proteins) glycolipids, and
sulfolipids. These compound lipids are present in all microorganisms and may
yield nitrogenous bases, phosphoric acids, etc., in addition to fatty acids
and glycerol upon hydrolysis. Derived lipids consist of a heterogeneous group
of compounds derived from, or chemically related to, other lipids. These
substances include steroids (hormones, ergosterols, cholesterols, etc.),
cartenoids, and polyisoprenoids and behave like lipids in that they are
extractible by lipid solvents. The feed and the digested sludges were
expected to contain all types of lipids of natural and synthetic origins,
although the relative proportions of the various lipid types are expected to
be altered due to anaerobic fermentation.
Since all lipid analytical methods rely on its extraction by selected
solvents, and because a chosen solvent does not selectively dissolve a
particular kind of lipid, the determined concentration represents a
heterogeneous group rather than a specific chemical classification. Lipid
analytical methods are simple in principle and involve solvent extraction of
this hydrophobic compound from an aqueous suspension followed by drying to
produce a moisture-free residue. The methods are necessarily empirical;
errors are introduced because low-boiling fractions are lost and certain non-
lipid substances may be extracted along with lipids.- Chloroform, for example,
dissolves certain carbohydrates to a limited extent. Similarly, elemental
sulfur and certain organic dyes are extracted as "hexane-soluble lipids."
Special precautions are necessary because some extractibles, especially
unsaturated fats and fatty acids, oxidize readily. However, replicable and
comparable results can be obtained by strict adherence and meticulous
attention to all procedural details. Consequently, the extraction technique
and the rate and time of extraction must be reproduced exactly for all determ-
inations because of varying solubilities of different kinds of lipids in the
selected solvent. Also, the length of time for drying and the drying tempera-
ture (which influences volatilization) as well as the cooling time — exces-
sive cooling time may result in an increase in lipid weight, presumably due to
oxidation of extractibles and the absorption of oxygen by the solvent — must
be closely controlled and kept constant to produce comparable and meaningful
results.
Because there appears to be no consensus as to which of the various lipid
analytical procedures is "best" for sewage sludges, three methods were
investigated. One of these methods was that recommended by the American
Society for Microbiology (ASM).*'' The ASM method was proposed in the quality
assurance plan considering that the Hanover Park raw sludge contained 60% by
weight of biological sludge. The other two methods investigated were the
71
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freon-extraction method outlined in the APHA Standard Methods58 for oil and
grease and the chloroform-methanol extraction procedure suggested by
O'Rourke72 for digester feeds and effluents. The ASM and the O'Rourke
procedures are semiwet methods utilizing chloroform-raethanol extractions, and
are probably not as accurate as the APHA Soxhlet extraction procedure. Since
Soxhlet extraction is recommended for oil and grease, it had to be compared
with the ASM and O'Rourke procedures to ascertain its capability to extract
biological lipids.
Recovery of "Standard" Lipids—As a first step, the three selected lipid-
determination methods were compared with respect to their abilities to recover
"standard" or common lipids. Crisco™ was used as the common natural lipid.
Motor oil was selected as the common synthetic lipid. The results reported in
Table 20 show that Soxhlet extraction exhibited precision and accuracy that
were comparable to those of the ASM and the O'Rourke methods. Also, it was
evident that lipid recoveries by Soxhlet extraction with freon were not
affected by the ratio of natural to synthetic lipids.
Recovery of Sludge Lipids—The three selected lipid-analysis procedures
were also compared in terms of their efficiencies to recover sludge lipids.
Analyses were conducted with sludge samples alone and with sludge samples
mixed with known quantities of an external standard, motor oil. Standard
recoveries were calculated from concentrations determined for sludge and the
sludge-standard mixture. Results reported in Table 21 show that freon Soxhlet
extraction was better than the other two methods in terms of biological lipids
recovery. Also, freon extraction recovered the non-biological lipid with
efficiencies comparable to those of the other two procedures.
Selected Lipid Analytical Method—Based on the analytical work described
above, it was concluded that the ASM method involved a slow solvent
evaporation rate and a lyophilization step. The O'Rourke method involves a
slow filtration step. Both methods are time-inefficient and require the use
of hazardous solvents. Quantitative lipid transfer from one step to another
was a problem, and results from these semiwet methods do not compare well with
those from the Soxhlet extraction procedure known to be more accurate for
oils, grease, and waxes.
Although the freon Soxhlet extraction procedure is not clearly specified
to be suitable for biological lipids, results of investigations reported above
showed that this method afforded increased recovery of sludge lipids over the
alternative techniques tested. It was felt that the Soxhlet method is simple,
straightforward, time-efficient, and at least as precise and accurate as the
other lipid-analysis methods; also, freon appears to be less hazardous than
the other solvents required for the semiwet techniques. Last, but not least,
the APHA procedure should be preferred to other methods because results from
this research can then be compared with those of others. One possible
disadvantage is that freon Soxhlet extraction may be more expensive than the
other extractions. Overall, the APHA Soxhlet procedure seemed to be better
than the ASM and O'Rourke methods, and it was selected for this project.
72
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TABLE 20. RECOVERIES OF COMMON LIPIDS BY THE SOXHLET, ASM, AND O'ROURKE METHODS
u>
Soxhlet method O'Rourke method ASM method
Sample
1*
2*
3
Extracted Recovery, Extracted Recovery, Extracted Recovery,
Standard lipid in sample lipid, g % lipld, g % lipid, g %
5 g Motor oil + 15 g Crisco 19.4774 97.4
15 g Motor oil + 5 g Crisco 19.3826 96.7
50 g Motor oil — — 48.5787 97.0
50 g Motor oil -- — 47.9892 96.0
I
5 g Motor oil — — — — 5.0601 101.2
5 g Motor oil — — — — 5.0209 100.4
Sample 1 could not be analyzed by the O'Rourke and the ASM methods because of quantitative lipid transfer
problems.
Sample 2 could not be analyzed by the ASM method because this procedure is designed for small samples.
-------
TABLE 21. RECOVERIES OF SLUDGE LIPIDS AND MOTOR OIL BY THE
SOXHLET, ASM, AND O'ROURKE METHODS
Raw sludge Recovery of motor oil
lipid cone.,* standard from mixed
Analytical method wt % of TS sludge-oil sample, %
Soxhlet freon extraction a) 27.6 94.1
b) 24.3 78.6
O'Rourke method (chloroform-
methanol extraction) 17.2 94.1
ASM method (chloroform-
methanol extraction) 16.5 —
Analysis was run on raw sludge sample only.
ANAEROBIC DIGESTIBILITY POTENTIAL TEST (ADPT)
Test Concept
The theoretical digestibilty potential of the digester feed sludge can be
calculated from its elemental analysis assuming stoichiometric conversion of
the organics to product gases. This theoretical potential, however, cannot be
achieved in practice because only a part of the organics (volatile solids) is
anaerobically biodegradable. An anaerobic digestibility potential (ADP) test
was conducted with the Hanover Park feed sludge to estimate the anaerobic
biodegradability potential of this substrate by long-term batch digestion at a
selected mesophilic reference temperature of 35°C. The final methane yield
and VS reduction obtained from this test serve as "bench marks" against which
other experimental yields and VS reductions can be compared to evaluate the
efficacy of the particular digestion system.
The ADP test is based on a concept similar to that of the long-term BOD
test; the final methane yield and VS reduction of the ADP test are anaerobic
counterparts of the "ultimate" BOD.
ADP Test Protocol and Data Analysis Procedure
The ADP test is started with an appropriate inoculum (seed) and a
selected volume of the test sludge to produce measurable volumes of gas during
selected incubation periods. In this research, the inoculum was obtained from
a single-stage high-rate digester, which was continuously fed with Hanover
Park sludge at an HRT of 7 days and exhibited satisfactory and stable
performance.
74
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The test is set up in triplicate by filling 282-mL-capacity glass serum
bottles with selected volumes of the digester feed sludge, the inoculum, and
deoxygenated water to obtain a final culture volume equal to about one-half
the volume of the bottle. All transfers were made anaerobically, and the
serum bottle was purged with a 20%-C02-80%-N2 gas mixture that was passed
through a heated copper column to remove any oxygen from this purge gas. The
bottle was stoppered, crimp-sealed, and incubated at 35°C in an inverted
position to minimize gas leaks. Control digester bottles were also prepared
in the same manner but without the test sludge to be able to correct for gas
production from the inoculum sludge, and thus to obtain net gas production
from the feed sludge only. Tests with feed and seed sludges were conducted in
triplicate.
Gas production and composition were determined for all bottles at
selected intervals; a computer program was utilized to perform the tedious
calculations necessary to determine accumulative and corrected biogas and
methane productions at various incubation times. All measured gas volumes
were reduced to dry volumes under the standard conditions of 15.55°F and
762 mm Hg mercury pressure. The ADP test was continued until gas production
leveled out and no further measurable gas production could be observed. At
termination, the contents of the bottles were mixed, and TS and VS analyses
were performed in triplicate on aliquots of digested residue sampled from the
bottles. Total and volatile solids balances were performed to check if gases
were lost during the test, and to estimate VS reduction achieved by long-term
digestion.
ENZYMATIC PRETREATMENT OF SLUDGE
Enzyme pretreatment of sludge was conducted using cellulase-cellobiase,
and lipase enzymes obtained from Novo Laboratories Inc. (Cellulast 1.5 L,
Novozym 188, and Novozym 225, respectively). These enzymes were selected on
the basis of work conducted by SYSTECH Corporation for the U.S. EPA.
Cellulase aids the breakdown of cellulosic substrates to glucose, cellobiose
and higher glucose polymers; cellobiase was used to convert cellobiose, a non-
fermentable carbohydrate, to glucose. Lipase was used to aid the hydrolysis
of feed sludge lipids to volatile fatty acids. Samples of these enzymes were
obtained from Novo Laboratories Inc. as liquid slurries; the TS contents of
the cellulase, cellobiase, and lipase were 0.665, 0.495, and 0.300 g/mL,
respectively.
Digester feed slurries were pretreated with cellulase and cellobiase for
Ik hours in containers Incubated at 35°C. Dosages of 2.76 g cellobiase TS/kg
feed TS and 0.28 g cellobiase TS/kg feed TS were used; the feed slurry was
adjusted to pH 5 with 2.5N HC1 prior to pretreatment and back to the original
slurry pH (about 5.5) with 2.5N NaOH after pretreatment. Lipase was dosed
directly to the acid-phase digestion with a timer-operated peristaltic pump
about 43 times per day at a dosage of 2.75 g lipase TS/kg feed TS. Lipase was
added directly to the acid-phase digester, instead of to the pretreatment
container because its activity is optimum at the pH of the acid-phase digester
(pH 6 to pH 7) and is greatly reduced at the pH used for the cellulase/
cellobiase pretreatment. The enzyme dosages used in this work were found to
be optimum by SYSTECH Corporation.
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SYSTEM START-UP AND OPERATION
Culture Start-Up and Acclimation
As indicated previously, eight different digesters were used to conduct
the various single-stage, separate acid-phase and two-phase digestion runs.
Each of these digesters was initially started with active mesophilic inocula
obtained from either ongoing bench-scale digesters operated at IGT or full-
scale digesters operated at MSDGC's West-Southwest wastewater treatment plant
in Stickney, Illinois. Prior to inoculation, each digester was filled with
water to expel air and then drained under a gas purge containing 70 mol %
methane and 30 mol % carbon dioxide. Gas purging was continued after the
water was drained until all traces of oxygen in the digester were removed, as
determined by periodic gas analyses. The inocula were then anaerobically
transferred to the digesters.
The mesophilic cultures were then acclimated to Hanover Park feed sludge
with daily feeding at HRT's of 15 to 20 days for the single-stage and methane-
phase digesters and at HRT's of 6 to 7 days for the acid-phase digesters. The
single-stage and methane-phase HRT's were gradually reduced to the target HRT
and loading-rate conditions while gas composition and effluent volatile acids
concentrations were monitored to ensure that the methanogenic populations were
not washed out of these digesters. Acid-phase HRT's were reduced more rapidly
to enrich the acidogenic populations in these digesters.
Thermophilic cultures were developed from acclimated mesophilic cultures
by increasing the digester temperature to 55°C in a single step after a volume
of feed sludge equal to about 10% of the culture volume was added. The
single-stage and methane-phase therraophilic cultures were left in batch for
several days until effluent volatile acids had decreased to acceptable levels
before daily feeding was started. Daily feeding was started immediately for
the thermophilic acid-phase cultures.
Frequency of Digester Feeding
As indicated in the experimental plan, various steady-state CFCSTR
digestion runs were to be conducted at digester HRT's of between 15 and
0.8 days. Digesters operated at HRT's lower than 15 days were fed, in small
slug doses, 12 to 40 times per day with the auto-feed systems described in a
previous section. The feed frequency was increased as the digester HRT was
reduced in consideration of the relationship between feed frequency and
microbial growth rate. Digesters were fed manually once per day after a
selected volume of digester contents was wasted (withdrawn) when the HRT was
15 days.
The frequency of digester feeding used in this research varied from once
to about 40 times per day. As will be evident from the following theoretical
considerations, the above feeding frequencies were selected so that
intermittent or semicontinuous feeding mode was for all practical purposes
equivalent to continuous feeding.
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Theoretical Basis for Equivalency of Intermittent and Continuous Feeding
Intermittent or semicontinuous digester operation is characterized by
regular withdrawal (or wasting) of a part of the spent medium (or digester
content) after a selected time interval of digestion and the replacement of
the part withdrawn by fresh substrate or digester feed slurry. When the
number of withdrawals and feedings per unit time is infinity or sufficiently
high, the semicontinuous or intermittent feeding converts to continuous
feeding. Under steady-state conditions in a CFCSTR digester, a dynamic equi-
librium is established between the increment of microbial mass in the digester
grown at the expense of the slug feed and its decrease with effluent drawoff,
so that the total mass of microorganisms in the digester after wasting is
constant. At steady state the specific growth rate, y, of the digester
organisms is related to the dilution rate by Fencl's equation, * as follows:
1 = (1 -£)n exp y (1)
_ i
where D = dilution rate = 9
8 = theoretical detention time = V/F
V = digester volume
F = flow rate
n = number of digester wastings and feedings per unit time.
When n is infinity, the semicontinuous process passes into the continuous
process, and Equation 1, in this case, can be rewritten as —
1 = lira E exp y(l - —)n
n •*• »
The solution of Equation 2 is —
MCF - D (3)
That is, for the "ideal" case of continuous feeding (CF) and withdrawal, the
specific growth rate, y^pt is equal to the dilution rate.
Further analyses of Equations 1 and 3 show that, in theory, there is
little difference between semicontinuous and continuous digestion provided 6
and n are sufficiently large. As 8 and n are decreased, the semicontinuous
process deviates more and more from the ideal continuous process in that the
specific growth rate of the organisms must be increasingly greater than the
dilution rate if steady-state digester operation is to be achieved.
For example, the specific growth rate at steady state for a CFCSTR
digester fed once per day (n = 1) at a 15-day HRT must be only 3% higher than
77
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the dilution rate (Figure 11). Thus, for all practical purposes, daily
feeding once per day is equivalent to continuous feeding at a 15-day HRT.
However, for a steady-state CFCSTR digester operated at a 2-day HRT with
daily feeding, the growth rate must be 39% higher than the dilution rate
(Figure 12). As the feed frequency is increased to 15 times per day or more,
the deviation between specific growth rate and dilution rate is reduced to
less than 3%. For this reason, feed frequencies for digesters operated at
HRT's of less than 15 days were selected so that the deviation between
specific growth rate and dilution rate would be 3% or less.
pH Control
Culture pH's were controlled only for the parametric-effects acid-phase
digestion runs because one of the objectives of these runs was to ascertain
the effects of selected pH's (pH 5 and pH 7) on acidogenesis of sludge. The
culture pH's were controlled continuously, with the apparatus described
previously, by dosing the cultures with 2.5N NaOH (for pH 7) and 2.5N HC1 (for
pH's below 7). Sodium bicarbonate (NaHCO^) and lime [Ca(OH)2J were considered
as pH control chemicals for the pH 7 runs but were rejected because
bicarbonate could act as a carbon source for gas production, and lime is
incapable of maintaining culture pH's above 6.8. Hydrochloric acid was used
to control the cultures below pH 7 (instead of sulfuric or nitric acids)
because the chloride ion is less toxic to anaerobes than the sulfate or
nitrate ions. The normalities of the pH control chemical solutions were
selected so that the volumes dosed for pH control were high enough to measure
accurately, but low enough so as not to significantly dilute the cultures or
affect the digester HRT's.
Several procedures were used to ensure that the pH controllers functioned
properly. During the first 2 months of operation, chart recorders were
attached to both controllers to provide a continuous record of pH; these
charts were scanned particularly to check for large pH excursions that may
have occurred during non—working hours. Analog pH meters incorporated in the
controllers were checked several times per day. Effluent pH measurements were
made at least three times per week with a bench-top pH meter and compared with
the controller pH meter readings. In addition, the in-line pH probes for both
controllers were calibrated at least once per week with standard buffer
solutions.
During the first few weeks of operation with automatic pH control,
several large pH excursions were observed. The problems were resolved by
lowering the pH probes further into the cultures to improve contact with the
culture and by moving the pH control delivery tubes closer to the pH probes to
improve pH response time. Thereafter, the controllers functioned
independently and maintained culture pH to within 0.15 pH units of the
setpoint.
Foam and Scum Control
Floating scum and foam were encountered during mesophilic operation at
short HRT's (less than 5 days) and high loadings (more than 10 kg VS/m3-day).
78
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JET
CD
0.075
0.070
CJU 0-065
0.060
ONE FEEDING/DAY = 103.4% /ic
FOR INTERMITTENT FEEDING
FOR CONTINUOUS FEEDING
_L
J_
_L
0 5 10 15 20 25 30 35
FREQUENCY OF INTERMITTENT FEEDING, Times/Day
40
A85070602H
Figure 11. Effect of feeding frequency on specific growth rates
in a CFCSTR digester operated at a 15-day HRT.
-------
oo
o
0.70
0.65
0.60
g
Of.
CD
O
O
UJ
Q.
0.50
0.45
i FOR ONE FEEDING/DAY = 138.6%
FOR INTERMITTENT FEEDING (//;>
_L
_L
_L
/z FOR CONTINUOUS FEEDING
_L
0 5 10 15 20 25 30 35 40
FREQUENCY OF INTERMITTENT FEEDING, Times/Day
A8507060IH
Figure 12. Effect of feeding frequency on specific growth rates
in a CFCSTR digester operated at a 2-day HRT.
-------
Scum and foam interfered with digester operation and gas collection; however,
these problems were not observed in the thermophilic digesters. In many cases
the scum or foam moved out of the digester with the product gases, fouling the
gas collections tubings and valves. Dissolved gases and foam in the digester
effluent resulted in loss of gas-liquid seals in the effluent overflows, which
interfered with effluent withdrawal.
Several strategies were investigated to eliminate these problems. An
antifoam agent (Dow-Corning FG-10) was added to the feed slurry and inter-
mittent mixing was instituted instead of continuous mixing. Neither of these
actions had any appreciable effect on scum formation, however. Foam traps
were then installed in the gas lines between the digesters and the gas
collection systems, and the effluent overflow systems were modified.
The foam traps consisted of 2-L vessels and were installed so that
product gases from the digesters entered at the bottom and exited at the top
of the vessels before passing to the gas collection systems. Thus, any foam
carried out of the digesters with the product gases could be collected in the
foam traps before it fouled the collectors. The traps were drained manually
as necessary. The original 1.9 to 2.5-cm-diameter overflow pipes were
replaced with larger 3.8 to 5.1-cm-diameter overflows to minimize gas locking
caused by the foam and scum in the effluent. In two of the digesters
(Digester Nos. 332 and 333), the overflow pipes were installed through the
digester walls and 90° elbows were installed on the pipes inside the
digesters. The open ends of the elbows were directed downward and were
submerged in the culture to a depth of about A cm so that only effluent from
beneath the foam and scum layer was withdrawn. A perforated plate was also
mounted in Digester No. 333 just below the culture surface to keep the foam
layer submerged and wetted. Although these modifications did not totally
eliminate the accumulation of scum and foam within the digesters, they did
resolve the problems associated with gas collection and effluent withdrawal.
Process Monitoring
Routine Monitoring—
Digestion runs were routinely monitored by determining digester HRT's,
culture temperatures, gas production rates (GPR), gas composition, and
effluent pH and volatile acids concentrations according to the schedule in
Table 22. These data were regularly plotted and reviewed to assess the
progress at each run and to determine when steady-state operation was
achieved. Gas production rates were monitored daily because this determina-
tion was the easiest and most accurate means of tracking the performance of
the runs and because it was the primary performance variable used for
selecting steady-state segments of the runs. Gas compositions and effluent pH
and volatile acids were measured less frequently because these parameters
varied less with time.
Steady-State Monitoring—
The schedule for process monitoring during steady-state operation was
similar to that followed during nonsteady-state operation (Table 22), except
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TABLE 22. ROUTINE PROCESS MONITORING SCHEDULE
Determination
Non-steady-state
frequency
Steady-state
frequency
Digester HRT
Culture temperature
Digester gas production rate
Gas composition
Effluent pH
Effluent volatile acids
Daily
3 to 7 times per week
Daily
1 to 2 times per week
3 to 7 times per week
1 to 2 times per week
Daily
3 to 7
Daily
2 to 4
3 to 7
2 to 4
times per week
times per week
times per week
times per week
that gas compositions and effluent volatile acids were measured more
frequently to ensure that these process variables were also stable with time.
As described previously, feed and effluent slurry samples were also collected
during steady-state operation and analyzed for solids, organic components,
alkalinity, and nitrogen contents.
Steady-State Criteria—
This research required collection of steady-state data for most of the
experimental phases. Steady-state was defined as a segment of a digestion run
during which the digester operating variables and performance parameters were
maintained at "constant" levels, permissible within the constraints of bench-
scale equipment operability and the available measurement techniques and for
which solids balances were between 85% and 115%. For complete-mix systems,
the steady-state duration was equal to at least twice the HRT. The criterion
used for achievement of steady state was the constancy of certain digester
operating and performance data during a selected run segment. A particular
parameter was assumed to have reached a constant level if the coefficient of
variation was less than that specified in Table 23. Digester HRT's, loading
rates, and culture temperatures were the parameters that defined the operating
conditions of each run and were thus used for the operation criteria. The
primary performance criteria were gas and methane productions, which were
measured more accurately and frequently than the other performance parameters.
Solids balances were also used as indicators of steady state because the
solids analyses could be completed quickly, and because good mass balances are
prerequisites for steady-state operation.
The levels of variabilities specified in Table 23 are reasonable in view
of the unavoidable variabilities associated with control of the operating
82
-------
TABLE 23. STEADY-STATE CRITERIA
Maximum acceptable
coefficient of
Process variable/performance parameter variation, %
Operation
HRT, days 20
Loading rate, Ib VS/ft3-day 20
Temperature, °C 5
pH* 5
Performance
Methane content, mol % 10
Methane yield, SCF/lb VS added 20
Methane production rate, vol/day-culture vol 20
This variable was a criterion for only the pH-controlled parametric-effects
acid-phase digesters.
variables at selected levels and measurement of the performance parameters.
For example, a 20% variability in sludge pumping rate is normal for the type
of equipment available commercially. A variability of 20% in HRT is thus
almost unavoidable. If feed sludge is delivered with a 20% variability in
rate, gas yield and production rate would also have the same variability.
Data Reduction
The collected raw data were reduced to provide the operating and
performance parameters indicated in Table 24. The reduced data were tabulated
and graphed, as appropriate, for evaluation and interpretation of the
experimental observations, and for arriving at conclusions with regard to
parametric effects on digestion process efficiency. Data reduction also
included the computation of such simple statistics as the mean, standard
deviation, coefficient of variation, and correlation coefficient.
Hydraulic retention times and organic loadings were calculated based on
daily measurements of feed slurry flow rates. Volatile solids concentrations
used for the loadings were based on direct analyses of the feed slurries
83
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TABLE 24. REDUCED OPERATING AND PERFORMANCE PARAMETERS
Analysis or measurement
Reduced data
Hydraulic retention time (HRT)
Organic loading rate
pU control chemical dosage
Total solids (TS)
Volatile solids (VS)
Fixed solids (FS)
Total suspended solids
Volatile suspended solids
Gas volume
Total gas and methane yield
Total gas and methane production rate
Gas composition
Volatile fatty acids (VFA)
Total VFA
PH
Total and bicarbonate alkalinities
Volatile fatty acids
COD (total and filtrate)
Nitrogen (ammonia)
Nitrogen (organic)
Crude protein
Lipids
Carbohydrate
Carbon and hydrogen
Sulfur
Phosphorous
Heating value
Feed component reduction
Solids balances
days
kg VS/m3 culture-day
meq/L feed
mg/L or wt 7,
mg/L or wt % of TS
mg/L or wt % of TS
mg/L or wt % of TS
mg/L or wt % of TS
Standard m3 (dry) wt 15.55°C and 762 mm Hg
Standard m3/kg VS added
Standard vol/culture vol-day
Normalized mol %
mg/L
mg/L as acetic
Dimensionless unit or moles/1 [H+]
mg/L as CaC03
mg/L as acetic acid
mg/L or g COD/g VS
mg/L NH3-N or wt % of TS
mg/L Org-N or wt % of TS
mg/L or wt % of VS
mg/L or wt % of VS
mg/L or wt % of VS
wt % of TS
wt % of dry solids
wt % of TS
kcal/kg (dry)
percent
percent
84
-------
during steady-state runs. During nonsteady segments of runs, the VS
concentrations were calculated on the basis of the concentrated feed solids
analyses and the dilution factor used to prepare the slurry. Chemical dosages
for the pH-controlled parametric-effects acid-phase runs were determined on
the basis of the daily flow rates of chemical solutions and feed slurry.
Gas production volumes were converted to standard volumes at standard
temperature and pressure (15.55°C and 762 mm Hg) on a dry basis using daily
barometric pressure and ambient temperature readings taken in the digester
laboratory. Gas yields were reported in units of standard m /kg VS added
instead of standard nr/kg VS reduced, sometimes used by other researchers,
because the former units better describe the conversion efficiency of feed
volatile solids to gas. Methane yields were calculated on a daily basis as
the product of the total gas yield and the measured methane content; on days
when gas composition was not analyzed the average of the previous and
subsequent methane contents was used to calculate the methane yield. Steady-
state methane yields were reported as the mean of these daily yields during
the steady-state segment of each run. Daily and mean steady-state methane
production rates were calculated in a similar manner. Analyzed gas
compositions generally totaled less than 100%, primarily due to water vapor in
the gas samples (which was not detected by the chromatograph) and experimental
error. For these reasons, gas compositions were reported on a normalized
basis; the individual gas components were multiplied by a constant factor to
bring the total to 100.0%.
Feed and effluent slurry analyses were generally reported in units of
mg/L to permit direct comparison of feed and effluent slurry characteristics.
Organic component analyses (crude protein, carbohydrates, and lipids) were
also reported as wt % of VS because these compounds were the major
constituents of volatile solids in the feed and effluent slurries.
VS Reduction Efficiency
Organic component reductions were calculated as the percent ratio of the
difference of feed and effluent concentrations to feed concentration.
Volatile solids reductions can be calculated by three different methods, as
follows:
Mop-16 Method
VS. - VS
VS
Mass of Gas Method
R VSt - (VS;L
W
VSR = jf- X 100 (5)
85
-------
Carbon-in-Gas and Carbon-in-Feed Method
F X C
VSR = Pvs g X 100 (6)
where VS-j^ = influent VS, decimal wt % of TS
VSQ = effluent VS, decimal wt % of TS
Wg = daily mass flow of product gases, g/day
VSj = daily mass flow of feed VS, g/day
C = daily mass flow of carbon in product gases, g/day
o
F = correlation factor (1.84), g VS/g carbon
Equation 4 was used to calculate VS reduction because this method is
recommended by the Water Pollution Control Federation. This method of
determining VS reduction is based on the assumption that the mass flow rates
of fixed solids in the feed and effluent slurries are the same and it accounts
for the changes in slurry volume which take place during digestion as a result
of gas production. It is, however, sensitive to errors in the determination
of the feed and particularly the effluent VS contents.
In general, errors in the determination of feed VS content are limited to
normal analytical errors, whereas determinations of effluent VS contents are
also subject to errors due to incomplete volatilization of the sample and
differences in the fixed solids contents relative to those of the feeds. The
physical/chemical characteristics of the effluent slurries are different than
those of the feed slurry as a result of digestion. Inorganic films develop on
dried effluent solids and shield the sample from complete volatilization. The
organic residue in effluent slurries may also have different volatilities than
the feed organic due to differences in composition, solids particle size, and
porosity. In addition, effluent slurries usually have higher bicarbonate
alkalinities than feed slurries due to conversion of organic carbon to
inorganic forms, which results in a net increase in fixed solids content.
These errors are further aggravated when external chemicals are added directly
to the digester, as was the case for the pH-controlled and enzymatic
pretreatment digestion runs.
For these reasons, two other methods of calculating VS reduction
(Equations 5 and 6) were investigated. Both methods are based on the
assumptions that the mass flow rates of feed VS and product gases can be
accurately determined, and the problems associated with effluent VS determina-
tion can be avoided. In Equation 5, the mass rate of gas production is
assumed to be equal to the rate of VS reduction (in other words, each gram of
VS reduction is equal to 1 gram of gas production). Although this assumption
seems reasonable, it is subject to potentially large errors because the weight
ratio of product gas formed per unit VS reduced varies between 0.5 and 1.6 g
gas/g VS converted, depending on the elemental composition of the reduced
86
-------
2
organic component. Ratios greater than 1 occur when a portion of the
hydrogen and oxygen in the methane and carbon dioxide product gases are
contributed by water during hydrolysis of the organic component. For example,
stoichiometric conversion of a carbohydrate with an assumed composition of
^6^10^5 results in tne following balanced reaction:
C6H10°5 + H2° T 3C°2 + 3CH4
For this reaction, the weight ratio of product gas to carbohydrate VS reduced
is 1.11. Similarly, the ratio for conversion of lipids is 1.6, assuming a
composition of C5nH90°6* Ratios lower than 1 may occur for conversion of
proteins because a portion of the carbon dioxide produced becomes chemically
bound to ammonia (produced during decomposition of amino acid groups) to form
ammonium bicarbonate. Thus, the weight ratio of product gas to VS reduced is
dependent not only on the elemental composition of each organic component but
also on reduction of each component.
Equation 6 was developed in an attempt to avoid the problems associated
with hydrolysis, inherent in Equation 5. In this method, the mass flow rate
of VS reduced is calculated as the product of the mass flow rate of product
gas carbon and a proportionality factor relating carbon to equivalent VS. It
was reasoned that carbon in the product gas could be produced only from con-
version of feed VS carbon. Thus, if a correlation between feed VS and carbon
content could be established, the mass rate of VS reduced could be calculated
based on gas production and composition data. The correlation factor used
(1.84 g VS/g carbon) was determined on the basis of a linear regression
analysis of carbon and VS contents in 10 sewage sludge feeds and 4 effluent
slurries (Figure 13). Volatile solids and carbon contents, which form the
basis for Figure 13, and the correlation analysis are detailed in Table 25.
The correlation coefficient for all 14 data sets was about 99% indicating a
strong correlation between carbon and VS in both feeds and effluents.
As a further check on the MOP-16 method, the data were examined to see if
concentration of ash (mg/L TS-mg/L VS) was the same in the feed and effluents
from the digesters. This calculation (see Table G-l) showed losses relative
to the total feed solids to be low, about ±2 percent. Surprisingly, these
small differences caused large discrepancies between VS^'s (volatile solids
reduction) calculated by the MOP-16 method and the material balance method.
The absolute differences ranged from -7 to 10% (see Table G-l). The methods
gave the same result when there was no ash loss. As is shown below, the
results by the two methods correlated better with each other than with results
of the mass-of-gas method:
Comparison Correlation Coefficient (r)
MOP-16 vs. Material Balance 0.84
Mass of Gas vs. MOP-16 0.70
Mass of Gas vs. Material Balance 0.78
The conclusions of the report would not be substantially changed if any
one of these three methods were used to calculate VSR. However, when the
inaccuracies in determining true volatile solids levels in the effluent were
considered, the mass-of-gas method appeared to be the best choice.
87
-------
09
OC
_J
D)
60
50 -
40 -
C 30
0
D
20
0
0
0
O FEED
A EFFLUENT
CARBON (g/L) = 0.543 X VS (g/L) + 0.776
COEFFICIENT OF CORRELATION =0.99
0 20 30 40 50 60 70
VoI ati le sol ids, g/L
80
Figure 13. Correlation between carbon and volatile solids
concentrations of raw and digested sewage sludges.
90 100
A85080629H
-------
TABLE 25. VOLATILE SOLIDS AND CARBON CONTENTS OF RAW AND
DIGESTED SEWAGE SLUDGES
Sample
no.
1
2
3
4
5
6
7
8
9
10
Source of sludge
Hanover Park mixed
primary/activated
Hanover Park mixed
primary/activated
SESD primary
(Salem, MA)
Hanover Park mixed
primary/activated
Stickney activated
Hanover Park mixed
primary/activated
Stickney activated
Hanover Park mixed
primary/activated
Disney World
primary (Orlando, FL)
Stickney activated
Raw
Volatile
solids,
S/L
14.66
51.73
38.64
45.10
79.24
45.07
92.06
77.02
27.84
43.98
sludge Digested sludge
Volatile
Carbon, solids, Carbon,
g/L S/L g/L
8.33 22.43 12.36
30.01 32.09 17.44
24.41
24.86 29.42 15.44
42.28
26.41
49.20
45.29
17.31 7.35 4.35
22.64
89
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SECTION 7
CHEMICAL CHARACTERIZATION OF PROCESS FEEDS
CHEMICAL CHARACTERIZATION OF UNPROCESSED RAW SLUDGES
Since raw sludges collected from the wastewater treatment plants were not
directly fed to the digesters, limited chemical analyses were conducted to
characterize them. More detailed chemical analyses were performed on the
digester feed sludges which were prepared by processing the collected raw
sludge.
The raw sludges were analyzed for TS and VS contents as reported in
Tables 26, 27, and 28. The mixed primary-activated raw sludge from Hanover
Park had VS contents between 68% and 76% depending on the season (Table 26).
The primary raw sludge from Downers Grove had VS contents between 76% and 80%
(Table 27). The activated sludge from Stickney had VS contents between 66%
and 67% (Table 28). The mixed primary-activated and activated raw sludges
were analyzed for total carbon, hydrogen, total sulfur, total nitrogen, total
phosphorous, and heating (or calorific) value; the results of these analyses
are reported in Table 29. Examination of the data in Table 29 showed that
higher carbon and VS contents of the sludge solids gave rise to higher heating
values, as expected. It is also evident that a unit mass of activated sludge
VS had lower carbon content and calorific value than those of a unit mass of
mixed primary-activated sludge VS; these observations indicated that the gas
and methane yield potentials per unit mass of VS would also be lower for
activated sludge.
The C/N and C/P ratios of the Hanover Park sludge were 8.3:1 and 28.5:1,
respectively. From these ratios, it was concluded that this sludge was not
deficient in nitrogen and phosphorus.
CHEMICAL CHARACTERIZATION OF DIGESTER FEED SLUDGE
Solids Analyses
Digester feed slurries were analyzed for total solids, volatile solids,
and fixed solids during the steady-state and non-steady-state operating
periods of the digestion runs. These data were reported in detail in
Table A-l. Efforts were made to maintain the feed solids concentrations at
levels specified under the experimental-design operating conditions outlined
in Tables 7 through 9 (Section 5). However, deviations from these desired
concentrations were unavoidable.
90
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TABLE 26. COLLECTION, PROCESSING, AND SOLIDS ANALYSES OF
HANOVER PARK RAW SLUDGE
Date lot
collected
11/82
12/82
4/83
6/83
7/83
11/83
Collected raw sludge
vs,
Lot Quantity, TS, wt % Batch
no. liters wt % of TS no.
1 1400 2.00' 73.47 1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
2 1200 — — 1
2
3
4
3 1400 — — 1
2
4 1200 — — 1
2
5 '3000 — — 1
2
3
4
6 3600 — — 1
2
3
4
Processed raw
sludge analyses3
Processing
method
none
FTBb
FTB
FTB
FTB
FTB
FTB
FTDC
FTD
FTD
FTD
FTD
FTD
FTD
FTD
FTD
.FTD
FTD
FTD
FTD
FTDB
FTD
FTD
FTD
FTD
FTD
FTD
FTD
FTD
FTD
FTD
TS,
wt '/,
2.00
4.99
4.56
11.98
4.51
3.65
3.62
4.37
4.91
4.54
4.95
5.83
4.82
5.10
5.13
8.03
8.64
6.89
9.82
11.39
6.86
7.70
8.08
6.09
10.48
12.30
11.62
9.31
9.88
14.11
12.96
VS,
wt %
of TS
73.47
73.13
74.08
59.74
74.27
74.47
73.39
72.68
74.25
73.54
64.56
72.91
73.14
72.36
73.16
75.11
73.99
73.76
75.40
70.47
69.97
72.25
71.76
64.61
71.08
69.54
70.00
68.10
68.29
68.45
68.97
(continued)
91
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TABLE 26 (continued)
Collected raw sludge
Date lot
collected
1/84
2/64
3/84
4/84
4/84
5/84
5/84
6/84
6/84
7/84
8/84
Lot
no.
7
8
9
10
11
12
13
14
15
16
17
Quantity,
liters
3600
1400
3600
600
600
900
600
1200
600
£00
600
VS,
TS, wt % Batch
wt % of TS no.
1
2
3
4
3.07 76.80 1
2
3
4
5
3.49 76.88 1
2
2.04 67.98 1
2
1
__ •»_ 1
!
1
1
» — — i
«.— —— j
Processing
method
FTD
FTU
FTD
FTD
LCd
LC
LC
FTD
FTD
FTB
FTB
FTD
FTD
FTD
FTD
FTD
PCe
PC
FTD
FTD
Processed raw
sludge analyses3
TS,
wt 7.
5.96
7.02
7.77
6.88
11.05
6.26
6.14
8.01
5.15
6.42
5.99
7.25
6.60
10.29
8.58
9.63
8.47
9.00
8.97
13.15
vs,
wt %
of TS
76.38
75.87
74.15
75.94
78.58
78.13
74.57
78.22
77.34
76.14
75.73
68.86
76.66
77.06
76.35
76.62
71.36
69.41
74.56
74.78
(continued)
92
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TABLE 26 (continued)
Collected raw sludge
Processed raw
sludge analyses3
Date lot
collected
Lot
no.
Quantity,
liters
TS,
wt 7,
VS.
wt %
of TS
Batch
no.
Processing
method
TS,
wt %
vs,
wt X
of TS
9/84
18
1400
11/84
19
1400
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
FTD
FTD
FTD
FTD
FTD
FTD
FTD
FTD
FTD
FTD
FTD
FTD
FTD
FTD
FTD
13.76
15.01
21.06
15.51
16.01
14.87
15.35
17.36
17.34
14.61
14.66
16.20
13.29
15.68
13.98
72.92
73.40
72.23
73.72
50.51
72.02
72.29
72.22
72.16
70.56
71.22
71.16
70.76
60.32
71.54
a These analyses were performed immediately after preparation of the sludge batches and
were used as guides to prepare digester feed slurries for the experimental runs.
Separate solids analyses were performed on the digester feed slurries.
FTB refers to raw sludge processing by freezing and thawing in 10-liter plastic bags
(Method 1 in text).
c FTD refers to raw sli/dge processing by freezing and thawing In 200-liter drums
(Method 1 in text).
LC refers to raw sludge processing by laboratory centrifuge (Method 3 in text).
e PC refers to raw sludge processing by pilot centrifuge (Method 4 in text).
93
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TABLE 27. COLLECTION, PROCESSING, AND SOLIDS ANALYSES OF
DOWNERS GROVE RAW PRIMARY SLUDGE
Collected raw sludge
Date lot
collected
10/84
12/84
12/84
12/84
12/84
Lot Quantity, TS,
no. liters wt %
22 50 4.90
23 58 3.78
24 15 4.63
25 18 4.34
26 20 4.26
VS,
wt % Batch
of TS no.
79.67 1
75.86 1
77.82 1
76.71 1
77.51 1
Processing
method
homogenize
homogenize
homogenize
homogenize
homogenize
Processed raw
sludge analyses
VS,
TS, wt %
wt % of TS
4.90 79.67
3.78 75.86
4.63 66.82
4.34 76.71
4.26 66.51
Table 28. COLLECTION, PROCESSING, AND SOLIDS ANALYSES
STICKNEY RAW ACTIVATED SLUDGE
OF
Date lot
collected
9/84
11/84
Collected raw
Lot Quantity, TS,
no. liters wt %
20 870 13.67
21 490 13.67
sludge
VS,
wt % Batch
of TS no.
65.68 1
66.55 1
Processing
method
D&B*
D&B
Processed raw
sludge analyses3
VS,
TS, wt %
wt % of TS
9.03 65.68
10.25 66.55
D&B refers to raw sludge cake processing by dilution and blending.
94
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Table 29. CHEMICAL CHARACTERISTICS OF UNPROCESSED RAW SLUDGES
Mixed primary-
activated sludge from Activated sludge
Hanover Park (Lot 1) from Stickney* (Lot 20)
Total carbon, wt !
Total carbon, wt '
Hydrogen, wt % of
Total sulfur, wt °
TKN, wt % of TS
Total phosphorus,
1 of TS
C of VS
TS
\ of TS
wt % of TS
41.65
56.91
6.25
1.50
4.99
1.46
37.60
51.46
5.68
0.85
6.47
2.00
Higher heating value
Btu/lb TS
Btu/lb VS
7,937
10,846
7,582
10,378
The Stickney activated sludge was mixed with Downers Grove primary sludge to
prepare the digester feed slurries.
Selected digester feed slurries were also analyzed for total, volatile,
and fixed suspended solids (TSS, VSS and FSS). These analyses are reported in
Table A-2. A summary of these analyses is presented in Table 30. About 78%
to 92 wt % of the total solids was insoluble or particulate matter with the
balance being soluble. Of the total residue (i.e., total solids upon
evaporation), 0.3% to 13.4 wt % was soluble inorganics (soluble fixed solids),
about 12% to 32 wt % insoluble inorganics, about 2% to 11 wt % soluble
organics (soluble VS), and 56% to 67 wt % insoluble organics. The average
contents of soluble inorganics, insoluble inorganics, soluble organics, and
insoluble organics were about 8.3, 21.4, 7.5, and 63.8 wt % TS, respectively.
The data also indicated that on the average, about 89 wt % of the sludge
organics were insoluble particulate matter. Direct measurement of suspended
and dissolved total and volatile solids indicated that about 89 wt % of VS was
insoluble and 11 wt % of the organics was soluble (Table 31). The information
developed above from the solids analyses clearly indicated that the sludge
feed was predominantly insoluble in nature, and hydrolysis of the particulate
organics was an important consideration in gasification and stabilization of
this substrate.
95
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TABLE 30. SOLIDS ANALYSES OF DIGESTER FEED SLURRIES
Digester feed
slurry prepared
from feed
lot/batch no Total residue,
Total
sol ids
5/3 71,600
5/4 40,280
5/4 39,350
5/4 74,380
5/4 77,710
6/2 80,340
6/2 69,460
8/5 59.3BO
8/5 55,960
Volatile
solids
50,280
28,660
28,100
48,780
52,620
53,580
46,930
44,960
42,890
mg/L
Fixed
solids
21,320
11,620
11,250
25,600
25,090
26,760
22,530
1 4 ,420
13.07U
Means
Total
suspended matter
mg/L
65,740
33,560
32,100
65,160
69,890
63,6r.O
62,170
46,140
43,740
wt 7.
of TS
91. H
83.3
81.6
87.6
89.9
79.2
89.5
77.7
78.2
84.4
Volatile
suspended matter
rnR/L
44,710
27,100
25,910
41,800
45,000
47,670
45,690
39,200
36,700
wt 5!
of TS
62.4
67.3
65.8
56.2
57.9
59.3
65.8
66.0
65. ft
63.8
Fixed
suspended matter
mg/L
21,030
6460
6190
23..)(.0
24,890
15,980
16,480
6940
7040
ut %
ot TS
29.4
16.0
15.7
31.4
32.0
19.9
23.7
11.7
12.fi
21.4
Total
soluble matter
mg/L
5860
6720
7250
9220
7820
16,690
7290
13,240
12,770
wt %
of TS
8.2
16.7
18.4
12.4
10.1
20.8
10.5
22.3
21.8
15.7
Volatile
soluble matter*
mg/L
5570
1560
2190
6980
7620
6580
1240
5760
6190
wt X
of TS
7.8
3.9
5.6
9.4
9.8
8.2
1.8
7.7
11.1
7.5
Fixed t
soluble matter
mg/L
290
5160
5060
8240
200
10,780
6050
7480
6030
wt I
of TS
0.41
12.8
12.9
3.0
0.25
13.4
8.7
12.6
10.8
8.3
Total, volatile, and fixed soluble matter contents of the feed slurries were determined by difference.
Reproduced from
copy.
-------
TABLE 31. DIRECT MEASUREMENTS OF TOTAL, SUSPENDED, AND DISSOLVED
* SOLIDS CONTENTS OF DIGESTER FEED SLURRIES
Digester feed slurry
prepared trim Total solids
feed lot/batch (no)s (TS), rafi/L
6/2 80,340'
6/2 69,460
Vol.itile solids
(VS), rns/l.
53,580
46,930
Suspended solids
(SS), mfi/L
Total Volatile
63,650 47,670
62,170 45,690
Dissolved solids
(DS), rag/L
Total Volatile
15,070 5,990
4980 5900
SS + DS*, mg/L
Total Volatile
78,720 53,660
67,150 51,590
Volatile solids,
% of total
Insoluble Soluble
88.8 11.2
88.6 11.4
Data reported in these columns compare favorably with the TS and VS data obtained independently in separate tests.
-------
Elemental Analyses and Calorific Value
Elemental analyses and calorific value determinations were performed on
selected digester feed slurries; the results of these analyses are reported in
Table 32. Given the nature of the material sampled and the difficulty of
collecting a "representative" sample, the accuracy of the data in Table 32 was
satisfactory. Also, comparing the analyses performed on samples collected
over a period of eight days, there seemed to be no evidence of decomposition
of the feed sludge during storage, as discussed in the next section.
From a comparison of the elemental and calorific-value analyses of the
raw and the digester feed sludge, it appears that the latter showed higher
carbon analysis and heating value and lower nitrogen and phosphorus concentra-
tions than those of the former. Consequently, the C/N and C/P ratios of the
digester feed sludge were slightly higher than those of the raw sludge. It
was speculated from the above observations that during sludge processing by
freezing, thawing, and decanting and discarding liquids, relatively more
soluble nitrogen and phosphorus than carbon were lost during the sludge
concentration process.
Chemical Oxygen Demand (COD) Analysis
Samples of digester feed slurries were also analyzed for total and
filtrate COD's, so that the data could be used to estimate theoretical methane
yield. Results of the COD analyses for several feed sludges are reported in
Table A-4. Table 33 shows that the total COD contents of Lots 5 and 6 Hanover
Park sludges ranged between about 1.3 and 1.6 g COD/g VS and averaged at 1.4 g
COD/g VS. About 93% of the sludge COD was due to particulate organic matter
and 7% due to soluble organics.
The COD of Lot 8 feed sludge was considerably higher than most samples
from Lots 5 and 6 sludges. About 91% of the COD was due to particulate
organics and 9% due to solubles.
Overall, the COD data indicated that 91.93 wt % of the sludge organics
was particulate matter, and this observation is in close agreement with that
made on the bases of suspended solids analyses showing that 90% of the sludge
VS was insoluble material.
Ammonia and Organic Nitrogens
Nitrogens present in sewage sludges are mainly found as ammonia and
organic nitrogens; nitrite and nitrate nitrogens are also present, but the
concentrations of these nitrogenous species are minor relative to those of
ammonia and organic nitrogens. Digester feed sludges were analyzed for
ammonia and organic nitrogens because these data are useful in assessing
1) the physical nature of the nitrogenous material, 2) the immediate and
potential availability of nitrogen, 3) the protein content of the sludge,
4) the potential buffering capacity that can be generated during digestion,
and 5) the degree of liquefaction taking place under various fermentation
conditions.
98
-------
TABLE 32. ELEMENTAL ANALYSES AND CALORIFIC VALUES OF DIGESTER FEED SLURRIES
PREPARED FROM HANOVER PARK SLUDGE*
Sample
date
1/6/83
1/18/83
7/25/83
7/27/83
7/29/83
8/2/83
Sludge
lot/batch
nos.
1/2
1/3
4/2
4/2
4/2
4/2
Elemental analysis, wt % of TS
Total Total Total
carbon Hydrogen TKN sulfur phosphorus
4.99
(0.62)f
3.82
(0.78)
43.05 6.71 4.03 1.19
43.01 6.79 — 1.19
42.54 6.54 — 1.29
44.11 6.63 — 1.28 1.22
Higher heating value
Btu/lb TS Btu/lb VS
—
8556 11,719
8685 11,612
8414 11,386
8613 11,655
The samples were collected directly from a refrigerated and mixed feed reservoir.
Number in parenthesis is NH3-N; organic nitrogen is (TKN)-(NH3-N).
-------
TABLE 33. CHEMICAL OXYGEN DEMAND ANALYSES FOR DIGESTER SLURRIES
o
o
Digester feed
slurry prepared from Volatile
feed lot/batch no(s) solids
5/1
5/3
5/3
5/3
5/3
5/3
5/3
5/4
5/4
5/4
6/2
6/2
8/5
8/5
8/5
mg/L
48,795
50,160
50,160
47,430
53,440
53,440
50,280
28,660
28,100
48,780
53,580
46,930
47,940
44,960
42,890
Total
mg/L
~
—
79,530
66,723
87,096
—
78,047
39,580
34,822
78,798
80,617
77,702
Means
85,983
81,896
76,394
Means
COD
B/g VS
—
—
1.585
1.406
1.629
—
1.552
1.381
1.239
1.615
1.504
1.655
1.507
1.793
1.821
1.781
1.798
Filtrate
(soluble) COD
mg/L
6390
4922
4696
5673
4918
4979
6547
2745
2601
—
4211
4605
7968
7753
7042
g/g vs
0.130
0.098
0.093
0.119
0.092
0.093
0.130
0.095
0.092
—
0.078
0.098
0.102
0.166
0.172
0.164
0.167
Particulate
COD (by diff)
mg/L
—
—
74,834
61,050
82,178
~
71,500
36,835
32,221
—
76,406
73,097
78,015
74,143
69,352
g/s vs
~
—
1.492
1.287
1.538
—
1.422
1.285
1.147
-_
1.426
1.558
1.394
1.627
1.649
1.617
1.631
Soluble
COD
Particulate
COD
% of total COD
—
__
5.9
8.5
5.6
—
8.4
6.9
7.5
—
5.2
5.9
6.8
9.3
9.5
9.2
9.3
--
—
94.1
91.5
94.4
—
91.6
93.1
92.5
—
94.8
94.1
93.2
90.7
90.5
90.8
90.7
-------
The ammonia and organic nitrogen analyses for a number of digester feed
slurries are presented in Table 34. The results of these analyses showed that
the ammonia-nitrogen (expressed as N) concentration of the raw feed slurries
ranged between about 220 to 620 mg/L (0.33 to 1.05 wt % of TS) depending on
the sludge lot. Lot 5 had the lowest ammonia nitrogen concentration arid Lot
16 the highest. However, even the lowest observed ammonia-nitrogen
concentration was adequate for anaerobic metabolism.
