AQUEOUS-PHASE OXIDATION OF SLUDGE
USING THE VERTICAL REACTION VESSEL SYSTEM
by
The City of Lonymont
Longmont, Colorado 80501
No. CS-809337-01
Project Officer
Edward J. Opatken
Land Pollution Control Division
Hazardous Waste Engineering Research Laboratory
Cincinnati, Ohio 45268
WATER ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45258
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DISCLAIMER
Although the research described in this document has been funded wholly
or in part by the United States Environmental Protection Agency through
assistance agreement number CS-809337 to The City of Longmont, Colorado, it
has not been subjected to Ayency review and therefore does not necessarily
reflect the views of the Agency and no official endorsement should be inferred.
Mention of trade names or commercial products does not constitute endorsement
or recommendation for use.
i i
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FOREWORD
The U.S. Environmental Protection Agency (EPA) is charged by Congress
with protecting the Nation's land, air, and water systems. Under a mandate of
national environmental laws, the agency strives to formulate and implement
actions leading to a compatible balance between human activities and the
ability of natural systems to support and nurture life. The Clean Water Act,
the Safe Drinking Water Act, and the 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 preserving and enhancing
the water we drink and for protecting the environment from toxic substances.
These laws direct the EPA to perform research to define our environmental
problems, measure the impacts, and search for solutions.
The IJater 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 prac-
tices 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 publica-
tion is one of the products of that research and provides a vital communication
link between the researcher and user community.
In the 1970's a system utilizing technology from oil well drilling was
developed for carrying out wet oxidation of municipal wastewater sludge under-
ground. The pressure needed for the process could be obtained from hydrostatic
head rather than by pumping. This report contains an evaluation of the process
carried out at the Longmont, Colorado Wastewater Treatment Plant.
Francis T. Mayo, Director
Water Engineering Research Laboratory
i i i
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ABSTRACT
The overall objective of this study was to provide plant-scale
operating data on the wet-oxidation of municipal wastewater sludge
utilizing the Vertical Reaction Vessel System. An important consideration
in the evaluation was the effect of the return flow from the wet-oxidation
process on the operation of the wastewater treatment plant. The
investigation was carried out at the Longmont, Colorado, Wastewater
Treatment Plant.
The Vertical Reaction Vessel System consists of a series of long
concentric tubes placed in the earth using conventional oil field
technology. Vertical construction produces a high hydrostatic head at the
bottom of the system. The high pressure prevents boiling at the
temperatures required for wet-oxidation. By utilizing hydrostatic
pressure, the only pumping required is that to overcome frictional
losses. The need to add energy for pressurization is eliminated. Sludge
is introduced along with air or oxygen into the multiphase fluid
downcomer, where it is heated by hot oxidized sludge rising in the
outermost concentric space within the vessel. In the bottom of the vessel
temperatures of 250°C or higher are attained and the oxidation of organic
materials takes place with resulting heat production. At the center of
the reaction vessel is a tubular heat exchange system which can either
extract excess heat or provide heat for startup of the process.
At temperatures above 260°C total chemical oxygen demand
reduction of about 80% and total volatile solids reductions of over 90%
were consistently achieved. For the 25-cm reaction vessel installed at
Longmont the capacity of the system using air was limited to five metric
tons per day. Using oxygen it was possible to increase capacity to about
30 metric tons per day. Returning the supernatant liquid from the process
to the wastewater treatment system did not significantly affect that
system.
This report was submitted in fulfillment of Cooperative Agreement
CS-809337-01 by the City of Longmont, Colorado, under the partial
sponsorship of the U.S. Environmental Protection Agency. This report
covers a period from February 1982 to September 1985, and work was
completed as of September 1985.
iv
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CONTENTS
Page
Foreword in
Abstract iv
Figures vi
Tables viii
Abbreviations and Symbols . x
Conversion Table xi
Acknowledgement xn
1. Introduction 1
1.1 Overall objective 1
1.2 Wastewater treatment plant limitations 1
1.3 Project development 4
1.4 VRV process overview 4
2. Conclusions 8
3. Recommendations 10
4. Materials and Methods 12
4.1 Laboratory analysis 12
4.2 Background limits to operations/testing 15
4.3 Process monitoring 22
4.4 Oxygen and chemicals 26
5. Operating Program 28
5.1 Overall program objectives 28
5.2. Chronology of operating program and results 28
5.3 Process modeling 35
6. Results and Discussion 40
6.1 System capacity 40
6.2 Energy balance 42
6.3 Chemical oxygen demand total (COOT) 48
6.4 Total volatile suspended solids (TVSS) 53
6.5 Total volatile solids (TVS) 65
6.6 Total suspended solids (TSS) 65
6.7 Biochemical oxygen demand total (BOOT) 70
6.8 Acid washes 88
6.9 Ammonia 89
6.10 Off-gas 91
6.11 Ash 92
6.12 Metallurgy 97
7. Operating and Capital costs 99
7.1 VRV system operating cost 99
7.2 VRV system capital costs 102
7.3 Economic analysis 102
References 103
Appendices 104
Glossary 110
v
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FIGURES
Number Title Page
1.2-1 Site Plan: City of Longmont WWTP 2
1.2-2 Longmont Plant Flow Schematic 3
1.4-1 VRV Subsurface Cross-Sectional Schematic 5
1.4-2 Process Flow Diagram 7
4.2-1 Insulated Tubular Performance 18
4.2-2 Oxygen-Enriched Air Flow Diagram 21
5.2-1 Chronology of Major Operating Campaigns 29
5.2-2 VRV Chronogram 30
5.2-3 Demonstration of Autogenous Capability 34
5.3-1 Pressure Profile 36
5.3-2 Time and Temperature Profile 38
5.3-3 LBR versus CODT Reduction 39
6.2-1 VRV Cross-Sectional Schematic 44
6.2-2 Non-Autogenous Energy Balance 45
6.2-3 Autogenous Energy Balance 47
6.2-4 Autogenous Energy Balance with Heat Removal 49
6.3-1 CODT Reduction vs Bottomhole Temperature 50
6.3-2 CODT Reduction vs Influent CODT Concentration 52
6.3-3 CODT Reduction vs Oxygen in Off-Gas 55
6.3-4 TVSS vs COOT - JSA Data 56
6.3-5 TVSS vs CODT - City of Longmont Data 57
6.3-6 TVS vs CODT - J&A Data 58
6.3-7 TVS vs CODT - City of Longmont Data 59
vi
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60
51
62
64
66
67
68
69
74
78
79
80
81
82
83
84
85
86
87
96
98
FIGURES
(continued)
Title
TSS vs CODT - J&A Data
TSS vs COOT - City of Longmont Data
TVSS Reduction vs Bottomhole Temperature
TVSS Reduction vs Influent TVSS Concentration
TVS Reduction vs Bottomhole Temperature
TVS Reduction vs Influent TVS Concentration
TSS Reduction vs Bottomhole Temperature
TSS Reduction vs Influent TSS Concentration
Longmont WWTP Flow Diagram
Influent Plant BODT Load, Sundays Only
Influent Plant BODT Load, Mondays Only
Influent Plant BODT Load, Tuesdays Only
Influent Plant BODT Load, Wednesdays Only
Influent Plant BODT Load, Thursdays Only
Influent Plant BODT Load, Fridays Only
Influent Plant BODT Load, Saturdays Only
Trickling Filter Efficiency
Rotating Biological Contactor Efficiency
Final Clarifier Efficiency Friday Operation Only
Solids Weight Percent vs Centrifuge Flow Rate
Wall Thickness of 7" Pipe
vii
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TABLES
Number Title Page
4.1-1 Chemical Analyses and Protocols 14
4.1-2 VRV System Analytical Testing Schedule 16
5.2-1 Objectives for Sustained Autogenic Operation 32
6.1-1 Operating Days 41
6.1-2 Operating Range Tested in Longmont 41
6.3-1 CODT Reductions With and Without Effluent Recycle 51
6.3-2 Oxygen Balance 54
6.4-1 TSS/TVSS Average for Longmont WWTP 63
6.7-1 Longmont CODT/BODT Reductions 70
Autogenous Without Recycle
6.7-2 Longmont CODT/BODT Reductions 71
Autogenous With Recycle
6.7-3 Longmont BOOT Reductions 71
Autogenous Without Recycle
6.7-4 Longmont BODT Reductions 72
Autogenous with Recycle
6.7-5 Longmont CODT Reductions 72
Autogenous Without Recycle
6.7-6 Longmont CODT Reductions 73
Autogenous With Recycle"
6.7-7 BOD5 Concentration For Longmont WWTP 75
6.7-8 BOD Percent Removal For Longmont WWTP 75
6.7-9 WWTP Monthly Average BODT 76
6.7-10 Statistical Analysis of Longmont WWTP
Influent BODT Loading by Day 77
6.8-1 Acid Washes 88
vii i
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Page
89
90
90
91
91
92
93
94
95
100
100
TABLES
(continued)
Title
Autogenous NH3-N Returned to WWTP With Recycle
Autogenous NH3-N Returned to WWTP
Without Recycle
Longnont WWTP Operation Without VRV System
Longmont WWTP Operation With VRV System
Off-Gas Analyses - Major Components
Trace Off-Gas Components
Elemental Ash Composition (wtS)
Results from EP-Toxicity Tests for
Longmont Ash
Data Summary Longmont Centrifuge Tests
Operating Cost for plant Utilizing a 10"
Reaction Vessel
Energy Credit
ix
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ABBREVIATIONS AND SYMBOLS
•c
degree Celsius
•F
degree Fahrenheit
Ag
silver
A1
aluminum
As
arsenic
ACS
American Chemical Society
ANSI
American National Standards Institute
ASTH
American Society for Testing S Materials
Ba
barium
BOD
biochemical oxygen demand
BOD5
biochemical oxygen demand 5-day test period
BODS
biochemical oxygen demand soluble
BODT
biochemical oxygen demand total
Btu
British thermal unit
Ca
Calcium
Cd
cadmium
Ce
cerium
CBOO
carbonaceous biochemical oxygen demand
C.I.
