PB85-147189
EPA-600/2-85-001
January 1985
DETERMINING THE STABILITY OF TREATED MUNICIPAL SLUDGES
by
John S. Jeris, Daniel Ciarcia,
Edward Chen, and Miguel Mena
Manhattan College
Bronx, New York 10471
Cooperative Agreement No. CR806809
Project Officer
R. V. V1l1iers
Wastewater Research Division
Water Engineering Research Laboratory
Cincinnati, Ohio 45268
WATER ENGINEERING RESESARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
Rf PRODUCED BY
NATIONAL TECHNICAL
INFORMATION SERVICE
US OEPARIMENI OF COMMERCE
SPRINGE I!ID »». 27161
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TECHNICAL REPORT DATA
(Please read Imiructions on the reverse before completing)
1. REPORT NO. 2.
EPA-600/2-85-001
3. RECIPIENT iACCJK^q^Dia-.-
PBS5 1 *71 /AS
4. title andsubtitle
DETERMINING THE STABILITY OF TREATED MUNICIPAL
SLUDGES
5. REPORT DATE
January 1985
6. PERFORMING ORGANIZATION CODE
7. AUTHORIS)
John S. Jeris, Daniel Ciarcia, Edward Chen, and
Miguel Mena
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Manhattan College
4513 Manhattan College Parkway
Bronx, New York 10471
10. PROGRAM ELEMENT NO.
CAZB1B
11. CONTRACT/GRANT NO.
C.A. CR806809
12. SPONSORING AGENCY NAME AND ADDRESS
Water Engineering Research Laboratory, Cin., OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Contact: J. B. Farrell (513) 684-7645
6. abstract objective of this project was to determine the potential for further
biological degradation biologically of municipal sludges which have undergone either
little or major treatment. A literature survey was conducted to determine the most
fruitful approaches, followed by laboratory scale studies.
The literature survey summarizes available information related to the character
istics and various stability parameters of municipal sludges that have undergone tre i
ment by anaerobic, aerobic or thermal conditioning processes. The laboratory study
built upon methods described in the literature for evaluating stability of sludges.
Stability of a variety of received sludges was evaluated by measuring response to
additional aerobic or anaerobic digestion of long duration, and by cumulative gener-
ation of hydrogen sulfide. Responses to aerobic digestion of the as-received
sludges were generally similar and showed substantial reductions in parameters such
as BOD and COD.^ Oxygen uptake eventually reached a low stable value. The same kind
of reduction in parameters occurred with anaerobic digestion. The hydrogen sulfide
generation test generally showed well defined points at which H2S generation virtu-
ally ceased as sludge storage increased. This test shows promise as a method for
comparing sludges for potential for further biological decomposition.
Although much has been learned about the response of various parameters indica-
tive of sludge stability to further digestion, a simple measurement indicating
sludge sfaMUfy wag nnf developed.
t-
17.
KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
c. cosati Field/Group
1* DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
205
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
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DISCLAIMER
Although the information described in this article has been funded
wholly or in part by the United States Environmental Protection Agency
through assistance agreement number CR806809 to Manhattan College, it has
not been subjected to the Agency's required peer and administrative review
and therefore does not necessarily reflect the views of the Agency and no
official endorsement should be inferred.
i 1
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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
A , the Safe Drinking Water Act, and the Toxics 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 pre-
serving and enhancing the water we drink, and for protecting the environ-
ment from toxic substances. These laws direct the 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
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 nature and controllability of releases of toxic substances to the air,
water, and land from manufacturing processes and subsequent product uses.
This publication is one of the products of that research and provides a
vital communication link between the researcher and the user community.
This report details the further aerobic and anaerobic biological
degradation possible of sludges generated from municipal sources, Raw
primary, waste activated, trickling filter and anaerobic digester sludges
from full-scale treatment plants were studied.
Francis T. Mayo, Director
Water Engineering Research Laboratory
iii
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ABSTRACT
The overall objective of this project was to determine the potential for
further degradation biologically of municipal sludges which may have under-
gone either little or major treatment. This objective was achieved by means of
a literature survey to determine the most fruitful approaches, followed by
laboratory scale studies.
The literature survey section of this report comprehensively summarizes
available information related to the characteristics and various stability
parameters of municipal sludges that have undergone treatment by anaerobic,
aerobic, or thermal conditioning processes. The starting materials being con-
sidered include raw primary sludge, activated sludge, and mixtures of the two.
The treatment processes produce sludges that have a broad range of instability
associated with them because design factors for the treatment processes from
which they are generated vary widely. Many of the parameters considered use-
ful in determining sludge instability are also reviewed in the literature
survey.
The laboratory study was built upon methods described in the literature
for evaluating stability of sludges. Sludges studied included primary,
trickling filter and activated sludges and sludges from full scale anaerobic
digesters, heat treatment processes, and aerobic digestion. Stability of
these as-received sludges was evaluated by measuring response to additional
aerobic or anaerobic digestion, and by cumulative generation of hydrogen
sulfide. Responses of the as-received sludges to aerobic digestion were
generally similar and showed substantial reductions in parameters such as
BOD and COD. Oxygen uptake eventually reached a low stable value for all
sludges. The same kind of reduction in parameters occurred in the as-
recived sludges with anaerobic digestion. The hydrogen sulfide generation
test showed well defined points at which H2S generation virtually ceased
as sludge storage increased but not for all sludges.
Although much has been learned about the response of various parameters
indicative of sludge stability to further digestion, a simple measurement
indicating sludge stability was not developed.
iv
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CONTENTS
Foreword m
Abstract .. iv
Figures vl
Tables
Acknowledgement xy
1. Introduction 1
2. Conclusions 2
3. Recommendations 3
4. Literature Survey A
5. Sources and Types of Municipal Sludges 98
6. Experimental Procedures and Apparatus 107
7. Laboratory Results 12b
8. Discussion of Results 173
References 180
Apprndix 187
V
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FIGURES
Number Page
1 The Fossillzation Pathway of the Carbon Cycle (2) 5
2 Relation Between Raw Sludge Detention Time and Volatile Matter
Reduction (23) 5
3 Graph Showing Comparison of Completion of Digestion at High
Rate Plants with Accepted Standards 13
4 Anaerobic Digestion Volatile Solids Destruction Vs. Waste
Activated Sludge/Primary Sludge Ratio (32) 19
5 Reduction of Organic Matter During First Test at 20°C (1), 30°C
(2), and 50°C (3) (22) 20
6 Effects of SRT and Temperature on Volatile Solid9 Reduction in a
Laboratory-Scale Anaerobic Digester (33) 22
7 Volatile Solids Reduction Vs. Temp. (°C) X SRT (Days), (3) 23
8 The Effect of Loading on Gas Production (39) 25
9 Sludge Gas and Methane Production During Prolonged Incubation
Time (22) 25
10 Bench Scale Digesters Die-Away Gas Production (Formerly Fed
With Raw Primary Sludge From Cedar Creek STP) 26
11 Bench Scale Digesters Die-Away Gas Production (Formerly Fed
With Thickened Activated Sludge From Cedar Creek STP) 27
12 Bench Scale Digesters Die-Away Gas Production (Formerly Fed
With 70% Raw Sluage Plus 30% Thickened Activated Sludge From
Cedar Creek STP) 28
13 Relationship of BOD of Sludge Supernatant to Detention Time
(40) 29
vi
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Number Page
14 Filtration Rate Versug Solids Concentration; Leaf Test Data for
Primary-Activated Sludge, East Lansing, Mich.; Medium, Poly-
ethylene 802 HF; Vacuum, 20 In. Hg Cycle, 3.6 Min.; Submergence,
25 Percent; Chemicals, 2% Percent FeCl. and 10 Percent Lime
(48) 35
15 Cake Solids es a Function of Feed Solids for Different Sludges
(52) 36
16 Cake Solids as a Function of Feed Solids for Different Sludges
(3) 38
17 Chemical Cost as a Function of Yield (52) 35
18 Rates of Inactivation of Coxackie-Virus Type B3 in Digester and
Controls at pH 7 and 32°C (59) 39
19 Rate of Coxackie-Virus Type B3 in Digester and Controls at pH 7
and 35°C (59) 39
20 Effect of Temperature on Rate of Loss of Recoverable Poliovirus
Infectivity (61) 49
21 Effect of Detention Time on Rate of Loss of Recoverable Polio-
virus Infectivity (61) 50
22 Poliovirus Recovery During Anaerobic Sludge Digestion (61) 51
23 Concentration of Coliforms Surviving as a Function of Detention
Time (74) 51
24 Concentration of Salmonellae Surviving as a Function of Deten-
tion Time (74) 56
25 Oxygen Utilization Rates (75) 56
26 Oxygen Uptake Rate Versus Temperature (76) 58
27 Specific Oxygen Uptake Rates at Various Operating Temperatures,
Batch Digestion of a 26% Total Volatile Solids Sludge (77) 59
28 Oxygen Uptake Rate Vs. Detention Time in Aerobic Digester (44).. 61
29 Maximum Odour Intensity Index Measured During 14 Days of
Storage Vs. Detention Time in Aerobic Digester (44) 62
30 Oxygen Uptake Rate and Degree of Stability (%) Vs. Temperature
in Aerobic Stabilization Unit, Primary Sludge (44) 62
vii
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Number Page
31 Variation of Performance Parameters with Tine for Primary
Sludge/Trickling Filter Humus Digested at 20°C (79) 64
32 Undrained Stability Index for Various Operating Temperatures
(77) 65
33 Undrained Stability Index for Various Feed Sludge Concentra-
tions. Batch Digestion at 30°C (77) 66
34 Comparison of Specific Oxygen Uptake Rate and Undrained
Stability Index for Digestion at 30°C (77) 67
35 Effect of Detention Time on Aerobic Digestion of Activated
Sludge (80) 69
36 Volatile Solids Reductions as a Function of Sludge Age 69.
37 Kinetics of Aerobic Sludge Digestion (82) .. 71
38 Reaction Rate K, Versus Aerobic Digester Liquid Temperatures
(3) 1 72
39 Versus Suspended Solids (83) 73
40 Effect of Temperature and Detention Time on the Volatile
Solids Content of Aerated Sludge (84) 73
41 Effect of Sludge Age on VSS Reduction (76) 74
42 Total Volatile Solids Reductions at Various Operating Tem-
peratures. Batch Digestion of a 2.6% Total Volatile Solids
Sludge (79) 75
43 Volatile Solids Reduction as a Function of Digester Liquid
Temperature and Digester Sludge Age (3) 76
44 Ammonia, and NO^ Versus Detention Time (84) 78
45 Solids, Alkalinity and pH Versus Detention Time (84) 79
46 Kjeldahl-Nitrogen, NO + NO_-Nitrogen, and Alkalinity Vs.
Detention Time (78) 80
47 Observed Ammonia Nitrogen Concentrations at Various Operating
Temperatures. Batch Digestion of a 2.6% Total Volatile Solids
Sludge (77) 81
vi i i
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Number Page
48 ATP/VSS Vs. Detention Time (78) 83
49 Settling Curves of Heat-Treated Activated Sludge (90) 85
50 Effect ot Process Temperature on the Fate of Solids During
Heat Treatment (90) 87
51 Effect of Process Temperature on the Fate of Nitrogenous
Compounds (90) 88
52 Response of Sludge Filterability to Non-Oxidative Thermal
Conditioning (91) 88
53 The Conditioning of Activated Sludge by Heat 90
54 The Conditioning of Primary/Activated Sludge by Heat (92) 91
55 The Conditioning of Humus Sludge by Heat (92) 92
56 The Conditioning of Digested Sludge by Heat (92) 93
57 The Effect of Solids Concentration on the Specific Resistance
of Heat Conditioned Digested Sludge (92) 94
58 Continuously Mixed Anaerobic Reactor Schematic 108
59 Schematic Layout of 1.5 Liter Reactor 110
60 Aerobic Reactor Schematic Ill
61 Phase I. Anaerobic Reactor Contents 119
62 Phase I. Aerobic Reactor Contents 120
63 Phase II. Anaerobic Reactor Contents 121
64 Phase II. Aerobic Reactor Contents 122
65 Beacon, N.Y. Aerobic Sludge - Aerobic Stability Parameters 133
66 Beacon, N.Y. and Cold Spring, N.Y. Aerobic Sludges - Aerobic
Stability Parameters 134
67 Cold Spring, N.Y. Aerobic Sludge - Aerobic Stability Parameters.135
68 Musconetong, N.J. Aerobic Sludge - Aerobic Stability Parameters.136
ix
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Number Page
69 Musconetong, N.J.and Stony Point, N.Y. Aerobic Sludge - Aerobic
Stability Parameters 137
70 Stony Point, N.Y. (Summer) Aerobic Sludge - Aerobic Stability
Parameters 138
71 Stony Point, N.Y. (Winter) Aerobic Sludge - Aerobic Stability
Parameters 139
72 Stony Point, N.Y. (Winter) Aerobic Sludge - Additional Aerobic
Stability Parameters 140
73 Rockland County, N.Y. Thermal Sludge - Aerobic Stability
Parameters 141
74 Rockland County, N.Y. and Poughkeepsie, N.Y. Thermal Sludge -
Aerobic Stability Parameters 142
75 Poughkeepsie, N.Y. Thermal Sludge - Aerobic Stability
Parameters 143
76 26th Ward, N.Y.C. Anaerobic Sludge - Aerobic Stability
Parameters 144
77 26th Ward, N.Y.C. Anaerobic Sludge - Additional Aerobic
Stability Parameters 145
78 Jamaica, N.Y.C. Anaerobic Sludge - Aerobic Stability Parameters.146
79 Jamaica, N.Y.C. Anaerobic Sludge - Additional Aerobic Stability
Parameters 147
80 Cedar Creek (Unit 1) 25% Primary + 75% Seed - Anaerobic
Stability Parameters ' 156
81 (Unit 2) 25% Cedar Creek Activated Sludge - 75% Seed -
Anaerobic Stability Parameters 157
82 (Unit 3) 35% Stony Point + 65% Cedar Creek Seed - Anaerobic
Stability Parameters 158
83 (Unit 4) Cedar Creek Seed - Anaerobic Stability Parameters 159
84 (Unit 5) Rockland County Thermal Sludge + 75% Seed - Anaerobic
Stability Parameters 160
85 (Unit 6) 25% Poughkeepsie Thermal Treated Sludge + 75% Seed
Anaerobic Stability Parameters 161
X
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Number Page
86 (Unit 7) Stony Point Aerobic Sludge - Anaerobic Stability
Parameters 162
87 (Unit 8) 26th Ward Anaerobic Sludge - Anaerobic Stability
Parameters 163
88 (Unit 9) Coney Island Anaerobic Sludge - Anaerobic Stability
Parameters 164
89 (Unit 10) Cedar Creek Anaerobic Sludge - Anaerobic Stability
Parameters 165
90 (Unit 11) Oyster Bay Anaerobic Sludge - Anaerobic Stability
Parameters 166
91 (Unit 12) Yonkers Anaerobic Sludge - Anaerobic Stability
Parameters 167
92 (Unit 13) Yonkers Anaerobic Sludge - Anaerobic Stability
Parameters 168
93 Capillary Suction Test and Specific Resistance - Units 1-4 169
94 Capillary Suction Test and Specific Resistance - Units 5-8 170
95 Capillary Suction Test and Specific Resistance - Units 9-12 171
96 Capillary Suction Test and Specific Resistance - Unit 13 172
97 Lead Acetate - Hydrogen Sulfide Odor Test - Anaerobic Sludges... 177
98 Lead Acetate - Hydrogen Sulfide Odor Test - Aerobic Sludges J 78
xi
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TABLES
Number Pane
1 Composition and Characteristics of Primary, Activated and
Digested Primary Sludge 6
2 Composition of Fresh and Digested Sewage Solids 7
3 Composition of Sewage Solids 8
4 Supernatant Characteristics of Digested Domestic Sludge for
Different Detention Times 9
5 Liters of Sludge Produced per Million Liters of Wastewater
Treated 9
6 Digestion of Primary and Activated Sludges 11
7 Summary of Operating Results of High Rate Digestion Tanks 14
8 Anaerobic Digestion of 100% Thickened Unox Waste Activated
Sludge (31) 17
9 Anaerobic Digestion Summary (32) 18
10 Gas Production for Several Compounds in Sewage Sludge 21
11 Variation of BOD in Sludge Liquor with Storage ^41) 31
12 Variation of COD in Sludge Liquor with Storage (41) 31
13 Changes in BOD of the Filtrate from a High-Rate Humus Sludge
After Various Conditions of Storage (42) 32
14 Changes in the Chemical Oxygen Demand of the Filtrate from
Activated Sludges During First 24 Hrs' Storage at 20°C (42) 32
15 Characteristics of Three Sludges: Particle Sizes and
Dewaterability (1) 34
16 Minimum Filter Rates After Chemical Conditioning (50) 40
17 Averaged Vacuum Filtration Performance Data (51) 40
xii
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Number Page
18 Typical Dewatering Performance Data for Rotary Vacuum Filters -
Cloth Media (3) 41
19 Typical Dewatering Performance Data for Rotary Vacuum Filters -
Coil Media (3) 42
20 Pathogenic Human Viruses Potentially in Wastewater Sludge (3)... 44
21 Pathogenic Human Bacteria Potentially in Wastewater Sludge (3).. 45
22 Pathogenic Human and Animal Parasites Potentially in Wastewater
Sludge (3) 46
23 Municipal Treatment Plant Killing and Inactivating Pathogens in
Sludges 47
24 Effect of Sewage Treatment Processes on Indicator and Pathogenic
Microbial Populations in Raw Sewage (65) 47
25 Rate of Loss of Recoverable Poliovirus Infectivity at 1.6
kVS/m -d (61) 48
26 Comparison of Methods and Experimental Conditions for Recent
Studies on Virus Recovery During Anaerobic Digestion (61,62).... 52
27 Survival in Anaerobic Digesters (68) 54
28 Pathogenic Bacteria in Sludge (1) 55
29 Pathogen Occurrence in Liquid Wastewater Sludges (3) 55
30 Lead Acetate Test - Primary Sludge (78) 63
31 Effect of Heating 1 Percent Activated Sludge to Different
Temperatures for 1 Hour With and Without Oxygen Present (90).... 86
32 LA/OMA Thermal Pretreatment Studies Comparison of Digester
Performance Waste Activated Sludge 96
33 LA/OMA Thermal Pretreatment Studies Laboratory Scale Anaerobic
Digestion (Mesophilic) Blend of Primary and Waste Activated
Sludge 97
34 Summary of Treatment Plant Operational Parameters for the
Activated Sludges Used 100
35 Summary of Treatment Plant Operational Parameters for the
Thermal Sludges 100
xiii
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Number Page
36 Poughkeepsie, N.Y., Sludge Characteristics 102
.37 Summary of Treatment Plant Operational Parameters for the
Anaerobic Sludges 103
38 Analytical Methods 115
39 Summary of Parameters - Aerobic Digestion 131
40 Summary of Parameters - Aerobic Digestion of Anaerobic Sludges..132
41 Anaerobic Units 153
XTV
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ACKNOWLEDGEMENT
I acknowledge with grateful appreciation the contribution of Mrs.
Eileen Lutomski for her suggestions and careful typing of the report
manuscript. The suggestions and assistance of EPA staff at Cincinnati's
Municipal Environmental Research Laboratory, particularly Mr. R. V.
Villiers, Mr. B. V. Salotto, and Dr. J. B. Farrell, are also acknowledged.
XV
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SECTION I
INTRODUCTION
The major and most offensive by-product of municipal wastewater treatment
is sludge. Early in the history of wastewater treatment, processes were
developed that ameliorated the obnoxious character, of sludge, and permitted its
disposal without creating intolerable conditions at the point of disposition.
The primary processes for improving the acceptability of (i.e., "stabilizing")
sludge are anaerobic and aerobic digestion. Thermal processes also have been
utilized in recent years for stabilizing sludge.
A sludge should be stable before final disposal. Unfortunately, the
term "stable" is unclear with 'respect to municipal sludges. Before disposal,
a sludge should have been stabilized to an extent where no adverse environ-
ment effect can be easily observed upon disposal. Sludges disposed by
means of land application should be sufficiently stable as not to cause odor
or health problems. Disposal of sludges into the ocean should not cause
adverse effects on the marine ecosystem. It is not within the scope of this
report to determine how stable a sludge should be before disposal. It is
however our concern to define stability with respect to equilibrium concen-
trations of various parameters achieved after long term biological digestion.
Sludges originating from aerobic, anaerobic and thermal processes were
studied in this project. These sludges in pure form and mixtures were fur-
ther degraded by means of aerobic or anaerobic digestion. Data obtained
during our study illustrates how various parameters behave after prolonged
digestion. Since changes occurred in sludge composition after further diges-
tion, were the sludges studied truly stable? It is the hope of the authors
of this report to better define stability with respect to municipal sludges
through this extensive laboratory work and literature survey.
1
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SECTION 2
CONCLUSIONS
1. Aerobically digested, expended aeration, thermaliy treated and anaero-
bically digested primary, activated sludge and trickling filter sludges
wert? not stable with respect to most parameters measured.
2. No single or combined parameter was found to be a standard which would
indicate sludge stability. Most sludges reached steady state with most
parameters studied in 20 to AO days.
3. Stability can be traced by monitoring the parameter of interest at a
specific treatment plant and then using the value obtained in the field
in future applications.
4. A specific oxygen uptake rate of 0.4-1.0 mgOj/gm VSS-hr may be a good
indicator of stabilized aerobically digested sludge. This measurement
is not applicable to anaerobic sludges.
5. Capillary suction tests and specific resistance measurements for dewat-
crability were inconsistent and are not satisfactory as stability indi-
cators.
6. The centrifuge button test appears to be a reasonable indicator of
hydrogen sulfide odor formation and is generally completed in 15 to 30
days for most sludges.
7. Total solids, volatile solids, BOD,. and COD continuously decreased for
all sludges until steady state was reached in typically from 20 to 40
days. These measurements are not particularly sensitive analyses of
stabilization.
8. pH, alkalinity and conductivity in general did not appear useful as
stability indicators; but in conjunction with nitrification and nitrate
formation, they may serve as indicators.
9. During anaerobic treatment of anaerobic sludges the rate of gas forma-
tion and the concentration of volatile acids decrease rapidly in 5-10
days, but this relationship to stability is not evident.
2
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SECTION 3
RECOMMENDATIONS
Continue testing the most promising indicators of sludge stability
as determined in this investigation using various municipal sludges,
in order to confirm their effectiveness.
J
Extend testing to include sludges from rotating biological contrac-
tors, trickling filters and solids from composting operations.
Develop and extend the centrifuge button technique for hydrogen sul-
fide odor production for more universal use, especially in conjunction
with treatment plant operation.
Continue the development of the ATP and crude fibre analyses.
Confirm the use of the specific oxygen uptake rate (SOUR) analyses as
an indicator of the stability of aerobically treated sludges.
Develop stability and drainability relationships using the capillary
suction test.
3
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SECTION 4
LITERATURE SURVEY
INTRODUCTION i
j ;
1 The term "stabilized sludge" is widely used and understood but surpris- J
j ingly difficult to define. Vesilind (1) has suggested that a stable sludge ;
j is one that can be disposed of without damage to the environment, and with- }
out creating nuisance conditions. Damage was defined as an undesirable rate j
; or method of degradation, or the toxic effect on existing ecology. Nuisance i
j was considered simply an affront to the senses of sight or smell. Based on ,
I'these definitions, he proposed many parameters such as odor, toxicity, re--"--!
1 duction in volatile solids, and others to define sludge stability. A scien-
| tific approach to defining stable sludge was presented by Hartenstein (2)
; and is shown in Figure 1. Digested anaerobic and aerobic sludges are shown !
' in the upper right hand corner of the figure. As sludges become stable they
move toward the bottom left hand corner. In stabilization, the sludges oxy-
gen to carbon and hydrogen to carbon ratios approach zero. In this process
however many intermediary compounds of increasing stability are formed.
Hartenstein suggests that a sludge is stabilized when it has been humified
as it appears to be non-putrescible at this stage of decomposition. !
EPA's recent sludge treatment and disposal manual (3) indicates the j
principal purpose of stabilization is to make the treated sludge less odor- j
ous and putrescible as well as to reduce the pathogenic organism content. !
The required stability of sludge depends primarily upon the final disposal j
method selected. For example, if the sludge is to be dewatered and incin- !
erated, frequently no stabilization procedure is employed, but if the sludge '
is to be applied to agricultural lands, highly stabilized sludge with mini- j
mum amounts of toxic materials, pathogens and odor generation potential
should be considered. Therefore, the determination of the degree of sludge
treatment or the instability of sludges is very important in terms of the j
ultimate disposal. \
i
The purpose of this literature survey is to summarize the available i
information that is related to the characteristics and various stability
parameters of municipal sludges that have undergone treatment by anaerobic, j
aerobic or thermal conditioning processes. Sludges, being considered, in- j
elude raw primary sludge, activated sludge, and mixtures thereof. These
sludges have a broad range of instability not only because of their differ-
ent characteristics but also due to the various process factors on which
they are designed. It is the condition of the product sludge that is of
major interest in this study. The parameters studied in this review were
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Demethanation
Dehydralion
Oocnrbosylrition
~i 1 T
02 04 06 oe
Ratio of o*yoen to riuhon
FIGURE 1 - THE FOSSILIZAT10N PATHWAY OF THE CARBON CYCLE (2)
h
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u
U
ct
a
u
H
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o
2
o.
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a
ul
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91
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O'GMTCa loao«h\» ACT 31-.
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k456
OtTtNTION IN DlCe.5T£R-DAV5
FIGURE 2 - RELATION BETWEEN RAW SLUDGE DETENTION TIME AND
VOLATILE MATTER REDUCTION (23)
-------
r. IZ
— p-
—•)
TABLE 1." COMPOSITION AND CHARACTERISTICS OF PRIMARY, ACTIVATED AND DIGESfED PRIMARYSLUDGE
Item
Primary
Activated
Digested Primarv
yt* - -
Range
Typical
Ref
Range
Typical
Ref
Range
Typical
Ref
Total Solids, %
2-7
4
(4)
0.83-1.16
(4)
*
6-12
10
(4)
Volatile Solids,
40-80
65
(4,5)
65-79
(4)
30-60
40
(4)
(%TS)
61-75
(6)
- • -
- - - -
-- --
-- -65-75 - -
- - - -
_ (5)- -
- — — —
. — —- _
59-70
(7)
Total Ash. %
20-40
-
(5,8)
25-38
(5,8)
40-55
-
(8)
Spec.Grav.of Sludge
-
1.02
(4)
1.005
(4)
0.95-1.03
-
(4)
Grease & Fats, (%TS)
7-35
-
(7,9)
5-12
(5,8)
5-20
—
(4)
6-30
-
(4)
-
Hemicellulose, (%TS)
-
3.2
(5,9)
-
-
1.6
(5)
Cellulose (%TS)
-
3.8
(5,8)
7.0
(7,8)
8-15
10
(4)
8-15
10
(4)
Lignin - -- -
— 5v8—-
—(5,9)-
•
—
— 8;4-
— (5)-
Protein (%TS)
20-30
25
(4)
32.4
(8)
15-20
18
(4)
22-28
-
(5,9)
37.5
(5)
16-21
Nitrogen (N,%TS)
1.5-4.0
2.5
(4,9)
2.4-5.0
-
(4,7)
1.6-6.0
3
(4,7
Phosphorus (P^O^XTS)
0.8-2.8
1.6
(4)
2.£-11
-
(4,7)
1.5-4.0
2.5
(4,7
Potash (K20%TS)
o
•
1
O
0.4
(4)
-
-
0-3.0
1.0
(4)
Iron (not as S )
2-4
2.5
(4)
-
-
3-8
4.0
(4)
Silica(Si02>%TS)
15-20
-
(4)
-
-
10-20
-
(4)
pH
5-8
6
(4,7)
6.5-7.5
(4,7)
6.5-7.5
7.0
(4,7
Alk.(mg/1 as CaCO^)
500-1,500 600
(4)
580-1,100
(4)
2,500-3,500
3,000
(1)
Vol.Acids(mg/1 as HAc)
200-2,000 500
•
(4)
1,100-1,700
-
(4)
100-600
200
(4)
Thermal Content
3,780-
1,500-
(Kilocal/Kg)
5,560
4,220
(4)
3,630
(10)
3,780
2,220
(4)
>
_ .
1
-------
^useful in determining a suitable instability index. This information served
ras a guide in the laboratory aspects of the project.
I
J
SLUDGE COMPOSITION AND CHARACTERISTICS
; The characteristics of sludge may vary depending on its origin, its age,
and the type of processing to which it has been subjected. Primary sludge,
from domestic wastewater, drawn from the bottom of primary settling tanks
will contain about 4 to 5 percent total solids. Most often it has undergone
practically no decomposition and is highly unstable and putrescible. Physi-
cal, chemical and biological analysis of primary sludge indicates that it is
usually grey-brown in color, slimy, extremely malodoroi'S, and does not drain
well on drying beds; but can be dewatered mechanically. It contains water,
jinorganic compounds, organic compounds (carbohydrates, fats, and proteins)
'as well as viruses, bacteria, protozoa and metazoa. The volatile matter ac-
counts for approximately 60 to 80 percent of the total solids. In general,
Iprimary sludge can be readily digested under suitable conditions of opera-
tion and is easier to manage than biological and chemical sludges. Typical
data on the composition and characteristics of untreated and digested sludges
jare reported in Table 1.
Substrate composition is basic to any biological process. A number of
workers have studied sewage sludges extensively in an attempt to describe
'average composition. Buswell and Neave (11) analyzed 39 samples of fresh
and digested sewage solids and their results are given in Table 2.
TABLE 2. COMPOSITION OF FRESH AND DIGESTED SEWAGE SOLIDS
I
Fresh Sewage
Digested Sewage
[ Constituent
|Solids
Solids
(% of dry
(% of dry !
Weight)
Weight) !
Grease (petroleum ether)
25.2
6.9 :
Crude fiber
10.8
9.8
Humic acid (pyridine
soluble)
4.0
8.6
Total
59.4
37.8
Volatile matter by analysis
60.9
39.6
Heukelekian (12) later considered the composition of sludge and presented
an approximate analysis which is given in Table 3.
7
-------
• [\ TABLE 3. COMPOSITION OF SEWAGE SOLIDS
1 1
j
i
j Constituent
i
i
1
i
Fresh Sewage
.'Solids
(% of dry
Weight)
Digested Sewage
Solids
(% of dry
Weight)
i Soluble in ether
j
34.40
8.18
j Soluble in cold and
hot water
9.52
5.48
Soluble in alcohol
2.49
1.59
' Hemicellulose
3.20
1.58
' Cellulose
3.78
0.56
| Lignin
5.78
8.37 ;
j Crude protein
27.12
19.68
Ash
24.13
56.00
j Total
110.42
101.44
;He also reported that about 68 percent of the volatiles in fresh sewage solids
were made up of 19.13 percent ether solubles, 25.08 percent total nitrogenous
jmatter, and 23.56 percent carbohydrates on a dry basis.
Supernatant characteristics from digesters may contain concentrated or-
ganic loads which are frequently returned to the primary settling tank or to
the aerators. Table 4 gives typical supernatant concentrations for a number
'of hydraulic detention times.
I
' Activated sludge in municipal secondary treatment plants varies in the
iamount of organic and inorganic material, and thus has variable physical
properties. The organic component of the floe consists extensively of or-
ganisms, the amount of which can be expressed in terms of organic nitrogen
or volatile matter. The inorganic component consists of different elements,
including sodiftim and potassium which can be a part of the cells. But these
,elements typically do not reach high values. Most of the inorganic material
consists of a limited number of elements e.g. silicon, aluminum, calcium and
phosphorous. Activated sludge has a yellow-brown fluffy appearance, an in-
offensive odor, is difficult to dewater and very active biologically. Typi-
cal data on the composition and characteristics of activated sludge is also
reported in Table 1.