The organic nitrogen concentration, which is a measure of particulate
proteinaceous material, ranged from about 1900 to 29DO mg/L (3.0 to 4.5 wt %
of TS) depending on the lot of raw sludge of the total nitrogenous material
(as measured by TKN) present in raw sludge Lots 1, 5, 6, 12, 13, 14, and 28, 9
to 15 wt % was soluble and 98 to 91 wt % was particulate proteinaceous
material that had to be hydrolyzed. Raw sludge Lots 8, 16, and 17 had higher
concentrations (18 to 20 wt %) of soluble nitrogenous materials and conse-
quently, lower concentrations of nitrogenous particulates. That raw sludge
Lot 8 had higher soluble organics than Lots 1, 5, 6, 12-14, and 28 was also
evident from considerations of COD and SS data analyses as presented in
Tables 30 and 33.
Acid-Base Characteristics
The pH values and alkalinities of the raw feed sludges are summarized in
detail in Table A-3 and summarized in Table 35. These analyses were conducted
to delineate the acid-base characteristics of these substrates, and to assess
the type of buffer capacities that would be generated during digestion.
Table 35 indicates that all sludges were acidic in nature with pH values
usually less than 6.5. The bicarbonate alkalinities were between 2160 and
5513 mg/L as CaCO^ which are regarded as satisfactory for digester feeds. It
was expected that additional alkalinities would be generated during the
digestion process to produce a high natural buffering capacity within the
digester.
About 20% to 40% of the bicarbonate alkalinity was due to ammonium
bicarbonate, except that for raw sludge Lots 8, 16, and 17 about 50% to 80% of
bicarbonate alkalinity was due to ammonium bicarbonate (Table 35), the reason
being that these thre6 sludge lots contained much larger concentrations of
ammonium compared to the concentrations in the other sludges. Interestingly,
sludges having higher ammonium-bicarbonate alkalinities also exhibited higher
volatile-acids-salts alkalinities. It may be speculated from these
observations that sludge Lots 8, 16, and 17 contained particulates that were
more readily liquefied than those of the other sludges.
Crude-Protein, Carbohydrate and Lipid Analyses
Hanover Park Sludge—
Feed slurries used to operate the sludge digesters were analyzed for the
three major organic components — crude protein, total carbohydrate, and
lipids. Generally, the samples were collected from the feed reservoir during
a steady-state operating period. In some cases feed slurry samples were also
101
-------
TABLE 34. AMMONIA AND ORGANIC NITROGEN CONTENTS OF DIGESTER FEED SLURRIES
Digester feed
slurry prepared
from raw sludge
lot/batch nos.
Total
solids
mg/1
1/8
4/2
4/2
5/1
5/3
5/3
5/3
5/4
5/4
6/2
6/2
8/5
8/5
8/5
12/1
13/1
13/1
13/1
13/1
14/1
16/1
16/1
16/1
17/1
17/1
17/1
45,
64,
45,
69,
67,
77,
71,
39,
82,
80,
69,
63,
59,
55,
41,
69,
67,
65,
67,
68,
67,
66,
46,
66,
68,
66,
100
390
810
635
420
930
600
350
170
340
460
020
380
960
560
870
530
310
530
440
250
735
045
540
960
430
Totak Kjeldahl
nitrogen, (TKN)
mg/L
2251
—
—
2599
2380
2544
2366
15B7
2688
2701
2263
3206
3187
2929
2104
3120
3122
3255
3254
2704
3337
3534
2440
3032
3067
3208
wt %
of TS
4.99
—
—
3.72
3.52
3.26
3.30
4.03
3.26
Means
—
—
Means
5.08
5.36
5.22
Means
5.06
4.45
4.61
4.97
4.81
Means
3.94
4.95
5.29
5.29
Means
4.55
4.43
4.82
Means
Amroonian nitrogen
mg/L
280
569
385
247
224
299
268
131
168
223
354
219
287
589
624
509
574
237
327
302
337
321
322
369
587
755
528
623
582
585
546
571
wt X
of TKN
12.4
—
—
9.5
9.4
11.7
11.3
8.3
6.3
9.4
13.1
9.7
11.4
18.4
19.6
17.4
18.5
11.3
10.5
9.7
10.4
9.9
10.1
13.6
17.6
21.4
21.6
20.2
19.2
19.1
17.0
18.4
wt ?.
of TS
0.62
0.88
0.84
0.35
0.33
0.38
0.37
0.33
0.20
0.33
0.44
0.31
0.38
0.93
1.05
0.90
0.96
0.57
0.46
0.44
0.51
0.47
0.47
0.53
0.87
1.13
1.14
1.05
0.87
0.84
0.82
0.84
Organic
mg/L
1971
—
—
2352
2156
2245
2098
1456
2520
2138
2347
2044
2196
2617
2563
2420
2533
1867
2793
2820
2918
2933
2866
2335
2750
2779
1912
2480
2450
2482
2662
2531
wt
of
87
90
90
88
88
91
93
90
86
90
88
81
80
82
81
88
89
90
89
90
nitrogen
%
TKN
.6
—
—
.5
.6
.3
.7
.7
.8
,6
.9
.3
.6
.6
.4
.6
.5
.7
.5
.3
.6
.1
89.9
86
82
78
78
79
80
80
83
.4
.4
.6
.4
.8
.8
.9
.0
81.6
wt %
of TS
4.37
—
—
3.37
3.19
2.88
2.93
3.70
3.06
3.18
2.92
2.94
2.93
4.15
4.31
4.32
4.26
4.49
3.99
4.17
4.46
4.34
4.24
3.41
4.08
4.16
4.15
4.13
3.68
3.59
4.00
3.76
28/1
66,840
3411
5.10
535
15.7
0.80
2876
84.3
4.30
102
-------
TABLE 35. ACID-BASE CHARACTERISTICS OF DIGESTER FEED SLURRIES
Digester feed
slurry prepared
from raw sludge
lot no. pti
1
4
5
6
8
12
13
14
16
17
28
6.74
~
6.4
6.8
6.7
5.9
5.9
6.2
6.4
6.2
6.1
Ammonia
nitrogen,
mg/L
280
477
223
287
574
237
414
369
623
571
535
Alkalinity, mg/L as CaC03
Ammonium
1000
1704
796
1025
2050
846
1479
1318
2225
2039
1911
Total
bicarbonate
3971
—
4426
3783
2493
2160
3850
5513
2975
3919
—
Volatile
acids alk.
671
—
857
579
2224
1090
1783
1662
2883
1798
__
Ammonium
alk./total
bicarbonate
alkalinity, 7.
Total
4642
—
5283
4362
4717
3250
5633
7175
5858
5717
4750
25.2
~
18.0
27.1
82.2
39.2
38.4
23.9
74.8
52.0
_ _
-------
collected during the nonsteady-state operating period. Results of these
analyses for the different feed slurries are reported in detail in Table A-6.
A summary of these analyses is presented in Table 36.
The crude protein content of the Hanover Park sludge varied between a low
analysis of about 27 wt % of VS to a high value of about 37 wt % VS
(Table 36). Similarly, the total carbohydrate and lipid contents varied
between 18 and 30 wt % of VS, and 20 and 38 wt % of VS. The average protein,
carbohydrate, and lipids contents of the feed slurries used during two years
of research were 32.5, 23.7, and 27.0 wt % of VS, respectively. Thus, crude
protein was the largest organic component and carbohydrate the lowest. Taken
together protein, carbohydrate and lipids accounted for 75 to 92 wt % of the
volatile solids or total organics depending on the time of sludge collection;
on the average, about 83 wt % of the organics could be accounted for by
protein, carbohydrate, and lipids. Short-chain fatty acids and alcohols could
form a significant part of the total organics. As shown in Table 36, 2 to
11 wt % of the feed sludge VS was accounted for by short-chain fatty acids
which are not detected as carbohydrates, lipids, or protein. Thus, the ana-
lyzed organics constituted about 88 wt % of the volatile solids, and 12 wt %
of the VS was unidentified organics. By comparison, Buswell and Neave
reported that lipids, carbohydrates and protein accounted for about 91 wt % of
raw sludge volatile solids.'-*
Inspection of the data shows that the protein, carbohydrate, and lipid
contents of the sludge varied from month to month, but there was no evidence
of any definitive type of cyclical variation.
Mixed Downers Grove Primary and Stickney Activated Sludge—
The sum total of the contents of crude protein, total carbohydrate, and
lipids of the mixed Downers Grove primary and Stickney activated (UGPSA)
sludges was the same as that of the Hanover Park sludge. However, the DGPSA
sludge had a significantly higher protein content and a much lower lipid
content than those of the Hanover Park sludge; both sludges had about the same
carbohydrate content.
104
-------
TABLE 36. CRUDE PROTEIN, TOTAL CARBOHYDRATE, AND LIPIDS ANALYSES OF
DIGESTER FEED SLURRIES PREPARED FROM HANOVER PARK SLUDGE
Digester feed
prepared from
sludge lot/batch nos.
1/8
3/2
4/1
4/2
5/1
5/3
5/4
6/2
8/5
12/1
13/1
14/1
16/1
17/1
28/1**
32/1**
Dace
sludge
collected
11/B2
4/83
6/83
6/83
7/83
7/83
7/83
11/83
2/84
5/B4
5/84
6/84
7/84
8/84 .
Means
11/84
*
12/84
Crude
protein
36.8
—
—
—
30.2
26.9
30.8
27.3
35.0
36.9
35.1
30.4
35.7
32.1
32.5
38.6
—
Organic
Total
carbohydrate
19.5
—
-_
—
—
26.5
29.6
18.4
26. j
23.1
23.1
28.4
19.3
22.7
23.7
22.4
33.2
component,
Upids
23.1
24.5
31.5
32.5
—
27.4
24.3
38.0
26.0
31.7
29.4
20.5
20.0
21.9
27.0
17.2
19.8
wt % of VS*
Short-chain
fatty acids +
ethanol'
2.33
—
—
—
—
2.50
1.94
2.78
7.11
4.77
4.84
4.71
9.78
5.06
4.58
10.62
5.81
Total of proetein,
carbohydrate, lipids,
vol. acids and ethanol
81.7
—
—
—
—
83.3
86.6
84.0
94.4
96.5
92.4
84.0
84.8
81.8
87.0
88.8
—
Average of all analyses performed on various samples of a particular sludge is reported here. Refer to
Table A-6 for listing of all analyses.
Ethanol content was very small and varied between 0-6 wt X of the mass tabulated in this column.
Sludges 28/1 and 32/1 were mixtures of Downers Grove primary and Stickney activated sludges.
105
-------
SECTION 8
STABILITY OF DIGESTER FEEDS
Raw sludge feed slurries stored in a refrigerated feed reservoir were
delivered to the digesters by intermittent pumping. The feed reservoir was
refrigerated, and the sludge remained at 2° to 4°C to minimize its degradation
to acids and gases during the storage period, which varied between 2 and 7
days depending on the HRT of a particular run. The feed reservoir contents
were sampled for solids and volatile acids determinations during an 8-day
storage period — this storage period is longer than 7 days and represents the
worst-case sludge storage. The results of these analyses are reported in
Table 37. Looking at the TS and VS analyses, it is clear that these solids
concentrations remained essentially unchanged during the 8-day period
indicating no significant degradation of the organic materials. The daily
samples were analyzed for volatile acids. Concentrations of the individual
volatile acids also remained virtually constant except for isobutyric acid,
which was present only in low concentrations, during the 8-day storage of the
feed slurry. Thus, the information presented in Table 37 showed that the feed
sludge composition probably remained quite stable under the conditions of
refrigerated storage.
106
-------
TABLE 37. TIME PROFILES OF SOLIDS AND VOLATILE ACIDS ANALYSES OF DIGESTER FEED SLURRY WHICH WAS
PUMPED CONTINUALLY FROM THE REFRIGERATED (4°C) FEED RESERVOIR TO THE ANAEROBIC DIGESTER
Sample lypp Reservoir Sample Day Analysis TS,
Ethanol,
Blended batch
FRb
FR
FR
FR
FR
FR
FR
FR
FR
a „
h FR
c HPP
« The
I7.S9
17.89
16.80
14.811
12.80
8.76
5.26
3.51
2.66
Is peristaltic pump
11/28/81
11/2J/81
II/23/K1
11/25/81
11/26/81
11/27/B}
11/28/81
11/29/83
11/10/81
12/1/81
wt I Total
t, P y . le c C pro c a acetic
IT" (1 11/25/81 4.5 1.1 68.11 2O4 220 15 28 51 13 0 450
PP » 11/25/81 4.4 l.n 68.1 176 222 9 21 14 60 388
1HTC (1 11/25/81 4.4 l.n 68.1 162 208 11 24 29 50 376
HPP 2 11/2S/81 4.1 1.1 69.4 179 21(1 4 17 28 60 384
IIPP 1 11/26/81 4.1 1.1 70.9 171 206 1 16 13 60 363
HPP 4 11/27/81 4.1 1.0 69.5 191 tin 12 21 16 70 411
HIT 5 I1/.I8/81 4.0 2.8 7(1.1 194 117 6 17 29 60 390
HPP 6 ll/Vl/81 — — — 197 190 2 15 22 70 380
HPP 7 11/10/81 4. II'1 1.4 7(1.6 211 196 1 15 22 70 400
HPP 8 12/2/81 4.ad 1.3 69.1 246 217 11 17 32 7 0 459
8
0
0
0
0
0
0
0
0
0
with l/4-in. l.D. tuning to collect sludge from different areal locations and depths of the reservoir feed slurry.
U refrigerated feed reservoir the contents of which were mixed at 86 rpm with a 5-ln. diameter 1-hlade propeller impel lor.
I* a hand-operated
accuracy of these
piston pump which served the same function as that of the peristaltic pump.
solids analysis was
poor because the reservoir liquid levels were very low on these days, and It was difficult to obtain samples of well-mixed feed sludge.
Reproduced from
best available copy. ^H§?
-------
SECTION 9
THEORETICAL GAS AND METHANE YIELDS OF DIGESTER FEED SLUDGE
Theoretical gas and methane yields were calculated for selected Hanover
Park raw feed sludges to estimate the maximum stabilization efficiency
corresponding to complete conversion of the organic carbon to methane, carbon
dioxide, and microbial cell mass. As discussed below, these calculations can
be based on the elemental, COD, or calorific-value analysis of the substrate.
THEORETICAL YIELDS BASED ON ELEMENTAL ANALYSIS
Theoretical total gas and methane yields were calculated for the Hanover
Park Lot 1 and Lot 4 mixed activated-primary raw sludges used as digester
feeds. These yield calculations were based on the elemental analyses of these
sludges and on the following assumptions:
• All of the analyzed total carbon in the feed is biodegradable.
• The feed carbon is incorporated in methane, carbon dioxide, and cellular
protoplasm.
• About 30% of the VS is utilized for cell synthesis.
• Complete stoichiometric conversion of the VS is' achieved.
As shown in Table 38, the Hanover Park feed sludge had theoretical total gas
and methane yields of 0.793 and 0.506 SCM/kg VS reacted (12.7 and 8.1 SCF/lb
VS reacted), respectively. The theoretical methane content of the digester
gas was calculated to be 64 mol %.
THEORETICAL METHANE YIELDS BASED ON THEORETICAL SLUDGE COD
Theoretical methane yields can be calculated on the basis that each mole
of methane produced is tantamount to a removal of two moles of COD (CH* + 20o
•»• C02 + 2H20). This means that 0.369 SCM (5.91 SCF) of methane produced is
equivalent to the removal of 1.0 Ib (0.454 kg) of COD. Thus, 369 L of methane
production is equivalent to the removal of 1 kg of COD removed. The
theoretical COD of the substrate was calculated from the empirical chemical
formula of the sludge substrate considering complete chemical oxidation of the
measured carbon, nitrogen (TKN), and sulfur, and no oxidation of the
phosphorus. This consideration entailed the implicit assumptions that
concentrations of sulfate, sulfites, and other oxidized forms can be
neglected, and that all the measured phosphorus remains in their oxidized
forms; furthermore, it means that a part of the substrate oxygen remains tied
108
-------
TABLE 38. THEORETICAL GAS AND METHANE YIELDS OF HANOVER PARK SLUDGE BASED ON ELEMENTAL ANALYSES
Sludge
lot/batch
no. Elemental analysis, wt % of TS
Total Total Total Oxygen
carbon Hydrogen TKN sulfur phosphorus (by diff.)
1/1 41.65 6.25 4.99 1.50 1.46 20.85
(0.62)*
4/2 42.87 6.67 4.08 1.24 1.22 19.07
Theoretical
yields, SCM/kg
VS reacted
Total
VS Ash gas Methane
73.2 23.30 0.784 0.493
[12. 56]* [7.90]
73.9 24.85 0.799 0.517
[12.80] [8.28]
Mean 0.793 0.510
[12.7] [8.17]
Theoretical
methane
content,
mol Z
62.9
64.7
64.3
The number in parenthesis is ammonia-nitrogen (NH3-N); organic nitrogen is (TKN)-(NH3-N).
Numbers in brackets are the theoretical yields expressed in units of SCF/lb VS added.
-------
with the phosphorus and is not available for the oxidation of carbon,
hydrogen, nitrogen, and sulfur.
The theoretical total and carbonaceous COD's of two raw feed sludges are
reported in Table 39. The theoretical total COD is comparable to the
analytical COD. The carbonaceous COD, which is less than the total COD, forms
the basis for digester methane production calculations. Table 39 indicates
that the carbonaceous COD was 88% and 92% of the total COD. On the average,
90% of the total COD was carbonaceous COD.
Theoretical methane yields of raw sludge Lots 1 and 2 were calculated to
be 0.506 and 0.487 SCM/kg VS reacted (8.1 and 7.8 SCF/lb VS reacted)
corresponding to complete conversion of the carbonaceous substrate COD; these
yields compared favorably with those calculated on the basis of elemental
analysis. (See Table 37.)
THEORETICAL METHANE YIELDS BASED ON ANALYTICAL COD
Methane yields were also calculated from the measured or analytical COU's
of the raw feed sludge samples. These yield calculations are summarized in
Table 40.
Based on the theoretical total and the analytical total COD's of raw
sludge Lot 1 (2.22 and 1.31 kg COD/kg VS, respectively), it appears that only
about 59 wt % of the raw sludge VS was chemically oxidizable. Since
biochemical anaerobic oxidation reactions occur under near-ambient
temperatures — as opposed to the high temperature of chemical oxidation — it
may be reasonable to assume that no more than 59% of the above sludge would be
biochemically convertible. Lot 1 raw sludge thus could be about 59%
biodegradable.
THEORETICAL METHANE YIELDS BASED ON CALORIFIC VALUE
Theoretical methane yields of the sludge feed could also be calculated
from its calorific value (higher heating value) as shown in Table 41. Feed
sludge Lots 1 and 4 thus had theoretical methane yields of 0.468 and
0.500 SCM/kg VS reacted (7.49 and 8.01 SCF/lb VS reacted), respectively.
Summary
Methane yields estimated on the basis of elemental analysis, theoretical
and analytical COD's, and calorific-value analysis of the feed sludges are
summarized in Table 42. Examination of the data in Table 42 shows that
theoretical methane yields calculated on the bases of elemental, theoretical
COD, and calorific-value analyses of a given feed sludge (e.g., Lots 1 or 4)
were within few percentage points of each other. Also, the mean theoretical
110
-------
TABLE 39. THEORETICAL METHANE YIELDS OF HANOVER PARK SLUDGE
BASED ON THEORETICAL CARBONACEOUS COD
Sludge
lot no.
1
4
vs> * Theoretical COD,
of TS Empirical chemical formula kg COD/kg VS
Total Carbonaceous
73.18 c3.468H6.188°1.301N0.356s0.047p0.047Ashx 2-22 1-95
(87. 7)'
73.9 C3.57H6>6040K764N0,,27S0-089P0_039Ashx 2.04 1.88
(92.2)
Theoretical
methane yield
SCM/kg VS SCF/lb VS
converted converted
0.504 8.07
0.486 7.78
The theoretical methane yield was calculated from the carbonaceous COD and assuming that 30% of the
carbonaceous matter is incorporated in cell mass.
Numbers in parentheses are the ratios of carbonaceous to total theoretical COD expressed as a percentage.
-------
TABLE 40. THEORETICAL METHANE YIELDS OF HANOVER PARK SLUDGE
BASED ON ANALYTICAL CARBONACEOUS COD'S
Feed sludge
lot no.
Analytical COD,
kg COD/kg VS
Theoretical
methane yield,
SCM/kg VS converted
(SCF/lb VS converted)
Totalt
Carbonaceous*
1 1
5 1
6 1
8 1
.314
.487
.580
.798
1
1
1
1
.183
.338
.422
.618
0
0
0
0
.305
.345
.367
.418
(4
(5
(5
(6
.89)
.53)
.88)
.69)
The theoretical methane yields were calculated from the analytical
carbonaceous COD's assuming that 30% of the carbonaceous matter is
incorporated in cell mass.
Total COD's in this table are means for the indicated lot.
Carbonaceous COD was assumed to be 90% of the total COD.
TABLE 41. THEORETICAL METHANE YIELD OF HANOVER PARK SLUDGE
BASED ON CALORIFIC VALUE
Feed sludge
lot no.
1
4
Mean higher
heating value,
kcal/kg VS
(Btu/lb.VS)
6026 (10,846)
6441 (11,593)
Methane yield,
SCM/kg VS reacted
(SCF/lb VS reacted)
0.468 (7.49)
0.500 (8.01)
The theoretical methane yield was calculated by
assuming that 30% of VS is incorporated in the cell
mass and that the calorific value of 1 SCM of methane
is 9014 kcal (1013 Btu/SCF).
112
-------
TABLE 42. SUMMARY OF THEORETICAL METHANE YIELDS FOR HANOVER PARK SLUDGE
Digester feed slurry prepared from lot nos.
Based on elemental analysis
Carbon dioxide yield,
SCM/kg VS reacted
SCF/lb VS reacted
Methane yield,
SCM/kg VS reacted
SCF/lb VS reacted
Carbon dioxide content, mol %
Methane content, nol %
Methane yield based on theoretical COD,
SCM/kg VS reacted
SCF/lb VS reacted
Methane yield based on analyzed COD,
SCM/kg VS reacted
SCF/lb VS reacted
Methane yield based on calorific value,
SCM/kg VS reacted
SCF/lb VS reacted
Methane methane yield for the lot
SCM/kg VS reacted
SCF/lb VS reacted
14568
0.291 0.282
4.66 4.51
0.493 0.518
7.90 8.29
36.3 35.2
63.7 64.8
0.504 0.486
8.07 7.78
0.305 — 0.345 0.367 0.418
4.89 — 5.53 5.88 6.69
0.468 0.500
7.49 8.01
0.488 0.501
7.82 8.03
(3.8) (3.2)
Overall
mean
0.286
4.58
(2.3)*
0.506
8.10
(3.4)
--
—
0.494
7.92
(2.6)
0.359
5.75
(13)
0.484
7.75
(4.7)
0.494
7.92
(1.9)
Numbers in parentheses are coefficients of variation.
Methane yields calculated on the bases of elemental analysis, theoretical COD, and calorific
value were used in computing the mean.
113
-------
methane yields of Lots 1 and 4 feed sludges were within about 2.5% of each
other. An overall mean of 0.499 SCM/kg VS reacted (7.99 SCF/lb VS reacted)
was regarded as the theoretical methane yield for the Hanover Park sludge; the
theoretical total gas yield was estimated at 0.787 SCM/kg VS added
(12.6 SCF/lb).
The data in Table 42 indicate that theoretical methane yields calculated
on the bases of elemental, theoretical COD, and calorific-value analyses were
in close agreement with each other. In addition, the theoretical methane
yields for the different lots also were about the same. In contrast to these
observations, methane yields calculated on the basis of analytical COD's were
different for different sludge lots apparently because the oxidizabilities of
the lots were different. This observation suggested that the anaerobic
biodegradabilities of the various feed sludges were different although they
were collected from the same source (Hanover Park sewage treatment plant); the
variation in sludge biodegradability may be attributed to the variation in the
organic composition of the sludge volatile matter. For example, it can be
seen from Table 43 that sludge Lot 1 which had the least analytical-COD based
methane yield also had the least ZCPL, (sum total of the masses of protein,
carbohydrate, and lipids). Thus, the higher the ECPL, the higher the
analytical-COD-based methane yield as indicated by Column 2 of Table 43.
114
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TABLE 43. DEPENDENCE OF POTENTIAL METHANE YIELD OF HANOVER PARK SLUDGE ON PROTEIN,
CARBOHYDRATE, AND LIPID CONTENTS
Digester feed
slurry prepared
from lot no.
1
6
8
Analytical COD-based
methane yield,
SCM/kg VS reacted
(SCF/lb VS reacted)
0.305 (4.89)
0.367 (5.88)
0.418 (6.69)
Theoretical
methane yield,
SCM/kg VS reacted
(SCF/lb VS reacted)
0.494 (7.92)
0.494 (7.92)
0.494 (7.92)
Sum total of protein,
carbohydrate and lipids,
Oxidizability,* % of sludge VS
61.7 81.7
74.2 84.0
84.5 94.4
Oxidizability was the ratio of the analytical COD-based methane yield to the theoretical methane yield.
-------
SECTION 10
BIODEGRADABILITY OF DIGESTER FEED SLUDGE
Anaerobic digestibility potential (ADP) tests were conducted with
mesophilic inocula in triplicate with samples of mixed primary-activated feed
sludge collected from the Hanover Park wastewater treatment plant of the
MSDGC. Details of the test conditions and protocol are described in
Section 6. Results of the ADP tests plotted in Figure 14 and shown in
Table 44 indicate that after an initial lag, gasification of the Hanover Park
Sludge proceeded at a rapid rate for about 17 days after which time there was
a dramatic decline in the rate of digestion. This observation seems to
indicate that the Hanover Park sludge had one or more highly biodegradable
components which were preferentially gasified rapidly during an initial 17-day
period. Methane content of the head gases at the end of this vigorous
digestion phase was about 73 mol % compared with a methane concentration of
74 mol % at the end of the ADP test. The data in Figure 14 indicate that
maximum total gas and methane yields of 0.454 and 0.312 SCM/kg VS added
(7.3 and 5.0 SCF/lb VS added) can be expected from digestion of this sludge
under mesophilic conditions. A volatile solids reduction of about 48% (which
is the higher of the two calculated reductions) was obtained during the ADP
digestion test (Table 45). Satisfactory TS, VS, and FS balances were obtained
for this ADP test as indicated in Table 45.
As indicated in a previous section, the Hanover Park sludges had a
theoretical total gas yield of about 0.787 SCM/kg VS reacted (12.6 SCF/lb VS
reacted) representing conversion of all the volatile solids. Comparing this
with the long-term ADP total gas yield of about 0.456 SCM/kg VS added
(7.3 SCF/lb VS added), it appears that about 58% of the sludge VS was
anaerobically biodegradable under mesophilic conditions. This biodegrad-
ability factor compares favorably with those reported in the literature. It
was concluded in a previous section that about 59% of the sludge carbonaceous
matter was chemically oxidizable. This oxidizability factor compared very
well with the anaerobic biodegradability of 58%.
As indicated by the ADP test data, a methane yield of about 0.252 SCM/kg
VS added (4.1 SCF/lb VS added) was obtained from digestion of the rapidly
biodegradable fraction after 35 days of incubation (Figure 14). Comparing
this methane yield with the maximum methane yield of 0.312 SCM/kg VS added
(5.0 SCF/lb VS added) at the end of the test, it may be reasoned that about
80% of the sludge VS was more rapidly biodegradable than a recalcitrant
fraction constituting 20% of the VS.
116
-------
0
-------
TABLE 44. GAS AND METHANE PRODUCTIONS FROM MESOPHILIC ANAEROBIC
DIGESTIBILITY POTENTIAL TEST CONDUCTED WITH
LOT 16 BATCH 1 HANOVER PARK. SLUDGE*
Incubation
period, days
5.6
17.8
25.8
29.7
34.7
50.0
125.0
150.9
187.9
Total gas yield,
SCM/kg VS added
(SCF/lb VS added)
0.022 (0.36)
0.052 (0.83)
0.177 (2.83)
0.266 (4.26)
0.360 (5.77)
0.397 (6.36)
0.435 (6.97)
0.444 (7.12)
0.454 (7.27)
Methane content,
mol %
7.9
39.2
68.1
64.4
70.4
69.8
69.0
69.1
68.8
Methane yield,
SCM/kg VS added
(SCF/lb VS added)
0.002 (0.03)
0.021 (0.33)
0.120 (1.93)
0.171 (2.74)
0.254 (4.07)
0.277 (4.44)
0.300 (4.81)
0.307 (4.92)
0.312 (5.00)
Data in this table are the averages of triplicate determinations and are
corrected for gas and methane production from the inoculum.
118
-------
TABLE 45. VOLATILE SOLIDS REDUCTION AND MASS BALANCES FOR THE MESOPHILIC
ADP TEST CONDUCTED WITH HANOVER PARK MIXED ACTIVATED-PRIMARY SLUDGE
Total solids (TS) , g
Initial
Final
Volatile solids (VS)
Initial, g
% of initial TS
Final g
% of final TS
VSR by MOP-16,* %
Mass of digester gas, g
co2
Methane
Total
VSR by mass of gas, %
Mass balance, % of initial
TS
VS
Replicate
1
0.4451
0.2968
0.3186
71.57
0.1756
59.16
42.5
0.0802
0.0641
0.1443
45.3
99.1
100.4
Test digesters
Replicate
2
0.4451
0.2942
0.3186
71.57
0.1726
58.67
43.6
0.0882
0.0694
0.1576
49.5
101.5
103.6
Replicate
3
0.4451
0.2780
0.3186
71.57
0.1591
57.23
46.8
0.0848
0.0682
0.1530
48.0
96.8
98.0
Mean
0.4451
0.2897
0.3186
71.57
0.1691
58.36
44.3
0.0844
0.0672
0.1516
47.6
99.2
100.7
t
**
Volatile solids reduction, VSR, was calculated by the formula suggested in
WPCF Manual of Practice (MOP) 16.
VSR was assumed to be at least equal to the mass of the dry gas produced.
Mass balance was expressed as the percent ratio of the sum of the masses of
material out and product gases to the initial mass of the material.
119
-------
SECTION 11
PERFORMANCE OF SINGLE-STAGE CFCSTR DIGESTERS
EXPERIMENTAL RUNS
A total of six single-stage high-rate digestion runs were conducted as
per the experimental plan to provide baseline data for comparison with two-
phase process performance under similar operating conditions. Three meso-
philic runs were conducted at mean temperatures between 34.7° and 35.9°C at
HRT's of about 15, 7, and 3 days (Table 46). The 7-day- and the 3-day-HRT
runs had a higher feed VS concentration than that of the 15-day URT run
because it was felt that substrate concentration should be increased to
support higher organism growth rates at the lower HRT's. A second set of
three runs was conducted at mean thermophilic temperatures between 54.7° and
56°C and at feed VS concentrations the same as the set of mesophilic runs.
SINGLE-STAGE CFCSTR PROCESS PERFORMANCE
The performance of the mesophilic runs at the three HRT's are compared in
Tables 47, 48 and 49. The gas production, effluent quality and digestion-
efficiency data in these tables show that the 7-day HRT run was best in terms
of organic reduction; this run, although fed with a more concentrated sludge,
exhibited a methane yield, gas-phase methane content, alkalinity, and effluent
filtrate COD that were comparable with those of the 15-day HRT run.
The mesophilic run conducted at a three-day HRT had lower gas and methane
productions and organic reductions, and showed much higher levels of propionic
and total VA accumulations indicating unbalanced acidogenic and methanogenic
fermentations. Compared to the 7-day HRT test, the 3-day HRT was very
unstable and was clearly unsuitable for mesophilic single-stage CFCSTR
digestion of sewage sludge.
A comparison of the gas production, effluent-quality, and digestion-
efficiency data reported in Tables 50, 51, and 52 for thermophilic single-
stage CFCSTR runs showed that the best thermophilic performance was obtained
at an HRT of 15 days. Under thermophilic conditions, gas and methane
production, and organic reductions decreased and propionate and total VA
concentrations increased as the HRT was decreased from 15 to 7 to 3 days.
Inhibitory levels of volatile acids were observed for the 3-day HRT test.
The steady-state performances of the mesophilic and thermophilic runs are
compared in Table 53, which shows that higher methane yields and production
rates were obtained at the thermophilic temperature in all cases.
Interestingly, volatile acids and ammonia-nitrogen concentrations of the
thermophilic effluents were in all cases higher than those of the mesophilic
120
-------
TABLE 46. ACTUAL OPERATING CONDITIONS FOR SINGLE-STAGE
CFCSTR DIGESTERS FED WITH HANOVER PARK SLUDGE
Run no.
Mesophilic
SS15M
SS7M
SS3M
Thermophilic
SS15T
SS7T
SS3T
Digester
no.
331
331
331
337
331
335
Run
duration,
days
77
90
65
43
44
25
Steady-state
duration,
days
57
54
19
25
26
17
Mean culture
temp. , °C
34.7 (2)*
34.9 (2)
35.9 (2)
56.0 (1)
55.8 (1)
54.7 (1)
Mean HRT,
days
15.0 (6)
7.0 (15)
3.1 (8)
15.0 (3)
7.0 (4)
3.2 (11)
Mean
loading rate,
kg VS/m3-day
2.00 (14)
7.51 (6)
15.38 (8)
2.11 (3)
7.10 (4)
15.63 (12)
Feed
total solids
cone. , g/L
40.2
76.1
63.8
41.5
68.2
66.7
Feed
volatile solids
cone., g/L
30.1
52.2
48.3
31.8
49.9
49.2
Data reported are the means of all data collected during the steady-state period. All runs were made with Hanover Park sludge
but batches were different. See Appendix Table F—1 for specific batch nuraers.
Numbers in parentheses are the coefficients of variation, expressed as the percent ratio of the standard deviation to the mean.
-------
TABLE 47. EFFECT OF HRT ON STEADY-STATE GAS PRODUCTIONS FROM MESOPHILIC
CFCSTR SINGLE-STAGE DIGESTERS OPERATED WITH HANOVER PARK SLUDGE*
HRT, days
Run No.
Operation
Feed VS concentration, mg/L
Loading, kg VS/m3-day
Performance
Total gas yield, SCM/kg VS added
Methane Yield, SCM/kg VS added
Gas Composition, mol %
Methane
Carbon dioxide
Nitrogen
Total gas production rate,
SCM/m3-day
Methane Production Rate,
SCM/m3-day
15.0
SS15M
30,060
2.00
0.320
(13)**
0.225
(13)
70.3
29.2
0.5
0.625
(11) '
0.440
(11)
7.0
SS7M
52,220
7.51
0.318
(13)
0.220
(16)
69.1
30.6
0.3
2.327
(12)
1.609
(13)
3.1
SS3M
48,290
15.38
0.160
(13)
0.089
(15)
55.6
43.9
0.5
2.457
(ID
1.365
(13)
JU
Data reported are means of all data collected during the steady-
state portion of the run.
Feed VS concentrations are the weighted averages of the various
feed slurry concentrations.
Numbers in parentheses are the coefficients of variation expressed
as the percent ratio of the standard deviation to the mean.
122
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TABLE 48. EFFECT OF HRT ON THE QUALITY OF STEADY-STATE
EFFLUENTS FROM MESOPHILIC CFCSTR SINGLE-STAGE DIGESTERS
OPERATED WITH HANOVER PARK SLUDGE*
HRT, days
Run no.
Effluent pH
Alkalinities, mg/L as CaCO,
Total
Bicarbonate
Volatile acids, mg/L
Acetic
Propionic
Isobutyric
Butyric
Isovaleric
Valeric
Caproic
Total as acetic
Ethanol, mg/L
Nitrogen, mg/L
Ammonia-N
Organi c-N
Chemical oxygen demand, mg/L
Total
Filtrate
Solids, mg/L
TS
VS
TSS '
VSS
Organic components, ttg/L
Crude protein
Carbohydrates
Lipids
15.0
SS15M
7.11
(IV
6072
6071
1
0
0
0
0
0
0
1
(203)
3
779
1429
29,690
2024
35,025
22,450
32,710
23,040
8976
4750
5797
7.0
SS7M
7.06
(0)
6368
6196
164
104
0
0
0
0
0
248
(29)
3
728
1966
67,450
2956
64,350
39,585
56,840
39,460
10,427
7014
11,389
3.1
SS3M
6.77
(0)
6475
4620
343
1571
191
39
329
86
0
2017
(20)
0
1122
2023
74,791
6331
55,240
40,480
—
•"••
12,644
6752
10,397
Data reported are means of one or more determinations made
during the steady-state portion of the run.
Numbers in parentheses are the coefficients of variation
expressed as the percent ratio of the standard deviation to
the mean.
123
-------
TABLE 49. EFFECT OF HRT ON STEADY-STATE ORGANIC REDUCTION
EFFICIENCIES OF MESOPHILIC CFCSTR SINGLE-STAGE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE3
HRT, days 15.0 7.0 3.1
Run No. SS15M SS7M SS3M
VS reduction, %
MOP16b
Wt-of-gas basisc
VSS reduction, %
COD (total) reduction, %
Reduction of organic components, %
Crude protein
Carbohydrates
Lipids
ICPLd
38.2
28.8
26.5
31.6
27.1
27.3
25.1
26.6
18.3
32.7
17.2
16.3
26.2
26.4
40.0
32.4
13.7
19.3
—
13.0
23.7
44.4
16.5
27.6
a Data reported are means of all data collected during the
steady-state portion of the run. The VSS, COD, and organic
component reductions are means of one or more determinations
made during the steady-state period.
These VS reductions were calculated according to the following
formula: VS£ = 100 X (VS± - VSo)/[VSi - (VS± X VSQ)].
c These VS reductions were calculated according to the following
formula: VSR m 100 X (wt of product gases)/(wt of VS fed).
^ ICPL means the sum of the masses of carbohydrates, crude
protein, and lipids.
124
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TABLE 50. EFFECT OF HRT ON STEADY-STATE GAS PRODUCTIONS
FROM THERMOPHILIC CFCSTR SINGLE-STAGE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGEa
HRT, days
Run No.
HRT, days
Operation
Feed VS concentration, mg/L
Loading, kg VS/m3-day
Performance
Total gas yield,
SCM/kg VS added
Methane Yield,
SCM/kg VS added
Gas composition, mol %
Methane
Carbon dioxide
Nitrogen
Total gas production rate,
SCM/m3-day
Methane production rate,
SCM/m3-day
15.0
SS15T
15.0
31,760
2.11
0.425
(5)c
0.280
(4)
66.1
33.7
0.2
0.894
(4)
0.591
(4)
7.0
SS7T
7.0
49,890
7.10
0.373
(5)
0.253
(5)
68.0
31.9
0.1
2.641
(3)
1.797
(4)
3.2
SS3T
3.2
49,250
15.63
0.180
(9)
0.114
(9)
63.3
36.4
0.3
2.798
(4)
1.770
(5)
a Data reported are means of one or more determinations made during
the steady-state portion of the run.
Feed VS concentrations are the weighted averages of the various
feed slurry concentrations.
c Numbers in parentheses are the coefficients of variation expressed
as the percent ratio of the standard deviation to the mean.
125
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TABLE 51. EFFECT OF HRT ON THE QUALITY OF
STEADY-STATE EFFLUENTS FROM THERMOPHILIC
CFCSTR SINGLE-STAGE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE*
HRT, days
Run no.
Effluent pH
Alkalinities, mg/L as CaCO-i
Total
Bicarbonate
Volatile acids, mg/L
Acetic
Propionic
Isobutyric
Butyric
Isovaleric
Valeric
Caproic
Total as acetic
Ethanol, mg/L
Nitrogen, mg/L
Ammonia-N
Organ! c-N
Solids, mg/L
TS
VS
Organic components, mg/L
Crude protein
Carbohydrates
Lipids
15.0
SS15T
7.47
(I)1
6500
5854
154
844
69
3
239
8
9
1037
(24)
0
1132
868
27,780
18,560
5425
5444
3185
7.0
SS7T
7.50)
(1)
10,450
8683
- 211
1708
163
0
624
0
60
2105
(13)
0
-
1646
1460
52,320
34,310
9125
8625
5134
3.2
SS3T
7.27
(1)
9026
6440
1045
1379
375
321
811
32
138
3205
(6)
0
1550
2212
62,340
42,705
13,825
8428
7195
Data reported are means of one or more determinations made
during the steady-state portion of the run.
Numbers in parentheses are the coefficients of variation
expressed as the percent ratio of the standard deviation to
the mean.
126
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TABLE 52. EFFECT OF HRT ON STEADY-STATE ORGANIC REDUCTION EFFICIENCIES OF
THERMOPHILIC CFCSTR SINGLE-STAGE DIGESTERS OPERATED WITH HANOVER PARK SLUDGEa
HRT, days 15.0 7.0 3.2
Run no. SS15T SS7T SS3T
VS reduction, %
MOP16
Wt-or-gas basis0
Reduction of organic components, %
Crude protein
Carbohydrate
Lipids
I!CPLd
36.8
45.9
53.5
25.3
68.2
51.5
32.9
39.6
47.8
10.8
47.8
38.1
19.0
20.2
20.4
10.4
22.9
18.4
a Data reported are means of all data collected during the
steady-state portion of the run. The organic component
reductions are means of one or more determinations made
during the steady-state period.
" These VS reductions were calculated according to the following
formula: VSR = 100 X (VS± - VSo)/[VSi - (VS± X VSO)].
c These VS reductions were calculated according to the following
formula: VSR = 100 X (wt of product gases)/(wt of feed VS).
" ZCPL means the sum of the masses of carbohydrates, crude protein,
and lipids.
127
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TABLE 53. COMPARISON OF STEADY-STATE PERFORMANCES OF
MESOPHILIC AND THERMOPHILIC CFCSTR SINGLE-STAGE
DIGESTERS OPERATED WITH HANOVER PARK SLUDGE
HRT, days
15
Run no.
Culture temperature
SS-15M
Meso
SS15-T
Thermo
SS7M
Meso
SS7T
Thermo
SS3M
Meso
SS3T
Thermo
Methane yield,
SCM/k.g VS added
Methane Production Rate,
0.225
0.280
0.220 0.253 0.089 0.114
SCM/n-^-day
Methane content, mol %
Effluent volatile acids,
mg/L as acetic
Effluent pH
VS reduction, %
MOP a
16 t.
wt-of-gas basis
Carbon-in-gas basis0
Based on theoretical
gas yieldd
Biodegradable VS
reduction6
Organic reductions, %
Crude protein
Carbohydrates
Lipids
ICPLf
0.440
70.3
1
7.11
38.2
28.8
29.1
29.7
51.2
27.1
27,3
25.1
26.6
0.591
66.1
1037
7.47
36.8
45.9
39.4
39.4
68.0
53.5
25.3
68.2
51.5
1.609
69.1
248
7.06
18.3
32.7
28.8
29.5
50.9
26.2
26.4
40.0
32.4
1.797
68.0
2105
7.50
32.9
39.6
34.7
24.6
59.7
47.8
10.8
47.8
38.1
1.365
55.6
2017
6.77
13.7
19.3
14.9
14.8
25.6
23.7
44.4
16.5
27.6
1.770
63.3
3205
7.27
19.0
20.2
16.7
16.7
28.8
20.4
10.4
22.9
18.4
These VS reductions were calculated according to the following formula:
VSR - 100 X
- VS)/[VS -
X VS0)].
These VS reductions were calculated according to the following formula:
VSR " 100 X (wt of product gases)/(wt of VS fed).
c These VS reductions were calculated according to the following formula:
VSR » 100 X (1.84 X wt of carbon in product gas)/(wt of VS fed).
<* These VS reductions are calculated by expressing the observed total gas
yield as a percentage of the theoretical gas yield of 1.078 SCM/kg VS added.
e The biodegradable VS reduction was calculated by dividing the theoretical
gas yield based VS reduction by a biodegradability fraction of 0.58.
ECPL means the sum of the masses of carbohydrates, crude protein, and
lipids.
128
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effluents suggesting a higher degree of solids liquefaction at the higher
temperature. Despite the prevalence of higher volatile acids concentrations
in the thermophilic digesters, the culture pH remained significantly above 7
apparently because the thermophilic process generated higher buffering
capacity as evidenced by the higher concentration of ammonium bicarbonate.
Overall, thermophilic digestion exhibited higher gas yields and produc-
tion rates and stabilization efficiencies than those of mesophilic digestion.
However, it is questionable whether this increased performance is sufficient
to justify process operation at a higher temperature. To justify thermophilic
operation it may be necessary to operate the digester at much higher feed
solid concentrations and to develop means of reducing the effluent VA.
Carbohydrate reduction was highest at the lowest HRT during mesophilic
digestion; the reverse was true for thermophilic digestion. In general,
carbohydrate reduction at the thermophilic temperature was about the same or
lower than that at the mesophilic temperature. Crude protein reductions at
the thermophilic and mesophilic temperatures were comparable at the lowest
HRT; higher crude protein reductions were obtained at the thermophilic
temperature at an HRT's of 15 and 7 days. At the mesophilic temperature, the
highest lipid conversion was obtained at an HRT of 7 days. Lipid reductions
at the thermophilic temperature were higher than those at the mesophilic
temperature at all HRT's.
COMPARISON OF CPL CONVERSIONS UNDER MESOPHILIC CONDITIONS
The percent conversions of carbohydrates, proteins, and lipids (CPL) were
about the same as each other at a 15-day HRT. By comparison, O'Rourke ^
observed lower "effective" destruction of influent "degradable" protein than
of influent "degradable" lipid.
Protein conversion was the same as the carbohydrate conversion at the
7-day HRT. Also, the conversion of the organic components at the 15-day and
the 7-day HRT's were about the same. Lipid conversion at the 7-day HRT was
higher than those of protein and carbohydrate. Lipids degradation was lowest
at the low HRT; a similar observation was made by O'Rourke. ^ Surprisingly,
carbohydrate degradation was maximum at the lowest HRT of 3 days.
COMPARISON OF CPL CONVERSION UNDER THERMOPHILIC CONDITIONS
Under thermophilic conditions protein degradation was maximized at the
7-day HRT. At the other two HRT's protein reductions were about the same as
those under mesophilic conditions. Lipid reduction was maximum at the 15-day
HRT and decreased with decreases in the HRT as opposed to being maximized at
the 7-day HRT.
Overall, the combined conversions of carbohydrate protein and lipid at
the thermophilic temperature were higher than those at the mesophilic
temperature at the 15-day and the 7-day HRT; the reverse was true at the 3-day
HRT. Since the thermophilic methane yields were higher than mesophilic
yields, it is apparent that the overall rate and yield of digestion (i.e.,
hydrolysis, acidification, and gasification) is higher at thermophilic
129
-------
temperature than at mesophilic temperature. However, the thermophilic
cultures were unable to convert all of the incoming volatile acids to gas
considering the significantly higher effluent volatile acids concentrations
observed at the thermophilic temperature.
MASS BALANCES
Volatile solids mass balances (defined as the ratio of sum of the masses
of effluent VS and gases to influent VS) performed with the steady-state data
showed that the effluent VS's were between 100% and 110% of influent VS.
Fixed solid balances (defined as the ratio of effluent FS to influent FS)
showed that effluent FS's were between 93% and 109% of the influent FS.
Details of the mass balances are shown in Figures B-l to B-6.
130
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SECTION 12
PERFORMANCE OF CFCSTR TWO-PRASE DIGESTION SYSTEMS
EXPERIMENTAL RUNS
Three sets of two-phase digestion runs (designated as meso-meso, meso-
thermo, and thermo-thermo in Table 54) were conducted with CFCSTR acid- and
methane-phase digesters at HRT's of about 15, 7, and 3 days. A meso-meso
digestion run was conducted with a mesophilic acid digester operated in series
with a mesophilic methane digester. Similarly, a meso-thermo system consisted
of a mesophilic acid-phase digester followed by a therraophilic methane diges-
ter and so on. The acid-phase digesters had an HRT of about 2 days except
when the system HRT was 3 days. For two-phase system HRT's of 3 days, the
acid-phase digester had an HRT of about 0.9 days. As with the single-stage
CFCSTR digestion runs (Section 11), higher feed VS concentrations were used
for the 7-day and the 3-day HRT runs.
The run durations and the steady-state durations for all experiments
were, in general, longer than three HRT's. The variabilities of the operating
parameters were generally lower than 15% for the digester runs listed in
Table 54.
PERFORMANCE OF MESO-MESO SYSTEMS
Acid-Phase Performance
The performance of the meso-meso two-phase systems at 15-, 7- and 3-day
HRT's are compared in Tables 55, 56, and 57 in terms of gas production and
quality, effluent quality, and organic-reduction efficiency. The acid
digester generally exhibited the highest gas and methane yields when it was
operated at a 2-day HRT and was charged with the higher VS concentration (47
and 50 g/L) feeds; gas and methane yields were lower at the lower HRT (0.8-0.9
days) or with the lower feed VS concentration. Residual volatile acids con-
centration in the acid digester e~ffluent was much higher at the 0.9-day HRT
than at an HRT of 2 days indicating that acidogenesis was favored over gasifi-
cation at lower HRT's. Gas and methane production rates from the acid-phase
digesters increased in direct proportion to the increase in loading rates.
Methane production was observed in all acid-phase runs, although the methane
content of the head gases decreased as the HRT decreased or the feed VS
concentration increased. It appears that methane production from the acid-
phase digester was predominantly by the hydrogen-oxidizing methane bacteria
which, by virtue of their higher growth rate, could survive at the low HRT's.
Methane formation by the aceticlastic reaction is not expected to be
significant at HRT's of 2 days or lower.
131
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TABLE 54. ACTUAL STEADY-STATE OPERATING CONDITIONS FOR PROCESS COMPARISON CFCSTR
TWO-PHASE DIGESTION SYSTEMS OPERATED WITH HANOVER PARK SLUDGE*
Total run
Digester duration,
Run no* nos. days
Meso-Meso
TP15M-M 332-333 70
TP7M-M 334-333 52
TP3M-M** 334-333 26
Lo
fvj ' Meso-Thermo
TP15M-T 334-337 70
TP7M-T 334-331 52
TJtermo-Therrao
TP7T-T 335-331 50
TP3T-T 335-331 19
Steady-state Mean acid
run digester
duration, days temp., °C
45 34.9
(3)t
23 35.3
0>t
13 35.7
U1
38 35.1
24 35.4
(2)
27 54.4
(1)
9 55.3
(1)
Mean methane
digester
temp. , °C
34. B
(2)
35.7
(1)
35.0
(1)
55.7
(1)
55.4
(2)
54.8
(1)
52.9
(3)
Mean methane
acid-digester
IIRT, days
2.0
(14)
1.9
(12)
0.91
(«)
2.1
(10)
1.9
(17)
2.1
(IH)
0.81
(13)
Mean
methane-digester
IIRT, days
13.2
(15)
4.9
(12)
2.15
(10)
11.0
(1)
(17)
6.0
(IB)
2.11
(13)
Mean
system
HUT, days
15.2
(15)
6.8
(12)
1.06
(9)
15.1
(3)
7.4
(18)
B.I
(18)
3.14
(ID
Mean
system loading, Feed total solids Feed volatile solids
' 8
1.94 41.8 29.5
(14)
7.29 67.7 49.7
(13)
14.7 66.4 A4.9
(9)
2.14 45.8 32.3
(5)
6.74 66.4 50.0
(17)
6.80 69.9 51.3
(19)
15.0 68.0 47.2
(14)
* Data reported are Che means of all data collected during the steady-state period. Specific hatch numbers for all runs are given in Appendix Table F-l.
* Numbers in parentheses are the coefficients of variation, expressed as the percent ratio of the standard deviation to the mean.