Confidence Interval
cm
centimeter(s)
cm2
square centiineter(s)
CODS
chemical oxygen demand soluble
CODT
chemical oxygen deoand total
Cr
Cliromi um
CRT
cathodic ray tube
Cu
copper
<1
<1iy(s) (English and metric units)
DO
dissolved oxygen
DS
dissolved solids
EP
extraction procedure
PC
final clarifier
Fe
iron
gal
gallon(s)
GC
gas chromatograph
GCMS
gas chromatography/nass spectrometry
gpd
gallons per day
gptn
gal Ions per tliinute
it
liour(s) (metric units only)
Hg
mercury
HHV
higher heating value
hp
horse power
hr
hour(s) (English units only)
ICIS
Tradename, data acquisition system hardware
K
potassium, or Kelvin
kg
kilogram!s)
I
Uteris I
lb
pound!s)
LBR
laboratory batch reactor
m3
cubic meter(s)
max
maximum
mg
milligram(s)
Hg
magnesium
mg/l
milligrams per liter
mgd million gallons per day
min minimum
in Btu/hr million British thermal units per hour
TtN/H2 neganewtons per square meter
HPa mega pa seal
HW megawatt(s)
Na Sodium
NH3 annonia
NH3-N annonia nitrogen
HI Nickel
HIOSH llat'l Inst, for Occupational Safety I Health
MI1R nuclear magnetic resonance
I1PDES Hat'l Pollutant Discharge Elimination System
No. number(s)
NYSS non-volatile suspended solids
P Phosphorous
Pb lead
PC Primary Clarifier
PEL permissible exposure limit
pH hydrogen ion solution concentration
P-lines pressure measurement lines
ppb parts per billion
ppra parts per million
psig pound(s) per square inch gauge
RBC rotating biological contactor
RCRA Resource Conservation and Recovery Act
RPH revolutions per minute
SI Systeme International d'Units
SO4 sulfate
Se selenium
Si silicon
Sr strontium
SS suspended solids
Std. Dev. standard deviation
TOS total dissolved sol Ids
TF trickling filter
Ti titanium
TKN total Kjeldalil nitrogen
TLV threshold limit value
TPD tons per day
TS total solids
TSS total suspended solids
TVS total volatile solids
TVSS total volatile suspended solids
USEPA U.S. Environmental Protection Agency
VRY Vertical Reiction Vessel
VTR Vertical Tube Reactor
UP working pressure
wt.S weight percent
WT working temperature
WWTP wastewater treatment plant
yr year(s)
Zn zinc
X
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CONVERSION TABLE
CUSTOMARY UNIT MULTIPLIER
SI UIIIT
Btu
X
1.055
a
kj
a
0.9478 X
Btu/lb
X
2.326
a
kJ/kg
•
0.4300
X
cu ft
X
2.832
X 10-2 ¦
bf3
•
35.31
X
cu ft
X
23.32
8
L*
8
3.531
X 10-2 x
cu in
X
16.39
X 10-6 .
j|3
¦
6.101
x 10* X
*F
0.
555 CF
-32) .
•c
a
1.8 fC + 32)
ft
X
0.3048
a
n
a
3.281
X
gal
X
3.785
a
L*
¦
0.2642
X
gal
X
3.785
X 10-3 „
m3
°
264.2
X
gal/min
X
6.303
x lO-5 ¦
m3/s
o
1.505
X 10* X
hp
X
745.7
a
U
a
1.341
X 10-3 X
in
X
2.540
M
fM
1
O
X
m
s
39.37
X
Ib(oass)
X
0.4536
a
a
2.205
X
lb/ft
X
1.488
a
kg/m
a
0.6720
X
mil gal
X
3 785
s
b>3
a
2.642
><
i
o
X
mgd
X
4.333
X 10*2 »
m3/s
a
22.83
X
mile
X
1.609
.
km
a
0.621 t
1 X
ppb(by weight)
X
10-3 .
1
mg/L*
a
1 000
X
ppo(by weight)
essentially •
ng/L*
=
essentially
psi
X
6895 •
1
Pa
m
1.450
X 10-4 X
psi
X
7.031
N
CM
1
o
X
kgf/cn
•
14.22
X
tons (short)
X
907.2
k9
B
1.102
X 10-3
* Wo: strictly an Si unit.
XI
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ACKNOWLEDGEMENT
The following individuals contributed to the completion of this report:
Leonard A. Kaufmann, Gerald C. Rappe, Hermann W. Peterscheck, William L.
Schwoyer, Fran M. Ferraro, Dean Sillerud, Bruce Kent, Bill Berg, Gil
Morrill, Edward J. Opatken, Carl A. Brunner, Ronald H. Hall, Arden Wallum,
and Howard Delaney.
xi i
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SECTION 1
INTRODUCTION
1.1 OVERALL OBJECTIVE
The overall objective of this study was to provide plant-scale
operating data on the destruction of municipal sludge utilizing the
Vertical Reaction Vessel (VRV) System for aqueous-phase oxidation.
Specific goals of the study were:
(1) to determine the operating parameters of the aqueous-phase
oxidation process which would provide effective reduction of
Chemical Oxygen Demand Total (COOT) and Total Suspended
Solids (TSS) in sewage sludge; and
(2) to determine the effects of return flow from the wet
oxidation process at the Longmont, Colorado Wastewater
Treatment Plant (WWTP) secondary biological treatment process.
1.2 WASTEWATER TREATMENT PLANT LIMITATIONS
Longmont, Colorado is a growing city which is situated
approximately forty miles north of Denver along the Colorado Rocky
Mountain Front Range. Residential and commercial development have
increased wastewater loads to the municipal treatment plant with resultant
increased generation of sewage sludge.
The Longmont WWTP is a 31 ,000 mVd [8.2 million gallons per day
(MGD)] facility which utilizes trickling filters in series with rotating
biological contactors (RBC's) for secondary treatment. Longmont produces
approximately 3,600 kg (8,000 lb) of sewage sludge daily, which after
anaerobic digestion is disposed of in liquid form (undewatered) on
agricultural land. Figure 1.2-1, the Site Plan of the Longmont WWTP,
shows the plant layout and the VRV System expansion. Figure 1.2-2 shows
the Plant Flow Schematic. The limiting unit process in Longmont's
wastewater treatment capability was sludge treatment. Most of Longmont's
WWTP processes were upgraded during previous expansion programs. The
sludge disposal system, however, had adequate capacity for several more
years. Industrial wastes concentrated in the sludge had retarded the
anaerobic digestion process-, requiring lower digester feed rates. This,
in turn, decreased the overall capacity of the sludge disposal system.
The digesters had experienced periodic upsets which greatly reduced the
solids handling capacity of the entire plant. In addition to the strong
odors produced by an upset digester and sludge thickener, the overall
plant performance dropped and operating costs increased. These increasing
sludge volumes and sludge hauling costs provided the incentive for
Longmont to consider alternative methods for sludge disposal.
- 1 -
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I
ro
I
IUILOIN
oiectT
COHMOL OUtLOIMO
o
TNICKltNO
mrm no. i
UtCIUMCAl
llTILDIMt
VRV
DILUTION
WATER
ILVO«t
TMtCKCUia
I IIAIfOH
1 1 NO. •
VRV EFFUUE
RETURN
• «0-0(«0
•UtDMI
VRV SLUDGE
TANK
VRV
BUILOING
WORK
SHOP
10 O to no l«0
« i ¦ 1 i I
1C IK OF fill
Fig. 1.2-1 Sfte Plan: City of Longmont WWTP
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-O-
C0HMIMU10H
PUMP
STA No \
PLANT
HECK
BAR SCREEN
MEIER
AIRAHD
GRIT
BASIN
PUHP
SIA No IB
T F FLOW
DIVIDER
PUMP
SIA
ROC
RBC
PUMP
SIA No 1A
V-
BEU
FILTER PRESS
TANK
DIGESTER
ASH TO
LANDFILL
LAHO
APPLICATION
Fig. 1.2-2 Longmont Plant Flow Schematic
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1.3 PROJECT DEVELOPMENT
Early in 1980, the City's sanitary consulting engineer, McCall,
Ellingson, and Morrill, Inc. of Denver, approached Longmont's Director of
Utilities. They presented a proposal to work with Dr. Jay McGrew, the
developer of the subsurface aqueous-phase oxidation technology, to seek an
EPA Demonstration Grant to construct and operate a prototype vertical
reaction vessel at the Longmont WWTP. In February, 1982, the United
States Environmental Protection Agency awarded Cooperative Agreement
CS-809337-01 to the City of Longmont. The purpose of the cooperative
agreement was to evaluate the Vertical Tube Reactor (VTR) Process,
referred to in this report as the Vertical Reaction Vessel (VRV) system,
for wet oxidation of municipal sludge.
1.4 VRV PROCESS OYERYIEW
The technology was further developed by VerTech Treatment Systems,
and introduced as an innovative approach to applying established
principles of aqueous-phase oxidation, commonly called "wet-air
oxidation." Figure 1.4-1 shows a typical cross-sectional schematic of the
Vertical Reaction Vessel (VRV). The design utilizes the natural laws of
gravity and thermodynamics. Sludge is diluted to desired CODT
concentration and pumped into the inner annular space of the concentric
vertical tubes (downcomer). The reaction vessel in Longmont is
constructed of stainless steel. Air or oxygen-enriched air is injected at
a specified depth into the waste stream and the mixture flows down the
tube. The process is initiated by heating the reaction vessel (and
surrounding earth formation) by means of a central heat exchanger until
reaching a temperature at which the oxidation process begins, about 175°C
(350°F). At the bottom of the vessel a peak natural pressurization of
about 9.6 MPa (1400 psig) is reached, due to the height and density of the
fluid column above.