The anaerobic digested sludge lias dark brown to black color and contains
a large amount of gas. Well digested sludge has a musty odor that is not at
all objectionable. Anaerobic digestion usually results in approximately a
50% reduction of volatile solids, (Table 1) and a significant destruction of
aathogenic organisms. Digested sludge can be disposed of directly on land,
jr'dewatered on drying beds or by mechanical means before ultimate disposal.
8
-------
TABLE 4. SUPERNATANT CHARACTERISTICS OF DIGESTED DOMESTIC SLUDGE FOR
I DIFFERENT DETENTION TIMES
Detention Time, Days
Parameter ' *—
; parameter
1
90
60
30
20
10
5
jPH
7.51
7.47
7.45
7.28
6.33
5.15
''Alkalinity, mg/I
! as CaCO
4
991
4
640
4
484
4
295
3
353
2
075
jNH^-Nitrogen
mg/I as N
1
215
1
079
1
029
938
921
518
¦Total volatile
acids, mg/1 as
i acetic acid
37
324
721
1
405
3
972
5
519
|% Butyric acid
2.56
9.88
9.49
15.00
24.85
25.17
;%¦-Propionic acid
3.23
23.23
28.00
26.17
35.78
39.91
\7o Acetic acid
59.31
63.05
61.66
47.56
38.55
34.10
j% Formic acid
20.84
2.11
0.54
0.67
C. 51
0.43
1% Lactic acid
14.06
1.24
0.33
0.60
0.11
0.40
Settleable solids,
B0D5,mg/l
1
464
1
738
3
036
6
081
8
527
11
014
! Included in Table 1 is the thermal content of various sludges. The
¦ thermal content of sludge is important'where incineration or some other com-
ibustion process is considered. Accurate bomb-calorimeter tests should be
conducted so that a heat balance can be made for the combustion system. The
thermal content of untreated primary sludge is the highest, especially if it
contains appreciable amounts of grease and skimmings.
Table 5 shows some typical average sludge production rates for compari-
son. It is emphasized that the designer should be very careful in calcula-
ting the sludge quantities considering the increased contributions from in-
dustry.
TABLE 5. LITERS OF SLUDGE PRODUCED PER MILLION LITERS
OF WASTEWATER TREATED
Raw Primary Sludge Waste Activated Sludge Ref¦
2,950 19,400 (13)
3,530 14,600 (14)
2,440 18,700 (15)
3,000 19,400 (16)
9
-------
The characteristics, concentration and quantity of sludges produced in
•wastewater treatment can vary tremendously from plant to plant because of the
^difference in types of wastewaters, and in the design and operation of waste-
water treatment plants. It is, therefore, necessary to obtain as much infor-
mation as possible on the nature of different sludges before studying the
parameters of sludge instability.
ANAEROBICALLY DIGESTED SLUDGE
Anaerobic, digestion is a treatment process employing facultative and
strictly anaerobic bacteria to decompose organic matter in wastewater. Proper
application of this process results in virtually complete destruction of put-
rescible organics, significant reduction in pathogens, conversion of hydro-
philic solids to water, minerals, methane and carbon dioxide gases and a
humus-like residue. The anaerobic digestion process can improve the dewater-
ability of the sludge. Rapidly increasing energy costs have made the methane
production aspect of this process more important. The major drawback of this
process is its reputation as an inherently unstable, difficult to control
process. This reputation may be unjustified. Many problems with anaerobic di-
gestion may be the result of improper operation and maintenance.
; The loss of volatile solids is an accurate measure of the loss of mass
I of solids of the sludge. The importance of this measure and the ease with
I which the volatile solids test is carried out have made volatile solids
J reduction the most important parameter indicating the changes in sludge thai,
jtake place during anaerobic and also aerobic digestion. Other parameters
| relating to changes taking place In digestion are Frequently related to
j this parameter.
One of the major objectives of anaerobic digestion is to decompose the
highly putrescible organic solids present in municipal wastewater by conver- i
sion to relatively stable or inert organic and inorganic compounds. Thus
the amount of solids for ultimate disposal can be reduced significantly.
The degree of volatile solids reduction in anaerobic digestion depends on
the characteristics of the sludge and the operating parameters of the diges-
tion system such as solids retention time, temperature, etc. In a controlled
anaerobic digester, the volatile solids reduction increases with the solids
retention time until it reaches 50 to 60 percent reduction. Beyond this
point, further reduction is minimal even with substantial increase in solids
retention time because only 60 to 80 percent of the volatile solids in munic-
ipal wastewater sludge is biodegradable; the remaining fraction consists
mainly of inert organics such as lignin and tannins. Rudolf (17) incubated
sludge samples for long-time digestion experiments and found that during 203
days of incubation the volatile matter was reduced by 67-70 percent. Another
long-term experiment showed that volatile mntter reduction in five and one-
half years amounted to 72.3 percent. He concluded that within a reasonable
time, volatile matter reduction rarely exceeds 70 percent under most care-
fully controlled conditions, and a 50 percent volatile solids reduction can
be considered satisfactory. Some of the volatile substances decompose more
readily such as some fatty substances and certain cellulosic compounds. In
10
-------
¦^¦(•the 203 days retention time study, cellulose disappeared almost completely,
i From 84 to 87 percent of the ether-soluble material was destroyed and total
carbon was reduced 6o to 75 percent.
i
Greases are of interest because normally they account for about 30 per-
cent of the volatile matter in raw wastewater sludge (18). However, over 50
;percent of the chemical oxygen demand reduction and methane production during
anaerobic digestion occurs as a result of grease degradation. Studies by
Sawyer (19) and McCarty (20) have shown that these materials are degraded
i more slowly than the bulk of sludge volatile matter. Therefore, the rates
of degradation of the major components of the grease fraction may be an im-
portant factor in determining the detention time required for a digester.
Woods (21) studied the digestibility of lipids, carbohydrates, proteins
! and volatile solids of primary and activated sludge mixtures in a two-stage
! digestion system for a total detention period of 78 days. His results indi-
i cated a conversion of more than 80 percent of the lipids and carbohydrates
j into simple compounds was accomplished during the first stage of digestion
; of 38"days. Volatile solids reduction reached a high of 60 percent, in addi-
! tion, approximately 38 percent and 27 percent of the proteins were hydrolyzed
! during the first and second stage of digestion, respectively. Maly (22) also
studied the digestibility of mixtures of primary and activated sludge at
j different temperatures for long periods of time. Table 6 gives the mean
I decomposition of particular components of organic matter in sludge digested
j at 30°C for 106 days.
(
TABLE 6. DIGESTION OF PRIMARY AND ACTIVATED SLUDGES
Parameter Percent Reduction
Volatile matter (%) 49.A
Fats (%) 64.9
Proteins (%) 57.9
The organic fraction in the sludge is the most likely cause of odor and '
also makes sludge handling and dewatering difficult. Therefore, the measure-
ment of volatile solids reduction is one of the most important parameters in-
dicating the instability of sludge. Rankin (23) studied the annual operation
records of about 20 representative municipal plants (Figure 2) and concluded |
that the percentage reduction in volatile matter will vary with the original
volatile content and retention time. The curves iji Figure 2 were derived ¦
from data on tanks operating at temperatures in the range of 29.5 to 35°C,
with only natural circulation and very little agitation. Solids detention
time under these conditions were concentrated between 30 to 70 days and the j
sources of sludges differed widely. However, in spite of these differences,
it seems that a close relationship does exist. Further, the high rate of re-
duction of volatile matter projected in the first ten days is especially sig-
nificant.
Estrada (24,25) further studied data from 20 municipal plants with high-
11
-------
-irate organic loadings ranging from 1.60 to 4.00 kg volatile solids per day
|per cubic meter< (0.10-0.25 lbs VS/cf-d) digester volume. The types of mixing
; raw sludge volatile solids concentration, retention time, and the volatile
I solids reduction are listed in Table 7'. In high-rate digestion systems it is
I obvious that satisfactory volatile solids reduction can be achieved in a much
!shorter detention time compared with the conventional digestion system. In
.'Figure 3 volatile solids reduction is plotted against percent volatile solids
in the raw sludge. Downes' (26) curve, shown in Figure 3, was derived from a
number of sludges obtained from different parts of the country and predicts
i the degree of digestion based on the relationship between percent destruction
of volatile matter and percent volatile matter in the raw sludge.
I
i Schlenz's (27) curve represents the data from 13 full scale treatment
; plants using values, based upon each operator's judgement, as to the deten-
; tion time the operator determined necessary to yield a sufficiently well-
¦ digested sludge. The Chicago Pump Company curve is designated for use when
' forecasting results of the active digester and does not include carry-over
i digestive action taking place in the storage portion of the tank system. In
the unheated storage tank this carry-over digestion amounts to approximately
an additional 10 percent reduction of volatile matter. When an additional 10
percent reduction is added to the Chicago curve criteria, it approximates the
Downes curve criteria (26). The large scatter of data points attained by the
20 high-rate plants do not give a conclusive relationship between volatile
solids reduction and percent volatile solids in raw sludge, probably because
of the varying sludge characteristics and operating parameters. However,
there is no doubt that the original content of volatile solids greatly influ-
ences the percent reduction of such solids that is necessary to obtain a well
digested sludge. It should be noted when estimating the reduction of solids
of a sludge with low volatile solids, a lower percentage reduction is ob-
tained than that of a raw sludge with high volatile solids. For example, by !
applying Schlenz's curve, a raw sludge with 65 percent volatile solids yields
a volatile solids reduction of approximately 54 percent to produce a resul-
tant digested sludge as stable as a sludge which originally contained 75 per-;
cent volatile solids but requires a volatile solids reduction of 73 percent i
by digestion to reach stability. ;
Primary, Waste-Activated, and Mixtures of the Two Sludges
Waste activated sludge has been blamed for the difficulties in reducing
volatile solids, creating foaming problems, as well as the poor thickening
and dewatering characteristics in digested sludge (28,29). Jeris (30) work-
ing with bench scale digesters with 20 and 30 days detention time studied
sludges taken from the Cedar Creek, New York wastewater treatment plant and
reported an average volatile solids destruction of 39 percent for thickened
activated sludge, 56 percent for raw primary sludge, and 55 percent for the
mixture of raw primary and thickened activated sludge at a ratio of 7:3 by
volume. The volatile solids in raw primary and waste activated sludge, be-
fore digestion, were 81.6 and 82.2 percent respectively. Following the
experiment, he stopped feeding the digesters and observed the volatile solids
reduction and gas production of the digested sludges for 151 days with or
without mixing. The average volatile solids destruction at the end of the
observation included: raw sludge 67 percent, activated sludge 48 percent,
and the mixture of the two, 64 percent. Actually, the volatile solids con-
12
-------
I!'
1, HARTFORD, CONN.
2, WILMINGTON, DEL.
3,. ARLINGTON, VA.
4 a be, SAWYER-PILOT
5, MORGAN - PILOT
6, ERIE, PA.
7, COLUMBUS, OHIO
8, ABINGTON, PA.
9, GRAND RAPIDS,MICH
10, TRACY, CAL.
11, BERGAN, N.J.
12, BOWERY BAY-PILOT
13, BOWERY BAY
14, MIDDLEBORO- PILOT
15, GREENWICH - PILOT
I6..BIVERSIDE -PILOT
17, AURORA, ILL.
18, SALT LAKE CITY
19, ROCKFORD, ILL.
20,KEEFER - PILOT
80
LJ
. a
.a
D
_l
U)
£
<
a
00
g
_j
o
CO
Ll)
_l
70
60
p 50
<
o
>
40
[4C
r-«—
15
? /
• 3
y
/
CURVE-CHICAGO
PUMP CO.
012
O
3®
Xb c
I x
©13/
'ie
CURVE- J.R.DOWNES
(1932)
r ¦ ¦
Yj,
20^
5 X
3?
017
®6
10 »
~
02
\.CURVE- SCHLENZ
(1937)
I
20
30
40
50
60
70
80
% DESTRUCTION OF VOLATILE SOLIDS BY DIGESTION
figure 3 - GRAPH SHOWING COMPARISON OF
COMPLETION OF DIGESTION AT HIGH RATE
PLANTS WITH ACCEPTED STANDARDS <25>
13
-------
1
2
3
4a
b
c
5
6
7
8
9
10
11
12
13
TABLE 7. SUMMARY OF OPERATING RESULTS OF HIGH RATE DIGESTION TANKS
Plant
Type
of
Agitation
Period
of Test
Months
Raw Sludge
% %
Solids V.M.
Loading
1 Kg VM/day-
Cubic Meter
Retention'
No. of '
— Days-
Digested
Sludge
Red. V.M...
Hartford, Conn. Pearth
Wilmington, Del.
Arlington, Va.
Sawyer-Pilot Ga
Rec.
Morgan-Pilot C.R.P.
Erie, Pa. (54)
Columbus, 0.
Abington, Pa.
Grand Rapids, Mich.
Tracy, Calif.
Bergen Co., NJ Mech.**
Bowery Bay, NY Mech.
Pilot Plant
1
7 *
69.4
2.80
18 :
63
3
6
59.0
1.62
22.5
61
9
4.5
79.0
3.56
12
66
2.5
4.42
74.5
3.36
10
55.8
II
II
II
2.24
15
57.2
II
II
II
1.60
20 |
58.2
12
7.37
60.5
4.20
10.1 ;
41.5
12
2.8*
65.5
Z.UU
9.6
56.5
10
6.6
59.2
2.63
13.9
40.4
2
3.3*
74.4
1.89
13.3
51.8
12
4.6
67.3
2.19
14.8
48
5
6.0
68.4
1.95
19.8
63.5
12
3.1*
80.0
1.74
15.7
57.3
6
5.1
74.5
2.88
13.3 :
42.5
Bowery Bay, NY
None
10.2
74.1
2.61
31.0
61
continued on next page
-------
Type Period . ; ' V Rav Sludge
of. of Test . Z Z
— Plant -— — -Agitation Months—; -Solids- ^:V.M:
Mlddleboro, Mass. Mech.(jDorr) 5.5 8.2 . 78.C
Pilot Plant
Greenwich, Conn. " "
PllotiPlant
Riverside, Calif. "
Pilot Plant
Aurora San.Dlst. V.P.E. Gas-
Aurora, 111. lifter
78.5
70.9
62.9
| Loading
, Kg VM/day-
•Cublc-Meter*
1 3.20
H 3.84
'2.10
VRetention
Ho. of
Days ~
22.0
18.8 / ^
25.5
15.1
»»»»:»*.'••. •s.'*.
Suburban San.Dlst.
Rocfcford, San.Dlst. "
Bockford, 111.
. Keefer-Pllot Pre-nixing(b)
Jamaica, L.I. Mech.(Dorr)
2.5
17
2.23
3.78
4.00 (c)
(a) , typical of about a year's operation experience. | ;
(b) Pre-irlyfng of raw and digested. i
* Computedby Author . •;'
** Agitated by use of Recirculating Puaps I
(c) Reconnended loading by Authors and results of August 1959
vhen this loading was carried out. ,
18.3
8.8;
12.51
-------
icentrations remained fairly constant from 'tKe'^yth day. By this time"the
jsludges had apparently stabilized.
i
The County Sanitation District of Los Angeles County also conducted an
jextensive investigation on the digestibility of 100 percent waste activated
.jsludge in pilot digesters. Table 8 (3i) shows the digester volumes, the
.monthly average data of volatile solids destruction, raw sludge character-
istics and operating conditions. The digester temperature was controlled in
¦ the mesophilic range with an average of 34.4°C. The organic loading was in
jthe range of 0.96-1.44 kg volatile solids per day per cubic meter (0.06-0.09 ;
|kg VS/cf-d) digester volume. Sludge characteristics remained fairly constant
! during the period of study. The monthly average volatile solid's destruction
ranged from 22.2 to 46.2 percent with a median value of 38 percent. It is
'interesting to note that the average volatile solids reduction is comparable
Jto Jeris' (30) results where both usedisimilar operating conditions. In an- !
jother pilot study, conducted by Austin;et al. (32) on 100 percent waste acti-
vated sludge, they concluded that under mesophilic operation (33.9°C), anaer-,
!obic digestion destroyed an average of'32 percent of the applied total vola- i
j.fQe solids and yielded. 0.924 cubic meters of total gas per kilogram (14.8
j cf/lb) of volatile solids destroyed. An average hydraulic detention period
iof 22 days and a daily volatile solids loading of 1.36 kg per cubic meter
' (0.085 lbs/cf) were maintained.
j Digestion of various ratios of combined primary and waste activated
;sludge were also studied (32). Table 9 summarizes the anaerobic digestion
(results evaluated at the Saugus-Newhall Water Reclamation plant. The vola- j
i tile solids reduction data were plotted in Figure 4 versus the waste acti-
vated sludge to'primary sludge ratio. Jeris' data were also included for i
i comparison. Volatile solids destruction in excess of 50 percent were consis-
1 tently obtained for all of the combined sludge ratios. Digestion of 100 per-1
'cent waste activated sludge produced volatile solids destruction of 39 to 50
percent. For 100 percent primary sludge, the volatile solids destruction
I was 56 to 62 percent. ;
All of the anaerobic digestion studies conducted to date indicate that ;
; waste activated sludge does not digest as well as primary sludge. Since
I a considerable amount of stabilization has already taken place within the
¦ aeration reactor, the biodegradable fraction of these sludges is lower than
primary sludge. Consequently, the volatile solids reduction associated with j
[ anaerobic digestion is also lower. ;
t Parameters of Sludge Instability
Potential parameters for measuring instability of anaerobically digested
sludge include volatile solids, gas production, BOD and COD, filterability,
odor production, and pathogen reductions. The following sections review thes*
parameters. T
| Temperature and Detention Time !
The most important operating parameters affecting volatile solids reduc-
. tion are detention time and digestion temperature. As shown in Figure 5 1
(22), a mixture of primary and waste activated sludges were digested for a
long period of time (186 days) at temperatures of 20°, 30°, and 50°C, with
16
-------
TABLE 8. ANAEROBIC DIGESTION OF 100% THICKENED UNOX WASTE ACTIVATED SLUDGE (31)
Oct- Jan- Apr- j
Dec Mar June May June July Aug Sep Oct Nov Dec Jan
1978 1979 1979 1979 1979 1979 1979 1979 1979 1979 1979 1980
Dig. No. 2^22^2 2 11
r
Dig. Vol. 37.9 37.9 37.9 37.9 45.4 37.9 45.4 37.9 45.4 45.4 45.4 45.4 45.4 37.9 37.9
(mY3) I
i ;
Temp. (°C) 34 34 34 34 34 34 35 34 36 37 36 33 33 34 34
Loading 1.18 1.06 1.13 1.40 1.33 1.06 1.06 1.30 1.17 1.15 .90 1.30 .91 .98 1.14
(kgVS/
m3-day)
i ;
Detention ;
Time(days) 25 30 27.6 23.8 25 28.2 27.9 26.3 29.3 25 31 25 27.6 26 22
| i
TS in_raw ....
activated
sludge (%) 3.7 4.0 4.1 4.2 4.2 3.9 3.9 4.5 4.5 3.8 3.6 4.2 3.3 3.2 3.1
VS in raw
activated
sludge (%TS) 80 79 77 79 79 76 76 76 76 76 77* 77 77 79 81
% VS i
Destroyed 37.7 46.2 41.9 42.0 38.0 40.3 35.7 44.0 35.0 22.2 26.7 35.0 27.7 41.0 43.0
-------
TABLE 9. ANAEROBIC DIGESTION SUMMARY (32)
Location
(% WAS1
- % primary)
Detention
Time
(days)
Volatile Solids
Loading
(kg/m3-day)
Volatile Solids
Destruction
(%)
Unit Total Gas
Production
m3/kg vs. destroyed
Saugus-Newhall
0 -
100
58
0.67
62
0.94
Saugus-Newhall
23 -
77
32
1.17
53
*
Valencia
23 -
77
43
0.96
50
*
Valencia
31 -
69
20
1.34
54
*
Saugus-Newhall
A3 -
57
24
1.36
57
0.87
Saugus-Newhall
50 -
50
19
1.67
57
*
Saugus-Newhall
64 -
36
28
1.30
54
*
Saugus-Newhall
70 -
30
23
1.92
60
0.69
Saugus-Newhall
73 -
27
23
1.69
59
•k
Saugus-Newhall
100 -
0
46
0.96
51
0.69
Saugus-Newhall
100 -
0
21
2.00
45
*
*gas data
scarce
and questionable.
waste activated
sludge.
-------
I ! i i ' 1 I 1 ! I I .
100 90 50 70 60 SO «0 30 20 10 0 Percent Prlnary Sludge
FIGURE 4 - ANAEROBIC DIGESTION VOLATILE SOLIDS DESTRUCTION VS.
WASTE ACTIVATED SLUDGE/PRIMARY SLUDGE RATIO (32)
-------
OQ45
FIGURE 5 - REDUCTION OF ORGANIC MATTER DURING FIRST TEST AT
20° C (1), 30°C (2), AND 50°C (3) (22)
20
-------
j the final reduction of organic matter reaching 49, 53, and 54 percent respec-
I tively. The low volatile solid3 reduction achieved was probably caused by
| the low volatile solids present in the raw sludge (50%). The time necessary
for satisfactory digestion was as follows: at 20°C, 80 to 100 days; at 30°C,
"T33 to 50 days; at 50°C, 20 days. Temperature seems to have a stronR influ-
ence on volatile solids reduction at the initial stage of digestion, as the
1 detention time increases, the temperature effect is less pronounced. Similar
, effects of solids retention time (SRT) and temperature on volatile solids
. reduction studied by O'Rourke (33) is shown in Figure 6. For temperatures
greater than 20°C, volatile solids reduction climbs rapidly to 50 to 60 per-
cent as the SRT increases. It is noted that the raw sludge had very differ-
ent characteristics than the one used by Maly and Fadrus (22).
The combined effect of SRT and temperature on volatile solids reduction
for primary, activated, and mixtures of these sludges is plotted in Figure 7
(3). Although the data points are somewhat scattered, they suggest that
primary sludge degrades faster than a mixture of primary and wasteactivated
sludge, which, in turn, degrades faster than straight activated sludge.
Gas Production
One of the major advantages of anaerobic digestion is the much smaller
amount of biological solids produced per unit of organic material consumed
than in aerobic systems. This is the result of the high energy-end product,
methane. Methane has a definite economic value as a fuel, and is used as a
source of energy for both heat and power in many installations. In a well-
operated digester, about 0.75-1.2 cubic meters (12-20 cf/lb) of gas can be
produced from each kg of volatile matter destroyed (34,35,36,37,38). If the
volatile content of the raw sludge is reduced by 50 percent, gas yield should
be about 0.37-0.62 cubic meters per kg (6-10 cf/lb) of volatile matter added.
Digester gas contains about 65-70 percent methane and 30-35 percent carbon
dioxide (21). Carbon dioxide in excess of 35 percent may be an indication
that the digestion process is not proceeding properly. The production of
gas in a sludge digester comes from the breakdown of organic matter by micro-
organisms. Both sludge characteristics and operating parameters are impor-
tant factors influencing gas production. Table 10 shows some specific gas
production values for the anaerobic digestion of fats, scum, grease, crude
fibers and protein.
TABLE 10. GAS PRODUCTION FOR SEVERAL COMPOUNDS IN SEWAGE SLUDGE
Specific Gad Production
Material cu m/kg destroyed
CH, Content,
4
Percent
Fats
1.12-1.44
62-72
Scum
.87-1.00
70-75
Grease
1.06
68
Crude Fibers
.81
45-50
Protein
.75
73
Fatty substances have a higher energy content per unit weight than other
forms of organic matter. Thus, the breakdown of a sludge with a high propor
21
-------
100
M
N>
ae
z"
o
j—
o
ID
O
ill
90
80
70
60
50
40
30
20
10
RAW SLUDGE CHARACTERISTICS
TYPE PRIMARY
SOLIDS CONC. 2.3%
VOLATILE CONTENT 80%
20 30 40
SOLIDS RETENTION TIME, days
FIGURE 6 -
temperature on volatile solids reduction
IN A LABORATORY-SCALE ANAEROBIC DIGESTER (33)
-------
60
50
40
30
?0
10
0
C-
',0
¦10
JO
;'u
10
o
60
c-o
jo
30
.-J
10
0
7
PRIMAIIV SLUDGE ONLY
• PHOT PI ANT
a PILOT PLANT
I I ! I I ' I L
activated SLUOGE Onl y
* I'll U r I'l •'•¦¦¦¦ T
• pilo: plan:
¦ (MOT PLANT
PIUMAHY ANU
ACTIVATED SLUDGE
I
• fULL SCALE
» pilot plant
¦ f-ULL scale
-uo •> c<: h( o r.-oo -.-(yj : nco : :?<)
rf-'p i*C! « soi!or. rtrir/.N :;vr o-w,,
VOLATILE SOLIDS REDUCTION VS. TEMP. (°C)
X SRT (DAYS), (3)
23
-------
; tion of fats, oils, and greases can be expected to yield a greater quantity
j of gas pet unit of solids destroyed (3).
Figure 8 shows the effects of temperature and loading on methane and
total gas production (39). The curve for methane production is almost hori- :
zontal which indicates that loading, in the range of the study, and methane
production per unit of volatile solids destroyed are independent. The ;
destruction of the volatile solids can produce a fixed amount of methane '
per unit of solids destroyed in the loading range between 0.64-3.2 kg volatile
jsolids per cubic meter per day (0.04-0.2 lbs VS/cf-d). The total gas pro- j
iduction increases with loading due to the fact that more carbon dioxide is !
Jproduced at higher loading rates. The effects of temperature are twofold; j
first, higher temperature increases the activity of microorganisms, and
secondly, temperature influences the solubility of gases, there is more
carbon dioxide and methane released at 35°C than that at 25°C.
Figure 9 shows the effects of temperature and retention time on gas pro-
! duction (22). There was a rapid increase in gas production at the initial
; stage of digestion. After this stage, it slowed down considerably. The
; total gas production at the three different temperatures varied slightly.
J Both the total gas produced and the plateau of methane production are reached
; sooner at 50°C than at 30°C, and require significantly increasing times as
, the temperature drops to 20°C. It is of interest to note that after a cer-
tain period of digestion, there is almost no gas produced indicating the de-
crease in metabolic activity. At this time, most of the available organic
• matter has been consumed and the sludge is very stable. Thus, a large reduc-
: tion in gas production rates can be an excellent indicator for measuring |
; sludge stability or instability.
I
Figures 10, 11, and 12 (30) show gas production data obtained after
. cessation of feeding digesters raw, activated and the mixture of the two ;
sludges. The majority of the gas production occurs in the first two to five '
days, depending upon the SRT, mixing regime and origin of the sludges. Gas
I production decreased significantly after the 5th day and reached a low rate
1 in 12-15 days which suggests that a stable sludge was obtained. It is note- j
i worthy that the digester fed activated sludge sustained a lower rate of gas ¦
. production initially but the rate of gas production decreased more gradually
j with increasing digestion period. !
BOD and COD of Supernatant '
The BOD and COD concentrations of digester supernatant have been re-
ported to decrease with increasing digestion retention time (40). Figure 13
shows the relationship of supernatant BOD.to detention time for a mixture of ;
primary and high-rate trickling filter sludge. The detention times selected
for study were 5, 10, 20, 30, CO and 90 days. The supernatant liquor was
allowed to settle for one hour, after which the liquid portion was examined
for its chemical characteristics. The BOD decreased rapidly during the first
30 days and leveled off gradually. After the 60th day, there is little BOD
reduction indicating a more stable sludge was obtained. It thus appears pos-
sible to estimate the stability of a sludge by making measurements of the BOD
(or COD) of the sludge liquor.
White (41) investigated the stability of various types of sludges during
storage, with regard to the changes in BOD, COD, and to the effect on the
24
-------
0 04
0 20
octi oiz oir.
loading - lb vs/cuft/d/.v
FIGURE 8 - THE EFFEGT OFJ^OADING ON GAS PRODUCTION (39)
15 000
10 000
£ sooo
a
cr>
a>
cr
T3
D
in
FIGURE 9 - SLUDGE GAS (SOLID LINE) AND METHANE (DASHED LINE)
PRODUCTION DURING PROLONGED INCUBATION TIME (22)
25
-------
N>
ON
Figure 10. Bench Scale Digesters Die-Away Gas Production (Formerly Fed With Raw
Primary Sludge From Cedar Creek STP).
-------
KJ
Z 3 + 5 6 7 8 3 10 M .:jZ :l5 '4- 15 lb >7 16 19 T> 2> V- ,22> &(i*l
Figure 11. Bench Scale Digesters Die-Away Gas Production (Formerly Fed With Thickened
Activated Sludge From Cedar Creek STP).
-------
N>
00
2 3 4 S 6 7 S 5> IO I.I !Z 13 14- 15 ife 17 lb 1^ Zb El . 22. 23 24^42.'.'
Figure 12. Bench Scale Digesters Die-Away Gas Production (Formerly Fed With 70% Raw Sludge
Plus 30% Thickened Activated Sludge From Cedar Creek STP.)
-------
: V- ( w ¦ v
DcLontion Time - Day:;
FIGURE 13 - RELATIONSHIP OF BOD OF SLUDGE SUPERNATANT TO
DETENTION TIME (40)
29
-------
I J r •:. "1 , •. . r%
il l ssyfilterability of the sludge. He indicated that the quality of the super- j
1:1 :;l | riatant liquor will depend on the type of the sludge and its activity. For ]
(example, a 5-8 percent concentrated waste activated sludge with a storage ;
jtime of 5 days had a concentration of BOD in the supernatant liquor of 7,300 i
img/£, while for a 1:5 mixture of primary and activated sludge, the concentra--
! tion of BOD was reduced to 4,200 mg/Ji, Primary, secondary, and anaerobically;
(digested sludges were collected and stored for several days. The BOD and COD
M ^concentrations in the filtrates were measured. White indicated the rate of
j ¦:¦ | change of BOD or COD with storage is a good measure? of stability. To compare,
! sludges having widely different solids contents, the BOD and COD are ex- '
;pressed as a proportion of the concentration of dry solids. Typical results
jare shown in Table 11 and 12. Day zero was taken as the day of initial sam- •
i pling for primary and secondary sludges. It can be seen that interstitial
I liquor from mixed primary sludge had high BOD and COD concentrations but
! showed no specific trend. With the exception of anaerobically digested
! sludge, all sludge interstitial liquors tended to increase in BOD and COD
'concentration. Tebbutt and White (42) collected a fresh primary sludge (4.4%
!t.S.) and measured the BOD concentration to determine its instability. The j
; interstitial water of a fresh sample had a BOD of 2100 mg/£ whereas after 1
i day of storage, the BOD of the filtrate increased to 3,060 mg/2. at 15°C and _
j 20°C respectively. The BOD of the settled sewage was 500 mg/Jl.
! 1
; The anaerobically digested sludge, extended-aeration and low-rate acti- j
. vated sludges seem to be relatively stable with respect to the release of
BOD and COD into the liquor. Sludges from high-rate biological treatment
processes were very unstable. For example, the BOD concentration in the
filtrate of a high rate biological filter sludge (humus 3.3% T.S.) at day 0
i was 858 mg/£, and increased to 1,949 mg/Z after only 2 days storage. It is
i noted that the data in Tables 11 and 12 were collected at 5°C. A substan- ]
j tially increased degree of solubilization of BOD from the solid phase would
| be expected at elevated temperatures. This is shown in Table 13. Both the j
I effects of temperature and continuous mixing (one rev/min) are reported. It ¦
j is clear that prolonged storage of sludge from high-rate plants should be
j avoided.
i j
J Table 14 shows the effect of loading on the changes in the COD of the j
i filtrate from activated sludges during' the first 24 hours storage at 20°C. j
! Again, it can be seen that all the sludge CODs increase, and that the higher
: the loading on the plant, the greater the release of COD and thus the greater
; the degree of instability. '
! Odor Production
| Evolution of odorous gases is one of the major problems for sludge hand-'
I ling and disposal. The principal odors of an organic nature arise from the
anaerobic decomposition of compounds containing nitrogen and sulfur. These
compounds include mercaptans, indoles, skatoles and various other nitrogen ;
and sulfur-bearing organics (43). The most common cause and readily identi-
fiable of the numerous odors associated with sludges is hydrogen sulfide.