**This run was conducted with mixed Downers Grove primary and Sttckney activated sludges.
-------
TABLE 55. EFFECT OF HRT ON STEADY-STATE GAS PRODUCTIONS FROM MESO-MESO CFCSTR
TWO-PHASE DIGESTION OF HANOVER PARK SLUDGE3
Operation
Feed VS concentration, c mg/L
HRT, days
Loading, kg VS/nr-day
Performance
Total gas yield,
SCM/kg VS added
Methane yield,'
SCM/kg VS added
Gas composition, mol %
Hydrogen
Methane
Carbon dioxide
Nitrogen
Total gas production rate,
SCM/m3-day
Methane production rate,
SCM/m3-day
Two-phase
Arid
digester
29,500
2.0
14.78
0.093
(18)d
0.058
(19)
62.6
36.1
1.3
1.345
(12)
0.841
(12)
at 15.2-day
Methane
digester
13.2
2.23
0.499
0.352
(16)
70.6
28.9
0.5
1.090
(9) '
0.770
(9)
HRT
System
15.2
1.94
0.592
(16)
0.410
(16)
69.3
30.1
0.6
1.124
0.779
(8)
Two-phase
Acid
digester
49,680
1.9
26.38
0.157
(16)
0.091
(16)
0.0
57.1
42.5
0.4
4.063
(5)
2.343
(5)
at 6.8-day
Methane
digester
4.9
10.08
0.310
(11)
0.212
(12)
68.2
31.6
0.2
3.089
(5)
2 . 1 00
(5)
HRT
System
6.8
7.29
0.467
(12)
0.302
(13)
64.7
35. 1
0.2
3.358
(4)
2.173
(4)
Two-phase
Acid
digester
46,600
0.9!
51.21
0.108
(7)
0.057
(10)
0.05
52,0
47.3
0.7
5.575
(6)
2.898
(9)
at 3.1-day
Methane
digester
2.15
21.68
0.197
(9)
0.124
(9)
0.0
63.1
36.5
0.4
4.293
(13)
2.708
(14)
HRTb
System
3.06
15.23
0.305
(6)
0.180
(8)
0.0
59.1
40.4
0.5
4.674
(12)
2.764
(12)
a The data reported are means of all data collected during the steady-state portion of the run.
This run was conducted with mixed Downers Grove primary and Sticknc-y activated sludge.
c Feed VS concentrations are the weighted averages of the various fc'od slurry concentrations.
Numbers in parentheses are the coefficients of variation expressed as the percent ratio of the standard deviation to the mean.
-------
TABLE 56. EFFECT OF HRT ON THE QUALITY OF STEADY-STATE EFFLUENTS FROM
MESO-MESO CFCSTR TWO-PHASE SYSTEMS OPERATED WITH HANOVER PARK SLUDGE3
Two-phase at
15.2-day HRT
Run no •
HRT, days
Effluent pH
Alkalinities, mg/L as CaC03
Total
Bicarbonate
Volatile acids, mg/L
Acetic
Propionic
Isobutyric
Butyric
Isovaleric
Valeric
Caproic
Total as acetic
Ethanol, mg/L
Nitrogen, mg/L
Ammonia-N
Organi c-N
Chemical oxygen demand, mg/L
Total
Filtrate
Solids, mg/L
TS
VS
TSS
VSS
Organic components, mg/L
Crude protein
Carbohydrates
Lipids
Acid
digester
Methane
digesterc
2.0 13.2
6.63
(l)d
3290
2926
295
328
40
24
84
15
0
663
(33)
3
621
970
35,760
2270
37,050
25,520
30,900
' 23,960
6094
5375
3458
7.10
(1)
4950
4944
20
8
0
0
0
0
0
26
(112)
4
646
795
26,080
958
30,355
18,535
28,120
19,890
4183
4404
1705
Two-phase at
6.8-day HRT
Acid
digester
Methane
digester0
1.9 4.9
6.63
(1)
7475
6368
721
728
109
160
136
61
31
1627
(15)
0
918
2241
__
--
60,720
42,480
— -
—
14,006
7791
7178
7.30
(1)
8100
8068
63
29
0
0
0
10
33
109
(44)
0
1049
1845
—
50,690
32,810
—
—
11,531
4932
3824
Two-phase at ,
3.1 -day HRTb
Acid
digester
Methane
digester0
0.91 2.15
6.48
(1)
6550
2059
2177
1403
288
749
596
1907
51
5518
(16)
19
1138
1927
—
61,600
39,320
__
—
12,044
9224
6448
7.19
(1)
8350
6735
218
1503
50
0
195
136
31
1680
(15)
0
1820
1682
—
57,450
35,040
__
—
10,512
5413
5879
a Data reported are means of one or more determinations made during the steady- state period.
This run was conducted with mixed Downers Grove primary and Stickney activated sludges.
c System effluent characteristics are the same as those of the methane-phase.
Numbers in parentheses are the coefficients of variation expressed as the percent ratio of the standard
deviation to the mean.
134
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TABLE 57. EFFECT OF HRT ON STEADY-STATE ORGANIC REDUCTION EFFICIENCIES OF MESO-MESO CFCSTR
TWO-PHASE SYSTEMS OPERATED WITH HANOVER PARK SLUDGE3
Ln
Run no.
HRT, days
VS reduction, 2
MOP16C d
Wt-of-gas basis
VSS reduction, I
COD (total) reduction, Z
Reduction of organic components, %
Crude protein
Carbohydrate
Lipids
ECPLe
Two-phase
Acid
digester
2.0
11.4
10.7
11.6
9.6
31.4
35.3
49.2
37.8
at 15.2-day
Methane
digester
13.2
29.2
58.0
17.0
27.1
31.4
18.1
50.7
31.0
•
HRT
System
15.2
37.2
63.4
26.6
34.1
52.9
47.0
75.0
57.1
Two-phase
Acid
digester
1.9
15.7
18.1
9.6
29.1
28.2
20.6
at 6.8-day HRT
Methane
digester System
4.9 6.8
21.2 33.6
33.4 51.5
17.7 25.6
36.6 55.1
46.7 61.8
30.0 44.4
Two-phase
Acid
digester
0.91
17.1
13.5
33.0
15.8
19.7
25.0
at 3.1-day
Methane
digester
TP1M— M
2.15
11.4
26.1
12.7
41.3
8.8
21.3
HRT
System
3.06
26.5
35.5
41.5
50.6
26.8
41.0
a The data reported are means of one or more determinations made during the steady-state period.
b This run was operated with mixed Downers Grove primary and Stickney activated sludges.
c These VS reduction were calculated according to the following formula: VSR - 100 X (VS± - VS0)/[VSt X VSQ)].
d These VS reduction were calculated according to the following formula: VSR - 100 X (wt of product gases)/(wt of VS fed).
e JCPL means the sum of the masses of carbohydrates, crude protein, and Hptds.
-------
The acid-digester gases did not contain any hydrogen except during oper-
ation at an HRT of 0.9 days, indicating that the rate of hydrogen utilization
by the syntrophic methane formers exceeded the rate of hydrogen production by
oxidation of the particulate sludge substrates. In all cases, the acid-phase
head gases contained more nitrogen than the methane digester gases, indicating
that reduction of nitrogen oxides to nitrogen gas (denitrification) was
favored in the acid digester. This is expected because substrate oxidation in
the acid-phase digester is expected to be coupled with hydrogen removal by
denitrifiers.
The pH's of the acid-phase digesters stabilized at about 6.5-6.6. The
bicarbonate alkalinity was maximum (about 6400 mg/L as CaCQ3) at a 2-day HRT
and with 50 g/L VS content feed, and it decreased as the flow-through rate
increased or the feed VS concentration decreased.
Carbohydrate and lipid reductions were higher at the higher HRT of 2
days, whereas crude protein reduction appeared to be lower at the 2-day HRT.
Methane-Phase Performance
Total gas and methane yields from the methane digesters decreased as the
methane-phase HRT was decreased from 13 to 5 to 2 days; conversely, the gas
and methane production rates increased with decreases in HRT and increases in
the loading rate.
It is noteworthy that methane production from the methane digester
amounted to 86% of the system methane production when the ratio of methane-
digester HRT to system-HRT was 0.87; similarly, 70% and 69% of system methane
production emanated from the methane digester when the ratios of methane-
digester HRT to two-phase system HRT were 0.72 and 0.69, respectively. Thus,
about 70% or more of the system methane production emanated from the methane
phase of the meso—meso two—phase process.
The methane content of the methane-digester gases were significantly
higher than those of the acid digesters. The pH and alkalinity of the methane
digesters were considerably higher than those of the acid digesters. The
methane digesters received a low bicarbonate alkalinity-content acidic feed.
The bicarbonate alkalinity increased substantially during methane fermenta-
tion, which had the effect of scrubbing C02 and was responsible, in part, for
enhancing the methane content of the methane digester gas.
It is interesting to note that ZCPL (sum of the masses of carbohydrate,
protein and lipid) reductions in the methane digesters were lower than those
in the acid digester indicating that liquefaction was more predominant in the
acid digester. The ECPL reductions at the 7-day and the 3-day HRT's were
about the same during two-phase operation.
Performance of the Overall System
Total gas and methane yield from the meso-meso two-phase system decreased
as the loading rate was increased from 1.9 to 15.2 kg VS/m^-day and the
corresponding reduction in HRT from 15 to 3 days. Gas and methane production
136
-------
rates at 7- and 3-day HRT's increased substantially by 390% and 270%,
respectively, compared to that observed at a 15-day HRT. The overall protein,
carbohydrate, and lipid reduction (ECPL) decreased progressively as the two-
phase system HRT was decreased. However, the decrease in ECPL reduction was
not significant when the HRT was decreased from 7 days to 3 days.
PERFORMANCE OF MESO-THERMO SYSTEMS
Acid-Phase Performance
Two meso-therrao two-phase runs were conducted at system HRT's of about 15
and 7 days (Tables 58 and 59). Gas and methane yields and the gas-phase
methane contents of the acid-phase digester decreased and residual volatile
acid concentration increased as the feed VS concentration was increased from
about 32 to 50 mg/L. Thus, acid formation was enhanced by the more concen-
trated feed. The gas and methane production rates from the acid-phase
digester increased almost in direct proportion to the increase in the loading
rate. The acid digester gases had high methane contents; no hydrogen was
detected in the gas phase. The two acid-phase runs at an HRT of about 2 days
exhibited a pH of about 6.6 and high bicarbonate alkalinity and ammonia
nitrogen concentrations (Table 59). Carbohydrate and lipid reductions
increased while protein reduction decreased almost in direct proportion to the
increase in feed VS concentration (Table 60).
Methane-Phase Performance
Gas and methane yields and production rates as well as effluent volatile
acids concentrations were higher at a 5.5-day HRT than at a 13-day HRT, while
organic reductions at these two HRT's were nearly equal. Methane production
from the thermophilic methane digester amounted to 67% of the system methane
production when the ratio of the methane digester HRT to two-phase system HRT
was 0.86. About 72% of the system methane production emanated from this
methane digester when the methane digester-HRT to system-HRT ratio was 0.74.
Overall, thermophilic methane digester operation at a 5.5-day HRT with a
concentrated feed appeared to be more attractive than that at a 13-day HRT.
Total carbohydrate-protein-lipid (ZCPL) reductions in the methane
digester were higher t-han those in the acid digesters; this indicated
continued and enhanced liquefaction-acidification under the thermophilic
conditions of the methane digester. By comparison, the meso-meso two-phase
system showed that ECPL reduction in the acid-phase digester was much higher
than that in the methane-phase digester, and that little liquefaction occurred
in the methane digester.
Performance of the Overall System
Gas and methane yields and production rate from the 7-day HRT meso-thermo
two-phase process were higher than those at a 15-day HRT, while ^CPL
reductions at these two HRT's were about the same; volatile solids reduction
was higher at the lower HRT. Overall, better meso-thermo two-phase
performance was observed at a 7-day system HRT.
137
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TABLE 58. EFFECT OF HRT ON GAS PRODUCTIONS FROM STEADY-STATE MESO-THERMO
TWO-PHASE SYSTEMS OPERATED WITH HANOVER PARK SLUDGE3
Run no.
Operation
Feed Concentration,'' mg/L
HRT, days
Loading, kg VS/nr'-day
Performance
Total gas yield, SCM/kg VS added
Methane Yield, SCM/kg VS added
Gas Composition, nol %
Hydrogen
Methane
Carbon dioxide
Nitrogen
Total gas production rate,
SCM/m3-day
Methane Production Kate,
SCM/m3-day
Two-phase
Acid
digester
32,300
2.1
15.52
0.163
(ll)c
0.104
(10)
0.0
63.7
35.9
0.4
2.514
(5)
1.604
(6)
at 15.1-day
Methane
digester
TP15M-T
13.0
2.48
0.290
(10)
0.198
(10)
U.O
68.3
31.3
0.4
0.720
(10)
0.492
(10)
HRT
System
15.1
2.14
0.453
(7)
0.302
(7)
0.0
66.8
32.8
0.4
0.954
(6)
0.637
(6)
Two-phase at 7.4-d;
Acid
digester
49,965
1.9
26.29
0.156
(17)
0.087
(17)
0.0
56.0
43.7
0.3
3.997
(7)
2.235
(7)
Methane
digester
- TP7M-T
5.5
9.06
0.342
(12)
0.231
(13)
0.0
67.4
32.3
0.3
2.993
(10)
2.022
(JO)
sy HRT
System
7.4
6.74
0.498
(13)
0.318
(13)
li. 0
63.8
35.9
0.3
3.251
(7)
2.077
(7)
Data reported are the means of all data collected during the steady—state portion of the run.
Feed VS concentrations are the weighted averages of the various feed slurries used during the steady-state
portion of the run.
c Numbers in parentheses are the coefficients of variation, expressed as the percent ratio of standard
deviation to the mean.
138
-------
TABLE 59. EFFECT OF HRT ON STEADY-STATE EFFLUENT QUALITIES
OF MESO-THERMO CFCSTR TWO-PHASE SYSTEMS OPERATED
WITH HANOVER PARK SLUDGE3
Run no.
HRT, days
Effluent pH
Alkalinities, mg/L as CaCCK
Total
Bicarbonate
Volatile acids, mg/L
Acetic
Propionic
Isobutyric
Butyric
Isovaleric
Valeric
Caproic
Total as acetic
Ethanol, mg/L
Nitrogen, mg/L
Ammonia-N
Organic-N
Solids, mg/L
TS
VS
Organic components, mg/L
Crude protein
Carbohydrates
Lipids
Two-phase at
15.1-day HRT
Acid Methane
digester digester"
TP15M-T
2.1 13.0
6.64 7.54
(2)c (1)
4952 7092
4094 6443
497 179
408 672
28 32
62 0
81 185
22 0
33 26
966 867
(17) (13)
0 0
756 1249
1642 1094
39,590 31,710
27,240 20,020
10,262 6838
4601 4228
6306 2264
Two-phase at
7.4-day HRT ,
Acid Methane
digester digesterb
TP7M-T
1.9 5.5
6.66 7.57
(1) (1)
6050 7975
4651 6246
892 441
849 1415
27 94
159 0
147 361
27 0
32 69
1826 1900
(13) (18)
0 0
874 1452
2365 1706
60,550 49,330
42,760 31,950
14,781 10,662
7487 6700
9875 3568
a Data reported are means of one or more determinations made during the steady-
state period.
" System effluent characteristics are the same as those of the methane-phase.
c Numbers in parentheses are the coefficients of variation expressed as the
percent ratio of the standard deviation to the mean.
139
-------
TABLE 60. EFFECT OF HRT ON STEADY-STATE ORGANIC REDUCTION EFFICIENCIES OF
MESO-THERMO CFCSTR TWO-PHASE SYSTEMS OPERATED WITH HANOVER PARK SLUDGEa
•
Run no.
HRT, days
VS reduction, Z
MOP16b
Wt-of-gas basis0
Reduction of organic components, %
Crude protein
Carbohydrates
Llpids
ECPLd
Two- phase
Acid
digester
at 15.1-day
Methane
digester
HRT
System
Two- phase
Acid
digester
*. r i -*i Ji t,
2.1 13.0
7.3 22.4
18.1 36.2
12.8 33.4
24.5 8.1
7.6 64.1
14.2 37.0
15.1
28.0
48.5
41.9
30.6
66.8
46.0
1.9
12.1
18.9
8.3
34.0
12.7
17.1
at 7.4-day
Methane
digester
TP7H-T
5.5
23.5
40.8
27.9
10.5
63.9
35.0
HRT
System
7.4
32.8
54.7
33.8
40.9
68.5
46.0
'
* The data reported here are means of one or more determinations made during the steady-state period.
These VS reductions were calculated according to the following formula:
VSR - 100 X (VSi - VS0)/lVSi - (VSt X VS0)).
c These VS reductions were calculated according to the following formula:
VSR - 100 X (wt of product gases)/(wt of VS fed).
ECPL means the sum of the masses of carbohydrates, crude protein, and llplds.
-------
PERFORMANCE OF THERMO-THERMO SYSTEMS
Acid-Phase Performance
As with the mesophilic acid digesters, gas and methane yields from the
thermophilic acid digester decreased and gas and methane production rates
increased as the HRT was decreased from 2.1 to 0.81 days (Table 61). The acid
digester gases had methane contents of 57-58 mol %, and no hydrogen was
detected even at an HRT of 0.81 days. As with the meso-meso system, the acid
digester gases contained much higher nitrogen contents than those of the
methane digesters. This observation indicated that the hydrogen removal rate
of the thermophilic syntrophic methane formers was higher than the substrate
oxidation-linked hydrogen production rate even at a low HRT of 0.8 days. In
contrast, there was evidence of hydrogen accumulation during mesophilic acid-
phase digestion at a comparable HRT of 0.9 days. This observation suggests
that thermophilic syntrophic methane formers have a higher growth rate than
those of the mesophilic syntrophic methanogens. The pH and volatile acid
concentrations in the thermophilic acid digesters were higher than those in
the mesophilic acid digesters under similar operating conditions. (See
Tables 56, 59, and 62.) Acetate was detected at the highest concentration
followed by propionic and other higher acids. These results provided evidence
of enhanced liquefaction-acidification under thermophilic conditions.
Methane-Phase Performance
Gas and methane yields from the thermophilic methane digester decreased
by 18-20% when the HRT was reduced from 6 days to 2.33 days, and even at these
low HRT's the digester gases had a methane content of 68%. A very high gas
production rate of 4.1 vol/culture vol-day was observed at an HRT of 2.33
days. About 81-84% of the thermo-thermo system methane production was
obtained from the thermophilic methane digester for methane digester-HRT to
two-phase system-HRT ratios of 0.43-0.74. By comparison, a lower proportion
of the system methane production was derived from the mesophilic methane
digester of the raeso-meso two-phase process under similar HRT conditions.
This difference was due to depressed methane production in the thermophilic
acid digester relative to that in the mesophilic acid digester.
COMPARISON OF MESO-MESO, MESO-THERMO, AND THERMO-THERMO TWO-PHASE SYSTEMS
Systems Comparison at a 15-Day HRT
A compilation of the summary data collected at a system HRT of 15 days
shows that the meso-meso two-phase system was better than the meso-thermo
system with respect to gas and methane yields and production rates, gas-phase
methane content, and VS and ECPL reductions (Table 63). The meso-thermo two-
phase process had a much higher effluent volatile acid concentration than that
of the meso-meso two-phase process and yet the effluent pH of the former
system was higher than that of the latter; this is explained by the fact that
the ammonia-nitrogen concentration and the bicarbonate alkalinity of the meso-
thermo process were considerably higher than those of the meso-meso two-phase
process. About 86% of the system methane production from the meso-meso two-
phase process was derived from the methane digester compared with 67% for the
141
-------
TABLE 61. EFFliCT OF HRT ON STEADY-STATE GAS PRODUCTIONS FROM CFCSTR
THERMO-THERMO TWO-PHASE SYSTEMS OPERATED WITH HANOVER PARK SLUDGE3
S3
Operation
Feed concentration, mg/L
HRT, days
Loading, kg VS/m-'-day
Performance
Total gas yield, SCM/kg VS added
i
Methane yield, SCM/kg VS added
Gas composition, mol %
Hydrogen
Methane
Carbon dioxide
Nitrogen
Total gas production rate,
SCM/m-day
Methane production rate,
SCM/m3-day
Two-phase
Acid
digester
51,340
2.1
33.50
0.071
(20)c
0.042
(22)
58.1
40.9
1.0
1.715
(14)
0.993
(13)
at 8.1-day
Methane
digester
6.0
8.53
0.253
(16)
0.177
(16)
70.2
29.4
0.4
2.119
(16)
1.485
(16)
HRT
System
8.1
6.80
0.324
(16)
0.219
(16)
67.6
31.9
0.5
2.015
(12)
1.358
(12)
Two-phase
Acid
digester
47,240
0.81
58.41
0.048
(30)
0.027
(28)
0.0
57.2
41.2
1.6
2.814
(30)
1.606
(28)
at 3.1-day
Methane
digester
2.33
20.24
0.207
(15)
0.141
(16)
0.0
68.2
31.7
0.1
4.133
(12)
2.818
(12)
HRT
System
3.14
15.03
0.255
(11)
0.168
(11)
0.0
65.9
33.8
0.3
3.793
(8)
2.506
(8)
a Data reported are the means of all data collected during the steady-state portion of the run.
Feed VS concentrations are the weighted averages of the various feed slurries used during the steady-state
portion of the run.
c Numbers in parentheses are the coefficients of variation, expressed as the percent ratio of standard
deviation to the mean.
-------
TABLE 62. EFFECT OF HRT ON STEADY-STATE EFFLUENT QUALITIES OF
THERMO-THERMO CFCSTR TWO-PHASE SYSTEMS OPERATED WITH HANOVER PARK SLUDGE2
Two-phase at
8.1-day HRT
Run no.
HRT, days
Effluent, pH
Volatile acids, mg/L
Acetic
Propionic
Isobutyric
Butyric
Isovaleric
Valeric
Caproic
Total as acetic
Ethanol, mg/L
Wt-of-gas VS reduction,11 %
Acid
digester
_ TD 7 T_
— — ir / JL
2.1
6.88
(Dc
994
723
215
198
465
5
31
2154
(24)
0
8.1
Methane
digester'3
T_____
— — — —
6.0
7.59
(1)
474
878
209
0
359
34
41
1580
(12)
0 ,
25.5
[33.7]e
Two-phase at
3.1 -day HRT
Acid
digester
T'DQT
— — — — irjl—
0.81
6.92
(1)
1192
667
197
268
446
164
48
2432
(31)
0
5.6
Methane
digester*3
2.33
7.59
(1)
1U2
910
40
0
190
233
59
1146
(29)
5
21.5
[27.1]
a Data reported are means of one or more determinations made during the
steady-state period.
System effluent characteristics are'the same as those of the methane-phase.
c Numbers in parentheses are the coefficients of variation expressed as the
percent ratio of the standard deviation to the mean.
^ The wt-of-gas VS reduction was calculated according to the following
formulas: VSR = 100 X (wt of product gases)/(wt of VS feed).
e Numbers in brackets are VS reductions for the system.
143
-------
TABLE 63. COMPARISON OF STEADY-STATE PERFORMANCES OF MESO-MESO
AND MESO-THERMO CFCSTR TWO-PHASE DIGESTION SYSTEMS
OPERATED AT A 15-DAY HRT WITH HANOVER PARK SLUDGE
Culture temperatures
Run no.
Methane yield, SCM/kg VS added
Methane production rate, SCM/m -day
Methane content, mol %
Methane production from methane digester, % of
system methane production
Effluent volatile acids, mg/L as acetic
Amtnonia-N, tog/L
Effluent pH
Methane digester bicarbonate alkalinity,
mg/L as CaCO-j
VS reduction, Z
MOPJ6a
Wt-of-gas basis"
Carbon-in-gas basis0
Based on theoretical yield"
Biodegradable VS reduction6
Organic reductionsi %
Crude protein
Carbohydrates
Lipids
ECPtf
Meso-meso
TP15M-M
0.410
0.779
69.3
86.0
26
646
7.10
4944
37.2
63.4
53.8
54.9
94.7
' 52.9
47.0
75.0
57.1
Meso-thermo
TP15M-T
0.302
0.637
66.8
67.2
867
1249
7.54
6443
28.0
48.5
40.9
42.0
72.4
41.9
30.6
66.8
46.0
a These VS reductions were calculated according to the following formula:
VSR - 100 X (VS£ - VS0)/[VS1 - (VSj X VS0)].
These VS reductions were calculated according to the following formula:
VSR « 100 X (wt of product gases)/(wt of VS fed).
c These VS reductions were calculated according to the following formula:
VSR - 100 X (1.84 X wt of carbon in product gas)/(wt of VS fed).
^ These VS reductions are calculated by expressing the observed total gas
yield as a percentage of the theoretical gas yield of 1.078 SCM/kg VS added.
e The biodegradable VS reduction was calculated by dividing the theoretical
gas yield based VS reduction by a biodegradability fraction of 0.58.
f ECPL means the sum of the masses of carbohydrates, crude protein, and
lipids.
144
-------
thermophilic digester of the meso-thermo system. Overall, the above observa-
tions indicated that the bulk of the two-phase system methane production was
derived from the methane digester at both mesophilic and thermophilic temper-
atures. The volatile acids and ammonia nitrogen concentrations and crude
protein and lipid productions in the thermophilic methane digester were higher
than those of the mesophilic methane digester, and yet the thermophilic
digester exhibited lower methane production. These observations indicated
that the thermophilic methane digester enhanced particulate hydrolysis and
acidification, but the hydrolysis products were probably not as efficiently
gasified as it was by the mesophilic methane digester. To achieve enhanced
thermophilic process performance, it may be necessary to develop special
thermophilic culture acclimation techniques, and to apply novel digester
designs to provide microbial SRT's that are considerably higher than the
HRT. Since thermophilic organisms have higher growth rates than mesophiles, a
higher-concentration feed should be used for the thermophilic system.
Systems Comparison at a 7-Day HRT
Comparing meso-meso, meso-thermo, and thermo-thermo two-phase operation
at a system HRT of 7 days, the meso-meso system was best in terras of methane
production rate and residual volatile acid concentration (Table 64). The
meso-thermo two-phase process exhibited slightly higher VS, protein, lipid,and
ECPL reductions and had higher effluent volatile acids and ammonia nitrogen
concentrations than those of the meso-meso two-phase process although the
methane yields from both systems were the same. Similar observations were
made during operation at a 15-day HRT. It may be inferred from these results
that there was a higher degree of liquefaction-acidification under
thermophilic conditions, and that the products of these reactions could not be
gasified by the thermophilic methanogens as efficiently as it was by their
mesophilic counterparts. From the above trends and characteristics of
thermophilic operation it would be expected that a thermo-thermo two-phase
process exhibited the lowest methane yield and production rate when compared
with the meso-meso and the meso-thermo systems.
As was the case with the 15-day HRT runs, the thermophilic methane
digesters had higher effluent acids and also a higher pH than those of the
mesophilic methane digester. This may be explained by the fact that the
ammonia nitrogen concentration at the thermophilic temperature was higher than
that at the mesophilic temperature.
As reported in Table 64, 70-80% of the two-phase system methane
production was derived from the methane digester at both mesophilic and
thermophilic temperatures.
Systems Comparison at a 3-Day HRT
The performances of the meso-meso and thermo-thermo two-phase systems at
an HRT of about 3 days are compared in Table 65. The data show the same
trends as observed at the higher HRT's in that the meso-meso two-phase process
exhibited higher methane yield and production rate than those of the thermo-
thermo system. As with other system HRT's discussed above, 69-84% of the two-
phase methane production was derived from the methane digester.
145
-------
TABLE 64. COMPARISON OF STEADY-STATE PERFORMANCES OF CFCSTR MESO-MESO,
MESO-THERMO, AND THERMO-THERMO TWO-PHASE DIGESTION SYSTEMS
OPERATED AT A 7-DAY HRT WITH HANOVER PARK SLUDGE
Culture temperatures
Run no.
Methane yield, SCM/kg VS added
Methane production rate, SCM/rc -day
Methane content, mol %
Methane production from methane digester,
% of system methane production
Effluent volatile acids, mg/L as acetic
Ammonia-N, mg/L
Effluent pH
Methane digester bicarbonate alkalinity,
mg/L as CaCOj
VS reduction, %
MOP,6a
Wt-of-gas basisb
Carbon-in gas basis0
Based on theoretical yield
Biodegradable Vs reduction6
Organic reductions, Z
Crude protein
Carbohydrates
Lipids
ICPLf
Meso-meso
TP7M-M
0.302
2.173
64.7
69.7
109
1049
7.30
8068
33.6
51.5
42.8
43.3
74.7
25.6
55.1
61.8
44.4
Meso-thenno
TP7M-T
0.318
2.077
63.8
72.3
1900
1452
7.57
6246
32.8
54.7
45.1
46.2
79.6
' 33.8
40.9
68.5
46.0
Thermo-thermo
TP7T-T
0.219
1.358
67.6
81.2
1580
—
7.59
—
33.6
29.6
30.1
51.8
—
These VS reductions were calculated according to the following formula:
VSR - 100 X
- VS0)/[VS1 - (VSi X VS0)].
k These VS reductions were calculated according to the following formula:
VSR - 100 X (wt of product gas)/(wt of VS fed).
c These VS reductions were calculated according to the following formula:
VSR • 110 X (1.84 X wt of carbon in product gas)/(wt of VS fed).
These VS reductions are calculated by expressing the observed total gas yield as
a percentage of the theoretical gas yield of 1.078 SCM/kg VS added.
e The biodegradable VS reduction was calculated by dividing the theoretical gas
yield based VS reduction by a biodegradability fraction of 0.58.
f ECPL means the sum of the masses of carbohydrate, crude protein, and lipids.
146
-------
TABLE 65. COMPARISON OF STEADY-STATE SYSTEM PERFORMANCES OF
MESO-MESO AND THERMO-THERMO CFCSTR TWO-PHASE DIGESTION SYSTEMS
OPERATED AT A 3-DAY HRT WITH CHICAGO SLUDGE
Culture temperatures
Run no.
Feed sludge3
Methane yield, SCM/kg VS added
•
Methane production rate, SCM/m -day
Methane content , mol %
Methane production from methane digester,
% of system methane production
Effluent volatile acids, mg/L as acetic
Effluent pH
VS reduction, %
MOP16b
Wt-ot-gas basis0
Carbon-in-gas basis
Based on theoretical yield6
Biodegradable VS reduction
Organic reductions, %
Crude protein
Carbohydrates
Lipids
£CPLg
Meso-meso
TP3M-M
DG-S
0.180
2.764
59.1
68.8
1680
7.19
26.5
35.5
28.5
28.3
48.8
41.5
50.6
26.8
41 JO
Thermo-therno
TP3T-T
HP
0.168
2.506
65.9
83.5
1146
7.59
27.1
23.5
23.6
40.8
—
a DG-S means mixed Downers Grove primary and Stickney activated sludges; HP
means Hanover Park sludge.
These VS reductions were calculated according to the following formula:
VSR - 100 X (VSj - VS0)/[VSi - (VSi X VS0)].
c These VS reductions were calculated according to the following formula:
VSR - 100 X (wt of product gases)/(wt of VS fed).
d These VS reductions were calculated according to the following formulas:
VSR • 100 X (1.84 X wt of carbon in product gas)/(wt of VS fed).
e These VS reductions are calculated by expressing the observed total gas
yield as a percentage of the theoretical gs yield of 1.078 SCM/kg VS added.
f The biodegradable VS reduction was calculated by dividing the theoretical
gas yield based VS reduction by a biodegradabillty fraction of 0.58.
8 ECPL means the sum of the masses of carbohydrates, crude protein, and
lipids.
147
-------
Summary
Overall, the results of the various two-phase experiments showed that
meso-meso two-phase operation seemed to be better than meso-thermo or thermo-
thermo two-phase operation in terms of gas production. The meso-thermo and
the thermo-thermo two-phase processes afforded higher organic reduction, but
lower gas yields than those of the meso-meso process. Gasification reactions
appeared to be less efficient under thermophilic conditions.
The acid digesters performed well at the 2-day and the 0.8-day HRT's at
both temperatures; however, acid accumulation was higher at the therraophilic
temperature while gas production was lower compared to those at the mesophilic
temperature.
The mesophilic methane digester exhibited higher gas yields than the
thermophilic methane digester at all HRT's. Although there was evidence of
enhanced liquefaction-acidification at the thermophilic temperature, gasifica-
tion of these reaction products was inefficient in a CFCSTR digester. For
overall system operation, HRT's of 1-2 days for the acid-phase and about 5-6
days for the methane-phase seemed optimum.
148
-------
SECTION 13
PROCESS COMPARISON: CFCSTR SINGLE-STAGE VERSUS CFCSTR TWO-PHASE
PROCESS COMPARISON AT A 15-DAY HRT
The performances of the single-stage CFCSTR and the two-phase CFCSTR runs
at a 15-day HRT are compared in Table 66. Both the meso-thermo and meso-meso
two-phase processes exhibited better performances than mesophilic or
thermophilic single-stage conventional high-rate digestion in terms of total
gas and methane yields and production rates, VS reduction, and conversion of
the carbohydrate fraction of VS (Figure 15). The methane yields of the meso-
meso and meso-thermo two-phase processes were 82% and 34% higher than those of
the mesophilic single-stage run (15-day HRT baseline run). Similarly, the
methane production rates from the meso-meso and meso-thermo two-phase
processes were about 77% and 47% higher than those of the single-stage
processes.
Volatile solids reductions for the single-stage and overall two-phase
systems were calculated by four different methods as explained in Table 66. It
appears that VS reductions calculated by the MOP-16 method were unrealistic
and inconsistent with the gas production data. This is probably due to the
lack of accuracy of the VS measurement procedure, particularly when alkali and
acids were added for pH control and/or sample preservation. The MOP-16 VS
reductions tended to be lower than those calculated from mass balances on
theoretical gas yields. Volatile solids reductions "calculated on the bases of
carbon content of digester gas and theoretical gas yield were within 2% of
each other, and appeared to be more realistic than those obtained by the MOP-
16 formula. Biodegradable VS reduction were calculated to afford a more
realistic assessment of process performance. These calculations were based on
an estimated biodegradability factor of 0.58 (see Section 10).
Information presented in Table 66 and Figure 15 shows that both meso-meso
and meso-thermo two-phase systems exhibited higher VS reductions than the
single-stage systems, and that the meso-meso two-phase system had the highest
VS and organics reductions. Considering conversions of individual organic
components, proteins and lipids were degraded at higher efficiencies than
carbohydrates under all conditions except in the case of the 15-day HRT
single-stage mesophilic run where all organic components were degraded about
equally.
The meso-meso two-phase digestion run exhibited the best performance in
all respects relative to the other runs. The observed methane yield from this
run was 82% of the theoretical compared with 60%, 56% and 45% for the meso-
thermo two-phase, single-stage mesophilic, and single-stage thermophilic runs,
149
-------
TABLE 66. COMPARISON OF STEADY-STATE PERFORMANCES OF CFCSTR SINGLE-
STAGE AND TWO-PHASE DIGESTION SYSTEMS OPERATED AT ABOUT A 15-DAY
SYSTEM HRT WITH HANOVER PARK SLUDGE
Run no.
Total gas yield, SCM/kg VS added
Methane yield, SCM/kg VS added
Observed methane yield as:
% of theoretical yield
7. of ADPT yield
Methane production rate, SCM/n -day
Methane content, raol %
Effluent volatile acids, mg/L as acetic
Effluent pH
Ammonia-nitrogen, rag/L
Single-stage
mesophillc
SS15M
0.320
0.225
45.0
70.8
0.440
70.3
1
7.11
779
Single-stage
thermophilic
SS15T
0.425
0.280
(24.4)a
56.0
88.1
0.591
(34.3)
66.1
1037
7.47
1132
Meso-thermo
two-phase
TP15M-T
0.453
0.302
(34.2)
60.4
95.0
0.637
(46.8)
66.8
867
7.54
1249
Meso-meso
two-phase
TP15M-M
0.592
0.410
(82.2)
82.0
128.9
0.779
(77.0)
69.3
26
7.10
646
Ratio of effluent bicarbonate alkalinity
to feed bicarbonate alkalinity
VS reduction, %
1.53
2.71
2.75
1.73
MOPJ6b
Wt-of-gas basis
Carbon-in-gas basis
Based on theoretical gas yield6
Biodegradable VS reduction'
Organic reduction, %
Crude protein
Carbohydrates
Lipids
£CPLg
38.2
28.8
29.1
29.7
51.2
27.1
27.3
25.1
26.6
36.8
45.9
39.4
39.4
68.0
53.5
25.3
68.2
51.5
28.0
48.5
40.9
42.0
72.4
41.9
30.6
66.8
46.0
37.2
63.4
53.8
54.9
94.7
52.9
47.0
75.0
57.1
a Numbers in parentheses are the percentage increases in the particular performance parameter over that
of the mesophllic single-stage high-rate process.
These VS reductions were calculated according to the following formula:
vsR = 100 x (vSj^ - vs0)/!vsi - (vsi x vs0)].
c These VS reductions were calculated according to the following formula:
VSR = 100 X (wt of product gases)/(wt of VS fed).
These VS reductions were calculated according to the following formula:
VSR = 100 X (1.84 X wt of carbon in product gas)/(wt of VS fed).
e These VS reductions are calculated by expressing the observed total gas yield as a percentage of the
theoretical gas yield of 1.078 SCM/kg VS added.
The biodegradable VS reduction was calculated by dividing the theoretical gas-yield based VS reduction
by a biodegradability factor of 0.58.
E ECPL means the sum of the masses of carbohydrates, crude protein, and lipids.
150
-------
REDUCTIONS AT SYSTEM HRT S OF ABOUT 15 DAYS
60
o 5°
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D
VOLATILE SOLIDS REDUCTION
ON WEIGHT-OF-GAS BASIS
TOTAL ORGANICS (Sum of
Protein, Carbohydrates and
Lipids) REDUCTION
SINGLE- SINGLE- TWO-PHASE TWO-PHASE
STAGE STAGE MESO- MESO-MESO
MESO"- THERMOPHILTC THERMO - - -- -
PHILIC
REDUCTIONS AT SYSTEM HRT S OF ABOUT 3 DAYS
REDUCTIONS AT SYSTEM HRT S OF ABOUT 7 DAYS
60 h
50
!40
O 30
o
E20
UJ
rr
10
a
a-
50
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-40
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o
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SINGLE- SINGLE- TWO-PHASE TWO-PHASE
STAGE STAGE MESO- MESO-MESO
MESO- THERMOPHILIC THERMO
SINGLE- SINGLE- TWO-PHASE TWO-PHASE
STAGE STAGE MESO- MESO-MESO
MESO- THERMOPHILIC THERMO
PHILIC
Figure 15. Comparison of organic reduction efficiencies of CFCSTR
single-stage and two-phase anaerobic digestion systems.
A850705I5
-------
respectively. The raeso-meso two-phase process effected complete conversion of
all the biodegradable volatile solids.
PROCESS COMPARISON AT A 7-DAY HRT
Table 67 compares the performances of mesophilic and therraophilic single-
stage digestion with those of thermo-thermo, meso-thermo, and meso-meso two-
phase runs, all at a 7-day system HRT. The summary data show that the meso-
thermo two-phase system exhibited the best performance in terms of gas yield
and VS and organic reductions. The next best performance at a 7-day HRT was
exhibited by the meso-meso two-phase process. Surprisingly, the thermo-thermo
two-phase process was worse than the meso-thermo and the meso-meso two-phase
runs. Comparison of the methane yields of methane digesters of the three two-
phase systems in Table 67 shows that the gasification efficiencies of the
methane digesters were comparable when they were operated in tandem with
mesophilic acid-phase digesters; but the methane digester gas production
declined sharply when it was preceded by a thermophilic acid-phase digester.
A plausible explanation for this phenomenon is that thermophilic acid-phase
digestion products retarded acetate and/or C02~H2 conversion directly;
alternatively, acetogenic conversion of higher fatty acids and other acetate
precursors to acetate could have been inhibited.
Lipid and carbohydrate degradations were higher for two-phase digestion
than for single-stage digestion. Crude protein and lipid conversions were
enhanced under thermophilic conditions. Carbohydrate reduction seemed to be
higher at the mesophilic temperature. The efficiency of lipid conversion was
higher than those of protein and carbohydrate.
Overall, the performances of the single-stage and two-phase systems at
the 15- and 7-day HRT's were essentially similar with the exception that the
meso-meso two-phase process performed significantly better at the 15-day HRT.
PROCESS COMPARISON AT A 3-DAY HRT
In contrast to system operation at HRT's of 15 and 7 days, the meso-meso
two-phase run exhibited the best performance at a 3-day system HRT (Table 68),
although it should be noted that a meso-thermo run was not conducted at this
HRT. Both the meso-meso and thermo-thermo two-phase processes were better
than the mesophilic and thermophilic single-stage runs at this low HRT. While
protein and lipid degradations were favored at a thermophilic temperature,
carbohydrate conversion was higher than those of protein and lipids at the
mesophilic temperature.
It is noteworthy that at a 3-day HRT the methane yield of the meso-meso
two-phase process was 102% higher than that of the single-stage process; this
increase was higher than those observed at system HRT's of 7 and 15 days.
Thus, the relative advantages of two-phase digestion were more conspicuous at
the shortest HRT.
152
-------
TABLE 67. COMPARISON OF STEADY-STATE PERFORMANCES OF CFCSTR
SINGLE-STAGE AND TWO-PHASE DIGESTION SYSTEMS OPERATED AT
ABOUT A 7-DAY HRT WITH HANOVER PARK SLUDGE
Run no.
Total gas yield, SCM/kg VS added
Methane yield, SCM/kg VS added
Observed methane yield as:
7, of theoretical yield
% of ADPT yield
Methane production rate, SCM/m -day
Methane content, raol %
Effluent volatile acids, mg/L as acetic
Efflvient pH
Ammonia-nitrogen, mg/L
Ratio of effluent bicarbonate alkalinity
to feed bicarbonate alkalinity
VS feduction, %
Wt-of-gas basis0
Carbon-in-gas basis
Based on theoretical methane yield6
Biodegradable VS reduction
Organic reduction, %
Crude protein
Carbohydrates
Lipids
Single-stage
mesophlllc
SS7M
0.318
0.220
44.0
69.2
1.609
69.1
248
7.06
728
1.43
18.3
32.7
28.8
29.5
50.9
26.2
26.4
40.0
32.4
Single-stage
thermophilic
SS7T
0.373
0.253
U5.0)a
50.6
79.5
1.797
(11.7)
68.0
2105
7.50
1646
2.26
32.9
39.6
34.7
34.6
59.7
47.8
10.8
47.8
38.1
Therm o-thermo
two-phase
TP7T-T
0.324
0.219
(0.0) •
43.8
68.9
1.358
(-15.6)
67.6
1580
7.59
—
—
33.6
29.6
30.1
51.8
—
Meso-thermo
two-phase
TP7M-T
0.498
0.318
(44.6)
63.6
100.0
2.077
(29.1)
63.8
19DO
7.57
1452
1.41
32. «
54.7
45.1
46.2
79.6
33.8
40.9
68.5
46.0
Meso-Neso
two-phase
TP7M-M
0.467
0.302
(37.3)
60.4
95.0
2.173
(35.0)
64.7
109
7.30
1049
2.09
33.6
51.5
42.8
43.3
74.7
25.6
55.1
61.8
44.4
a Numbers in parenthesis are the percentage increases in the particular performance parameter over that of the
mesophilic single-state high-rate process.
These VS reductions were calculated according to the following formula:
VSR = 100 X (VSj - VSQ)/[VS1 - (VSi X VS0)].
c These VS reductions were calculated according to the following formula:
VSR - 100 X (wt of product gases)/(wt of VS fed).
These VS reductions were calculated according to the following formula:
VSR - 100 X (1.84 X wt of carbon in product gas)/(wt of VS fed).
e These VS reductions are calculated by expressing the observed total gas yield as a precentage of the theoretical
gas yield of 1.078 SCM/kg VS added.
The biodegradable VS reduction was calculated by dividing the theoretical gas yield based VS reduction by a
biodegradability fraction of 0.58.
g ICPL means the sum of the masses of carbohydrates, crude protein, and lipids.
153
-------
TABLE 68. COMPARISON OF STEADY-STATE PERFORMANCES OF CFCSTR
SINGLE-STAGE AND TWO-PHASE DIGESTION SYSTEMS OPERATED AT
ABOUT A 3-DAY HRT WITH HANOVER PARK SLUDGE
Run no.
Total gas yield, SCM/kg VS added
Methane yield, SCM/kg VS added
Observed methane yield as:
% of theoretical yield
% of ADPT Yield
Methane production rate, SCM/m-'-day
Methane content, mol %
Effluent volatile acids, mg/L as acetic
Effluent pH
Ammonia-nitrogen, mg/L
Ratio of effluent bicarbonate alkalinity
to feed bicarbonate alkalinity
VS reduction, X
MOP16C
Wt-of-gas basisd
Carbon-in-gas basis6
Based on theoretical gas yield
Biodegradable VS reduction^
Organic reduction, %
Crude protein
Carbohydrates
Lipids
tctLh
Single-stage
mesophilic
SS3M
0.160
0.089
17.8
28.0
1.365
55.6
2017
6.77
1122
1.88
13.7
19.3
14.9
14.8
25.6
23.7
44.4
16.5
27.6
Single-stage
thermophilic
SS3T
0.180
0.114
(28.1)b
22.8
35.8
1.770
(29.7)
63.3
32U5
7.27
1550
2.35
19.0
20.2
ID. 7
16.7
28.8
20 .A
10.4
22.9
18.4
Thermo-thermo
two-phase
TP3T-T
0.255
0.168
(88.8)
33.6
52.8
2 . 506
(83.2)
65.9
1146
7.59
—
—
27.1
23.5
23.6
40.8
—
—
Meso-meso
two-phase3
TP3M-M
0.305
0.180
(111.2)
36.0
56.6
2.764
(102.5)
59.1
1680
7.19
li>2u
5.41
26.5
35.5
'28.3
48.8
41.5
50.6
26.8
41.0
' This run was operated with mixed Downers Grove primary and Stickney activated sludges.
1 Numbers in parenthesis are 'the percentage increases in the particular performance parameter over that of
the raesophilic single-stage high-rate process.
These VS reductions were calculated according to the following formula:
VSR = 100 X (VSt - VS0)/IVS1 - (VSi X VS0)].
These VS reductions were calculated according to the following formula:
VSR " 100 X (wt of product gases)/(wt of VS fed).
These VS reductions were calculated according to the following formula:
VSR « 100 X (1.84 X wt of carbon in product gas)/(wt of VS fed).
These VS reductions were calculated by expressing the observed total gas ield as a percentage of the
theoretical gas yield of 1.078 SCM/kg VS added.
The biodegradable VS reduction was calculated by dividing the theoretical gas-yield-based VS reduction
by a biodegradability factor of 0.58.
ICPL means the sum of the masses of carbohydrates, crude protein, and lipids.
154
-------
CHARACTERISTICS OF THERMOPHILIC DIGESTION
Examination of the data in Tables 66, 67, and 68 shows that essentially
all thermophilic systems exhibited much higher residual effluent volatile
acids than the mesophilic systems. However, acids accumulations under
thermophilic conditions were higher in the single-stage runs at HRT's of 7 and
3 days than in the two-phase runs. These observations suggested the
following:
• Volatile acids were not gasified as efficiently under thermophilic
conditions as they were at the mesophilic temperature.
• Under thermophilic conditions, the efficiency of volatile acids
conversion by two-phase digestion seemed to be higher than that by
single-stage digestion.
It was reasoned that acids accumulation under thermophilic conditions
probably occurred due to one or both of the following reasons:
• Inhibition of acetogenic bacteria and retarded conversion of higher fatty
acids and other acetate-precursors to acetate
• Inhibition of acetate-utilizing methane bacteria and retarded conversion
of acetate to methane and carbon dioxide.
The effluent volatile acids data shown in Table 69 indicated that under
similar operating conditions, the thermophilic acid digester experienced
higher accumulation of acetate, butyrate, and iso-valerate than the mesophilic
acid-phase digester, suggesting that utilization of these acids was retarded
under thermophilic fermentation conditions. It is probable that acetate-
utilizing methanogens, and butyrate and valerate-utilizing acetogens were
inhibited more during thermophilic digestion than they were during mesophilic
digestion.
The phenomenon of acids accumulation was clearly evident in the thermo-
philic methane digesters of the two-phase systems (Table 70). Whereas there
was hardly any volatile acids accumulation in the mesophilic methane digester
at HRT's of 13 and 5 days, acetate, propionate, iso-butyrate, iso-valerate,
and caproate accumulated at much higher concentrations during thermophilic
metabolism. Interestingly, butyrate which tended to accumulate in the
thermophilic acid-digester did riot accumulate at all in the methane digester.
Also, there was no accumulation of valeric acid in the thermophilic methane
digester. Thus, butyrate and valerate were metabolized at the higher HRT's
prevalent in the methane digester. Under thermophilic conditions propionate
accumulated in the highest concentration followed by acetate (Table 70). It
is noteworthy that accumulation of all the acids increased almost in direct
proportion to the increase in dilution rate as the HRT was decreased from 13
days to 5 days. The above observations indicated the following effects of
thermophilic digestion:
• Aceticlastic gasification (acetate conversion) was retarded during acid-
phase digestion at a short (2-day) HRT and during methane-phase digestion
155
-------
TABLE 69. STEADY-STATE EFFLUENT VOLATILE ACIDS CONCENTRATIONS IN
MESOPHILIC AND THERMOPHILIC CFCSTR ACID-PHASE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE AT ABOUT A 2-DAY HRT
Mesophilic Thermophilic
acid-phase acid-phase
Two-phase system run no. TP7M-M TP7M-T TP7T-T
Feed VS concentration, g/L 49.7 50.0 51.3
Volatile acids, mg/L
Acetic 721 892 994
Propionic 728 849 723
Isobutyric 109 27 215
Butyric 160 159 198
Isovaleric 136 147 465
Valeric 61 27 5
Caproic 31 32 31
Total as acetic 1627 1826 2154
at even higher HRT's of 5 and 13 days suggesting that thermophilic
methanogens are inhibited by certain metabolite(s) of thermophilic
digestion
• Propionate-utilizing acetogens were inhibited even at a high HRT of
13 days
• Butyrate and valerate metabolism was not affected under thermophilic
conditions, but caproate conversion was affected even at a high HRT of
13 days
• Thermophilic bacteria which utilize the branch-chain fatty acids (iso-
butyrate and iso-valerate) experienced inhibition even at high HRT's
• The above inhibitory effects at the thermophilic temperature of 55°C
increased in direct proportion to the increase in dilution rate.
It is indeed true that acetate-utilizing methanogens and propionate-,
caproate-, iso-butyrate-, and iso-valerate-utilizing acetogens are inhibited
in the methane-phase digesters under thermophilic conditions, then higher
accumulations of these very acids would also be predicted for thermophilic
single-stage digesters. Data presented in Table 71 show that the experimental
observations were in total agreement with these predictions. As expected from
the above considerations, acids accumulations in the single-stage thermophilic
digester were considerably higher than those in the single-stage mesophilic
156
-------
TABLE 70. STEADY-STATE EFFLUENT VOLATILE ACIDS CONCENTRATIONS IN MESOPHILIC AND THERMOPHILIC
CFCSTR METHANE-PHASE DIGESTERS OF TWO-PHASE SYSTEMS FED WITH HANOVER PARK SLUDGE*
Two-phase system run no.
System feed VS concentration, g/L
Volatile acids, mg/L
Acetic
Propionic
Isobutyric
Butyric
Isovaleric
Valeric
Caproic
Total as acetic
13-day
Mesophilic
methane-phase
TP15M-M
29.5
20
8
0
0
0
0
0
26
HRT
Thermophilic
methane-phase
TP15M-T
32.3
179
672
32
0
185
0
26
867
5-day
Mesophilic
methane-phase
TP7M-M
49.7
63
29
0
0
0
10
33
109
HRT
Thermophilic
methane-phase
TP7M-T
50.0
441
1415
94
0
361
0
69
1900
The acid-phase digesters of the two-phase systems were operated at 2-day HRT's.