Oxidation of the waste substances occurs in the liquid phase, when
sufficient oxygen, temperature, and pressure are present. The exothermic
oxidation process produces excess heat which may be removed through the
central heat exchanger for useful application at the surface. The fluid
used in the central heat exchanger in Longmont is a high temperature
organic heat transfer fluid, generally referred to as Dowtherm A.
The diameter and length of the vertical tubes are designed to
provide sufficient residence time and hydrostatic head to complete the
oxidation reactions. This high length-to-diameter ratio allows for
efficient counterflow heat exchange between the downcomer influent and
upcomer effluent, thereby conserving energy. The depth of the VRV
provides the pressure necessary to keep the liquid from vaporizing.
The pumps injecting the diluted sludge need only overcome wall
friction and a small differential head between upcomer and downcomer.
They are not required to supply the high pressures experienced at the
bottom of the well, thus reducing pump and compressor horsepower.
- 4 -
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Process oxygen
lor air)
30m/120m
1580m (194mm & 127mm tubes)|r.
1585m (254 mm tube)
1600m Concrete
Concrete
Primary casing
340mm
Heat exchanger
Influent
Effluent
Surface casing
High boiling
oil-filled
annulus
Insulated
tubular
Oxidation
unit
upcomer
254mm
Oxidation
unit
downcomer
194mm
Heat transfer fluid
127mm
US. Patent No 4,272,383
Fig. 1.4-1 VRV Subsurface Cross-Sectional Schematic
- 5 -
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The CODT of the influent waste is significantly reduced during its
residence time in the oxidation zone of the reaction vessel. The reacted
effluent returns to the surface in an outer annular space (upconer) of the
vessel. The effluent flows into a gas/liquid separator and then to a
solids/liquid separator. The low volume of inert solids from the VRV
process dewaters more easily than the organic sludges obtained from
conventional biological processes. The solids are reduced both in volume
and in weight, with a small amount of inert ash remaining which can be
disposed of in a sanitary landfill.
The process flow diagram for the Longmont VRV and associated
surface equipment, with sampling points, is shown in Figure 1.4-2.
- 6 -
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OXYGEN >
OO—*¦
Alft COM'HKISOR
OFF-GASES
EFFLUENT (S-4) "mmo?
¦OO-
FEED (S-3)
IRNATANT (S-5)
-J »RAW SLUDGE (S-1)
JZWf*—oo-fT^
siunoi
oniiuin KuiS
LONOMONT
SLUDGE FEED
UNDERFLOW
.SOLIDS (S-0)
DILUENT n«n '
REACTION
VESSEL
F1g. 1.4-2 Process Flow Diagram
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SECTION 2
CONCLUSIONS
1. Major program objectives were met.
2. With the use of air, the system capacity was limited to 5 metric tons
per day for the Longmont 10-inch reaction vessel. The use of oxygen
increased system capacity to 30 metric tons per day.
3. For bottomhole temperatures of 5006F and above, CODT reductions of
75-80X were achieved and reproducible. Temperature had the largest
effect on CODT reduction. By recycling the effluent, the reduction
in CODT was increased about 5%.
4. BODT in the VRY effluent stream was readily biodegradable, showing a
1404 increase in the efficiency of the trickling filter. As a
result, the Longmont WWTP was able to process all the recycled BODT
and still meet its NPDES discharge limit, even during periods when
additional sludge was hauled in.
5. During autogenous operation TVSS reductions averaged 96.5%, TVS
reductions averaged 93.9%, TSS reductions averaged 78.7%, and CODT
reductions averaged 76.3%.
6. An Industrial Hygiene Survey indicated that trace components in the
off-gas were usually about two orders-of-magnitude below the
permissible limit for an 8-hour worker exposure.
7. A metallurgical inspection of the reaction vessel by Material Science
Corp. showed insignificant corrosion, consistent with a 20-year life.
Materials of construct!on for the YRV and the surface equipment
proved satisfactory.
8. Based on the Longmont demonstration, it was possible to establish
operating and maintenance costs for a 10-inch reaction vessel
operating at maximum capacity. Operating and maintenance costs for a
Longmont-sized unit are below $100 per metric ton with an energy
recovery credit of $17 per metric ton.
9. The ash is non-hazardous. Leachates from the EP Toxicity Test were
below limits set by EPA, usually be two orders-of-magnitude.
10. Ash in the VRV effluent was easily dewatered. Solid contents of
40-75* were obtained after dewatering by a centrifuge without any
optimization of centrifuge operation.
- 8 -
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11. The system operated from non-autogenous to extraction of heat.
Operation in the autogenous mode was extremely smooth. Wash-out heat
was limited to a temperature rise between influent and effluent of
11-17C0 (20-30F0) during autogenous operation.
12. High mechanical availability (96.7%) of the system and its components
did not limit the test program in any substantial way.
13. CODT reduction for the full-scale system at Longmont was successfully
predicted from laboratory batch reactor (LBR) tests.
14. VRV operation was consistent and reproducible at fixed operating
parameters.
- 9 -
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SECTION 3
RECOMMENDATIONS
The following are recommendations for improving system design, based on
the results of the demonstration period:
1. Biological treatment of the reaction vessel effluent should be further
investigated to optimize COOT reduction. Benefits of anaerobic
polishing should be tested.
2. The VRV effluent return appeared to influence the biological
speciation and caused more rapid reduction of BODT. Identification of
biological species before, during, and after oxidation system
operating periods should be included in future tests.
3. Returning the VRV effluent stream to the headworks of the Longmont
WWTP will provide flow equalization and reduce concentration prior to
undergoing biological degradation. An option should be provided to
allow VRV effluent return either to the headworks or to the trickling
fi1ters.
4. The unit installed at Longmont was oversized. A new reaction vessel
more closely matching Longmont's sludge generating capacity should be
installed and tested.
5. Higher influent heat transfer fluid temperatures were required for
start-up due to welding failures which occurred in four sections of
the insulated tubular. Coupling design also contributed to greater
heat loss than expected. However, the system was still able to reach
required bottomhole temperatures. Improved insulated tubular design
will eliminate failures in future installations. The performance of
the insulated tubular has minimal effect during autogenous operation.
6. Pressure measurement tubing caused organic fouling and suffered
mechanical damage during installation and operation. Organic fouling
limited the length of operating runs. This fouling is not anticipated
to occur in a commercial reaction vessel, since downhole pressure
measurements will not be required for VRV operation.
7. Mechanical dewatering of the ash slurry should be installed. Polymer
addition should be optimized to reduce dewatering costs.
8. The use of ash as a filler material for brick manufacture was
demonstrated and could be implemented at future installations where
appropriate.
- 10 -
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9. The VRV vessel should be insulated or constructed so as to reduce heat
losses to the formation. High boiling temperature oil should not be
present in the annular space between the reaction vessel wall and the
primary casing string. These improvements will reduce initial heat-up
and time to restart after a shutdown, as well as increasing the heat
recovery.
- 11 -
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SECTION 4
MATERIALS AND METHODS
4.1 LABORATORY ANALYSIS
4.1.1 Sample Storage
Samples of all sludge (S-l), dilution water (S-2), diluted feed
(S-3), reaction vessel effluent (S-4), liquid/solid separator supernatant
(S-5), and underflow solids (S-6) were immediately stored in closed
polyethylene or glass vessels at 4±2°C. Sample containers were
affixed with a pressure sensitive label which contained the following
information in indelible ink: sampling date and time, sample point
location, type of sampling (composite, split, or intensive), specific
tests to be run, name of sampler, preservative added and any other
specific information for that particular sample. The samples were
transported in a closed, insulated carton from the test site to the J&A
Associates, VerTech's testing laboratory, on a daily basis. Immediately
upon receipt at the laboratory, samples were logged in, assigned
individual sample numbers and again stored at (4l2°C). Samples were
removed from the storage unit only long enough to withdraw the amount
required for testing. All samples were held for a period of 30 days
pending completion of analyses.
4.1.2 Comparison of Longmont and J&A Associates Chemical Analyses
When reviewing and comparing the analytical results obtained by
the Longmont WWTP Laboratory and the J&A Associates Laboratory for any
given day, the method of sample collection was taken into account.
Longmont worked almost exclusively on 24-hour composite samples
comprised of two-hour samples. Periodically, Longmont split the composite
sample with J&A Associates thereby affording a direct comparison of
results obtained for a given sample.
The majority of the samples analyzed by J&A Associates were
single-grab intensive samples taken over a specific test run considered to
be performed under ideal operating conditions. These samples were taken
at short-time intervals, generally 5 or 15 minutes, over a 4-hour run.
CODT and solids were the primary parameters measured by both
Longmont and J&A Associates over any given test period. Longmont employed
a 2 ml sample for running CODT by the Hach Method. J&A Associates
employed a 20 ml sample with a 2-hour reflux time for conducting all their
CODT analyses. The USEPA recognizes both methods as being acceptable for
CODT determination.
Data evaluation was limited to operating conditions at 250°C
(500°F) or higher and VRV flow rates of 22.7 m-Vhr (100 gpm) or
greater. These conditions indicated normal reaction vessel operation.
- 12 -
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Samples taken during start-up and shutdown were erratic due to the
continual change of operating parameters.
4.1.3 Analytical Protocols - J & A Associates
All chemical analyses were conducted in accordance with
EPA-600/4-79-020, "Methods for Chemical Analyses of Water and Wastes,"
U.S. Environmental Protection Agency, 1979 (2). When these guidelines did
not apply, "Standard Methods for the Examination of Water and Wastewater,"
15th Edition (3) was followed. (Analytical protocols and procedures
included the full quality assurance/quality control procedures recommended
in the specific protocol.) Table 4.1-1 identifies each chemical parameter
analyzed during the course of the program and the specific protocol used
to determine it.
When necessary, modifications of existing USEPA or Standard
Methods protocols were developed in order to meet specific requirements.