Because of the large number of potential odor-causing compounds and the :
difficulty of measuring the strength a!nd type of an odor quantitatively,
.i
V V 30
'•Ti/ji. •<
-------
TABLE 11. VARIATION OF BOD IN SLUDGE LIQUOR WITH STORAGE (41)
Dry
Weight of BOD in solution as a percentage of total DS
Sludge type
Solids
In settlement
In interstitial liquor after storage for(days)
(percent)
tank effluent
0
1 2 3 4 5
6 7
Mixed primary
3.3
0.6
3.6
3.1 3.9
Humus (low-rate)
4.9- -
- <0.1 •
- 0.9
- 1.5- 2.8-— — .
. — 6.9r_
Humus (high-rate)
3.3
0.3
2.6
5.3 5.8
Activated (extended-aeration) 1.1
0.1
0.1
0.2 0.4
0.3
Activated (low-rate)
2.2
0.1
0.1
0.4 1.0 1.1
Activated (high-rate)
2.0
0.1
0.1
0.5 1.3
Anaerobically digested ..
2.5
1.1
0.2
0.1
TABLE 12. VARIATION OF COD IN SLUDGE LIQUOR WITH STORAGE (41)
Dry
Weight of COD
in solution as a percentage of total
DS
Sludge type
Solids
In settlement
In Interstitial liquor after storage
for(days)
(percent)
tank effluent
0
1 2 3 4 5 6
7 9
Mixed primary
3.3
0.9
7.1
5.8 6.7 7.5
Humus (low-rate)
4.9
0.2
1.5
2.4 3.2 4.5
10.2
Humus (high-rate)
3.3
0.6
3.7
8.0 8.9
16.7
Activated (extended-aeration) 1.1
0.6
0.8 0.8 1.0
1.5
Activated (low-rate) ...
2.2
0.7
1.8 2.7 2.9
Activated (high-rate) ..
2.0
1.8
3.6
5.2
Anaerobically digested .
2.5
2.7
1.0 0.8
DS - Dry solids
-------
LMVfc
t»:xt __
i-irni' »4-
DifuPlTD
Hi'
I if.. i
srciKH..'!.;
tin-:!' w-
W L_l N I l_l I
of r/-Gr
A
IMAGF
TABLE 13. CHANGES IN BOD OF THE FILTRATE FROM A HIGH-RATE HUMUS SLUDGE
AFTER VARIOUS CONDITIONS; OF STORAGE (42)
(Initial solids content of sludge, 2.1 percent
Conditions of storage
Period of
J storage
! (days)
10°C
20°C
Quiescent
Stirred
Quiescent
Stirred
BOD of liquid phase (mg/1)
0
1
2
3
4
700
1700
1750
1800 •
2800
700
3333
5170
6000
9750
700
,1250
5750
6700
8000
700
6000
9500
10000
13000
TABLE 14. CHANGES IN THE CHEMICAL OXYGEN DEMAND OF THE FILTRATE FROM
ACTIVATED SLUDGES DURING FIRST 24 HRS' STORAGE AT 20°C (42)
Origin of activated sludge
Period of
storage
(hr)
Laboratory fill-
and-draw plant (H)
(extended aeration)
Sewage Works I
low-rate plant
Sewage Works J
high-rate plant
COD (mg/1)
0
1
5
14
24
44
42
46
38
62
48
42
64
76
160
205
230
265
550
!•:
32
i t ,|
i -.
-------
-little research.-*work has been done which has been associated with odor poten-]
tial in sludges. However, it is one of the most important parameters related;
to the instability of sludge. Eikum and Paulsrvd (44) have suggested a def- j
inition of sludge stability which is related to storage and has been acceptedj
by the Commission of the European Communities. In use the "Odor Intensity
jlndex (45) should not exceed 11 at anytime during 14 days of storage at 20°C,;
unless the odor>can clearly be classified as a typical soil odor." The mea- ¦
surement of odor intensity index is tedious and laborious, and the result is
somewhat subjective.
i
Another method measuring odor potential is the panel method (46) which
involves submitting a number of people to various odors, their opinions are
, recorded and analyzed. This indicates an average opinion of the strength of
; a certain odor.'
! Ruffer (47) introduced the lead acetate test for measuring the degree of[
: sludge stabilization. A number of 100 m£ bottles with glass stoppers were
! filled with 50 m£ of sludge. A strip of lead acetate paper was fastened be-
j tween the bottle and the stopper. The1 evolution of caused the color of i
\ the lead acetate paper to change from white to brown. The time required for ,
I the color to change is a good indicator of sludge stability. It should be
¦ borne in mind that H^S is by no means the only source that causes odor. It is
; probably the most important malodorous^ gas produced by unstable sludge. This
i method is simple and inexpensive to perform in both laboratory and sewage
1 treatment plant operation.
I
j Filterability
Filterability has been suggested as a measurement of sludge stability. |
| The belief is that sludge dewaterability increases as stability increases. i
i White (41) studied the filtration characteristics of various sludges with ;
| respect to their storage time and used' the specific resistance results as a
i measure of sludge instability. On the' other hand, Veslind (1) and Eikum (44);
! suggested that filtration properties have nothing to do with the stability of1
; a sludge due to the inconsistent filtration results obtained by many investi-
gators. The most common means of dewatering wastewater sludge is vacuum
filtration and there are many factors that could affect the performance of !
the process such as the characteristics of the sludge and the operating con-
ditions. Among the characteristics of a sludge which affect filtration are
included: (48, 49, 50, 51)
(1) Solids concentration
(2) Type and nature of sludge including volatile content, size,
shape and charge of the solid particles
(3) Sludge compressibility
(4) Sludge age and temperature
(5) Chemical composition
(6) Viscosity of sludge
Among the operating variables which affect filtration are:
33
-------
R!T (1) Vacuum J
I (2) Drum speed '
(3) Filter media
• (4) Conditioning of sludge prior to filtration
i
j It is not the intent of this report to review all of these variables.
„,;However, some of the most important parameters that relate to the sludge
characteristics and to the determination of sludge instability are reviewed.
i
I
: Dewateral'ility of activated, raw and digested sludges is a characteris-
tic of great importance to better and more economical sludge management.
[Studies by Karr, reported by Vesilind (1), are summarized in Table 15. These
idata characterize three typical wastewater sludges in terms of filterability
;and particle size.
TABLE 15. CHARACTERISTICS OF THREE SLUDGES:
' SIZES AND DEWATERABILITY (1)
PARTICLE
Type of.Sludge
Raw Primary
Sludge
Activated
Sludge
Mixed Digested
(Anaerobic)
Sludge
iSpecific Resistance (m/kg) 2.1 x 10
iCST (sec) 17
jTotal Solids (mg/1) 9698
iRigid Settleable >100ym 6452
| (percent of TS mg/£)
I
iFragile Settleable-settle 1 hr. 2320
! (percent of TS mg/£)
[Supracolloidal > lum
| (percent of TS mg/2.)
iTrue Colloidal >0.001um
(percent of TS mg/£)
iDissolved
(percent of TS mg/£)
355
45
526
4.8 x 10"
14
8841
1920
6587
84
243
9.3 x 10
144
10,266
3374
4054
1997
301
540
14
Schepman (48) studied the effect of solids concentration on filtration
rate using the filter leaf test and found that the sludge filtration rates in-
crease directly in proportion to the increase in feed sludge solids concentra-
tion (Figure 14), The slope of the curve in Figure 14 may change depending
on the types of sludges used. There is, however, a practical upper limit
(probably 8 to 10 percent solids for sewage sludge) which, when exceeded,
makes mixing and pumping with chemicals, and sludge distribution difficult.
The straight line relationship between feed solids concentration and filtra-
tion rates was confirmed by Bennett (52) and is shown in Figure 15. The
34
-------
FIGURE 14. FILTRATION RATE VP' 'US SOLIDS CONCENTRATION;
LEAF TEST DATA FG. ^IMARY-ACTIVATED SLUDGE,
EAST LANSING, MICH. MEDIUM, POLYETHYLENE
802 HF; VACUUM, 20 * . Hg CYCLE, 3.6 MIN.;
SUBMERGENCE, 25 PERCL T; CHEMICALS, 2 1/2
PERCENT FeCl AND 10 PERCENT LIME. (48)
35
-------
FEED SOLIDS (%)
FIGURE 15 - CAKE SOLIDS AS A FUNCTION OF FEED SOLIDS
FOR DIFFERENT SLUDGES (52)
36
-------
sludges under study included anaerobically digested sludge, raw primary
sludge, aerobicaily digested activated 'sludge, and a mixture which was made
up of approximately 35 percent raw primary, 20 percent digested, and 45 per-
cent activated sludges. It is interesting to note that the filtration rates
for both primary, and anaerobically digested sludges were the highest among
the four and the aerobicaily digested activated sludge had the lowest yield,
while the blendeid sludges gave intermediate yields. Figure 16 shows that in-
creasing the feed solids concentration for filtration would result in the in-
crease of cake solids concentration for various types of sludges. Again,
aerobicaily digested activated sludge was found to form the least concentrated
cake solids.
The difficulty of dewatering waste activated sludge has been concluded
by many investigators (53,54,55). In a recent study conducted by Austin et
al. (32) on the filterability of digested waste activated sludge, they found
that a heavy dosage of chemicals was required for the anaerobically digested
activated sludge' in order to operate the vacuum filters without failure. The
maximum cake solids concentration obtained was only 14 percent with a maximum
filter yield of approximately 16.6 kg/h'r-sm (3.4 lb/hr-sf). With the aero-
bicaily digested activated sludge, a cake solids concentration of 11 to 15
percent total solids was obtained while filter yields varied from 2.4 to 4.9
kg/hr-sm (0.5 to 1.0 lb/hr-sf). This is comparable to Bennett's results
(Figure 17) which showed the relationship of filtration rates versus chemical
cost (dosage of ferric chloride and lime; for four sludges. In general, the
filter yield increased wich higher chemical dose but both the aerobicaily
digested activated and the blended sludges needed the most chemicals and gave
a very low filter yield. The anaerobically digested and primary sludges
showed a rapid increase of filter yield at low chemical doses. Bennett
suggested that this result was due to the high fiber content of anaerobically
^digested and primary sludges. He indicated that the qjiemicals act as coagu-
lants and agglomerate the small particles to the fiber, thus preventing
blinding by the small particles at the filter medium surface and reducing
the amount of dose required. Activated sludge contains very little fiber,
thus sufficient chemicals must be added to cause a precipitation on each fine
particle and the development of a granular matrix of larger particles. As a
result, the chemical cost for conditioning of activated sludge is extremely
high. Furthermore, it is difficult to filter activated sludge because it
tends to form a compact mat under vacuum which leaves a small void ratio for
passage of the liquid.
The performance of filtration of different sludges has been reported as
varying widely. For example, Trubnick (50) studied sludges from various
sources before and after digestion. In Table 16 he reported that fresh
sludges are more filterable after chemical conditioning than digested sludges,
and primary sludge is more filterable than secondary sludge. Burd (51) re-
viewed the operating records of about 60 sewage treatment plants having used
ferric salts and/or lime and summarized the average date in Table 17. It is
seen that, except for the digested primary sludge, the raw primary and di-
gested sludges when blended with activated sludge are more difficult to de-
water than raw sludges. It is evident that activated sludge when present in
a mixture causes the deterioration in filterability. Tables 18 and 19 list
some typical performance data comparing cloth and coil media rotary vacuum
37
-------
35
30
25
Q 20
McCARTY
15
10
IMARY
ACTIVATED
11 gm/L CaO, 3.7 gm/L FeCI3
1 23456789 10
FEED SOLIDS (%)
FIGURE lb -CAKE SOLIDS AS A FUNCTION- OF FEED SOLIDS F.CLR.
DIFFERENT SLUDGES. (3)
38
-------
4 € e fO 12 H '6 18 30 2? ?4
CHEMICAL COST (S/TON SOLIDS)
FIGURE 17. CHEMICAL COST AS A FUNCTION OF YIELD. (52)
O VIRUS IN CALF SERUM
Q V1RU3 tH HANKS' SOLUTION
O VIRUS M OIGCSTtMQ SLUOOt
A VIRUS IN SLUDGE TREATED
AT 60*C FOR 1 NOl'ft
},
0
S>
f 4
1 3
*> *
~ VIRUS M CALF SCRUM
O ****** « HANKS' SOLUTION
O VtRUS M DIQEST1NQ tlUDOt
A VIRUS M PAS'.TUfUZCD
\ \ N N
\
1 1 ^£=*<5— q_
o ' » S * s »
DAVS
FIGURE 18. RATES OF INACTIVA-
TION OF COXACKIE-
VIRUS TYPE B3 IN
DIGESTER AND CON-
TROLS AT pH 7 AND
3 2 0 C . (59)
FIGURE 19. RATE OF COXACKIE-
VIRUS TYPE B3 IN
DIGESTER AND CON-
TROLS AT pH 7 AND
35°C . (59)
39
-------
f^nrtNEror
< i'v r
i *
' CENTER"
TABLE 16.? MINIMUM FILTER RATES jAFTER CHEMICAL CONDITIONING (50)
Thickened to at least 3 percent solids.
Type
I
I
l
of Sludge ;
Filter
(kg/sm-
i
Rate |
-hr) |
Fresh
Digested !
7 Primary
i
i
1
3.70
34.2 "" |
Primary &
trickling filter :
34.2
29.3 |
1
Primary &
activated
29.3
24.4 j
Activated
or trickling filter
i
14.6
TABLE 17. AVERAGED VACUUM FILTRATION PERFORMANCE DATA (51)
-•
Chemical Dose
CO
Rate
Yield
Cake
Moisture
Type of Sludge
Ferric Chloride
Lime
(kg/sm-hr)
(%)
1. Raw Primary
2.1
8.8
33.7
69.0
2. Digested primary
3.8
12.1
35.2
73.0
3. Elutriated digested
primary
3.4
-0-
36.6
69.0
4. Raw primary + fil-
ter humi's
2.6
11.0
34.7
75.0
5. Raw primary + acti-
vated sludge
2.6
10.1
22.0
77.5
6. Raw activated sludge
7.5
-0-
-
84.0
7. Digested primary +
activated sludge
5.3
15.0
22.5
77.5
8. Digested primary +
activated sludge
5.6
18.6
19.5
78.5
9. Elutriated digested
primary + activated
sludge:
'
(a) Average w/o lime
(b) Average w/lime
8.4
2.5
-0-
6.2
18.6
18.6
79.0
76.2
iO
-------
w
rn..
O;
TABLE 18. TYPICAL DEWATERING PERFORMANCE DATA FOR ROTARY VACUUM FILTERS - CLOTH MEDIA (3)
Chemical
dosage,a
J
Feed
solids
kg/metric dry solids
Yield,
Cake,
Type of sludge
concentration,
CaO
1
percent
percent
FeCl^
kg/sm-hr
solids
Raw primary (P)
4.5
-
9.0
20-40
80-100
1.71-39.1
27-35^
Waste-activated sludge (WAS)
2.5
-
4.5
60-100
120-180
4.9-14'. 6
13-20
P plus WAS
3
-
7
25-40
90-120
12.2-29.3
18-25
P plus trickling filter (TF)
4
-
8
20-40
90-120
14.6-34.2
23-30
Anaerobically digested
i
P
4
-
8
30-50
100-130
14.6-34.2
25-32
P plus WAS
3
-
7
40-60
150-200
9.8-24.4
18-25
P plus TF
5
-
10
40-60
125-175
17.1-39'. 1
20-27
Aerobically digested no pri-
2.5
-
6
30-70
75-120
-7:3-19.-5-
16-2-3-
mary clarification
Elutriated anaerobic digested
P
5
-
10
25-40
0-50
19.5-39.1
27-35
P plus WAS
4.5
-
8
30-60
0-75
14.6-29.3
18-25
Thermally conditioned
P plus WAS
6
—
15
0
0
19.5-39.1
35-45
3k.
All values shown are for pure FeCl^ and CaO. They must be adjusted for anything else.
k Filter yields depend to some extent on feed solids concentrations. Increasing the con-
centration normally gives a higher yield.
A
-------
TABLE 19. TYPICAL DEWATERING
PERFORMANCE
DATA FOR ROTARY VACUUM FILTERS - COIL! MEDIA
(3) !
Feed
solids
Chemical dosage,
kg/mctric ton dry solids
t
Yield,bi
Cake, i
Type of sludge
concentration,
percent
FeCl3
CaO
kg/ sm-hr>
percent!
solids :
Raw Primary (P)
8
- 10
20-40
80-120
31.7-39.1
28-32 j
Trickling filter (TF)
4
- 6
20-30
50-70
29.3-39.1
20-28 |
P plus waste-activated sludge
(WAS)
3
- 5
10-30
90-110
12.2-19.5
3-27 :
Anaerobically digested
P plus TF
P plus WAS
5
4
- 8
- 6
25-40
25-40
120-160
100-150
19.5-29.3
17.1-22.0
27-33 !
20-25 j
Elutriated anaerobically
digested primary
8
- 10
10-25
15-60
19.5-39.1
28-32 \
J
!
All values shown are for pure FeCl^ and CaO. This must be adjusted for anything else.
Filter yields depend to some extent on feed solids concentration. Increasing the
solid® concentration normally gives a higher yield.
-------
^filters as reported in the EPA Sludge Treatment and Disposal Manual (3). It
is again evident" that for both the coil1 and cloth rotary vacuum filters the
raw primary and digested primary with or without ejjutriation give higher
filter yields than any blend which contains raw or digested activated sludge.
Raw and digested1 trickling filter sludge also gave high yields.
Pathogenic Organisms Reductions in Anaerobic Digestion
The reduction of pathogenic organisms in sludge is especially important
when the sludge is applied to land or the ocean for ultimate disposal. An-
aerobic digestion reduces the number of the pathogenic organisms, but does
not totally destroy them. Salmonella typhosa, Entamoeba histolitica, and
lAscaris eggs can' survive after 30 days of digestion (56,57). Palfi (58) has
reported that digestion may reduce the virus concentration of raw sludge by
95 percent, but found several different' virus types even in the digested
sludge. If sludges are held in a digester for 3-8 weeks, all viruses should
be destroyed (59). However, because of short-circuiting, and continuous draw-
off and feed to a digester, a portion of the raw sludge does not receive suf-
ficient residence time for complete treatment. In addition, improper design
and overloading of digesters can result in high numbers of pathogenic organ-,
isms in digester, effluents.
The primary pathogens that are present in sludge include viruses, bac-
teria, and parasites. These organisms enter waste treatment systems from a
number of sources such as feces, urine of human and pet wastes, food wastes,
hospital wastes,' and other sources. Sludges, particularly raw primary sludge,
have been known to concentrate the pathogens in sewage. Tables 20, 21, and
22 (2) list the most important viruses, bacteria and parasites together with
the diseases they cause and Tables 23 and 24 give a summary of treatment
effectiveness of a number of wastewater treatment processes.
Viruses
Eisenhardt (59) studied the rate of inactivation of coxackivirus B3
during anaerobic digestion and found it to be two log units in 24 hours at
pH 7.0 and 35°C. Figure 18 shows that the rate of inactivation at 32°C in
ia high protein solution (serum) is lower than in a low protein solution
(Hank's salt solution). In digesting sludge, virus is inactivated at about
the same rate as in the salt solution, but pasteurized sludge appears to in-
activate virus even faster than the digesting sludge. Figure 19 was obtained
when all the tests were conducted at 35°C with the remaining conditions kept
the same as in the previous run. It can be seen that the inactivation pattern
did not change but the inactivation rate increased at the higher temperature.
Bertucci (60) seeded viruses into bench scale digestion units operating
at 35°C and 14 days detention time. He reported the inactivation of Polio-
virus I (Sabin), Coxsackivirus A-9, Coxsackivirus B-4, and Echovirus II was
98.8, 99.7, 99.0, and 92.5 percent, respectively,«after 48 hours of digestion.
He concluded that using the anaerobic digestion process inactivation of
viruses follows a first-order reaction pattern. Sanders et al. (61) studied
the effects of temperature and detention time of high-rate anaerobic digestion
on recovery of solids-incorporated poliovirus type I (Chat). He found that at
43
-------
TABLE 20. PATHOGENIC HUMAN VIRUSES POTENTIALLY
IN WASTEWATER SLUDGE (3)
j Name
! Disease
i
• 1
j Adenoviruses
I
Adenovirus infection '>
Coxsackie virus, Group A
•
' Coxsackie infection; viral ;
meningitis; AFRI , hand,
foot, and mouth disease
Coxsackie virus, Group B
Coxsackie infection, viral
meningitis; viral cardi-
tis, endemic pleuodynia,
AFRI3
ECHO virus, (30 types)
ECHO virus infection;
aseptic meningitis; AFRI
Poliovirus (3 types)
Poliomyelitis
Reoviruses
Reovirus infection
Hepatitis virus A
Viral hepatitis
Norwalk agent
Sporadic viral gastro-
enteritis
Rotavirus
Winter vomiting disease
AFRI is acute febrile respiratory illness.
4,4
-------
TABLE 21. PATHOGENIC HUMAN BACTERIA POTENTIALLY
IN WASTEWATER .'SLUDGE (3)
r — . . .
| Species'-
1
1 Disease I
!
J Arizona hinshawii
l
1
Arizona infection .
i .
I Bacillus cereus
1
! j
B. cereus gastroenteritis; food |
poisoning ;
1 '
j Vibrio cholerae,
Cholera '
j Clostridium perfringens
C. perfringens gastroenteritis; ]
food poisoning 1
I . ! , |
i Clostridium tetani
Tetanus
1 i
> Escherichia coli
I
1
Enteropathogenic E. coli infection; '
acute diarrhea
I Leptospira sp
Leptospirosis; Swineherd's disease
j Mycobacterium tuberculosis
Tuberculosis
Salmonella paratyphi, A, B, C '
Paratyphoid fever i
Salmonella sendai
Paratyphoid fever i
Salmonella sp. (over 1,500 serotypes)
Salmonellosis; acute diarrhea !
Salmonella typhi
Typhoid fever i
Shigella sp.
Shigellosis; bacillary dysentery; !
acute diarrhea !
Yersinia entero'colitica
Yersinia gastroenteritis (
1
Yersinia pseudotuberculosis
Mesenteric lymphadenopathy 1
-------
TABLE 22. PATHOGENIC HUMAN AND ANIMAL PARASITES
POTENTIALLY IN WASTEWATER SLUDGE (3)
Species'
Disease
B.
C.
Protozoa !
Acanthamoeba sp
Balantidium coli
Dientamoeba fragilis
Entamoeba histolytica
Giardla lamblia
Isospora bella
Naegleria fowleri
Toxoplasma gordii
Nematodes
Ancyclostoma dirodenale
Ancyclostoma sp
Ascaris lumbricoides
Enterobius vermicularis
Necator americanus
Strongyloides stercoralis
Toxocara canis
Toxocara cati
Trichusis trichiura
Helminths
Diphyllobothrium latum
Echino. 'ecus granulosis
Echinococcus multilocularis
Hymenolepis diminuta
Tymenolepis nana
Taenia saginata
Taenia solium
! Ameobic meningoencephalitis
Balantidiasis, Balantidial dysentery
Dientamoeba infection
' Amoebiasis; amoebic dysentery
Giardiasis
i Coccidiosis
Ameobic meningoencephalitis
Toxoplasmosis
Ancylostomiasis; hookworm disease
Cutaneous larva migrans
Ascariasis; roundworm disease;
Ascaris pneumonia
Oxyuriasis; pinworm disease
Necatoriasis; hookworm disease
Strongyloidiasis; hookworm disease
Dog roundworm disease, visceral larva
migrans
Cat roundworm disease; visceral larva
migrans
Trichuriasis; whipworm disease
i
Fish tapeworm disease
Hydated disease
Aleveolar hydatid disease
Rat tapeworm disease
Dwarf tapeworm disease
Taeniasis; beef tapeworm disease |
Cysticercosis; pork tapeworm disease ,
-------
O!
_ r~
15.
TABLE 23;.
. "'U-i
MUNICIPAL TREATMENT[?LANT KILLING AND INACTIVATING
PATHOGENS IN SLUDGES (64)
1 "" •'
!i ~
12.
Lime treatment
Range of Effectiveness
(42) a) Kills pathogenic bacteria
— b)-~At-high pH j (>11. 5)- highly
effective in killing
and inactivating
Heat treatment (44)
- pasteurization
j3. Composting (45)
a) Destroys pathogens at
70°C for 1/2-1 hour
a) Mechanical: Pathogen
free after 1 day;
spores 1 week
Anaerobic digestion (47)
I a) Bacteria: Reduced at
approximately natural
die-off rate
b) Helminth ova: At least
1 month for destruction
c) Cysts: Destroyed in 10
days at 30cC
d) Virus: Some survive long
periods e.g. Polio
Aerobic digestion (48)
a) Reduces pathogens to low
numbers.
Cost
Cents/1000 gallons
0.8 primary (43)"
1.5—secondary-
2.2-11.5 (44)
5.0-3.5 (46)
1.5-0.9 (49)
(10 MGD-50 MGD)
1.8-1.0 (49)
(10 MGD-50 MGD)
^ote: The effectiveness and cost data are expressed as in the literature.
The information is fragmentary in that the quality of the influent is
not known now are variations in performance of the processes. Dates
for the costs were only given for 3 (1976 $) and for 4 and 5 (1973 $).
TABLE 24. EFFECT OF SEWAGE TREATMENT PROCESSES ON INDICATOR AND PATHOGENIC
MICROBIAL POPULATIONS IN RAW SEWAGE (65)
iType of Sewage Treatment
jPrimary
^Septic Tanks
Trickling Filters
Activated Sludge ,
'Anaerobic Digestion ;
,Waste Stabilization Pond9
;Tertiary (Flocculation, Sand Filtration, etc.)
47
Removal Range for
Various Organisms (%)
5-40
25-75
18-99
25-99
25-92
60-99
93-99.99
i ¦
i 11 '¦
! i h
Van
i
>:< '
I ): ;i :
i \i-,t ;
II I I 'S
K.'i'j;:
i a > ,<
-------
t '
i"^3A°C and 37 °C thte rates of inactlvatiori were very rapid for the first 24
ihours, ranging f,rom 84 to 99 percent per day; but a slower, steady rate of 30
!to 60 percent per day resulted from 24 (hours until the end of the run. The
secondary rates determined at different temperatures and detention times are
listed in Table 25. Temperature is probably the most significant parameter
on poliovirus inactivation. As shown in Figure 20, when temperature increases
ithe rate of loss of recoverable poliovirus infectivity also increases. The
data were obtained for sludge samples with a digester detention time of 10
' 2
Jdays and a loading rate of 1.6 kg VS/m d (0.1 lb VS/cf-day). It can be seen
Ithat at 50°C, loss of infectivity reaches almost 100 percent. However, in the
mesophilic range, the loss of recoverable infectivity accounted for 46 to 61
percent per day.! The effect of detention time is given in Figure 21. As the
temperature increases, the detention time seems to have a decreasing role in
'recovery. This is especially true at 50°C, where detention time has no effect
on recovery because the rate of loss of recovery was so rapid. At 34°C, the
leffect of detention time is more significant, as shown by the lower curve.
jSanders et al. (61) also compared their results with other investigations and
,'plotted them as shown in Figure ^2. It is seen that for a ten day retention
'time at a loading of 1.6 kg VS/m -d (0.1 lb VS/cf-d), four logs of viruses
jwere lost in 10 days at 37°C and 3 logs at 34°C. It will take 30 days at 30°C
ito obtain four logs of virus loss according to Moore et al. (62). Sanders
|and her co-workers (61) claimed this difference was probably caused by the
method of adding the virus, the digester operation, or sample preparation.
jThese parameters are listed in Table 26.
TABLE 25. RATE OF LOSS OF RECOVERABLE POLIOVIRUS
| INFECTIVITY AT 1.6 kVS/m3 - d (61)
I
jTemperature
Rate
1 (°c)
Sample
a/d)
r2
34
Control
22
0.97
5-day detention
37
0.88
l
10-day detention
48
0.96
37
Control
34
0.86
5-day detention
59
1.00
10-day detention
56
0.98
15-day detention
61
0.99
50
Control
99.999998
0.97
5-day detention
99.999998
1.00
10-day detention
99.999998
1.00
Parasites
Potential parasitic disease agents in sludge are protozoan and metazoan
parasites having a 9tage in man which releates infective cysts or eggs into
feces or urine, or animal parasite eggs and cysts entering sewage via
slaughterhouse wastewater or street drainage. Some of the parasitic eggs and
48
-------
I , I . I •.: ; Ly: •
I I !< 'I .
20 30 40
TEMPERATURE CC)
FIGURE 20 - EFFECT OF TEMPERATURE ON RATE OF LOSS OF
RECOVERABLE POLIOVIRUS INFECTIVITY. (61)
49
-------
FIGURE 21. EFFECT OF DETENTION TIME ON
RATE OF LOSS OF RECOVERABLE
POLIOVIRUS IN FE CTIVITY. (61)
50
-------
'.'¦I . M
0 5 10 15 20
TIME (days)
FIGURE 22. POLIOVIRUS RECOVERY DURING ANAEROBIC
SLUDGE DIGESTION. (61)
5
i/i
i
8
a
s
r
NVWOfM or DA*S O* OCTCNUON
.J
Figure 3. Concentration of Conforms Surviving as n Function of Detention Tim*.
FIGURE 23. CONCENTRATION OF COLIFORMS SURVIVING
AS A FUNCTION OF DETENTION TIME. (74)
51
-------
TABLE 26. COMPARISON OF METHODS
VIRUS RECOVERY DURING
AND EXPERIMENTAL CONDITIONS FOR RECENT STUDIES ON
ANAEROBIC DIGESTION (61,62)
Present
Study
Conditions
Ottier Recent Studies
Parameter
Moore en al.^^ Bertucci et al.^^ Wardj and "Ashley
Type digester
Continuous
Batch Continuous (fill & draw) Batch
I Theoretical
• detention time
Mixing
^Temperature ,_°C
Virus
Virus addition
(fill & draw)
5,10,15 days
Continuous
34,37,50
Poliovirus 1
(Chat)
Incorporation
into MLSS
N/A
None
30. ___
Poliovirus 1
(Chat)
Incorporation
into MLSS
14 days
continuous
35
Poliovirus 1 (Sabin)
Mixed with sludge
N/A
Initial 15 min.
| only
i
28
Poliovirus 1
j (Chat)
Mixed with sludge!
i Preparation for
[ assay
pH
Direct plate
6.0 to 7.2
Homogenized
with tryptose
phosphate
broth, sepa-
rated, eluate
assayed
7.0 to 7.5
Dilution (10x) in 5%
FCS 3% BE; 1% gelatine;
sonication for 20 min-
utes; direct assay
7.2 to 7.4
Sonication for 2
minutes with
sodium dodecyl
sulfate in PBS
at various
dilutions;
direct assay
i .
or. separated
-------
i : . r 'ii
^cysts have resistant stages that are likely to pass through a sewage plant in
a viable state. ¦ Recent research (66) has shown that the only processes which
have been found to remove or destroy resistant stages are dependent upon the
mechanisms of filtration or settling. The weight of an egg or cyst determines
its settleability. For example, helminth eggs, particularly Ascaris eggs are
heavier and therefore settle ou'- rather, rapidly. Protozoan cysts are lighter;
,they are more frequently found in the liquid effluent. Liebmann (67) re-
ported that a 2 hour sedimentation period was sufficient to remove all eggs
with a specific gravity of 1.1 or greater. It was reported that 68 percent
of the eggs of Taenia saginata were settled in raw sewage after 2 hours, and
89 percent in 3 hours.
In general, secondary treatment processes including the trickling filter
and activated sludge processes are' ineffective in destroying parasites (66,
68, 69). All reports on the-effect of the trickling filter or activated
sludge process confirm that the eggs will eventually accumulate in the sludge,
with some lighter eggs and cysts remaining suspended in the effluent liquid.