-------
TABLE 71.. STEADY-STATE VOLATILE ACIDS CONCENTRATIONS IN MESOPHILIC AND
THERMOPHILIC SINGLE-STAGE CFCSTR DIGESTERS OPERATED WITH HANOVER PARK SLUDGE
Run no.
Feed VS concentration, g/L
Volatile acids, mg/L
H-
Ln
°° Acetic
Propionic
Isobutyric
Butyric
Isovaleric
Valeric
Caproic
Total as acetic
Methane yield, SCM/kg VS added
VS reduction, %
SCPL reduction, %
15-day
Mesophilic
single-stage
SS15M
30.1
i
0
0
0
0
0
0
1
0.225
28.8
26.6
HRT
Thermophilic
single-stage
SS15T
31.8
154
844
69
3
239
8
9
1037
0,280
45.9
51.5
7-day
Mesophilic
single-stage
SS7M
52.2
164
104
0
0
0
0
0
248
0.220
32.7
32.4
HRT
Thermophilic
single-stage
SS7T
49.9
211
1708
163
0
624
0
60
2105
0.253
39.6
38.1
3-day
Mesophilic
single-stage
SS3M
48.3
343
1571
191
39
329
86
0
2017
0.089
19.3
27.6
HRT
Thermophilic
single-stage
SS3T
49.2
1045
1379
375
321
811
32
138
3205
0.114
20.2
18.4
-------
digester, although methane yield, VS reduction, and total carbohydrate-
protein-lipid (SCPL) reduction under thermophilic conditions were
significantly higher than those of mesophilic digestion. By comparison, acid
accumulations in the thermophilic two-phase systems were significantly lower
than those in the single-stage process under comparable conditions of HRT and
feed VS concentration.
In light of the above discussions, it may be concluded that relative to
mesophilic conditions, the thermophilic temperature enhanced the hydrolysis of
the particulate matter and acidification of the hydrolysate, but retards
acetogenic conversion of propionate, branch-chain acids, and caproate as well
as acetate fermentation with the result that these metabolites accumulated in
the digester. This problem was aggravated more as the HRT of the thermophilic
digester is reduced. Volatile acids accumulation in thermophilic two-phase
anaerobic digestion systems were significantly lower than those in the single-
stage thermophilic process. This indicated that the thermophilic two-phase
process promoted enhanced acetogenic and methanogenic activities than
conventional single-stage digestion.
The acid-phase digesters of the two-phase systems were operated at HRT's
of about 1.9-2.1 and 0.8-0.9 days which were expected to be lower than the
critical HRT for acetate-utilizing methanogens. Consequently, the methano-
genic activity in the acid-phase digesters would be primarily attributable to
that of the hydrogen-utilizing methanogens. A concern that is worth consid-
ering is whether the hydrogen-utilizing methane bacteria were also adversely
affected by thermophilic metabolites in a similar manner as the acetogens and
acetate-utilizing methanogens were impacted during thermophilic digestion.
Table 72 was prepared to elucidate this question. Considering thermophilic
and mesophilic acid-phase digestion under similar operating conditions, there
was evidence of a higher degree of acidification at the thermophilic tempera-
ture. Yet, methane yield at the therraophilic temperature was less than one-
half that at the mesophilic temperature. It may be inferred from these
observations that certain thermophilic sludge ^degradation products could also
be inhibitory to the hydrogen-oxidizing methanogens. Alternatively, the
kinetics of methanogenic bacteria (i.e., the saturation constant) may be
strongly affected by temperature; i.e., it may be lower at thermophilic than
at mesophilic temperature.
Plausible Causes for Inhibition
It is plausible to conclude that inhibition of the acetogenic and methan-
ogenic activities during thermophilic digestion was caused by carbohydrate-,
protein-, or lipid-degradation product(s). Carbohydrate degradation products
under thermophilic conditions were not expected to be inhibitory to methane
fermentation considering that cellulosic feeds reportedly digest better under
thermophilic conditions than at mesophilic temperatures. ' Comparison of
steady-state data included in Table 73 on mesophilic and thermophilic diges-
tion of the cellulosic fraction of municipal solid waste showed that there was
no evidence of higher volatile acids accumulation during thermophilic
fermentation. Thermophilic methane yield was also higher than the
mesophilic methane yield. Thus, products of thermophilic digestion of
cellulosics do not seem to have any adverse effect on the acetogenic and
159
-------
TABLE 72. COMPARISON OF STEADY-STATE METHANE YIELDS AND EFFLUENT
VOLATILE ACIDS CONCENTRATION FROM MESOPHILIC AND THERMOPHILIC CFCSTR
ACID-PHASE DIGESTION OF HANOVER PARK SLUDGE OPERATED AT ABOUT A 2-DAY HRT
Mesophilic
acid-phase
Thermophili c
acid-phase
Two-phase system run no.
TP7M-M
TP7M-T
Acetic
Propionic
Isobutyric
Butyric
Isovaleric
Valeric
Caproic
Total as acetic
721
728
109
160
136
61
31
1627
892
849
27
159
147
27
32
1826
TP7T-T
HRT, days
Feed VS concentration, g/L
Methane yield, SCM/kg VS added
Volatile acids, mg/L
1.9
49.7
0.091
1.9
50.0
0.087
2.1
51.3
0.042
994
723
215
198
465
5
31
2154
methanogenic organisms. In view of this, and considering that carbohydrate
was degraded the least during thermophilic sludge digestion (Table 74) it may
be inferred that products of protein and lipid degradation may have been
inhibitory to thermophilic acetogens and methanogens.
Stability of Two-Phase Digestion
One major reason for digester instability is the accumulation of volatile
acids and the concomittant drop in pH, both of which are inhibitory to the
methanogens. The rate of pH drop and the magnitude of the final pH depend to
a large extent on the buffer capacity of the digester contents; digester
buffer capacity is mainly due to the bicarbonate alkalinity generated during
the digestion process. Bicarbonate alkalinity increases with increases in gas
(C02) and ammonia-nitrogen concentrations. Generally, the two-phase systems
exhibited higher CO, and ammonia-nitrogen productions than those of the
corresponding single-stage processes. In particular, the methane phases of
the two-phase systems generated significantly higher bicarbonate alkalinities
and buffer capacities than those of the single-stage processes, and this
differential increased as the system HRT decreased (Tables 66, 67, and 68).
For example, at a 15-day system HRT, the bicarbonate alkalinity of the meso-
160
-------
TABLE 73. STEADY-STATE EFFLUENT VOLATILE ACIDS CONCENTRATIONS IN
MESOPHILIC AND THERMOPHILIC SINGLE-STAGE CFCSTR DIGESTERS OPERATED WITH THE
CELLULOSE FRACTION OF MUNICIPAL SOLID WASTE AT A 7-DAY HRT
Mesophilic Thermophilic
HRT, days
Feed VS concentration, g/L
Methane yield, SCM/kg VS added
Volatile acids, rag/L
Acetic
Propionic
Isobutyric
Butyric
Isovaleric
Valeric
Caproic
Total as acetic
7.3
32.8
0.131
30
360
0
0
0
0
0
330
7.1
35.3
0.156
31
132
0
0
0
3
0
139
7.1
48.9
0.131
12
124
0
1
0
14
18
130
TABLE 74. PROTEIN, CARBOHYDRATE, AND LIPIl) CONVERSIONS AT
STEADY-STATE IN THERMOPHILIC CFCSTR METHANE-PHASE DIGESTERS
FED WITH HANOVER PARK SEWAGE SLUDGE
Two-phase system run no. TP15M-T TP7M-T
Methane-phase HRT, days 13.0 5.5
Feed VS concentration, g/L 32.3 50.0
Reduction of organic components, %
Crude protein 33.4 27.9
Carbohydrates 8.1 10.5
Lipids 64.1 63.9
161
-------
meso two-phase system was 73% higher than the feed compared to a 53% increase
for the single-stage process (Table 66). The corresponding increases at a 1-
day HRT were 109% and 43%. At the very short system HRT of 3 days the
bicarbonate alkalinity of the two-phase process increased by 441% compared
with only 88% in the single-stage process. It is well accepted that the
higher the buffer capacity of the culture the less vulnerable is the
methanogenic culture to volatile acids accumulation and the more stable is the
overall digestion process. The two-phase digestion process is more stable,
and therefore, more reliable than single-stage digestion because a higher
buffer capacity is maintained in the separated methane phase. The enhanced
stability of the two-phase process relative to single-stage digestion
increased by larger and larger amounts as the system HRT was decreased from 15
to 7 to 3 days.
162
-------
SECTION 14
PERFORMANCE OF ACID-PHASE RUNS: PARAMETRIC-EFFECT STUDIES
EXPERIMENTAL RUNS
Six mesophilic and six thermophilic acid-phase runs were conducted with
Hanover Park sewage sludge at HRT's of 2.0-2.4 and 1.3-1.5 days and at pH's of
7.0-7.1, 6.0-6.2, 5.5, and 5 (Table 75). Sodium hydroxide was used to control
the pH at 7, whereas hydrochloric acid was used to control the pH at 6 or
lower. All runs were conducted for a minimum duration of four HRT's. Most
runs continued for a duration of about 10 HRT's. The maximum variability
(coefficient of variation) of the culture pH and temperature were 4%. The
variability of the digester HRT was between 2% and 13%. All runs were
conducted with feed VS concentrations ranging between 46 and 54 g/L with an
average concentration of about 50 g/L, which was the target VS consistency.
MESOPHILIC ACID-PHASE RUNS
pH Effects at a Two-Day HRT
The effects of pH on mesophilic acid-phase digester performance with
Hanover Park sewage sludge feed are apparent from the data presented in
Tables 76 through 78 and Figure 16. Consideration of the gas production and
volatile acids production data shows that the optimum pH for acid-phase
digestion of the feed sludge was between about 5.5 and 6.2. At an HRT of
2 days, protein and lipids reductions were 18% and 23% higher at a pH 5 than
they were at pH 7; however, total carbohydrate reduction at pH's 7 and 5 were
the same.
Hydrogen gas was not detected in any of the runs; consequently, inhibi-
tion of acetogenic organisms probably did not occur. Reduction of the total
mass of carbohydrate-protein-lipid (ZCPL) was higher at pH 5 than at pH 7.
pH Effects at an HRT of 1.3 Days
Data presented in Tables 79, 80, and 81 show that at an HRT of 1.3 days,
acid-phase digester performance at pH 5 was worse than that at pH 7 when
compared in terms of gas and volatile acids productions; and protein, carbo-
hydrate and lipid reductions. These observations were opposite of those made
during acid digester operation at a 2-day HRT. Apparently, a combination of
low pH and low HRT adversely affected acid-phase digestion of sewage sludge
under mesophilic conditions.
163
-------
TABLE 75. ACTUAL STEADY-STATE OPERATING CONDITIONS FOR PARAMETRIC-EFFECTS
CFCSTR ACID-PHASE DIGESTERS FED WITH HANOVER PARK SLUDGE*
Digester
Run no. no.
Mesophilic
AP2M7 334
AP2M6 334
AP2M5.5 334
AP2M5 334
AP1.3M7 334
AP1.3M5 334
Thermophlic
AP2T7 335
AP2T6 335
AP2T5.5 335
AP2T5 335
AP1.3T7 335
AP1.3T5 335
Total run Steady-state
duration, duration,
days days
63 40
20 20
9 9
13 13
30 22
13 12
98 79
11 9
18 17
20 11
56 39
15 14
Culture
temperature,
°C
(0-
35.7
(1)
35.8
(1)
35.5
(1)
15.2
(1)
15.7
(1)
54.3
(3)
56.4
(2)
54.4
(4)
54.8
(1)
55.4
(1)
55.2
(1)
Mean
culture
PH
6.99
(3)
6.17
(4)
5.47
(2)
5.02
(1)
69.6
(4)
5.04
(2)
7.08
(2)
5.95
(3)
5.53
(2)
5.07
(2)
7.04
(1)
4.99
(2)
Mean
HRT,
days
2.1
(12)
2.4
(20)
2.2
(6)
2.1
(5)
1.3
(10)
1.5
(10)
2.1
(13)
2.1
(2)
2.0
(16)
2.1
(3)
1.3
(7)
1.3
(7)
Mean loading
rate,
kg VS/m3-day
23.43
(11)
22.20
(25)
23.40
(6)
24.62
(5)
34.08
(10)
32.76
(10)
25.48
(12)
24.25
(2)
26.13
(21)
24.03
(3)
36.02
(12)
38.74
(6)
Feed
total solids
concentration, g/L
69.8
65.3
65.5
67.3
60.1
68.4
76.1
65.5
69.2
65.3
62.7
67.5
Feed
volatile solids
concentration, g/L
48.3
52.4
50.3
51.5
46.0
48.5
52.8
50.0
53.6
50.0
47.9
51.1
Data reported are the means of all data collected during the steady-state period. Batch numbers for the various runs are shown in Appendix Table F-l.
Numbers in parentheses are the coefficients of variation, expressed as the percent ratio of standard deviation to the mean.
-------
TABLE 76. EFFECT OF pH ON STEADY-STATE GAS PRODUCTIONS FROM MESOPHILIC
CFCSTR ACID-PHASE DIGESTERS OPERATED WITH HANOVER PARK SLUDGE AT ABOUT
A 2-DAY HRTa
Culture pH
Run no .
Operation
Feed VS concentration," mg/L
HRT, days
o
Loading, kg VS/mJ-day
pH-control chemical (2.5N)
pH-control dosage, meq/L feed
Performance
Total gas yield, SCM/kg VS added
Methane yield, SCM/kg VS added
Gas composition, mol %
Hydrogen
Methane
Carbon Dioxide
Nitrogen
Total gas production rate,
SCM/m3-day
Methane production rate,
SCM/m3-day
7.0
AP2M7
48,270
2.1
23.43
NaOH
32.9
0.049
(22)c
0.035
(21)
—
71.4
27.0
1.6
1.124
(17)
0.804
(17)
6.2
AP2M6
52,390
2.4
22.20
HC1
23.4
0.133
(14)
0.071
(14)
—
53.2
46.6
' 0.2
2.887
(13)
1.542
(16)
5.5
AP2M5.5
50,310
2.2
23.40
HC1
46.0
0.093
(12)
0.048
(12)
—
51.7
48.0
0.3
2.166
(8)
1.120
(8)
5.0
AP2M5
51,460
2.1
24.62
HC1
80.9
0.058
(23)
0.029
(24)
0.0
50.1
49.2
0.7
1.424
(21)
0.713
(23)
Data reported are means of all data collected during the steady-state
portion of the run.
Feed VS concentrations are the weighted averages of the various feed slurry
concentrations.
Numbers in parentheses are the coefficients of variation, expressed as the
percent ratio of the standard deviation to the mean.
165
-------
TABLE 77. EFFECT OF pH ON STEADY-STATE EFFLUENT QUALITITES OF MESOPHILIC
CFCSTR ACID-PHASE DIGESTERS OPERATED WITH HANOVER PARK SLUDGE AT
ABOUT A 2-DAY HRT*
Culture pH
Run no .
Alkallnities, mg/L as CaCO^
Total
Bicarbonate
Volatile acids, mg/L
Acidic
Propionic
Isobutyric
Butyric
Isovaleric
Valeric
Caproic
Total as acetic
Ethanol, mg/L
Nitrogen, mg/L
Ammonia-N
Organic-N
Chemical oxygen demand, mg/L
Total
Filtrate
Solids, mg/L
TS
VS
TSS
VSS
Organic components, mg/L
Crude protein
Carbohydrates
Lipids
7.0
AP2M7
8160
6963
662
646
100
118
195
13
2
1457
3
505
1638
68,480
5064
62,120
39,650
55,080
40,280
10,238
7851
14,444
6.2
AP2M6
__
—
1145
1113
128
335
271
109
11
2592
0
— —
—
__
—
__
—
—
— —
—
—
5.5 5.0
AP2M5.5 AP2M5
2520
13
1465 1087
1223 740
160 17b
547 524
1002 932
185 282
39 5
3657 2880
0 79
923
2150
— _~
— —
59,290
44,590
— —
— —
13,438
10,561
10,988
Data reported are means of one or more determinations made during
steady-state period.
166
-------
TABLE 78. EFFECT OF pH ON STEADY-STATE ORGANIC REDUCTION EFFICIENCIES
OF MESOPHILIC CFCSTR ACID-PHASE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE AT ABOUT A 2-DAY HRTa
Culture pH
Run no.
VS reduction, %
7.0 6.2 5.5 5.0
AP2M7 AP2M6 AP2M5.5 AP2M5
MOP16b
Wt-of-gas basis0
VSS reduction
COD (total) reduction, %
Organic component reduction,
15.3
5.2
11.8
11.9
16.0
11.6
5.2
3.5
Crude protein
Carbohydrates
Lipids
£CPLd
20.0
9.3
21.7
18.4
24.7
9.4
27.2
21.6
Data reported are means of one or more determinations made during
steady-state period.
These VS reductions were calculated according to the following formula:
VSR = 100 X (VSiO - VS0)/[VS1 - (VS± X VS0)J.
c These VS reductions were calculated according the following formula:
VSR = 100 X (wt of product gases)/(wt of VS fed).
ECPL means the sum of the masses of carbohydrates, crude protein, and
lipids.
HRT Effect
Comparing mesophilic acid-digester performances at pH 7 at HRT's of 2.0
and 1.3 days, gas and volatile acids productions, and protein, carbohydrate
and lipid reductions were significantly higher than at the lower HRT
(Table 82). Similar comparison of acid-phase digester performances at pH 5
showed that whereas gas and acid productions at HRT's of 2.0 and 1.3 days were
about the same, protein and lipid reductions were lower at .the lower HRT
(Table 83); carbohydrate conversion at 1.3-day HRT, however, was higher than
that at a 2-day HRT.
167
-------
Oo
i-»
re
0)
{D
S! W
to Ch
OQ Hi
ro
o
01 Pt
|_4
c o
H IX *t>
0) OP
rf (D *o
(D EC
m
O rt O
Mi 3
CO
g-3 §
O K 0)
C !« O !
rt H X)
N> O H-
W It) M
!^ PJ O
TO O*
O p}
< C O
to rt H-
I NJ 3"
CX to
CD D. CO
<<• B) (0
• X
0) p.
H-
(U Oq
am
to
rt
0> H-
O
M 3
O
CO O
3 ce
QQ pp
3
O
ro
n
METHANE
CONTENT,
mo I %
§
o
o
TOTAL GAS AND METHANE
YIELDS, SCM/kg VS added
p p
o — ro
TOTAL VOLATILE ACIDS IN
EFFLUENT, mg/L as acetic
£ o - ro
2 TOTAL GAS AND METHANE PRODUCTION
x RATE, Std vol/vol-day
-------
TABLE 79. EFFECT OF pH ON STEADY-STATE GAS PRODUCTIONS FROM MESOPHILIC
CFCSTR ACID-PHASE DIGESTERS OPERATED WITH HANOVER PARK SLUDGE
AT ABOUT A 1.3-DAY HRTa
Culture pH
Run no .
Operation
Feed VS concentration," mg/L
HRT, days
Loading, kg VS/nH-day
pH-control chemical (2.5N)
pH-control dosage, meq/L feed
Performance
Total gas yield, SCM/kg VS added
Methane Yield, SCM/kg VS added
Gas composition, mol %
Hydrogen
Methane
Carbon dioxide
Nitrogen
Total gas production rate,
SCM/m3-day
Methane production rate,
SCM/m3-day
7.0
AP1.3M7
46, DUO
1.3
34. Ob
NaOH
69.2
0.085
(12)c
0.056
(16)
—
65.3
34.1
0.6
2.889
(9)
1.891
(15)
5.0
AP1.3M5
48,490
1.5
32.76
HC1
52.8
0.062
(23)
0.031
(19)
0.04
50.3
48.9
0.8
2.075
(15)
1.046
(12)
a Data reported are means of all data collected during the steady-
state portion of the run.
Feed VS concentrations are the weighted averages of the various
feed slurry concentrations.
c Numbers in parentheses are the coefficients of variation,
expressed as the percent ratio of the standard deviation to the
mean.
169
-------
TABLE 80. EFFECT OF pH ON STEADY-STATE EFFLUENT QUALITIES OF
MESOPHILIC CFCSTR ACID-PHASE DIGESTERS OPERATED WITH
HANOVER PARK SLUDGE AT ABOUT A 1.3-DAY HRT
Run no.
AP1.3M7
AP1.3M5
Culture pH
Alkalinities, mg/L as CaCOp
Total
Bicarbonate
Volatile acids, mg/L
Acetic
Propionic
Isobutyric
Butyric
Isovaleric
Valeric
Caproic
Total as acetic
Ethanol, mg/L
Nitrogen, mg/L
Aminonia-N
Organic-N
Chemical oxygen demand, mg/L
Total
Filtrate
Solids, mg/L
TS
VS
TSS
VSS
Organic components, mg/L
Crude protein
Carbohydrates
Lipids
7.0
7950
4116
2498
1641
258
536
382
91
0
4648
0
1008
1916
75,480
8973
51,060
35,410
38,370
31,620
11,975
7114
9202
5.0
5660
3872
1140
963
148
565
485
317
22
2889
22
757
2084
60,890
43,200
13,025
10,849
9176
Data reported are means of one or more determinations made
during the steady-state period.
170
-------
TABLE 81. EFFECT OF pH ON STEADY-STATE ORGANIC REDUCTION
EFFICIENCIES OF MESOPHILIC CFCSTR DIGESTERS OPERATED WITH
HANOVER PARK SLUDGE AT ABOUT A 1.3-DAY HRTa
Run no.
AP1.3M7
AP1.3M5
Culture pH
VS reduction,
MOP
16
Wt-of-gas basis0
VSS reduction
COD (total) reduction,
Organic reductions, %
Crude protein
Carbohydrates
Lipids
ECPLd
7.0
27.4
9.6
19.3
7.5
24.6
42.1
21.4
29.0
5.0
0.0
8.1
10.8
20.4
6.6
13.2
a Data reported are means of one or more determinations made
during the steady-state period.
b These VS reductions were calculated according to the
following formula:
VSR = 100 X (VSi - VS0)/[VSi - (VSi X VSQ)].
c These VS reductions were calculated according to the
following formula:
VSR = 100 X (wt of product gases)/(wt of VS fed).
d ECPL means the sum of the masses of carbohydrates, crude
protein, and lipids.
THERMOPHILIC ACID-PHASE RUNS
pH Effects at a Two-Day HRT
Tables 84, 85, 86 and Figure 17 present experimental data collected to
delineate the effects of pH on thermophilic acid-phase digestion of Hanover
Park sewage sludge at an HRT of 2 days. Apparently, optimum thermophilic acid
171
-------
TABLE 82. COMPARISON OF STEADY-STATE PERFORMANCES OF
MESOPHILIC AND THERMOPHILIC ACID-PHASE DIGESTERS
OPERATED WITH HANOVER PARK SLUDGE AT pH 7
HRT, days
Run no.
Culture temperature
NaOH dosage, raeq/L feed
Total gas yield, SCM/kg VS added
Methane yield, SCM/kg VS-day
Methane content, mol %
Total gas production rate, SCM/m -day
Effluent volatile acids, mg/L as acetic
VS reduction, %
MOP16a
Wt-of-gas basisb
Carbon-in-gas basisc
VSS reduction, %
COD (total) reduction, %
Organic reduction f %
Crude protein
Carbohydrates
Lipids
ZCPLd
2
AP2M7
Mesophilic
32.9
0.049
0.035
71.4
1.124
1457
15.3
5.2
4.4
11.8
11.9
20.0
9.3
21.7
18.4
2
AP2T7
Thermophilic
30.5
0.014
0.008
58.6
0.345
3220
3.7
1.6
1.2
2.8
1.8
42.2
48.9
31.1
40.6
1.3
AP1.3M7
Mesophilic
69.2
0.085
0.056
65.3
2.889
4648
27.4
9.6
7.9
19.3
7.5
24.6
42.1
21.4
29.0
1.3
AP1.3T7
Thermophilic
17.6
0.046
0.026
57.2
1.615
4184
5.9
5.9
4.2
17.2
10.5
34.4
22.8
15.2
25.2
These VS reductions were calculated according to the following formula:
VSR - 100 X (VSj - VS0)/[VSi - (VSj X VS0)].
These VS reductions were calculated according to the following formula:
VSR - 100 X (wt of product gases)/(wt of VS fed).
These VS reductions were calculated according to the following formula:
VSR • 100 X (1.84 X wt of carbon in product gas)/(wt of VS fed).
ICPL means the sum of the masses of carbohydrates, crude protein, and lipids.
172
-------
TABLE 83. COMPARISON OF STEADY-STATE PERFORMANCES OF
MESOPHILIC AND THERMOPHILIC ACID-PHASE DIGESTERS
OPERATED WITH HANOVER PARK SLUDGE AT pH 5
HRT, days
Run no.
Culture temperature
HC1 dosage, meq/L feed
Total gas yield, SCM/kg VS added
Methane yield, SCM/kg VS-day
Methane content, mol %
Total gas production rate, SCM/mJ-day
Effluent volatile acids, mg/L as acetic
VS reduction, %
MOPJ6a
Wt-of-gas basis"
Carbon-in-gas basis0
Organic reduction, %
Crude protein
Carbohydrates
Lipids"
ZCPLd
2
AP2M5
Mesophilic
80.9
0.058
0.029
50.1
1.424
2880
5.2
3.5
5.4
24.7
9.4
27.2
21.6
2
AP2T5
Thermophilic
69.5
0.031
0.015
49.1
0.745
3494
7.1
4.0
2.8
22.9 -
13.8
28.0
22.2
1.3
AP1.3M5
Mesophilic
52.8
0.062
0.031
50.3
2.075
2889
0.0
8.1
5.9
10.8
20.4
6.6
13.2
1.3
AP1.3T5
Thermophilic
58.3
0.017
0.009
50.6
0.663
3222
4.8
2.2
1.5
17.0
8.4
23.0
16.8
a These VS reductions were calculated according to the following formula:
VSR • 100 X (VSA - VS0)/[VSf - (VSj X VS0)].
These VS reductions were calculated according to the following formula:
VSR » 100 X (wt of product gases)/(wt of VS fed).
c These VS reductions were calculated according to the following formula:
VSR • 100 X (1.64 X wt of carbon in product gas)/(irt of VS fed).
ECPL means the sum of the masses of carbohydrates, crude protein, and lipids.
173
-------
TABLE 84. EFFECT OF pH ON STEADY-STATE GAS PRODUCTIONS FROM
THERMOPHILIC CFCSTR ACID-PHASE DIGESTERS OPERATED WITH HANOVER PARK
SLUDGE AT ABOUT A 2-DAY HRTa
Culture pH
Run no.
Operation
Feed VS concentration,*5 mg/L
HRT, days
Loading, kg VS/m3-day
pH-control chemical (2.5N)
pH-control dosage, meq/L feed
Performane
Total gas yield, SCM/kg VS added
Methane yield, SCM/kg VS added
Gas composition, mol %
Hydrogen
Methane
Carbon dioxide
Nitrogen
Total gas production rate,
SCM/m3-day
Methane production rate,
SCM/m3-day
7.1
AP2T7
52,750
2.1
25.48
NaOH
30.5
0.014
(24)c
0.008
(22)
—
58.6
38.6
2.8
0.345
(22)
0.202
(20)
6.0
AP2T6
49,960
2.1
24.25
HC1
33.2
0.052
(9)
0.024
(13)
—
46.0
53.2
0.8
'1.251
(9)
0.575
(12)
5.5
AP2T5.5
53,560
2.0
26.13
HC1
58.6
0.024
(21)
0.009
(40)
—
38.4
57.7
3.9
0.499
(25)
0.230
(37)
5.1
AP2T5
49,980
2.1
24.03
HC1
69.5
0.031
(11)
0.015
(11)
o.z
49.1
49.2
1.5
0.745
(10)
0.366
(10)
a Data reported are means of all data collected during the steady-state
portion of the run.
Feed VS concentrations are the weighted averages of the various feed slurry
concentrations.
c Numbers in parentheses are the coefficients of variation, expressed as the
percent ratio of the standard deviation to the mean.
174
-------
TABLE 85. EFFECT OF pH ON STEADY-STATE EFFLUENT QUALITIES
OF THERMOPHILIC CFCSTR ACID-PHASE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE AT ABOUT A 2-DAY HRT*
Culture pH
Run no.
Alkalinities, mg/L as CaCO^
Total
Bicarbonate
Volatile acids, mg/L
Acetic
Propionic
Isobutyric
Butyric
Isovaleric
Valeric
Caproic
Total as acetic
Ethanol, mg/L
Nitrogen, mg/L
Ammonia-N
Organic-N
Chemical oxygen demand, mg/L
Total
Filtrate
Solids, mg/L
TS
VS
TSS
VSS
Organic components, mg/L
Crude protein
Carbohydrates
Lipids
7.1
AP2T7
8900
5680
1445
986
336
461
686
50
0
3220
11
980
1370
81,120
10,820
72,245
49,745
67,030
46,430
7870
6934
9735
6.0
AP2T6
_—
—
2171
1219
326
580
652
89
24
4223
0
—
—
—
—
—
—
—
— —
—
—
5.5 5.1
AP2T5.5 AP2T5
3000
1255
1944 1976
1229 845
220 177
833 376
412 734
144 43
19 1
3994 3494
24 86
959
2204
__ __
— —
57,710
43,260
— —
— —
13,775
9943
10,539
Data reported are means of one or more determinations made during the
steady-state period.
175
-------
TABLE 86. EFFECT OF pH ON STEADY-STATE ORGANIC REDUCTION EFFICIENCIES
OF THERMOPHILIC CFCSTR ACID-PHASE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE AT ABOUT A 2-DAY HRTa
Culture pH
7.1
6.0
5.5
5.1
Run no.
VS reduction, %
Wt-of-gas basis1-
VSS reduction
COD (total) reduction, %
Organic component reduction,
AP2T7
3.7
1.6
2.8
1.8
AP2T6
AP2T5.5
7.0
3.1
AP2T5
7.1
4.0
Crude protein
Carbohydrates
Lipids
ECPLd
A2.2
48.9
31.1
40.6
22.9
13.8
28.0
22.2
a Data reported are means of one or more determinations made during steady-
state period.
These VS reductions were calculated according to the following formula:
VSR = 100 X (VS-jO - VSQ)/[VSi - (VSi X VS0)].
c These VS reductions were calculated according the following formula:
VSR = 100 X (wt of product gases)/(wt of VS fed).
° ECPL means the sum of the masses of carbohydrates, crude protein, and
lipids.
176
-------
100
_ 50
g 0
O
OCO Q) n ,
ZQ1J 0.1
LU D
O-CO
O >0.05
LU
_JZ 0>
0
TOTAL GAS
PRODUCTION
RATE
METHANE
PRODUCTION-
RATE
TOTAL GAS
YIELD
0
-P
4000 o
D
(0
D
_
D)
3000
h-
LJ
L_
U_
LU
2000
1000
CO
Q
»— i
O
<
LU
_l
n
O
<
o
I-LUO
HO)
6
pH
o
HH
O
D
0
2°- -5
LU >
Z\
X 0
I- >
LU
2IT5
QCO
.i ,
CO
COLU
CD<
o:
O
A85070600H
Figure 17. Effect of pH on thermophilic acid-phase digestion of
Hanover Park sewage sludge at an HRT of about 2.1 days and a
loading rate of about 25 kg VS/m3-day.
177
-------
digester performance was obtained at a pH of 6. Protein, carbohydrate, and
lipid degradations were higher at pH 7 than at pH 5; volatile acids production
at these two pH's were about the same. The depressed hydrolytic activities at
pH 5 may have resulted due to the presence of hydrogen in the gas phase at pH
5. The presence of hydrogen indicated that the production of this gas was
greater than its removal by the hydrogen-utilizing methanogens. This
observation could be indicative of the fact that hydrogen-oxidizing
thermophilic methane bacteria are inhibited at pH 5.
Crude protein and carbohydrate reduction were much lower at pH 5 than
they were at pH 7; however, lipid degradation were about the same at these two
pH's.
pH Effect at an HRT of 1.3 Days
Data reported in Tables 87, 88, and 89 show that at a 1.3-day HRT gas and
methane production at pH 5 were significantly lower than those at pH 7. These
results suggest that the activities of the syntrophic methane formers were
depressed under thermophilic conditions at a pH of 5. The presence of
hydrogen in the gas phase at pH 5 attests to this hypothesis.
Table 88 indicates that protein, carbohydrate, and SCPL reductions were
lower, but lipid conversion was higher at pH 5 than they were at pH 7.
Volatile acids production at pH 7 was significantly greater than that at pH 5.
HRT Effect
Comparing thermophilic acid-digester performances at pH 7 at HRT's of 2.0
and 1.3 days, gas and volatile acids productions were higher at 1.3 days,
although organic reductions were lower at the lower HRT (Table 82). Similar
comparison at pH 5 showed that the thermophilic acid-ndigester performance
deteriorated significantly when the HRT was decreased from 2.0 to 1.3 days
(Table 83). At pH 5 gas and volatile acids productions and organic reductions
were lower at a 1.3-day HRT than they were at a 2-day HRT.
EFFECT OF TEMPERATURE ON ACID-PHASE DIGESTION
Consideration of data presented in Tables 82 and 83 indicated that at a
2-day HRT, the thermophilic acid digester exhibited higher liquefaction-
acidification efficiency than the mesophilic acid digester at both pH 7 and pH
5. The same was also true at an HRT of 1.3 days at pH 5, but not at pH 7. At
pH 7 and a 1.3-day HRT the mesophilic acid digester exhibited slightly higher
volatile acid production, and carbohydrate and lipid reductions than the
thermophilic acid digester. It is noteworthy that gas and methane productions
from the thermophilic acid digester were lower than those of the mesophilic
acid digester under all operating conditions. Thus, the activities of the
thermophilic syntrophic methanogens were considerably lower than those of
their mesophilic counterparts. It is speculated that thermophilic metabolites
of sludge organics could be instrumental in depressing the activities of the
syntrophic methanogens.
178
-------
TABLE 87. EFFECT OF pH ON STEADY-STATE GAS PRODUCTIONS
FROM THERMOPHILIC CFCSTR ACID-PRASE DIGESTERS OPERATED
WITH HANOVER PARK SLUDGE AT ABOUT A 1.3-DAY HRTa
Culture pH
Run no .
Operation
Feed VS concentration,'3 mg/L
HRT, days
0
Loading, kg VS/mJ-day
pH-control chemical (2.5N)
pH-control dosage, meq/L feed
Performance
Total gas yield, SCM/kg VS added
Methane yield, SCM/kg VS added
Gas composition, mol %
Hydrogen
Methane
Carbon dioxide
Nitrogen
Total gas production rate,
SCM/m3-day
Methane production rate,
SCM/m3-day
7.0
AP1.3T7
47,900
1.3
36.02
NaOH
17.6
0.046
(24)c
0.026
(25)
—
57.2
41.8
1.0
1.615
(15)
0.923
(16)
5.0
AP1.3T5
51,140
1.3
38.74
HC1
58.3
0.017
(13)
0.009
(14)
0.4
50.6
45.6
2.4
0.664
(14)
0.335
(14)
a Data reported are means of all data collected during the steady-state
portion of the run.
Feed VS concentrations are the weighted averages of the various feed
slurry concentrations.
c Numbers in parentheses are the coefficients of variation, expressed
as the percent ratio of the standard deviation to the mean.
179
-------
TABLE 88. EFFECT OF pH ON STEADY-STATE EFFLUENT QUALITIES OF
THERMOPHILIC CFCSTR ACID-PHASE DIGESTERS OPERATED WITH
HANOVER PARK SLUDGE AT ABOUT A 1.3-DAY HRT*
Culture pH
7.0
5.0
Run no.
Alkalinities, mg/L as CaCC?
Total
Bicarbonate
Volatile acids, mg/L
Acetic
Propionic
Isobutyric
Butyric
Isovaleric
Valeric
Caproic
Total as acetic
Ethanol, mg/L
Nitrogen, mg/L
Ammonia—N
Organic-N
Chemical oxygen demand, mg/L
Total
Filtrate
Solids, mg/L
TS
VS
TSS
VSS
Organic components, mg/L
Crude protein
Carbohydrates
Lipids
AP1.3T7
8625
5079
1756
1306
416
689
984
66
0
4184
1308
1582
68,400
10,070
53,410
40,340
36,910
30,400
9885
9036
9451
AP1.3T5
4915
2227
1946
786
162
405
312
101
18
3222
85
916
2398
60,860
45,170
14,988
10,595
11,466
Data reported are means of one or more determinations made
during the steady-state period.
180
-------
TABLE 89. EFFECT OF pH ON STEADY-STATE ORGANIC REDUCTION EFFICIENCIES
OF THERMOPHILIC CFCSTR DIGESTERS OPERATED WITH HANOVER PARK SLUDGE
AT ABOUT A 1.3-DAY HRTa
Culture pH
7.0
5.0
Run no.
VS reduction, %
Wt-of-gas basis1-
VSS reduction
COD (total) reduction,
Organic reductions, %
Crude protein
Carbohydrates
Lipids
ECPLd
AP1.3T7
5.9
5.9
17.2
10.5
34.4
22.8
15.2
25.2
AP1.3T5
4.8
2.2
17.0
8.4
23.0
16.8
a Data reported are means of one or more determinations
made during the steady-state period.
These VS reductions were calculated according to the
following formula:
VSR - 100 X (VSi - VS0)/[VS.j_ - (VSi X VS0)].
c These VS reductions were calculated according to the
following ^formula:
VSR = 100 X (wt of product gases)/(wt of VS fed).
j
a ECPL means the sum of the masses of carbohydrates, crude
protein, and lipids.
ANALYSIS OF VARIANCE AND STATISTICAL INFERENCE
As mentioned in a previous section, the acid-phase parametric-effect
studies were conducted according to a factorial experiment design to explore
the effect of the control (or treatment) variables (or factors) of culture
temperature, pH, and HRT on such observable response variables or variates as
gas yield, gas production rate, volatile acid production, and reductions of
major organic components (e.g., carbohydrates, proteins and lipids) at steady
181
-------
state. Temperature was set at levels of 35°C and 55°C, pH at 5 and 6, and HRT
at 2 days and 1.3 days. There were eight treatments (or runs), each at a
different combination of the control variables. Two to 12 replicates of each
variate at steady state were considered for each run. The results of analysis
of variance (ANOVA) of the steady-state acid-phase digestion data are shown in
Tables 90 and 91. The ANOVA results may be interpreted as follows:
• The culture pH appeared to have a strong effect on carbohydrate, crude
protein, lipid, and ECPL (sum of the carbohydrate, protein and lipid
masses) reduction efficiencies almost regardless of the levels of the
other variables (temperature and HRT in this case). The effect of
increasing the culture pH from 5 to 7 was to increase carbohydrate,
protein, lipid and ECPL reductions by about 19, 14, 14 and 23 percentage
points, respectively. It should be noted, however, that the above ANOVA
analysis does not identify the existence of a probable optimum pH lying
between the values of 5 and 7.
• Increases in culture temperature and digester HRT both tended to increase
carbohydrate reduction; however, the effects of these two control
variables cannot be viewed independently because of the large interaction
effect.
• Increase in HRT tended to increase protein reduction, but the HRT effect
was influenced strongly by the culture pH.
• Temperature had no significant effect on lipid reduction.
• Increase in HRT from 1.3 to 2 days increased lipid reduction by about 13
percentage points. The HRT effect was not influenced by pH or
temperature.
• Increases in temperature and HRT increased ZCPL reduction, but effects of
these control variables cannot be separated.
• The digester HRT, temperature, and culture pH, each independently
influenced the acid-digester gas yield. The gas yield decreased as the
digester HRT and culture temperature increased, and it increased as the
culture pH was increased.
• The digester temperature independently acted on the acid-phase gas pro-
duction rate, which decreased substantially (by 1.04 vol/culture vol-day)
as the temperature was increased from 35°C to 55°C.
• The effects of pH and HRT on acid-digester gas production could not be
separated because of the large pH-HRT interaction effect. However, an
increase in pH tended to increase the gas production rate. On the other
hand, an increase in HRT decreased gas production rate.
• An increase in HRT increased the methane content of the acid-digester
gas, regardless of the levels of pH and temperature. Increases in pH and
temperature seemed to have the effect of increasing the methane content,
but the effects of these variables cannot be viewed separately.
182
-------
TABLE 90. RESULTS OF ANALYSIS OF VARIANCE (ANOVA) OF ACID-PHASE DIGESTION STEADY-STATE DATA
TO ASSESS THE EFFECTS .OF THE CONTROL VARIABLES OF CULTURE TEMPERATURE, pH,
AND HRT ON REDUCTIONS OF CARBOHYDRATES, PROTEIN, AND LIPIDS
Source of
Carbohydrate reduction, % Mean
Treatmemts
> Error
L/ Protein reduction, X Mean
P^ Treatments
Error
Llpid reduction, X Mean
Treatments
Error
ECPL* reduction, 2 Mean
Treatments
Error
Sum of
8710.66
4699.13
437.90
9818.09
1204.40
15.10
5572.35
500.04
15.68
35,397.30
4099.62
79.62
1
7
11
1
7
7
1
7
3
1
7
43
1.71
39
172
2
71
5
585
1
.1(1
.HI 16.86
_
.06
.16 79. 7«
—
.43
.21 13.67
—
.66
,85 116.29
—
1.01
—
—
3.79
—
—
8.89
—
—
2.24
Control
Temp, °C
PH
HRT, day;
Temp, °C
PH
IIRT, day;
Temp, °C
pll
HRT, days
Temp, °C
pll
HRT, days
Main
11.47
19.48
6.1!
11.30
13.92
7.68
1.43
14.17
13.16
11.67
21.10
17.84
95Z confidence
5.06 to 17.88
13.07 to 25.89
-0.09 to 12.72
9,50 to 13.11
12.11 to 15.73
5.87 to 9.49
-2.88 to 5.73
9.87 to 18.48
8.85 to 17.46
10.90 to 12.44
22.54 to 24.07
17.07 to 18.60
Temp-pH
Temp-IIRT
pH-HRT
Temp-pH
Temp-HRT
pH-HRT
Temp-pH
Temp-HRT
pH-HRT
Temp-pH
Temp-IIRT
pH-HRT
Interaction
7.60
18.98
U40
6.05
-0.02
-5.71
-4.80
5.50
3.85
4.48
15.59
6.22
951 confidence
1.19 to 14.01
12.57 to 25.39
-5.00 to 7.81
4.24 to 7.86
-1.83 to 1.78
-7.52 to -3.90
-9.11 to -0.49
1.20 o 9.81
-0.45 o 8.16
3.71 o 5.25
14.82 o 16.36
5.45 o 6.98
If zero is contained within the confidence interval, it indicate? that thp effect IB not significant at the ">% level.
ZCPL means the sum of the masses of carbohydrate, crude protein, and liplds.
Reproduced from
best available copy.
-------
TABLE 91. RESULTS OF ANALYSIS OF VARIANCE (ANOVA) OF ACID-PHASE DIGESTION STEADY-STATE
DATA TO ASSESS THE EFFECTS OF THE CONTROL VARIABLES OF CULTURE TEMPERATURE, pH, AND
HYDRAULIC RESIDENCE TIME (HRT) ON TOTAL GAS YIELD, GAS PRODUCTION RATE, AND METHANE CONTENT
oc
Response
Source of
variable variance
Total gas yield, Mean
SCM/kg VS added Treatments
Error •
Total gas production rate, Mean
SCM/m3-day Treatments
Error
Methane content, nol X Mean
Treatementa
Error
Sum of
squares
0.0989
0.0247
0.0016
88.702
29.216
1.070
128,460.00
2038.37
235.21
Degrees of Mean
freedom square
1
7
40
1
7
40
1
7
32
0.0035
0.000039
4.174
0.027
291.20
7.92
Computed
F
90.60
155.999
36.80
F-crltical
a - 0.05
2.25
2.25
2.32
Control
variable
Temp, °C
PH
HRT, days
Temp, 'C
PH
HRT, days
Temp, °C
pH
HRT, days
Main
effects
-0.0369
0.0063
-0.0148
-1.036
0.266
-0.901
8.55
18.28
29.01
Response variable
Total gas yield,
SCM/kg VS added
Total gas production rate,
SCM/m3-day
Methane content, mol X
95% confidence
limits
-0.0406 to
0.0027 to
-0.0184 to
-0.132 to
0.171 to
-0.997 to
6.74 to
16.47 to
27.20 to
-0.0333
0.0099
-0.0112
-0.941
0.362
-0.806
10.36
20.09
30.82
Interactions
Temp-pH
Temp-HRT
pH-HRT
Tenp-pH
Terap-IIRT
pH-HRT
Temp-pH
Temp-HRT
pH-HRT
Interaction
effect
-0.0007
0.0059
-0.0198
0.011
0.307
-0.616
13.57
4.92
15.09
951 confidence
limits*
-0.0044 to
0.0026 to
-0.0234 to
-0.085 to
0.212 to
-0.712 to
11.76 to
3.11 to
13.28 to
0.0029
0.0095
-0.0162
0.106
0.402
-0.521
15.38
6.73
16.9
* If zero Is contained within the confidence Interval, It Indicates that the effect is not significant at the 5% level.
-------
• Increases in temperature, pH and HRT increased volatile acids productions
by acid-phase digestion, but the independent effects of these variables
cannot be ascertained separately.
The above interpretations of the ANOVA analysis suggested that enhanced
hydrolysis of the major organic components of sludge may not be achieved at
the lower pH, HRT, and temperature of 5, 1.3 days, and 35°C, respectively.
The analysis also suggested that the acidification process, which follows
hydrolysis, was also not the most efficient at pH 5, 35°C, and a 1.3-day
HRT. According to the ANOVA results, hydrolysis and acidification
efficiencies were higher at the thermophilic temperature and at a pH higher
than 5. This is in agreement with discussions presented in the earlier
sections which indicated that a pH of about 6 would be optimum for these
reactions; this pH appeared to be optimum also for maximized gas production
rate and gas yield. The statistical analysis indicated that a thermophilic
temperature and a pH 5 decreased gas yield and gas production rate; this
inference suggested that the syntrophic methane formers were probably
inhibited under these operating conditions. Similar conclusions were also
drawn from the results of the single-stage CFCSTR and two phase digestion
studies.
185
-------
SECTION 15
ADVANCED TWO-PHASE DIGESTION TESTS: APPLIED STUDIES
TWO-PHASE PROCESS IMPROVEMENT WITH NOVEL UPFLOW REACTORS
As discussed in detail in Section 4 of this report, the application of a
high-SRT reactor — that is, a reactor in which the SRT is considerably longer
than the HRT — has the effect of significantly enhancing the substrate con-
version efficiency relative to that achieved with a CFCSTR digestion reactor
in which SRT equals HRT. It is also important to note that there are only a
few anaerobic reactor designs which can promote efficient digestion of
particulate solids and simultaneously effect prolonged retention of microbial
and substrate solids to exhibit high SRT's. Bioreactors that provide
efficient solids retention may also experience short-circuiting, creation of
dead zones, and accumulation of unreacted solids. Thus, the benefits of
having high SRT's could be readily neutralized by the detrimental effects of
short-circuiting, dead zones, and the accumulation of biologically inert
solids if an appropriate reactor design is not utilized. Since little work
has been done on characterizing novel reactor performance, guidelines for the
design of appropriate high-SRT reactors for acid- and methane-phase digestion
of wastewater sludge were not available. Consequently, the reactor develop-
ment approach utilized in the applied studies was an empirical one and
involved the design, construction, and testing of an innovative biodigester
that incorporated structural and operating features which were expected to
promote solids retention, and to exhibit higher sludge stabilization
efficiencies than the CFCSTR digester.
The innovative digesters utilized in the applied studies were of the
upflow type. This particular type of bioreactor was used for acid- and
methane-phase digestion of a difficult-to-treat wastewater sludge in a
previous research project, and exhibited better performance than the CFCSTR
digesters.23 The upflow digesters used in the applied studies were improved
versions of the earlier design which provided for a vertical standpipe feed
inlet and a canopy solids deflector directly above it. As described in detail
in Section 6, the acid digester (Digester 338) incorporated the above
mentioned features, and in addition, included vertical baffles and hoppered
bottoms to facilitate the containment of floating scum and the controlled
withdrawal of a volatile acids-rich underflow stream that was pumped to the
methane digester. The upflow methane digester (Digester 339) included static
horizontal ring baffles and rotating impellers between them to minimize short
circuiting, and to achieve plug-flow characteristics. Provisions were made to
recycle methane digester effluents to the acid digester to promote hydrogen
removal.
186
-------
Optimum Operating Conditions for Two-Phase Digestion
Information compiled from the process-comparison and the parametric-
effect acid-phase runs (Sections 11 through 14) was used to select the optimum
operating conditions for the advanced two-phase run. A mesophilic temperature
was preferred to the thermophilic temperature which was found to inhibit
acetogenic and methanogenic conversions (see Section 13). However, thermo-
philic digestion studies were also conducted after termination of the meso-
philic run to investigate the feasibility of thermophilic two-phase digestion
with high-SRT digesters. An HRT of 7 days and a feed VS concentration of
about 50 g/L were selected for the advanced two-phase run because the process-
comparison studies indicated this HRT-feed-VS concentration combination to be
optimum from the viewpoint of methane production and solids stabilization.
HRT's of about 2 and 5 days were selected for the acid- and methane-phase
digesters. Based on the information collected from the parametric-effect
acid-phase runs, a pH of about 6.5 was regarded as optimum for sludge acido-
genesis. Since this pH is "naturally" obtained during sludge acidogenesis,
the need for pH control with external chemicals entailing added operating cost
was ruled out.
Mesophilic Two-Phase Digestion With Upflow Reactors
A two-phase system comprised of the upflow acid- and methane-phase
digesters described above was operated under the optimum digestion conditions
delineated in the foregoing section. The upflow two-phase system was operated
for about 2.5 months at a mesophilic temperature and at a system HRT of about
7.5 days (Table 92). Steady-state operating conditions and performance
characteristics of the upflow acid and methane digesters are detailed in
Tables 92, 93, and 94.
Conventional CFCSTR digesters are generally operated for about three
HRT's at steady state once constant performance levels are reached. Since no
such criterion was available for unconventional reactors, the upflow acid- and
methane-phase digesters were operated for about 36 and 13 HRT's, respectively,
to ensure the achievement of steady state. The variabilities of total gas and
methane yields, production rates, and volatile acid productions during a
37-day period of operation of the upflow two-phase system were comparable to
those of the CFCSTR two-phase and the CFCSTR single-stage runs at steady state
(see Tables 93 and 94). These variabilities were indicative of the fact that
the upflow system was at steady state — variabilities of acid digester gas
yields and methane digester effluent volatile acids were rather high due to
the low levels of these parameters and the associated inaccuracies and poor
precision of measurements. Achievement of a steady-state operation of the
upflow digesters was also indicated by the constancy of the volatile acids
profiles in the acid- and methane-phase digesters (Table E-2).
The upflow two-phase system treatment resulted in a methane yield of
0.352 SCM/kg VS (5.64 SCF/lb VS) added which was higher than those of other
CFCSTR two-phase runs. This methane yield was 70% of the theoretical methane
yield. The upflow system gas yield was 87% of the ADP yield indicating nearly
complete conversion of the biodegradable VS. As indicated in Table 93, the
methane yield of the CFCSTR two-phase process was 37% higher than that of
187
-------
TABLE 92. STEADY-STATE OPERATING CONDITIONS FOR ADVANCED UPFLOW TWO-PHASE
DIGESTION RUNS CONDUCTED WITH HANOVER PARK SLUDGE
Upflow acid phase
Mesophilic
Mesophtllc
Upflow methane phase
Digester
Run no. no.