4.1.4 Analytical Protocols - City of Longmont
To insure that the data produced to assess the effectiveness and
feasibility of the VRV System were both reliable and representative, the
EPA required that a Project Quality Assurance (Q.A.) Plan be developed and
submitted for approval. This plan was a joint effort of the Longmont
Water Quality Laboratory staff and project engineers and technicians fron
VerTech Treatment Systems. The Quality Assurance Plan was reviewed and
approved by the Project Director, Project Quality Assurance Coordinator,
VerTech Project Manager, EPA Project Officer, and EPA Quality Assurance
Officer.
The Quality Assurance Plan addressed the following topics: Q.A.
objectives, sampling procedures, sample custody, calibration procedures
and frequency, analytical procedures, data reduction, validation and
reporting, internal quality control checks, performance and system audits,
preventive maintenance, specific routing procedures used to assess data
precision, accuracy, completeness, and corrective action. The procedures
outlined in the plan were followed closely throughout the duration of the
project.
All analytical methods used for the analyses were EPA approved.
Internal quality control checks included the analysis of spiked,
duplicate, standard, and EPA reference samples. Spiked and duplicate
samples were run on every tenth sample. A standard was run daily on CODT
analysis. EPA reference samples were run weekly.
A 9S% confidence interval (C.I.) compiled from at least 20 data
points, consisted of the mean + 1.96 S.D. Upper and lower control limits
were established in this manner and revised monthly. Whenever spike and
standard recoveries fell outside these established limits, data were
rejected and the analytical method investigated and the problem corrected.
- 13 -
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TABLE 4.1-1
J & A ASSOCIATES
CHEMICAL ANALYSES AND PROTOCOLS
ANALYSIS
Biochemical Oxygen Demand (BODT)
Chemical Oxygen Demand (CODT)
Total Solids (TS)
Total Suspended Solids {TSS)
Total Volatile Solids (TVS)
Total Volatile Suspended Solids (TVSS)
Total Kjeldahl Nitrogen (TKN)
Ammonia Nitrogen (AN)
Anions (inorganic)
Volatile Acids
Metals
pH
EP Toxicity Test
Off-Gases
Higher Heating Value (HHV)
C/H/N
PROTOCOL
EPA 504.1 (2)
Std. Methods 508 (3)
EPA 160.3' (2)
EPA 160.2 (2)
EPA 160.4 (2)
EPA 160.4 (2)
EPA 351.3 (2)
EPA 350.2 (2)
Ion Chromatography*
Ion Chromatography*
EPA 202.1 - 289.1 (2)
EPA 150.1 (2)
EPA SU846 - 8.49 through 8.60 (1)
NIOSH, GC, 5840 hp (4)
ANSI/ASTM D2015-66 (5)
Perkin-Elmer 240C Elemental
Analyzer*
*J & A Associates Internal Procedures
- 14 -
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Precision of the analytical procedure was determined using
duplicate analyses, and 95% C.I. was established for the analyses. Again,
the 95£ C.I. was + 1.96 (S.D.). An upper control limit for the range
percent was established and periodically revised. Whenever the upper
control limit was exceeded, data were rejected and the analytical method
investigated until the problem was identified and corrected.
Twice during the duration of the project, the Longmont laboratory
analyzed a set of performance evaluation samples sent by the EPA's Quality
Assurance Branch in Cincinnati.
A variety of analyses were performed to control the operation and
assess the performance of the VRV. Additional analyses were run to
characterize the effect of the VRV System on the wastewater treatment
plant. Table 4.1-2 lists the sampling schedule followed for the program.
The analyses run in conjunction with the project included the following:
total and soluble CODT and BODT, chlorides, total solids, total suspended
solids, total volatile suspended solids, total volatile solids, Total
Kjeldahl nitrogen, ammonia nitrogen, dissolved sulfate, total alkalinity,
volatile acids, calcium, magnesium, aluminum, chromium, cadmium, copper,
iron, lead, manganese, nickel, selenium, silver, and zinc.
CODT was the most closely monitored parameter throughout the
project. The Longmont laboratory analyses were performed, throughout the
project, using the EPA-approved Hach CODT test system.
Total CODT and BODT analyses were run on the unfiltered sample.
Soluble CODT and BODT analyses were performed on filtrate that passed
through a Whatman, Mo. 934-AH glass microfibre filter.
Heavy metals analyses were performed by the atomic absorption
spectrophotometer methods. All samples were digested according to the
method outlined in the revised edition of the EPA 600/4-79-020, "Methods
for Chemical Analysis of Water and Wastes."(2) Soluble metals were
determined after filtration of the sample through a Whatman 934-AH glass
microfibre filter.
4.2 BACKGROUND LIMITS TO OPERATIONS/TESTING
4.2.1 Heat Supply and Removal System
4.2.1.1 Heat Supply
One early limitation to operation was an inadequate heat supply
system to deliver start-up heat to the VRV. A decision was made to
surround the lower portion of the VRV with a stagnant high boiling
temperature oil. This modification increased the amount of heat leakage
to the surrounding earth formation.
- 15 -
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Table 4.1-2 VRV System Analytical Testing Schedule
BY LONGMONT WATER AND WASTEWATER LABORATORY
PARAMETER
TH [ST-
RAW
SLUDGE DILUENT
Chiorldes
COD
COD (Soluble)
B0D5
DOD5 (Soluble)
TS
TSS
TVS
TVSS
NII3-N
TKN-N
SO4
pll
Total Alkalinity
Bicarbonate Alkalinity
Volatile Acids
Calcium (Total)
Magnesium
Aluminum
Chromium (Total)
Cadmium
Copper
I ron
Lead
Manganese
Nickle
Selenium
Silver
Zinc
Ash Toxicity (EP Test)
D
W
W
D
211
2W
2 W
D
ZU
2W
2W
2W
2W
D
2W
2W
m—
REACTOR
INFLUENT
D*
D
2W
D
D
D
D
2W
2W
1W
D
1W
1W
1W
0
D
1M
1W
1M
1W
1W
1M
1M
1M
1M
1M
1M
5AMPLE LOCATION
~~m—
REACTOR
EFFLUENT
D
D*
D
2W
2W
D
D
D
D
2W
2W
1W
D
1W
1W
1W
D
D
1M
1W
1M
1W
1W
1M
1M
1M
1M
1H
1M
151
SETTLED
EFFLUENT
D
D
D
D
D
D
D
D
2W
2W
211
D
1W
1W
1W
0
2W
1M
1W
114
1W
1W
1M
1M
1M
1M
1H
IM
—in—
LAMELLA
UNDERFLOW
ZW
2W(G)
2W(G)
—m—
ASM PIT
SUPERNATANT
2W
2H
NOTE: All Lamella effluent metal analyses
are total and soluble.
*Morning and/or afternoon "grab"
sample split from composite.
Sampling Frequency:
2W(G)
2H(G)
1M(G)
1WG
1 M( G J
1W(G)
1 W( G)
1M(G)
1M(G)
1M(G)
1M(G)
1M(G)
1M(G)
1 Mf G)
D - Daily
(K)W - Times per Week
(X)M - Times per month
G - Grab Sample
-------
A second limitation was encountered during the early testing
phase, when it was found that the insulation quality of the insulated
tubular string had apparently deteriorated.
At start-up, heat transfer fluid flows down the inside of the
insulated tubular string and reaches the bottom of the reaction vessel at
the maximum temperature with minimal heat loss. This delivers the
greatest amount of heat to the bottom of the VRV. The upflowing heat
transfer fluid exchanges heat with the aqueous upcomer via radial transfer
through the aqueous downcomer.
The deteriorated insulated tubular string caused a partial short
circuiting of heat from the inside to the outside of the string. This
caused an increase in the heat transfer fluid return temperature with two
effects: higher wash-out heat from the water circuit and an overall
increased temperature profile (especially at the top of the reaction
vessel) which increased heat losses to the surrounding earth formation.
Unexpected heat losses required an increase in the start-up heat
supply system. A conventional oil field hot oil truck (truck mounted pump
and propane fired heater system) was temporarily brought on site to pump a
higher volume of heat transfer fluid through the system and to increase
the total heat supplied to the VRV. Additional heat was supplied by a
small oil fired heater. These facilities allowed testing of the system at
temperatures greater than 260°C (500°F), until permanent modifications
were purchased and installed.
A second furnace with an economizer was purchased to increase the
overall heat absorption capacity to 2.46 MW (8.4 MM Btu/hr). Two new
pumps (one operating and one spare) were added to the system to increase
heat transfer fluid flow rates. With the new heat supply equipment
installed and operational, the VRV System could be brought to operating
temperatures from a cold start in a matter of hours.
4.2.1.2 Insulated Tubular
Figure 4.2-1 presents representative calculated thermal
conductivities throughout the operating period. The effective thermal
conductivity more than doubled over the course of the project, introducing
greater heat losses across the insulated tubular and consequently causing
longer start-up periods.
During testing, this problem was overcome with the additional heat
supply capacity installed after start-up. Upon removal of the VRV in
September 1985, inspection of the insulated tubular revealed that four of
the 133 joints had failed. All failures occurred near the top of the
reaction vessel, and accounted for the heat losses across the insulated
tubular to the aqueous stream upcomer and downcomer.
- 17 -
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0 48
0.46
042
040 -
0.38 -
o o
u
-------
Failures occurred at the welds between the inner and outer
joints. Excess hardness levels in the heat-affected zone were noted on
all defective inner tubulars. In one case insufficient fusion of the
casing to the weld ring resulted in joint failure under high thermal
stress. These stresses resulted from the large temperature difference
between the hot heat transfer fluid (approximately 390°C) in contact with
the inside surface of the inner tube and the cold return heat transfer
fluid (approximately 80°C) in contact with the outer surface of the outer
tube. Further examination of the failed areas showed these failures can
be prevented in future designs. Hardness checks and other test procedures
will eliminate any problem welds before shipment from the factory.