The fate of cysts and eggs during anaerobic digestion is important. The
efficiency of destroying parasitic cysts and eggs is dependent upon the oper-
ating temperature and detention time. Hays (68) summarized the available re-
search on the survival of parasitic eggs or cysts during anaerobic digestion
at various temperatures and detention times (Table 27). He indicated that an-
aerobic digestion can destroy all protozoan cysts but was less effective on
eggs. Operating temperatures in the thermophilic range (> 45°C) are helpful
in destroying eggs. Since most anaerobic digesters were operated in the
mesophilic range with continuous feed and draw-off, it was difficult to ob-
tain 100 percent removal efficiency.
Bacteria
( Tables 28 and 29 (1, 3) list some typical concentrations of pathogenic
bacteria in various sludges. The results vary widely depending on the source
and type of sludge, the sensitivity of assay techniques, and the operating
conditions of the digesters. Ruchhoft (70) found 25 to 75 percent removal of
Salmonella typhosa depending on retention time while McKinney et al. (71)
;reported 84 and 92.4 percent reductions' after 6 and 20 days, respectively.
Mom et al. (72) were unable to detect the presence of viable S. typhosa after
,6 to 8 days. It'was observed by two groups (73). that there was 90 and 69
percent removal of Mycobacterium tuberculosis, while others (73) noted "sur-
vival" of M. tuberculosis after anaerobic digestion. In general, anaerobic
digestion reduces bacterial counts by one to four orders of magnitude (3,74).
Increasing bolh temperature and detention time also increases the reduction
rate. Figures 23 and 24 chow the effect of anaerobic detention time on the
survival of coliforms and salmonellae (74).
53
-------
TABLE 27. SURVIVAL IN ANAEROBIC DIGESTERS (68)
f ¦ ¦
1
!
Temperature
Survival
Time in !
of digester
of eggs or cyst
Organism 1
digester ;
(°C)
(%)
i
Ascaris lumbricoides
Cram 1943 '
6 months '
20°C
10
Reyes et al., 1963
30 days
38
0
20 days
45
0
20 min
55-60
0
Hookworm
"Cram 1943
64 days
20
some
survival
,
41 days
30
some
survival
36 days
room temp.
some
survival
Taenia saginata
Newton et al., 1949
6 months
24-30
some
survival
Vasskova, 1966
3%
(from Kabler 1959)
Schistosoma japonicum
Newton et al., 1948
21 days
15-24
0
9 days
20-32
.0
Jones 1947
25-35 days'
10%
(from Kabler 1959)
Mijares 1964
more than 21
30
0
days
Entamoeba histolytica
>12 days
20
0 ;
Cram 1943 ;
>10 days
30
0
>4 days
-12 to r9°c
0 ;
-------
TABLE 28. PATHOGENIC BACTERIA IN SLUDGE (1)
Coliform
Salmonella
Pseudomonas
Sludge
(106/m£)
(per 100 m£)
(per 100 mi)
Raw Primary
11.0-11.4
460
46,000
Activated
2-2.8
74-23,000
1,100-24,000
Trickling Filter
11.5
93
11,000
Mixed Digested
0.4
29
34
Source
Farrell (1974)
Farrell (1974)
Farrell (1974)
TABLE 29. PATHOGEN OCCURRENCE IN LIQUID WASTEWATER SLUDGES (3)
Concentration, number/100 ml
Unstabilized raw ,
a 3D
Pathogen Name or species sludge Digested sludge '
Bacteria
Clostridia sp
6
X
106
2 x 107
Bacteria
Fecal coliform
109
3
X
10^ - 6 x
106
Bacteria
Salmonella sp.
8
X
103
BDLC- 62
Bacteria
Streptococcus faecalis
3
X
107
4
X
104 - 2 x
106
Bacteria
Total coliforms
5
X
109
6
X
10A - 7 x
107
Bacteria
Mycobacterium tubercu-
107
106
losis
£
Type of sludge usually unspecified.
k Anaerobic digestion; temperature and detention times
varied.
C BDL is below detection limits, <3/100 ml.
55
-------
FIGURE 24.
CONCENTRATION OF SALMONELLAE
SURVIVING AS A FUNCTION OF
DETENTION TIME. (74)
FIGURE 25. OXYGEN UTILIZATION RATES.
(75)
56
-------
iirXl" _ _ _ ' - _ A*
HFKh ^AEROBICALLY DIGESTED SLUDGE j~ ~ "" " !
p V j ""i
p.^-y.vp ! Aerobic digestion is a process designed to stabilize sludges from aero- j
"'![1 j bic secondary processes by conversion of the degradable portion of sludges
j into carbon dioxide and water through microbial metabolism and extended
^ ".'jI periods of aeration. When there is inadequate external substrate available, j
^microorganisms can consume their own cellular mass for metabolism, and this |
l is "referred"to "as "endogenous'respiration". The ideal" product is a stable, !
I non-odorous sludge.
Parameters of instability include specific oxygen uptake rate, odor pro-
duction, volatile solids reduction, nitrification, and adenosine triphosphate
concentration. The following sections review these parameters.
Specific Oxygen Uptake Rate
j In aerobic digesters, microorganisms consume oxygen while degrading the |
:substrate. The specific oxygen uptake rate (SOUR) is a reliable index mea- ,
; suring the activity of the cells or the instability of sludge. A high SOUR
j would indicate a very active, viable sludge, while a low SOUR indicates a
j more stable slucige which has reached a state of respiration where its bio-
j-logical action i9 minimal. i'---'
| Important factors that affect the SOUR are: type and history of sludge,
I temperature, sludge age, and digester operating conditions. For example,
1 primary sludge has a high SOUR and tends to promote sludge synthesis. De-
pending on the loading rate waste activated sludge may have a high to low
SOUR. Extended aeration studies may be in a state of endogenous respiration.;
! Specific uptake rates of primary sludges in excess of AO -"(» 0^/g VSS-hr have j
1 been measured. Typical SOUR values for conventional activated sludge, ex-
I tended aeration sludge, and aerobically digested sludge are in the range of
10-15, 5-8, and 0.5-4 mg 0„/g VSS-hr, respectively. Figure 22 shows the
1 effect of sludge age and temperature on the specific uptake rate. Data were ,
I obtained from a number of sewage treatment plants and the total sludge age
; was defined as age in the digester plus the age when wasted to the digester
(75). It is seen that the specific uptake rate decreases with increasing
sludge age and decreasing digestion temperature. The biological activity
• approaches a minimum after a total sludge age of 120 days. Sludge has prob- ,
' ably reached its most stable stage at this point. Thus, Ahlberg et al. (75) 1
j suggested that under normal conditions, a specific uptake rate of less than
1 one usually indicates a stable sludge. Loers et al. (76) studied the uptake i
, rate for aerobically digested activated sludge at a low temperature and con- ,
j firmed Ahlberg's suggestion for sludge digested at 20°C, but not at 10°C and
; 5°C. Figure 26' shows the effects of temperature and sludge age on oxygen
uptake rates for raw and digested waste activated sludge. A sludge with a
SOUR value of 1' mg/g VSS-hr at 5°C would have a higher SOUR value than when
' subjected to temperatures of 10°C or 20°C. Thus, at ]ow temperatures, SOUR ;
j must be adjusted for measuring sludge jinstability. It is noted that the 1
J digester sludge age was defined as the weight of VSS in the digester divided ;
by the weight of VSS wasted from the digester each day.
11 ' ' : 1 , ¦ !
i .v : : 'r,1 ! Hartman (77) compared the SOUR measured during the batch digestion j , ,, , f
i j: ''--period at high temperatures and plotted the results in Fig. 27. The sludge J ,|; ( (
i 1'AOi/ iCin.)
:•! /iii
-------
{/)
>
E
o»
\
c
E
<
q:
uj
*
h
a
Z)
TEMPERATURE (°C)
FIGURE 26. OXYGEN UFTAKE RATE VERSUS TEMPERATURE. (76)
58
-------
FIGURE 27. SPECIFIC OXYGEN UPTAKE RATES AT VARIOUS OPERATING
TEMPERATURES, BATCH DIGESTION OF-A 26% TOTAL VOLA-
TILE SOLIDS SLUDGE. (77)
59
-------
blunder study was mixed primary and trickling filter humus. There was a sig-
nificant increase in rate at all temperatures during the initial phase of
!aerobic digestion. This was interpreted as the increase in the active bio-
jmass utilizing the substrate available in the primary sludge fraction of the
'feed material. This initial increase was followed by a rapid decline and
:levelling-off phases which were related to a corresponding decrease in the
active mass during the remaining digestion periocf.
| Eikum and Paulsrud (44) studied oxygen uptake rates for various types of
I sludges during aerobic digestion at 18°C. The results are shown in Figure
128. Again, the;oxygen uptake rate increases at the initial stage of diges-
jtion, but is followed by a gradual decrease. They defined a fully aerobic
-------
FIGURE 28. OXYGEN UPTAKE RATE VS. DETENTION TIME
IN AEROBIC DIGESTER. (44)
61
-------
FIGURE 29. MAXIMUM ODOUR INTENSITY INDEX
MEASURED DURING 14 DAYS OF
STORAGE VS. DETENTION TIME IN
AEROBIC DIGESTER. (44)
8
0*
5
JM
V '1
<
*—
Q.
1 •
z
Ui
o
3 o-
o 5 to IS 20 ?S
TEMPERATURE CC) IN A£R0B1C DIGESTER.
FIGURE 30. OXYGEN UPTAKE RATE AND DEGREE
OF STABILITY (%) VS. TEMPERA-
TURE IN AEROBIC STABILIZATION
UNIT, PRIMARY SLUDGE. (44)
62
-------
1
TABLE 30. LEAD ACETATE TEST - PRIMARY SLUDGE (78)
)
' I
jUNIT
. I
Prim.
Al
A2
A3
A4
A5
. ^ . .. . .
'^Detention Time
| (days)
0
5
10
15
25
35
|Temp. °C
-
18
18
18
18
18
•Days Before
iColor Appears
10
min
. 4
4
NC
NC
NC
I
.NC indicates no
color in 20 days
jthe color of the paper, indicating a very unstable sludge which produced a
¦large amount of 1^0 gas and an offensive odor. For aerobically digested
sludge with 5 and 10 days detention time, 4 days were required to color the
strip, indicating the greater stability of the sludge. When the detention
jtime exceeded 10 days, l^S evolution during the 20 days of testing was not
idetected.
Hartman et al. (79) modified the lead acetate paper procedure by placing
'10 ml of sludge sample in a six inch test tube and incubating at 37°C. The
temperature of 37°C was chosen because it was claimed that temperatures in
,the range of 30 to 50°C are optimum for the growth of Desulfovibvio, the
species that produces H2S. Typical results are shown in Figure 31. It is
seen in the lower curve that the stability index (i.e., days to produce a
color change in the paper strip) is low and is constant initially indicating
instability but then increases rapidly as a more stable sludge is produced.
Both the volatile solids reduction and SOUR curves show little change with
increased digestion time at this stage indicating that they may not be as
sensitive an indicator of sludge instability.
Figures 32 and 33 show the effects of temperature and volatile solids
concentration on sludge stability index. The mixture of primary and trick-
ling filter humus was digested aerobically at 20, 30, 40, and 50°C. The
stability index was plotted with digestion time. The sludge digested at 30°C
(Figure 33), the required digestion period for a desired product stability
increased as the initial volatile solids concentration of the feed sludge
increased.
The stability index was also plotted against the specific oxygen uptake
rate shown in Figure 34 for comparison. For an active biological sludge with
a high SOUR value, the stability index is very small. However, as the SOUR
decreased, the stability index increased slowly. When the uptake rate
dropped below 2 mg/g VSS-hr, the stability exhibited a dramatic increase.
It should be borne in mind that there are many other compounds contribu-
63
-------
F [CURE 31. VARIATION OF PERFORMANCE PARAMETERS
WITH TIME FOR PRIMARY SLUDCE/TRICK-
LING FILTER HUMUS DIGESTED AT 20°C.
pO)
64
-------
in
<
Q
a
Q
Z
>-
H
CQ
<
H
c/l
5 10 15 20 25 30 35
DIGESTION time, oays
FIGURE 32. UNDRAINED STABILITY INDEX FOR VARIOUS OPERATING
TEMPERATURES. (77)
65
-------
FIGURE 33 - UNDRAINED STABILITY INDEX FOR VARIOUS FEED SLUDGE
CONCENTRATIONS. BATCH DIGESTION AT 30°C. (77)
66
-------
>
20
1
1 1 1
w
£.
N
O
E
X BATCH, 30°.C
O CONTINUOUS. 30*C (LABORATORY
RATE,
15
"1
1
• CONTINUOUS, 30*C (PILOT)
UPTAKE
10
-
-
OXYGEN
3
!v
SPECIFIC
A
. X
X \
X
0
i
-X ——*—J—*
. 0 ° 1 1
C
5
10 15 20 25
STABILITY INOEX, DAYS
FIGURE 34. COMPARISON OF SPECIFIC OXYGEN UPTAKE RATE
AND UNDRAINED STABILITY INDEX FOR DIGESTION
AT 30°C. (77)
67
-------
t,,v^ OF PAGE
Hffii: Wting" odor "problems"' irTadd i tion tfo' H^S gas. The le " acetate" paper "test'pre-
'sents a simple and practical thod asuring the evolution of f^S. The
U-.VU'S
PK'.
basic premise of the lead acetate test is that H^S is the predominant gas
producing odor in sludge, and can be used as a measure of sludge instability.
i
.Volatile Solids Reduction
I V-y -
In aerobic digestion, the volatile solids concentration decreases with
Increasing detention time. After some jtime, the percent volatile solids
'reaches a constant value. Many investigators suggested that constant vola-
tile solids concentration indicates a stable sludge. However, some disagreed
,(1,44,77,78), because small variationsjin the percent reduction of volatile
matter may reflect large changes in the stability. When sufficient data is
available, it may be possible to correlate volatile solids reduction rate
with SOUR, odor production potential, and other parameters to measure sludge
'stability. j
i
t
| Reduction of volatile solids as a jfunction of detention time and sludge
age are given in Figures 35 and 36 respectively.(80,81). In general, most u
of the volatile solid destruction willjoccur during the first 10 to 15 days
of aeration detention time.
i
The change in biodegradable volatile solids can be represented by he
following first order model:
dxd
Kjxj (3)
where:
dt Td
dxd
= rate of, change of biodegradable volatile solids
concentration
K, = decay rate (day "^"j
d
= biodegradable volatile solids concentration (y^)
t = time (day)
Equation (3) can be integrated to yield:
Xd ~Kdt
-pr- = e (4)
Xd
where:
x° = initial biodegradable volatile solids concentration (7^) ; • '
" ^ j 1
; v.
68 j (;< .!
-------
FIGURE 35. EFFECT OF DETENTION TIME ON AEROBIC DIGESTION
OF ACTIVATED SLUDGE. (80)•
FIGURE 36. VOLATILE SOLIDS REDUCTIONS AS A FUNCTION OF SLUDGE AGE, (81)
69
-------
Equation (A) will yield a straight line when plotted on semilog paper,
xd
Values of —73- are plotted on the v axis with time plotted on the x axis,
xd
The slope of the resulting line will be Kd> Figure 37 (82) depicts an ex-
ample of the destruction of volatile solids and the analysis for obtaining
the decay rate (K^).
The reaction rate constant K, Ik a function of sludge type, temperature,
a
solids concentration. Figure 38 shows the effect of temperature on the re-
action rate constant. It increases rapidly with temperature from 10°C to
40°C, and levels off from 45°C to 65°C. The data shown are for several dif-
ferent types of waste sludge, therefore, the curve only represents an aver-
age value of K^. Also note that in Figure 38, no effort was made to correct
K, values for sludge age.
d
Reynolds (83) studied the effect of suspended solids concentration on
K, values for waste activated sludge and concluded that the reaction rate
d
constant decreases with increasing suspended solids (Figure 39).
Jaworski et al (84) studied the effects of detention time and tempera-
ture on volatile solids reduction for the mixture of primary and activated
sludge under aerobic digestion. Typical results are shown in Figure 40.
Volatile solids reduction increases with increasing temperature (15-35°C)
and detention time. Volatile solids reduction of 40 to 50 percent can be
achieved at approximately 15 days detention time. Beyond that point, only
slight increases of volatile solids reduction can be obtained. Also shown
in Figure 40 is the effect of loading rate which varied inversely with the
detention time in these studies. They suggested that the optimum loading,
based on volatile solids reduction is approximately 0.1 lbs of volatile
solids per cubic foot per day. Figure 41 (76) shows the effects of digester
sludge age and temperature on volatile suspended solids reduction for waste
activated sludge digested at low temperature. The reduction of volatile
solids increases with increasing temperature to a maximum of 20°C. Even at
20°C, it took approximately 70 days to reach a 50 percent solids reduction
Indicating that waste activated sludge is more difficult to degrade than
primary sludge, or their mixture. Hartman et al (77) studied the effect of
temperature, ranging from 20 to 50°C, on volatile solids reduction of pri-
mary and trickling filter humus in batch aerobic reactors. The results are
reported in Figure 42. At 30°C, volatile solids reduction reached 75 percent
in approximately 25 days. Digestion temperatures higher than 30°C reduced
the digestibility significantly. Figure 43 (3) shows the combined effect- of
temperature and sludge age on volatile solids reduction taken from many
pilot and full scale studies of several types of municipal sludges. This
curve indicates that a much slower increase in volatile solids removal above
a product value of temperature and sludge age of about 250 for the tempera-
ture range studied.
Nitrification
In aerobic digestion, the nitrogen cycle follows from organic nitrogen
to ammonia to nitrite and finally to nitrate. The degree of nitrification
70
-------
6000
5000 -
4000
(3
Z
2 3000 -
<
s
Ui
s
W
>
2000 -
1000 -
i 2 4 6 8 10 12
BATCH AERATION TIME. d«y»
(a)CHRONOLOGICAL DESTRUCTION OF VSS IN BATCH REACTOR
10,000
2
<
2
in
s
V)
>
UJ
a
<
Q
<
&
O
UJ
Q
100
10
kj-0.141 (bau 10)
- 0.32S (1mm a)
0 5 10 15 20
BATCH AERATION TIME. OAYS
FIGURE 37. KINETICS OF AEROBIC SLUDGE
DIGESTION. (82)
71
r
-------
X
O
~
¦
A
+
PILOT PLANT
PILOT PLANT
FULL SCALE
PILOT PLANT
PILOT PLANT
PILOT PLANT
PILOT PLANT
PILOT PLANT
10 20 30 40 50
TEMPERATURE OF LIQUID IN AEROBIC DIGESTER, °C
60
FIGURE 38 - REACTION RATE Kd VERSUS AEROBIC DIGESTER LIQUID TEMPERATURES.
-------
i
I
FIGURE 39 - K, VERSUS SUSPENDED SOLIDS (83)
a
FIGURE 40 - EFFECT OF TEMPERATURE AND DETECTION TIME ON THE
VOLATILE SOLIDS CONTENT OF AERATED SLUDGE (84)
73
-------
I
z
o
F
o
3
a
60
50
40
30
20
10
• CONTINUOUS FEED/AUTOMATIC DECANT
¦ DAILY FEED/MANUAL DECANT
* O.W.R.C. (FULL SCALE)
t t I > I I
I I I I 1 1
5 10 20 , 50
DIGESTER SLUDGE AGE (DAYS)
100
FIGURE 41 - EFFECT OF SLUDGE AGE ON VSS REDUCTION (76)
74
-------
0 5 10 15 20 25 30 35 40
DIGESTION TIME, PAYS
FIGURE 42. TOTAL VOLATILE SOLIDS REDUCTIONS
AT VARIOUS OPERATING TEMPERATURES.
BATCH DIGESTION OF A 2.6% TOTAL
VOLATILE SOLIDS SLUDGE. (79)
75
-------
r,if\
hp: i
<. ¦ i\' i .
L' ¦ ¦ l"
;: ¦> I
! 'I Hi
in
z
o
H
0
Z3
a
01
cc
to
Q
-I
O
CO
LU
O
>
z
ID
O
CC
Ui
a.
60 i-
50
40 -
30 -
20 -
10 -zi
PILOT
FULL
PILOT
FULL
PILOT
PILOT
PILOT
FULL
PLANT
SCALE
SCALE
SCALE
PLANT
PLANT
PLANT
SCALE
i-
0 200 400 600 800 1000 1200 1400 1600 1800 2000
TEMPERATURE °C x SLUDGE AGE, days
FIGURE 43.
VOLATILE SOLIDS REDUCTION AS A
FUNCTION OF DIGESTER LIQUID
TEMPERATURE AND DIGESTER SLUDGE
AGE. (3)
7.6
-------
i;.inay thus be a good indicator of stability under aerobic conditions. Jaworski
et al (84) studied the relationship between ammonia, nitrite and nitrate in
aerobic fermentation at various temperatures and plotted the results shown in
; Figure 44. The sludge under study consisted of a 1.75 to 1.00 ratio (dry
solids basis) of; primary and activated sludge. It is seen that more than 600
ppm nitrate-nitrogen was formed at a continually increasing rate to 60 days
'¦ detention time, indicating that more organic and ammonia nitrogen were being
"'converted to nitrate. - As-the ammonia was oxidized, both H and N0» were
I
produced. Hydrogenions will then combine with HCO^ alkalinity to form CO2
and 1^0. Some of the will be stripped off and the result is a reduction
in alkalinity. Figure 45 shows the alkalinity decreases from 700 ppm to less
than 100 ppm in about 30 days at the temperatures studied. ThepH increased
to approximately 8 in about 10 days, and then decreased gradually to values
near 5. It is interesting to note that the pH and nitrite peaked and the
ammonia reached a low at the approximate point where the solids destruction
ceased.
Eikum (78) studied nitrification of primary sludge and he found that
during aerobic digestion at different temperatures, the Kjeldahl-nitrogen
decreased with increasing detention time and the loss was interpreted as the
results of nitrification and denitrification. Figure 46 shows the decrease
of Kjeldahl-nitrogen and the increase of NO2 and NO^ nitrogen. Also shown
is the decrease of alkalinity with detention time.
Hartman et al (77) observed ammonia-nitrogen concentrations at high
temperatures of 20, 30, 40 and 50°C and are shown in Figure 47. They found
.that the ammonia concentration increases during the initial stage of diges-
tion then declines rapidly as nitrification ensues. A mixture of primary
settled and trickling filter sludges was aerated in a series of five aerated
reactors in bench scale work and a series of three reactors for pilot scale
'studies.
Adenosine Triphosphate (ATP)
Paterson et al (85,86) investigated the occurrence of adenosine triphos-
phate (ATP) in activated sludge as a measure of metabolic activity and/or
biomass. Since ATP is a high energy compound in viable cells, it is more
direct to express the cellular activity by the concentration of ATP than the
standard parameter mixed liquor volatile suspended solids (MLVSS). Experi-
ments conducted at the University of Florida with sludge taken from a con-
tact stabilization plant indicated that only 15 to 20*percent of tiie MLVSS
may be active biomass. ATP analyses onactivated sludge samples-from both
batch fed and continuously fed laboratory units have consistently yielded ATP
pools of 1.4 to 2.0 ug per mg VSS (85). Weddle et al (87) found that thr ATP
content of activated sludge solids increased with growth rate. At low growth
rates (0.1-0.2 days ^"), the ATP concentration was in the range of 0.3-0.8
ug/mg VSS. While at high growth rates (2 days *), the ATP content appeared
to reach a limit of 1.0 to 1.5 ug ATP/mg VSS. They also found that the ATP
content per viable cell did not vary significant.ly over a growth rate renge
77
-------
FIGURE hti. AMMONIA, NO -, and NO. VERSUS DETENTION
TIME. (84)
78
-------
M.' .ii\
'< i
I - •
7v
{¦ i;
»• • :i
j
FIGURE 45. SOLIDS, ALKALINITY AND pH VERSUS
DETENTION TIME. (84)
* ' J,
-------
7001
Primofy lIudQ*
OI'C
-••— •^au,c
2VC
Drlrnllon liny {^oj\)
Pnmn'y tl'Mjt
O 6 20 K
Dtltntion lim* (doyi)
FIGURE 46. KJELDAHL-NITROGEN, N02 + NO^-NITROGEN,
AND ALKALINITY VS. DETENTION TIME. (78)
80
-------
OIGESTION TIME, DAYS
FIGURE 47. OBSERVED AMMONIA NITROGEN CONCENTRATIONS AT VARIOUS
OPERATING TEMPERATURES. BATCH DIGESTION OF A 2.6%
TOTAL VOLATILE SOLIDS SLUDGE. (77)
81
-------
— _L -g
from 0.03 to 6.4 day . The ATP content per viable cell was between 10
—8
and 10 ug.
Eikum (78) studied the effects of temperature and* detention time on the
ATP pool for primary sludge associated with aerobic digestion. " Figure 48
shows the viable portion of the volatile suspended solids increased from
approximately 0.05 ug ATP/mg VSS in the raw primary sludge to a maximum value
of 0.57 ug ATP/mg VSS at 25°C and 25 days detention time. At lower tempera-
tures (7°C and 12°C), a lower maximum value of 0.27 ug ATP/mg VSS was ob-
tained with a detention time of approximately 10 days indicating a smaller
portion of the VSS will be viable cells. It was concluded that during
:aerobic digestion, a very low content of active cells are present in the
volatile suspended solids.
It is possible to correlate the ATP and oxygen uptake rates with the
stability of aerobically digested sludge. Since the ATP level will decline
and stabilize when most organisms are in a very low energy or endogenous
respiration state, this would correspond to a low oxygen uptake rate thus
indicating the degree of sludge stability.
82
-------
Dttmlion t*r* .'doyil
FIGURE 48. ATP/VSS VS. DETENTION TIME. (78)
83
-------
THERMALLY CONDITIONED SLUDGE
Thermal conditioning, in low and high pressure systems, involves heating
of wastewater sludge to temperatures of 180 to 260°C (350-500°F) in a rea-
tion vessel under pressures of 1720-13790 k N/m^ (250-2000 psi) for periods
of 15 to 40 minutes. The main purpose of chermal conditioning a sludge is to
change its physical character so that it can be dewatered more readily.
With mechanical dewatering equipment following the thermal process, it has
been reported that as much as 30 to 50 percent cake solids concentrations can
be formed without adding chemical conditioners (88). Other advantages include
(1) increasing volatile solids destruction in subsequent anaerobic digestion,
(2) its suitability for treatment of many types of sludges than cannot be
stabilized biologically because of the presence of toxic materials (3,89),
and (3) the processed sludge is sterilized but is susceptible to recontamina-
tion). However, there are also disadvantages associated with this process.
Among these are:
1. Production of an odorous gas stream which must be collected and
treated before releasing.
2. A strong decant liquor stream composed of organic acids, ammonia
nitrogen, sugars, polysaccharides, amino acids, etc. is produced
depending on the characteristics of the feed sludge, reaction
time and temperature.
3. The process may require heat energy and high cost in operation and
maintenance expenses.
Brooks (90) studied the effect of temperature and heating time on the
characteristics of activated sludge. Figure 49 shows the effect of temper-
ature and reaction time on the settleability of heat treated activated
sludge. The settleability at temperatures below 130°C was poor. However,
temperature in the range of 163 to 197°C seemed to give excellent settle-
ability. This was confirmed by the Buchner funnel tests. Samples heated to
100 and 130°C, even for 24 hours, were extremely difficult to filter through
the filter paper because of the gelatinous nature of the sludge. Solids
formed after heat treatment at 163°C and above were found to filter easily
and produce greater than 40 percent solid cakes. At higher temperatures
(163°C-197°C), heating times exceeding 0.5 hours seem to have minor effect
on the settleability. Table 27 shows the effect of temperature and oxygen
on the characteristics of 1 percent activated sludge.
It is interesting to note that a significant amount of suspended solids
were solubilized into the liquid, thereby causing a large increase in dis-
solved solids. Both the organic and ammonia nitrogen concentration in the
liquor increased after heat treatment due to the conversion of solid nitro-
gen forms to soluble forms. The effect of temperature on the fate of solids
and nitrogenous compounds are shown in Figures 50 and 51 respectively. It
can be concluded that thermal conditioning results in significant changes in
the nature and in the composition of waste activated sludge. The high tem-
peratures and pressures break down the cellular material found in sludge.
Cell walls are ruptured and release protoplacm, proteinaceous matter, and
suspended solids. The external cellular slime layer is also catabolized.
The solubilized matter includes ammonia, volatile acids, and other organic
84
-------
FIGURE 49. SETTLING CURVES OF HEAT-TREATED ACTIVATED
SLUDGE. (90)
85
-------
TABLE 31. EFFECT OF HEATING 1 PERCENT ACTIVATED SLUDGE TO DIFFERENT TEMPERATURES
FOR 1 HOUR WITH AND WITHOUT OXYGEN PRESENT (90)
Results, except where stated otherwide, in mg/1
Temperature (°C)
Initial
100
130
163
197
100
130
163
197 |
Oxygen available
.
nil
nil
nil
nil
6200
„200
6200
6200
i
Chem. Oxygen demand...
.
3040
3660
5100
5450
3450
3990
5150
4950
Permanganate value:
3 min
4-hour
1.0
2.8
140
344
236
593
376
920
374
1204
167
415
240
685
369
937
418
950
Organic N(liquid)
0.04
247
389
462
452
282
375
413
328
Ammoniacal N (liquid).
0.25
21
41
103
172
31
66
158
293
Nitrogen in solid
(per cent)..
7.82
7.13
6.24
4.4
3.93
6.88
6.28
4.21
3.48
'
o
T>
Dissolved solids
500
3016
4194
4682
4348
3470
4204
^604
3510
^ "O
>
o
! m
Suspended solids
10^00
6735
5300
4430
3205
7085
5110
3980
3575
Colloidal solids
30
3170
1260
700
360
2790
740
590
310
Total nitrogen
782
748
761
760
750
800
762
739
745
Total solids
10530
-
10754
9812
7913
-
10054
9174
7395
Total solids and
volatile acids
10530
10950
10201
8424
—
10300
9393
8230
pH value
7.5
7.0
6.5
5.9
5.6
6.75
5.9
5.05
5.9
Total soluble
phosphate..
—
—
—
31.6
9.8
-
-
18.6
4.9
Colour (5 mm cells)..
0
-
-
4.0
7.0
-
-
7.5
8.5
-f
>
-------
FIGURE 50. EFFECT OF PROCESS TEMPERATURE ON THE FATE
OF SOLIDS DURING HEAT TREATMENT. (90)
87
-------
FIGURE 51. EFFECT OF PROCESS TEMPERATURE ON THE
FATE OF NITROGENOUS COMPOUNDS. (90)
IUI*i MACttO*
FIGURE 52. RESPONSE OF SLUDGE FILTERABILITY TO
NON-OXIDATIVE THERMAL CONDITIONING.
(91)
88
-------
compounds. The resulting dark brown liquor is very high in COD and is very
odorous. The dewatering characteristics of the solids are greatly improved.
Marshall et al. (91) studied the filtration properties of heat treated
activated sludge obtained from the biological waste treatment yystems treat-
ing pulp and paper wastes. Figure 52 shows the effect of temperature and
reaction time on the specific resistance of waste activated sludge. In order
to eliminate any variation in specific resistance due to differences in
solids concentration, the sludge concentration was maintained at one percent
f.r comparison. Within the temperature range of 177 to 204°C (350 to 400°F)
sludge specific resistance was reduced significantly to within 3-10 x 107
sec2/gm. This is well within the range for successful filtration. Brooks
(92) compared the effect of temperature and reaction time on the specific
resistance of activated, primary/activated, humus, and digested sludges as
shown in Figures 53, 54, 55 and 56 respectively. All the sludges were stan-
dardized at approximately 3 percent solids concentration for comparison.
These figures indicate that increasing temperatures and reaction times de-
crease the resistance to filtration. Figure 57 shows Uhat increasing solids
concentration causes an increase in the specific resistance of heat condi-
tioned sludge. A similar variation in specific resistance was found when a
sample was diluted to various concentrations with tap water after heat treat-
ment .