UAP2HR* 338
UAP2M 338
Mean
temperature , °C
35.4 (3)1
36.0 (3)
Mean
HRT, days
2.0 (12)
2.3 (19)
Mean loading,
kg VS/m3-day
26.1 (13)
21.4 (19)
Mesophllic UMP5M
Meso-meso two-phase
System (UAP2MR and UMP5M) UTP7M-M
339 33.8 (3) 5.5 (11) 9.35 (11)
7.5 (11) 6.87 (11)
oo
oo
Upflow acid phase
Mesophilic
Mesophillc
Upflow methane phase
Feed total solids
concentration, g/L
67.6
68.4
Feed volatile solids
concentration, g/L
51.3
49.9
Total run
duration, days
73
60
Steady-state run
duration, days
37
41
Mesophilic
Meso-meso two-phase
System (UAP2MR and UMP5M)
67.6
51.3
73
73
37
37
Methane-phase effluent from acid-phase run UAP2MR was recycled to this acid-phase digester at
a rate of about 35 vol % of the system feed rate.
Numbers in parentheses are the coefficients of variation, expressed as the percent ratio of standard
deviation to the mean.
-------
TABLE 93. COMPARISON OF STEADY-STATE GAS PRODUCTIONS FROM MESO-MESO UPFLOW
TWO-PHASE, MESO-MESO CFCSTR TWO-PHASE AND MESOPHILIC CFCSTR SINGLE-STAGE SYSTEMS
OPERATED WITH HANOVER PARK SLUDGE AT ABOUT A 7-DAY HRT*
Upflow two-phase t
Run number
Operation
Feed VS concentration, mg/L4
HRT, days
Loading, kg VS/nr-day
Performance
Total gas yield,
SCM/kg VS added
Methane yield,
SCM/kg VS added
Gas composition, mol %
Hydrogen
Methane
Carbon dioxide
Nitrogen
Total gas production
rate, SCM/n^-day
Methane production rate,
SCM/m3-day
Acid
digester
UAP2MR
51,320
2.0
26.13
0.144
(24)**
0.083
(25)
0.4
57.7
41.2
0.7
3.256
(16)
1.874
(17)
Methane
digester
UMP5M
—
5.5
9.35
0.400
(12)
0.269
(12)
0.0
67.4
32.2
0.4
3.359
(10)
2.263
(10)
System
UAP7M-M
—
7.5
6.87
0.544
(16)
0.352
(15)
64.8
34.6
0.5
3.332
(12)
2.160
(12)
CFCSTR two-phase
Acid
digester
51,000
1.9
26.38
0.157
(16)
0.091
(16)
0.0
57.1
42.5 '
0.4
4.063
(5)
2.343
(5)
Methane
digester System
TP7M-M
—
4.9
10.08
0.310
(ID
0.212
(12)
68.2
31.6
0.2
3.089
(5)
2.100
(5)
~
6.8
7.29
0.467
(12)
0.302
(13)
64.7
35.1
0.2
3.358
(4)
2.173
(4)
CFCSTR
single-stage
SSS7M
52,220
7.0
7.51
0.318
(13)
0.220
(16)
69.1
30.6
0.3
2.327
(12)
1.609
(13)
t
t
Data reported are means of all data collected during the steady-state period.
In this upflow mode of operation acid-phase underflow was 12 vol % of the system flow rate. Also, methane
digester effluents were recycled to the acid digester at the rate of 35 vol % of the system flow rate.
+ Feed VS concentrations are weighted averages of the various feed slurry concentrations.
Numbers in parentheses are the coefficients of variation, expressed as the percent ratio of standard deviation
to the mean.
189
-------
TABLE 94. COMPARISON OF STEADY-STATE EFFLUENT QUALITIES OF MESO-MESO UPFLOW
TWO-PHASE, MESO-MESO CFCSTR TWO-PHASE, AND MESOPHILIC SINGLE-STAGE SYSTEMS
OPERATED WITH HANOVER PARK SLUDGE AT ABOUT A 7-DAY HRT*
Upf low two-phase '
Acid Acid
digester digester
overflow underflow
Run number
HRT, days
Effluent, pH
Alkalinities, mg/L as CaCO^
Total
Bicarbonate
Volatile acids, mg/L
Acetic
Propionic
Iso-butyric
Butyric
Iso-valeric
Valeric
Caproic
Total as acetic
Ethanol, mg/L
Nitrogen, mg/L
Ammonia-N
Organic-N
Solids, mg/L
TS
vs
Organic components, mg/L
Crude protein
Carbohydrates
Lipids
6.77
8325
7020
1277
1147
266
377
581
192
37
3118
(16)**
4
1269
2000
60,150
42,980
12,500
9259
2.0
6.66
8480
5384
2438
1518
425
1024
688
361
31
5289
(18)
18
1185
2285
70,260
51,920
14,281
11,661
Methane
digester"1"
UMP5M
5.5
7.29
9415
9248
145
180
0
0
0
3
4
295
(51)
0
1378
1891
59,640
39,790
11,819
5650
4849
CFCSTR Two-phase
Acid Methane
digester digester*
1.9
6.63
7475
6368
721
728
109
160
136
61
31
1627
(15)
0
918
^241
60,720
42,480
14,006
7791
7178
4.9
7.30
8100
8068
63
29
0
0
0
10
33
109
(44)
0
1049
1845
50,690
32,810
11,531
4932
3824
CFCSTR
single-stage
SS7M
7.0
7.06
6368
6196
164
104
0
0
0
0
0
248
(29)
' 3
728
1966
64,350
39,585
10,427
7014
11,389
* Data reported are means of one or more determinations made during the steady-state period.
^ In this upflow mode of operation acid-phase underflow was 12 vol % of the system flow rate. Also, methane
digester effluents were recycled to the acid digester at the rate of 35 vol % of the system flow rate.
* Numbers in parentheses are coefficients of variation, expressed as the percent ratio of standard deviation
to the mean.
** System effluent qualities are the same as those of the methane digester.
190
-------
single-stage CFCSTR digestion under similar operating conditions showing the
beneficial effect of the phase-separated fermentation mode. Similarly, the
methane yield of the upflow two-phase process was about 17% higher than that
of CFCSTR two-phase high-rate digestion. This additional increase in methane
yield could be attributed to the reactor effect. Other notable performance
characteristics of the upflow two-phase process were as follows:
• The upflow acid digester gases contained hydrogen gas and a higher
concentration of nitrogen gas than the CFCSTR acid digester. The
presence of hydrogen gas in the upflow acid digester indicated that there
was no acetogenic activity in this reactor. Hydrolysis and acidification
were the major reactions in the upflow acid digester.
• Volatile acids production in the upflow acid digester was much higher
than that in the CFCSTR acid digester (Table 95); acids concentrations in
the underflow were about double those in the overflow. Increased acids
production in the upflow acid digester was due to the fact that this
reactor had an SRT which was considerably higher than that of the CFCSTR
digester.
• The upflow acid and methane digesters developed bicarbonate alkalinities
which were considerably higher than those of the CFCSTR digesters, and
therefore was less prone to upsets owing to organic overloads.
• The upflow two-phase digestion process effected much higher protein,
carbohydrate, and lipid reduction than the CFCSTR two-phase digestion
process (Table 96).
Data presented in Table 95 showed that the right (or second) chamber of
the acid digester accumulated Co and higher volatile acids in larger concen-
trations than the first chamber. This observation suggests that the
hydrolysis and liquefaction processes continued to be operative in the second
chamber indicating effective utilization of the entire digester.
Volatile acids concentration profile in the upflow methane digester
showed that acetate as well as the higher acids were readily converted to
their respective end-products within the bottom one-half of the culture depth.
Acetogenesis, aceticla(stic methane formation, and syntrophic methane fermenta-
tion were the predominant reactions in the upflow methane digester.
Effect of Inter-Phase Effluent Recycling
The steady-state upflow two-phase run discussed above was conducted with
methane-phase effluents recycled to the feed side of the acid-phase digester.
The intent of the recycle was to promote removal of hydrogen (or electron
flow) and substrate oxidation to produce volatile acids or their precursors.
Hydrogen is removed by reduction of sulfates, nitrates/nitrites, and carbon
dioxide with the production of sulfides, and nitrogen and methane gases by the
sulfate-reducing, denitrifying, and hydrogen-utilizing syntrophic methane
bacteria. Steady-state data reported in Table 97 show that for similar
operating conditions, methane and nitrogen yields and production rates in the
acid digester were much higher when methane digester effluents were recycled
191
-------
TABLE 95. STEADY-STATE pH, OR?, AND VOLATILE ACIDS AND ETHANOL CONCENTRATION PROFILES IN
MESO-MESO UPFLOW TWO-PHASE DIGESTERS OPERATED WITH HANOVER PARK SLUDGE AT ABOUT A 7-DAY HRT*
VO
NJ
(
pH
ORP, mV
Volatile acids, mg/L
Acetic
Propionic
Iso-butyric
Butyric
Iso-valeric
Valeric
Caproic
Total as acetic
Ethanol, mg/L
Left chamber
^influent side)
—
—
i
2576
1282
314
990
368
218
39
4870
89
Underflow
(right chamber
on effluent side)
6.66
-234
2438
1518
425
1024
688
361
31
- 5289
18
Overflow
6.77
-241
1277
1147
266
377
581
192
37
3118
4
Bottom
port
—
—
3
0
0
0
0
0
0
3
0
11.5-L
port
7.29
-327
173
290
0
0
0
3
4
412
0
15.5-L
port
—
—
211
311
0
0
0
3
4
467
0
Effluent
(19-L port)
7.29
-371
145
180
0
0
0
3
4
295
0
Data reported are means of all determinations made during the steady-state period.
-------
TABLE 96. COMPARISON OF STEADY-STATE ORGANIC REDUCTION EFFICIENCIES OF MESO-
MESO UPFLOW TWO-PHASE, MESO-MESO CFCSTR TWO-PHASE, AND MESOPHILIC SINGLE-
STAGE SYSTEMS OPERATED WITH HANOVER PARK SLUDGE AT ABOUT A 7-DAY HRTa
ID
LO
Up flow tw«
HRT
VS
, Days
reduction, %
MOPjgC
Wt-of-gas baslsd
Carbon-in-gas basis
Based on the theoretical
gas yield i
Biodegradable VS reduction^
Acid
digester
2.0
14.1
14.6
11.8
13.4
23.0
o-phaseu
Methane
digester
5.5
21
37
33
37
64
.2
.1
.1
.1
.0
System
CFCSTR two-phase
Acid
digester
UTP / M— M
7.5
32
51
44
50
87
.3
.7
.9
.5
.0
1.9
15.7
18.1
14.3
14. ft
25.1
Methane
digester
4.9
21.2
33.4
28.5
28.8
49.6
System
6
3}
51
42
43
74
.8
.6
.5
.8
.3
.7
CFCSTR
single-stage
7.0
18.3
32.7
28.8
29.5
5U.9
Reduction of organic components, %
Crude protein
Carbohydrates
Lipids
£CPLh
29.0
29.0
37.8
32.0
7
36
49
28
.0
.4
.1
.3
34
54
68
51
.0
.8
.4
.2
9.6
29.1
28.2
20.6
17.7
36.6
4h.7
30.0
25
55
61
44
.6
.1
.8
.4
26.2
2h.4
40.0
32.4
Data reported are means of one or more determinations made during the steady-state period.
Methane phase effluents were recycled to the 'acid-phase digester at A rate of 35 vol X of the system feed rate.
c These VS reductions were calculated according to the following formula: VSR = 100 X (VSj - VS^/lv^ - (VSj X VSQ)) .
These VS reductions were calculated according to the following fornula:
VSR = 100 X (wt of product gases)/
-------
TABLE 97. COMPARISON OF STEADY-STATE GAS PRODUCTIONS FROM MESOPHILIC
UPFLOW ACID-PHASE DIGESTION OF HANOVER PARK SLUDGE WITH AND WITHOUT
METHANE-PHASE EFFLUENT RECYCLE
Run number
Operation
Feed VS concentration, mg/L
HRT, days
Loading, kg VS/nr-day
Performance
Total yield, SCM/kg VS added
Methane yield, SCM/kg VS added
Gas composition, mol %
Hydrogen
Methane
Carbon dioxide
Nitrogen
Mesophilic
without
recycle
UAP2M
49,900
2.3
21.36
0.090
0.052
57.7
41. -8
0.5
Mesophilic
with
recycle
UAP2MR
51,320
2.0
26.13
0.144
0.083
0.4
57.7
41.2
0.7
Total gas production rate,
SCM/m3-day
Methane production rate,
SCM/ra3-day
Nitrogen production rate,
SCM/m3-day
1.928
1.112
0.0096
3.256
1.874
,0.0228
Methane phase effluent was recycled to the acid-phase digester
at 35% of the system feed rate.
Feed VS concentration are weighted averages of the various feed
slurry concentrations.
194
-------
to it than those observed without such recycle. Data presented in Table 98
show that the rates of volatile acids production with methane-phase effluent
recycle were higher than those obtained without recycle. These observations
strongly suggested that methane-digester effluent recycling accelerated
hydrolysis and acidification of the sludge solids.
Thermophilic Two-Phase Digestion With Innovative Upflow Reactors
Thermophilic Acid-Phase Digestion—
Upon termination of the mesophilic runs, the upflow acid-phase digester
was acclimated to a thermophilic temperature; the overflow effluents from the
acid digester were fed to the upflow thermophilic methane digester. Methane
digester effluents were not recycled to the acid digester, as it was during
the mesophilic operation. Operating data from three consecutive acid-phase
runs at a 2-day HRT are presented in Tables 99 and 100 and show that gas and
methane productions and gas-phase methane contents under thermophilic
conditions were much lower than those under mesophilic conditions.
Examination of the volatile acids production data for acid-phase Runs UAP2T,
UAP2.1T and UAP1.9T shows that although thermophilic acids production during
the initial Run UAP2T was higher than that at the mesophilic temperature, the
volatile acid yields dropped upon continued operation at the 2-day HRT
(Table 100).
Meso-Thermo and Thermo-Thermo Upflow Two-Phase Digestion
In the meso-thermo two-phase run, the upflow acid digester had a
mesophilic temperature of 35°C while the upflow methane digester was
maintained at a temperature of 55°C. The HRT's of the acid and methane
digesters were 4.5 and 12.1 days, respectively. Operating and performance
data presented in Tables 101 and 102 show that the mesophilic acid-phase
digester exhibited higher gas and methane yield and production rates and
methane content than the methane digester. Concentrations of all individual
volatile acids were about 50% higher in the thermophilic methane digester
compared to those in the mesophilic acid digester despite the fact that the
HRT of the former digester was three times that of the latter. Data presented
in Table 103 showed that additional volatile acids over those prevalent in the
acid digester were produced in the methane digester. It was obvious from
these observations that the thermophilic methane digester experienced little
acetogenic and methanogenic conversions, and that it behaved as an acid
digester. The meso-thermo upflow two-phase operation was discontinued after
about two weeks of operation.
In the next upflow two-phase run the acid digester temperature was
changed to 55°C for thermophilic operation. It was rationalized that if the
acid digester was maintained at a thermophilic temperature then the
liquefaction-acidification process would be enhanced in this digester with a
concommitant decline in acidification activity in the thermophilic methane
digester.
In the thermo-thermo two-phase run the acid and the methane digesters
were operated at HRT's of about 2.1 and 5.4 days, respectively. The perform-
195
-------
TABLE 98. COMPARISON OF VOLATILE ACIDS PRODUCTION RATES FROM
MESOPHILIC AND THERMOPHILIC UPFLOW ACID-PHASE DIGESTION OF HANOVER
PARK SLUDGE WITH AND WITHOUT METHANE-PHASE EFFLUENT RECYCLE
Mesophilic
without
recycle,
overflow
Mesophilic
with
i *
recycle
Run number UAP2M
Effluent pH 6.60
Volatile acids, g/day
Acetic 4.14
Propionic 4.40
Iso-butyric 0.86
Butyric 1.25
Iso-valeric 1.18
Valeric 0.89
Caproic 0.28
Total as acetic 10.51
Total 13.00
Ethanol, g/day 0.00
UAP2MR
6.67
4.96
4.17
1.00
1.59
2.08
0.74
0.13
11.83
14.66
0.02
Methane-phase effluent was recycled to the acid-
phase digester at a rate of 35% of the system
feed rate. Effluent from this run was continuously
wasted from the top (overflow) and bottom (underflow)
of the digester. The overflow and underflow rates
were 88 and 12% of the total effluent rate, respectively.
196
-------
TABLE 99. COMPARISON OF GAS PRODUCTIONS FROM MESOPHILIC AND
THERMOPHILIC UPFLOW ACID-PHASE DIGESTION OF HANOVER PARK SLUDGE
\D
Run number
Run duration, days
Operation
Feed VS concentration, rog/L
HRT, days
Loading, kg VS/m^-day
Performance
Total yield, SCM/kg VS added
Methane yield, SCM/kg VS added
Gas composition, raol %
Hydrogen
Methane
Carbon dioxide
Nitrogen
Total gas production rate, SCM/m'-day
Methane production rate, SCH/m'-day
Therraophilic
(55°C)
UAP2T
16
50,200
2.0
24.55
0.021
0.009
44.8
52.6
2.6
0.525
0.235
Thermophilic
(54°C)
UAP2.1T
9
49,930
2.1
24.24
0.020
0.009
0.0
45.8
48.5
5.7
0.475
0.218
Thermophilic
(54°C)
UAP1.9T
7
24,900
1.9
13.11
0.030
0.014
46.4
49.6
4.0
0.394
0.183
Mesophllic
(35°C)
UAP2M
41
49,900
2.3
21.36
0.090
0.052
57.7
41.8
0.5
1.928
1.112
Feed VS concentration are weighted averages of the various feed slurry concentrations.
-------
00
TABLE 100. COMPARISON OF EFFLUENT QUALITIES FROM MESOPHILIC AND THERMOPHILIC UPFLOW
ACID-PHASE DIGESTION OF HANOVER PARK SLUDGE WITHOUT METHANE-PHASE EFFLUENT RECYCLE
Run number
Effluent, pH
Volatile acids, mg/L
Acetic
Propionic
Iso-butyrlc
Butyric
1 so-valeric
Valeric
Caproic
Total as acetic
Therraophilic
(55°C)
UAP2T
6.44
2516
1531
514
792
972
54
71
5287
Thermophilic
(54°C)
UAP2.1T
6.48
1360
693
226
411
452
120
74
2731
Thermophilic
(54°C)
UAP1.9T
6.55
803
414
153
188
268
8
46
1557
Mesophilic
(35°C)
UAP2M
6.60
1183
1256
246
358
337
254
79
3002
Ethanol, mg/L
10
16
-------
VO
TABLE 101. COMPARISON OF GAS PRODUCTIONS FROM MESO-THERMO AND THERMO-THERMO UPFLOW TWO-PHASE
AND THERMO-THERMO-THERMO THREE-STAGE DIGESTION SYSTEMS OPERATED WITH HANOVER PARK SLUDGE
Meso-thermo two-phase
Thermo-thermo two-phase
Meeo— therno
Mesophlllc (35*C) Thermophlllc (55°C) two-phase Thermophlllc (54°C)
acid digester methane digester system acid digester
Run number UAP4.5M UMP12T
Operation
Feed VS concentration, mg/L - _____ 49,100 - - -
HRT, days 4.46 12.09
Loading, kg VS/m3-day 11.22 4.13
Performance
Total gas yield, SCH/kg VS added 0.182 0.060
Methane yield, SCM/kg VS added 0.109 0.032
Gas composition, ool X
Hydrogen
Methane . 59.8 53.8
Carbon dioxide 39.7 45.2
Nitrogen 0.5 1.0
Total gas production rate, SCH/m3-day 2.046 0.248
Methane production rate, SCM/m3-day 1.224 0.133
UTP17M-T UAP2.1T
16.55 2.06
3.02 24.24
0.242 0.020
0.141 0.009
0.0
58.3 45.8
41.1 48.5
0.6 5.7
0.732 0.475
0.426 0.218
Thermophllic (52°C) Thermo-thermo
methane digester system
UMP5.4T UTP7T-T
5.35 7.41
9.34 6.74
0.029 0.049
0.015 0.024
52.0 49.4
45.6 47.0
2.4 3.6
0.271 0.326
0.141 0.160
* Feed VS concentrations are weighted averages of the various feed slurry concentrations.
(continued)
-------
TABLE 101 (continued)
o
o
Thermo-thermo-thermo three-stage
Run number
Operation
Feed VS concentration, rag/L
HRT, days
Loading, kg VS/m3-day
Performance
Total gas yield, SCH/kg VS added
Methane yield, SCM/kg VS added
Gas composition, nol X
Hydrogen
Methane
Carbon dioxide
Nitrogen
Total gas production rate, SCM/m -day
Methane production rate, SCM/m -day
ThermophlHc (54°C)
acid digester
UAP1.9T
1.91
13. U
0.030
0.014
46.4
49.6
4.0
0.394
0.183
ThermophlUc (49°C) Thermaphlllc (52°C)
upflow methane CFCSTR methane Three-stage
digester digester system
UMP5.2T
S.18
4.83
0.051
0.031
61.1
38.3
0.6
0.249
0.152
CMP13T UTP20T-T-T
13.30 20.39
1.88 1.23
0.267 0.348
0.209 0.254
78.3 72.9
20.8 25.9
0.9 1.2
0.501 0.427
0.392 0.311
* Feed VS concentrations are weighted averages of the various feed slurry concentrations.
-------
TABLE 102. COMPARISON OF EFFLUENT QUALITIES FROM MESO-THERMO AND THERMO-THERMO UPFLOW TWO-PHASE
AND THERMO-THERMO-THERMO THREE-STAGE DIGESTION SYSTEMS OPERATED WITH HANOVER PARK SLUDGE
Meso-thermo two-ph.ise Thermo-tftprmo two-phase Thermo-thermo-thermo three-stage
Mesophilic (35°C) Thermophtllc (55°C) Thermophi tic (54°C)
arid digester methane digester acid digester
Run number UAP4.5M UMP12T UAP2.IT
Effluent, p" 6.9U 7.20 6.48
tsj Volatile acids, mg/X
O
'-' Acetic 1(146 16I>I 1160
Proplonlc 976 1465 h93
Iso-hiityrlc 116 3h8 226
Duty Ic 162 207 411
1*0- alerir 224 678 452
Vale ic 114 0 120
tapr Ir 104 112 74
Tola as ac-cllr 2280 3697 2731
ht Hanoi, mg/L 0 0 16
Thermophllic (54°C)
ThermophlUc (52°C) upflow acid
methane digester digester
UMP5.4T UAP1.9T
7.06 6.55
1742 803
1264 414
339 153
437 188
628 268
158 8
2 ^b
3759 1557
18 0
Thermophlltc (49°C)
upflow methane
digester
UMP5.2T
6.78
.1345
685
235
227
410
43
73
2519
0
Thermophllic (52°C)
CFCSTR methane
digester
CHP13T
7.64
229
782
178
0
303
13
78
1211
0
System effluent quantities are the same as those of the methane phase digester.
Reproduced from
best available copy.
-------
TABLE 103. SOLIDS, pH, ORP, AND VOLATILE ACIDS CONCENTRATION PROFILES IN THERMOPHILIC
UPFLOW METHANE-PHASE DIGESTER OPERATED IN TANDEM WITH THERMOPHILIC UPFLOW ACID-PHASE DIGESTER
Run number
Solids, g/L
Total
Volatile
Fixed
M P"
M ORP, mV
Volatile acids, rag/L
Acetic
Propionic
Iso-butyric
Butyric
Iso-valeric
Valeric
Caproic
Total as acetic
Acid-phase
effluent
UAP2.1T
—
—
6.48
-371
136U
693
226
411
452
120
74
2731
Methane-phase
bottom port
68.56
47.02
21.54
6.98
-399
1643
1153
320
443
601
166
4
3551
Methane-phase
7-L port
78.16
47.59
30.57
7.02
-391
1732
1248
339
462
642
155
6
3762
Methane-phase
1 1.5-L port
66.83
44.84
21.99
7.04
-378
1708
1248
3J9
462
642
152
6
37J6
Methane-phase
15.5-L port
62.86
42,69
20.17
6.99
-36M
1769
1264
347
477
658
155
6
3836
Methane-phase
19-L port (top)
64.00
43.75
20.25
7.03
-317
1720
1263
340
467
643
157
7
3769
Methane-phase
overflow (effluent)
57.70
39.94
17.76
7.06
-373
1742
1264
339
437
628
158
2
3759
Ethanol, tng/L
16
-------
ance of the upflow acid digester changed dramatically when the operating
temperature was changed from mesophilic to thermophilic. As would be evident
from Tables 101 and 102, gas and methane production, and gas-phase methane
content decreased, and volatile acids production and denitrification activity
increased substantially in the acid digester as a result of this temperature
change. Gas and methane yields from the upflow thermophilic methane digester
were lower when it received thermophilic acid digester effluent than they were
when it was fed with mesophilic acid digester effluents. Surprisingly,
volatile acids accumulations in the thermophilic methane digester at an HRT of
5.4 days during the thermo-thermo run were about the same as those experienced
at an HRT of 12 days during the meso-thermo run. Clearly, conversion of the
upflow acid digester from mesophilic to thermophilic operation, and decrease
in methane digester HRT from 12 to 7 days had no effect on the performance of
the methane digester. As would be evident from Table 101, methane yield from
the thermo-thermo upflow two-phase process at a system HRT of about 7 days was
about one-seventh that of the meso-thermo two-phase run at an HRT of about 17
days. However, methane yields from both the above two-phase runs were very
low. The thermo-thermo two-phase run was terminated after about 9 days of
operation.
The results of the meso-thermo and thermo-thermo upflow two-phase runs
demonstrated that the thermophilic upflow methane digester showed little
acetogenic and methanogenic activities. In addition, gas production from the
upflow acid digester decreased substantially when the operating temperature
was changed from mesophilic to thermophilic. Thus, the inhibitory effects of
thermophilic temperature observed during CFCSTR single-stage and two-phase
runs were also observed during upflow two-phase operation; in fact, the
inhibitory effects of the thermophilic metabolites was more severe on the
upflow thermophilic digesters than the CFCSTR thermophilic digesters. This is
evidenced by the fact that methane yield and production rate from the upflow
thermophilic methane digester were considerably lower than those of the CFCSTR
thermophilic methane digester (see Tables 93 and 101).
THERMO-THERMO-THERMO UPFLOW THREE-STAGE DIGESTION
In the three-stage thermo-thermo-thermo operation, the upflow acid and
the upflow methane digesters were operated at HRT's of about two and 5.2 days
as in the case of the thermo-thermo two-phase run discussed above (Table 101).
In addition, a CFCSTR methane-phase digester was also operated at an HRT of
about 13.3 days and in series with the thermo-thermo upflow two-phase system
to promote gasification of the accumulated volatile acids. The CFCSTR
thermophilic methane digester was first operated at about 60°C — this
thermophilic temperature is higher than the "normal" thermophilic temperature
of 55°C — expecting that methanogenic conversion at this temperature would be
better than at the 55°C temperature used for all thermophilic operations. It
was observed that gas production at 60°±1°C was very low (about 1 L/day)
indicating that this digester temperature was unacceptable for CFCSTR methane-
phase operation. A thermophilic temperature of 52°±1°C was used next. In
response to this change, gas production from the thermophilic digester
increased from 1 L/day at 60°C to 20 L/day at 52°C showing that the latter
temperature should be preferred. The three-stage system was operated at about
one-half the loading rate of the meso-meso and the meso-thermo two-phase
203
-------
systems to alleviate inhibition of the gasification process during
thermophilic operation. The operating and performance data for the three-
stage system are presented in Tables 101 and 102. It is apparent from these
data that the three-stage system performed better than the meso-thermo or the
thermo-thermo two-phase runs primarily because the CFCSTR thermophilic methane
digester exhibited higher gasification efficiency than the upflow thermophilic
methane digester.
Information compiled from the thermo-thermo upflow two-phase digestion
runs seemed to indicate that a much higher degree of inhibition of thermo-
philic digestion was experienced in the high-SRT upflow digester than in the
CFCSTR digester. This may be due to the fact that whereas there is continual
flushing of digesting substrate solids and their breakdown products in a
CFCSTR digester, these substances, which plausibly produce inhibitors for the
thermophiles, accumulated in the upflow digesters; thus, unlike the CFCSTR
digesters, the upflow reactors contained a larger reservoir of the inhibitor-
producing compounds. This is apparent considering that for similar dilution-
rate and loading-rate conditions, the thermophilic upflow methane digester
contained 40-47 g/L of VS and 3600-3800 mg/L of volatile acids (see solids and
VA profiles in Table 103) compared with 34-g/L of VS and about 2100 mg/L of VA
in the thermophilic CFCSTR single-stage system (see Table 51, Section 11).
The three-stage thermophilic run was terminated after about 10 days of
operation (in October 1984).
FINAL THERMO-THERMO UPFLOW TWO-PHASE RUN
Based on the experience gained from the thermophilic upflow two-phase
digestion runs described above, it was decided that successful thermophilic
operation of the upflow two-phase system could be achieved perhaps with
prolonged enrichment and acclimation of the acidogenic and methanogenic
populations under conditions of gradually increasing loading and hydraulic
dilution rates and by changing the digester feed. The upflow acid and methane
digesters were operated according to this strategy for about two months with
Hanover Park sludge; the operating and performance data for the last three
weeks of this run, operated with mixed Downers Grove primary and Stickney
activated sludges are depicted in Figures 18 through 20. These figures show
that with gradual acclimation of the acidogenic and methanogenic thermophiles
to decreasing HRT and increasing loading rate, it was possible to steadily
improve the methane yields and production rates of the upflow two-phase
system. At the time of termination of this run, the methane yield and
production rate, and system effluent volatile acids concentration of this
thermo-thermo upflow two-phase system were 0.32 SCM/kg VS added, 1.40 vol/vol-
day, and 2100 mg/L, respectively, which compared well with the corresponding
performance parameters of the thermophilic CFCSTR two-phase process (see
Tables 61 and 62, Section 12).
Although operation of the above upflow thermophilic system could not be
continued due to time constraints, data collected during the transient phase
of operation suggested that upflow thermophilic digesters could be sensitive
to certain feed sludges and that a long enrichment and acclimation period is
required before efficient system operation can be expected.
204
-------
O
Ul
O METHANE PHASE
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0
7
9 11 13 15 17 19
Feed date: December 1984
23 25
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Figure 18. Operating conditions of the thermo-thermo two-phase system
fed with a mixture of Downers Grove primary and Stickney activated sludge.
-------
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a-
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, , 1.5
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0.4
O METHANE PHASE
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40
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Feed date: December 1984
23
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A85080626H
Figure 19. Methane yield and production rate from the thermo-thermo
two-phase system fed with a mixture of Downers Grover primary
and Stickney activated sludges.
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TWO-PHASE PROCESS IMPROVEMENT WITH ENZYME TREATMENT OF DIGESTER FEED
As described in Section 6, efforts were directed towards improving two-
phase process performance by pretreating the feed sludge with cellulase-
cellobiase while also dosing the acid-digester with lipase. These enzymes
were expected to accelerate hydrolysis of the polymeric cellulosic and lipid
particles, thereby promoting further conversion of the hydrolytic products to
volatile fatty acids, hydrogen, and carbon dioxide which are substrates for
methane fermentation.
That the selected cellulase-cellobiase enzyme system was an effective
hydrolyzer is evident from the data in Table 104 which shows that during
incubation (and before digestion) the enzyme-treated feed produced more than
twice as much volatile acids as produced by the untreated raw sludge. The
presence of residual hydrogen gas' in this pretreatment vessel was indicative
of the occurrence of oxidation reactions involved in the conversion of sludge
hydrolysates to fatty acids. Since methane and nitrogen are end products of
hydrogenation of carbon dioxide, and nitrates, respectively, and since the
contents of these gases in the pre-treatment vessel were unusually high and
that of carbon dioxide was very low, if could be concluded that considerable
dehydrogenation of the sludge feed occurred following cellulose-cellobiase
treatment and prior to the addition of this sludge to the digester.
Comparison of two-phase digestion data obtained at a system HRT of three
days with untreated and enzyme-treated sludges showed that gas and methane
yields and production rates from the mesophilic acid and methane digesters and
the two-phase system receiving enzyme treatment were considerably higher than
those observed with the untreated sludge feed (Tables 105 and 106). The
methane contents of the digesters' gases were also higher when enzyme treat-
ment was used. As expected, the acid-phase and the two-phase system carbohy-
drate reductions of about 50% and 64% obtained with cellulase-cellobiase
treatment of the feed were much higher than those observed with untreated
feeds (Table 107). Similarly, methane-phase and two-phase system lipid
reductions with lipase addition were 36% and 39% compared with about 9% and
27%, respectively observed without such treatment. Gas and methane yields and
production rates from digestion of the enzyme treated sludge were signifi-
cantly higher than those from digestion of untreated sludge (Table 105).
Similarly, residual effluent volatile acids from the system receiving enzyme-
treated feed were much lower than those from the two-phase system receiving
untreated sludge (Table 106).
It is noteworthy that lipase dosing had the effect of shifting lipid
reduction from the acid to the methane digester, probably because this
external enzyme was relatively ineffective at the low pH of 6.4 prevalent in
the former digester. Another reason for this low lipid reduction in the acid
digester could be that with cellulase-cellobiase treatment, the acidogenic
organisms metabolized carbohydrates in preference to the more recalcitrant
lipid substrates because this mode of fermentation was energetically more
favorable. Lipase activity in the acid digester receiving enzyme-treated feed
appeared to be much lower than that evidenced with untreated feeds. The acid
digester exhibited higher indigenous lipolytic activity than the methane
digester during two-phase process operation with untreated raw sludge.
208
-------
TABLE 104. EFFECT OF CELLULASE-CELLOBIASE PRETREATMENT ON
VOLATILE ACIDS AND GAS PRODUCTION DURING INCUBATION FROM MIXED
DOWNERS GROVE PRIMARY AND STICKNEY ACTIVATED DIGESTER FEED SLUDGES
Untreated Enzymatically
feed pretreated
slurry feed slurry
Initial 6.25 4.69
After 24 hrs — 5.77
Volatile acids, mg/L
Acetic 1484 1891
Propionic 799 965
Iso-butyric 0 395
Butyric 214 1538
Iso-valeric 0 828
Valeric 42 918
Caproic 43 42
Total as acetic 2324 5739
Ethanol, mg/L 171 402
Gas composition, mol %
Hydrogen — 4.0
Methane — 88.3
Carbon dioxide — 6.4
Nitrogen — 1.3
This raw feed was pretreated for 24 hours at 35°C
with cellulose (Novo Celluclast 1.5L) and cellobiase
(Novozym 188) enzymes at dosages of 2.76 g/kg feed TS
and 0.28 g/kg feed TS, respectively. Prior to
pretreatment the feed pH was adjusted to <5 with
2.5 N HC1.
209
-------
TABLE 105. EFFECT OF CELLULASE-CELLOBIASE AND LIPASE TREATMENT ON
STEADY-STATE GAS PRODUCTIONS FROM MESO-MESO CFCSTR TWO-PHASE SYSTEMS
OPERATED WITH MIXED DOWNERS GROVE PRIMARY AND STICKNEY
ACTIVATED SLUDGES AT AN HRT OF ABOUT 3 DAYS*
Two—phase digestion with
untreated raw sludge
Two-phase digestion with
enzyme treated sludge
Acid Methane
digester digester
System
Acid
digester
Methane
digester
System
Run number
Operation
Feed Vs concentration, mg/L*
HRT, days
Loading, kg VS/m -day
Performance
TP3M-M
46,600
0.91 2.15 3.06
51.21 21.6? 15.23
— TP3M-M(E)
0.93 2.31 3.24
50.99 20.49 14.62
Total gas yield, SCM/kg VS added
Methane yield, SCH/kg VS added
Gas composition, mol %
Hydrogen
Methane
Carbon dioxide
Nitrogen
Total gas production rate,
SCM/m3-day
Methane production rate,
SCM/m3-day
0<12£
(7)**
0.057
(10)
0.05
52.0
47.3
0.7
5.575
(6)
2.898
(9)
0.197
(9)
0.124
(9)
0.0
63.1
36.5
0.4
4.293
(13)
2.708
(14)
0.305
(6)
0.180
(7)
0.0
59.1
40.4
0.5
4.674
(12)
2.764
(12)
0.121
(23)
0.070
(26)
0.05
57.3
42.3
0.4
6.245
(12)
3.567
(15)
0.230
(18)
0.152
(19)
—
65.9
34.1
0.0
4.749
(7)
3.128
(7)
0.351
(18)
0.222
(19)
—
63.0
36.9
0.1
5.178
(7)
3.254
(7)
Data reported are the means of all data collected during the steady-state period.
The feed slurry for this run was pretreated with cellulase (Novo Celluclast 1.5 L) and cellobiase
(Novozym 188) at dosages of 2.76 g/kg feed TS and 0.28 g/kg feed TS, respectively. Lipase (Novozym 225)
was added to the acid digester at a dosage of 2.75 g/kg feed TS.
+ Feed VS concentrations are weighted averages of the various feed slurry concentrations.
Numbers in parentheses are the coefficients of variation expressed as the percent ratios of standard
deviation to the mean.
210
-------
TABLE 106. EFFECT OF CELLULASE-CELLOBIASE AND LIPASE TREATMENT
ON STEADY-STATE EFFLUENT QUALITIES OF MESO-MESO CFCSTR TWO-PHASE
SYSTEMS OPERATED WITH MIXED DOWNERS GROVE PRIMARY AND STICKNEY
ACTIVATED SLUDGES AT ABOUT A 3-DAY HRT
Two-phase digestion
with untreated
raw sludge
Two-phase digestion
with enzyme treated
sludge*3
Acid Methane
digester digesterc
Run number
HRT, days
Effluent, pH
Volatile acids
Acetic
Propionic
Iso-butyric
Butyric
Iso-valeric
Valeric
Caproic
Total as acetic
Ethanol, mg/L
Solids, mg/L
TS
VS
_««.__ ft? I'M Vf
0.91
6.48
2177
1403
288
749
596
1907
51
5518
U6)d
19
61,600
39,320
2.15
7.19
218
1502
50
0
195
136
31
1680
(15)
0
57,450
35,040
Acid Methane
digester digester0
TP3M-M(E)
0.93
6.36
1206
1310
230
585
426
626
33
3458
(28)
11
60,410 54
39,170 33
2.31
7.19
208
978
27
4
60
17
12
1066
(20)
5
,900
,820
Organic compounds, mg/L
Crude protein 12,044 10,512
Carbohydrates 9224 5413
Lipids 6448 5879
7882
5729
8990
5729
a Data reported are means of one or more determinations made during the
steady-state period.
The feed slurry for this run was pretreated with cellulase (Novo Celluclast
1.5L) and cellobiase (Novozym 188) at dosages of 2.76 g/kg feed TS and
0.28 g/kg feed TS, respectively. Lipase (Novozym 225) was added to the
acid digester at a dosage of 2.75 g/kg feed TS.
c System effluent qualities are the same as those of the methane digester.
Numbers in parentheses are the coefficients of variation, expressed as the
percent ratio of standard deviation to the mean.
211
-------
TABLE 107. EFFECT OF CELLULASE-CELLOBIASE AND LIPASE TREATMENT
ON STEADY-STATE ORGANIC REDUCTION EFFICIENCIES OF MESO-MESO CFCSTR
TWO-PHASE SYSTEMS OPERATED WITH MIXED DOWNERS GROVE PRIMARY AND
STICKNEY ACTIVATED SLUDGES AT ABOUT A 3-DAY HRTa
Two-phase digestion
with
untreated raw sludge
Run number
HRT, days
VS reduction, %
MOP16C
Wt-of-gas-basisd
Carbon-in-gas basis6
Based on theoretical gas yieldf
Biodegradable VS reduction8
Reduction of organic components, %
Crude protein
Carbohydrates
Lipids
Acid
digester
0.91
17.1
13.5
10.1
10.0
17.3
33.0
15.8
19.7
Methane
digester
2.15
11.4
26.1
18.4
18.3
31.5
12.7
41.3
8.8
System
3.06
26.5
35.5
28.5
28.3
48.8
41.5
50.6
26.8
Two-phase digestion
with
enzyme treated sludge
Acid
digester
0.93
14.2
14.5
11.4
11.2
19.4
__
49.9
4.1
Methane
digester
2.31
13.0
30.3
21.6
21.3
36.8
27.3
36.3
System
3.24
25.4
39.5
33.0
32.6
56.1
63.6
38.9
8 Data reported are means of one or more determinations made during the steady-state period.
The feed slurry for this run was pretreated with cellulase (Novo Celluclast 1.5L) and cellobiase (Novozym
188) at dosages of 2.76 g/kg feed TS and 0.28 g/kg feed TS, respectively. Lipase (Novozym 225) was
added to the acid digester at a dosage of 2.75 g/kg feed TS.
c These VS reductions were calculated according to the following formula:
VSR = 100 X (VSj - VS0)/[VS1 - (VSi X VS0)].
These VS reductions were calculated according to the following formula:
VSR = 100 X (wt of product gases)/(wt of VS fed).
e These VS reductions were calculated according to the following formula:
VSR = 100 X (1.84 X mass flow rate of product gas carbon)/mass flow rate of VS fed.
These VS reductions were calculated by expressing the observed total gas yield as a percentage of the
theoretical gas yield of 1.078 SCM/kg VS added.
£ The biodegradable VS reductions were calculated by dividing the theoretical-gas-yield-based VS reduction
by a biodegradability factor of 0.58.
212
-------
Overall, cellulase-cellobiase and lipase treatments of sludge increased
the methane yield from the mesophilic CFCSTR two-phase system by about 23%
over that obtained with untreated feeds. This increase is significant at the
low HRT level of 3 days selected for the tests.
213
-------
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Sewage Sludge." Paper presented at 46th Ann. Conf. Wat. Pollut. Contr.
Fed., Cleveland, Ohio, September 30-October 5, 1973.
51. Brown, A. H., "Bioconversion of Solar Energy." Chemtech., 434-37, July
1975.
52. Norrman, J. and Frostell, B., "Anaerobic Waste Water Treatment in a Two-
Stage Reactor of a New Design." Paper presented at the Purdue University
Industrial Waste Conference, West Lafayette, Indiana, May 10, 1977.
53. Therkelson, H. H. and Carlson, D. A., "Thermophilic Anaerobic Digestion
of a Strong Complex Substrate." Paper presented at 50th Ann. Wat.
Pollut. Cont. Fed., Philadelphia, Pennsylvania, October 2-7, 1977.
54. Keenan, J. D., "Two-Stage Methane Production From Solid Wastes." Paper
No. 74-WA/Ener-ll presented at the ASME Winter Annual Meeting, New York,
November 17-22, 1974.
55. Johnson, A. L., "Final Report on Research in Methane Generation." U.S.
Office of Sci. and Technol. Work performed under Contract No. AID/ta-C-
1278, Project No. 931-17-998-001-73, El Segundo, California. The
Aerospace Corporation, September 1976.
56. Ghosh, S., "Solid-Phase Methane Fermentation of Solid Wastes." Proc.
1984 Natl. Waste Processing Conf., Engineering; The Solution, 683-89,
Am. Soc. Mech. Eng., New York, 1984.
57. Ghosh, S., "Gas Production by Accelerated In Situ Bioleaching of
Landfills." U.S. Patent No. 4,323,367, April 6, 1982.
58. "Standard Methods for the Examination of Water and Wastewater," 15th Ed.,
American Public Health Association, American Water Works Association,
Water Pollution Control Federation, Washington, D.C. (1980).
59. "Annual Book of ASTM Standards, Part 26." 1982 Ed., American Society for
Testing and Materials, Philadelphia, Pennsylvania, 1982.
60. Unger, P. et al., "Analyses of Cell Metabolic Products and Fermentation
Gases by Gas Chromatography." J. Appl. Chem. Biotechnol., 27, 150-54,
(1977).
61. Stevens, T. G. and van den Berg, L., "Anaerobic Treatment of Food
Processing Wastes Using a Fixed-Film Reactor." Proc. 36th Ind. Waste
Conf., Purdue University, May 12-14, 1981, Ann Arbor Science, Ann Arbor,
Michigan, 1982.
218
-------
62. Ackman, R. S., "Porous Polymer Bead Packings and Formic Acid Vapor in the
GLC (Gas Liquid Chromatography) of Volatile Free Fatty Acids," J.
Chromatographic Science, 10, 560-62 (1972).
63. Brumm, T. J. and Nye, J. C., "Dilute Swine Waste Treatment in an
Anaerobic Filter." Proc. 36th Ind. Waste Conf., Purdue University, May
12-14, 1981, Ann Arbor Science, Ann Arbor, Michigan (1982).
64. Khan, A. W. and Trottier, T. M., "Effect of Sulfur-Containing Compounds
on Anaerobic Degradation of Cellulose to Methane by Mixed Cultures
Obtained From Sewage Sludge." Applied Environ. Microbiol., 35, 1027-34
(1978).
65. Johns Mansville Bulletin FF-202A, April 1980.
66. Dische, Z., Methods Carbohydrate Chemistry, (Ed. by R. L. Whistler and M.
L. Wolform) j_, 477-517, Academic Press, New York, 1962.
67. American Society of Microbiology, Manual of Methods for General
Bacteriology, 16, 333-34, 1981.
68. Herbert, D., Phipps, P. J. and Strange, R. E., "Chemical Analyses of
Microbial Cells." Methods in Microbiology, 3_> 265-82, Norris and Ribbons.
69. Balmat, J. L., "Chemical Composition and Biochemical Oxidation of
Particulate Fractions in Domestic Sewage." Ph.D. dissertation, Rutgers,
The State University, 1955.
70. Heukelkian, H. and Balmat, J. L., "Chemical Composition of the
Particulate Fractions of Domestic Sewage." Sewage and Industrial Wastes,
31, 413-23, 1959.
71. Hunter, J. V. and Heukelkian, H., "The Composition of Domestic Sewage
Fractions." J. of Wat. Pollut. Contr. Fed., 37, 1142-63, 1965.
72. O'Rourke, J. T., "Kinetics of Anaerobic Waste Treatment at Reduced
Temperatures." Ph.D. dissertation, School of Sanitary and Municipal
Engineering, Stanford University, 1968.
73. Systech Corporation, "Improved Municipal Wastewater Treatment Through
Enzymatic Hydrolysis." Draft report prepared for U.S. Environmental
Protection Agency, 1984.
74. Fencl, Z., "Synthesis of Biomass in Single- and Multi-Stage Continuous
Cultivation." Conference on Fermentation, Smolenica, Czechoslavakia,
1961.
75. Buswell, A. M. and Neave, S. L., "Laboratory Studies on Sludge
Digestion." 111. State Water Surv. Bull. 30, 1934.
219
-------
76. Pfeffer, J. T., "Progress Report: Reclamation of Energy From Organic
Refuse." Solid Waste Program, EPA Grant No. EP00364. Urbana:
Department of Civil Engineering, University of Illinois, September 1971.
77. Ghosh, S. et al., "BIOGAS® Process Development." Paper presented at the
Biomass and Wastes Conversion Workshop, San Diego, California, Gas
Research Institute, August 20-21, 1984.
220
-------
APPENDIX A
FEED SLURRY ANALYSES
TABLE A-l. DIGESTER FEED SLURRY SOLIDS ANALYSES"
Digester feed
prepared
from sludge
lot/batch nos.
1/8
1/14
4/2
4/2
5/2
5/2
5/3
5/3
5/3
5/3
5/4
5/4
5/4
5/4
5/4
6/1
6/1
6/1
6/1
6/1
6/1
6/1
6/1
6/2
6/2
6/2
6/2
6/2
6/2
6/2
6/2
6/4
7/4
Run in
which used
SS15M
SS15M
SS7M
SS7M
TP15M-M
TP15M-M
AP2M7
AP2T7
AP2M7
AP2T7
AP2M7
AP2T7
TP15M-M
AP2T7
TP15M-M
TP15M-M
TP15H-M
TP15M-M
TP15M-M
TP15M-M
TP15M-M
TP15M-M
TP15M-M
SS7M
AP2M7
SS7M
AP2M7
AP2M7
SS7M
AP2M7
SS7M
SS7M
SS3M
Digester
no(s).
331
331
331
331
332-333
332-333
334
335
334
335
334
335
332-333
335
332-333
332-333
332-333
332-333
332-333
332-333
332-333
332-333
332-333
331
334
331
334
334
331
334
331
331
331
SS/
SS/NSSt
SS
NSS
NSS
NSS
NSS
NSS
NSS
SS
NSS
SS
NSS
SS
SS
SS
SS
NSS
NSS
NSS
NSS
NSS
NSS
NSS
NSS
SS
NSS
SS
SS
SS
SS
SS
SS
NSS
NSS
-
Sample date(s)"1"
1/6/83
3/10/83
7/25/83
7/27/83
8/24/83
8/26/83
10/3/83
10/3/83
10/14/83
10/14/83
10/26/83
10/26/83
11/5/83
11/9/83
11/11/83-11/14/83
11/23/83
11/28/83
11/25/83
11/25/83-11/27/33
11/26/83
11/27/83
11/28/83
11/30/83
12/9/83
12/9/83
12/9/83-12/11/83
12/9/83-2/11/83
12/9/83-12/14/83
12/12/83-12/14/83
12/12/83-12/14/83
12/31/83-1/9/84
1/10/84-1/19/84
3/3/84-3/12/84
Fixed solids
Total
mg/L
45,100
50,740
64,390
65,760
45,810
46,000
71,850
77,930
67,420
71,600
74,380
77,710
40,280
82,170
39,350
44,260
43,950
43,610
41,800
42,630
42,650
39,690
34,210
64,080
70,160
67,300
68,580
69,460
75,760
70,430
80,340
56,310
65,740
solids
wt %
4.51
5.07
6.44
6.58
4.58
4.60
7.19
7.79
6.74
7.16
7.44
7.77
4.03
8.22
3.94
4.43
4.40
4.36
4.18
4.26
4.27
3.97
3.42
6.41
7.02
6.73
6.86
6.95
7.58
7.04
8.03
5.63
6.57
Volatile
mg/L
33,500
36,720
47,010
49,190
33,410
32,750
50,160
53,440
47,430
50,280
48,780
52,620
28,660
53,860
28,100
30,140
30,040
30,240
28,130
30,240
29.66U
27,880
24,150
43,950
49,480
45,400
47,160
46,930
49,750
46,700
53,580
36,530
50,650
solids
wt %
of TS
74.28
72.37
73.01
74.80
72.93
71.20
69.81
68.57
70.35
70.22
65.58
67.71
71.15
65.55
71.41
68.10
68.35
69.34
67.30
70.94
69.54
70.24
70.59
68.59
70.52
67.46
68.77
67.56
65.67
66.31
66.69
64.87
77.05
(by
mg/L
11,600
14,020
17,380
16,570
12,400
13,250
21,690
24,490
19,990
21,320
25,600
25,090
11,620
28,310
11,250
14,120
13,910
13,370
13,670
12,390
12,990
11,810
10,060
20,130
20,680
21,900
21,420
22,530
26,010
23,730
26,760
19,780
15,090
diff)
wt %
of TS
25.72
27.63
26.99
25.20
27.07
28.80
30.19
31.43
29.65
29.78
34.42
32.29
28.85
34.45
28.59
31.90
31.65
30.66
32.70
29.06
30.46
29.76
29.41
31.41
29.48
32.54
31.23
32.44
34.33
33.69
33.31
35.13
22.95
(continued)
221
-------
TABLE A-l (continued)
Digester feed
prepared
from sludge
lot/batch nos.
8/1
8/1
8/1
8/1
8/5
8/5
8/5
Run in
which used
SS3M
TP7M-M(NG)
AP1.3M7
API. 317
AP1.3T7
SS3M
AP1.3M7
Digester
no(s).