4.2.1.3 Heat Removal
In early 1985, high capacity tests were run to determine the
maximum capacity of the VRV as installed. The heat removal system was
originally sized to discharge approximately 0.37 MW (1.25 MM Btu/hr) to
the atmosphere with an air fin type cooler. This system took the reversed
heat transfer fluid flow from the reaction vessel and cooled it before
returning to the expansion tank. A number of high capacity tests were
restricted for safety reasons due to the limited size of this heat removal
system.
4.2.2 Fouling
Organic plugging occurred on the pressure measurement tubes
(P-lines) in the VRD. The P-lines suffered mechanical damage due to an
improper welding procedure at the weld connecting the pieces of tubing.
Tangled P-lines in each annul us caused multiple partial blockages inside
the VRV, causing a -high differential pressure across the reaction vessel.
The solids fouled on the massed P-lines were periodically removed by
various washing techniques. Excessive fouling significantly reduced the
operating period between washings, and increased chemical consumption.
The tangled tubing provided multiple locations to catch and retain
solids and stringy material in the incoming sludge. Improved material
selection, welding inspection and testing techniques can eliminate this
problem in future installations. The amount of instrumentation required
for a commercial VRV System is substantially less than that provided for
tests at the demonstration plant at Longmont. Future commercial plants
can be operated without downhole pressure or temperature measurements on
the process side if necessary.
4.2.3 Other Capacity Testing Limitations
The original VRV System design capacity was sized for
approximately 5.4 metric tons per day (6 tons/day) of CODT using air as
the source of oxygen. This design capacity closely matched the sludge
production rate of the Longmont WWTP. Subsequent testing with
oxygen-enriched air demonstrated that the VRV was capable of processing
greater quantities of sludge than the City of Longmont could produce.
- 19 -
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Therefore, In an attempt to establish the maximum capacity of the reaction
vessel, sludge was imported by trailer truck from the nearby cities of Ft.
Collins and Lafayette. This imported sludge was mixed with the City of
Longmont sludge in a temporarily unused digester at the longmont WWTP.
With the additional supply of concentrated sludge, extended runs at high
capacity were performed on various mixtures of the sludges.
When the oxygen-enriched air tests were designed, the system size
set for the oxygen supply system was approximately 21.8 metric tons per
day using 99.5% pure oxygen. As can be seen in Figure 4.2-2, the oxygen
supply system consisted of a liquid oxygen -tank, a cryogenic pump,
atmospheric vaporizers, and flow controls. This equipment was leased from
a commercial liquid oxygen supplier, and allowed operation over a wide
range of oxygen feed rates.
4.2.4 Improvements to Increase System Capacity and Reliabilities
Certain improvements were installed to remedy plant limitations
and to allow testing of the ultimate capacity of the VRV. Provision of
automatic operating control equipment increased system reliability.
Oxygen addition allowed an increase in reaction vessel capacity.
Additional sludge pumping capacity was required to provide sufficient feed
for the VRV. The plant normally operated with a single sludge feed pump
with a 100% installed spare available. Modifications to the pump drive
systems allowed their individual capacities to be increased by
approximately a factor of 2. Modifications to the electrical switch gear
allowed simultaneous operation of both pumps to increase the available
feed capacity by approximately a factor of 4.
4.2.5 Improvements and Modifications to Mechanical Equipment
In order to accommodate construction and operation of the VRV
System, several modifications were required at the Longmont WWTP.
Increased natural gas service to the WWTP was sufficient to supply the VRV
System, however, an additional electric meter was needed to monitor demand
and power usage by the wet-oxidation test facility. A pump was installed
in the chlorine contact tank influent well to provide dilution water for
the influent sludge. Potable water mains were extended to provide service
water, fire protection, and a back-up water supply for sludge dilution.
Sludge piping was extended from the WWTP sludge drying beds to a new
mechanically mixed storage tank adjacent to the test site. Effluent
return flow piping was installed from the Lamella separator overflow to
the influent well of the WWTP trickling filter feed pumps.
Originally, VRV effluent pressure was controlled by a pressure
control valve directly in the three-phase effluent stream. This presented
mechanical difficulties due to erosion on the downstream side of the
letdown valve. A conventional gas/liquid separator was added in the
effluent line which provided liquid hold-up to reduce fluctuations in flow
to downstream solids separation equipment and to eliminate erosion. The
- 20 -
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LIQUID
OXYGEN
HOLDING TANK
GASEOUS
OXYGEN
INfLUENT
>D
1 EFFLUENT
CUSTOMER
STATION
ATMOSPHERIC
VAPORIZERS
Fig. 4.2-2 Oxygen-Enriched Air Flow Diagram
-------
addition of this equipment permitted stable operating conditions even
during transient test conditions.
4.2.6 Back-up System for Sludge Treatment
A belt filter press and facilities for lime stabilization of raw
sewage sludge were also installed as a back-up system for sludge treatment
in the event that the aqueous-phase process was out-of-service for
maintenance or modifications at a time when the anaerobic digesters were
unable to accommodate the daily WWTP sludge production. All WWTP
modifications were funded by the EPA grant, except for the belt filter
press and lime stabilization equipment which was installed at the City's
expense.
4.3 PROCESS MONITORING
4.3.1 Data Acquisition
All wastewater treatment unit processes were monitored at the
Longmont WWTP during 1984 and 1985 to determine the effects of return flow
from the VRV System on the Longmont WWTP. Composite samples were
collected daily from the influent of each unit process and analyzed by the
Longmont Water Quality Laboratory for TSS and BODT. A computerized data
base was created from the WWTP and VRV System operating data to track
performance of the Lonpont WWTP during the various system operating
campaigns.
4.3.1.1 Operating Data
The VRV System operating data were acquired using conventional
instrumentation combined with both manual and computer data acquisition
and storage. Manual data collection was utilized for acquisition of data
for non-critical process operations and non-critical equipment. The
computer data acquisition system instrumentation was hard-wired to a
central computer facility. The data were recorded on a regular schedule,
and available to the operator on request.
4.3.1.2 Demonstration Plant Data Logger
Process information, such as flow rates, temperatures, and
pressures, was acquired by instrumentation at identified points. An ICIS
850 data acquisition system with CRT's, keyboards, printer and standby
power was used to log data from hard wired instrumentation. These data
were stored as 15-minute averages. Regular storage of data occurred for
pressures, temperatures, flows, analysis signals and status indications.
Regular data were acquired by the computer and averaged at one-second
intervals. One-minute averages of these signals were output to CRT's and
printers for the operators. The data logger then stored on disk 15-minute
averages of the one-minute averages for each data point. Upon special
request by the operator, or upon activation of a special trigger due to an
alarm data point, the computer would store on disk the one-minute readings
- 22 -
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for a more detailed future analysis of a transient condition which had
occurred in the process operation. The system proved valuable in
evaluating the effect that an unexpected event, such as a power failure,
had on the process operation. Some instrumentation was added for the high
rate tests conducted early in 1985.
4.3.1.3 Manual Data Acquisition
Operating information that was either non-critical in nature or
otherwise did not justify hard wiring to the computer was acquired on a
manual basis by the process operator. This included such information as
water consumption, air compressor operator data, oxygen supply system, and
acid wash operation.
4.3.1.4 Spot Data
Spot data were also acquired for unexpected events and for special
tests. Process operator observations were helpful in determining the
effects of special operating conditions that were tested. This included
such tests as the use of polyelectrolyte addition to improve settling in
the liquid/solid separator and ash pits, centrifuge tests for ash
dewatering and small-scale biological polishing tests of the VRV System
effluent.
4.3.2 Sample Acquisition
Samples were collected by both the City of Longmont's laboratory
and VerTech personnel. The City of Longmont conducted all the sampling
for their WWTP process, special WWTP studies, and the composites of
certain VRV streams at defined sampling points. VRV sample streams are
shown in Figure 1.4-2. These stream points included the sludge pumped
from the Longmont WWTP (S-l), final clarifier effluent used as diluent
(S-2), VRV influent (S-3), VRV effluent (S-4), the liquid/solid separator
clarified effluent (S-5), and the liquid/solid separator concentrated ash
(S-6).
4.3.2.1 VRV Unit Composites/Splits
VRV influent (S-3) and effluent (S-4) samples were collected by
the City of Longmont every two hours from 7 A.M. to 7 P.M. daily. Fixed
volumes of liquids were added to the liquor taken at the previous sample
times, and the mixed composite was refrigerated. Composite samples
collected were split daily with half the samples sent to J&A Associates,
Inc., VerTech's testing laboratory, and the remaining sample sent to the
City of Longmont's laboratory for analyses. Total COOT, pH and metals
measurements were then made by both laboratories.
4.3.2.2 Intensive Sampling
Periodic intensive sampling was conducted by VerTech to obtain a
data base for statistically determining the CODT reduction through the
- 23 -
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unit for a given set of operating conditions. Samples were taken of the
feed (S-3) and the effluent (S-4) at 15-minute intervals. A delay period
equal to the hold-up time in the VRY for any given fl-ow rate separated the
start and finish of sampling for the feed and the effluent. The delayed
sampling period gave VerTech matched sets of feed and effluent samples,
and took into account the reaction vessel hold-up time. An intensive
sampling period consisted of a minimum of 6 to 10 matched sets of influent
and effluent samples. The individual samples were routinely analyzed for
CODT. Composites of each matched set were analyzed for TS, TSS, TVS,
TVSS, TKN, NH3-N, BOD5, metals, inorganic anions, organic acids and pH.
An intensive sampling period included a grab sample of the sludge
being used for the feed (S-l) taken during the sampling period. This
sample was analyzed for CODT, TS, TVS, carbon, hydrogen, nitrogen and
higher heating value (HHV).
Samples taken during acid washes also allowed VerTech to determine
the amount and components of the scale material.
4.3.2.3 Spot (Grab Sample)
VerTech operators took spot samples whenever they encountered an
operating condition that they felt should be recorded in the data base.