Much of the methane production potential of residual organic materials
is lost as a result of the inability of microorganisms to completely ferment
them. Research by McCarty (93) has concentrated on increasing the biodegrad-
ability of lignocellulosic and nitrogenous materials. These materials are a
major source of residt al organics available for biological conversion to
methane gas. Heat treatment of sludge seems to be a good method for increas-
ing biodegradation However, in some cases, the products formed during heat
treatment are toxic to methanogenic bacteria.
Lignocellulose is comprised predominately of cellulose, hemicellulose
and lignin. Cellulose and hemicellulose by themselves are readily biodegrad-
able, but when associated wich the lignocellulose complex, they may be less
than 50 percent available to microbial cultures. Heat treatment can break
the lignocellulose complex. McCarty found that methane production was opti-
mized with thermal pretreatment at 200°C at pH 13.
Microorganisms also have difficulty degrading nitrogenous materials.
Nitrogenous organics are generally components of larger biological structures
such as cell walls and cell membranes. At the optimum temperature of 1756C
heat treatment increased the production of methane from nitrogenous organics.
However, in order to take advantage of the increased biodegradability, the
waste had to be diluted to prevent toxicity.
Because of the changes in the sludge nature and composition caused by
heat treacment, digestibility of certain sludges is enhanced. Haug et al.
(89) evaluated the effect of sludge heat treatment on undigested sludge.
Experiments were conducted on primary sludge, waste activated sludge, and
mixtures of both in two liter reactors. Thermal pretreatment of waste acti-
vated sludge yielded the most encouraging results. Methane production was
89
-------
Rf ACTION TIMC (mia)
FIGURE 53. THE CONDITIONING OF ACTIVATED SLUDGE
BY HEAT. (92)
90
-------
JOO'C
H0*C
IS M 41
RfACTION TIHL (min)
FIGURE 5 A. THE CONDITIONING OF PRIMARY/ACTIVATED
SLUDGE BY HEA^. (92)
91
-------
REACTION TIME (min)
FIGURE 55. THE CONDITIONING OF HUMUS
SLUDGE BY HEAT . (92)
92
-------
MACTION TIHC (rnln)
FIGURE 56. THE CONDITIONING OF DIGESTED SLUDGE
BY HEAT. (92)
93
-------
O CONC. VARIED BEFORE HfAT TREATMENT
X CONC VARIED AFTER Hf AT TREATMENT
X
o
o
Q
0
X
j l
MEO SOLlOS (par
-------
increased 60%, and volatile suspended solids destruction increased 36%.
The County Sanitation Districts of Los Angeles (94) conducted an exten-
sive study on sludges associated with themal treatment and anaerobic diges-
tion. Both waste activated sludge and a blend of 65 percent primary and 35
percent waste activated sludge were investigated. The thermal conditioning
unit was operated in the low pressure oxidation (LPO) mode: pressure was
_2
2758 KPa (400 psig), 3.4 x 10 standard cubic meters per minute (1.2 scfm)
of air was added, and the detention time was 29 minutes. Temperature was
controlled at approximately 204°C (400°F). The digesters were operated on
bench and pilot scale size. Both mesophilic and thermophilic sludge diges-
tion were studied following heat treatment. The results are presented in
Tables 32 and 33. In Table 32, it can be seen that except for the volatile
solids destruction, the laboratory LPO conditioned waste activated sludge
digesters did not perform as well as the control laboratory digesters for
both mesophilic and thermophilic digestion. The volatile acids concentra-
tion was very high (2,200 and 1,830 mg/£, respectively) and the gas produc-
tion was poor. The high volatile solids destruction but low gas production
in the LPO digesters was interpreted as the difficulty in establishing a
stable methane forming bacterial population in the laboratory. However, the
pilot scale digesters had low volatile acids concentration and much higher
gas production than the laboratory digesters. It was concluded that the
toxicity problems noted in laboratory tests as found by Haug et al. (89),
were not encountered during pilot scale digestion. The results of a contin-
uing LA/OMA study is given in Table 33 and show that the controls performed
better than the LPO conditioned digesters.
CONCLUSIONS OF LITERATURE SURVEY
The scope of this literature review was confined to the stabilization of
municipal sludges originating from aerobic and anaerobic biological processes
and from thermal processes. Its primary objective was to review the litera-
ture, gather information on sludge instability and njake it available to the
scientific community and provide ideas for the laboratory work. In this
context, therefore, it is essential to define a stable sludge. The best
indicator of sludge stability is probably the inability of the sludge to
degrade further biologically. For anaerobically digested sludge, parameters
such as gas production, methane to carbon dioxide ratio, volatile solids
reduction, ATP, BOD, COD concentration and others may be important parameters
for measuring the potential for further biological degradation. Odor produc-
tion potential could be very important in determining the stable state of a
sludge. For example a sludge following 30 days of digestion will be less
odorous than a sludge digested for 15 days. It is hoped to establish a sim-
plified method for measuring sludge and relating it with other parameters
discussed previously to obtain a sludge stability index.
For aerobically digested sludge, specific oxygen uptake rate, ATP, BOD,
COD, organic nitrogen, ammonia nitrogen, nitrate, and others are important
parameters measuring biological activity of the sludge. Operating parameters
such as temperature, degree of mixing, organic loadings, solids retention
time, and feed sludge characteristics are factors that also affect the sta-
bility of the product sludges.
95
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TABLE 32. LA/OMA THERMAL PRETREATMENT STUDIES
COMPARISON OF DIGESTER PERFORMANCE
WASTE ACTIVATED SLUDGE
LAB
SCALE DIGESTERS
45.4 cu m
(12,000) GALLON
DIGESTERS
Parameter
Control
Meso
Control
Thermo
LPO
Meso
LPO
Thermo
Control
Meso
Control
Therm.
LPO
Therm.
VS Loading
lb/ft3 day
Kg/m3 day-
0.065
1.041
0.065
1.041
0.049
0.785
0.049
0.785
0.085
1.362
0.074
1.185
0.05
0.8
Detention time
days
21
21
21
21
21
21
21
VS destruction
33/
41%
52%
56%
32%
39%
46%
COD Removal
36%
40%
30%
39%
33%
31%
43%
Volatile Acids
mg/1
60
100
2200
1830
5
90
580
Gas Production
ft3/lb VS dest.
ra3/Kg
11.0
0.680
10.9
0.680
5.4
0.337
6.0
0.375
14.8
0.924
17.0
1.061
13.7
0.855
Methane Production
ft3/lb COD dest.
4.6
5.3
3.9
3.6
5.8
8.5
6.0
m /Kg
0.287
0.331
0.243 0.225
0.362
0.531
0.375
-------
TABLE 33. LA/OMA THERMAL PRETREATMENT STUDIES
LABORATORY SCALE ANAEROBIC DIGESTION (MESOPHILIC)
BLEND OF PRIMARY AND WASTE ACTIVATED SLUDGE
May 26, 1977-July 1977
I
II
III
Operating Parameters
LPO Conditioned
Control
Control
Digester Volume
liters
12
12
12
Feed Rate
1/dy
.49
.49
.48
Detention Time
days
24.4
24.4
24.4
Volatile Solids Loading
K
3 y
m -day
0.592
0.817
0.817
Volatile Solids Destruction
%
37.8
38.9
to
00
COD Removal
%
50.6
46.6
51.8
Gas Production
1/dy
1.2
4.5
4.5
Gas Composition
% CH.,
50
67
64
Gas Production m3
/ky Vol.Sol.Dest.
0.456
1.180
1.317
Methane Production
m3/Kg COD Dest.
0.077
0.340
0.298
Temperature
°F
96
96
96
Constituents
Influent Effluent
Influent Effluent
Influent Effluent
Total Solids
%
2.02
1.50
2.9 2.09
2.9
2.22
Volatile Solids
% TS
71.4
60.1
68.8 58.3
68.8
58.6
Volatile Solids
g/dy
7.07
4.41
9.77 5.97
9.77
6.37
Fixed Solids
g/dy
2.9
2.9
4.4 4.3
4.4
4.5
COD
mg/1 0
31,400
15,500
38,850 20,700
38,850 18,700
Soluble COD
mg/1 0
12,100
8,320
4,570 897
4,570
775
PH
Units
5.6
6.9
6.4 7.4
6.4
7.4
Volatile Acids
mg/1 CH3COOH
1,700
2,920
850 132
850
188
Alkalinity
mg/1 CaC0 3
2,000
3,210
2,350 3,800
2,350
3,700
-------
SECTION 5
SOURCES AND TYPES OF MUNICIPAL SLUDGES USED IN OUR EXPERIMENTAL WORK
Sludges were obtained frcm eleven tnuinicipal treatment plants in New York
State and New Jersey. These sludges included the following major types:
Extended aeration activated sludge
Aerobically digested activated sludge
Anaerobically digested primary sludge
Anaerobically digested activated sludge
Anaerobically digested primary and activated sludge
Anaerobically digested primary and trickling filter sludge
Thermally treated primary and activated sludges
As the source and pretreatment of these sludges may be important in the
initial instability condition of the sludge, a brief description of the
treatment plants follows.
AEROBIC SLUDGES
Six different aerobic sludges were studied from six municipalities. They
range in size from small extended aeration plants of 0.4 mgd flow to a large
85 mgd plant. The following are descriptions of the treatment plants from
which sludges were obtained and Tables 34 and 35 give a summary of the treat-
ment plant major parameters.
Beacon, New York
Beacon has an activated sludge plant with typical primary and secondary
settling. Recycle is returned to the aeration tank from the secondary
clarifier. The activated sludge wasted is aerobicrflly digested. The plant
was designed for 6 mgd but during the period the samples were "taken the
average daily flow ranged from 1.9-5.2 mgd which is the typical summer dry
weather flow. The operator estimates the flow includes about 1 mgd of
industrial process water. Dyes from two industries cause occasional colored
influents but are not believed to cause toxicity problems. Good operating
results were being obtained at the time the sludge was taken for the studies.
The food to mass loading factor of the aeration tank was about 0.4 (F/M = 0.4)
with an average aeration detention time of 8.8 hours. The F/M ratio was
typically computed based on 30% BOD,, removal by the primary clarifier. Waste
activated sludge is fed daily to the aerobic digestion tank which has a six
day detention time. The sludge sample studied was taken from this aerobic
98
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.digestion tank. The sludge is then pumped into a thickener where it is mixed
;with primary clarifier sludge. Following thickening it is incinerated.
Cold Spring, New York
Cold Spring has primarily a domestic wastewater with a contributor
population of approximately 2300 people. The average flow to the extended
aeration treatment plant is about 0.45 mgd. with peaks to about 0.91 mgd. Its
design capacity is 0.50 mgd. The treatment process includes aerated grit
chambers, extended aeration tanks, secondary clarifiers and effluent chlori-
nation. Extended aeration averages close to one day detention time and the
study sample was taken from this treatment unit. The food to mass ratio is
about 0.046.
Musconetcong Sewerage Authority, New Jersey
Between 0.8 and 0.9 mgd of primarily domestic water is treated at the
Musconetcong treatment plant. About 0.3 mgd is treated in a Can-Tex pre-
fabricated contact stabilization unit and the remaining flow by a conven-
tional activated sludge plant. In these studies, sludge from the Can-Tex
plant was used.
The Can-Tex plant treatment sequence consists of aeration for about five
hours followed by clarification. Settled sludge is reaerated for 12 to 24
hours and is returned to the aeration tank for further contact. Once daily,
sludge is pumped from the clarifier into the aerobic digester. Each week the
air supply to the aerobic digester is shut overnight and in the morning the
supernatant is withdrawn. About one-third of the sludge is withdrawn to a
holding tank. Thus the aerobic digestion time is approximately 21 days.
Overall, the plant is very well run with BOD,, and suspended solids removal
running higher than 90 percent.
Following aerobic digestion the sludge goes to a holding tank prior to
vacuum filtration. Sometimes it remains for days in the holding tank and
anaerobic reactions take place. Odors arise during vacuum filtration,
especially during warm weather.
Stony Point, New York
Stony Point has t one mgd extended aeration treatment plant". " The waste
water is primarily domestic in nature. This facility includes an aerated grit
chamber followed by a splitter'box for distribution of recycle activated
sludge and wastewater to the four extended aeration basins. No primary set-
tling tanks are incorporated in the treatment plant. Secondary settling
follows extended aeration and the settled sludge is recycled to the splitter
box at the head end of the aeration tanks. When the mixed liquor suspended
solids are high in the extended aeration tank, settled sludge is wasted to one
of two aerobic digesters. ' It digests aerobically for an additional 2 to 3
99
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TABLE 34.
SUMMARY OF TREATMENT
PLANT OPERATIONAL
PARAMETERS
FOR THE
ACTIVATED SLUDGES
USED
bod5
Sus.
Solids
Ave.
Aerator
Aeration
Aerobic
August 1980
mg/«.
m
g/£
Flow
MLSS
Volume
Ratio
Time
Digestion
Inf Eff
Inf
Eff
mgd
mg/1
mg
F/M
hrs.
Time days.
Beacon, N.Y.
191 24
75
23
3.15
910
.386
0.40
8.8
6
Cold Spring, N.Y.
214 1.4
117
6.5
0.45
4180
0.5
0.046
27
Musconetcong, N.Y.
248 19
252
24
0.30
4730(A)
8740(R)
.064
0.047
5.1(A)
12-24(R)
21
Stony Point, N.Y.
187 23
214
27
0.69
3000
1.0
0.062
34.8
7
(summer)
Stony Point, N.Y.
(winter)
Nov. 1980 Avg.
192 22
199
25
0.67
3000
1.0
0.064
35.8
14
TABLE 35. SUMMARY OF TREATMENT PLANT OPERATIONAL PARAMETERS
FOR THE THERMAL SLUDGES
B^5 Sus. Solids Ave. Aerator Aeration Aerobic
August 1980 mg/1 mg/H Flow MLSS Volume Ratio Time Digestion
Inf Eff Inf Eff mgd mg/2, mg F/M hrs. Time days.
Rockland County, N.Y. 144 18 164 20 14.7 1150 2.48 0.21 3.9
Poughkeepsie", N.Y. 60 12 83 5 4.1 946 1.35 0.13 7.9
(A) - Contact aeration tank
(R) - P.eaeration tank
-------
weeks before discharge onto sand drying beds. A three inch depth of aerobic
sludge dries very nicely during warm months but a six inch layer will not dry
well and causes odors. Winter drying may also produce odofs as the sludge
will not dry rapidly and tends to build up.
The average flow into the plant during the periods when the sludge sam-
ples were collected were 0.69 and 0.67 mgd during August and November, 1982
respectively. The influent and effluent BOD,, were 187 and 23 in August and
192 and 22 mg/2 respectively during Novembver, 1982. Based on this informa-
tion the F/M ratio was calculated as about 0.06.
Sludge from the aerobic digester was used as seed during this study.
The seed samples were obtained on August 20th and December 3rd of 1980. The
average August and November temperatures were 23 and 15°C respectively.
Rockland County, N.Y. Sewer District No. 1
The Rockland County wastewater treatment plant was designed to handle a
10 mgd flow but was averaging about 14.7 mgd at the time of the sampling.
This secondary treatment plant has step aeration activated sludge with pri-
mary and secondary clarification. Aeration time at the 14.7 mgd flow rate is
4.1 hours. Waste activated sludge is pumped to the head of the primary clar-
ifiers from where it is pumped to thickeners as a mixture of primary and
secondary sludges. From the thickening process the sludge is pumped into
anaerobic digesters or directly into the Zimpro wet oxidation process. An-
aerobic treatment of the sludge mixture is maintained at 95-100°F with a
total detention time of close to 30 days in the cwo stage digesters. Mixing
of the first stage digester is accomplished using draft tube mixers. The
second digester is not mixed.
Sludge enters the Zimpro thermal process through a sludge storage tank
and then into the wet oxidation reactor. Compressed air is combined with
pressurized sludge at a pressure of about 800 psi. The influent temperature
of the reactor is about 390°F and the treated sludge exits at close to 470°F.
Sludge for the study was taken from the bottom of the decant tank which
follows <:he thermal reactor. The decant tank supernatant is returned to the
treatment plant influent while the sludge is cooled, dewalered on a vacuum
filter and the cake is disposed on a land fill site.
Poughkeepsie, New York
Poughkoepsie has a secondary plant for wastewater treatment and is com-
posed of aerated grit chambers, primary settling, mechanically aorated
activated sludge and secondary settling. The plant was designed Tor a flow
of 8 mgd and at the time of sampling was operating at an average of 4.1 mgd.
Industrial wastewater flow is relatively small but there* are a number of
fabric dyeing operations which contribute sufficient dye to make "the waste-
water rather colorful at frequent intervals. The wastewater is rather
weak in character averaging less than 100 nig/?, for both BODj. and suspended
101
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solids. Aeration detention time (excluding recycle) is approximately 7.9
hours with a F/M ratio of 0.13. Waste activated sludge is returned to the
primary clarifier where it is thickened with the raw sludge in the clari-
thickener section of the clarifier. The plant manager estimates the thick-
ened sludge to be about 50 percent each of activated'and raw sludges.
Thickened sludge is pumped to the sludge holding tank and then into the
Zimpro thermal treatment process. Operating conditions of the process are
310-330 psi pressure at a temperature of 355-360°F. A treated sludge hold-
ing tank follows the reactor and a bottom sludge sample was taken from this
tank for analysis. Heat treated sludge from the bottom of the holding tank
is centrifuged and the solids cake was being landfilled at the time the
sample was collected. Decant from the holding tank and the centrate are
returned to the head of the plant. Table 36 summarizes the characteristics
of the sludge for the month of August 1980.
TABLE 36. P0UGHKEEPS1E, N.Y., SLUDGE CHARACTERISTICS
Sludge
Location
Percent
Total Solids
Percent
Volatile Solids
Clarithickener eff.
(Zimpro Inf.)
2.2
89.0
Zimpro effl.
1.9
75.1
Centrifuge inf.
(Zimpro settled eff.)
14.3
57.9
Centrifuge cake
36.7
57.9
ANAEROBIC SLUDGES
Seven anaerobic sludges from five municipal wastewater treatment facil-
ities were studied in this investigation. Averages of the pertinent treat-
ment plant operational data are given in Table 37 for the month of November
1980 tor all but one of the Cedar Creek sludges in which the August 1980
data are included. These averages were chosen as being the most representa-
tive of the contents of the digesters when the samples were taken for study.
102
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TABLE 37. SUMMARY OF TREATMENT PLANT OPERATIONAL PARAMETERS
FOR THE ANAEROBIC SLUDGES
BOD
mg/
5
£
Sus. Solids
mg/l
Ave.
Flow
Aeration
Time
Ratio
Anaerobic
HRT & SRT
Loading
lbs VS/
% VS
November 1980
Inf
Eff
Inf
Eff
mgd
hrs.
F/M
days
cf *d
Destroyed
26th Ward,
New York City
71
12
81
17
83
3.0
0.19
19
0.11
42
Coney Island,
New York City
136
62
146
84
100
2.3
1.94
24
0.18
56
Cedar Creek,
New York
164
36
169
87
26
4.5
0.33
34
0.07
54
Oyster Bay,
New York
105
18
83
26
1.9
-
*
73
37
0.04
62
Yonkers, NY
(Primary
sludge)
169
6
135
7
77
4.3
0.81
13
0.31
51
Yonkers, NY
(waste acti-
vated sludge)
169
6
135
7
77
4.3
0.81
18
0.08
27
Cedar Creek,
New York
(August 1980)
164
22
208
46
26
4.4
0.14
35
0.07
49
ic
Trickling filter organic loading lb BOD^/IOOO CF-day
-------
New York City, New York - 26th Ward Plant
The 26th Ward water pollution control plant is a step aeration activated
sludge plant with an average flow of 85 mgd. Primary sedimentation, four-
pass aerators and secondary clarification comprise the major units for treat-
ment of this municipal wastewater. Sludges from the clarifiers are gravity
thickened, digested anaerobically and disposed into the Atlantic Ocean.
Aeration of the four-pass aerators is accomplished using fine bubble diffu-
sers. Each of the bays is 404 feet long by 30 feet wide and 15 feet deep and
a total usable volume of 1,380,000 cubic feet. The average detention time is
almost three hours at an organic loading of 49 pounds BOD,, "per 1000 cubic
feet per day.
Anaerobic digestion of the primary and waste activated sludge was accom-
plished in two heated (95°F) 86 foot diameter primary digesters followed by
two secondary digesters of equal diameter. The primaries have 30 feet side
water depth while the secondary are 29 feet deep. The cone depth is 9 feet.
The volumes of the primary and secondary tanks are 191,500 and 186,000 cubic
feet eaci. respectively. The digesters have fixed covers, are equipped with
external sludge heaters and are continuously mixed using gas recirculation.
The average hydraulic and solids detention time is 19 days. Organic loading
averages 0.11 pounds of volatile solids per cubic foot per day. Following
digestion the sludge enters a holding tank from which it is barged out to sea.
New York City, New York - Coney Island Plant
Coney Island has a 100 mgd modified aeration secondary municipal waste-
water treatment plant. The system includes grit removal, modified aeration
(no primary settling), and secondary sedimentation. Crease is collected but
it is not anaerobically digested at this plant or at any of the city treat-
ment facilities. Approximately 2.3 hours aeration is provided by modified
aeration and the organic loading is 89 pounds BOD,, per .1000 cubic feet per
day. Four aerators containing two passes each are used.
Sludge from the secondary clarifiers is gravity thickened to 8 to 9
percent solids and is then digested anaerobically in four 71 foot diameter
primary tanks. The digesters are fixed cover, continuously mixed using gas
recirculation and heated using external heat exchangers to about 98°F. Fol-
lowing primary digestion the sludge is pumped into a secondary storage di-
gester from where it is pumped to a dock facility for barging to sea. The
digesters have an organic loading of 0.18 pounds of volatile solids per
cubic foot per day with a 24 day hydraulic detention time.
Nassau County, New York - Cedar Creek Plant
Nassau County's Cedar Creek secondary treatment plant has a design capa-
city of 45 mgd and during the time of these studies was operating at 31 mgd.
About 5 mgd was being diverted for advanced wastewater treatment in a separ-
ate train of treatment units. The secondary plant unit operations consist of
aerated grit removal, primary clarification, step aeration activated sludge
and final clarification. Disinfection is provided during the warm months of
thi year.
104
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The primary sludge is pumped directly to anaerobic digesters while the
waste activated sludge is provided air flotation for thickening before an
aerobic digestion. Digestion is accomplished in two 105 foot diameter pri-
mary digesters with almost two million gallons capacity each. Approximately
45 days hydraulic detention time is provided. These two digesters are con-
tinuously mixed using gas recirculation while heating to about 95°F is accom-
plished using external heat exchangers. Both digesters have floating covers.
Following primary digestion the sludge enters one secondary digester.
As no separation takes place, the secondary digester merely serves as a hold-
ing tank and further digestion. A smaller holding tank follows the secondary
tank from which it is pumped to the Bay Park treatment facility for barging
to sea.
Oyster Bay, New York
Oyster Bay has a secondary wastewater treatment facility employing high
rate trickling filters. The major process components include grit removal,
primary settling, trickling filters and secondary sedimentation. Recycle of
secondary sedimentation effluent is employed at a usual rate of approximately
0.9 to 1.0 recycle to raw flow respectively. The sludges from the primary
and secondary clarifiers are digested anaerobically. Two 70 foot diameter
trickling filters with six-feet of 3 to 6 inch crushed trap rock are used
which treat the 1.93 mgd average flow. Sludge from the secondary clarifier
is returned to the primary clarifier for further thickening prior to diges-
tion.
Anaerobic sludge digestion equipment includes a primary digester, a
secondary digester, vacuum filter and glass covered drying beds. Sludge from
the primary clarifier is pumped into the 35 foot diameter primary digester.
Temperature is maintained at about 92-93°F by recirculation of sludge through
a heat exchanger. Raw and trickling filter sludges entering the digester are
preheated in the exchanger. The liquor operating l'jvel in the primary diges-
ter is 25 feet, yielding a volume of 180,000 gallons. A Perth gas recircula-
tion system provides mixing for about 9 hours each day and a floating cover
is used. Approximately 4900 gpd of the mixture of primary and secondary
sludges was being pumped daily into the digester for a 37 day detention time
and 4900 gallons of supernatant was transferred to the secondary digester
each day. Once every two weeks primary digested sludge of about 7 percent
total solids was transferred from the bottom of the primary digester to the
secondary digester. This was the source of sludge for the experiment.
The secondary digester has a diameter of 35 feet and maximum operating
sludge liquor level of 22.5 feet, providing a volume of 160,000 gallons. It
acts as a quiescent holding tank with supernatant return by gravity to the
primary clarifier.
105
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iWestchester Couritv, Yonkers. New York
i
' Municipal treatment facilities for most of the wastewater of Westchester
I County is treated at the Yonkers Joint secondary plant. Treatment consists
of aerated grit removal, primary sedimentation, activated sludge step aera-
tion, secondary,sedimentation and chlorine disinfection (during the warm
imonths of the year). The flow averages about 77 mgd.
Sludges from the primary clarifiers was provided anaerobic digestion in
two heated digesters of 900,000 and 560,000 gallons capacity each. This
sludge is prethickened before digestion using picket type thickeners. The
digesters were being fed approximately 116,000 gallons daily for a detention
period of close to 13 days. Following digestion the sludge enters a holding
tank from which it is pumped onto a barge and hauled out to sea for final
disposal. Both digesters have fixed covers and are mi&ed using a gas recir-
culation system.
Waste activated sludge was thickened using air flotation and digested
in five anaerobic digesters of 718,000 gallons capacity each. They are of
the fixed type with gas recirculation for mixing and employ external heat ex-
changers for heating. About 205,000 gallons per day of waste activated
sludge were being fed to these digesters for an average of 18 days detention
time.
106
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SECTION 6
EXPERIMENTAL PROCEDURES AND APPARATUS
DESCRIPTION OF APPARATUS
Anaerobic Digesters
The purpose of our work was to determine how stable a sludge is and the
point where a sludge may be considered stable. In this laboratory work, sim-
ulation of field conditions was attempted, but some field conditions.could
not be duplicated. Obviously, our reactors had to be much smaller than full
scale installations. Initially our anaerobic reactors contained 18 liters of
sludge. Mixing these reactors also may not be representative of actual field
conditions. A vigorous complete mix was used. Hence, the reactors had a
higher power to reactor volume ratio than typically found in actual treatment
plants. Another important difference between the reactors and those found in
treatment plants is the feeding schedule. Treatment plant digesters are fed
on a regular basis, while our reactors were never fed.
The reactors were maintained at a temperature of 35°C, which is typical
of full scale digesters. The reactor consisted of a 20 liter pyrex aspirator
bottle sealed with a rubber stopper (Fipure 58). The rubber stopper had two
openings. One opening was connected to a wet test gas meter, and the other
was used for mechanical mixing. The mixing apparatus consisted of a length
of tygon R3603 tubing 0.953 ID cm x 1.429 OD cm (3/8" ID x 9/16" OD) sealed
at the bottom by doubling over, and bound with copper wire. The upper end of
the tube extended beyond the top of the stopper and was left open. A 0.318
cm (1/8") bent steel drill rod approximately 60 cm (23.6") was inserted into
the tube and the remaining space between the tube and the rod was filled with
vegetable oil. A Barber Coleman Byqm-33510-12 DC gear head motor was used to
drive the mixing rod. Speed was controlled by varying voltage to the motor.
Gear heads on these motors deteriorated after several months continuous use,
and needed to be replaced. These motors were replaced by RAE Model 101921
gear head AC-DC type motors. Speed was controlled at about 150 RPM using a
variable transformer. These motors proved very successful in use. The rod
was connected to the motor by a chuck which made servicing and access to the
reactor simple.
The tygon tube used for mechanical mixing was replaced on a regular
basis to prevent its breaking and leaking of vegetable oil into the reactor.
Approximately once every six weeks proved to be an adequate replacement time.
Gas samples were removed through a glass tee on the exhaust gas line
equipped with a rubber septum. Liquid samples were removed through the
aspirator opening. Gas samples were obtained using a 1 ml gas tight syringe,
and injected directly into the gas chromatograph. In addition to the 18
107
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FIGURE 58. Continuously Mixed Anaerobic Reactor Schematic
108
-------
liter reactors, 1.5 liter reactors were also set up. The major differences
between the 18 liter and 1.5 liter reactors are mixing, sampling, and gas
measurement. The 18 liter reactors were mixed continuously, while the 1.5
liter reactors were mixed by hand once daily. The 1.5 liter reactors were
not sampled on a regular basis.
Gas production was measured using 1300 ml glass collection cylinders
attached to the 1.5 liter reactors with tygon tubing as shown in the schem-
atic drawing in Figure 59. To insure a low solubility for carbon dioxide,
the confining fluid was composed of a saturated solution of sodium chloride
in 10% sulfuric acid. In order to facilitate the readings of gas volume, the
confining fluid was colored using methyl orange. All anaerobic reactors were
kept in a walk-in room in which the temperature was held constant at 35°± l°C.
Heat was supplied by a portable electric heater.
Aerobic Digesters
Aerobic reactors used in our study consisted of 19 liter (5-gallon) fish
tanks equipped with porous stone air diffusers (Figure 60). Air flow rates
were regulated to assure complete mixing. These tanks were covered and water
was added to compensate for evaporation.
Some important differences existed between the bench scale laboratory
reactors used in the study and the aerobic digesters in full scale operation.
Although no temperature control was used in our aerobic studies, the bench
scale reactor temperature variance was limited to the ambient temperature of
the laboratory (20-26°C). Full scale aerobic digesters at the locations from
which the samples were taken are operated at lower temperatures than found in
the laboratory. Another important difference between the bench scale reac-
tors and full scale operations is the feeding schedule. Full scale aerobic
digesters may or may not be fed on a regular basis, while the bench scale
reactors were never fed.
The amount of air input into our bench scale reactors was probably not
representative of full scale operations. No measurement of gas flow rates
were made during the course of the experiment. However, flow rates to main-
tain good mixing on the lab scale most likely exceeded rates found in full
scale operations.
ANALYTICAL TECHNIQUES
Samples were removed from the laboratory reactors five times weekly
during the first six weeks of the study, and then as required for the re-
mainder of the study. The size of rhc sample was determined by the volume
of sample required for the tests to be performed on that day. On some days
an excess of sample was removed and preserved for future analysis. Sludge
stability was monitored by testing for a variety of parameters on a regular
basis, and observing changes with respect to time.
109
-------
FIGURE 59. SCHEMATIC LAYOUT OF 1.5 LITER REACTOR
110
-------
COVER
DIFFUSERS
COMPRESSOR
19 LITER FISHTANK
FIGURE 60. Aerobic Reactor Schematic
-------
Standard Analyses
Many of the conventional tests used by environmental engineers as well
as some new testing procedures were performed on the samples. The majority
of tests performed were in accordance with Standard Methods for the Exami-
nation of Water and Wastewater 14th Edition 1975. Procedures for some of
the tests performed were found in the literature, and in a few cases were
adapted as necessary based on laboratory experience. A complete list of all
tests performed and methods used are given in Table 38.
ATP Measurement
Although a significant effort was extended to ATP measurements, no ATP
data is given in this report because of difficulties encountered in the ana-
lyses. First, the Aminco photometric instrument arrived later than promised
and the project had been started. Due to inexperience with the analysis and
a defective photometer, the analyses proved to be unsatisfactory. A new
instrument was received but unfortunately, the procedure was not mastered in
time to make the needed analyses. The following describes the .procedures
that were used.
A number of methods for measuring adenosine triphosphate (ATP) appear
in the literature as well as bulletins from instrument manufacturers and
reagent distributors. The first method used in our study required the ex-
traction of ATP from cells by boiling the cells in tris buffer. During our
study Tris extracted ATP samples were analyzed using the internal standard-
ization procedure. Unfortunately, the procedure followed did not allow a
sufficient concentration difference between the sample and background
lumenescence and the data collected was not satisfactory. Because of this
difficulty and the time consuming nature of the Tris buffer extraction pro-
cedure, a new procedure recommended for better results was adopted.