331
332-333
334
335
335
331
334
SS/
NSST
NSS
NSS
NSS
NSS
SS
SS
SS
Fixed solids
Sample date(s)+
3/7/84
3/7/84
3/7/84
3/7/84
3/18/84-3/27/84
3/28/84-4/6/84
3/28/84-4/6/84
Total
mg/L
62,290
61,670
59,710
59,770
55,960
63,020
59,380
solids
wt %
6.23
6.17
5.97
5.98
5.60
6.30
5.94
Volatile
mg/L
48,280
47,920
46,290
46,400
42,890
47,940
44,960
solids
wt %
of TS
77.51
77.70
77.52
77.63
76.64
76.07
75.72
(by
mg/L
14,010
13,750
13,420
13,370
13,070
15,080
14,420
diff)
wt %
of TS
22.49
22.30
22.48
22.37
23.36
23.93
24.28
12/1
SS15T
337
SS
5/31/84-6/9/84 41,560 4.16 31,630 76.11 9,930
23.89
13/1
13/1
13/1
13/1
14/1
14/1
16/1
16/1
16/1
16/1
16/1
lb/1
lb/1
17/1
17/1
17/1
28/1
32/1
AP2T5
AP2M5
UTP7M-M
AP1.3T5
TH7M-M(NC)
AP1.3M5
SS7T
SS3T
TP15N-T
SS3T
TP15M-T
SS3T
TP15M-T
TP7M-T
TP7M-M(NG)
TP7H-M
TP3M-M
TP3M-M(E)
335
334
338-339
335
332-333
334
331
335
334-337
335
334-337
335
334-337
334-331
332-333
334-333
334-333
334-333
SS
SS
SS
SS
NSS
SS
SS
SS
SS
SS
SS
SS
ss
SS
NSS
SS
SS
SS
6/12/84-6/16/84
6/19/84-6/23/84
6/28/84-7/1/84
6/28/84-7/2/84
7/1/84
7/2/84-7/6/84
8/2/84-8/6/84
8/8/84-6/12/84
8/8/84-8/12/84
8/8/84-8/17/84
8/8/84-8/17/84
8/13/84-8/17/84
8/13/84-8/17/84
9/10/84-9/14/84
9/1/84-9/15/84
9/25/84-9/29/84
12/17/84-12/21/84
1/8/85-1/12/85
65,310
67,530
69,870
67,530
67,230
68,440
67,250
67,510
47,060
66,735
46,045
65,960
45,030
66,430
68,960
66,540
68,500
69,470
6.53
6.75
6.99
6.75'
6.72
6.84
6.73
6.75
4.71
6.67
4.60
6.60
4.50
6.64
6.90
6.65
6.85
6.95
49,840
51,460
52,230
50,750
48,220
47,970
49,740
49,240
32,900
48,615
32,420
47,990
31,940
48,640
50,640
48,860
46,600
47,420
76.31
76.20
74.75
75.15
71.72
70.09
73.96
72.94
69.91
72.85
70.41
72.76
70.93
73.22
73.43
73.43
68.03
68.26
15,470
16,070
17,640
16,780
19,010
20,470
17,510
18,270
14,160
18,120
13,625
17,970
13,090
17,790
18,320
17,680
21,900
22,050
23.69
23.80
25.25
24.85
28.28
29.91
26.04
27.06
30.09
27.15
29.59
27.24
29.07
26.78
26.57
26.57
31.97
31.74
Data reported are the averages of triplicate determinations.
+ 'SS' means the sample was collected during steady-state operation; 'NSS' means the sample was collected during
non-steady-state operation.
A single sample data indicates that the analysis was conducted on a grab sample collected that day. A time period
under this column indicates the start and end dates of collection of a grab or time-composite sample used for
analysis.
222
-------
TABLE A-2. DIGESTER FEED SLURRY SUSPENDED SOLIDS ANALYSES*
Digester f iM'd
prepared
fr
1/14
5/1
5/4
5/4
5/4
5/4
6/2
6/2
B/5
8/5
Ktill In
which used
SS15M
AI'2T7
AP2M7
AH2T7
THISM-M
TH 1 5M-M
AP2M7
SS7M
AP1.1T7
AH.3M7
Dinest or
no(s).
Til
315
314
115
312-TH
3 12-133
114
3)1
135
134
ss/
NNS+
NSS
SS
NSH
S.S
SS
SS
SS
SS
SS
SS
Sample c!atc(«)
3/1D/H1
10/14/H1
ltl/26/HI
KI/2H/81
1I/5/H1
II/I1/81-11/U/8J
12/9/81-I2/14/H1
I2/31/B3-1/9/H4
3/18/B4-1/27/H4
3/28/84-4/h/84
Ttit.-il solldn
mtt/l.
50,740
71 ,b(UI
74,18(1
7/.7KI
40.2BO
39,350
b9,460
80,140
55,9hO
59,380
wt %
5.07
7.16
7.44
7.77
it. (11
3.94
ft. 95
8.03
5. hi)
5.94
Volatile
mi:/l.
36,720
50,28(1
4B,78()
52,620
28,660
2B.1IIO
46,910
53,580
42.H9I)
44,960
solids
wt Z
of TS
72.17
70.22
h5.58
67.71
71.15
71.41
67.56
66.69
76.64
75. Ti
Y\ xvd sol Ids
(by dlCO
mg/I.
14,020
21 ,120
25,60(1
25,09(1
11, MO
1 1,250
22,510
26, /6()
11,070
14,1.20
wl Z
of TS
27.63
29.70
14.42
12.29
28.85
28.59
12.44
11.11
21.16
24.28
lot^l
KUKpendt'd
sol ids
"*/'•
48,000
65,740
65,160
69,8'W
33,560
32,100
62,170
hi, 650
41,740
46,140
wt Z
of TS
94.60
91.82
87.60
89.94
81.12
81.58
89.50
79.21
78.16
77.70
Volatile
suspended
solids
mg/L
36,270
44,710
41, BOO
45,000
2 7 , 1 00
25,910
45,690
47,670
36,700
39,200
wt %
of TS
71.48
62.44
56.20
57.91
67.28
65.84
65.78
59.34
65.58
66.02
Fixed suspended
solids (by diff)
O.R/L
11,730
21,030
23,360
24,890
6,460
6,190
16,480
15,980
7,040
6,940
wt i
of TS
23.12
29.37
31.41
32.03
16.04
15.73
23.73
19.89
12.58
11.69
Data reported arc the averages of triplicate determinations.
'SS1 meant; tin: Kample van collected during steady-state operation; 'NSS1 means the sample was collected dnrinR non-sti-ady-Btate operation.
A .single sample date Indicates that the analysis was conducted on a grab sample collected that day. A time period under this column indicates the start and end dates of
collection of a grab or time-composite sample used for analysis.
Reproduced from
best available copy.
-------
TABLE A-3. DIGESTER FEED SLURRY pH, AMMONIA NITROGEN, AND ALKALINITY ANALYSES*
IsJ
Digester feed
prepared
from sludge
lot/batch nos.
1/8
1/9
1/9
4/2
4/2
5/1
5/3
5/3
5/3
5/3
5/4
5/4
6/1
6/1
6/1
6/2
6/2
6/2
6/2
8/5
8/5
8/5
8/5
8/5
8/5
12/1
12/1
13/1
13/1
13/1
13/1
13/1
13/1
13/1
13/1
Run in
which used
SS15M
SS15M
SS15H
SS7M
TP15M-M
AP2M7
AP2M7
AP2T7
AP2M7
AP2T7
AP2T7
TP15M-M
TP15M-M
AP2T7
TP15M-M
AP2M7
SS7M
AP2M7
SS7M
AP1.3T7
AP1.3T7
SS3M
AP1.3M7
SS3M
AP1.3M7
SSI5T
SS15T
AP2T5
AP2M5
AP2T5
AP2M5
UTP7M-M
AP1.3T5
UTP7H-M
AP1.3T5
Digester
no(s).
331
331
331
331
332-333
334
334
335
334
335
335
332-333
332-333
335
332-333
334
331
334
331
335
335
331
334
331
334
337
337
335
334
335
334
338-339
335
338-339
335
SS/
NSST
SS
SS
SS
NSS
NSS
NSS
NSS
SS
NSS
SS
SS
SS
SS
NSS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
Sample date(s)+
1/6/83
1/18/83
1/20/83
7/25/83
7/25/83
9/22/83
10/3/83
10/3/83
10/14/83
10/14/83
11/9/H3
11/11/83-11/14/83
11/28/83
11/30/83
12/2/83
12/9/83-12/14/83
12/14/8J
12/14/83
12/31/83-1/9/84
3/18/84-3/27/84
3/20/84
3/28/84-4/6/84
3/28/84-4/6/84
4/1/84
4/U84
5/31/84-6/9/84
6/10/84
6/12/84-6/16/84
6/17/84
6/17/84
6/19/84-6/23/84
6/28/84-7/1/84
6/28/84-7/2/84
7/6/84
7/6/84
Ammonia
nitrogen,
pH mg/L
__
6.H4
b.f>4
—
6.48
6.20
—
—
f>.43
—
7.19
6.58
7.00
—
h.42
6. hi
—
6.01
—
—
6.05
6.16
5.94
——
5.86
5.85
—
—
—
6.04
5.87
280
—
—
569
385
247
—
299
224
2h8
168
131
—
—
219
—
—
3W
509
—
5H9
624
—
—
237
—
337
—
—
302
327
321
—
Total
alkalinity,
mg/L as CaCO-j
__
4583
4700
_ —
_„
5200
5050
—
—
5600
—
3140
4720
3185
__
5390
5373
—
__
5200
—
4575
4375
___
3250
__
4820
4870
—
—
—
5500
7340
Bicarbonate
alkalinity,
mg/L as CaCOj
„
3912
4029
— —
—
4318
4106
—
—
4855
__
2838
4352
2883
—
4334
4510
—
__
3091
—
2455
1933
__
2160
__
2844
3125
—
3766
5665
(continued)
-------
TABLE A-3 (continued)
K)
Ul
Digester feed
prepared
from sludge
lot/batch nos.
14/1
14/1
16/1
16/1
16/1
16/1
16/1
16/1
17/1
17/1
17/1
17/1
17/1
17/1
28/1
28/1
Run in
which used
AP1.3M5
AP1.3M5
SS7T
SS7T
SS3T
TP15M-T
SS3T
TP15M-T
TP7M-T
TP7M-M(NG)
TP7M-M(NG)
TP7M-T
TP7M-M
TP7M-M
TP3M-M
TP3M-M
Digester
no(s).
334
334
331
331
335
334-337
335
334-337
334-331
332-333
332-333
334-331
334-333
334-333
334-333
334-333
SS/
NSS'
SS
SS
SS
SS
SS
SS
SS
SS
SS
NSS
NSS
SS
SS
SS
SS
SS
Sample date(s)+
7/2/84-7/6/84
7/6/84
7/30/84
8/2/84-8/6/84
8/8/84-8/17/84
8/8/84-8/17/84
8/16/84
8/17/84
9/10/84-9/14/84
9/11/84-9/15/84
9/13/84
9/13/84
9/25/84-9/29/84
9/29/84
12/17/84-12/21/84
12/19/84
PH
6.16
6.16
—
—
—
6.37
6.52
__
—
6.00
6.33
—
6.37
__
6.06
Ammonia
nitrogen,
mg/L
369
587
755
528
—
—
546
585
—
—
582
—
535
"
Total
alkalinity,
mg/L as CaCO-j
7175
6850
—
6105
4618
5250
6050
5850
__
4750
Bicarbonate
alkalinity,
mg/L as CaC03
5513
3845
__
2737
2343
__
3473
4421
3863
__
1245
Data reported are the averages of duplicate or triplicate determinations.
'SS' means the sample was collected during steady-state operation; 'NSS' means the sample was collected during
non-steady-state operation.
A single sample data indicates tha the analysis was conducted on a grab sample collected that day. A time period
under this column indicates the start and end dates of collection of a grab or time-composite sample used for
analysis.
-------
TABLE A-4. DIGESTER FEED SLURRY TOTAL AND FILTRATE CHEMICAL OXYGEN DEMAND (COD) ANALYSES
-N)
N>
Digester feed
prepared
from sludge
lot/batch nos.
1/14
5/1
5/3
5/3
5/3
5/3
5/3
5/3
5/4
5/4
5/4
6/2
6/2
8/5
8/5
8/5
Run In
which used
SS15M
AP2M7
AP2M7
AP2M7
AP2T7
AP2T7
AP2M7
AP2T7
AP2M7
TP15M-M
TP15M-M
AP2M7
SS7M
AP1.3T7
SS3M
AP1.3M7
Digester
no(s).
331
334
334
334
335
335
334
335
334
332-333
332-333
334
331
335
331
334
SS/
NSS'
NSS
NSS
NSS
NSS
SS
SS
NSS
SS
NSS
SS
SS
SS
SS
SS
SS
SS
Sample date(s)*
3/10/83
9/22/83
10/3/83
10/3/83
10/3/83
10/3/83
10/14/83
10/14/83
10/26/83
11/5/83
11/11/83-11/14/83
12/9/83-12/14/83
12/31/83-1/9/84
3/18/84-3/27/84
3/28/84-4/6/84
3/28/84-4/6/84
Total
COD,
mg/L
48,270
__
—
79,530
—
87,096
66,723
78,047
78,798
39,580
34,822
77,702
80,617
76,394
85,983
81,896
Total
COD,
g/g vs
1.315
__
—
1.586
—
1.630
1.407
1.552
1.615
1.381
1.239
1.656
1.505
1.781
1.794
1.822
Filtrate
COD,
mg/L
5324
6390
4922
4696
4979
4918
5673
6547
—
2745
2601
4605
4211
7042
7968
7753
Filtrate
COD,
g/g vs
0.145
0.131
0.098
0.094
0.093
0.092
0.120
0.130
—
0.096
0.093
0.098
0.079
0.164
0.166
0.172
Paniculate
(by dlff)
COD, mg/L
42,946
_..
—
74,834
—
82,178
61,050
71,500
—
36,835
32,221
73,097
76,406
69,352
78,015
74,143
Partlculate
(by dlff)
COD, g/g VS
1.170
.._
—
1.492
—
1.538
1.287
1.422
—
1.285
1.147
1.558
1.426
1.617
1.627
1.649
Data reported are the averages of two or more determinations.
'SS' means the sample was collected during steady-state operation; 'NSS1 means the sample was collected during non-steady-state
operation.
* A single sample date indicates that the analysis was conducted on a grab sample collected that day. A time period under this column
indicates the start and end dates of collection of a grab or time-composite sample used for analysis.
-------
TABLE A-5. DIGESTER FEED SLURRY AMMONIA, ORGANIC, AND TOTAL KJELDAHL NITROGEN ANALYSES
Digester feed
prepared
from sludge
lot/batch nos.
Run in
which used
Digester
no(s).
SS/
NSST
Sample date(s)+
Ammonia nitrogen
Organic nitrogen
Total
Kjeldahl nitrogen
1/8
4/2
4/2
5/1
5/3
5/3
5/3
5/4
5/4
6/2
6/2
8/5
8/5
8/5
12/1
13/1
13/1
13/1
13/1
14/1
SS15M
SS7M
TP15M-M
AP2M7
AP2T7
AP2M7
AP2T7
AP2T7
TP15M-M
AP2M7
SS7M
AP1.3T7
SS3M
AP1.3M7
SS15T
AP2T5
AP2M5
UTP7M-M
AP1.3T5
AP1.3M5
331
331
332-333
334
335
334
335
335
332-333
334
331
335
331
334
337
335
334
338-339
335
334
SS
NSS
NSS
NSS
SS
NSS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
1/6/83
7/25/83
7/25/83
9/22/83
10/3/83
10/14/83
10/14/83
11/9/83
11/11/83-11/14/83
12/9/83-12/14/83
12/31/83-1/9/84
3/18/84-3/27/84
3/28/84-4/6/84
3/28/84-4/6/84
5/31/84-6/9/84
6/12/84-6/16/84
6/19/84-6/23/84
6/28/84-7/1/84
6/28/84-7/2/84
7/2/84-7/6/84
mg/L
280
569
385
247
299
224
268
168
131
219
354
509
589
624
237
337
302
327
321
369
wt %
of TS
0.62
0.88
0.84
0.35
0.38
0.33
0.37
0.20
0.33
0.32
0.44
0.91
0.93
1.05
0.57
0.52
0.45
0.47
0.48
0.54
wt %
of VS
0.84
1.21
1.15
0.51
0.56
0.47
0.53
0.31
0.47
0.47
0.66
1.19
1.23
1.39
0.75
0.68
0.59
0.63
0.63
0.77
mg/L
1971
—
—
2352
2245
2156
2098
2520
1456
2044
2347
2420
2617
2563
1867
2918
2820
2793
2933
2335
wt %
of TS
4.37
—
— -
3.38
2.88
3.20
2.93
3.07
3.70
2.94
2.92
4.32
4.15
4.32
4.49
4.47
4.18
4.00
4.34
3.41
wt %
of VS
5.88
—
—
4.82
4.20
4.55
4.17
4.68
5.18
4.36
4.38
5.64
5.46
5.70
5.90
5.85
5.48
5.35
5.78
4.87
mg/L
2251
—
— -
2599
2544
2380
2366
2688
1587
2263
2701
2929
3206
3187
2104
3255
3122
3120
3254
2704
wt %
of TS
4.99
—
—
3.73
3.26
3.53
3.30
3.27
4.03
3.26
3.36
5.23
,— 5.09
5.37
5.06
4.98
4.62
4.47
4.82
3.95
wt %
of VS
6.72
—
—
5.33
4.76
5.02
4.71
4.99
5.65
4.82
5.04
6.83
6.69
7.09
6.65
6.53
6.07
5.97
6.41
5.64
(continued)
-------
TABLE A-5 (continued)
Digester feed
prepared
from sludge Run In
lot/batch nos. which used
Digester
no(s).
SS/
NSST
Sample date(s)
Ammonia nitrogen
Organic nitrogen
Total Kjeldahl nitrogen
to
00
16/.1
16/1
16/1
17/1
17/1
17/1
28/1
SS7T
SS3T
TP15M-T
TP7M-T
TP7M-M(NG)
TP7M-M
TP3M-M
331
335
334-337
334-331
332-333
334-333
334-333
SS
SS
SS
SS
NSS
SS
SS
8/2/84-8/6/84
8/8/84-8/17/84
8/8/84-8/17/84
9/10/84-9/14/84
9/11/84-9/15/84
9/25/84-9/29/84
12/17/84-12/21/84
mg/L
587
755
528
546
585
582
535
wt % wt %
of TS of VS
0.87
1.13
1.15
0.82
O.H5
0.87
.18
.55
.63
.12
.16
.19
0.78 1.15
mg/L
2750
2779
1912
2662
2482
2450
2876
wt %
of TS
4.09
4.16
4.15
4.01
3.60
3.68
4.20
wt ^
of VS
5.53
5.72
5.90
5.47
4.90
5.01
6.17
mg/L
3337
3534
2440
3208
3067
3032
3411
wt %
of TS
4.96
5.30
5.30
4.83
4.45
4.56
4.98
wt Z
of VS
6.71
7.27
7.53
6.60
6.06
6.21
7.32
Data reported are the averages of duplicate or triplicate determinations.
t ,
SS' means the sample was collected during steady-state operation; 'NSS' means the sample was collected during non-steady-state operation.
+ A single sample date indicates that the analysis was conducted on a grab sample collected that day. A time period under this column
indicates the start and end dates of collection of a grab or time-composite sample used for anaysis.
-------
TABLE A-6. ORGANIC COMPONENT ANALYSES FOR DIGESTER FEED SLURRIES3
rO
Run in
Feed designation which used
Lot no. /batch no.
1/8
3/2 (diluted)"1
4/1 (diluted)
4/2 (diluted)
5/1 (diluted)
5/3 (diluted)
5/4 (diluted)
6/2 (diluted)
8/5 (concentrated)
12/1 (diluted)
13/1 (diluted)
14/1 (diluted)
SS15M
SS15M
SS15M
—
—
—
--
—
— —
—
—
—
AP2T7
—
AP2T7
AP2T7
TP15M-M
TP15H-M
TP15M-M
SS7M
SS7M
AP2M7
A1.3T7
SS3M
SS3M
AP1.3M7
SS15T
AP2T5
AP2M5
AP2M5
UTP7M-M
UTP7M-M
AP1.3T5
AP1.3T5
AP1.3M5
SS/NSSb
SS
ss
ss
NSS
NSS
NSS
NSS
NSS
NSS
NSS
NSS
SS
NSS
SS
ss
ss
ss
ss
ss
ss
ss
ss
ss
ss
ss
ss
ss
ss
ss
ss
ss
ss
ss
ss
Digester
no(s).c
331
331
331
332-333
332-333
331
331
331
334
334
334
335
334
335
335
332-333
332-333
332-333
331
331
334
335
331
331
334
337
335
334
334
338-339
338-339
335
335
334
Sample date(s)
l/b/83
1/6/83
l/b/83
b/4/83
7/11/83
7/25/83
7/27/83
7/27/83
9/22/83
9/22/83
10/3/83
10/3/83
10/14/83
10/14/83
11/9/83
11/10/83
11/11-11/14/83
11/13/83
12/12-12/14/83
12/31/83-1/9/84
12/9-12/14/83
3/18-3/27/84
3/28-4/b/84
3/28-4/6/84
3/28-4/6/84
5/31-6/9/84
6/12-6/16/84
6/19-6/23/84
6/19-6/2 )/84
6/28-7/1/84
6/28-7/1/84
6/28-7/2/84
6/28-7/2/84
7/2-7/6/84
TS
mg/b
45,100
45,100
45,100
53,500
71,700
64,390
65,760
65,760
71,850
67,420
71,850
77,930
67,420
7 1 , 600
82,170
39,350
39,350
39,350
75,760
80,340
69,460
55,960
63,020
63,020
59,380
41,560
65,310
67,530
67,530
69.87O
69,870
67,530
67,530
68,440
VS
mg/L wt 7. of TS
33,500
33,500
33,500
37,434
51,803
47,010
49,190
49,190
50,160
47,430
50,160
53,440
47,430
50,280
53,860
28,100
28,100
28,100
49,750
53,580
46,930
42,890
47,940
47,940
44,960
31,630
49,840
51,460
51,460
52,230
52,2)0
50,750
50,750
47,970
74.27
74.27
74.27
Means
69.97
72.25
73.00
74.80
74.80
Means
69.81
70.35
69.81
68.57
70.35
70.22
65.54
71.41
71.41
71.41
Means
65.66
66.69
67.56
Means
76.64
76.07
76.07
75.71
Means
76.10
76.31
76.20
76.20
74.75
74.75
75.15
75.15
Means
70.09
Crude protein
rag/L wt % of VS
12,315
—
—
—
—
—
—
14,700
14,700
__
14,031
13,475
13,112
15,750
—
9100
—
14,669
12,775
15,125
16,536
—
16,019
1 1 ,1,69
18,238
17,625
—
—
17,456
18,331
14,594
36.76
—
—
36.76
—
—
— _
—
—
29.31
37.99
__
26.25
28.41
26.07
29.24
—
32.38
—
30.81
27.37
27.22
27.30
35.26
34.11
—
35.62
35.00
36.89
36.59
34.24
—
—
33.42
36.12
35.09
30.42
Total carbohydrate
mg/L wt % of VS
6532
—
—
—
—
—
—
__
—
13,567
14,100
12,350
13,300
__
—
8307
—
9,958
9,036
—
12,118
12,012
11,538
12,724
7,292
10,994
11,813
11,956
13,934
10,786
12,016
13,637
19.49
—
—
19.49
—
—
__
—
—
._
—
27.04
26.38
26.03
26.45
__
—
29.56
—
29.56
20.01
16.86
—
18.44
28.25
25.05
23.69
28.30
26.32
23.05
__
21.36
22.95
22.89
26.67
21.25
23.67
23.13
28.42
Liplds
mg/L wt % of VS
9288
6700
7239
9160
16,294
14,100
17,933
15,300
__
—
13,400
14,600
14,100
__
6,200
7,450
__
18,929
19,068
__
12,392
—
11,736
10,030
__
15,104
—
—
—
9,824
27.72
20.00
21.60
23.11
24.47
31.45
29.99
36.45
31.10
32.51
_
26.71
27.32
28.04
._
22.06
26.51
24.28
._
35.32
40.63
37.98
_.
25.85
26.10
25.98
31.71
__
29.35
—
—
29.35
20.48
(Continued)
-------
TABLE A-6 (continued)
Run In
Feed designation which used*
Lot No. /Batch No.
16/1 (diluted) SS7T
SS7T
SS3T
SS3T
TP15M-T
17/1 (diluted) TP7M-T
TP7M-T
—
TP7M-M
to TP7M-M
OJ
o
28/1 (diluted) TP3M-M
TP3M-M
32/1 (diluted) TP3M-M(E)
SS/NSS
SS
SS
SS
SS
SS
SS 1
SS
NSS
SS
SS
SS
SS
SS
Digester
no*
331
331
335
335
33/1-337
334-331
334-331
332-333
331-333
334-333
334-333
334-333
334-333
Sample date(s)
8/2-8/6/84
8/2-8/6/84
8/8-8/17/84
8/8-8/17/84
8/8-8/17/84
9/10-9/14/84
9/10-9/14/84
9/11-9/15/84
9/25-9/29/84
9/25-9/29/84
12/17-12/21/84
12/17-12/21/84
1/8-1/12/85
TS
mg/L
67,250
67,250
66,735
66,735
46,045
66,430
66,430
68,960
66,540
66,540
68,500
68,500
69,470
VS
mg/L
49,740
49,740
48,615
48,615
32,420
48,640
48,640
50,640
48,860
48,860
46,600
46,600
47,420
vt % of TS
73.96
73.96
72.84
7.2.84
70.40
Means
73.21
73.21
73.43
73.42
73.42
Means
68.02
68.O2
Means
68.25
Crude
mg/L
17,188
—
17,369
—
11,950
16,638
—
15,512
15,312
—
17,975
—
—
protein
wt 7. of VS
34.55
—
35.72
—
36.85
35.71
34.20
30.63
31.33
__
32.05
38.57
—
38.57
—
Total carbohydrate
mg/L
9,292
10,238
10,363
8,497
5,943
12,202
11,114
10,594
11.71B
10,610
10,459
11,452
15,734
wt Z of VS
18.68
20.58
21.31
17.47
18.33
19.27
25.08
22.84
20.92
22.87
21.71
22.68
22.44
24.57
23.50
33.18
Llplds
mg/L wt * of VS
9,705
8,952
7,156
11,994
__
9,314
8,026
9,370
19.51
18.41
22.07
20.00
24.66
19.06
21.86
17.22
17.22
19.75
8 Data reported In this table were averages of replicate determinations.
b SS means that the run was at steady state during sampling; NSS Is not steady state.
0 One digester number Indicates a single-stage digester. Two digester numbers Indicate a two-phase system
consisting of two digesters operated In series.
Digester feed slurry was prepared by appropriately diluting the Indicated feedstock.
-------
APPENDIX B
EFFLUENT ANALYSES FOR SINGLE-STAGE CFCSTR DIGESTERS
TABLE B-l. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. SS15M: CFCSTR SINGLE-STAGE MESOPHILIC (35°C) DIGESTER OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 15-DAY HRT
Hydrogen,
Date mol %
1/2/83
1/8/83
1/10/83
1/14/83
1/29/83
2/5/83
2/8/83
2/10/83 0.00
2/18/83 0.00
Carbon dioxide,
mol %
30.59
29.66
29.63
28.73
29.00
29.63
28.93
29.15
28.89
Nitrogen,
mol %
0.71
0.27
0.65
1.04
0.00
0.63
0.48
0.00
0.81
Methane ,
mol %
68.69
70.07
69.72
70.23
71.00
69.75
70.59
70.85
70.30
231
-------
TABLE B-2. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING
STEADY-STATE RUN NO. SS15M CFCSTR SINGLE-STAGE MESOPHILIC (35°C)
DIGESTION OF HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 15-DAY HRT
Acetic,
Date mg/L
12/31/82
1/8/83
1/14/83
1/21/83
1/28/83
2/5/83
2/8/83
2/12/83
2/19/83
0
0
0
0
0
2
0
3
0
Proplonlc,
mg/L
0
0
0
0
0
0
0
0
0
Isobutyrlc,
mg/L
0
0
0
0
0
0
0
0
0
Butyric,
mg/L
0
0
0
0
0
0
0
0
0
Isovalerlc,
mg/L
0
0
0
0
0
0
0
0
0
Valeric,
mg/L
0
0
0
0
0
0
0
0
0
Caproic,
mg/L
0
0
0
0
0
0
0
0
0
Total
as acetic,
mg/L
0
0
0
0
0
2
0
3
0
Ethanol,
mg/L
__
— -
—
—
—
7
0
3
0
-------
OJ
Total Blurry
FS 9 25.7 wt X of TS
VS 8 74.3 wt X
TS
Protein 9 36.8 wt X of VS
Carbohydrate 9 19. 5 wt X
Upida g 23.1 wt X of VS
ICPL*
VA 0 2.4 wt X of VS
Other organic* (by dlff)
INPUT
4.51 kg
1 24 kg " Ti-- -••>
0.77 >
2.66 kg
(79.4 wt X of VS)
0.08 kg >
0.61 kg - >
(18.2 wt X of VS)
Run no. SSI 5M
CPCSTR
single-stage
Temp: 35"C
Lo ad Ing :
2.0 Kg VS/m3-d
HRT: 15.0 days
OUTPUT
0.75 SCM CH4
0.31 SCM COj
0. 54 kg carbon
6801 kcal
3.51 kg
> (3 25.8 wt X of VS 0 58
1.96 kg
(87.0 wt X of VS)
- ^ > 0.29 kg
M2. 9 wt I nf VS1
REDUCTION/
(PRODUCTION)
32. 8X
27.1X
27.3
26.6 X
1 00. OX
52. 5X
FS balance: effluent/feed - 109X
VS balance: effluent/feed - 100X
Carbon recovery In gas - 281
Energy recovery In gas - 32*
* KTl. IB the sun of protein, carbohydrate, and llplds.
Figure B-l. Mass balances for single-stage CFCSTR mesophilic
Run SS15M conducted with Hanover Park sludge at a 15-day HRT
-------
TABLE B-3. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. SS7M: CFCSTR SINGLE-STAGE MESOPHILIC (35°C) DIGESTON OF
HANOVER PARK SLUDGE CONDUCTED AT A 7-DAY HRT
Date
Hydrogen,
mol %
Carbon dioxide,
mol %
Nitrogen,
mol %
Methane,
mol %
11/27/83
12/4/83
12/11/83
12/19/83
12/28/83
1/2/84
31.87
30.45
29.85
30.45
31.17
30.19
0.81
0.80
0.14
0.00
0.00
0.00
67,32
68.75
70.01
69.55
68.83
69.81
234
-------
TABLE B-4. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. SS7M
CFCSTR SINGLE-STAGE MESOPHILIC (35°C) DIGESTION OF HANOVER PARK SLUDGE CONDUCTED AT A 7-DAY HRT
10
Date
11/28/83
12/5/83
12/12/83
12/19/83
12/26/83
1/3/84
Acetic,
mg/L
189
170
136
121
95
272
Propionlc, Isobutyric,
mg/L mg/L
117
128
88
99
86
105
0
0
0
0
0
2
Butyric,
mg/L
0
0
0
0
0
0
Isovaleric,
mg/L
0
0
0
0
0
0
Valeric,
mg/L
0
0
0
0
0
0
Caproic,
mg/L
0
0
0
0
0
0
Total
as acetic,
mg/L
284
274
207
201
164
359
Ethanol ,
mg/L
0
0
0
0
17
0
-------
rO
Total alurry
FS 9 33.8 we X of TS
VS C' 66.2 we X
TS
Protein 9 27.3 wt X of VS
Carbohydrate 8 18.4 wt X of VS
Llplda 9 36.8 wt X of VS
ICPL*
VA 8 2.9 wt X of VS
Other organlca (by dlff)
INPUT
I OU kg ->
5 17 — - -- _ ...... y
7.81 kg
1 41 kg -~ >
1.90 >
4. 26 kg
(82. 5 we t of VS)
0 1 5 kg - — — >
0.76 kg >
(14.7 wt X of VS)
PS t
VS 1
Carl
Enei
[
Run no. SS7M
CKSTR
single-stage
Temp: 35°C
Loading:
7.5 kg VS/m3-d
HRT: 7.0 day.
alance: effluent/feed - 9t
alance: effluent/feed > IK
on recovery In gaa - 27
•gy recovery In gas . 3
OUTPUT
1.14 SCM CH4
0.50 S(X CO.!
0.83 kg carbon
10,21)0 kcal
> @ 38.5 wt I of TS 2.48 kg
6.44 kg
— > 9 1 7. 7 wt I of VS 0. 70
> @ 28.8 wt X of VS 1.14
2.«B kg
(72.8 wt X of VS)
— > C O.S wt I of VS 0.03 kg
"•*• > 1.0 5 kg
(26.5 we I of VS)
X
)t
I
REDUCTION/
(PRODUCTION)
23.4 Z
26.2 :
26.4
40.0
32.4 t
93.3 *
(40.8Z)
* ICPL la the am of protein, carbohydrate, and llplda.
Figure B-2. Mass balances for single-stage CFCSTR mesophilic
Run SS7M conducted with Hanover Park sludge at a 7-day HRT
-------
TABLE B-5. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. SS3M: CFCSTR SINGLE-STAGE MESOPHILIC (35°C) DIGESTION
OF HANOVER PARK SLUDGE CONDUCTED AT A 3-DAY HRT
Hydrogen, Carbon dioxide, Nitrogen, Methane,
Date mol % mol % mol % mol %
3/25/84 — 45.19 0.50 54.31
3/30/84 — 44.43 0.50 55.07
4/3/84 — 40.58 0.50 58.92
4/8/84 — 42.56 0.47 56.98
237
-------
TABLE B-6. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. SS3M
CFCSTR SINGLE-STAGE MESOPHILIC (35°C) DIGESTION OF HANOVER PARK SLUDGE CONDUCTED AT A 3-DAY HRT
Date
£ 3/23/84
00
3/30/84
3/31/84
4/4/84
4/9/84
Acetic,
mg/L
610
350
389
247
121
Proplonic,
mg/L
1,520
1,600
1,727
1,766
1,243
Isobutyric,
mg/L
267
205
220
176
85
Butyric,
mg/L
91
48
52
0
2
Isovalerlc,
mg/L
486
360
334
232
234
Valeric,
mg/L
114
96
97
61
62
Caproic,
mg/L
0
0
0
0
0
Total
as acetic,
mg/L
2,439
2,087
2,227
1,971
1,363
Ethanol,
mg/L
0
0
0
0
0
-------
INPUT
OUTPUT
Total Blurry
FS <» 23.9 wt Z of TS
VS 9 76.1 wt I
TS
Protein 8 34.6 wt Z of VS
Carbohydrate ? 25.4 wt Z
Llplds 9 26.0 wt X of VS
Is, ICPt*
VA 6 6.2 wt Z of VS
Other organlca (by dlff)
r
471 "5
6.30 kg
1.66 kg >
of VS 1.22 >
1 25 — ^
4.13 kg
(86.0 wt Z of VS)
0. 30 kg >
(7.5 wt Z of VS)
CFSTR
single-stage
Temp: 35°C
Loading:
15.4 kg VS/nt3-d
HRT: 3. 1 days
> fl 73.3 wt Z of TS
> (8 31.2 wt Z of VS
> p 16. 7 wt Z of VS
(73.
> 9 6.3 wt Z of VS
0.43 SCM CH
0.14 SCM CO
0. 39 kR car
3850 kcal
4.05
5.52 kg
1.26 kg
0.6R
1.04
2.98 kg
6 wt Z of VS)
0.26 kg
" "•"•™™ — ~— •unir.TT .1. i._..________i __~._i_ ._ j. ,_,, v, „ .^
(20.0 wt % of VS)
REDUCTION/
(PRODUCT ION)
15.4 Z
23.7 Z
44.4
16.5
27.6 Z
13.3 X
(125.01)
FS balance: effluent/feed - 97Z
VS balance: effluent/feed - 1041
Carbon recovery in gas •> 14Z
Energy recovery In gas - 12%
* £CPL la the sum of protein, carbohydrate, and llpids.
Figure B-3. Mass balances for single-stage CFCSTR mesophilic
Run SS3M conducted with Hanover Park sludge at a 3-day HRT
-------
TABLE B-7. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. SS15T: CFCSTR SINGLE-STAGE MESOPHILIC (55°C) DIGESTION
OF HANOVER PARK SLUDGE CONDUCTED AT A 15-DAY HRT
Hydrogen, Carbon dioxide, Nitrogen, Methane,
Date mol % mol % mol % mol %
5/27/84 — 34.36 Q.ll 65.53
6/3/84 — 33.39 0.28 66.34
6/1/84 — 33.38 0.13 66.49
6/11/84 — 32.91 0.21 66.88
240
-------
TABLE B-8. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. SS15T
CFCSTR SINGLE-STAGE MESOPHILIC (55°C) DIGESTION OF HANOVER PARK SLUDGE CONDUCTED AT A 15-DAY HRT
KJ
Date
5/27/84
6/3/84
6/9/84
6/11/84
Acetic,
mg/L
209
162
118
128
Proptonic,
mg/L
1,043
864
746
721
Isobutyric,
mg/L
121
89
33
34
Butyric,
mg/L
6
5
0
0
Isovalerlc,
mg/L
258
427
37
234
Valeric,
mg/L
0
0
16
16
Caproic,
mg/L
11
25
0
0
Total
as acetic,
mg/L
1,299
1,191
776
882
Ethanol,
mg/L
0
0
0
0
-------
INPUT
OUTPUT
RF.HUCTiriM/
(PRODUCTION)
0.89 SCM CH4
0.45 SCM CO,
NJ
Total slurry
FS 9 25.9 wt I of TS
VS 8 76.1 wt X
TS
Protein 8 36.9 wt X of VS
Carbohydrate « 23.0 wt X of VS
Upldi 9 31.7 wt X of VS
ECPL*
VA 9 4.6 wt X of VS
Other organic* (by dlff)
4. 16 kg
i
of VS
.
1.17 kg >
0. 73 >
1.00 >
2.90 kg
(91.6 wt X of VS)
0.15 kg >
0.12 kg >
(3.8 wt X of VS)
r ~
single-stage
Temp: 55°C
Loading;
2.1 kg VS/in3-d
HRT: 15*0 daya
> $) 29.2 wt X of VS
> @ 29.3 wt X of VS
> 3 |7.2 wt X of VS
(75.
> 9 7. 1 wt X of VS
(17.
0. 6fl kg cat
8010 kcal
2. 78 kg
0.54 kg
0.54
0.32
1.40 kg
7 wt X of VS)
0.13 kg
-> 0.33 kg
7 wt X of VS)
41.3 X
53.5 X
15.3
ftq.2
51.5 X
13.3 X
(175.0X)
FS balance: effluent/feed - 93X
VS balance: effluent/feed * 104X
Carbon recovery In gas » 37X
Energy recovery In gas - 39X
EC PL Is the am of protein, carbohydrate, and llpide.
Figure B-4. Mass balances for single-stage CFCSTR thermophilic
Run SS15T conducted with Hanover Park sludge at a 15-day HRT
-------
TABLE B-9. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. SS7T: CFCSTR SINGLE-STAGE MESOPHILIC (55°C) DIGESTION
OF HANOVER PARK SLUDGE CONDUCTED AT A 7-DAY HRT
Hydrogen, Carbon dioxide, Nitrogen, Methane,
Date mol % mol % tool % mol %
7/27/84 0.04 31.52 0.00 68.43
7/29/84 0.10 31.43 0.17 68.31
8/3/84 0.07 32.24 0.00 67.69
243
-------
N5
TABLE B-10. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. SS7T
CFCSTR SINGLE-STAGE MESOPHILIC (55°C) DIGESTION OF HANOVER PARK SLUDGE CONDUCTED AT A 7-DAY HRT
Date
7/27/84
7/29/84
8/3/84
Acetic,
mg/L
145
135
352
Propionic,
mg/L
1,530
1,876
1,718
Isobutyrlc,
mg/L
122
69
298
Butyric,
mg/L
0
0
0
Isovaleric,
mg/L
572
653
648
Valeric,
mg/L
0
0
0
Caproic,
mg/L
47
64
70
Total
as acetic,
mg/L
1,829
2,121
2,365
Ethanol,
mg/L
0
0
0
-------
INPUT
r
OUTPUT
1.26 SCH Cli^
0.59 SCM CO ^
-> 1.96 kg total R,i8
0.94 kg carbon
11,350 kcal
RFDHCTION/
(PRODUCTION)
Ln
Total Blurry
FS 9 26.0 wt X of TS
VS @ 74.0 wt X
TS
Protein « 35.1 wt I of VS
Carbohydrate (? 19.4 wt X of VS
Llpids @ 19.8 wt X of VS
ICPL*
VA 0 8.7 wt X of VS
Other organlcs (by dlff)
iuu kg
1.75 kg
4.97
6.72 kg
>1
>
3.68 kg
(74.3 wt X of VS)
(17.3 wt I of VS)
Run no, SR7T
CFCSTR
single-stage
Loading:
7.1 kg VS/m'-d
> 0 34.4 wt X of TS
__„__._-. __> @ 65 6 wt t of TS
(66.
(25.
1.80 kg
3 43
5.23 kg
- .VI kg
2.2S kg
7 wt x or vs)
0. 28 kg
4 wt X of VS)
31.0 X
47.8 I
10. B
47.8
38.1 X
14.9 X
(1.2X)
FS balance: effluent/feed - 103Z
VS balance: effluent/feed - 108Z
Carbon recovery In gaa - 32X
Energy recovery In gas - 35X
* ICPL Is the sum of protein, carbohydrate, and Upids.
Figure B-5. Mass balances for single-stage CFCSTR thermophilic
Run SS7T conducted with Hanover Park sludge at a. 7-day HRT
-------
TABLE B-ll. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. SS3T: CFCSTR SINGLE-STAGE MESOPHILIC (55°C) DIGESTION
OF HANOVER PARK SLUDGE CONDUCTED AT A 3-DAY HRT
Hydrogen, Carbon dioxide, Nitrogen, Methane,
Date mol % mol % mol % mol %
8/7/84 0.00 36.82 0.35 62.83
8/11/84 0.00 37.54 0.38 62.09
8/16/84 -- 35.28 0.36 64.37
8/17/84 — 33.62 0.28 66.10
246
-------
TABLE B-12. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. SS3T: CFCSTR
SINGLE-STAGE MESOPHILIC (55°C) DIGESTION OF HANOVER PARK SLUDGE CONDUCTED AT A 3-DAY HRT
ro
-c-
Date
8/7/84
8/10/84
8/15/84
8/17/84
Acetic,
mg/L
937
1,128
1,052
1,064
Propionic,
mg/L
1,324
1,496
1,373
1,322
Isobutyric,
mg/L
473
461
300
267
Butyric,
mg/L
390
338
299
258
Isovaleric,
mg/L
863
890
772
717
Valeric,
mg/L
0
0
126
0
Caproic,
mg/L
126
131
148
148
Total
as acetic,
mg/L
3,172
3,476
3,178
2,992
Ethanol,
mg/L
0
0
0
0
-------
INPUT
OUTPUT
RKDItCTTOM/
(PftomiCTIOH)
to
4J-
oo
0.55 SCM CH4
0.12 SCM C02
> 0.97 kf? total g
0.44 kg carbon
5000 kcal
Total slurry
rs 9 27.2 vt Z of TS
VS 9 72.8 Ht Z
TS
Protein 9 35.7 Ht Z of VS
Carbohydrate 9 19, 3 vt Z of VS
Llpids 9 19.2 wt Z of VS
ICPL*
VA 9 10. I wt Z of VS
Other organic* (by dlff)
1 81 kg
4*86
6.6? kg
f\ 0*1 ^
3.61 kg
(74.2 Ht Z of VS)
0. 49 kg >
(15.6 Ht Z of VS)
CFCSTS
single-stage
Loading:
15.6 kg VS/m3-d
HRT: 3. 3 days
(68.
> @ 9.6 Ht Z of VS
(22.
.96 kg
6.23 kg
1.3fl kg
2.92 kg
9 Ht Z of VS)
0.41 kg
0 wt Z of VS)
!?.!
20.4 r.
10.4
2?. 9
IH.4 Z
16. 3 Z
(23.7Z)
FS balance: effluent/feed - 10BZ
VS balance: effluent/feed - 1081
Carbon recovery in gas • 15Z
Energy recovery in gas - I6Z
* EC PL, Is the sun of protein, carbohydrate, and llplds.
Figure B-6. Mass balances for single-stage CFCSTR thermophilic
Run SS3T conducted with Hanover Park sludge at a 3-day HRT
-------
TABLE B-13. VOLATILE SOLIDS AND ORGANIC COMPONENT CONCENTRATIONS AND REDUCTIONS OBSERVED DURING STEADY-STATE
MESOPHILIC (35°C) AND THERMOPHILIC (55°C) CFCSTR SINGLE-STAGE DIGESTION OF HANOVER PARK SEWAGE SLUDGE
Run Sample Sample date(s)°
SS15M Feed 1/6/83
1/6/83
1/6/83
Effluent 2/11/83
2/12-2/15/83
2/12-2/15/83
2/13/83
5J 2/16-2/19/83
^ 2/16-2/19/83
SS7M Feed 12/12-12/14/83
12/31-1/9/84
Effluent 12/12-12/14/81
12/31-1/9/84
SS3M Feed 3/28-4/6/84
3/28-4/6/84
Effluent 3/28-4/6/84
3/28-4/6/84
Lot
1
1
1
Run neansc
Feed means
Final menus*
1
1
1
1
1
1
6
6
Run moans
Feed means
Final mc.ius
6
h
8
8
Run means
Feed npans
8
8
Bnt.-li
3
3
3
3
1
3
3
3
3
2
2
2
2
5
5
5
5
TS VS
mp,/l, mK/L t
45,100 13,500
45,101! 33,500
45,100 13,500
45,100 11,500
35,280 22,780
34,770 22,120
35,025 22,450
75.7WI 49,750
80,140 53,58(1
7K.050 51,61,',
54,910 12,510
71,7/0 46,hfiO
64,150 19,585
61,020 47,940
61,020 47,940
61,020 47,940
55,240 40,4811
55. 240 40,480
55,24(1 411,480
wt 7. wt %
f TS ros/l. of VS IT
4.28 12,115 16.76
4.28
4.28
74.28 16.76
Hi. 76
12,115 Ui.76
,4.57
8781 18.55
|).62
R918 40.41
9068 40.99
i4.!0 B97(, !9.98
.5.1,7
,6.69 14,1,69 27.18
,d. 18 ;>7. 1«
27. 10
14,1.", .','. 14
59.18
,1.5' I0,i.'7 .'li.l'i
7(i.o7 1 (,, 156 t'(. 1 1 1
76. 07 — — 1
15.00
16,51,8 li.56 1
M..M I2,6'|4 11. .'4
71.."*
7 !..!« 12,644 1I.J4
(runt in, led)
Reproduced irom ir,
best available copy. ^
.arbohvdr.H....
ut X
S/L of VS
6512 19.50
19.50
19.50
h', 12 19.50
4769 20.94
't840 21.25
4710 21.29
.'.750 21. Hi
9958 20.02
9016 Id. 86
IH.'.4
9V7 IH.44
6811 21.01
6716 14,44
70 1', I7.7J
J.lll ' V',.06
,158 21.69
24. 1«
2ii.)2
2,151 1 ', . \ 5
H527 16.12
H978 17.24
675' 16.1,8
* ^
Llpids
wt ?
• R/t. Of VS
7239 21.61
<)28B 27.73
670(1 2(1.00
21.11
21.11
7742 21.11
5078 22.29
6490 29.14
',797 25. H2
IB, 929 35.13
15.53
17.98
I8.D92 1h.76
11,4211 28.77
11,184 28.77
12,192 25.85
25.85
25.98
12,455 25.98
IO.J97 25.68
10, "197 25.68
Organic reductions, 2
Protein Carbohydrate tlpidfl
27.11 27.28 25.12
26.18 26.38 40.03
21.68 44.44 - 16.52
-------
TABLE B-13 (continued)
Run Sample Sample date(s)b
SS15T Feed 5/31-6/9/84
Effluent 5/31-6/9/84
SS7T Feed 8/2-8/6/84
8/2-8/6/84
Effluent 8/2-8/8/84
8/2-8/SM
LJ| SS3I Feed 8/8-8/17/84
Q 8/8-8/17/84
Effluent 8/8-8/17/84
lx>t Batch
12 1
Run means
Feed means
Final means
12 1
lf> 1
16 1
Run means
Feed means
Final means
16 1
16 I
16 1
16 1
Run means
Final means
16 1
TS
ms/l-
41.560
41,5611
27,780
27,780
67,2511
67,250
67,2511
52,120
K.no
52,320
66,735
66.735
66,735
62.340
62,340
VS
"K/l.
31,630
11,6)0
18,560
18,560
49,741)
49.740
49,740
34,110
34,110
34,310
48,615
48.615
48,615
42.705
42.705
wt 7,
of TS
76.11
76.il
66.81
66. HI
71.96
73.96
73.96
65. 5«
65. 5H
65.58
72.85
72.85
72.85
68.50
68.50
Crude (tr*
nu/l.
11.669
11,669
5425
5425
17,188
—
17,479
9125
9125
17,369
— -
"17,365
13.825
13,825
itein
wt "
or vs
36. »9
16.H9
3fi.«9
36.«9
29.23
29.21
34.56
34.56
35.71
35.14
26.60
26.60
35.73
•35771
35.71
-31772
12.37
•JITTT
C.irhoh
mi!/'-
7292
7292
5444
5444
9292
10.238
9674
8856
8194
8625
10,363
8479
WiT
8428
842TT
vdrates
wt Z
of VS
23.05
21.115
23.05
21.05
29.33
29.33
18. 68
20.58
19.63
19.27
19.45
25. HI
24.47
IsTTi"
21.32
17.48
19.40
19.27
T97T4
19.74
19.74
Llptds
">g/t
10.030
10,030
3185
3185
9705
—
9829
5134
-5T3T
«952
—
9334
7195
7f95~
wt 7.
of VS
31.71
31.71
31.71
31.71
17.16
17.16
19.51
19.51
20.00
19.76
14.96
74796"
18.41
18.41
20.00
19.20
16.85
16.85
Organic reductions, X
Ptotein Carbohydrate Liplds
53.51 25.34 68.25
47.79 10.84 47.77
20.39 10.36 22,92
* Data reported are the averages of duplicate or triplicate determinations.
^ A single sample date indicates that the analyses were conducted on a >jrah sample collected that day. A time period under this column Indicates
the start and end dates of collection of a grab or tlrae-coraposlte sample used for the analyses.
c Run means are the averages of the feed analyses conducted for a particular steady-state run on a single feed lot and batch.
<* Feed neana are the average organic contents (expressed as weight percent of VS) of all steady-state samples collected for
a particular feed lot and batch.
e Final means are the average feed slurry organic concentrations and contents used tn determine the organic reductions.
The organic contents are the average of the feed and run organic contents. Organic Feed concentrations were calculated
as the product of the final mean organic feed contents and the average* feed volatile solids concentration for the run.
-------
APPENDIX C
EFFLUENT ANALYSES FOR TWO-PHASE CFCSTR DIGESTION STUDIES
TABLE C-l. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. TP15M-M: CFCSTR MESO-MESO TWO-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 15-DAY HRT
Hydrogen,
Date mol %
Acid-phase (Digester No
10/9/83
10/16/83
10/22/83
10/29/83
11/6/83
11/13/83
11/14/83
11/20/83
Methane-phase (Digester
10/9/83
10/16/83
10/22/83
10/29/83
11/6/83
11/13/83
11/14/83
11/20/83
Carbon dioxide,
mol %
. 332)
38.24
39.25
37.04
36.05
35.03
33.78
35.09
34.78
No. 333)
29.45
28.80
29.16
28.77
28.79
29.12
28.88
28.60
Nitrogen,
mol 7,
1.56
0.98
1.25
0.81
1.51
0.74
2.89
0.95
1.26
1.43
0.60
0.42
0.00
0.00
0.00
0.00
Methane,
mol %
60.21
59.77
61.72
63.14
63.46
65.49
62.02
64.26
69.28
69.77
70.25
70.81
71.21
70.88
71.12
71.40
251
-------
TABLE C-2. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. TP15M-M:
CFCSTR MESO-MESO TWO-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 15-DAY HRT
ro
Ui
Date
Acid-phase
10/17/83
10/21/83
10/29/83
11/7/83
11/14/83
11/15/83
11/21/83
Acetic, Propionic, Isobutyrlc,
mg/L mg/L mg/L
(Digester No.