These samples were refrigerated at 4+2°C and transported to J&A Associates
laboratories the morning of the following day.
4.3.2.4 Off-Gases
During the last eight months of the demonstration period, VRV unit
off-gases were continually monitored by an on-line gas chromatograph
(GC). The samples were taken from the pressurized line feeding the
gas/liquid separator. The gas chromatograph was set on a 15-minute
analysis cycle. The cycle was set to coincide with the process data being
collected by the data acquisition system. This allowed VerTech to have a
match up of off-gas analyses with downhole operating conditions. The
off-gases were analyzed for oxygen, nitrogen, carbon dioxide, carbon
monoxide, methane, and hydrogen.
Gas samples were occasionally collected at various points in the
system for analyses. These samples were collected either in a pressurized
stainless steel bomb attached directly to the pressurized line leading to
the gas/liquid separator or by a gas bag or charcoal tube from a sample
pump which took the gaseous discharge from the gas/liquid separator.
These samples were analyzed by Gas Chromatography (GC), Gas
Chromatography/Mass Spectrometry (GCMS), or High Performance Liquid
Chromatography (HPLC).
Chemicals that were best analyzed by high pressure liquid
chromatography were collected in a midget bubbler containing Girard-T
reagent.
- 24 -
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4.3.2.5 Ash Pits
The ash .pits were not sampled on. a fixed schedule. Samples were
generally taken from the four corners and center of the pit then
composited prior to analysis. A USEPA Extraction Procedure (EP) Toxicity
metals analysis (1) was performed on each composite.
4.3.3 Instrumentation
Conventional process instrumentation was used to measure the
operating parameters of the process streams.
4.3.3.1 P-lines
The operating conditions inside the VRV did not allow internal use
of conventional instrumentation to measure pressures at various points.
Therefore, conventional pressure measuring equipment was placed at the
surface to measure the pressure required to bubble a small amount of air
through a line to various depths within the reaction vessel. A small
supply of air, available at approximately 3,500 psig, was bubbled through
a flow controlling device at which point the pressure was measured. The
computer corrected the surface pressure readings to values corresponding
to the pressures at the depth inside the reaction vessel by calculating
the effect of the weight and density of the air inside the respective
P-line.
4.3.3.2 Temperature Readings
Thermocouples located inside protective thermowells were used to
measure temperatures at various points in the process. Temperature
readings were available to the operator from a panel-mounted temperature
indicator display system and were also sent directly to the data
acquisition system. The operator also had available the display of
various temperature readings on his CRT. The operator generally selected
2, 3, or 4 critical temperature parameters, especially downhole
temperature, to be displayed on a minute-by-minute basis for his
observation.
4.3.3.3 CODT Versus Mass Flow
There was no equipment available to measure the COOT of influent
or effluent streams on a current or continuous basis. Therefore, process
control was affected by measuring the mass flow of the solids entering the
VRV System. An initial assumption was made of the CODT to total solids
ratio. This provided adequate control for start-up and was later
corrected for effluent oxygen concentration as mentioned below.
4.3.3.4 Other Flow Measurements
Air flow, heat transfer fluid flow, and oxygen flow were all
measured utilizing mass flow meters with good success. The use of mass
- 25 -
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flow meters eliminated the problems associated with conventional orifice
readings where variations in density of the fluid causes errors in the
flow measurement. Heat balances and mass balances were simplified
because the use of mass flow readings eliminated pressure and temperature
variation errors in measurements of the reactants.
4.3.3.5 pH
The pH of influent and effluent streams and of streams during acid
washes was measured using hand-held pH meters and in-line
instrumentation. Hand-held pH meters were utilized during special tests
and acid washes to observe and control the pH during these operations.
4.3.3.6 Dissolved Oxygen
Dissolved oxygen readings were initially used to determine the
concentration of oxygen remaining in the effluent after passage through
the VRV System. This measurement was eventually replaced by direct
observation of the oxygen in the effluent off-gas.
4.3.3.7 Effluent Off-Gas Component Concentration Measurement
To monitor the performance of the VRV System, a gas chromatograph
was installed to check the concentrations of various components in the
effluent off-gas. This gas chromatograph system continuously sampled the
effluent off-gas and analyzed it for the concentration of oxygen,
nitrogen, carbon dioxide, carbon monoxide, and other components. After
every 15-minute analysis cycle, the oxygen concentration was available to
the operator in the control room for his observation and correction of
oxygen flow rates or sludge feed rate. This allowed more precise process
control to compensate for the variations in sludge CODT loading for a
constant mass flow rate of solids, particularly during the period when
sludge was hauled in from neighboring communities and sludge quality was
questionable.
4.4 OXYGEN AND CHEMICALS
4.4.1 Oxygen
The VRV System originally operated with compressed air as the
oxygen source. In the second half of 1984, an oxygen supply system was
commissioned at the site to allow testing with varying percentages of
oxygen for sludge destruction. The oxygen supply system operated with few
mechanical difficulties. Liquid oxygen pump suction supply problems were
eliminated with pressure and timing modifications to the controls. Heat
tracing of the oxygen line eliminated freeze problems. The pump plunger
packing failed once of an unknown cause. It was repaired and put back
into service without further problems.
- 26 -
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4.4.2 Polyelectrolytes
Polyelectrolytes-were added to the effluent stream to facilitate
solids separation and decrease solids in the liquid effluent return to the
Longmont WWTP. Various tests were run with polymer injection to the
liquid/solid stream flowing to the Lamella separator, and also to the
Lamella underflow going to the ash pits.
- 27 -
-------
SECTION 5
OPERATING PROGRAM
5.1 OVERALL PROJECT OBJECTIVES
Program definition and analysis were based on a number of primary
program objectives. Documentation of the technical viability of the VRV
System was the overall objective, which included performance
characteristics of the subsurface reaction vessel, reduction of Chemical
Oxygen Demand (COD), and overall interaction and impact on the City of
Longmont WWTP. Specific technical objectives included:
1. Reduce sludge volume
2. Achieve maximum reduction of TSS, TVS, TVSS and CODT
3. Demonstrate the use of air, oxygen-enriched air,
and oxygen-enriched air up to 100? as oxidant sources
4. Achieve maximum downhole temperatures
5. Operate autogenously
6. Operate to recover energy
7. Validate hydrodynamic models for two-phase flow
in the downcomer and upcomer
8. Demonstrate environmental acceptability of by-products
9 Demonstrate ease of operations
The operating program conducted at Longmont was substantially
modified from the original program specified under the EPA Cooperative
Agreement. The operating program was modified to permit testing with
oxygen-enriched air and subsequently with 100® pure oxygen. Successful
results led to testing the system at sufficiently high sludge rates to
operate the system autogenously and finally, in a mode to recover energy
from the system.
5.2 CHRONOLOGY OF OPERATING PROGRAM AND RESULTS
Operation under the EPA Cooperative Agreement was initiated on
July 1, 1984, and completed in September 1985. Major operating campaigns
from April 1984 through November 1985 are shown in Figure 5.2-1. A
chronogram illustrating the development and demonstration of the VRV
System is shown in Figure 5.2-2.
Aqueous-phase oxidation technology had been under development for
more than ten years. Preliminary testing of the fundamental principles of
vertical tube aqueous-phase oxidation began with construction of a
Laboratory Batch Reactor (LBR) in 1973. After initial tests proved
encouraging, a 460-meter (1500-foot) pilot plant reaction vessel was
constructed at the Lowry Bombing Range in Denver and operated from 1977 to
1981. In 1982, the United States Environmental Protection Agency (EPA)
issued a technology assessment of the VRV System, under the name Vertical
Well Chemical Reactor.
- 28 -
-------
Validate Hydrodynamic Models ¦
Achieve 500»°F Downhole
Temperature with Atr 1
EPA Grant' Supported 1
Operation
Improve System Performance
Demonstrate Oxygen . ,
Enriched Air
Oemonstrafe 100% Oxygen * *
Prepare for Sustained _____
Autogenous Operation
Sustained Autogenous
Operation
Intermittent Autogenous
Operation
Recover Energy ¦
Apr May Jun Jul Aug Sep Oct. Nov. Dec .fan Feb. Mar Apr May Jun Jul Aug Sap. Oct
1 9 B A 1 9 8 5
Fig. 5-2.1 Chronology of Major Operating Campaigns
-------
Lab Bench Lowry
Reactor Pilot Plant
V
'I
1973 1977 1981
Fig. 5.2-2
Longmont
Design 8
Construction
Ready for
Commercialization
Retrofit
Start-Up
EPA Grant
Supported
Operation
1982
1983
1984 1985 1986
VRV Chronogram
-------
Construction of the system at Longmont began in October 1982, and
the original start-up period began in June 1983. Prior to reaching design
downhole temperature' and CODT reduction, the unit was shutdown in August
1983 to make necessary modifications. At this time Bow Valley Resource
Services Ltd. (BVRS) exercised its option to purchase rights to the
patented waste destruction technology. BVRS is a diversified
international company engaged in natural resource development and energy
services. Private capital from BVRS was used for construction of the
prototype facility. From September to November 1983, a detailed
engineering review of the design criteria and operating results of the VRV
and above-ground systems was conducted. The study led to an improved and
simplified system design in the areas of installation, structural
integrity, instrumentation, process control and data acquisition, reduced
frictional pressure drop, heat transfer, and scale control. From November
1983 to March 1984, fabrication of below-ground components occurred with
delivery beginning in February of 1984. Modifications to topside
equipment began in February 1984, and were completed in May 1984.
Installation of downhole piping and instrumentation began in April 1984
and was completed in May 1984.
In October 1984, VerTech installed a liquid oxygen supply system
which greatly increased the sludge treatment capacity of the process. The
VRV System was then able to treat more sludge than Longmont's WWTP
produced. VerTech upgraded the plant during the winter of 1984-85 to
process up to 27 metric tons per day (30 tons per day) of sludge. The
first autogenous test runs were made during February 1985 in preparation
for the sustained autogenous test period. During March and April,
additional raw and digested sludge was hauled in and the process was
tested exclusively at high capacity under autogenous operating conditions.