The procedure followed was an adaptation of the method recommended by
Lumac Systems, Inc. This method was chosen because of its utilization of
the internal standardization principle in which the relationship of ATP in
the sample to light intensity emitted by the sample is linear. However,
the dynamic range of the instrument used to measure tight intensity may
distort the linearity of this relationship in certain ranges. The micro-
photometer used In our analysis had a dynamic range of approximately five
decades.
Since our measurements were made on sludge, turbidity was present in
our samples. If a calibration curve was generated using an ATP standard,
turbidity would be negligible when compared to a sample containing sludge.
Since turbidity absorbs light and light emission is the basis of our re-
sults, erroneous results caused by turbidity need to be accounted for. The
internal standardization procedure accounts for turbidity in samples when
standardizing. Tn this procedure, standardization is made by mixing a
known amount of ATP with the sample and measuring luminescence. The sample
is then measured with no additional ATP. By subtracting the amount of lum-
inescence given off by the sample, the amount of ATP in the presence of the
sample is known. Any quenching of light energy by turbidity in the sample
112
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is therefore corrected for by standardizing in the presence of the sample.
This procedure is repeated for every sample.
Apparatus
a) Microphotometer - A Chem-Clow Photometer (Model J4-7441) was used
for all of the analysis. This model features a reaction chamber
containing the photomultiplier tube which permits sample injection
through a rubber septum into the cuvette. This enables sample
measurement immediately after the bioluminescent reaction begins.
b) Strip chart recorder - A Cole Parmer (Model 8376-30) recorder was
used to measure bioluminence peak heights. Best results are ob-
tained using an electronic intergrator timer.
c) Cuvettes - 6 x 50 mm, Kimble products No. 73500
Reagents
All reagents used were purchased from Analytical Luminescence Labora-
tory, Inc.
a) Purified firefly extract (Luciferin-^uciferase) - This reagent
emits light when mixed with ATP, Mg and oxygen. Analytical
Luminescence markets this as "firelight".
b) Hepes buffer, pH 7.75 (firelight buffer) - this buffer is used to
reconstitute the purified firefly extract.
c) ATP standard - adenosine triphosphate in pure form is required for
standardization of the instrument.
d) ATP extraction reagent (extralight) Lumac NRS or NRB. This re-
agent is used to release ATP from cells.
Procedure
a) Background Correction -
1. Place 100 u£ of distilled water, and 200 uI of extralight
into a cuvette and mix.
2. Place cuvette into microphotometer and inject 100 u£ of fire-
light.
3. Read peak value from recorder.
4. Perform analysis in triplicate and record average as x„,
or v. Blank
D
b) Sample Measurement
1. Place 200 u£ of sample at the proper dilution into a cuvette,
Note: Sample peak height should be 1/2 to 1/5 the reading
obtained when 200 u£ sample is mixed with 10 uJI ATP STANDARD
SOLUTION, (x. = 1/2 to 1/5 xJ.
A B
2. Add 200 uJE, of extralight to cuvette and mix
3. Place cuvette into microphotometer and inject 100 u£ of fire-
light
4. Read peak value from recorder
5. Perform analysis in triplicate and record average as x
113
-------
c) Internal Standard
1. Place 200 u£ of sample at proper dilution into 3 cuvettes and
add 10 u£ of ATP standard
2. Repeat steps 2 through 4 from above
3. Perform analysis in triplicate and record average as x^
ATP = k - ATP ADDED (ug)
Luminesce Unit x_ - x.
B A
ATP in sample = k(*A - Xg)
,, ATP in sample
No. of cells =
ATP per cell
Centrifuge Button
One of the major causes of odor problems associated with sludges is the
production of hydrogen sulfide gas (H.S). Hydrogen sulfide is produced by a
species of bacteria known as desulfovibrio. These organisms utilize various
sulfur compounds as final electron acceptors in their oxidation of various
organic compounds. Since hydrogen sulfide has a repugnant odor, detection
of hydrogen sulfide produced by sludges would indicate that the sludge is
unstable with respect to odor. Hydrogen sulfide may be detected by lead
acetate paper, as the paper is discolored in the presence of hydrogen sul-
fide. This procedure closely follows the technique described by Hartman et
al. (79).
Procedure followed in Phase I of project:
1) Sludge samples were taken as identified in Figures 61 and 62.
2) Place 50 mJI of the sludge into a centrifuge tube, centrifuge
at 5000 RPM for 15 minutes.
3) Decant off most of the supernatant leaving a small amount to
keep the sludge wet (about 3 m£).
4) Cap tube with a rubber stopper having a slit cut on its bottom
to hold lead acetate paper.
5) Incubate tubes at 35°C until discoloration occurs.
6) Record tine at which discoloration occurs.
In Phase II of the project the anaerobic sludges were diluted to 1%
solids and the aerobic sludges to 0.5% solids. This was done to make the
solids concentration uniform in all the centrifuge tubes set-up and elimi-
nate the effect of varying solids from tube to tube. Also, the amount of
discoloration of the lead acetate paper used to define the end point of the
experiment was decreased to about 10% blackening of the aren of the paper in
order to increase the sensitivity of the test. In Phase I, greater than 50%
of the paper was blackened when a test was considered completed.
As will be discussed later, the Phase I procedure gave consistent resultB
with few points that appear out of order. However, the procedure used in
114
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TABLE 38. ANALYTICAL METHODS
Analysis
Schedule
Method
pH
Equipment
pH
2/veek
Standard Methods (SM)
(Ref 46)
Orion Model 70lA
Digital Ionalyzer
Alkalinity
2/week
(SM); endpoint titration,
Anaerobic pH 4.0
Orion Model 701A
Digital Ionalyzer
Specific oxygen
uptake rate (sour)
2/week
(SM); oxygen consumption
rate
YSI Model 54 Oxygen Meter
Total solids
2/week
(SM); total residue dried
at 103-105°C
NAPCO
Model 410 Oven
Total suspended
solids
2/week
(SM); total non-filterable
residue dried at I03-105°C
Millipore Filter Apparatus
NAPCO Model 410 Oven
Volatile solids
2/week
(SM); total volatile and
fixed residue at 550°C
Thermolyne Model F-A1740
Muffle Furnace
Volatile suspended
solids
2/week
(aerobic only)
(SM); volatile and fixed
matter in non-filterable
residue and semisolid samples
Thermolyne Model F-A1740
Muffle Furnace
Millipore Filter Apparatus
Dissolved solids
2/week
(aerobic only)
(SM); total filterable residue
residue, dried at 103-105°C
Millipore Filter Apparatus
Conductivity
2/week
(SM); conductivity
Industrial Instruments
Model RC 16B2
Conductivity Bridge
-------
TABLE 38. (cont'd)
Analysis
Schedule
Method
Equipment
BOD
1/week
(SM); Oxygen demand
(biochemical), membrane
electrode method
YSI Dissolved Oxygen
Meter Model 54
Nitrate
1/week
(SM); nitrate,
cadmium reduction method
Bausch & Lomb Spectronic 20
Spectrophotometer
Ortho-
Phosphorus
1/week
(SM); stannous chloride
method
Bausch & Lomb Spectronic 20
Spectrophotometer
Total
Phosphorus
1/week
(SM); preliminary digestion
steps for total phosphorus
stannous chloride method
Bausch & Lomb Spectronic 20
Spectrophotometer
Volatile acids
1/week
(anaerobic only)
(SM): Chromatographic
separation method for organic
acids
Chromatographic column
Grease and oil
1/2 weeks
(SM); oil and grease extrac-
tion method for sludge sam-
ples
Soxhlet extraction appara-
tus
Total Kjeldahl
1/week
(SM); Nitrogen (organic)
macro-Kjeldahl method
Kjaldahl digestion rack
Ammonia
1/week
(SM); nitrogen (ammonia)
Ammonia distillation rack
Nitrogen titrimetric method
-------
TABLE 38. (cont'd)
Analysis
Schedule
Method
Equipment
Lignin
COD
ATP
Centrifuge Button
Buchner Funnel
CST
L/month
1/week
Variable
1/2 week
1/2 week
Forage fiber analysis
Agriculture Handbook No. 379
U.S.D.A.
Ref. 95
See Section-Analytical Tech-
niques, ATP Measurement
See Section-Analytical Tech-
niques, Centrifuge Button
Ref. 79
Ref. 96
Ref. 97
As specified in handbook
Capillary Suction Time
Apparatus, Triton Electron-
ics, Model WPRL Type 130
-------
Phase II, which was intended to be an improvement over the Phase I procedure,
proved unsatisfactory. The data points obtained were so inconsistent that they
were of no value. The reason for these poor results was most likely the change
from 50% to 10% blackening to indicate instability. It is believed that 10%
blackening of the lead acetate paper is not a sufficient indicator of hydrogen
sulfide. Continuing studies eventually showed that on a number of occasions,
the edges of the lead acetate paper would discolor (about 10% of the paper)
and show no increase in blackened area for long periods of time. In such
cases, the result based on 10% of the area being blackened, would indicate
an unstable sludge at an early time whereas if 50% of the area were to be
blackened, the time required would be much longer.
Lignin
In the experimental phase of the project, analyses for lignin were
attempted. The analysis is rather long and tedious requiring a significant
amount of laboratory training. Because of the limited experimental time
available, the procedure was not satisfactorily developed to yield meaningful
results.
EXPERIMENTAL PROCEDURE
The experimental procedures employed were designed to extend the bio-
logical digestion process far beyond where it is normally terminated in con-
ventional digestion processes. Completely mixed anaerobic digesters typi-
cally have detention times of about 20-30 days. Tn our study, sludge taken
from such conventional digesters was further digested for more than 100 days.
Aerobic digesters have detention times on the order of 10 to 20 days. Sludge
taken from aerobic processes was further digested an additional 100 days.
All laboratory reactors were seeded using sludges obtained from treat-
ment plants in the New York Metropolitan area. During the course of our
study, a total of 13 anaerobic and 9 aerobic reactors were set up and moni-
tored in our laboratory. Anaerobic reactors 1 through 6 and aerobic reac-
tors 1A through 6A were analyzed during the fir.t phase of the study. An-
aerobic reactors 7 through 13 and aerobic reactors 7A through 9A were ana-
lyzed during the second phase of the study.
Figures 61 through 64 illustrate the scheme by which our various aero-
bic and anaerobic reactors were prepared. For example, Figure 61 shows the
various anaerobic reactors which were prepared during the first phase of the
study. In the first box in the upper left hand corner, the one indicates
the reactor number. Cedar Creek, New York 25% raw indicates that 25 percent
of the reactor contents is raw sludge taken from the Cedar Creek plant. The
75% seed indicates that 75 percent of the reactor volume is seed. Figure 61
shows that the seed is digested primary and activated sludge from the Cedar
Creek plant. Reactor four contained 100% seed and may be used for seed
corrections and was used to seed the other reactors.
In Figure 62 time of digestion and type of digestion process is indi-
cated on the figure. For example, u:>it 1A was taken from an aerobic diges-
tion process having a detention time of six days.
118
-------
to
1
Cedar Creek, N.Y.
25% Raw
75% Seed
4
Cedar Creek, N.Y.
100% Digested
Primary and Acti-
vated Sludge
Seed Control
2
Cedar Creek, N.Y.
25% Step Aeration
Activated Sludge
75% Seed
5
Rockland County, N.Y.
25% High Pressure Heat
Treated Primary and
Activated Sludge
75% Seed
3
Stony Point, N.Y.
35% Aerobic Digester
65% Seed
6
Poughkeepsie, N.Y.
25% Low Pressure Heat
Treated Primary and
Activated Sludge
75% Seed
Figure 61. Phase I. Anaerobic Reactor Contents
-------
1A
Beacon, N.Y.
6 Days Digestion
2A
Cold Spring, N.Y.
1.1 Days Aeration
3A
Musconetong, N.J.
21 Days Digestion
N>
o
4A .
Stony Point, N.Y.
14 Days Digestion
5A
Rockland County, N.Y.
16% High Pressure
Heat Treated Primary
and Activated Sludge
84% Stony Po'int Seed I
6A
Poughkeepsie, N.Y.
1.6% Low Pressure
Heat Treated Primary
and Activated Sludge
98.4% Stony Point Seed
Figure 62. Phase I. Aerobic Reactor Contents
-------
7
Stony Point, N.Y.
Aerobic Digestion
Sludge
8
26th Ward, N.Y.C.
Anaeroblcal ly
Digested Primary
and Activated
Sludge*
9
Coney Island, NYC
Anaeroblcally
Digested Primary
and Activated
Sludges
10
Cedar Creek, S.Y.
Anaeroblcally
Digested Primary
and Activated
Sludges
11
Oyster 3ay, N.Y.
Anaeroblcally
Digested Primary
and Trickling
Filter Sludges
12
Yonkers, N.Y.
Anaeroblcally
Digested Primary
Sludge
13
Yfenkers, N.Y.
Anaeroblcally
Digested Activated
Sludge
Figure 63. Phase II. Anaerobic Reactor Contents
-------
to
to
7A
Stony Point, N.Y.
100% Aerobic
Digester
Seed - Control
8A
26 Ward, N.Y.C.
35% Anaerobic
Digester
65% Seed
9A
Jamaica, N.Y.C.
35% Anaerobic
Digester
65% Seed
Figure 64. Phase II. Aerobic Reactor Contents
-------
Start-up of Reactors
Anaerobically digested primary and activated sludges from the Nassau
County, New York, Cedar Creek plant was used as seed in the Phase I anaero-
bic digestion experiments. Reactor 4 contained 100% Cedar Creek sludge, and
was used as the seed control. The remaining five reactors contained differ-
ent amounts of Cedar Creek seed and an amount of the sludge under investiga-
tion (Figure 61). The reactors were maintained at a temperature of 35±°C,
and were completely mixed throughout the course of the experiments. The
volume of the reactors was initially 18£, but declined in volume as samples
for analysis were removed.
Phase I aerobic digestion experiments continued the aeration of sludges
obtained from three aerobic digestion plants. A sample from the Cold Spring,
New York extended aeration process was also further digested aerobically.
Sludge from Stony Point, N.Y. was digested in Reactor 4A and was also
used as seed. Different thermal treatment sludges were mixed with Stony
Point seed to form reactors 5A and 6A (Figure 62). These reactors were
operated at room temperature and completely mixed by diffused air aeration.
The initial volume of the reactors was 18£.
All Phase II anaerobic reactors contained anaerobic sludges except
reactor 7 which contained Stony Point aerobic digestion sludge. (Figure 63)
Phase II aerobic reactors were also seeded with Stony Point sludge.
Reactor 7A was the seed control while reactors 8A and 9A contained mixtures
of the seed and anaerobic sludges (Figure 64).
Before sealing, the anaerobic reactors were purged with nitrogen gas.
Mixing was initiated one day after set-up to assure no oxygen was present.
No special precautions were made in the set-up of the aerobic units.
123
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SECTION 7
LABORATORY RESULTS
AEROBIC DIGESTION
Sludges from four different aerobic treatment plants were analyzed during
the course of the study. The sources of the sludges were Beacon, New York,
Musconetcong, New Jersey, Cold Spring and Stony Point, New York. Sludges
studied are shown in Figures 62 and 64. Aerobic digestion of anaerobic sludge
and thermally treated sludge was conducted in our laboratory using Stony Point
sludge as seed. Tables 39 and 40 give the zero and sixty day results and the
number of days required for the various parameters to reach equilibrium.
Pure Sludges
Analysis of data obtained with pure sludges was simple in contrast to the
case of sludges mixed with seed sludge where evaluation of effects requires
comparison with the behavior of the seed sludge. Some data are tabularized
to facilitate comparisons. Most data are presented ip graphical form so that
trends may be easily observed. In order to minimize the number of plots re-
quired, several parameters are plotted together. The scales frequently are
different and the technique used is to use a scale multiplication factor(s)
after the parameter. As an example in Figure 65a for %TS, the scale must
be multiplied by 10"^ or 0.1; thus the zero day %TS (Total Solids) is 0.44.
Beacon, New York (Reactor 1A)
Results of tests performed sludge from the aerobic digester at the
Beacon, New York wastewater facility are shown in Figures 65 and 66. Total
solids, volatile solids, suspended solids, and volatile suspended solids all
show a downward trend and approach equilibrium in approximately 40 days as
seen in Figure 65a. Solids reduction may typically be characterized by an
initial rapid decrease in concentration followed by a slowly leveling trend.
The curves for all these solids, tend to parallel each other. A similar
downward trend leveling off in about 20 days may be seen for BOD,, is more
sensitive than COD when trying to identify stability as BOD reduction was
about 75% whereas COD reduction was 25% in the 20 day period. It may also
be seen in Figure 65b that the curve for specific oxygen uptake rate (SOUR)
resembles the curve for BOD . The SOUR approaches a steady state value of
about 1.2 mg 02/gm VSS-hr.
The plot of alkalinity in Figure 63c shows a rapid decrease from 430 mg/J,
to 20 mg/I in about 20 days. It is also of interest to note the relationship
between pH and conductivity. The two curves approximate mirror images of each
other, but the minimum and maximum points are displaced by about 10 days.
Figure 65d illustrates the relationship between organic and ammonia
nitrogen. The organic nitrogen concentration declines rapidly over the first
124
-------
20 days, and then levels off. Initially we see a conversion of organic
nitrogen to ammonia nitrogen as seen in Figure 65d. As the concentration of
organic nitrogen decreases, we see a corresponding increase in ammonia
nitrogen concentration. As the organic nitrogen concentration reaches
equilibrium, we see the ammonia nitrogen concentration decline and eventually
achieve equilibrium. This ammonia nitrogen peak occurred about 17 days into
the experiment. It is important to note the different scales used for these
two parameters in the Figure 65b.
The filterability of this sludge did not change much during the first 34
days of the experiment. The capillary suction time (CST) was relatively
constant at about 12 seconds. No significant change in specific resistance
] 3
was observed. Values averaged about 9.5 x 10 m/kg in Figure 66a. Grease
and oil was measured three times for the Beacon sludge. These points plotted
in Figure 66b show that percent grease decreased from about 18 to 6.5 percent,
a reduction of 64%, in approximately 28 days.
Cold Spring, New York (Reactor 2A)
Figures 66 and 67 show the data collected during our study on sludge
from the Cold Spring, New York extended aeration process. All forms of
solids measurement, percent total, percent volatile, suspended, and volatile
suspended solids all yielded a decreasing trend which slowly leveled off as
illustrated in Figure 67a. Figure 67b shows that BODj. is again a much more
senstive indicator of sludge stability than COD. It^is of interest to note
that the curve for SOUR exhibits a relatively gentle decreasing slope from
the beginning of the study reaching a steady state value of 0.6 mgO./gm
VSS-hr.
Figure 67c shows a relationship between pH and conductivity. Decreases
in pH correspond closely to increases in conductivity and vice versa. A
rapid drop in alkalinity is observed over the first 20 days decreasing from
200 to 30 mg/P. as given in Figure 67c. Ammonia and organic nitrogen are
plotted in Figure 67c. The initial and final concentration of ammonia nit-
rogen is about 1.0 mg/t but on day 27 an ammonia peak of 26 mg/£ is reached.
Organic nitrogen drops rapidly during the first 20 days from 290 to 160 mg/S..
Parameters measuring filterability are shown in Figure 66c. The capil-
lary suction time remains constant at about 5 seconds during the first 49
days of the study. During this same period the specific resistance remains
12
constant at about 1.4 x 10 m/kg. Figure 69b shows the grease and oil
concentration declining. Although only three points are reported for grease
and oil, these points strongly suggest a downward trend.
Musconetcong, New Jersey (Reactor 3A)
Sludge taken from the aerobic digester at Musconetcong, New Jersey was
further digested in our laboratory, and results are presented in Figures 68
and 69. Data for solids indicates a trend where concentration decreases
rapidly initially, and then levels off. Data indicates that solids concen-
tration, both total and volatile, is reduced by approximately one half in 50
125
-------
days. After 50 days, the sludge is resistant to further biodegradation
concentration. This plot is typical of what was obtained seen in the other
aerobic reactors.
Figure 68b shows the relationship between BOD,., COD, and SOUR. The
curve for ROD shows a decrease from 3300 mg/£ to about 100 mg/£ in 40 days.
The COD curve shows a similar trend decreasing from 18000 to 500 mg/£ in 50
days. BOD,., COD and SOUR attain equilibrium between 20 to 30 days. A de-
crease in SOUR from 3.6 to 0.4 mg02/gm VSS-hr is given in Figure 68b.
No relationship is apparent between conductivity and pH as can be seen
from Figure 68c. The figure also shows a drop in alkalinity from 600 to
zero mg19, in about 40 days. If the data point collected on day 44 were
erroneous, the peak in the conductivity curve would be eliminated and the
three curves would correspond better.
Figure 68d illustrates the relationship between organic and ammonia
nitrogen. The initial and final concentration of ammonia nitrogen is about
10 mg/f.. On day 2.? a peak in ammonia nitrogen of 90 mg/£ was observed. Or-
ganic nitrogen has an initial concentration at 680 mg/Z and levels off to
200 mg/£ in approximately 60 days. Figure 69a shows a very slight increase
in CST and specific resistance during this same period. Figure 69b indi-
cates a markedly decreasing trend for grease and oil. This is typical of
what was observed for the previous reactors.
Stony Point, New York (Reactor 4A)
This reactor was established using sludge taken from the Stony Point
treatment plant during the summer. The data from this reactor was also used
as a seed correction for the thermally treated sludges undergoing aerobic
digestion.
Solids data indicate a decreasing trend followed by leveling off in 20
to 30 days as shown in Figure 70a. This trend in data is similar to trends
seen in the previous reactors. Although the trends are similar, the value
at which the various solids parameters reach equilibrium may vary with the
parameter and the reactor. In general, suspended and volatile suspended
solids seem to be more sensitive by exhibiting greater rates of change and
approach steady state sooner than do the corresponding total solids.
Figure 70b shows the relationship between BOD,., COD and SOUR. COD de-
clines from 5600 to 3000 mg/£ in about 30 days. BOD,, and SOUR curves are
similar to those discussed previously. The SOUR reaches an equilibrium
value of approximately 0.8 mg02/gm-VSS-hr. Again, pH and conductivity are
as mirror images of each other as shown in Figure 70c. Data from Beacon and
Cold Spring behaved in a similar fashion. Alkalinity declined to a value of
zero in approximately 20 days. Figure 70d shows a peak in ammonia nitrogen
occurring on day nine. Correspondingly organic nitrogen decreased from 330
to 100 mg/I in approximately 30 days. Figure 69c shows the capillary suc-
126
-------
tion time and specific resistance of this sludge remaining constant at
13
approximately 10 seconds and 1.7 x 10 m/dg, respectively, throughout the
course of our study. A decreasing trend for grease and oil is shown in Fig-
ure 69d.
Stony Point, New York (Reactor 7A)
Sludge taken from the Stony Point aerobic digester during the winter
was used as seed in experiments evaluating the aerobic digestibility of an-
aerobic sludges. Small variations exist between this sludge and Stony Point
sludge taken during the summer. Although the COD of the winter sludge is
higher, BOD^. concentrations of the summer sludge are more than twice the
concentration encountered in the winter Stony Point sludge. The SOUR for
the summer sludge was about 3 times that of the winter sludge. The summer
Stony Point sludge appears to be more active biologically than the winter
sludge, even though both were aerobically digested at room temperature.
Figure 71a shows the trends that the solids follow. When compared to the
summer sludge reactor (Figure 70a), the curves for the winter sludge show
smaller removal rates, indicating a more stable sludge. More solids des-
truction occurred in the summer sludge than in the winter sludge. The SOUR
rate was a constant 0.5 mg02/gm VSS-hr for the winter sludge throughout the
course of the study as Figure 71b illustrates. Reductions in COD and BOD^
are typical of the other aerobic sludges studied as can be seen in Figure
71b. The plot of conductivity shown in Figure 71c was constant at about
1600 uhmos/cm throughout the course of the experiment? The alkalinity of
the winter sludge behaves similar to the summer sludge dropping sharply
during the first 20 days. The pH of the summer sludge declines and then
rises again. The pH of the winter sludge declines and then levels off as
seen in Figure 71c. Comparison of Figures 71d and 70d show that ammonia and
organic nitrogen in both Stony Point reactors behave in a similar fashion.
Figure 72a shows specific resistance and CST of the sludge remained constant
during the study. The CST shows no real trend. The specific resistance of
the winter Stony Point sludge is higher than the summer sludge. Grease and
oil concentration can be seen decreasing from 9.6 to 1.9 mg/£. This is typ-
ical when compared to the other aerobic sludges studied.
Mixtures with Thermally Treated Sludges
Sludges from the wet oxidation processes at Rockland County, New York
and Poughkeepsie, New York were used in this part of the study. Sludge taken
from the Stony Point plant during the summer was used as seed in the reac-
tors. One reactor consisted of 16 percent by volume Rockland County heat
treated sludge in Stony Point seed. The other reactor was 1.6 percent by
volume Poughkeepsie'heat treated sludge in Stony Point seed.
Rockland County, New York (Reactor 5A)
Since the wet oxidation process tends to concentrate sludges, ^he ini-
tial concentrations of this reactor are higher than those found in reactors
containing aerobic sludges. Typically, percent total solids, suspended
127
-------
solids and volatile suspended solids are found to be higher in concentration
in the thermally treated sludges. Figure 73a shows that although percent
""otal solids, suspended solids, and volatile suspended solids are higher, per-
nt volatile solids is less than percentages found in pure aerobic sludge
reactors. This is due to oxidation of much of the volatile material in the
sludge during the wet oxidation process. Although little change is observed
in the SOUR rate as shown in Figure 73b, BOD,, and COD are quite responsive to
aerobic digestion. The curves for B0D5 and COD level off in approximately 20
days. The BOD,, concentration of this reactor is typical of concentrations
found in the pure sludge reactors, however, the COD concentration is much
higher than concentrations found in the pure anaerobic sludge reactors as
given in Table 39.
Pure aerobic sludges studied in the laboratory exhibit an initial drop
in pH followed by an increase and leveling off trend. The mixture of sludge
from the Rockland County and Stony Point plants shows an initial increase in
pH followed by a decrease and eventual leveling off as can be seen in Figure
73c. Figure 73c shows conductivity decreasing slowly. This is not typical
of what was observed for pure aerobic sludges which increased in conductivity
initially then a decrease and eventually leveled off. A decreasing alkalinity
trend, which at the end of the run approached zero, is typical of what was ob-
served for pure aerobic sludge reactors. The reactor containing the Rockland
County thermal sludge approached an equilibrium alkalinity concentration of
approximately 340 mg/i.
Both ammonia and organic nitrogen followed trends typical of the pure
aerobic sludges. The ammonia nitrogen reached a peak value of 85 mg/£ in
approximately 15 days. Although the initial organic nitrogen concentration
was higher, the equilibrium concentration of organic nitrogen was similar to
ncentrations encountered for pure aerobic sludges. Filtjjrability seems to
-inprovc slightly as indicated in Figure 74a. Figure 74a shows that specific
resistance declined, while CST remained constant. Figure 74b shows grease and
oil decreasing which was the typical trend observed for pure aerobic sludges.
Poughkeepsie, New York (Reactor 6A)
Figure 75a illustrates the degradation of solids in the reactor contain-
ing 1.6 percent Poughkeepsie heat treated sludge and 98.4% Stony Point aero-
bic sludge. No major differences exist between the reduction of solids in
this reactor, and the reduction encountered in the pure aerobic sludge reac-
tors. Both BOD,, and COD concentrations drop off rapidly, and level off in
approximately 40 days. Little change is observed in the SOUR. The seed
sludge had an initial SOUR of approximately 2.1 mg0o/gm VSS-hr. Since the
seed SOUR is higher than the SOUR in the Poughkeepsie reactor, toxicity might
be suspected or it could be affected by the dilution. The higher volatile
suspended solids concentration which was inactivated by the heat treatment is
also in part responsible for the lower SOUR. Figure 75c shows conductivity
declining whereas pure aerobic sludges tend to have increasing conductivity
values. The pi! of the Poughkeepsie reactor shows a sharp increase initially
although the pH declines to the original value before rising slowly again.
128
-------
Alkalinity also declined rapidly during the first 20 days but remained at
steady state. This trend is similar to that observed for pure aerobic sludges.
Organic and ammonia nitrogen concentrations behave in a fashion similar to
what was observed for pure aerobic sludges although ammonia nitrogen did not
reach a sharp peak as shown in Figure 75d. All other aerobic units discussed
previously showed sharp ammonia nitrogen peaks. Figure 74c shows the CST to
be fairly constant while the specific resistance of this sludge rose slightly.
A curve indicating a decreasing concentration of grease and oil is given in
Figure 74b and is typical of what was observed in reactors containing pure
aerobic sludges.
Aerobic Digestion of Anaerobically Digested Sludges
In this part of the research study, sludges from anaerobic digesters were
mixed with aerobic sludge and aerobically digested. Anaerobic sludges were
taken from the New York City 26th Ward and Jamaica treatment plants. 26th
Ward sludge was used in this portion of the study was identical to the sludge
used in the anaerobic digestion study. The reactors were seeded using Stony
Point winter aerobic sludge. Each of the reactors contained 34 percent anaer-
obic sludge and 65 percent Stony Point sludge.
26th Ward Mixture (Reactor 8A)
The addition of anaerobic sludge to the aerobic sludge created, upon aer-
ation, a more concentrated aerobic sludge. This reactor consisted of 35 per-
cent 26th Ward anaerobic sludge and 65 percent Stony Point aerobic sludge.
Comparison of the pure Stony Point seed and this sludge mixture may be made
using Table 40. The 26th Ward mixture has higher concentrations of suspended
solids, volatile suspended solids, as well as percent total solids. When com-
pared to the Stony Point seed percent volatile solids is about the same for
both the 26th Ward mixture and Stony Point. Figure 76a shows the behavior of
solids throughout the study. A comparison of Figures 76a and 71a shows that
the percentage change in total and volatile solide of 26th Ward sludge and
Stony Point sludge are about the same. Figure 76b shows the SOUR of the 26th
Ward mixture dropping from about 2.0 to 0.3 mg02/gmVSS-hr whereas the Stony
Point seed had a fairly stable SOUR of 0.4 mg02/gmVSS-hr as shown in Figure
71b. The COD concentration of the 26th Ward mixture is reduced much like the
COD concentration of the seed, although the 26th Ward mixture has higher
concentrations. COD and BOD5 reduction can be observed in Figure 76b. The
BOD5 reduction of the 26th Ward sludge is more rapid than the seed.
The BOD,. decreased from 1300 to 150 mg/£ in 25 days. Although the .seed
shows a slight increase in conductivity, the 26th Ward mixture shows a sig-
nificant increase in conductivity after 40 days. The pH of 26th Ward mix-
ture decreased from 8 to 4.2 as shown in Figure 76c while the pH of the seed
declined close to one unit during the course of the experiment. Figure 76
shows alkalinity of the 26th Ward mixture dropping from 1600 to 0 mg/I in less
than 30 days. During this same period, the Stony Point seed alkalinity drops
from 40 to 8 ng/jl.
129
-------
Data from pure aeration of aerobic sludges showed an ammonia nitrogen
peak during the first two weeks of each study. Ammonia nitrogen of the 26th
Ward mixture decreased from 315 mg/t to almost zero in less than 50 days as
can be seen in Figure 76d. Although a peak concentration of 200 mg/Z occurs
in the Stony Point seed, the 26th Ward mixture shows a steadily declining
trend. Figure 76d shows a decreasing organic nitrogen trend similar to the
Stony Point seed, and typical of what was observed in the pure aerobic
sludge reactors. Specific resistance and capillary suction time remain rel-
atively constant throughout the study for the 26th Ward mixture. Values for
specific resistance and capillary suction time are higher for the 26th Ward
mixture in comparison to values for the Stony Point seed. Figure 77b shows
grease and oil concentrations also decreasing. In general, the trends in
changes in concentration were similar in the anaerobic sludges mixed with
seed and the pure aerobic sludges, except that the concentrations were fre-
quently much higher in the anaerobic sludges.