324
464
396
282
201
212
188
Methane-phase (Digester
10/17/83
10/21/83
10/29/83
11/7/83
11/14/83
11/15/83
6
51
23
37
0
1
. 332)
340
468
402
331
258
219
275
No. 333)
3
13
0
30
0
0
49
66
57
35
24
28
23
0
0
0
0
0
0
Butyric,
mg/L
32
62
48
7
0
4
16
0
0
0.
0
0
0
Isovalcric,
mg/L
91
119
111
79
65
71
51
0
0
0
0
0
0
Valeric,
mg/L
14
24
20
15
4
9
18
0
0
0
0
0
0
Caprotc,
mg/L
0
0
0
0
0
0
0
0
0
0
0
0
0
Total
as acetic,
mg/L
716
1,014
871
635
467
458
478
8
61
23
62
0
1
Ethanol,
mg/L
0
12
0
0
—
—
—
0
15
0
0
—
— _
-------
INPUT
OUTPUT
Total slurry
FS g 28.6 wt Z of TS
VS 9 71.4 wt Z
TS
Protein @ 31.6 wt Z of VS
Carbohydrate @ 29.6 wt Z
Llpids 8 24.3 wt Z of VS
ICPL*
rO
Ui
OJ VA 9 1.5 wt Z of VS
Other organlcs (by dlff)
100 kg >
2.81 — — — ->
3.94 kg
0 6fl ^
2.40 kg
(85.5 wt Z of VS)
0.04 kg >
(13.2 wt Z of VS)
[
CFCSTR
acid— phase
Loading:
14.8 kg VS/m*-d)
HRT: 2.0 days
0. 1ft SCM CH
O.OQ SCM CO
0.13 kg car
1470 kcal
_„„____„-> (? 68 9 wt X of TS 2 55
3.70 KR
> P 13.4 wt Z of VS 0.34
1.49 kg
(58.4 wt % of VS)
> (3 3. 1 wt Z of VS 0. 08 k(?
(38.4 wt Z of VS)
(PKOIlllCTIOH)
9.2 Z
31.4 Z
35.3
49.2
37.8 Z
(i no.oz)
(164.9Z)
FS balance: effluent/feed - 102Z
VS balance: effluent/feed - 101X
Carbon recovery In gas • 8Z
Energy recovery In gae - 81
* ZCPL 1* the sun of protein, carbohydrate, and llpida.
Figure C-l. Mass balances for mesophilic CFCSTR acid-phase
digester for meso-meso CFCSTR two-phase Run TP15M-M
conducted with Hanover Park sludge at a 15-day HRT
-------
INPUT
OUTPUT
to
Total slurry
FS 9 31.1 vt I of TS
VS 9 68.9 we X
TS
Protein @ 23.9 vt I of VS
Carbohydrate 9 21.1 wt X of VS
Llplda 9 13.4 wt X of VS
ICPL*
VA 8 3. 1 wt X of VS
Other organic* (by dlff)
2.55
3.70 kg
— — — . _ _ „„„,«._ «.„.««•••««_ _......%
1 o. 34 >
1.49 kg
(58.4 wt X of VS)
0.98 kg >
(38.4 wt X of VS)
r~
CFCSTR
me thane- phase
Loading:
2.2 kg VS/m3-d
0.99 SCM Cl
0.41 RCM «
0.71 k« c«
8,920 kcal
3.04 kg
—————> ^ 9* 2 wt X of VS 0 17
1.03 kg
(55.6 wt Z of VS)
.«__«.._«.««_«_««.____«_»«....__.__ — y 0. ft 3 kg
(44.6 wt Z of VS)
REDUCTION/
(PRODUCTION)
27.1 X
31.4 X
18.1
5n.7
31.0 *
ion.n x
(15.31)
FS balance: effluent/feed - 103Z
VS balance: effluent/feed « 129Z
Carbon recovery In gas - 4BX
Energy recovery In gas - 54X
* ICPL Is the sun of protein, carbohydrate, and llplda.
Figure C-2. Mass balances for mesophilic CFCSTR methane-phase
digester for meso-meso GFCSTR two-phase Run TP15M-M conducted
with Hanover Park sludge at a 15-day system HRT
-------
IN PIT
OUTPUT
Ul
Ul
Total slurry
FS 0 28.6 wt X of TS
VS <« 71.4 wt X
TS
Protein @ 31.6 wt X of VS
Carbohydrate 9 29.6 wt I of VS
Llplds 9 24.3 wt X of VS
ECPL*
VA ? 1.5 wt X of VS
Other organlcs (by dlff)
3.94 kg
0.89 kg >
I 0. bo — — .— —^
2.40 kg
(85.5 wt X of VS)
0.04 kg >
(13.2 we X of VS)
I
two-phase system
Temp: 35-35°C
Loading:
1.9 kg VS/o3-d
HRT: 15.2 days
> (3 22.6 wt X of VS
> @ 9.2 wt X of VS
(55.
> (9 0.2 wt X of VS
(44.
1.15 SCM CH
0.50 SCM CO
0. R4 kg car
10,390 kcal
3.04 kg
0.42 kg
0.17
1.03 kg
6 wt X of VS)
0.00 kg
6 wt X of VS)
REDUCTION/
(PRODUCTION)
31.8
52.9 X
47.0
75.0
57.1 t
100.0 X
(124.31)
FS balance: effluent/feed - 104X
VS balance: effluent/feed - 127*
Carbon recovery In gas - 51%
Energy recovery In gas - 57X
* ECPL Is the sum of protein, carbohydrate, and llplda.
Figure C-3. Mass balances for meso-meso CFCSTR two-phase
Run TP15M-M conducted with Hanover Park sludge
at a 15-day system HRT
-------
TABLE C-3. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. TP7M-M: CFCSTR MESO-MESO TWO-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 7-DAY HRT
Hydrogen,
Date mol %
Acid-phase (Digester No
9/21/84
9/24/83 0.00
9/26/84
9/28/84
Methane-phase (Digester
9/21/84
9/24/84
9/26/84
9/28/84
Carbon dioxide,
mol %
. 334)
42.25
43.07
42.53
40.94
No. 333)
31.56
31.51
32.00
32.25
Nitrogen,
mol %
0.12
0.67
0.33
0.42
0.14
0.00
0.05
0.42
Methane,
mol %
57.63
56.26
57.14
58.65
68.31
68.49
67.95
67.32
256
-------
Ul
--J
TABLE C-4. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. TP7M-M:
CFCSTR MESO-MESO TWO-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 7-DAY HRT
Date
Acid-phase
9/21/84
9/24/84
9/26/84
9/28/84
Acetic, Proplonic, Iso-butyric,
mg/L mg/L mg/L
(Digester No,
703
861
845
475
Methane-phase (Digester
9/21/84
9/24/84
9/26/84
9/28/84
81
99
72
1
, 334)
701
753
764
693
No. 333)
11
9
47
47
87
113
116
121
0
0
0
0
Butyric, Iso-valeric,
mg/L mg/L
136
214
207
82
0
0
0
0
103
137
149
155
0
0
0
0
Valeric,
mg/L
42
38
58
107
6
32
2
0
Caproic,
mg/L
68
55
2
0
62
44
26
0
Total
as acetic,
mg/L
1,544
1,826
1,808
1,329
125
148
124
39
Ethanol ,
mg/L
0
0
0
0
0
0
0
0
-------
INPUT
OUTPUT
REDUCTION/
(PRODUCTION)
0.44 SCM CH4
0.12 SCM C02
> 0.90 kg total f>a
0. 39 kg carbon
3960 kcal
Total slurry
FS 6 26.6 wt Z of TS
VS 9 73.4 wt X
TS
Protein @ 31.7 wt Z of VS
Carbohydrate S 22.5 wt Z of VS
Liplds 9 20.5 wt Z of VS
ICPL*
CO VA 8 5.6 wt Z of VS
Other organlca (by dlff)
4.88
6.65 kg
„_„„_„.., mj^JJJJ«— N
1.55 kg >
3.65 kg
(74.7 wt Z of VS)
n Qfi it a ----- — *s
(19.7 wt Z of VS)
CFCSTR
ac Id-phase
Temp: 35'C
Loading:
26. A kg VS/ra3-d
> 0 7o.o wt X of TS
> 0 33.0 wt X of VS
v a t a t ». » r Tie>
(68.
(27.
.82 Kg
4.25
6.07 kg
1.40 kg
2.90 k«
2 wt X of VS)
1 wt X of VS)
12.9 Z
9.6 Z
29.1
2«.2
20.6 Z
25.9 Z
(19.8Z)
ECPL la the Bin of protein, carbohydrate, and llplda.
FS balance: effluent/feed - 103Z
VS balance: effluent/feed - 106Z
Carbon recovery In gas • 14Z
Energy recovery In gaa • 13Z
Figure C-4. Mass balances for mesophilic CFCSTR acid-phase
digester for meso-meso CFCSTR two-phase Run TP7M-M conducted
with Hanover Park sludge at a 7-day system HRT
-------
INPUT
OUTPUT
REDUCTION/
(PRODUCTION)
S3
Ui
VO
Total slurry
YS 9 30.0 wt Z of TS
VS @ 70.0 wt Z
TS
Protein 9 33.0 wt Z of VS
Carbohydrate 0 18.3 wt X of VS
Upids 9 16.9 wt Z of VS
ECPL*
VA g 4.6 wt Z of VS
Other organlca (by dlff)
1.03 SCM
0.48 SCM
-> 1.59 kg total ga«
0.77 kg carbon
9330 kcal
100 kg -
4.25
6.07 kg
of VS
07ft S
* / O "• ~ ^
0.72 >
2.9() kg
(68.2 wt Z of VS)
(27.1 wt Z of VS)
CFCSTR
methane phase
Temp: 35'C
Loading:
10.1 kg VS/m3-d
„__„_____>. p 64.7 wt Z of TS
> $ 15.0 wt Z of VS
> 9 11.6 wt Z of VS
(61.
(38.
1.79 kg
3 28
5.07 kg
1.15 kg
0.49
0.38
2.02 kg
7 wt Z of VS)
0.01 kg
-> 1.25 kg
1 wt Z of VS)
22 8 Z
17.7 Z
36.6
46.7
30.0 Z
95.0 Z
(8.7Z)
TS balance: effluent/feed - 98Z
VS balance: effluent/feed - 115Z
Carbon recovery In gas - 31Z
Energy recovery In gas - 34Z
1CPL la the aim of protein, carbohydrate, and llplda.
Figure C-5. Mass balances for mesophilic CFCSTR methane-phase
digester for meso-meso CFCSTR two-phase Run TP7M-M conducted
with Hanover Park sludge at a 7-day system HRT
-------
IHPlfT
oirmrr
REDUCTION/
(PRODUCTION)
Total slurry
FS ? 26.6 wt X of TS
VS 9 73.4 wt X
TS
Protein @ 31.7 wt X of VS
Carbohydrate 9 22. 5 wt X of VS
Llplds 9 20.5 wt Z of VS
ICPL*
O VA 8 5.6 wt X of VS
Other organlcs (by dlff)
6.65 kg
of VS
1.00
3.65 kg
(74.7 wt X of VS)
0.96 kg
(19.7 wt X of VS)
.__„;>
V
— >
.___s
f
CFCSTR
two-phase system
Loading:
7.3 kg VS/m3-d
> 9 11.6 wt X of VS
(6
(3(
1.47 SCM CH4
O.BO SCM CO,
> 2.49 kg total gas
1.16 kg carbon
13,290 kcal
1.79 kg
3.28 32.8 X
5.07 kg
1.15 kg 25.6 X
0.49 55.1
0.18 61.B
2.02 kg 44.4 X
(61.7 wt X of VS)
0.01 kg 96.3 X
> 1.25 kg (30.2X)
(38.1 wt X of VS)
FS balance: effluent/feed - 101X
VS balance: effluent/feed - HBX
Carbon recovery in gas - 4IX
Energy recovery In gas - 42X
ECPL la the sun of protein, carbohydrate, and lipids.
Figure C-6. Mass balances for meso-meso CFCSTR two-phase
Run TP7M-M conducted with Hanover Park sludge
at a 7-day system HRT
-------
TABLE C-5. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. TP3M-M: CFCSTR MESO-MESO TWO-PHASE DIGESTION OF MIXED
DOWNERS GROVE PRIMARY AND STICKNEY ACTIVATED SLUDGES CONDUCTED
AT A 3-DAY HRT
Date
Acid-phase
12/13/84
12/15/84
12/18/84
12/20/84
Hydrogen,
mol %
(Digester No
—
—
—
0.05
Methane-phase (Digester
12/13/84
12/15/84
12/18/84
12/20/84
—
—
—
0.00
Carbon dioxide,
mol %
. 334)
47.88
48.06
45.59
44.48
No. 333)
35.10
36.64
36.02
38.06
Nitrogen,
mol %
0.63
1.68
0.32
0.29
0.00
1.59
0.00
0.00
Methane,
mol %
51.50
50.26
54.08
55.18
64.90
61.77
63.98
61.95
261
-------
TABLE C-6. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. TP3M-M:
CFCSTR MESO-MESO TWO-PHASE DIGESTION OF MIXED DOWNERS GROVE PRIMARY AND STICKNEY ACTIVATED SLUDGES
CONDUCTED AT A 3-DAY HRT
KJ
Acetic, Proplonic, Isobutyric,
Date mg/L mg/L mg/L
Acid-phase (Digester No,
12/13/84 2
12/15/84 2
12/18/84 2
12/20/84 1
Methane-phase
12/13/84
12/15/84
12/18/84
12/20/84
,133
,477
,336
,762
(Digester
187
293
276
114
. 334)
1,344
1,312
1,615
1,342
No. 333
1,306
1,336
1,746
1,620
282
294
321
254
18
19
68
95
Butyric,
mg/L
781
849
778
588
0
0
0
0
Isovalerlc,
mg/L
626
682
618
458
68
201
267
245
Valeric,
mg/L
3,559
2,014
1,063
991
136
69
75
264
Caproic,
mg/L
0
101
18
83
0
52
0
71
Total
as acetic,
mg/L
6,405
5,956
5,391
4,319
1,379
1,575
1,939
1,827
Ethanol,
mg/L
0
37
0
39
0
0
0
0
-------
INPUT
011T Pin-
Total slurry
FS 9 32.0 wt X of TS
VS 9 68.0 wt X
TS
Protein 9 38.6 wt X of VS
Carbohydrate 9 23.5 wt X of VS
Uplds ? 17.2 wt X of VS
ICPL*
2) VA 8 10.1 wt X of VS
Other organlcs (by dlff)
1 00 VP — •—— — — .— ,——™™— -.-—_—._ ~\
f. ££ ™» S
6.85 kg
1 80 kg >
of VS 1 10 ->
0. 80 >
3. 70 kg
(79.4 wt X of VS)
040 fcir ••-• — -^
(tO. 5 wt X of VS)
CFCSTR
acid- phase
Lo ad Ing :
49.3 kg VS/m3-d
0.27 SCM CH
0.25 SCM CO
0.27 k* car
24RO kcal
A. 16 kg
> 9 16.4 wt X of VS 0.64
2.76 kg
(70.5 wt X of VS)
> 0.45 kg
(11.4 wt X of VS)
REDUCTION/
(PRODUCTION)
15.7 X
33.0 X
15.R
19.7
25.0 X
(53.2 X)
(8.21)
FS balance: effluent/feed - 102Z
VS balance: effluent/feed - 102X
Carbon recovery in gas m tOX
Energy recovery In gas - BX
* ICPL Is the Bum of protein, carbohydrate, and Uplds.
Figure C-7. Mass balances for mesophllic CFCSTR acid-phase
digester for meso-tneso CFCSTR two-phase Run TP3M-M conducted with
mixed Downers Grove primary and Stickney activated sludges
at a 3-day system HRT
-------
INPUT
OUTPUT
REDUCTION/
Total slurry
FS 8 36.2 we Z of TS
VS @ 63.8 wt X
TS
Protein 9 30.6 wt X of VS
Carbohydrate 8 23.5 wt X of VS
Llplds @ 16.4 wt X of VS
ICPL*
VA 0 18.2 wt X of VS
Other organlcs (by dlff)
2.23 kg —
6.16 kg
__..«_ N
>
1.20 kg >
0. 64 >
2. 76 kg
(70.5 wt X of VS)
0.72 kg >
(11.4 wt X of VS)
r~
Run no. TP3M-M
me thane-pha se
Temp: 35°C
loading:
20.9 kg VS/m3-d
HRT: 2.2 days
0.60 SCM CH4
0.15 SCM CO,
0.48 kg carb
5420 kcal
> 9 39. 0 wt X of TS 2. 24 kg
— • > @ 61.0 wt X of T*5 3.50
5.74 kg
> 0 30.0 wt X of VS 1.05 kg
> (3 16.8 wt X of VS 0.59
2.18 kg
(62.2 wt X of VS)
> 0 6. 1 wt X of VS 0.21 kg
(31.7 wt X of VS)
10.9 X
12.7 X
41.3
8.8
21.1 X
70.8 X
(146.7*)
FS balance: effluent/feed - 1002
VS balance: effluent/feed -116*
Carbon recovery in gaa - 21%
energy recovery In ga» - 11X
* ICPL IB the sun of protein, carbohydrate, and llpida.
Figure C-8. Mass balances for mesophilic CFCSTR methane-phase
digester for meso-meso CFCSTR two-phase Run TP3M-M conducted with
mixed Downers Grove primary and Stickney activated sludges
at a 3-day system HRT
-------
INPUT
OUTPUT
REDUCTION/
(PRODUCTION)
I
0.87 SCM CU4
0.60 SCM C02
-> 1.71 kg total gas
0.75 kg carbon
7900 kcal
NJ
Total slurry
FS @ 32.0 wt X of TS
VS 9 68.0 wt X
TS
Protein 9 38.6 ut X of VS
Carbohydrate 9 23.5 wt X of VS
Uplda 9 17.2 wt X of VS
ICPL*
VA 0 10. I wt X of VS
Other organic* (by dlff)
2. 19 kg -
4.66
6. 85 kg
of VS
1.80 kg
1.10
0.60
3.70 kg
(79.4 wt I of
0.47 kg
0.49 kg
(10.5 wt X of
V
VS)
VS)
Run no. TP3M-M
CPCSTR
two-phase system
Temp: 35-35*C
Loading:
14.7 kg VS/m3-d
HRT: 3. 1 days
> ? 39.0 wt X of TS
> 9 61.0 wt X of TS
(62.
(31.
2.24 kg
3.50
5.74 kg
1.05 kg
0.54
0.59
2. 18 kg
2 wt X of VS)
0.21 kg
-> I. 11 kg
7 wt X of VS)
24.9 X
41.5 X
50.6
26.B
41.0 X
55.3 X
(126.5X)
FS balance: effluent/feed - 102X
VS balance: effluent/feed - 112X
Carbon recovery In gas - 28X
Energy recovery In gas - 26X
* ECPL la the sun of protein, carbohydrate, and llplds.
Figure C-9. Mass balances for meso-meso CFCSTR two-phase
Run TP3M-M conducted with mixed Downers Grove primary and
Stickney activated sludges at a 3-day system HRT
-------
TABLE C-7. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. TP15M-T: CFCSTR MESO-THERMO TWO-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 15-DAY HRT
Date
Acid-phase
7/20/84
7/27/84
8/3/84
8/7/84
8/11/84
8/16/84
Hydrogen,
mol %
(Digester No
—
—
0.00
0.00
0.00
—
Methane-phase (Digester
7/20/84
7/27/84
8/3/84
8/7/84
8/11/84
8/16/84
—
--
—
0.00
0.00
—
Carbon dioxide,
mol %
. 334)
38.83
38.43
33.74
34.03
34.86
33.27
No. 337)
32.26
31.48
30.54
31.51
31.39
30.55
Nitrogen,
mol %
0.42
0.36
0.47
0.30
0.37
0.58
0.32
0.17
0.66
0.20
0.62
0.37
Methane,
mol %
60.75
61.21
65.79
65.67
64.77
66.15
67.42
68.35
68.79
68.28
67.99
69.09
266
-------
TABLE C-8. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. TP15M-T:
CFCSTR MESO-THERMO TWO-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 15-DAY HRT
Date
Acid-phase
7/20/84
7/27/84
8/3/84
8/7/84
8/10/84
8/16/84
Acetic, Propionic, Isobutyric,
mg/L rag/L mg/L
Butyric,
•ng/L
Isovaleric,
mg/L
Valeric,
mg/L
Caproic,
mg/L
Total
as acetic,
mg/L
Ethanol,
mg/L
(Digester No. 334)
396
284
590
502
605
602
Methane-phase (Digester
7/20/84
7/27/84
8/3/84
8/7/84
8/10/84
8/16/84
271
213
122
119
203
143
453
313
i
448
351
504
377
No. 337)
836
579
713
633
621
648
49
46
29
37
7
0
0
17
106
68
0
0
71
50
74
70
43
64
0
0
0
0
0
0
108
84
83
83
75
52
197
143
231
191
185
165
75
43
0
14
0
0
0
0
0
0
0
0
17
13
20
29
29
92
22
27
34
23
24
25
962
684
1,082
931
1,106
1,030
1,076
792
925
803
827
779
0
0
0
0
0
0
0
0
0
0
0
0
-------
INPITT
00
Total slurry
tS @ 29.6 wt X of TS
VS ? 70.4 wt X
TS
100 kg
1.36 kg
3.24
4.60 kg
Protein 9 36.3 wt X of VS
Carbohydrate 9 18.8 wt X of VS
Llplds 9 21.0 wt X of VS
ICPL*
VA 9 10.3 wt X of VS
Other organic! (by dlff)
>
0 51 — ->
2.47 kg
(76.1 wt X of VS)
0.33 kg >
0.44 kg >
(13.6 wt X of VS)
—
CFCSTR
acld-phaae
Loading:
15.5 kg VS/m3
HRT: 2. 1 days
.___ — ___ _
> 9 68.8 wt X of TS
(77.
> 0 4.2 wt X of VS
(18.
OUTPtfT
0.34 SCH CH4
0.19 SCH C02
-> 0.58 kg tota
0.27 kg carh
3040 kcal
1.24 kg
2.72
3.96 kg
0.63
2.12 kg
8 wt X of VS)
0.11 kg
-> 0.49 kg
0 wt X of VS)
REDUCTION/
(PRODUCTION)
16.1 X
12.8 X
24.5
7.6
14.2 X
66.7 1,
(11.4X)
FS balance: effluent/feed - 91X
VS balance: effluent/feed - 102X
Carbon recovery In gas - 14X
Energy recovery In gaa - 15X
* ECPL IB the Bin of protein, carbohydrate, and llpldg.
Figure C-10. Mass balances for mesophilic CFCSTR acid-phase
digester for meso-thermo CFCSTR two-phase Run TP15M-T
conducted with Hanover Park sludge at a 15-day system HRT
-------
to
Total slurry
FS 9 31.2 wt Z of TS
VS 9 68.8 wt Z
TS
Protein 9 37.7 wt Z of VS
Carbohydrate 9 16.9 wt Z of VS
Llplds 8 23.2 wt Z of VS
ICPL*
VA 9 4.2 wt X of VS
Other organic* (by dlff)
INPUT
3.96 kg
of VS 0.46 >
0.63 >
2.12 kg
(77.8 wt Z of VS)
(18.0 wt Z of VS)
f
methane-phase
Loading:
2.5 kg VS/m3-d
> g 21.1 wt Z of VS
> 9 11.3 wt Z of VS
(66.
(28.
OHTPITT
0.64 SCM CH4
0.29 SCM C02
0.48 kg carbon
5790 kcal
3. 18 kg
0.42
0.23
1.33 kg
6 wt Z of VS)
0. 1 1 kg
0 wt Z of VS)
REDUCTION/
(PRODUCTION)
8.1
64.1
37.0 Z
FS balance: effluent/feed - 95%
VS balance: effluent/feed - 110Z
Carbon recovery In gas - 30Z
Energy recovery In gas - 33Z
* gCPL Is the sum of protein, carbohydrate, and llplds.
Figure C-ll. Mass balances for thermophilic CFCSTR methane-phase
digester for meso-thermo CFCSTR two-phase Run TP15M-T conducted with
Hanover Park sludge at a 15-day system HRT
-------
INPOT
OUTPUT
REDUCTION/
(PRODUCTION)
0.98 SCM CH4
0.48 SOI C(>
NJ
«-J
O
Total slurry
rs ? 29.6 wt X of TS
VS 9 70.4 wt Z
TS
Protein 0 36.3 wt Z of VS
Carbohydrate 9 18.8 wt Z of VS
Llplds 9 21.0 wt Z of VS
ICPL*
Vk 9 10.3 wt Z of VS
Other organic* (by dlff)
100 kg
3 24 —
4.60 kg
of VS
.•~_~^.W«W_ K -. M«S
1.18 kg >
2.47 kg
(76.1 wt Z of VS)
0.33 kg >
0 &A kff — >
(13.6 wt Z of VS)
f
two-phase system
Temp: 35-35'C
Loading:
2.1 kg VS/m3-d
HRT: 15.1 days
> 0 34.2 wt Z of VS
(66.6 wt Z of VS)
> 0 5.5 wt Z of VS
(28.0 i
l.S/ kg total gas
0.75 kg carbon
8830 kcal
1.18 kg
3.18 kg
0.68 kg
1.33 kg
0.11 kg
it Z of V"O
38.3 Z
41.9 Z
30.6
66.8
46.0 Z
66.7 X
(27. 3t)
FS balance: effluent/feed - 87Z
VS balance: effluent/feed - 110Z
Carbon recovery In gas - 40Z
Energy recovery In gas - 42Z
* £CPL Is the sun of protein, carbohydrate, and llplde.
Figure C-12. Mass balances for meso-therrao CFCSTR two-phase
Run TP15M-T conducted with Hanover Park sludge
at a 15-day system HRT
-------
TABLE C-9. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. TP7M-T: CFCSTR MESO-MESO TWO-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 7-DAY HRT
Hydrogen,
Date mol %
Acid-phase (Digester No
8/24/84
8/31/84
9/7/84
9/10/84 0.00
9/12/84 0.00
9/16/84
Methane-phase (Digester
8/24/84
8/31/84
9/7/84
9/10/84
9/12/84 0.00
9/16/84
Carbon dioxide,
mol %
. 334)
43.73
44.43
43.73
43.51
43.22
43.76
No. 331)
31.22
30.96
32.51
32.98
32.55
33.38
Nitrogen,
mol %
0.19
0.09
0.00
0.36
0.63
0.65
0.09
0.61
0.03
0.49
0.16
0.26
Methane,
mol %
56.09
55.48
56.27
56.13
56.15
55.59
68.69
68.43
67.45
66.53
67.29
66.36
271
-------
TABLE C-10. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. TP7M-T:
CFCSTR MESO-THERMO TWO-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 7-DAY HRT
K>
Acetic, Proplonic, Isobutyric,
Date mg/L tng/L mg/L
Acid-phase (Digester No
8/24/84 1
8/31/84
9/7/84
9/10/84
9/12/84
9/14/84
Me thane-phase
8/24/84
8/31/84
9/7/84
9/10/84
9/12/84
9/14/84
,040
839
755
903
858
958
(Digester
220
278
442
605
574
528
. 334)
962
913
824
847
790
757
No. 331
1,274
1,608
1,356
1,540
1,338
1,375
116
30
0
0
6
9
0
86
0
189
155
134
Butyric, Isovalerlc,
mg/L mg/L
287
151
91
127
144
155
0
0
0
0
0
0
201
190
101
118
114
158
73
435
203
456
471
530
Valeric,
mg/L
60
60
0
0
0
40
0
0
0
0
0
0
Caproic,
mg/L
38
53
31
48
22
0
52
78
46
83
65
87
Total
as acetic,
mg/L
2,267
1,878
1,560
1,771
1,679
1,800
1,322
1,936
1,684
2,294
2,076
2,090
Ethanol,
mg/L
0
0
0
0
0
0
0
0
0
0
0
0
-------
NJ
Total slurry
FS 0 26.8 wt X of TS
VS 9 73.2 wt X
TS
Protein P 33.1 wt X of VS
Carbohydrate @ 23.3 wt X of VS
Llplds 9 23.3 wt X of VS
ICPL*
VA 9 4.6 wt X of VS
Other organlca (by dlff)
INPUT
100 kg r •»•"•----—•••- -..„,_,._>
1 7R Its -- —-———.-— --..^^-.^ s
4.86 _>
6.64 kg
of VS 1.13 >
1.13 >
3.87 kg
(79.7 wt X of VS)
0.77 kg >
(1S.8 wt X of VS)
r
Run no TP7M-T
CFCSTR
acid- phase
Temp: 35*C
Loading:
Z6.3 kg VS/m3-d
1IRT: 1.9 days
OUTPUT
n.42 SCM CH4
0.33 SCM C02
> 0.91 kg total gas
0. 38 kg carbon
3810 kcal
> (a 29.4 wt X of TS 1.78 kg
6.116 kg
> P 17.5 wt X of VS 0.75
> @ 23.1 wt X of VS 0.99
3.22 kg
(75.2 wt X of VS)
(19.9 wt X of VS)
REDUCTION/
(PRODUCTION)
11.9 X
8.3 X
34.0
12.7
17.1 X
4.6 X
(10.4X)
FS balance: effluent/feed - 100%
VS balance: effluent/feed - 107X
Carbon recovery In gas - 13X
Energy recovery in gaa - 12X
* [CPU Is the sun of protein, carbohydrate, and llplda.
Figure C-13. Mass balances for mesophilic CFCSTR acid-phase
digester for meso-thermo CFCSTR two-phase Run TP7M-T conducted with
Hanover Park sluge at a 7-day system HRT
-------
INPUT
OUTPUT
REDUCTION/
(PRODUCTION)
NJ
Total slurry
rs 9 29.4 wt X of TS
VS 9 70.6 wC X
TS
Protein @ 34.6 wt X of VS
Carbohydrate ? 17.5 wt X of VS
Liplds 9 23.1 wt X of VS
ICPL*
VA 8 5.0 wt X of VS
Other organlca (by dlff)
I
1.12 SCM CM4
0.54 SCM r.02
—> 1.76 kg total ga
0.84 kg carbon
10,130 kcal
1 78 kg —
4.28
6.06 kg
of VS
...u. V
0. 75 >
0.99 >
3.22 kg
(75.2 wt X of VS)
(19.9 wt X of VS)
CFCSTR
me thane- phase
Loading:
9.1 kg VS/m3-d
-> (? 21.0 wt X of VS
. > @ \\m2 wt X of VS
(65.6
f?fi_6
1.74 kg
4.93 kg
1.07 kg
0.67
0 36
2.10 kg
wt X of VS)
0.24 kg
at 1 r\f VO
25.5 X
27.9 7.
10.5
63.9
34.9 Z
(14.3Z)
(O.OZ)
FS balance: effluent/feed • 9ftX
VS balance: effluent/feed - 116Z
Carbon recovery in gas • 34X
Energy recovery In gas - 37X
* ECPL Is the sun of protein, carbohydrate, and Hplds.
Figure C-14. Mass balances for therraophilic CFCSTR methane-phase
digester for meso-thermo CFCSTR two-phase Run TP7M-T conducted
with Hanover Park sludge at a 7-day system HRT
-------
•vl
Ul
Total slurry
FS 9 26.8 wt X of TS
VS
3.87 kg
(79.7 vt X of VS)
(15.8 vt X of VS)
f
CFCSTR
two-phase system
Loading:
6.7 kg vs/m3-d
OUTPUT
1.54 SCM CH4
0.87 SCM C02
1. 22 kg carbon
13,940 kc«l
> @ 35. 2 wt % of TS 1.74 kg
4.93 kg
> fl 1 1 . 2 wt X of VS 0. 36
2.10 kg
(65.6 wt X of VS)
(26.6 wt X of VS)
REDUCTION/
(PRODUCTION)
68. «5
46.0 X
FS balance: effluent/feed - 9RZ
VS balance: effluent/feed - 121X
Carbon recovery In gas - 43X
Energy recovery in gas - 45X
* rCPL la the sin of protein, carbohydrate, and llplds.
Figure C-15. Mass balances for meso-thertno CFCSTR two-phase
Run TP7M-T conducted with Hanover Park sludge at a 7-day system HRT
-------
TABLE C-ll. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. TP7T-T: CFCSTR THERMO-THERMO TWO-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 7-DAY HRT
Hydrogen,
Date mol %
Acid-phase (Digester No
10/20/84
10/27/84
11/3/84
11/9/84
Methane-phase (Digester
10/20/84
10/27/84
11/3/84
Carbon dioxide,
mol %
. 335)
40.65
41.65
41.63
43.94
No. 331)
28.40
28.45
30.01
Nitrogen,
mol %
1.18
0.65
0.80
1.51
0.19
0.68
0.31
Methane ,
mol %
58.17
57.70
57.57
54.55
71.41
70.87
69.68
276
-------
to
•vl
TABLE C-12. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. TP7T-T:
CFCSTR THERMO-THERMO TWO-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 7-DAY HRT
Acetic, Propionlc, Isobutyrlc, Butyric,
Date mg/L mg/L mg/L mg/L
Acid-phase (Digester No.
10/19/84
10/26/84 1
11/2/84 1
Methane-phase
10/19/84
10/26/84
11/2/84
718
,229
,036
(Digester
519
496
406
. 335)
594
865
710
No. 331)
904
932
798
167 134
260 248
219 211
190 0
225 0
213 0
Isovaleric,
mg/L
355
572
468
339
433
305
Total
Valeric, Caproic, as acetic,
mg/L mg/L mg/L
14 0 1,622
0 94 2,660
0 0 2,180
77 0 1,625
24 124 1,738
0 0 1,378
Ethanol,
mg/L
0
0
0
0
0
0
-------
TABLE C-13. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. TP3T-T: CFCSTR THERMO-THERMO TWO-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 3-DAY HRT
Hydrogen,
Date mol %
Acid-phase (Digester No
12/13/84
12/15/84
12/18/84
12/20/84 0.00
Methane-phase (Digester
12/13/84
12/15/84
12/18/84
12/20/84 0.00
Carbon dioxide,
mol %
. 335)
42.92
42.06
41.30
36.67
No. 331)
30.06
32.23
32.29
30.92
Nitrogen,
mol %
0.95
2.02
1.95
1.45
0.00
0.59
0.00
0.00
Methane,
mol %
56.13
55.91
56.75
61.88
69.94
67.18
67.71
69.08
278
-------
N)
~J
VO
TABLE C-14. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. TP3T-T:
CFCSTR THERMO-THERMO TWO-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 3-DAY HRT
Acetic, Propionic, Isobutyric,
Date mg/L mg/L mg/L
Acid-phase (Digester No
12/13/84 1,
12/15/84 1,
12/18/84 1,
12/20/84
Methane-phase
12/13/84
12/15/84
12/18/84
12/20/84
272
393
475
627
(Digester
140
94
145
30
. 334)
761
704
853
348
No. 331)
1,017
799
1,073
752
230
218
256
82
77
10
71
0
Butyric, Isovaleric,
mg/L mg/L
302
307
400
64
0
0
0
0
468
506
519
289
370
269
112
7
Valeric,
mg/L
176
208
134
139
561
220
87
62
Caproic,
mg/L
0
105
0
87
0
115
0
121
Total
as acetic,
mg/L
2,630
2,796
2,997
1,306
1,564
1,095
1,180
743
Ethanol,
mg/L
0
0
0
0
0
0
0
18
-------
TABLE C-15. VOLATILE SOLIDS AND ORGANIC COMPONENT CONCENTRATIONS AND REDUCTIONS OBSERVED DURING
STEADY-STATE MESO-MESO' AND MESO-THERMO CFCSTR TWO-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE3
N3
TP15M-M Feed
Acid-phase
effluent
Methane-phase
effluent
TP7M-M Feed
Acid-phase
effluent
Methane-phase
effluent
TPSM-M' Feed
Acld-phaae
effluent
Methane-phase
effluent
11/10/83
11/11-11/14/83
11/13/83
11/5-11/7/83
11/10/83
11/11-11/14/81
11/11-11/14/83
11/5/83
11/10/83
Il/M-11/14/83
11/13/83
9/25-9/29/84
9/25-9/29/84
9/25-9/29/84
9/25-9/29/84
9/25-9/29/84
9/25-9/29/84
12/17-12/21/84
12/17-12/21/84
12/17-12/21/84
12/17-12/21/84
12/17-12/21/84
12/17-12/21/84
Lot
5
5
5
Run menn<3c
Feed means0
Final means*
5
5
5
5
5
5
5
1 5
17
17
Feed means
17
17
17
17
21
21
Run means
Feed means
Final means
21
21
21
21
Batch TS
4
4
4
4
4
4
4
4
4
4
4
1
1
1
I
1
1
1
1
1
1
mR/l.
19,150
19,150
37,280
—
—
36.820
j /,iiiu
25,150
15,560
~
JO, 115
66, 540
66,540
66,540
60,720
Ml, 720
50,1,90
68,500
68.500
68,500
61,600
61,600
61,6011
57,450
57,450
57,450
-
VS Crude protein Carbohydrates
wt V.
niR/L of TS mR/L
28,100 71.41 9100
—
28, KKI 71.41
H880
25,660 68.81
25,380 68.91 6060
15,050 59.84
22,020 61.92 4969
—
18,5)5 61.06 4181
48,861) 71.41 15,112
4H.860 71.41
48,8611 71.41
1 5, .48')
42,480 69.96 1/4,006
42,480 69.96
42,480 69.96 1'4,006
12,810 64.71 11,511
12,810 64.71
12,810 64.71 11,511
46,600 6H.OI 17,97')
46,600 68.01
46,hOO 68. 1)1
1 l.-il;
19,120 61.81 1 !,04ri
39,12(1 61.81
19,120 61.81 I.!,o44
35,040 60,99 10,512
15,040 60.99
15,040 6H.99 10,512
(coin Imird)
wt Z vt 7.
of VS mR/L of VS
12.18 H107 29.56
12.18 29.56
10.81 29.56
11.60 8107 29.56
5700 20 27
21. 88 5'>42 21.84
,: i ,iin ') 1 7 'i 2 1 .1)1)
•'216 28.21
22.57 42*9 19.10
J2.V 1404 21.76
11.14 11,178 22.88
10,1,10 21.72
11.14 22. til
12.05 22. 6H
11. /O IO,'!H9 22. 1')
12.97 «|9I 19.28
7186 1?.)9
!.!.<>; 7791 IK.l.'i
l'>. 14 5'44il 16.58
4'.2'4 1 1.48
15.11 1912 I5.IM
18. W 10,159 .'1.80
11,452 24. 5K
IH.S7 21.1'J
)8.',7 21.19
IX.'i? 111, '!',', .M.51
10.61 9)99 21.90
9056 2!. 01
10.61 9!;'/4 21.46
10.00 6206 17.71
4622 11.19
lO.on y,|l 15.45
Reproduced from m
best available copy. ^1
I-lpi
-------
TABLE C-15 (continued)
Run Sample I
TP15M-T Feed
Acid-phase
effluent
Methane— phase
effluent
T?7M-T Feed
N>
00
Acid-phase
effluent
Methane-phase
effluent
Sample date(s)D
8/8-8/17/84
8/8-8/17/84
8/8-8/17/84
8/8-8/17/84
9/10-9/14/84
9/10-9/14/84
9/17/84
9/17/84
9/10-9/14/84
9/10-9/14/84
Lot Batch TS VS
16
Run means
Feed means
Final means
16
16
16
17
Run means
Feed means
Final means
17
17
17
17
mg/1. mK/L
1 46.045 32,420
46,045 32,42(1
1 39,590 27,241)
1 39.590 27.240
39.590 27,240
1 31.790 20.020
31,790 20,020
1 66,430 48,640
1 66,430 48.640
66,430 48,640
1 60.350 42,760
1 60,550 42,760
60,550 42,760
1 49,330 31,950
1 49.330 31.950
49,330 31,950
wt *!
of TS
70.41
70.41
68.81
68.81
68.81
1.2.98
62.98
73.22
73.22
73.22
70.62
70.f>2
70.62
64.77
64.77
64.77
Crude protPin
mg/L
11.950
11,762
10,262
10,262
6838
68)8
16,638
16,114
14,781
14,781
10,652
10,662
wt ".
of VS
36.86
36.86
35.71
36.28
37.67
37.67
34.16
14.16
34.21
34.21
32.05
33.13
34.57
34.57
33.37
33.37
Car boll yd rates
mR/L
5943
6095
4601
4601
4228
4228
12,202
11,114
7918
709]
6880
6520
6700
wt %
of VS
18.33
18.33
19.27
18.80
16.89
16.89
21.12
21.12
25.09
22.85
23.97
22.68
23.32
18.52
16.50
17.51
21.53
20.41
20.97
Llplds Organic reductions, Z
mg/L
7156
6821
6250
6363
6306
2264
2264
11,994
11.-3I4
9875
9875
3568
3568"
wt 7.
of VS Protein
22.07
22.0?
20.00
21.04
22.94
23.36
23.15 12.75
11.31
11.31 33.37
System 41.86
24.66
24.66
21.86
23.26
23.09
23.09 8.27
11.17
TT7T7 27.87
System 33.83
Carbohydrate Llpids
24.51 7.55
8.11 64.10
30.63 66.81
33.99 12.72
10.51 63.87
40.93 68.46
* Data reported are the averages of duplicate or triplicate determinations.
A single sample date indicates that the analyses were conducted on a grab sample* collected that day. A time
the start and end dates of collection of a grab or time-composite sample used for the analyses.
c Run means are the averages of the feed analyses conducted for a particular steady-state run on a stngle feed
period under this
lot and hatrh.
collected for
column Indicates
a particular feed lot and batch.
e Final means are the average feed slurry organic concentrations and contents used to determine the organic reductions.
The organic contents are the average of the feed and rtin organic contents. Organic fped concentrations were calculated
ae the product of the final mean organic feed contents and the average feed volatile solids concentration for the run.
Steady-state run TP3M-M was conducted with mixed Downers Grove primary and Sttekney activated sludges.
-------
APPENDIX D
EFFLUENT ANALYSES FOR PARAMETRIC-EFFECT ACID-PHASE DIGESTERS
TABLE D-l. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. AP2M7: CFCSTR MESOPHILIC (35°C) ACID-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT pH 7 AND A 2-DAY HRT
Hydrogen, Carbon dioxide, Nitrogen, Methane,
Date mol % mol % mol % mol %
12/4/83 — 31,45 2.12 66.43
12/11/83 — 24.77 1.13 74.10
12/19/83 — 33.62 1.40 64.98
1/2/84 — 35.52 1.11 63.37
1/10/84 — 22.41 1.28 76.31
282
-------
TABLE D-2. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. AP2M7:
CFCSTR MESOPHILIC (35°C) ACID-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE
CONDUCTED AT pH 7 AND A 2-DAY HRT
Acetic, Proptonic,
Date mg/L mg/L
r\3
CO
co
12/5/83
12/12/83
12/19/83
1/3/84
1/10/84
529
610
528
817
826
577
706
693
539
716
Isobutyric,
mg/L
81
97
102
107
114
Butyric,
mg/L
115
133
133
99
108
Isovaleric,
rag/L
167
166
182
213
247
Valeric,
mg/L
0
0
0
22
42
Caproic.
mg/L
0
0
6
0
4
Total
as acetic,
mg/L
1,228
1,437
1,360
1,532
1,730
Ethanol,
mg/L
0
0
0
0
0
-------
INPUT
OUTPUT
ro
00
Total slurry
FS @ 32.4 vt 1 of TS
VS d 67.6 wt I
TS
Protein ? 27.3 wt I of VS
Carbohydrate @ 18.4 wt X of VS
Lip Id 8 @ 39.3 wt I of VS
ZXPL*
VA 9 2.5 wt I of VS
Other organics (by dlff)
2»je 1,,. ^_ _ __ s
* £.j Kg .«^— ™^ -.———-. »»—.••— ——^
4,77 . ->
6.95 kg
1.85 >
3. 99 kg
(84.9 wt t of VS)
(12. 6 wt Z of VS)
FS.I
VS
Car
Ere
0. !ft5 SCM CM.
O.Of.2 SCM CO,
r
Run no. AP2M7
CFCSTR
acid phase
Temp: 35°C
Loading:
23.4 kg VS/m3-d
HRT: 2. 1 days
pH: 7.0
0. 1 1"i kg carbon
1480 kcal
> (j -jh. 2 wt t of TS 2.25 WR
> (3 63 8 wt 7 of TS 3 96
ft. 21 kg
> @ 36.4 wt % of vs U44
3.24 kg
(82.0 wt 7. of VS)
m.9 wt t of v«n
Balance: effluent/feed - iOOZ
balance: effluent/feed - 89!
ion recovery In gas - 43!
rgy recovery tn gas - 5X
(PRODUCTION)
15.7
2O.O Z
9.3
21,7
18.4 Z
(41.7t)
(6.BJ)
* £CPL Is the sun of protein, carbohydrate, and llpids.
Figure D-l. Mass balances for mesophilic CFCSTR acid-phase Run AP2M7
conducted with Hanover Park sludge at pH 7 and about a 2-day HRT
-------
TABLE D-3. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. AP2M6: CFCSTR MESOPHILIC (35°C) ACID-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT pH 6 AND A 2-DAY HRT
Hydrogen, Carbon dioxide, Nitrogen, Methane,
Date mol % mol % mol % mol %
5/13/84 — 46.03 0.24 53.73
5/21/84 — 47.05 0.24 52.72
5/27/84 — 46.95 0.23 52.82
285
-------
TABLE D-4. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. AP2M6:
CFCSTR MESOPHILIC (35°C) ACID-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE
CONDUCTED AT pH 6 AND A 2-DAY HRT
ro
00
cr^
Date
5/13/84
5/21/84
5/27/84
Acetic,
mg/L
1,755
698
981
Proptonlc,
mg/L
1,205
1,178
957
Isobutyric,
mg/L
161
113
109
Butyric,
mg/L
467
253
285
Isovaleric,
mg/L
262
272
277
Valeric,
mg/L
84
108
135
Caproic,
mg/L
8
11
14
Total
as acetic,
mg/L
3,369
2,133
2,274
Ethanol ,
mg/L
0
0
0
-------
ro
CO
TABLE D-5. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. AP2M5.5: CFCSTR MESOPHILIC (35°C) ACID-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT pH 5.5 AND A 2-DAY HRT
Hydrogen, Carbon dioxide, Nitrogen, Methane,
Date mol % raol % mol % mol %
6/3/84 — 48.70 0.35 50.95
TABLE D-6. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE
RUN NO. AP2M5.5 CFCSTR MESOPHILIC (35°C) ACID-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT pH 5.5 AND A 2-DAY HRT
___
Acetic, Propionlc, Isobutyric, Butyric, Isovalerlc, Valeric, Caprolc, as acetic, Ethanol,
Date mg/L mg/L mg/L rag/L mg/L mg/L rag/L mg/L mg/L
6/3/84 1,465 1,223 160 547 1,002 185 39 3,657 0
-------
TABLE D-7. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. AP2M5: CFCSTR MESOPHILIC (35°C) ACID-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT pH 5 AND A 2-DAY HRT
Hydrogen, Carbon dioxide, Nitrogen, Methane,
Date mol % mol % mol % mol %
6/10/84 — 46.91 0.71 52.38
6/12/84 — 50.01 0.60 49.39
6/14/84 — 49.82 0.94 49.25
6/16/84 0.00 49.82 0.81 49.36
6/19/84 0.00 48.69 0.70 50.60
6/22/84 — 51.12 0.69 48.19
288
-------
00
TABLE D-8. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. AP2M5;
CFCSTR MESOPHILIC (35°C) ACID-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE
CONDUCTED AT pH 5 AND A 2-DAY HRT
Date
6/10/84
6/12/84
6/14/84
6/16/84
6/19/84
6/21/84
Acetic,
mg/L
1,315
956
1,115
1,088
1,082
964
Proptonic,
mtj/L
906
853
700
639
661
679
Isobutyric,
mg/L
179
125
183
198
188
183
Butyric,
mg/L
477
391
552
569
530
627
Isovalerlc,
mg/L
1,329
939
1,300
1,199
380
446
Valeric,
mg/L
200
272
289
301
289
341
Caproic,
mg/L
12
8
11
0
0
0
Total
as acetic,
mg/L
3,401
2,715
3,123
3,010
2,500
2,529
Ethanol,
mg/L
41
49
90
114
77
101
-------
INPUT
OUTPUT
(PRODUCTION)
ro
to
O
0.149 SCM CH^
0.147 SCM C02
-> 0.377 kg total gaa
0.150 kg carbon
1340 kcal
Total slurry
FS 9 23.8 ut X of TS
VS 9 76.2 «t X
TS
Protein 9 34.7 wt X of VS
Carbohydrate 9 22.6 wt X of VS
Uplds 9 29.4 wt X of VS
ICPL*
VA 8 5.3 wt X of VS
Other organic* (by dlff)
100 kg —
1.61 kg —
5.14 —
6.75 kg
of VS
y
-
^^x }
1.78 kg >
1. 16 >
1.51 >
4.45 kg
(86.7 wt X of VS)
0. 27 kg >
Oft f Ir IT *T
(8.2 wt X of VS)
Run no. AP2H5
CFCSTR
acid-phase
Temp: 35'C
Loading:
24.6 kg VS/s>3-d
HRT: 2. 1 day*
pH: 5.0
> (3 24.8 wt X of TS
> 9 75.2 wt X of TS
> (8 30. 1 wt X of VS
> p 23.4 wt X of VS
> (1 24.6 wt X of VS
(78.
> 0 8.5 wt X of VS
(13.
1.47 kg
4.46
5.93 kg
1.34 kg
1.04
1.10
3.48 kg
0 wt X of VS)
0.38 kg
-> 0.60 kg
4 wt X of VS)
13.2 X
24.7 X
9.3
27.2
21.6 X
(40.7X)
(42.9X)
FS balance: effluent/feed - 91X
VS balance: effluent/feed - 94X
Carbon recovery In gas - 5X
Energy recovery In gae • 4X
* CCPL is the sun of protein, carbohydrate, and llpida.
Figure D-2. Mass balances for mesophilic CFCSTR acid-phase
Run AP2M5 conducted with Hanover Park sludge
at pH 5 and about a 2-day HRT
-------
ro
ID
TABLE D-9. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. AP1.3M7: CFCSTR MESOPHILIC (35°C) ACID-PRASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT pH 7 AND A 1.3-DAY HRT
Hydrogen,
Date mol %
3/25/84
4/4/84
4/8/84
Carbon dioxide,
mol %
34.37
32.66
28.58
Nitrogen,
mol %
0.88
0.63
0.59
Methane,
mol %
64.76
66.71
70.83
TABLE D-10. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. AP1.3M7:
CFCSTR MESOPHILIC (35°C) ACID-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE
CONDUCTED AT pH 7 AND A 1.3-DAY HRT
Date
3/30/84
3/31/84
4/4/84
Acetic,
mg/L
2,549
2,454
2,491
Propiontc,
mg/L
1,556
1,604
1,764
Isobutyrlc,
mg/L
237
261
277
Butyric,
mg/L
477
572
559
Isovaleric,
mg/L
379
380
386
Valeric,
mg/L
91
97
85
Caproic,
mg/L
0
0
0
Total
as acetic,
mg/L
4,573
4,603
4,767
Ethanol,
mg/L
0
0
0
-------
OUTPUT
REDUCTION/
(PRODUCTION)
0. 252 SCM CH4
0.130 SCM C02
PO
«3
INO
Total Blurry
FS @ 24.1 wt X of TS
VS 9 75,7 wt X
TS
Protein 9 35.3 wt Z of VS
Carbohydrate 9 27.3 wt X of VS
Llpldi 8 26.0 vt * of VS
ECPL*
VA 0 7.7 wt I of VS
Other organlcs (by dlff)
1.44 kg
5.94 kg
1.59 kg >
1. 17 >
3.99 kg
(88.6 wt X of VS)
(3.6 wt 1 of VS)
Run no. AP1.3M7
CFCSTR
acid-phase
Tenp: 35°C
loading:
34.1 kg VS/n3-d
> g 30.6 wt X of TS
> (3 69.4 wt Z of TS
> @ 33,8 wt Z of VS
> (? 26.0 wt X of VS
(79.