Plans were made to haul the VRV effluent in the event that the
Longmont WWTP could not treat higher recycle biological load. This proved
unnecessary since the WWTP efficiency was improved during operation of the
VRV System.
After the steady state run was completed, the VRV system operated
intermittently to process all the sludge. From May to August 1985, the
VRV system was tested to determine the effect of start-ups and shutdowns
on the Longmont WWTP. In September 1985, the reaction vessel internal
strings of pipe were pulled for inspection. Insignificant corrosion was
observed, making it possible to reinstall the unit.
5.2.1 Validate Hydrodynamic Model
The initial objective of validating the hydrodynamic model began
in May 1984. At a given temperature, the flow rate of water was held at a
predetermined constant rate, and the gas flow rate was varied. A
comparison of Longmont VRV data and predictions of the hydrodynamic model
are provided in Section 5.3.
- 31 -
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5.2.2 Achieve Oownhole Temperatures
The objective to achieve greater than ^50°C •(5G0+°F)
bottomhole temperature required several system modifications which were
described in detail in Section 4. These modifications were completed from
July to December of 1984.
5.2.3 Demonstrate with Oxygen-Enriched Air
The primary reason for the shift from use of air to use of oxygen
enrichment was the capacity limitations encountered when using air. An
oxygen customer station was designed, engineered and installed from August
to October 1984. A schematic of the oxygen customer station is shown in
Figure 4.2-2, page 21.
The first tests with oxygen enrichment were carried out in October
1984. Since the air compressor was oil lubricated, a potential hazard
existed with the injection of oxygen into the air stream. Oxygen was
introduced into the diluted sludge directly, rather than combining with
air upstream of the VRV. Immediate performance improvements were noticed
when shifting to oxygen enrichment. More sludge was processed, a higher
bottomhole temperature was attained and was easier to maintain, influent
and back pressure on the reaction vessel were reduced, and higher CODT
reductions were achieved. Tests were conducted at 40* oxygen, 50® oxygen,
80% oxygen and then 1004 oxygen.
5.2.4 Autogenous Operation and Energy Recovery
The objectives for the sustained autogenous operation of the unit
are shown in Table 5.2-1.
rABLE i.2-1
OBJECTIVES FOR SUSTAINED AUTOGENOUS OPERATION
1. Determine the Lowest Possible Operating Rate of the VRV with
Sludge from the City of Longmont.
2. Determine the Maximum Possible Operating Rate of the VRV System.
3. Study CODT Reduction as a Function of:
+ Bottomhole Temperature;
+ Residence Time; and
+ Influent Concentration.
4. Determine the Effect of Effluent Recycle on CODT Reduction and the
Reaction Vessel Temperature Profile.
5. Determine the Effect of the Topside Heat Recovery on VRV
Performance and Energy Balance.
6. Determine the Effect of High VRV System Operating Rates on
Longmont's Waste Treatment Plant,
- 32 -
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Several systems required modification to process sludge at rates of
18,000 kg/day (20 tons/day), since the original system design was for
5,400 kg/day {£ tons/day). A milestone schedule for autogenous operation
was prepared, as part of the overall test plan, and is shown in Figure
5.2-3.
A series of short duration (20-48 hours) autogenous tests were carried
out in February and March 1985. Sludge processing rates as high as 18,000
kg/day (20 tons/day), bottomhole temperature up to 270°C (520°F) with C0DT
reductions up to 88.54 were obtained. These results are discussed in
Section 6.
Sustained autogenous tests were carried out in March and April 1985.
Sludge was trucked in from nearby communities of Ft. Collins and
Lafayette. During the autogenous test period, the system processed waste
activated sludge and digested sludge, raw sludge and sludge from long-term
storage in a l.agoon.
As the capacity of the system was raised above 10,000 kg/day (11
tons/day), sufficient heat was generated from the exothermic oxidation
reactions to shut off the external heat transfer fluid heater. As the
bottomhole temperature continued to increase, the heat transfer fluid flow
was reversed, and heat was brought to the surface and rejected to the
atmosphere through an external air cooler. The capacity of the system was
tested at rates of 23,000-27,000 kg/day (25-30 tons/day). Operation could
not be sustained at these levels due to limited sludge supply, under
capacity of the heat transfer fluid cooling system and oxygen supply
system.
5.2.5 Environmentally-Acceptable By-Products
During the Longmont test program Chemical Oxygen Demand (COD)
reductions were between 75S and 88.5% with an 80% average reduction. The
remaining CODT, returned to Longmont's trickling filter, consisted of an
environmentally-acceptable and readily biodegradable weak acetic acid
stream which also contained other low molecular weight organic acids, such
as formic and glycolic acid. An ash slurry consisting of oxidized inert
solids was pumped into drying beds producing an odorless and sterile
material which was removed periodically. Centrifuge dewatering tests
showed the ash was readily dewatered to 50 vtt.% solids (see Table 6.11-3).
Ash was determined to be a suitable filler for brick manufacturing. A
more detailed report of the study is found in Appendix B.
Carbon dioxide comprised the majority of off-gas released from the air
separation system with small amounts of carbon monoxide and oxygen
present. Other organic components were present only in trace amounts at
concentrations well below levels required for health and environmental
consideration.
- 33 -
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PROJECT SCHEDULE
NOV. , DEC. | JAN. | FEB. | MAR. | APR. |
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
9 16 23 30 7 14 21 28 4 II 18 25 1 8 15 22 1 8 15 22 29 5 12 19 26 30
TASKS
WINTERIZ ATION
FACILITY
MODIFICATIONS
SLUDGE STORAGE
INSTRUMENTATION
1
!
\
1
TESTING
10 T/D TEST
AUTOGENOUS TEST PLAN
RECYCLE REACTION
VESSEL EFFLUENT
ENRICHED- AIR
~
!J J J I 1
fl 1 1
l 1 1
Fig. 5.2-3 Demonstration of Autogenous Capability
-------
Most organically-bound nitrogen in the sludge feed exited the VRV
process as soluble ammonia-nitrogen. Longmont had no NPDES ammonia
discharge limitation at the time of testing although a limit may be
implemented in the future. Trends toward anmonia discharge suggest the
need for ammonia polishing. Amnonia stripping is a viable system design
which could recover a 20% ammonia solution to be used as fertilizer.
5.2.6 Demonstrate Ease Of Operation
Many system changes were made to automate, simplify, and improve
overall control. Improvements to the heat transfer fluid system,
modifications to mechanical equipment, improvements of data collection,
and improvements to system capacity and reliability were described in
Section 4. These changes included mass air flow measurement to smooth out
fluctuations in air supply and to simplify use of ratio control of air to
total solids in the sludge feed. A gas chromatograph was installed to
control oxygen feed rate. Installation of a data monitoring and
collection system to provide the operator with one-minute averages for
many of the temperatures, pressures, and flow rates was used to control
the system. Installation of tanks and metering pumps simplified periodic
acid washing of the reaction vessel.
5.3 PROCESS MODELING
5.3.1 Hydrodynamic Model
The hydrodynamic model is used to predict pressure profiles in the
VRV. Given a temperature profile in the VRV and influent flow rates for
liquid and vapor, the pressures can be calculated from two-phase flow
relationships. The model is also used to assist in sizing of reaction
vessels. The size of the tubing used for the downcomer and upcomer
sections will determine the pressure drop and the vapor fraction
throughout the vessel. Correct selection of tube sizes will give the
required flow rates to get adequate mass transfer between the liquid and
the oxygen in the gas phase.
The hydrodynamic model was used to help size the Longmont reaction
vessel and to determine the required pressures topside. As discussed in
section 5.2.1, verifying the hydrodynamic model flow calculations an
initial major objective. Figure 5.3-1 demonstrates the accuracy of the
hydrodynamic model simulations during the Longmont start-up tests, when no
heat was supplied, only air and water flowed through the system. This
model was often used to verify plant conditions and to predict response of
the system before a process change was made.
5.3.2 Heat Exchange Model
The heat exchange model predicts the temperature profile in the
VRV, given a pressure profile and flow conditions. It accurately
calculates temperatures throughout the VRV and surrounding rock, as well
as the energy balance, at any given reaction vessel conditions.
- 35 -
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- 2000
12 -
- 1500
to -
N
-1000
OL
- 500
COLD TESTS (77'F)
AIR FLOW 15 fb/mln
LIQUID FLOW 122 gpm
- 0
1.4
0.4
0.8
1.0
1.2
1.6
0.2
0.6
O
(Thousands)
Depth (Meiers)
~ Actual Measurements
Fig. 5.3-1 Pressure Profile
-------
5.3.3 Laboratory Batch Reactor
Since the -hydrodynamic and heat transfer models can accurately
simulate the actual reaction vessel conditions of temperature and pressure
at different depths, they are used to create time, temperature, and
pressure profiles to be used in the laboratory batch reactor (LBR).
The laboratory batch reactor duplicates the conditions of an
element of fluid in the VRV. An element of fluid enters the reaction
vessel at ambient temperature. In the downcomer, the fluid temperature
and pressure increase with increasing depth in the VRV, as heat is
exchanged from the upcomer and is produced from the combustion reaction.
At the bottom of the VRV, the element of fluid is at the maximum
temperature and pressure. In the upcomer, the fluid temperature and
pressure decrease with decreasing depth in the reaction vessel, releasing
heat to the downcomer and to the surroundings. At the surface, the fluid
is only 16 C° higher than inlet temperature.
The hydrodynamic and heat transfer models produce the time,
temperature, and pressure profile necessary for the LBR to properly
duplicate the flow of an element of fluid under various operating
conditions. Placing a mixture in the LBR with sufficient oxygen, the
batch reactor is then heated to bottomhole conditions following the
prescribed time and temperature profile, and is then cooled to outlet
temperature. By following a time, temperature, and pressure profile
calculated from the models, and by supplying adequate mixing, the LBR
simulates the flow of an element of fluid through the VRV.