Jamaica Mixture (Reactor 9A)
A mixture was made using 35% Jamaica, New York anaerobic sludge and 65%
Stony Point aerobic sludge. This Jamaica mixture was aerobically digested
and results are presented in Figures 78 and 79. Percent total solids, sus-
pended solids, and volatile suspended show an initial decreasing trend and
approach equilibrium concentrations in approximately 30 days. Reduction in
percent volatile solids seems to follow a straight line decreasing trend as
can be observed in Figure 78a. Percent volatile solids does not seem to be
approaching any equilibrium value, but is only decreasing at a rate of about
6% in 80 days. Initially, the SOUR of this sludge was 1.8 mgO^/gmVSS-hr and
equilibrium was reached in approximately 15 days when the SOUR levels off at
0.4 mg02/gn.VSS-hr. as shown in Figure 78b. Both the BOD and COD decreased
very rapidly in the fir;jt 30 days of the aeration process and achieved a
steady state condition.
Figure 78c shows a major decline in pH from 8.0 to 5.2 in approximately
25 days. During this same period we see a similar significant decrease in
alkalinity from 1250 to 50 mg/£. Conductivity remained constant for close
to 45 days then rose slightly. Figure 78d shows the organic nitrogen con-
centration remaining relatively constant throughout the study. The ammonia
nitrogen concentration was higher than typical concentrations encountered in
pure aerobic sludges. The ammonia nitrogen concentration decreased from 250
to 3 mg/£ in about 60 days.
The filterability of this sludge appears to deteriorate with increasing
digestion time. The capillary suction time increased with further digestion
as can be seen in Figure 79a. After 60 days digestion, specific resistance
of the sludge also increased. A steady decrease in grease and oil concen-
tration is clearly evident in Figure 79b. Percent grease and oil decreased
from nine percent to less than two percent in 55 days. Figure 79c shows an
increase in nitrates accompanied by a decrease in total nitrogen concentra-
tion. In approximately 60 days, both parameters achieve equilibrium concen-
trations .
130
-------
TABLE 39. SIWARY OF PARAMETERS - AEROBIC DIGESTION
Beacon Cold Springs Musconetcong Stony Pc. Rockland Poughkeepsle
IA 2A 3A 4A 5A 6A
Days Days Days DayA Days Days
Day Day to ^ Day Day to Day Day co Day Day to Day Day to Day Day to
Paracetc r 0 60 Equ. 0 60 Equ. 0 60 F.qu. 0 60 Equ. 0 60 Equ. 0 60 Equ.
BODng/l
780
140
20
480
50
30
1600
40
40
350
40
35
3300
150
30
1000
100
50
C0D.br/1
4000
1800
40
4700
3000
35
18000
5000
40
5600
2700
30
29000
10000
40
9400
5000
40
SOUR ng 02
(gnVS-hr'
7.8
1.2
20
1.5
0.6
50
7.0
0.4
40
1.9
0.6
25
0.9
0.6
0.8
0.6
TS I
0.45
0.30
35
0.55
.40
-
1.3
0.7
50
0.70
0.47
30
2.4
1.5
20
1.1
0.7
40
VS I
76
f>:
35
65
63
-
70
59
50
60
50
30
50
40
50
60
51
45
SS.Bg/l
3600
2000
20
5200
3 SO 0
40
12000
7000
5C
6400
4000
20
22000
15000
40
9600
6200
40
VSS.ng/t
3000
1600
30
3600
2000
45
aooo
4000
50
tooo
2000
20
11000
8000
-
6000
3600
40
ConJucClv.
(unhos/cu)
900
1320
60
400
480
55
960
1800
50
1200
1400
60
2000
600
50
1240
1160
60
pH
6.8
5.6
45
6.1
6.0
50
6.4
4.0
40
5.4
5.1
40
5.6
7.0
50
5.4
5.4
40
Alk.ng/l
430
20
20
200
30
30
600
0
40
240
0
20
800
360
50
520
40
20
NHj-N mg/l
10
10
40
1.0
1.0
40
6
30
80
8
2
25
10
10
70
4
. 4
60
Org-!! ng/l
470
£0
25
290
140
35
680
140
60
330
90
30
980
100
50
480
140
t>0
CST,Sec
9
10
-
6
6
-
11
18
30
10.5
10.5
-
11
11
0
-
10
35
* *
S.R.
1200
1200
i"
14
14
-
200
1250
30
190
170
-
170
100
-
50
110
-
*
Equilibrium
** |i
Specific Resistance (a/kg)xI0
-------
TABLE 40. SUMMARY OF PARAMETERS - AEROBIC DIGESTION OF ANAEROBIC SLUDGES
Stony
7A
Point(control)
65% Stony
8A
Point + 35%
26 Ward
9A
65% Stony Point + 35%
Jamaica
Parameter
Day
0
Day
60
Days
to
Equil
Day
0
Day
60
Days
to
Equil
Day
0
Day
60
Days
to
Equil
BOD mg/£
130
80
30
1,300
150
15
500
60
30
COD mg/£
8,100
5,200
30
20,500
13,500
35
11,000
7,000
30
mg 0
SOUR —.... .
gmVSS-hr
0.4
0.4
0
2.0
0.5
35
1.8
0.4
25
% TS
0.88
0.72
30
1.75
1.50
25
1.04
0.87
25
% VS
61
57
-
60.0
53.0
40
62.0
57.0
-
SS mg/£
7,100
5,300
40
16,000
13,000
40
9,200
6,500
25
VSS mg/£
4,800
3,550
45
9,600
6,400
30
5,700
4,500
25
Conductivity
umhos/cm
1,600
1,600
0
3,200
4,900
_
2,300
2,600
PH
5.5
4.8
10
8.0
4.1
40
8.0
5.2
35
Alk mg/£
40
15
5
1,600
0
25
1,250
50
25
NH3-N mg/£
0
1
20
315
5
50
250
3
60
Org-N ng/£
310
290
30
670
460
50
360
360
0
CST, sec
17
18
0
25
25
0
16
16
0
*
Spec. Resistance
800
500
-
5,150
6,400
35
5,000
10,000
-
NO^-N mg/£
95
,140
50
60
360
70
60
180
-
TKN mg/£
320
290
35
1,005
485
60
620
350
50
TOTAL-M mg/£
380:
380
0
1,065
830
50
680
530
50
Specific Resistance (m/kg) x 10**
-------
FIGURE 65. Beacon, K.*. Anaerobic Sludge - Aerobic Stability ?ara»eters
-------
BEACON, N.Y.
I-
u>
.c-
10 20 30 i.0 50 60 7U 80 90
10 20 30 40 50 60 70 80 W
FIGURE 66. Beacon, N.Y. and Cold Spring, N.Y. Aerobic Sludges - Aerobic Stability Parameters
-------
FIGURE 67. Cold Spring, N.Y. Aerobic Sludges - Aerobic Stability Parameters
-------
FIGURE 68. Musconetong, N.J. Aerobic Sludge - Aerobic Stability Parameters
-------
MUSCONETCONG
FIGURE 69. Musconetcong, N.J. and Stony Point, N.Y. Aerobic Sludges - Aerobic Stability Parameters
-------
FIGURE 70. Stony Point, N.Y. (Summer) Aerobic Sludge - Aerobic Stability Parameters
-------
FIGURE 71. Stony Point, N.Y. (Winter) Aerobic Sludge - Aerobic Stability Parameters
-------
FIGURE 72. Stony Point, N.Y. (Winter) Aerobic Sludge - Additional Aerobic Stability Parameters
-------
FIGURE 73. Rockland County, N.Y. Thermal Sludge - Aerobic Stability Parameters
-------
ROCKJLA.ND COUNTY, N.Y.
FIGURE 74. Rockland County, N.Y. and Poughkeepsie, N.Y. Thermal Sludge - Aerobic Stability Parameters
-------
OJ
doco '
faOCO
6 -
(b)
vj
•J" COD ri
\ BOD (.""-'AS'.V-)
SOW )
10 2D 30 40 50 to TO ao
(d)
FIGURE 75. Poughkeepsie, N.Y. Thermal Sludge - Aerobic Stability Parameters
-------
FIGURE 76. 26th Ward, N.Y.C. Anaerobic Sludge - Aerobic Stability Parameters
-------
FIGURE 77. 26th Ward, N.Y.C. Anaerobic Sludge - Additional Aerobic Stability Parameters
-------
20 -
lj -
oO
30 >000
^0
50C«
7
VSS(cg,/;. 3:0 )
in jO )0 -0 3'j * 0 c 0
(b)
SOUR (
=8 0._,
gin VSS-hr
;)
3 CI
,L ,
C01) (n3/i SlO )
~~i—"zr-s—s-—
BODj (mg/r.)
: 0 20 30 iO 30 60 70 SO
(c )
10
CONDI C r IV i TV
t_n
3000 600
2 300 300
2000
pH
o o
-C U
ALV.A1.IMTY (ir.g/:)
20 30 40 50 60 70 80
I >00 -
1000
500 100
¦
(d)
0 _ ORGASIC-S (mg/O
Q
G
O u
f c
v - - Q
0
'X
X,
.
AMMOSIA-S (ng/1)
\£--
i t .j i ..ii. hi J * ¦
10 JO 30 UO 50 60 70 hO
FIGURE 78. Jamaica, N.Y.C. Anaerobic Sludge - Aerobic Stability Parameters
-------
FIGURE 79. Jamaica, N.Y.C. Anaerobic Sludge - Additional Aerobic Stability Parameters
-------
ANAEROBIC STABILIZATION
A total of 13 anaerobic digestion units were set up as illustrated in
Figure 61 (Phase I) and Figure 63 (Phase II). In Phase I mixtures of diges-
ted sludge (primary and waste activated) from the Cedar Creek, New York
Wastewater Treatment Plant was used as the seed (Unit 4 served as the seed
control). Sludges fed to the individual units included: Cedar Creek, N.Y.
primary 9ludge (Unit 1), Cedar Creek, N.Y. Waste Activated Sludge (Unit 2),
(Summer Stony Point N. Y. aerobically digested sludge (Unit 3), Rockland
County, N.Y. High Pressure Heat Treated Sludge (Unit 5), and Poughkcepsie,
N.Y. Low Pressure Heat Treated Sludge (Unit 6). In presenting the data from
these units in this section, a correction for the seed was not made. In the
Phase II study no seed was used. Rather the sludges shown in Figure 63
(Units 7-13) were put directly into reactors and maintained from then on
under anaerobic conditions. Actually only the sludge in Unit 7 had not been
subject to anaerobic treatment prior to the additional anaerobic stabiliza-
tion conducted. Units 8, 9 and 10 received anaerobically digested mixtures
of primary and waste activated sludge from three different treatment plants
in which the anaerobic digestion was being conducted at different loadings.
Unit 11 ieceived anaerobically digested primary and trickling filter sludges
and unit 12 received primary sludge only. Unit 13 received anaerobically
digested activated sludge. Table 41 gives the summary data of these anaero-
bic studies, giving the zero and 60 day results and the number of-days
required to reach steady state.
Phase I Seeded Sludges
Cedar Creek N. Y. - Primary Sludge (1)
Figure 80 illustrates the pattern of change for anaerobic stabilization
of this sludge. Both total solids and volatile fraction exhibited signifi-
cant reductions during the first 10 days and reached equilibrium values of
2.3 to 2.and 51 to 52% respectively after 20 days. BOD also declined rap-
idly during the same period and stabilized in the region of 2000 mg/1 within
20 days. COD followed the same pattern but did not stabilize in value until
30 days of incubation. However, SOUR exhibited a different pattern, i.e., an
increase over the first 20 days followed by a leveling off and a slight
trend downward after 40 days. pH exhibited a similar pattern to SOUR except
that the rise to a level value was reached in the first 5 days. Alkalinity
should have slowly increased reflecting the increase in pH and ammonia. Al-
though the alkalinity did increase during the run the data were erratic indi-
cating analytical problems. Gas production (cumulative) and volatile acid
concentration were mirror images of each other indicating stabilization
during the first 10 days. Volatile acids and daily gas production were
essentially negligible after 10 days. As indicated, a continual gradual in-
crease in ammonia-N was observed as was a continuous decrease in organic-N.
Consequently, total nitrogen was essentially constant.
14 S
-------
Cedar Creek N.Y. Waste Activated Sludge (2)
As indicated in Figure 81 the pattern of change in parameters for this
sludge was qualitatively similar to that for Cedar Creek Primary. Within a
10 to 20 day period, % total solids, X volatile solids, BOD, cumulative gas
production, and volatile acids reached steady state values. Here again, pH
remained virtually constant, ammonia-N slowly increased, organic-N slowly de-
creased, and COD reached a plateau in about 30 days. A different pattern was
observed for SOUR which had an initial high rate and reached equilibrium
after 6 days. Alkalinity exhibited a gradual increase over the first 30 days
and then became constant.
Stony Point N.Y.-Aerobically Digested Sludge (3)
These data are presented in Figure 82. Solids destruction in this
sludge was much less obvious than the previous sludges. Total solids de-
creased at a continuous low rate. Volatile solids data exhibited consider-
able fluctuation but also seemed to decrease at a very low rate. The pattern
for the oxygen parameters was also quite different than previously. BOD drop-
off was not as sharp and took almost fifty days to reach a steady value, while
COD decreased relatively quickly reaching equilibrium within 25 days. Over
the first 30 days alkalinity increased rapidly, slowly decreased over the next
20 days and then leveled off. SOUR exhibited a relatively rapid rise before
leveling off at 25 days. The pattern for the other parameters was similar to
that observed before except that it took somewhat longer for the gas produc-
tion to reach steady state.
Cedar Creek Digested Sludge (Seed Material) (4)
This unit represents continued anaerobic digestion of sludge previously
subjected to digestion. The results are given in Figure 83. Volatile solids
and total solids exhibited virtually no change or a low linear rate of de-
crease. COD decrease was significant during the first 20 days but BOD re-
moval was slight over the complete period of digestion. Gas production, vol-
atile acids level, pH, ammonia-N, and organic-N exhibited similar patterns to
that presented previously. The alkalinity pattern is again un3xpected and
probably due to analytical error because alkalinity values are much higher
than justified by the ammonia-N level.
Rockland County Thermal Sludge (High Pressure) (5)
These results presented in Figure 84 are again similar to those from the
units previously discussed. Solids changes were at a relatively low constant
rate. Both BOD and COD dropped off relatively quickly and " ached a steady
state in 20 to 30 days. SOUR and pH remained relatively constant. Alkalin-
ity and volatile acids increased, reaching a steady state value in about 20
to 30 days. No gas production was recorded. These latter data are not reason-
able in light of the reported BOD and COD decreases unless volatile organics
were formed in the thermal process and were released in the completely mixed
digester. Again the general pattern of ammonia-N increase and organic-N de-
crease is noted.
149
-------
Poughkeepsie Thermal Sludge (Low Pressure) (6)
The data for this unit is presented in Figure 85. Virtually no change
in % volatile solids took place but a decrease in total solids from 3% to
2.4% after 30 days was observed. This result appears anomalous unless some
of the fixed solids were destroyed. Actually a fall in % volatile solids
occurred early in the run corresponding to the time period when % TS a3so
decreased, but later in the run the X volatile solids rose again. Analytical
errors are probably the cause of these data. Roth the ROD and COD fell to
steady state values. The ROD reaching steady state in 30 days, while the COD
required almost 50 days. The SOUR exhibited c significant rise to a peak and
then fell during the first 20 days. It remained at its original value for
the remainder of the run. The alkalinity, pH, volatile acids, and gas pro-
duction showed a pattern similar to that observed previously: alkalinity rose
to steady state in 20 days, volatile acids fell to essentially zero in 20
days, pH remained essentially constant, and gas production was almost com-
plete in 20 days. Total nitrogen, ammonia nitrogen, and organic nitrogen
also exhibited their familiar pattern. Ammonia slowly increased, organic
nitrogen decreased, and total nitrogen was constant.
Phase II Unseeded Sludges
Stony Point Aerobically Digested Activated Sludge (7)
The results of the anaerobic digestion of previously aerobically diges-
teJ activated sludge are presented in Figure 86. Total solids showed a
modest decrease from 0.88% to 0.75% in 30 days and then remained essentially
constant; volatile solids also decreased similarly (6Q%-55%). Both COD and
ROD declined in a similar fashion to that observed for the other„anaerobic
units in Phase I. BOD reached steady state in about 20 days at 80-85 mg/1.
COD did not reach steady state for almost 40 days at about 6,500 mg/1. Vola-
tile acids were very low (0-50 mg/1) during the run as was the gas production
of only 3 liters.
The gas production has been plotted as flat but due to the large diges-
ter gas and liquid volume and small production, solubility effects make
interpretation difficult. pH rose over the first 20 days of the run from 5.5
to 6.9 and remained steady. Alkalinity increased from 40 to over 1000 mg/1,
reaching steady state in 50 days. Ammonia slowly increased from 0 to 60 mg/1
over the run and organic nitrogen decreased from 310 mg/1 to 260 mg/1. Thus
total nitrogen remained unchanged. The major difference between the results
here (Unit 7) and for unit 3 was the presence of the anaerobic seed in Unit
3. Some of the reactions were accelerated by the seed some were quantita-
tively due to the decomposition of the seed itself, rather than Stony Point
Sludge.
26th Ward N.Y.C. Anaerobically Digested Primary & Waste Activated Sludge (8)
Figure 87 illustrates these results. Total solids fell from 3.4% to
2.9% at a rather uniform rate for most of the run. Volatile solids fell from
56.3% to 50% over the first 30 days and remained essentially constant. Both
150
-------
COD and BOD reached steady state within 30 days at a COD of approximately
32,000 mg/1 and BOD of about 1,100 mg/1. pH remained essentially constant at
close to 7.2. Alkalinity rose from 4,600 to about 7,500 mg/1 over the first
50 days. Gas production rose rapidly during the first 10 days and then very
slowly increased. Volatile acids dropped sharply to zero in the first few
days and remained at that level. The usual ammonia increase and organic
nitrogen decrease took place. It is interesting to note the discrepancy be-
tween ammonia levels and alkalinity reported here. In an anaerobic digester
the major buffer cation is ammonia. The bicarbonate alkalinity associated
with ammonia is 3.57 mg/1 alkalinity as CaCO^ per mg/1 of ammonia. In most
of these runs the alkalinity was much higher than could be accounted for by
the ammonia level. This may indicate analytical error or the presence of
another buffer system.
Coney Island,N.Y. Anaerobically Digested Primary and Waste Activated
Sludge(9)
The performance of this unit is given in Figure 88. The results are sim-
ilar to those from the previous unit. Total solids decreased from 3.25% to
2.8% gradually over the 70 days of the run. Volatile solids decreased from
59.3% to close to 55% during the first 20 days and then remained constant.
COD declined from 42,000 mg/1 to approximately 34,000 mg/1 in twenty days and
then reached steady state. BOD fell from 4600 mg/1 to 1,000 mg/1 in 35 days.
pH was constant at close to 7.4. Alkalinity gradually rose from 6,600 mg/1
to 12,000 mg/1. Gas production rose rapidly for the first 10 days and slowly
afterward to a value of about 50 liters total. Volatile acids were essenti-
ally zero throughout the run. The typical ammonia increase and organic
nitrogen decrease took place.
Cedar Creek N.Y. Anaerobically Digested Primary and Waste Activated Sludge(lO)
The results of this run are illustrated in Figure 89. This unit is es-
sentially identical to unit 4 of phase I except that the sample being diges-
ted was taken at a different time. Both the % total solids and % volatile
solids decreased slightly in the first 10-20 days and then remained constant
at about 1.6% total solids and 59.5% volatile solids. Both BOD and COD
declined to a steady state in 20-30 days; BOD reached 900 mg/1 and COD 17,000
mg/1. pH increased slightly during the run. Alkalinity rose from 5150 mg/1
to 6,500 mg/1 gradually through the run. Gas production rose rapidly for 5
days and then quite slowly to a total accumulation of 20 1. Volatile acids
were negligible throughout the run. Ammonia nitrogen again increased during
the first 30-40 days and organic nitrogen fell during the same period. In
general the results here were the tame as those for unit 4.
Oyster Bay N.Y. Anaerobically Digested Primary & Trickling Filter Sludges(ll)
This unit represents continued plug flow dt.^e. ':ion of primary and trick-
ling filter sludge previously digested in a complet-. mix digester. As shown
in Figure 90, both solids parameters decreased to a steady state in less than
30 days. Total solids reached 6%, volatile solids approximately 53%. Both
BOD and COD fell to steady state values in 30 to 40 days. BOD reached about
2700 mg/1 and COD 62,500 mg/1. Again pH was fairly constant at close to 7;
151
-------
alkalinity slowly increased from 4,800 mg/1 to 6,800 mg/1 in 40 days and vol-
atile acids were essentially zero throughout the run. Gas production contin-
ued for a slightly longer period than previously and was complete after 20
days with the cumulative production of almost 50 liters. Again nitrogen
forms exhibited the typical pattern. Organic-N decreased from 2,500 mg/1 to
2,000 mg/1. Ammonia rose from 200 mg/1 to 650 mg/1.
Yonkers N.Y. Digested Primary Sludge (12)
These data are given in Figure 91 and can be seen to be typical of the
situation of continued anaerobic digestion of previously anaerobically diges-
ted sludge. Solids decreased at slightly higher rates initially and seemed
to continuously decrease at a slow rate. Total solids reached 2.3% and vola-
tile solids 44%. COD and BOD reached steady state in about 20 days at 25,000
mg/1 for COD and 1,300 mg/1 for BOD. pH was constant at 7.2, and volatile
acids were negligible. Gas production was rapid during the first 10 days and
was leveling off in 30 days at approximately 50 liters total production.
Alkalinity rose from 4,900 mg/1 to 6,300 mg/1 in 10-20 days. Similarly, alka-
linity, ammonia-N and organic-N reached steady state rather quickly in 10-15
days. Ammonia-N increased from 890 mg/1 to 1,300 mg/1 while organic-N fell
from 1,100 mg/1 to 700 mg/1.
Yonkers, N.Y. Anaerobically Digested Waste Activated Sludge (13)
Data for this unit are given in Figure 92. An air leak occurred after
40 days so the data are curtailed. However, these data again show similar
patterns to that observed previously. Here total solids arid volatile solids
reached steady state in 20 to 30 days at levels of 1.65% and 62.5% respec-
tively. COD reached steady state in about 30 days. The BOD data are suspect
so are not discussed here. pH became steady at 7.4 after rising from 6.8
during the first 5 days. Alkalinity rose from 3,500 mg/1 to 6,000 after 10
days. Volatile acids here were originally 140 mg/1 but fell to zero in less
than 10 days. Gas production was complete with 80 1 in 15 days. The nitro-
gen changes observed were somewhat more erratic than previously but the same
rapid rates occurred as in unit 12 and the decrease in organic-N quantita-
tively matched the increase in NH^-N.
Additional Analyses
In addition to the results discussed, periodic measurements of grease
and oil, and sludge filterability were made. Because of occasional errors in
analyses not enough data on grease and oil was collected to yield definitive
trends. In general, approximately 50% destruction of grease and oil was ob-
served in most runs.
Table 41 and Figures 93-96 present the data on the capillary suction
test and specific resistance. It can be seen that little change in these
dewaterability parameters was observed during the 13 anaerobic runs. A few
of the sludges exhibited a trend towards increasing resistance while a few
showed the opposite effect or a decreasing resistance to dewatcring as a re-
sult of extended anaerobic stabilization.
152
-------
TABLE 61. AKALP.OBIC LI!ITS
1 2 3 4 5 6
Day
0
Dav
60
Days
co*
Equ
Day
0
Dav
60
Days
to
Equ.
Dav
0*
Dav
60
Days
to
Equ.
Day
o'
Day
60
Days
Co
Equ.
Day
0
Day
60
Days
Co
Equ.
Day
0
Day
60
Days
Co
Equ.
BODafc/i
5300
2000
15
5600
1300
20
1300
600
25
1400
1000
20
7100
5200
20
3500
1400
30
SOUR
)
gaVS-hr
4.9
6.9
30
9.2
6.6
5
6.2
8.0
25
6.4
7.4
25
6.0
6.0
0
5.8
6.0
20
TS X
3.3
2.2
20
3.0
2.3
:o
1 .9
1.7
20
2.5
2.2
20
4.5
4.1
35
2.9
2.3
30
vs I
62
52
6
62
50
10
56
50
22
51
51
0
48
48
-
51
51
0
COD .sag/I
33750
18000
30
28000
19000
40
20200
13000
30
31000 16000
25
50000
41000
20
30000
19000
50
Crease &
Oil og/t
14.7
6
35
12. I
5.7
_
1 1
6
12.5
5
13
_
_
13.6
5.6
_
PH
6.8
7.5
15
7.3
7.4
0
7.4
7.4
0
7.4
7.4
-
6.9
6.9
0
7.0
7.2
20
Alk.cg/t
6500
8000
30
6000
7900
35
46CO
5600
60
6000
-
-
5600
8200
30
5000
7700
20
VA.eg/l
1600
100
15
1500
20
?0
220
80
10
I00C
50
:o
980
2200
30
760
30
20
gnfl.O)
0
95
10
0
97
10
0
30
15
0
37
15
0
0
-
0
85
10
NIl-j-N
820
960
15
760
960
40
600
770
40
600
1000
40
760
1040
?5
840
960
40
Org-N
1000
740
25
960
660
50
720
520
45
1000
720
30
1400
1190
25
960
6S0
50
CST.Sec
**
s.n.
64
75
-
53
60
-
48
34
-
42
42
-
23
1.5
-
43
56
-
6. 1
15
-
14
15
-
14
12
-
3
14
-
1.5
3
-
4.7
9.4
-
* * * 1'»
Equilibria Specific Rcslscanco (n/kc x 10 )
-------
TABLE 41. (cont'd)
7
8
9
10
Day
0
Day
60
Days
to*
Equ
Day
0
Day
60
Days Day
to 0
Equ.
Day
60
Days
to
Equ.
Day
0
Day
60
Days
to
Equ.
BOD mg/ 9.
130
-
20
3400
2000
20
4500
1800
-
1700
1400
20
TS %
0.88
0.74
30
3.4
2.9
-
3.2
2.9
20
1.8
1.6
0
VS %
60.5
55.5
25
56.4
50.4
30
59.4
54.7
20
63.5
59.1
10
COD,mg/£ 81000
64500
40
41500
31000
25
39500
31500
20
25000 :
17000
30
PH
5.2
6.9
20
7.2
7.4
0
7.2
7.8
0
7.0
7.3
0
Alk.mg/£
40
1100
-
4600
7800
40
5300
6000
40
5200
6000
30
VA.rog/I
30
-
0
48
-
0
0
-
0
0
0
0
Gas,(I)
0
-
0
0
42
20
0
51+
20
0
20+
10
NH^-N mg/£
6.0
53
35
1100
1400
40
835
1350
20
800
950
35
Org-N mg/£
360
275
35
1185
900
40
1200
810
25
980
610
35
CST,Sec
**
S.R.
17
20
-
26
46
-
57
206
-
180
296
-
6.2
2.1
-
2.8
2.6
-
8.6
16
-
10.4
10.9
-
*
Equilibrium
**
Specific
Resistance
(m/kg x
1014)
-------
TABLE 41. (cont'd)
11
12
13
Day
0
Day
60
Days
to
Equ.
Day
0
Day
60
Days
to
Equ.
Day
0
Day
60
Days
to*
Equ
BOD mg/£
4200
2800
30
3100
1300
20
_
__
15
TS %
6.5
6.2
25
3. 1
2.4
20
23
-
20
VS %
57
54
20
57.5
43.8
30
57
54
20
COD.mg/I
72000
63000
30
41500
31000
25
39500
31500
30
pH
6.5
7.2
0
7.3
7.5
0
6.8
6.5
5
Alk.mg/2.
4800
7200
25
4900
6600
10
5100
6500
10
VA,mg/£
0
-
0
25
-
0
1420
-
0
Gasi(£)
0
58+
15
0
50+
30
0
82+
10
NH3-N mg/l
200
600
25
870
1270
15
890
1450
15
Org-N mg/ 9.
2550
2000
10
920
700
10
1250
750
15
CST.Sec
**
S.R.
40
200
-
100
279
-
285
350
-
3.1
14.8
-
10.2
%
98
-
5
26
-
*
Equilibrium
14
Specific Resistance (m/kg x 10 )
-------
FIGURE 80. (Unit 1) Cedar Creek 25% Primary + 75% Seed - Anaerobic Stability Parameters
-------
U1
^4
IO lO 30 40 SO GO 70 flO
(c)
MjLAUhJlTY (*"Vc&Ol)
fl 'j£ w—o-e—e-°-®-o-
&
-o
"*~1 S*5 (f)
— i—L-O
r .oc^t)
5 00
A A
P"
coo rytsid
m*~7. A—
1 A
s
I • *~i
-
Q 1 U U1 O
> ° ° Q SOUR
~
ft ft BOD i-y*sio>)
o - u u u
O
50
IC
•O 70 30 to 7o 8o
IO 2D 3D
so
to 70 OD
(d)
i
a
n
o
MO
cm
Htrloaoi l*"Y0 O
UtD
. .
0 SKS*nQ
tCDO
•
*&-0
o
¦»-—£-
A
A CMMC /H/A
M-T^OeO'l
.
IO to 3o
40
wir
SO
to id eo
FIGURE 81. (Unit 2) 25% Cedar Creek Activated Sludge - 75% Seed - Anaerobic Stability Parameters
-------
FIGURE 82. (Unit 3) 35% Stony Point + 65% Cedar Creek Seed
- Anaerobic Stability Parameters
-------
Ln
vO
(a)
foo—a— rrr
a _ Q ~
u J TbVS (Slo','
LC-Oo—o—OQ-oOo-n - Cl_
-OtJ-
V0T5
I I I I I I I L_
10 20 30 AO SD to 70 BO
••AfJ
17.
(c)
ALK.rvi
8 -
(b)
a a «
o a
CQE>(*"*/k$lOV)
aO ^
JO 2D JO
£ODt^/jB_^k5TT
SO 60 70 &0
ieco ¦
I boo
MOO
190Q
roq^l
(d)
o a totaL (~j/ \
NnTOBEKl*. M
a
»«»CmiA / w/ V
— n W
NITCCfcCM I
CO o
£ A
vimctoH -/a)
IO 20 iO 40 SO "70 90
iAfJ
FICURE 83. (Unit 4) Cedar Creek Seed - Anaerobic Stability Parameters
-------
FIGURE 84. (Unit 5) Rockland County Thermal Sludge + 75% Seed
- Anaerobic Stability Parameters
-------
FIGURE 85. (Unit 6) 25% Poughkeepsie Thermal Treated Sludge + 75% Seed - Anaerobic Stability Parameters
-------
UA^S DAYS
FIGURE 86. (Unit 7) Stony Point Aerobic Sludge - Anaerobic Stability Parameters
-------
<3\
u>
(a)
^—l«i & A.«.A,S
X V5
'C 1 '* ~ i»
¦ — %¦ T5- (510 : )
_i I I I 1—: i L
0 10 20 30 40 SO 60 70 80
DATS
'
A1K {ag.lt S10 )
¦ ^ <**1 \
t=
-£> -i.
" ££>
1000
(d)
NiyH (»gyt)—
oau-.i Cag/O
o : ° %
o
io :u io
*0 50
\)A\S
60 70 80
FIGURE 87. (Unit 8) 26th Ward Anaerobic Sludge - Anaerobic Stability Parameters
-------
¦C*
5000
. 4000
-.-WOO-
2000
(b)-
. I !._ ! ...i ...
^ ; . £
-33-r
"V X ¦*'
r3T-..
>Y !' !| "-¦
•— ¦
iooo —
" 10 -pj-
_i ! I i i i :—1 i L
10 20 It) iO 50 • 60 71) 80
' D)\TS '
(c) i
0 10 20 30 40 50 60 70 t>6
i "" " DAVS ! ' !
• '--jz
& ±
S' '
r%~~
ALK (sg/t)
^ .
A •
9. pH
£ .
-a* CUM. GAS (t S101)
-1
f. , . * T * ,VA (P|
g/i sio )
8000 ' 3000
7000 - '
6000 ; 2000
5000
¦ looolr"^
__!". :
... TOTAL-N. (ag/'i)
t» 0
* —E)
g~: —p-Q—D ~—
• • -au-N (t«g/s>-:;
A 3 A» A
&
o-
A J.