(5.1
0. 193 kg carbon
2270 kcal
1.56 k(?
3.55
5.11 kg
1.20 kg
0.92
2.B3 kg
9 wt X of VS)
vt 1 of VS)
21.1 Z
24.6 Z
21.4
29.0 X
FS balance: effluent/feed - 108Z
VS balance: effluent/feed - 8BX
Carbon recovery In gas •* 7X
Energy recovery In gas - 8X
* CCPL la the sun of protein, carbohydrate, and llplds.
Figure D-3. Mass balances for mesophilic CFCSTR acid-phase
Run AP1.3M7 conducted with Hanover Park sludge
at pH 7 and about a 1.3-day HRT
-------
TABLE D-ll. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. AP1.3M5: CFCSTR MESOPHILIC (35°C) ACID-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT pH 5 AND A 1.3-DAY HRT
ro
to
GO
Hydrogen,
Date raol %
6/24/84
7/1/84 0.00
7/2/84 0.00
7/3/84 0.11
i
Carbon dioxide,
mol %
51.77
49.71
47.47
46.45
Nitrogen,
mol %
0.70
0.56
1.10
0.84
Methane,
mol %
47.53
49.73
51.43
52.60
TABLE D-12. VOLATILE ACIDS AND ETHANOL
CONCENTRATIONS OBSERVED DURING
CFCSTR THERMOPHILIC (35 °C) ACID-PHASE DIGESTION
CONDUCTED AT pH 5 AND A 1.
OF HANOVER
3-DAY HRT
STEADY-STATE RUN NO. AP1.3M5
PARK SEWAGE SLUDGE
Acetic, Propionic, Isobutyrlc,
Date mg/L mg/L mg/L
6/24/84 1,286 809 207
7/1/84 1,139 1,131 180
7/2/84 1,078 985 102
7/3/84 1,056 927 103
Butyric, Isovaleric
mg/L mg/L
748 597
581 542
457 431
472 369
, Valeric,
mg/L
360
403
294
211
Total
Caproic, as acetic, Ethanol,
mg/L mg/L mg/L
0 3,155 88
56 3,158 0
0 2,684 0
33 2,557 0
-------
INPUT
OUTPUT
ro
«.JD
Total slurry
FS 0 29.9 wt I of TS
VS 9 70.1 wt Z
TS
100 kg
2.05 kg
4.79
6.84 kg
Protein 9 30.4 wt Z of VS
Carbohydrate ? 28.4 wt Z of VS
Llplds @ 20.5 wt Z of VS
ECPL*
VA @ 4.6 wt Z of VS
Other organics (by dlff)
1.46 kg
1.36
0.98_
3.80 kg
(79.3 wt X of VS)
0. 22 kg >
0.77 kg
(16.1 wt Z of VS)
r~
Run no. AP1.3M5
CFCSTR
acid-phase
Loading:
32.8 kg VS/m3-d
> fa 29. 1 wt % of TS
> 0 70.9 wt X of TS
(76.
(15.
0. 1 48 SCM C
0.145 SCM C
0.150 kg ca
1340 kcal
1.77 kg
4.12
6.09 kg
3. 30 kg
4 wt Z of VS)
3 wt % of VS)
RF.nUCTIfW
(PRODUCTION)
9.8 Z
10.8 I
20,4
6.6
13.2 I
(18.91)
16.7 Z
FS balance: effluent/feed - 86*
VS balance: effluent/feed - 98%
Carbon recovery tn gaa - 5X
Energy recovery In gas - 4Z
* ICPL Is the sun of protein, carbohydrate, and llplds.
Figure D-4. Mass balances for mesophilic CFCSTR acid-phase
Run AP1.3M5 conducted with Hanover Park sludge
at pH 5 and about a 1.3-day HRT
-------
TABLE D-13. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. AP2T7: CFCSTR THERMOPHILIC (55°C) ACID-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT pH 7 AND A 2-DAY HRT
Hydrogen,
Date mol %
9/20/83
9/25/83
10/2/83
10/6/83
10/9/83
10/16/83
10/22/83
11/13/83
11/20/83
Carbon dioxide,
mol %
38.45
33.91
38.77
41.49
40.15
40.08
35.60
34.11
37.84
Nitrogen,
mol %
4.16
4.93
2.57
1.79
2.76
3.22
2.68
1.30
2.88
Methane,
mol %
57.39
61.16
58.65
56.72
57.09
56.70
61.72
64.59
59.27
295
-------
TABLE D-14. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. AP2T7:
CFCSTR THERMOPHILIC (55°C) ACID-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE
ONDUCTED AT pH 7 AND A 2-DAY HRT
ro
Acetic,
Date mg/L
9/18/83
9/26/83
10/3/83
10/17/83
10/21/83
10/29/83
11/7/83
11/15/83
1,531
1,443
1,458
1,372
1,379
1,480
1,462
1,434
Proplonic,
mg/L
1,011
857
875
989
924
1,109
1,094
1,031
Isobutyric,
mg/L
342
272
307
306
324
427
371
337
Butyric,
mg/L
565
403
391
378
438
535
475
499
Isovaleric,
mg/L
804
578
643
625
676
645
739
780
Valeric ,
mg/L
109
33
33
35
30
29
42
86
Caproic,
mg/L
0
0
0
0
0
0
0
0
Total
as acetic, Ethanol,
mg/L mg/L
3,505
2,957
3,041
3,028
3,062
3,430
3,384
3,349
-------
INPUT
OUTPUT
ro
Total slurry
FS g 30.3 wt Z of TS
VS 6 69.7 wt Z
TS
Protein @ 26.5 wt Z of VS
Carbohydrate @ 26.4 wt Z of VS
Liplds 8 27.5 wt Z of VS
ECPL*
VA 8 2.3 wt Z of VS
Other organlcs (by dlff)
5 14 — - - — — >
7.37 kg
1.36 kg — >
o{ vs i jf, >
1.41 >
4.13 kg
(80.4 wt Z of VS)
0 g9 |tg ™__>
(17.3 wt X of VS)
r
CFCSTR
acid- phase
Loading :
25.5 kR VS/m^-d
0.041 SCM C
n.oafi SCM D
0.036 left ca
370 kcal
-—--—-—> (9 5ft 9 wt % of TS 4 97
7.22 kg
> 3 19.6 wt Z of VS 0.17
2.45 kg
(49.3 wt X of VS)
> 0 8. 1 wt Z of VS 0.40 kg
> 2.12 kg
(42.7 wt Z of VS)
REDUCTION/
(PRODUCTION)
3.3 *
42.2 I
4R.9
31.1
40.6 X
(231. 37.)
(13R.2Z)
FS balance: effluent/feed - I01Z
VS balance; effluent/feed • 981
Carbon recovery In gas - IZ
Energy recovery In gas - IZ
* ECPL Is the sun of protein, carbohydrate, and liplds.
Figure D-5. Mass balances for thermophilic CFCSTR acid-phase
Run AP2T7 conducted with Hanover Park sludge
at pH 7 and about a 2-day HRT
-------
to
OO
TABLE D-15. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. AP2T6: CFCSTR THERMOPHILIC (55°C) ACID-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT pH 6 AND A 2-DAY HRT
Hydrogen, Carbon dioxide, Nitrogen, Methane,
Date mol % mol % mol % mol %
5/27/84 — 51.69 1.05 47.26
TABLE D-16. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE
RUN NO. AP2T6: CFCSTR THERMOPHILIC (55°C) ACID-PHASE DIGESTION OF HANOVER PARK
SEWAGE SLUDGE CONDUCTED AT pH 6 AND A 2-DAY HRT
_____
Acetic, Proplonlc, Isobutyrtc, Butyric, Isovaleric, Valeric, Caprolc, as acetic, Ethanol,
Date mg/L rog/l< "ig/L "ig/L mg/L mg/L mg/L mg/L
5/27/84 2,450 1,167 407 588 818 73 24 4,610
-------
10
TABLE D-17. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. AP2T5.5: CFCSTR THERMOPHILIC (55°C) ACID-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT pH 5.5 AND A 2-DAY HRT
Hydrogen,
Date mol %
5/6/84
5/13/84
Carbon dioxide,
mol %
65.85
54.00
Nitrogen,
mol %
6.80
1.25
Methane,
mol %
27.35
44.76
TABLE D-18. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. AP2T5.5:
CFCSTR THERMOPHILIC (55°C) ACID-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE
CONDUCTED AT pH 5.5 AND A 2-DAY HRT
Date
5/7/84
5/13/84
Acetic,
mg/L
1,639
2,249
Proptonic,
mg/L
1,019
1,438
Isobutyric,
mg/L
173
266
Butyric,
mg/L
542
1,124
Isovaleric,
mg/L
365
459
Valeric,
mg/L
105
182
Caproic,
mg/L
17
21
Total
as acetic,
mg/L
3,238
4,750
Ethanol,
mg/L
0
47
-------
TABLE D-19. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. AP2T5: CFCSTR THERMOPHILIC (55°C) ACID-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT pH 5 AND A 2-DAY HRT
Hydrogen, Carbon dioxide, Nitrogen, Methane,
Date mol % mol % tnol % nol %
6/10/84 — 48.67 1.19 50.15
6/12/84 — 49.59 1.50 48.92
6/14/84 — 49.64 1.88 48.48
6/16/84 0.16 48.41 1.73 49.70
6/19/84 0.22 49.88 1.41 48.50
300
-------
TABLE D-20. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. AP2T5:
CFCSTR THERMOPHILIC (55°C) ACID-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE
CONDUCTED AT pH 5 AND A 2-DAY HRT
CO
o
I—1
Date
6/10/84
6/12/84
6/16/84
6/19/84
Acetic,
mg/L
1,789
1,952
2,107
2,054
Proplonlc,
mg/L
727
873
884
895
Isobutyrlc,
mg/L
154
182
182
190
Butyric,
mg/L
341
393
375
393
Isovaleric,
mg/L
920
1,041
748
227
Valeric,
mg/L
4
66
54
49
Caproic,
mg/L
3
0
0
0
Total
as acetic,
mg/L
3,260
3,702
3,674
3,340
Ethanol,
mg/L
55
73
128
88
-------
INPUT
OUTPUT
RPmiCTION/
(PRODUCTION)
GO
O
ro
0.075 SCM CH4
0.076 SCM C02
-> 0.196 kg total gas
0.077 kg carbon
670 kcal
Total alurty
FS 8 23.7 wt X of TS
VS 0 76.3 wt X
TS
Protein e 35.8 wt X of VS
Carbohydrate @ 23.1 wt X of VS
Lipids g 29.4 wt X of VS
ZCPL*
VA 8 4.8 wt X of VS
Other organlcg (by diff)
4 gg
6. 53 kg
,
of VS
1.78 kg
1. 15
1.46
4. 39 kg
(88.3 wt X of VS)
0.35 kg
(7.0 wt X of VS)
v
>
>
>
'
CFCSTR
ac Id-phase
Temp: 55°C
Loading:
24.0 kg VS/m3-d
> @ 75.0 wt X of TS
> p 31.8 wt I of VS
> 0 23.0 wt X of VS
> (3 24.4 wt X of VS
(79
(9.
4.33
5.77 kg
1.38 kg
1.00
1,06
3.44 kg
. 5 wt X of VS)
7 wt X of VS)
13.1 X
22.9X
n.8
22.2 X
FS balance: effluent/feed - 91%
VS balance: effluent/feed - 911
Carton recovery In gas • IX
Energy recovery In gas - 2X
* ICPL IB Che sun of protein, carbohydrate, and liplds.
Figure I>-6. Mass balances for thermophilic CFCSTR acid-phase
Run AP2T5 conducted with Hanover Park sludge
at pH 5 and about a 2-day HRT
-------
TABLE D-21. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. API .317: CFCSTR THERMOPHILIC (55°C) ACID-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT pH 7 AND A 1.3-DAY HRT
Hydrogen, Carbon dioxide, Nitrogen, Methane,
Date mol % mol % mol % mol %
2/21/84 -- 37.51 1.79 60.70
3/5/84 __ 40.20 0.92 58.88
3/12/84 — 43.05 0.73 56.22
3/25/84 — 39.98 0.51 59.52
303
-------
TABLE D-22. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. AP1.3T7;
CFCSTR THERMOPHILIC (55°C) ACID-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE
CONDUCTED AT pH 7 AND A 1.3-DAY HRT
co
o
-Fa
Date
2/20/84
2/27/84
3/5/84
3/12/84
4/29/84
Acetic,
mg/L
1,773
1,722
1,813
1,851
1,620
Pijopionlc,
mg/L
997
1,109
1,127
1,738
1,559
Isobutyric,
mg/L
373
400
400
446
459
Butyric,
mg/L
652
653
659
819
662
Isovalerlc,
mg/L
753
1,064
1,051
1,117
933
Valeric,
mg/L
52
0
0
175
104
Caproic,
mg/L
0
0
0
0
0
Total
as acetic,
mg/L
3,753
3,964
4,066
4,881
4,257
Ethanol,
mg/L
0
0
0
0
0
-------
INPUT
OUTPUT
RKntJCTTON/
(PROnUCTION)
0.112 SCM CHA
0.082 SCM CO,
total gas
CO
O
on
Total slurry
FS 9 23. It wt Z of TS
VS 9 76.6 wt %
TS
Protein 9 35.1 wt X of VS
Carbohydrate 8 27.3 wt Z of VS
Llplds 9 26.0 wt I of VS
CCPL*
VA 9 6.9 wt Z of VS
Other Organlca (by dlff)
1.31 kg •
4.29
5.60 kg
of VS
1.17 >
, 1,12 >
3.80 kg
(88.4 wt Z of VS)
0. 30 kg >
(4.4 wt Z of VS)
Run no. API. 3T7
CFCSTR
acid-phase
Temp: 55°C
Loading:
36.0 kg VS/m3-d
HRT: 1.3 days
pH: 7.0
> @ 24. 5 wt X of TS
> @ 75. 5 wt Z of TS
> (> 22.4 wt Z of VS
(70.
(16.
-> u. 2)2 kg tc
0.099 kg c
1010 kcal
1.31 kg
4.n3
5.34 kg
0.99 kg
0.90
2.83 kg
3 wt Z of VS)
0.52 kg
9 wt Z of VS)
6.1 Z
34.4 Z
22.8
15.2
25.2 Z
(73.3Z)
(257.9Z)
FS balance: effluent/feed - 100J
VS balance: effluent/feed - 99Z
Carbon recovery In gas « 4Z
Energy recovery In gas - 4Z
ICPL Is the sun of protein, carbohydrate, and Hplds.
Figure D-7. Mass balances for thermophilic CFCSTR acid-phase
Run AP1.3T7 conducted with Hanover Park sludge
at pH 7 and about a 1.3-day HRT
-------
TABLE D-23. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. AP1.3T5: CFCSTR THERMOPHILIC (55°C) ACID-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT pH 5 AND A 1.3-DAY HRT
Hydrogen, Carbon dioxide, Nitrogen, Methane,
Date mol % mol % mol % mol %
6/24/84 — 47.54 2.75 49.71
7/1/84 0.30 45.99 2.45 51.26
7/2/84 0.37 45.29 2.46 51.88
7/3/84 0.60 45.63 2.16 51.61
306
-------
TABLE D-24. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE RUN NO. AP1.3T5:
CFCSTR THERMOPHILIC (55°C) ACID-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE
CONDUCTED AT pH 5 AND A 1.3-DAY HRT
co
o
-~J
Date
6/21/84
6/24/84
7/1/84
7/2/84
Acetic, Propionlc,
mg/L mg/L
1,966
2,072
2,023
1,722
797
792
824
731
Isobutyric,
rag/L
168
190
171
120
Butyric, Isovaleric,
mg/t, mg/L
420
434
400
366
249
333
330
338
Valeric,
mg/L
98
96
101
109
Caproic,
mg/L
0
0
73
0
Total
as acetic,
«g/L
3,217
3,392
3,372
2,909
Ethanol,
mg/L
115
97
85
74
-------
INPUT
OUTPUT
CO
o
00
Total slurry
FS ? 24.£ wt X of TS
VS 8 75.2 wt X
TS
Protein 9 35.6 wt X of VS
Carbohydrate 9 22.B wt X of VS
Llpldn 3 29.4 wt X of VS
ICPL*
VA 9 4.4 wt X of VS
Other organlca (by dlff)
It 7 l,a N
• UD _-LJl.-UU .•!-• — •• — -—«• Pi - .IP, I. -«. ^
6.75 kg
1.81 kg >
1.49 >
4. 46 kg
(67.8 vt X of VS)
0 40 kg — —- — >
(7.9 vt X of VS)
acid-phase
Temp: 55°C
Loading:
38.7 kg VS/m3-d
> @ 33.2 vt % of VS
> @ 25.4 wt X of VS
(82
(9.
0.046 SCM Cl
0.039 SCM C(
0.042 kg ca
410 kcal
. 57 kg
6.09 kg
1.50 kg
1.15
3.71 kg
. 1 wt X of VS)
. 37 kg
7 wt X of VS)
REDUCTION/
(PRODUCTIOH)
total gas
11.0 X
17.0 X
8.4
23.0
16.8 X
(68. 2X)
(10.01)
FS balance: effluent/feed - 94X
VS balance: effluent/feed - 91t
Carbon recovery In gas - IX
Energy recovery In gag - IX
* ICPL it the aim of protein, carbohydrate, and llplds.
Figure D-8. Mass balances for thermophilic CFCSTR acid-phase
Run AP1.3T5 conducted with Hanover Park sludge
at pH 5 and about a 1.3-day HRT
-------
TABLE D-25.
VOLATILE SOLIDS AND ORGANIC COMPONENT CONCENTRATIONS AND REDUCTIONS OBSERVED DURING
STEADY-STATE MESOPHILIC (35eC) AND THERMOPHILIC (55°C) CFCSTR ACID-PHASE
DIGESTION OF HANOVER PARK SEWAGE SLUDGE WITH pH CONTROL3
Run Sample Sample date(s)n
AP2M7 Feed 12/9-12/14/83
Effluent 12/9-12/14/83
12/9-12/14/83
AP2M5 Peed 6/19-6/23/84
6/19-6/23/84
Effluent 6/19-6/23/84
CO
O AP1.3H7 Feed 3/28-4/6/84
IO
Effluent 3/28-4/6/84
3/38-4/6/84
AP1.3HS Feed 7/2-7/6/84
Effluent 7/2-7/6/84
AP2T7 Teed 10/3/83
10/14/83
10/14/83
10/3/83
10/14/83
Lot
6
Run raeansc
Feed means
Final meanse
6
6
13
13
Run meani
Feed means
Final means
13
8
Run means
Feed means
Final means
8
8
14
Run means
Feed means
Final means
14
5
5
5
Run means
Feed means
Final means
5
5
Batch
2
2
2
t
1
1
5
5
5
2
2
3
3
3
3
3
TS
m(!/L
69,460
69,460
62,12(1
62.120
62,120
67,53(1
67.350
67, 510
59.290
59,290
59,180
59,180
51,061)
51.061)
51,060
68.440
68,440
6*0, 890
60,810
77,910
71,601)
71,6110
73,711)
73,710
70.760
Ti, 245
VS
mg/L
46.910
46,9iO
39,650
3°. (.50
39,(>5(1
51,460
51.460
51 ,<*M>
44.590
44,590
44 ,960
44,V60
35,410
35,410
35,410
47.971)
4 7,970
43.21)0
41,200
53,4411
50,2B(l
50.280
51, W
50,050
49.440
49,745
Crude protein
vt %
nf TS
67.56
67.56
61.81
63.83
63. 8j
76.20
76.20
76.35
76. I'l
75.72
75.72
69.35
69.15
69.15
70.09
7r>.<)9
70.95
70.95
6B.57
70.22
711.22
69.67
67.88
69.87
6H.H6
mg/L
12.775
J2,791
10.21R
10,218
17,625
17,841"
13, a 18
1 1,4'JH
16,019
15,880
11,975
14.594
14.514
11,025
11,025
14,1111
11.112
7994
7613
7H7I)
ut X
of VS
27.22
27.22
27.10
27.26
25.H2
25. HZ
14.25
35.119
34.67
10.14
30.14
35.61
J5.nl
55.011
15. 12
11. 82
11.82
10.42
ill. 42
10.42
in. 42
10.15
10.15
211.26
26.HH
21.. 17
26.91
26754-
15,97
15.66
15. S2
Carbohydrates
«t X
mg/1. of VS
IB. 44
8654 18.44
7992 20.16
7708 19.44
7851 19.80
10,994 21.16
11.813 22.96
— u. ih
21.11
11,650 22.64
10.561 21.17
10,561 21.17
12,724 28.30
2H.10
26.12
12,279 27.11
6917 19.51
7111 20.65
7114 20.119
11,617 28.41
28.41
2B.4.)
11,617 2H.4I
10.S49 J5.ll
ID, 849 25.11
1 4 , 1 0(1 26 . IK
11,10(1 26.45
26. /,2
26. 4K
11,578 26.45
6912 13.94
6914 13.94
Upids
niR/L
19,068
18,443
14, 444
14,444
15,104
15,104
1<1,98B
ll),9B«
11.716
1 I, 71)8
9202
92117
9824
9176
9176
14,600
14,100
14,127
9700
9956
9735
wt %
of VS
40.63
40.63
37.98
39.10
36.43
36.41
29.35
29.15
29.15
29.35
24.64
24.64
26.10
26.1(1
25.9R
26.114
25.99
25.99
20.48
20.48
20. 4R
20.48
21.24
21.24
27.12
28.04
27.68
27.36
2T75T
19.18
19.76
19.57
Organic reductions, X
Protein Carbohydrate Lipids
19.97 9.28 21.68
24.68 9.35 27.25
24.59 42.06 21.40
10.75 20.44 6.60
42.23 48.93 31.09
(c
intinued)
Reproduced from
best available copy. %|^
-------
TABLE D-25 (continued)
Run Sanple Sample date(s)b
AP2T5 Feed 6/12-6/16/84
Effluent 6/12-6/16/84
6/12-6/16/84
6/12-6/16/84
AP1.3T7 Feed 3/18-3/27/84
Effluent 3/18-3/27/84
CO 3/18-3/27/64
1— >
o
AP1.3T5 Feed 6/28-7/2/84
6/28-7/2/84
Effluent 6/28-7/2/84
Lot Batch
13
Run neans
Feed means
Final means
13
13
13
8
Run neans
Feed neans
Final means
8
8
13
13
Run neans
Feed neans
Final means
11
1
1
1
5
5
5
1
1
1
TS
ng/1.
65.310
65,310
57,710
57,710
57.710
57,710
55.960
55,960
53,410
53.410
51,410
67,510
67.530
67,530
60,860
60,860
VS
ms/L
49,840
49,840
43.260
43,260
43,260
43,260
42.890
42,890
40,340
40,340
40,340
50,750
50.750
50,750
45,170
45,170
Crude protein
wt X
of TS
76.31
76.31
75.98
75.98
75.98
75.98
76.64
76.64
75.53
75.53
75.53
75.15
75.15
TsTTT
74.22
74.22
Bg/L
18,238
17,863
13,775
11,775
15,125
15,067
9885
9885
18.331
18,067
14.988
14,988
wt 2
of VS
36. 59
TSTsT
35.09
15
31
3T
35
35
35
35
24
24
36
36
35
35
33
33
.84
.84
784"
.26
.26
.00
.13
.5(1
.50
.12
.12
.09
.Ml
.18
.18
mg/L
11,528
10,116
11,230
8479
9941
12,118
Ti,700
8478
9595
9036
10,786
12.016
10,595
10,595
wt % wt X
of VS mg/L of VS Protein Carbohydrate Llplds
23
IT
23
25
19
22
28
28
26
.13 29.35
.13 14,628 29.35
.38 10,539 24.36
.96
.60
.98 10,539 24.36 22.89 13.75 27.95
.25
.25
.32 25.98
27.28 11,143 25.98
21.02 9451 23.43
23. ?9
22.40 9451 23.43 34.39 22.72 15.18
21.25
23. (.R
24
23
22
23
23
.26
.13 29.35
.80 K,895 29.35
.46 11,466 25.38
.46 11,466 25.38 17.04 8.43 23.02
* Data reported are the averages of duplicate or triplicate
° A single sample date Indicates that the analyses were con<
the start and end dates of collection of a grab or ttme-c
c Run neane are the averages of the feed analyses conducted
• particular feed lot and batch.
determinations.
ducted on a grab sample collected that day* A time
onposlte sample used for the analyses.
for a particular steady-state run on a single feed
s weight percent of VS) of all steady-state samples
period under this
lot and batch.
collected for
column Indicates
The organic contents are the average of the feed and run organic contents. Organic feed concentrations were calculated
as the product of the final mean organic feed contents and the average feed volatile solids concentration' for the run.
-------
APPENDIX E
EFFLUENT ANALYSES FOR ADVANCED TWO-PHASE DIGESTION SYSTEMS
TABLE E-l. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. UTP7M-M: UPFLOW MESO-MESO TWO-PHASE DIGESTION OF
HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 7-DAY HRT
Hydrogen,
Date mol %
Acid-phase (Digester No
5/30/84
6/4/84
6/14/84
6/16/84
6/18/84
6/23/84
6/26/84
6/29/84
7/2/84 0.36
Methane-phase (Digester
5/30/84
6/4/84
6/14/84
6/16/84
6/18/84
6/23/84
6/26/84
6/29/84
7/2/84 0.00
Carbon dioxide,
mol %
. 338)
41.27
41.23
42.57
41.44
38.30
47.86
39.76
40.31
42.39
No. 339)
32.14
31.77
31.83
32.87
32.15
32.13
31.65
32.65
32.11
Nitrogen,
mol %
0.90
1.35
1.30
0.54
0.62
0.88
0.45
0.13
0.21
1.41
0.91
0.89
0.05
0.45
0.22
0.23
0.00
0.11
Methane ,
mol %
57.83
57.41
56.13
58.02
61.08
51.26
59.78
59.56
57.03
66.45
67.32
67.28
67.08
67.40
67.65
68.12
67.35
67.78
311
-------
TABLE E-2. VOLATILE ACIDS AND ETHANOL CONCKNTRATIONS OBSERVED DURING STEADY-STATE RUN NO. UTP7M-M:
UPFLOW MESO-MESO TWO-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 7-DAY HRT
Date
Sample
location
Acetic,
mg/L
Propionlc,
mg/L
Isobutyric,
mg/L
Butyric,
mg/L
Isovaleric,
mg/L
Valeric,
mg/L
Caproic,
mg/L
Total
as acetic,
mg/L
Ethanol,
mg/L
Acid-phase (Digester No. 338)
6/28/84
6/30/84
6/14/84
6/17/84
6/24/84
6/28/84
6/30/84
7/3/84
5/3/84
6/4/84
6/14/84
6/17/84
6/24/84
CO 6/28/84-7/1/84
£_. 7/3/84
Left Chamber
Left chamber
Underflow
Underflow
Underflow
Underflow
Underflow
Underflow
Overflow
Overflow
Overflow
Overflow
Overflow
Overflow
Overflow
2589
2564
2523
2325
2713
1832
3175
2714
1163
945
1559
1659
1085
1224
1302
1206
1358
1406
1536
1565
1667
1607
1278
925
710
1199
1232
1682
1249
1033
390
239
420
440
498
303
563
452
242
144
330
314
307
268
254
1061
919
1204
947
1373
602
1496
1085
335
187
604
580
350
222
360
457
278
649
772
908
422
855
789
1032
686
465
513
580
310
478
248
187
440
370
375
235
424
490
119
72
258
233
207
191
265
43
35
49
51
0
34
42
40
64
0
34
39
0
82
42
4993
4746
5435
5214
6011
4204
6655
5570
3016
2192
3610
3726
3359
2908
3016
79
99
0
35
0
0
70
24
0
0
0
28
0
0
0
Methane-phase (Digester No. 339)
6/28/84
6/30/84
6/28/84
6/30/84
6/28/84
6/30/84
5/31/84
6/4/84
6/14/84
6/17/84
6/24/84
6/28/84
6/30/84
7/3/84
7/6/84
Bottom port
Bottom port
11.5-L port
11.5-L port
15.5-L port
15.5-L port
Effluent
Effluent
Effluent
Effluent
Effluent
Effluent
Effluent
Effluent
Effluent
0
6
168
178
198
224
104
205
78
102
55
160
152
346
106
0
0
436
144
448
174
85
115
373
226
0
351
108
241
117
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
6
0
6
0
0
0
10
10
0
5
0
0
0
0
0
8
0
0
8
0
0
12
25
0
0
3
0
0
0
6
529
295
564
370
172
298
393
304
55
447
241
542
201
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
• — — > — , ' , , _________________
This sample was taken from the bottom of the left-hand chamber (feed side) of the acid-phase digester.
-------
OUTHIt
0.4} SCM CK^
U.I I SCK CO;
> O.flfl kg total gaa
0*30 kg carbon
1410 teal
REDUCTION/
(HOOUCTtOH)
CO
Total alurry 100 kg -
TS o.91 kg
rrotaln « M.I vt X of VI
Carbohydrate t 24.0 vt I at VI
Llplda * 29.4, vt X of Vt
ICFL*
Vt • 4.7 vt X of VS
Othar organlca (by dlff)
tread, q | 1 ... ., | ""ertlov. 0.885 q I I UndetElov 0.115 0 t 1 Total 1
*
1.79 k| >
4.57 kg
(87. t, vt I of VS)
0.25 kg >
0.40 kg >
(7.7 M I of VI)
tun no. UTP7K-H
Upflov
ac Id-pnaae
Ta»p: 35'C
Loading:
2t.l kg VS »3-d
HITl 2.0 daya
> £ 28.6 vt X of TS 1.52 kg 8 H.I vt X of TS 0.21 kg 1.7} kj
5.32 kg O.S1 kg 6.13 kg
> 0 2«.| vt X of VS 1. II kg « 27,5 vt X o( VS 0.1* kg 1-27 k| 29.0 X
> ( i|. s ,t x 0| vs 0.82 t 22.5 vt t of VS 0.11 0.95 17^8
2.69 kg 0.42 kg 3.11 kg 12.0 X
(70. 6 vt X of VS) (70.0 vt 1 VS) (70.5 vt X of VS)
(l«.l vt X of VS)
fS balance: affluent/feed - 97t
VS ealancai «f1luant/fa«d - IOIX
Carbon raeovary In gat • 12X
•nargy raeovary In gai • 12X
* ten la tba ava of arotala. earbohy^rau, and llpldl.
Figure E-l. Mass balances for mesophilic upflow acid-phase
digester for meso—meso upflow two—phase Run UTP7M-M
conducted with Hanover Park sludge at a 7-day system HRT
-------
IHPUT
OUTPUT
REDUCTION/
(PRODUCTION)
CO
Total Blurry
FS 9 28.2 wt I of TS
VS @ 71.8 wt X
TS
Protein 3 28.9 wt X of VS
Carbohydrate 9 20. 2 wt X of VS
Llplds 9 21.6 wt X of VS
ICPL*
VA 9 9.5 wt I of VS
Other organic* (by dlff)
4 40 -—
6*13 kg
of VS
^
1 go __— %
0.96 >
3.11 kg
(70.7 wt X of VS)
0.87 kg ->
(19.8 wt X of VS)
methane-phase
Loading!
9.4 kg VS/m3-d
> (? 33. 3 wt X of TS
> C 66.7 wt X of TS
(56.
(42.
1.40 SCM CH4
0.67 SCM C02
1.06 kg carbon
12.670 kcal
1.98 kg
3.98
5.96 kg
1.18 kg
0. 57
2.24 kg
1 wt X of VS)
0.04 kg
7 wt X of VS)
9.5 X
7.0 X
36.4
28.3 X
90.5 X
(95.4X)
FS balance: effluent/feed - 1142
VS balance: effluent/feed - 141X
Carbon recovery in gas - 41X
Bnergy recovery in gag • 45X
* ICfl, la the BUD of protein, carbohydrate, and Itpids.
Figure E-2. Mass balances for mesophilic upflow methane-phase
digester for raeso-meso upflow two-phase Run UTP7M-M
conducted with Hanover Park sludge at a 7-day system HRT
-------
CO
Total slurry
FS 0 25.2 wt Z of TS
VS 9 74.8 wt Z
TS
Protein & 34.3 wt Z of VS
Carbohydrate 9 24.0 wt Z of VS
LipId8 @ 29.4 wt X of VS
ECPL*
VA 0 4.7 wt Z of VS
Other organlcs (by dlff)
INPUT
5 22 —————— .._______.,_>
6.98 kg
1.79 kg >
of VS 1.25 >
1.53 >
4.57 kg
(87.6 «t X of VS)
0.25 kg >
0 40 kg - >
(7.7 wt Z of VS)
I""
Run no. UTP7M-M
Up flow
two-phase system
Temp: 35-35°C
Loading:
6.9 kg VS/m3-d
HRT: 7. 5 days
OUTPUT
1.83 SCM CH4
0.98 SCM CO 2
1.44 kg carbon
16,580 kcal
> P 33.3 wt Z of TS 1.98 kg
> @ 66.7 wt i of TS 3,98
5.96 kg
> p 29.7 wt X of VS 1.18 kg
> 0 14.2 wt Z of VS 0. 57
> ? 12.2 wt Z of VS 0.49
2.24 kg
(56.1 wt Z of VS)
> ? 1.0 wt t of VS 0.04 kg
(42.7 wt Z of VS)
SEDUCTION/
(PRODUCTION)
23.8 Z
34.0 Z
54. R
68.4
51.2 Z
84.0 Z
FS balance: effluent/feed - 112Z
VS balance: effluent/feed - 135Z
Carbon recovery In gas » 47Z
Energy recovery In gaa - 49Z
1CPL la the aum of protein, carbohydrate, and llplds.
Figure E-3. Mass balances for tneso-meso upflow two-phase
Run UTP7M-M conducted with Hanover Park sludge
at a 7-day system HRT
-------
TABLE E-3. NORMALIZED GAS COMPOSITIONS OBSERVED DURING
RUN NO. UAP2M: UPFLOW MESOPHILIC (35°C) ACID-PHASE DIGESTION
OF HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 2-DAY HRT
Hydrogen,
Date mol %
7/13/84
7/20/84
7/27/84
8/3/84
9/11/84
8/16/84
8/17/84
Carbon dioxide,
mol %
44.17
43.36
39.02
39.98
42.25
41.79
42.73
Nitrogen,
mol %
0.63
0.73
0.31
0.83
0.35
0.37
0.59
Methane,
mol %
55.20
56.90
60.67
59.18
57.40
57.84
56.68
316
-------
TABLE E-4. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING RUN NO. UAP2M: UPFLOW
UPFLOW MESOPHILIC (35°C) ACID-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE
CONDUCTED AT A 2-DAY HRT
Date
CO 7/12/84
"^ 7/13/84
7/20/84
7/27/84
8/3/84
8/10/84
8/17/84
Acetic,
mg/L
1380
1147
1072
873
865
1685
1258
Propionic,
mg/L
1569
1577
1405
1652
798
978
815
Isobutyric,
mg/L
289
317
155
271
179
305
209
Butyric,
fflg/L
522
489
372
282
75
535
231
Isovaleric,
mg/L
362
390
294
207
279
473
355
Valeric,
mg/L
420
375
284
180
111
234
175
Caproic,
mg/L
48
44
24
44
215
102
79
Total
as acetic,
mg/L
3689
3448
2923
2840
2025
3519
2571
Ethanol ,
mg/L
0
0
0
0
0
0
0
-------
TABLE E-5. NORMALIZED GAS COMPOSITIONS OBSERVED DURING
RUN NO. UAP2T: UPFLOW THERMOPHILIC (55°C) ACID-PHASE DIGESTION
OF HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 2-DAY HRT
CO
i—i
00
Hydrogen,
Date mol %
9/12/84
9/14/84
9/24/84
9/26/84
Carbon dioxide,
mol %
54.21
53.85
52.58
49.93
Nitrogen,
mol %
1.97
4.17
2.33
1.78
Methane,
mol %
43.82
41.98
45.10
48.29
TABLE E-6. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING RUN NO. UAP2T: UPFLOW
THERMOPHILIC (55°C) ACID-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE CONDUCTED AT A 2-DAY HRT
Date
9/12/84
9/14/84
9/19/84
9/21/84
Acetic,
mg/L
2766
3038
1852
2411
Propionic,
mg/L
1591
1829
1117
1586
Isobutyric,
mg/L
642
658
285
470
Butyric,
mg/L
827
918
571
852
Isovalerlc,
mg/L
1101
1370
493
926
Valeric, Caproic,
mg/L mg/L
0 88
0 2
0 0
217 189
Total
as acetic,
mg/L
5750
6401
3633
5367
Ethanol ,
mg/L
0
0
0
42
-------
TABLE E-7. NORMALIZED GAS COMPOSITIONS OBSERVED DURING
RON NO. UPT17M-T: MESO-THERMO TWO-PHASE DIGESTION OF
HANOVER PARK SLUDGE CONDUCTED AT A 17-DAY HRT
Hydrogen, Carbon dioxide, Nitrogen, Methane,
Date mol % mol % mol % mol %
Acid-phase (Run no. UAP4.5M)
8/24/84 — 42.74 0.60 56.66
8/31/84 — 36.68 0.52 62.80
Methane-phase (Run no. UMP12T)
8/24/84 — 46.30 0.00 53.70
8/31/84 — 44.06 2.04 53.89
319
-------
TABLE E-8. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING RUN NO. TP17M-T: UPFLOW
MESO-THERMO TWO-PHASE DIGESTION OF HANOVER PARK SLUDGE CONDUCTED AT A 17-DAY HRT
Acetic,
Date mg/L
Acid-phase (Run no.
8/24/84 1511
8/31/84 580
Methane-phase (Run
8/24/84 1398
8/31/84 1924
Propionlc,
rag/L
UAP4.5M)
1158
794
no. UMP12T)
1291
1639
Isobutyrlc,
mg/L
215
18
226
511
Butyric,
mg/L
325
0
135
279
Isovaleric,
mg/L
351
98
546
809
Valeric,
mg/L
229
0
0
0
Caproic,
mg/L
93
115
87
136
Total
as acetic,
mg/L
3207
1353
3057
4337
Ethanol,
mg/L
0
0
0
0
-------
TABLE E-9. NORMALIZED GAS COMPOSITIONS OBSERVED DURING
RUN NO. UTP7T-T: UPFLOW THERMO-THERMO TWO-PHASE DIGESTION
OF HANOVER PARK SLUDGE CONDUCTED AT A 7-DAY HRT
Hydrogen, Carbon dioxide,
Date mol % mol %
Acid-phase (Run UAP2.1T)
10/2/84 — 51.33
10/4/84 — 50.21
Nitrogen, Methane,
mol % mol %
2.34 46.34
4.02 45.77
Methane-phase (Run UMP5.4T)
9/29/84 — 45.17 1.52 53.31
10/5/84 — 46.12 3.28 50.60
321
-------
TABLE E-10. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING RUN NO. UTP7T-T:
UPFLOW MESO-THERMO TWO-PHASE DIGESTION OF HANOVER PARK SLUDGE CONDUCTED AT A 7-DAY HRT
Acetic,
Date mg/L
Propiontc,
mg/L
Isobotyric,
mg/L
Butyric,
mg/L
Isovaleric,
mg/L
Valeric,
mg/L
Caprolc,
mg/L
Total
as acetic,
mg/L
Ethanol,
mg/L
Acid-phase (Run UAP2.1T)
U)
ro
1X3
9/29/84
10/2/84
10/4/84
10/5/84
Methane-phase
9/28/84
10/2/84
10/5/84
1527
1587
1167
1159
(Run
1495
1766
1965
912
813
575
471
UMP5.4T)
1354
1251
1188
246
275
204
180
373
339
374
438
441
406
359
264
463
584
488
553
399
368
510
632
742
168
123
99
91
155
148
172
74
58
73
92
0
7
0
3156
3163
2379
2226
3370
3789
4118
39
13
12
0
55
0
0
-------
TABLE E-ll. NORMALIZED GAS COMPOSITIONS OBSERVED DURING RUN
NO. UTP20T-T-T: UPFLOW/CFCSTR THERMO-THERMO-THERMO THREE-PHASE
DIGESTION OF HANOVER PARK SLUDGE CONDUCTED AT A 20-DAY HRT
Hydrogen, Carbon dioxide, Nitrogen, Methane,
Date mol % mol % mol % mol %
Upflow acid-phase (Run UAP1.9T)
10/8/84 0.00 49.61 3.97 46.42
Upflow methane-phase (Run UMP5.2T1
10/13/84 — 38.33 0.60 61.07
CFCSTR methane-phase (Run CMP13T)
10/13/84 — 20.80 0.89 78.32
323
-------
TABLE E-12. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING RUN NO. UTP20T-T-T:
UPFLOW/CFCSTR THERMO-THERMO-THERMO THREE-PHASE DIGESTION OF
HANOVER PARK SLUDGE CONDUCTED AT A 20-DAY HRT
Date
Acetic, Proplonic, Isobutyrlc, Butyric, Isovaleric,
mg/L mg/L mg/L mg/L mg/L
Total
Valeric, Caproic, as acetic, Ethanol,
mg/L mg/L mg/L mg/L
00 Upflow acid-phase (Run UAP2.1T)
10/13/84 803 414 153 188 268
Upflow methane-phase (Run UMP5.2T)
10/13/84 1345 685 235 227 410
CFCSTR methane-phase (Run CMP13T)
10/13/84
229 782 178 0 303
8 46 1557 0
43 73 2519 0
13 78 1211 0
-------
TABLE E-13. NORMALIZED GAS COMPOSITIONS OBSERVED DURING STEADY-STATE
RUN NO. TP3M-M(E): CFCSTR MESO-MESO TWO-PHASE DIGESTION OF
ENZYMATICALLY PRETREATED, MIXED DOWNERS GROVE PRIMARY AND
STICKNEY ACTIVATED SLUDGES CONDUCTED AT A 3-DAY HRT
Hydrogen,
Date mol %
Acid-phase (Digester no
12/27/84 0.11
12/29/84
1/5/85
1/7/84 0.00
1/8/85
1/9/85
Methane-phase (Digester
12/27/84
12/29/84
1/5/85
1/7/85
1/8/85
1/9/85
Carbon dioxide,
mol %
. 334)
42.14
44.77
43.90
41.79
41.30
38.77
no. 333)
34.70
34.30
34.72
34.43
33.49
32.72
Nitrogen,
mol %
0.48
0.26
0.51
0.32
0.24
0.36
0.00
0.00
0.00
0.00
0.00
0.00
Methane,
mol %
57.28
54.97
55.59
57.89
58.45
60.87
65.30
65.70
65.28
65.57
66.51
67.28
325
-------
co
ro
01
TABLE E-14. VOLATILE ACIDS AND ETHANOL CONCENTRATIONS OBSERVED DURING STEADY-STATE
RUN NO. TP3M-M(E): CFCSTR MESO-MESO TWO-PHASE DIGESTION OF ENZYMATICALLY
PRETREATED, MIXED DOWNERS GROVE PRIMARY AND STICKNEY
ACTIVATED SLUDGES CONDUCTED AT A 3-DAY HRT
Acetic, Vropionlc, Isobutyric,
Date mg/L mg/L mg/L
Acid-phase (Digester no
2/27/84 1
2/29/84
1/5/85 1
1/7/85 1
1/8/85 1
1/9/85 1
1/11/85 1
Methane-phase
12/27/84
12/29/84
1/5/85
1/7/85
1/8/85
1/9/85
1/11/85
,269
88
,234
,462
,249
,452
,687
(Digester
188
77
202
238
274
257
168
. 334)
1,100
1,099
1,214
1,527
1,431
1,368
1,430
no. 333)
751
895
1,029
1,270
1,058
1,004
838
191
0
239
279
268
296
334
0
0
33
21
62
52
19
Butyric, Isovaleric,
mg/L mg/L
504
233
658
694
571
721
711
0
0
0
0
0
30
0
293
256
417
462
458
528
569
0
27
74
97
79
75
68
Valeric,
mg/L
226
376
685
755
691
823
826
0
0
31
22
22
27
18
Caprolc,
mg/L
47
24
38
46
19
28
30
7
34
22
22
0
0
0
Total
as acetic,
mg/L
2,964
1,522
3,497
4,102
3,666
4,063
4,394
800
836
1,131
1,364
1,233
1,187
911
Ethanol,
mg/L
0
0
19
24
0
34
0
0
0
0
0
0
32
0
-------
TABLE E-15. VOLATILE SOLIDS AND ORGANIC COMPONENT CONCENTRATIONS AND REDUCTIONS OBSERVED DURING
STEADY-STATE ADVANCED MESO-MESO TWO-PHASE DIGESTION OF HANOVER PARK SEWAGE SLUDGE*
CO
Run Sample Sample date(s)"
UTP7H-M Feed
Acid-phase
effluent
Methane-phase
effluent
TP3M-M* Feed
Acid-phase
effluent
Methane-phase
effluent
6/28-7/1/84
6/28-7/1/84
6/28-7/1/84
6/28-7/1/84
6/28-7/1/84
6/28-7/1/84
6/28-7/1/84
6/28-7/1/84
1/8-1/12/85
1/8-1/12/85
1/8-1/12/85
Lot Batch TS
13
13
Run meansc
Feed means
Final means6
13
13
13
13
13
13
23
Run means
Feed means
Final means
21
23
mg/L
1 69,870
1 69,870
69,871)
1 61,310
1 61.310
61,310
1 59,640
I 59,640
1 59,640
I 59,640
59,640
1 6?. 470
69,470
1 60,410
60,410
1 54.900
54,900
VS
mg/L
52,230
52.211)
52,230
44,ri|0
44,)l 10
44,010
3^,790
39,790
39,790
39,790
39,790
46.530
46,510
39.170
19,170
33,820
33.H20
wt %
of TS mg/L
74.75 17, 456
74. !5
17,894
71.78
71.78 12,706
71. 7H 12,706
66.72 11,819
66.72
66.72
66.72 —
68.26
68.26
64.84
64. B4
6 1 .60
61.60 —
wt X
of VS mg/L
31.42 11,956
13,934
13.42
35.09
14.26 12,514
8344
28.87 9421
'2S.87 8881
29.70 5830
5656
6101
4818
29.70 5650
15,734
—
15,734
7882
7882
5729
wt "
of VS
22.89
26.1.8
24.78
21.13
23.96
18.96
21.47
20.18
14.65
14.21
15.84
12.11
14.20
21.80
21. BO
21.80
21.39
20.12
20.12
16.94
lb.96
Lipids
t»g/L
-
15,130
9534
9534
4849
4849
9370
9375"
8990
ij990~
5729
5729
wt *
of VS Protein
,-
29.35
29.35
21.66
21.66 28.99
12.19
T27T9" 6.98
System 33.95
20.14
20.14
20.14
19.76
22.95
16.94
16.94
System
Organic reductions, Z
Carbohydrate Liplds
29.03 37.81
36.38 49.14
54.85 68.37
49.90 4.06
27.32 36.27
63.59 38.86
a
b
c
d
e
Data reported are the averages of duplicate or triplicate determinations.
A single sample date Indicates that the analyses were conducted on a grab sample collected that day. A time
time-composite sample used for the analyses.
Run means are the averages of the feed analyses conducted for a particular steady-state run on a tingle feed
Feed means are the average organic contents (expresssed as weight percent of VS) of all steady-state samples
period under this column Indicates the start and end dates
lot and hatch.
collected for a particular feed lot and batch.
of collection of a grab or
Organic feed concentrations were calculated as the product of the final mean organic feed contents and the average feed volatile solids concentration for the run.
Steady-state run TP3M-M(E) was conducted with mixed Downers Brove primary and Stickney activated sludges. The feed was treated for 24 hrs at 35°C with cellulase (Novo Celluclast 1.51) and
celloblase (Novozym 188) enzymes at dosages of 2.75 g/kg feed TS and 0.28 g/kg feed TS, respectively. Upasc (Novozym 225) was added to the acid digester at a dosage of 2.75 g/kg feed TS.
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APPENDIX F
FEED SLUDGE LOTS AND BATCHES USED DURING STEADY-STATE DIGESTION RUNS
TABLE F-l. FEED SLUDGE LOTS AND BATCHES USED DURING
STEADY-STAGE DIGESTION RUNS
Run number
SS15M
SS7M
SS3M
SS15T
SS7T
SS3T
TP15M-M
TP7M-M
TP3M-M
TP3M-M(E)
TP15M-T
TP7M-T
TP7T-T
TP3T-T
UTP7M-M
AP2M7
AP2M6
AP2M5.5
AP2M5
AP1.3M7
AP1.3M5
AP2T7
AP2T6
AP2T5.5
AP2T5
AP1.3T7
AP1.3T5
Feed sludge lot/batch number"
1/8-9
6/1-3
8/5
12/1
16/1
16/1
5/3-4
17/1
28/1
32/1
16/1
17/1
18/5-7
19/3-6
13/1
6/2-3
12/1
12/1
13/1
8/5
13/1
5/3-4
12/1
12/1
13/1
8/5
13.1
Analyses of these feed sludges are shown in Appendix A, Tables 1-6.
328
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APPENDIX G
COMPARISON OF CALCULATION OF VOLATILE SOLIDS BY MOP-16
FORMULA WITH MATERIAL BALANCE METHOD
TABLE G-l. COMPARISON OF CALCULATION OF VOLTAILE SOLIDS REDUCTION
BY MOP-16 FORMULA WITH MATERIAL BALANCE METHOD1
Volatile solids reduction Percent loss
in ash VS reduction
Material relative to (Wt.-of-gas
Run number balance2 MOP-16J Difference total solids method)
SS15M
SS7M
SS3M
SS15T
SS7T
SS3T
TP15M-M
TP7M-M
TP3M-M
TP15M-T
TP7M-T
33.0
27.3
15.6
41.3
31.0
12.1
34.0
32.8
24.8
38.2
34.3
38.2
18.3
13.7
36.8
32.9
19.0
37.2
33.6
26.5
28.0
32.8
-5.2
5.0
1.9
4.5
-1.9
-6.9
-3.2
-0.8
-1.7
10.2
1.5
-2.17
2.07
0.51
1.71
-0.74
-2.27
-0.55
-0.20
-0.38
1.92
0.41
28.8
32.7
19.3
45.9
39.6
20.2
63.4
51.5
35.5
48.5
54.7
1 Data used are from Tables B-13 and C-15.
9
Material balance: Assumes volume in = volume out,
we - mg VS/L in feed - mg VS/L in effluent
V o_ ~ ~TT?* it • ------ 1^ '~Z~ ..... "" " """" "" ™
R mg VS/L in feed
n
J MOP-16: Assumes ash in = ash out,
VS - VS
VS °
R VS. -(VS. XVS )
i i o
where VS. n = VS as fraction of TS at influent and effluent
1 >°
4 . . Trt00. -/ TrtQO _ mg ash/L in feed - mg ash/L in effluent ... inn
Ash LOSS: /. LOSS -- „,„ /T — - — - — - - X 100
mg TS/L in feed
5 VS reductions were taken from Tables 49, 52, 57, and 60.
329
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