OKG-H (mg/?) '
10 JO 30 AO 50 OU 70 80
DAYS
10 20 30 UO 50 60 70 80
DAYS
FIGURE 88. (Unit 9) Coney Island Anaerobic Sludge - Anaerobic Stability Parameters
-------
FIGURE 89. (Unit 10) Cedar Creek Anaerobic Sludge - Anaerobic Stability Parameters
-------
FIGURE 90. (Unit II) Oyster Bay Anaerobic Sludge - Anaerobic Stability Parameters
-------
FIGURE 91. (Unit 12) Yonkers Anaerobic Sludge - Anaerobic Stability Parameters
-------
o¦>
00
<.¦>)
100
A ~V5 ¦
2 0
Q "? ft O
J l_
J TS (S
-1- —
10 :)
_i : i i l
5000
4000
j3(H)0-
2000
1000
(b)
a: ¦¦
.. ..
\ : . "--A
\; - =•
.• : cod iaiJii sio >
_ o
:"o~—o.
J I I 1
BPD,i(ap~/R j ' = •" :':'f
0 10 20 30 40 50 60 ' 70 80
-1500
•1000
: A
^ * : Nrf3-N (ragII '
% / - *
y ¦
o
0RC-S(=;;/i
500 -
0 10 :0 30 -0 50 60 70
' I I 1 I 1 1 1—
0 10 :0 30 40 50 60 70 no
FIGURE 92. (Unit 13) Yonkers Anaerobic Sludge - Anaerobic Stability Parameters
-------
o>
vO
80
40
20
UNIT I
-
o
' . v
O
—
o
-
-
o
-
i J
c
-
0
a
1
1
i i
• i
"
20
40
DAYS
60
80
w 80
i
H . _
V) 60
o
40
20
UNIT 3
O
n
u:
-D n-
J
18
16
14
12
10
a
6
20 40 60 80
. DAYS ,,
S.R. Specific Resistance (m/lcg x 10 )
u
80
60
40
20
UNIT 2
o o
CL
7F
I I I
20
40 60
DAYS
DAYS
20
1 6
12
8
4
80
FIGURE 93. Capillary Suction Test and Specific Resistance - Units 1-4
-------
80
60
40
20
UNIT 5
80 .
u 60 .
tA
I
t/i
U
2C
Ia—
20
40
60
DAYS
UNIT 7
O CJ o-
_2 2_
n
. d» b—¦—°—n g^j
20
40
60
DAYS
80
80
S.R. Specific Resistance (m/kg x 10 )
DAYS
FIGURE 94. Capillary Suction Test and Specific Resistance - Units 5-8
-------
2 50
200
v> 150
v) 100
50
•
UNIT 9
¦
0 - ° o
° «
1
0
>
o
/
J
L_a y
a
i
0 20
40
DAYS
60
80
UNIT 12
250
200
u 150
10
8
6
U
2
0
S.R. Specific Resistance (o/kg x 10 ")
FIGURE 95. Capillary Suction Test and Specific Resistance - Units 9-12
-------
600
500
400 -
DAYS
JL 1 A V
S.R. Specific Resistance (m/kg x 10 )
FIGURE 96. Capillary Suction Test and Specific Resistance - Unitl3
-------
SECTION 8
DISCUSSION OF RESULTS
CHARACTERISTICS OF SLUDGES
Tables 34, 35,36 and 37 present the characteristics of all of the
sludges used in this study. It can he seen that both the aerobic and anaero-
bic sludges exhibited a wide range of processing characteristics. Sludges
were taken from highly loaded activated aludge plants and those loaded at
modest levels. The detention time in aerobic digestion that the sludges ex-
perienced prior to being collected for these experiments was in one case less
than one day and in another case as long as 21 days. The HRT of the anaero-
bic sludges ranged from 13 days to 35 days. The feed to the anaerobic diges-
ter included raw primary sludge, waste activated sludge alone and mixtures of
raw primary and waste activated or trickling filter sludges. In general all
of the sludges used were within the range of processing parameters normally
used in practice.
AEROBIC DIGESTION OF SLUDGES
Nine sludges, five which had been subjected to aerobic treatment, two
which had been subjected to heat treatment, and two which had been subjected
to anaerobic digestion, were aerobically digested in the studies conducted
under this project. A summary of the pertinent data is presented in Tables
39 and 40. These data were selected from the plots of Figures 65 through 79.
The selected data in Tables 39 and 40 include the sludge parameter at time 0,
after 60 days of digestion and the time required to reach a steady state
value of the parameter. A total of 15 sludge parameters are recorded in
these tables. Rather than discuss these individually they will, in the dis-
cussion which follows, be grouped as follows: solids parameters, oxygen
demand parameters, pH-alkalinity-conductivity, nitrogen forms, dewatering
characteristics-grease.
Aerobic Digestion of Aerobic Sludges
Similar patterns of change in parameter magnitudes were observed for all of
the aerobic sludges (Beacon, Cold Springs, Musconetcong, Stony Point summer
and Stony Point winter). In most cases, all forms of solids decreased rela-
tively quickly over the first 20-30 days and then rather slowly. Oxygen
demand exhibited a similar pattern with higher fractional decreases in BOD
and SOUR than COD. Only the Stony Point winter sludge was different, exhib-
iting virtually no change in SOUR. However, the final SOUR of this sludge
was the same 0.4 mg O^/g VSS-hr as for all the other aerobic sludges. Per-
haps the low initial BOD of the Stony Point winter sludge (130 mg/1) accounts
for the constant SOUR.
173
-------
All changes in pH-alkalinity and conductivity were similar, again with
the minor exception of the Stony Point winter sludge. Alkalinity rapidly
decreased to quite low levels in about 20 days; less than 10 for Stony Point
winter. The pH first decreased to a minimum over the first 20 days (usually
into the pH range 4-5) and typically returned to the original pH value. The
conductivity exhibited the reverse pattern, first rising and then falling.
The conductivity peak occurred a few days after the pH minimum. The Stony
Point winter sludge exhibited essentially no change in conductivity or pH.
The shift in conductivity is a response to the increase in hydrogen ion con-
centration (low pH) because of the high specific conductance of this ion.
The nitrogen forms pattern was again similar for all units except the
Stony Point winter sludge. Organic nitrogen decreased rapidly as a result of
the endogenous metabolism of the cellular material. The nitrogen is released
into the liquor in the form of ammonia resulting in the initial increase of
this nitrogen form. Ammonia removal primarily by nitrification and to a
minor extent by stripping takes place concurrently. Once the organic nitro-
gen breakdown is complete there is no feed of ammonia to the system so the
ammonia level peaks and starts to decrease. It is important to note that
this ammonia peak correlates well with the stabilization of SOUR, BOD, organ-
ic nitrogen and to a lesser extent, with alkalinity. Undoubtedly the pH
changes observed are due to the changes in nitrogen forms and stripping of
ammonia and carbon dioxide. Unfortunately, measurement of nitrate in solu-
tion and ammonia and carbon dioxide in the off gas of aerobic digesters was
not conducted. It appears that the Stony Point winter sludge was well diges-
ted prior to the start of the run. The specific resistance and CST measure-
ments indicated in general no significant change as digestion proceeded,
although there was a tendency for a rise and fall pattern as shown on several
of the curves.
In all cases, significant grease removal Look place (greater than 50%)
over the first 20 to 30 days for all sludges. This along with nitrate forma-
tion may account for the drop in pH observed during the initial period of
stabi]ization.
Aerobic Decomposition of Heat Treated Sludges
The heat treated sludges (Rockland and Poughkeepsie) exhibited similar
patterns of change in solids, oxygen demand, nitrogen forms and grease as for
the aerobic sludges discussed above. However, the pH pattern was different.
For both of these sludges the pH first rose and then*returned to near the ori-
ginal level. This rise then fall is what would normally be expected in batch
aeration of sludge rather than the pattern observed previously because as
ammonia is released during protein breakdown, ammonium bicarbonate would tend
to be formed first followed by nitric acid as nitrification of the ammonia
occurs. It may be that in the five aerobic sludges discussed above, a large
population of nitrifiers was present at time "0" which would foster rapid ini-
tial nitrification; while heat treatment would retard nitrifiers, thus delay-
ing the onset of nitrification. Figure 74 indicates that specific resistance
decreases and CST remained constant for one of these sludges while there was
an increasing trend for both parameters with the other sludge. No reason can
be given for this pattern.
174
-------
Aerobic Digestion of Anaerobically Digested Sludges
The pattern of parameter change with time of aeration was again similar
to that observed previously in aerobic stabilization. The main area of dif-
ference was in the pH-conductivity pattern and in the ammonia nitrogen pat-
tern. For aerobic digestion of anaerobic sludge it was found that pH rapidly
decreased and then remained constant while conductivity rose as pH fell. The
ammonia nitrogen a<. time zero was at a high level (due to protein breakdown
under anaerobic ci nditions with no possibility of nitrate formation). Both
the organic and anmonia nitrogen decreased with time as aerobic stabilization
converted ammonia to nitrate. Thus no ammonia peak was observed. The speci-
fic resistance rose while the CST remained constant.
SUMMARY OF AEROBIC STABILIZATION
The results obtained for aerobic decomposition indicate a consistent pat-
tern set for a group of parameters. All forms of solids, all forms of oxygen
demand, grease, alkalinity and organic nitrogen typically exhibited a rela-
tively rapid decrease to a steady state value. The decreasing pattern could
probably be fit by a first order or retardent type of curve. Changes in pH,
conductivity, ammonia nitrogen, specific resistance and CST depended on the
source of the unstabilized sludge. The changes in these latter parameters
were consistent within each sludge source and depended on the initial popula-
tion of nitrifiers present and the initial level of ammonia nitrogen.
Although a reproducible pattern of change in a number of common para-
meters was observed, no quick test emerged to indicate when sludge could be
considered stabilized. Perhaps the specific 0^ uptake rate (SOUR) parameter
could prove to be valuable as an indicator of stabilization as most sludges
seemed to stabilize in the 0.4-1.0 mg 0?/gm VSS»hr. Being a specific para-
meter, it has the advantage of giving the same answer for most aerobic
sludges. Other parameters such as solids, COD, etc. will have variable con-
centrations when stability is reached, depending on the concentration of the
original sludge. Therefore for the individual treatment plant, which would
typically operate at uniform concentrations, a sludge could be considered
stable in respect to any of the parameters tested, when given aerobic treat-
ment as provided in these experiments. For example, when given 30 to 40 days
of aerobic digestion treatment, a sludge would be stable in respect to COD.
In genpral, stabilization occurred in the detention period of 20 to 40 days
as evidenced by stpady state values for a number of parameters but continuous
testing with time is required to identify the stabilization pattern.
ANAEROBIC DIGESTION OF SLUDGES
Thirteen sludges were subjected to prolonged anaerobic stabilization.
These included raw sludges, mixtures of raw sludge and waste activated or
trickling filter sludge, waste activated sludge alone, heat treatment sludge,
sludge which had been previously anaerobically digested and sludge which had
been previously aerobically digested. A summary of the parameter changes ob-
175
-------
served is given In Table 41. These values were selected from Figures 80
through 92.
A similar pattern of changes in measured parameters was observed for all
of these units regardless of the source of the sludge. There are several dis-
continuities in the general patterns observed but these are felt to be due to
experimental difficulties which were discussed previously rather than basic
differences in the pattern of stabilization. Quantitative differences between
units can be traced to the degree of stabilization which had taken place in
these sludges prior to the start of the stabilization in this study.
The basic pattern observed includes:
1) Modest continuous decreases in both total and volatile solids. In some
cases a rapid initial decrease took place followed by a slow gradual de-
crease .
2) Relatively significant reductions in BOD and COD in a 20 to 30 day
period, with the BOD genera]ly decreasing more rapidly than the COD.
3) A rapid decrease in volatile acids occurred concurrent with gas produc-
tion except for unit 6 Rockland County thermal sludge which probably was
inhibitory and volatile acids increased to 2200 mg/J1. Except for unit
6, gas production ended when the volatile acids were consumed. As would
be expected, alkalinity rose as the volatile acids ''ell. pH exhibited
little change except for an occasional slight rise uuring the gasifica-
tion period in some units.
A) Organic nitrogen decreased and was almost exactly balanced by an ammonia
nitrogen increase. This is anticipated as under anaerobic conditions all
nitrogen released from organic breakdown must be in the ammonium ion
form. The rate of change in these parameters decreased as the run pro-
gressed until steady state was achieved.
5) As indicated previously, essentially no change in sludge filterabilitv
took place and grease was reduced typically by more than 50%.
LEAD ACETATE-HYDROGEN SULFIDE ODOR TEST
One of the tests described in the experimental procedures section was
the centrifuge button test. In this procedure the stability of a centrifuged
button of sludge is determined by the length of anaerobic incubation required
to blacken a lead acetate paper. The release of H0S is the agent for blacken-
L.
ing the paper. The more stable the sludge, the longer it should take to
blacken the paper. Test results obtained during the Phase I porcion of the
study are given in Figures 97 and 98. In Figure 97 are plotted the results
of the anaerobic stabilization of the sludges in units 1 through 6. It can
be seen that all sludges were relatively unstable at time zero except unit 3
which contained seed plus aerobically digested sludge. The most unstable
sludge initially was unit I which contained primary sludge and turned the
lead acetate paper black in one day. After 10 to 15 days stabilization, a
sudden change took place in that unit 1 became the most stable sludge followed
bv unit 4, the seed control. Unit 2 containing activated sludge became more
stable than unit 3 which contained aerobically digested sludge. Units 5 and 6
were equally unstable at time zero according to this test but as the run pro-
176
-------
FIGURE 97. Lead Acetate - Hydrogen Sulfide Odor Test - Anaerobic Sludges
-------
Aerob i c Units
o 1A - Beacon (0.4% T.S.)
A-2A Cold Spring ((h6%)-
~ 3A - Musconeitcong (1.3%)
5A (2.5) A AA - Stony Point (0.7%)
- - • - -- • 5A Stony-Point"+ Rockland~(2.-5%)—j—
9 6A - Stony Point +, Poughkeepsie (1.1%)
(:T . S Total Sojl id s )| - i
Total Solids
DIGESTION TIME, DAYS
FIGURE 98. Lead Acetate - Hydrogen Sulfide Odor Test - Aerobic Sludges
-------
gressed, unit 6 became more stable than unit 5 but both were unstable with
respect to odor production. To some extent these results mirror the rate of
stabilization observed uith other parameters in the runs previously described.
For example, unit 5 parameters plotted in Figure show minimum stabilization
and it can be observed that no gas production took place a'nd-volatile acids
increased thus supporting the lead acetate-H^S results. However, the data
from Figures 81 and 82 indicate that units 2 and 3 do not clearly show that
either unit stabilized more quickly than the other, but the centrifuge button
test clearly shows that unit 2 stabilized faster than unit 3..
Figure 98 shows the results of the centrifuge button test for the
aerobic units of Phase I. It is evident that over the first 15 days of
digestion time all the sludges are fairly unstable as they discolored the
lead acetate paper in 1 to 5 days. By 20 to 30 days of digestion time,
however, the results show a significant stabilization has taken place for all
sludges. Sludges 5A and 6A contained heat treated sludges and Stony Point
sludge as seed and are amongst the slowest to be stabilized as would be
expected. The only apparent reason why sludges 3A and 4A should be less
stable than sludges 1A and 2A is that they had higher concentrations of
solids and could produce more gas. The results achieved indicate some
validity to this test procedure but much more work on the test details
previously discussed in Section 6 is needed before it can be used as a
reliable indicator of sludge stability. In addition, pH differences can
affect the rate of H^S evolution. The presence of nitrate
will prevent formation, and the I^S content of gas in the test chamber
which produces a specific color change must be determined. Perhaps the test
could be modified so that a sulfide monitor is used to directly measure the
sulfide level in the gas phase. Also it should be noted that there are many
other compounds which can contribute odor problems in addition to hydrogen
sulfide gas, such as mercaptans, indoles and various other nitrogen and sul-
fur containing organics. But in general, hydrogen sulfide is the most common
cause and readily identifiable odor associated with sludges and the lead ace-
tate test shows promise as an indicator of the odor production potential of a
sludge.
The anaerobic stabilization tests and parameter changes described suffer
from the same deficiency as that for the aerobic stabilization, i.e., as yet
there is no absolute standard of sludge stability. Thus, the parameter change
with time of stabilization must be traced. A simple, easy, one-time parameter
measurement or combination of measurements for assessing sludge stability was
not developed.
179
-------
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180
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17. Rudolf, W., "Gas Yield from Sewage Sludge", Sewage Works Journal, 4,
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18. Novak, J.T., and D.A. Carlson, "The Kinetics of Anaerobic Long Chain
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19. Sawyer, C.N., and H.K. Roy, "A Laboratory Evaluation of High-Rate
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20. McCarty, P.L., "Kinetics of Waste Assimilation in Anaerobic Treatment",
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D.C. (1966)
21. Woods, C.E., and J.F. Malina, "Stage Digestion of Wastewater Sludge",
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22. Maly, J., and H. Fadrus, "Influence of Temperature on Anaerobic Diges-
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23. Rankin, R.S., "Digestion Capacity Requirements", Sewage Works Journal,
20, 478 (1948)
24. Estrada, A.A., "Design and Cost Considerations in High Rate Sludge
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25. Estrada, A.A., "Anaerobic Digestion Discussion", Proceedings of a
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26. Downes, J.R., "Gas Collection and Sludge Heating", Sewage Works
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27. Schlenz, H.E., "Standard Practice in Separate Sludge Digestion",
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28. Parker, D.G., C.W. Randall, and P.H. King, "Biological Conditioning
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29. Tavery, M.A., and J. Nelson, "New Problems Can Occur With Anaerobic
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30. Jeris, J.S., "Analysis of Anaerobic Digestion Sludge Processing and
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Facility, Nassau County Department of Public Works (1979)
181
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r.'i REFERENCE (cont'd)
r
I
31. Unpublished Pilot Plant Monthly Data of 100% Activated Sludge Digestion
conducted by County Sanitation Districts of Los Angeles County (1979)
32. Austin, S.R., J.R. Livingston, and L. Tortorici, "Waste Activated
Sludge Processing", County Sanitation Districts of Los Angeles
County. (1979)
33. O'Rourke, J.T. "Kinetics of Anaerobic Treatment at Reduced Temper-
atures", Doctoral Dissertation, Stanford Univ.* Palo Alto, Ca. (1968)
34. Malina, J.F., "The Effect of Temperature on High-Rate Digestion of
Activated Sludge" 16th Purdue University Industrial Wastes Conference,
232 (1961)
35. Eckenfelder, W,W. "Mechanisms of Sludge Digestion", Water and Sewage
Works, 114, 207 (1967)
36. Torpey, W.N., and N.R. Melbinger "Reduction of Digested Sludge Volume
by Controlled Recirculation", JWPCF, 39, 1464 (1967)
37. Torpey, W.N., "High-Rate Digestion of Concentrated Primary and Acti-
vated Sludge", Sewage and Industrial Wastes, 26,479 (1954)
38. Torpey, W.N., "Loading to Failure of a Pilot High-Rate Digester",
Sewage and Industrial Wastes, 26,479 (1955)
39. Pfeffer, J.T., M.Leiter, and J.R. Worlund, "Population Dynamics in
Anaerobic Digestion", JWPCF, 39, 1305 (1967)
40. Swanwick, J.D., W.J. Fisher and M.Foulkes, "Some Aspects of Sludge
Technology including New Data on Centrifugation", Water Pollution
Manual, Thunderbird Enterprises, Harrow, 141 (1972)
41. White M.J.D., R.C. Baskerville, and C.F. Lockyear "Continuous Thicken-
ing of Biological Sludges, and the influence of Stability" Water Pollu-
tion Control. P. 86, (1977)
42. Tebbutt T.H.Y., and M.J.D. White, "Sludge age and Stability", NATO
Advanced Study Inst., University of Delaware, Newark, Delaware, (1979)
43. Dague R.R., "Fundamentals of Odor Control", JWPCF, 44,593 (1972)
44. Eikum A.S. and B. Paulsrud, "Methods of Measuring The Degree of Sta-
bility of Aerobic Stabilized Sludges" Water Research, 11,763 (1977)
45. "Standard Method of Test for Odor in Water, American Society for
Testing and Materials D1292 (1975)
46. Standard Methods, 14th Edition, APHA-AWWA-WPCF. (1975)
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REFERENCES (cont'd)
47. Ruffer, H. (1966) "IJntefstichunger Zur Characterisierung Aerob
Biologisch Stabilisierter Schlamme", Vom Wasser, Band 13 pp.
255-282 (From Eikum A.S. 1973, ph.D Thesis)
48. Schepman B.A., and C.F. Cornell, "Fundamental operating Variables in
Sewage Sludge Filtration", Sewage and Industrial Wastes, 28, 3443
(1956)
49. Halff, A.H., "An Investigation of The Rotary Vaccuum Filter Cycle as
Applied to Sewage Sludges", Sewage and Industrial Wastes. 24,962 (1952)
50. Trubnick, E.H., and P.K. Mueller, "Sludge Dewatering Practice", Sewage
and Industrial Wastes. 30,1364 (1958)
51. Burd, R.S., "A Study of Sludge Handling and Disposal", Water Pollution
Control Research Series, Publication WP-20-4.
52. Bennett, E.R., D.A. Rein, and K.D. Linstedt, "Economic Aspects of Sludge
Dewatering and Disposal" ASCE. 99,55 (1973)
53. Morris, R.H., "Polymer Conditioned Sludge Filtration", Water and Wa9tes
Engineering, 2,68 (1965)
54. Albertson, O.E., and E.J. Guidi, "Advances in The Centrifugal Dewatering
of Sludges", Water Works and Wastes Engineering, R-133 (1967)
55. Parker, D.C., C.W. Randall, and P.H. King, "Biological Conditioning for
Improved Sludge Filterability", JWPCF, 44,2067 (1972)
56. McKinney, R.E., H.E. Langley and H.D. Tomlinson, "Survival of Salmonella
Typhosa During Anaerobic Digestion", Sewage and Industrial Wastes, 30,12
(1959)
57. Peterson, J.R., C. Lue-Hing, and D.R. 7,eng, "Chemical and Biological
Quality of Municipal Sludge", in Recycling Treated Municipal Wastewater
and Sludge through Forest and Cropland, W.E. Sopper and L.T, Kardos,
Eds. (University Park, PA: Pennsylvania State University Press) (1973)
58. Palfi A. "Survival of Enterovirus during Anaerobic Sludge Digestion",
Proc. 6th Int. Wat. Pollut. Res. Conf. (1972)
59. Eisenhardt, A., E. Lund, and B, Nissen, "The Effect of Sludge Digestion
on Virus Infectivity". Water Research, 11, 579 (1977)
60. Bertucci, J.J., C.Lue-Hing, D. Zeng, and S.J. Sedita, "Inactivation of
Viruses during Anaerobic Sludge Digestion" JWPCF, 49, 1642 (1977)
61. Sanders, D.A., J.F. Malina, Jr. B.E.Moore, B.P. Sagik, and C.A. Sorber,
"Fate of Poliovirus during Anaerobic Digestion". JWPCF, 51, 333 (1979)
183
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REFERENCES (Cont'd)
Moore, B.E. et al, "The Effect of High Rate Anaerobic Digestion on
Viruses." Paper presented at 49th Annual Conf., WPCF, Minneapolis,
Minn. (1976)
K 63. Ward, R.L. and C.S. Ashley, "Inactivation of Poliovirus in Digested
Sludge." Applied Environ. Microbiol., 31, 921 (1976)
Y 64. Dorcey, A.H.J, and R.S. Love, Public choice and the land application of
municipal wastewaters and sludges. In: Risk Assessment and Health
Effects of Land Application of Municipal Wastewaters and Sludges, B.P.
Sagik and C.A. Sorber, eds. Center for Applied Rasearch and Technology,
The University of Texas at San Antonio, pp. 303-324. (1978)
X 65. Geldreich, E.E., "Bacterial populations and indicator concepts in
feces, sewage, stormwater and solid wastes" 51-97, In: "Indicators of
viruses in water and food" edited by Berg, G., Ann Arbor Science (1978)
66. Englande, A.J., "Fate of Parasites and Viruses". NATO Advanced Study
Institute Univ. of Delaware (1979)
67. Liebmann H., "Parasites in Sewage and the possibilities of their
extinction". Adv. in Wat. Pollution Res. Proc. 2nd Int. Conf., 269,
(1964)
68. Hays, B.D., "Potential for Parasitic Disease Transmission with Land
Application of Sewage Plant Effluents and Sludges". Water Research,
11, 583 (1977)
69. Cram, E.B. "The Effect of Various Treatment Processes on The Survival
of Helminth Ova and Protozoan Cysts in Sewage". Sewage Works Journal,
15, 1119 (1943)
70. Ruchhoft, C.C., "Studies on the Longevity of Bacillus Typhosus in
Sewage Sludge". Sew. Works Jour. 6, 1054 (1934)
71. McKinney, R.E., H.E. Langley, and H.P, Tomlinson, "Survival of Sal-
monellae Typhosa During Anaerobic Digestion" Sew. and Ind. Wastes,
30, 1469 (1958)
72. Mom, C.P., and C.O. Schaeffer, "An investigation into the Hygienic
Significance of Sewage Purification in the Tropics in Regard to Typhoid
Fever". Sew. Works Jour., 12,715 (1940)
73. Kabler, P. "Removal of Pathogenic Microorganisms by Sewage Treatment
Processes". Sew. and Ind. Wastes, 31, 1373 (1959)
74. Cooke, M.B., E.L. Thackston and G.W, Malaney, Water and Sewage Works,
50, 125 (1978)
W-
• )
I
i
:62.
184
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REFERENCES (Cont'd)
75. Ahlberg, N.R., and B.I. Boyko, "Evaluation and Design of Aerobic
digesters'". JWPCF, 44,634 (1972)
76. Koers, D.A., and D.S. Mavinic, "Aerobic Digestion of Waste Activated
Sludge at low Temperatures". JWPCF, 49,460 (1977)
77. Hartman, R.B., D.G. Smith, E.R. Bennett, and K.D. Linstedt, "Sludge
Stabilization through aerobic digestion". JWPCF. 51, 2353 (1979)
78. Eikum, A.S. "Aerobic Stabilization of Primary and Mixed Primary/Chem-
ical (Alum) Sludge" Ph.D Thesis. University of Washington (1973)
79. Hartman, R.B., E.R. Bennett, and K.D. Linstedt, "New Procedure Deter-
mines Aerobic Sludge Stability". Water and Sewage Works. p. 42 (1978)
80. Viraraghavan, V. "Digesting sludge by aeration", Water Works and Wastes
Engineering 2, Sept. 1965.
81. Eckenfelder, W.W., Jr. and C.J. Sathanam, "Sludge Treatment", Chapter 8,
Marcel Dekker, Inc., New York (1981)
82. "Secondary and Tertiary Treatment", Manhattan College Summer Institute
Course Text, Chapter I (1981)
83. Reynolds, T.D. "Aerobic Digestir i of Thickened Waste Activated Sludge."
Proceedings 28th Purdue Industrial Waste Conference. Purdue University,
Lafayette, Indiana (1973)
84. Jaworski, N., G.W. Lawton, and G.A. Rohlich "Aerobic Sludge Digestion".
Int. J. Air and Water Poll. 4,106 (1961)
85. Patterson, J.W., P.L. Breznick, and H.D. Putnam, "Measurement and
Significance of Adenosine Triphosphate in Activated Sludge" Environ-
mental Science & Technology, 4, 569 (1970)
86. Brezonik, P.L., and J.W. Patterson, "Activated Sludge ATP-Effects of
Environmental Stress" ASCE, SA6, 8-13 (1971)
87. Weddle, C.L., and D. Jenkins, "The Viability and Activity of Activated
Sludge". Water Research, 5, 621 (1971)
88. Haug, R.T., "Sludge Processing to Optimize Digestibility and Energy
Production" JWPCF 49,1913 (1977)
89. Haug, R.T., D.C. Stuckey, J.M. Gossett, and P.L. McCarty, "Effect of
Thermal Pretreatment on Digestibility and Dewaterability of Organic
Sludges". JWPCF, 50,73 (1978)
90. Brooks, R.B., "Heat Treatment of Activated Sludge", Water Pollution
Control, 67, 592 (1968)
185
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REFERENCES (Cont'd)
91. Marshall, D.W., W.J. Gillespie, "Comparative Study of Thermal Techniques
for Secondary Sludge Conditioning", Proceedings of the 29th Ind. Waste
Conf., Purdue Univ. Press, Ind., 589 (1974)
92. Brooks, R.B., "Heat Treatment of Sewage Sludge", Water Pollution Control,
69, 92 (1970)
93. McCarty, Perry, Lilly Y. Young, Joseph B. Healy, Jr., William F. Owen,
and David C. Stuckey. "Thermochemical Treatment of Lignocellulosic and
Nitrogenous Residuals fcr Increasing Anaerobic Biodegradability", Annual
Fuels from Biomass Symp. 2nd Proc. , p. 787-821. (1978)
94. Lebrun, T.J. and L.D. Tortoric, LA/OMA Thermal Treatment Anaerobic Diges-
tion Study. July, 1978. Study conducted by Research Section County
Sanitation Districts of Los Angeles.
186
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11
12
13
14
15
16
23
24
25
27
28
30
1GU1
1
2
3
4
5
6
8
9
13
14
15
17
18
19
20
21
22
25
APPENDIX
Tabulation of Copyright Holders
Who Granted Permission to Reproduce the Tables
and Illustrations Indicated
Literature
Page Citation Copyright Holder
17 31 Los Angeles County Water Pollution
Control Districts
18 32 Los Angeles County Water Pollution
Control Districts
31 41 Water Pollution Control Federation
31 41 Watet Pollution Control Federation
32 42 University of-Delaware
32 42 University of Delaware
34 1 Ann Arbor Science Publishers
40 50 Water Pollution Control Federation
47 64 University of Texas
47 65 Ann Arbor Science Publishers
48 61 Water Pollution Control Federation
54 68 Pergamon Press
55 1 Ann Arbor Science Publishers
63 78 University of Washington
5 2 American Association for the Advance-
ment of Science
5 23 Water Pollution Control Federation
13 25 Manhattan College
19 32 Los Angeles County Water Pollution
Control Districts
20 22 Water Pollution Control Federation
22 33 Stanford University
25 39 Water Pollution Control Federation
25 22 Water Pollution Control Federation
29 40 Water Pollution, Harrow, England
35 48 Water Pollution Control Federation
36 52 American Society of Civil Engineers
39 52 American Society of Civil Engineers
39 59 Pergamon Press
39 59 Pergamon Press
49 61 Water Pollution Control Federation
50 61 Water Pollution Control Federation
51 61 Water Pollution Control Federation
56 75 Water Pollution Control Federation
187
-------
Illustration
Page
Literature
Citation
Copyright Holder
(FIGURE)
26
58
76
Water Pollution Control Federation
27
59
77
Water Pollution Control Federation
28
61
44
Pergamon Press
29
62
44
Pergamon Press
30
62
44
Pergamon Press
32
65
77
Water Pollution Control Federation
33
66
77
Water Pollution Control Federation
34
67
77
Water Pollution Control Federation
37
71
82
Manhattan College
39
73
83
Ann Arbor Science Publishers
40
73
84
Pergamon Press
41
74
76
Water Pollution Control Federation
44
78
84
Pergamon Press
45
79
84
Pergamon Pres
46
80
78
University of Washington
47
81
77
Water Pollution Control Federation
48
83
78
University of Washington
49
85
90
Water Pollution Control Institute,
England
50
87
90
Water Pollution Control Institute,
England
51
88
90
Water Pollution Control Institute,
England
52
88
91
Ann Arbor Science Publishers
53
90
92
Water Pollution Control Institute,
England
54
91
92
Water Pollution Control Institute,
England
55
92
92
Water Pollution Control Institute,
England
56
93
92
Water Pollution Control Institute,
England
57
94
92
Water Pollution Control Institute,
England
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