An example of a time and temperature profile used for a
correlation run during a non-autogenous test is shown in Figure 5.3-2.
The steep climb matches the observed non-autogenous temperature profile
where the temperatures are higher in the top of the VRV.
A plot illustrating the accuracy of the LBR predictions is shown
in Figure 5.3-3. Each square on the plot represents an LBR run made to
match conditions in the VRV. Each LBR run matches a different time,
temperature, and pressure profile predicted from the models. If the LBR
simulated conditions in the reaction vessel exactly, all of the points
would line up at corresponding CODT reductions. The line on Figure 5.3-3
is a best fit curve to the data points shown. The straight line fit
indicates that the predicted CODT reductions from the LBR are lower than
those obtained in the VRV at longmont. This allows VerTech to test any
sample in the LBR and be confident that the predicted reduction will be at
least as good as that obtained in a full-scale VRV.
- 37 -
-------
600
300-
500
250-
-400
200-
o
-300 £
150-
I-
<
K
Ul
Q.
2
Ul
100-
-200
50-
-100
0-
10
40
20
30
50
TIME (mfn.)
Fig. 5.3-2 Time and Temperature Profile
-------
90
85
BO
70
90% CONFIDENCE INTERVAL
65
60
55
50
50
70
90
LONGMONT COO REDUCTION
Fig. 5.3-3 LBR versus CODT Reduction
-------
SECTION 6
RESULTS AND DISCUSSION
6. T SYSTEM CAPACITY
6.1.1 Operating Range at Longmont
The operating program at Longnont covered the time period fron
June 1984 to September 1985. Table 6.1-1 summarizes the operating period,
showing the number of days operated and the amount of sludge processed for
each month of operation. VRV System operation was intermittent fron May
1985 to September 1985. This allowed Longnont to store sludge to permit
autogenous operation. During this time period, the VRV operated 295 days
and processed a total of 1,283 dry tons of sludge. The reaction vessel
capacity was increased by the change from air to oxygen as the oxidation
source, and the system was successfully operated using sludge as the sole
heat source. The days that the VRV did not operate were nainly due to
system modifications expected in a demonstration facility. Mechanical
reliability was 95.7". The only problens encountered involved shutdowns
of less than 24 hours.
One of the advantages of the VRV System was the wide operating
range of the reaction vessel. The operating program in Longmont was split
into two distinct modes of operation for data analysis and reporting
purposes: non-autogenous and autogenous operation. Mon-autogenous
operation included all times when the VRV required additional outside heat
to overcome the combined losses to the effluent and to the rock. This
included all those periods of operation from June 1984 to February 1985.
During this time period, the system operated with air and oxygen-enriched
air, but insufficient sludge was available to supply the heat needed for
autogenous operation.
Autogenous operation included all times when the system operated
with oxygen-enriched air and pure oxygen, and when sufficient sludge was
available to overcome the combined losses to the effluent and to the
rock. During autogenous operation, sludge was either hauled in from
outside sources, or Longnont stored sludge for intermittent operation.
The capacity of the Longmont WWTP was insufficient for sustained
autogenous operation. The energy balance for the two modes of operation
is discussed in Section 6.2.
Table 5.1-2 shows the ranges tested for non-autogenous and
autogenous operation and the results obtained from intensive sampling.
Better CODT reductions were obtained while operating autogenously. This
was partly due to the higher concentrations processed and the generally
higher downhole temperatures during autogenous operation. The results
summarized in Table 5.1-2 include all operating conditions tested, though
not necessarily the most desirable. Reported CODT reductions were
determined across the VRV without recycle. CODT reductions, as discussed
in Section 5.3.3, were higher with recycle.
- 40 -
-------
TABLE'6.1-1
OPERATING DAYS
SLUDGE PROCESSED
YEAR
MONTH
DAYS OPERATED*
(Dry Tons)
1984
June
15
40
July
29
109
August
22
75
September
28
58
October
14
32
November
25
146
December
17
81
1985
January
25
81
February
25
88
March
23
173
April
30
216
May
15
41
June
1
2
July
8
30
August
15
111
September
2
0
Total
295
1,283
~Includes acid washes.
TABLE 6.1-2
OPERATING RANGE TESTED IN LONGMONT
NON-AUTOGENOUS AUTOGENOUS
Average Range(Low-High) Average Range(Low-High)
Influent CODT S-3 (mg/L)
7,700
1,600-20,900
23,000
12,500-48,500
Effluent CODT S-4 (mg/L)
2,400
640-8,420
4,950
1,400-10,130
CODT Reduction (%)
67.7
51.0-86.1
78.2
65.8-88.5
Sludge Loading (lb/hr)
520
90-1,450
1,330
710-1,930
Sludge Solids {%)
6.7
2.4-10.5
4.7
1.9-7.2
Sludge Flow (gpm)
17
5-50
58
15-80
Total Flow (gpm)
118
100-180
109
68-134
Air Flow (lb/hr)
13.9
3.4-22.5
0.6
0-6.2
Oxygen Flow (lb/hr)
2.9
0-18.8
18.2
9.5-25.3
Heat Transfer Fluid (lb/min)
414
290-470
44.0*
0-300
Bottonhole Temp. (°F)
510
501-528
522
484-539
Number of Samples
498
158
~Extracting heat while autogenous.
- 41 -
-------
6.1.2 Minimum Capacity
The reaction vessel was operated at an extremely low operating
rate, but additional heat was then required to maintain the desired
temperature profile. Since the external heat exchange system at Longmont
provided enough heat to overcome the heat losses to the rock and to the
effluent, the operation was not limited by low concentrations.
6.1.3 Maximum Capacity
There were four factors which limited the capacity of the VRV:
heat transfer cooling system, oxygen flow rate, influent feed
concentration, and liquid flow rate.
The maximum capacity at Longmont was limited by the liquid oxygen
supply pump and the heat transfer fluid cooling system (no energy recovery
system was installed). To increase the system capacity, VerTech installed
an oxygen trailer. At start-up, when the surrounding formation was cold,
it was possible to operate at a high sludge feed rate, thus simulating a
higher heat removal capacity from the heat transfer fluid system. The
reaction vessel was operated at a maximum capacity of 30,000 kg (33 tons)
of CODT per day.
The hydraulic loading was not a limitation at Longmont since the
inlet sludge density stayed at 6-7 wt.S and dilution was required.
Typical liquid flow rates at Longmont were 80-120 gpm.
6.2 ENERGY BALANCE
6.2.1 Parameters Affecting Heat Losses at Longmont
Heat generated from the exothermic oxidation reaction was lost to
the rock formation surrounding the well bore, and to the effluent liquid
stream. Flush-out losses to the effluent were due to the higher
temperature in the effluent stream. This heat could be advantageously
applied to downstream biological processes. Warm water will alleviate
problems normally associated with operation during winter months. The
temperature difference between influent and effluent streams is generally
low, 8-17 C° (15-30 F°), due to efficient countercurrent heat transfer
between the downcomer and upcomer flow.
While running non-autogenously, radial heat losses across the
insulated tubular were greater than originally expected (see Section
4.2.1.2). Heat losses from the insulated tubular were transferred to the
aqueous-phase downcomer and then to the upcomer. This increased the
entire temperature of the aqueous streams, and increased the flush-out
losses unexpectedly. Inefficiencies of the insulated tubular created an
artificially greater radial temperature differential throughout the
length of the VRV. Because of this higher temperature difference, heat
losses to rock were greater during non-autogenous operation than during
- 42 -
-------
autogenous operation. An improved design will reduce heat losses
considerably during non-autogenous operation.
Losses to the rock are determined by materials in the heat path
between the reaction vessel and the formation, and by the radial
temperature difference. A cross section of the VRV and surroundings is
shown in Figure 6.2-1. The heat path between the VRV and the rock
consists of four layers: insulation, convecting fluid, cement, and rock.
Heat transfer coefficients for natural convection in a liquid
medium are an order of magnitude higher than those for natural convection
in air. High boiling temperature oil was used in the annular space
between the reaction vessel and the primary casing so that the reaction
vessel housing would only have to withstand its own weight. The oil
substantially increased heat losses to the rock. Use of a better quality
cement with a lower conductivity, between the casing and the rock, helped
reduce heat losses to the surroundings.
The type of rock also affects the heat losses. Heat conduction
away from the well bore depends on the temperature driving force and the
thermal diffusivity of the rock. The lithology in Longmont is largely
shale, with some layers of sandstone.
6.2.2 Non-Autogenous Operation
Non-autogenous operation requires energy input from the heat
transfer fluid system to achieve the necessary downhole temperatures. This
operating mode is necessary for initial start-up and after an acid wash.
The only other time the reaction vessel requires additional heat input is
when the heat produced from the exothermic oxidation reaction is less than
the sum of the heat lost to the rock and the heat lost to the effluent
stream.
The Longmont installation operated non-autogenously from June 1984
to February 1985. A typical energy balance during non-autogenous
operation is shown in Figure 6.2-2. Energy inputs to the VRV are from the
oxidation of the sludge (0.53 MW) and added heat from the heat transfer
fluid (2.34 MW). Energy out of the VRV is lost to the rock (1.41 MW) and
flushed out in the effluent (1.40 MW) as calculated below:
CALCULATIONS:
Heat of Reaction
Assume 6,000 Btu/lb heat of combustion
(430 lb sludge/hr) X (.7 lb reacted/lb feed) X (6,000 Btu/lb)
= 1,810,000 Btu/hr = 0.53 MW
Added Heat from Heat Transfer Fluid
Inlet Fluid Enthalpy = 318.3 Btu/lb
Outlet Fluid Enthalpy = 37.5 Btu/lb
(474 lb/min) X (318.3 - 37.5 Btu/lb)
= 7,990,000 Btu/hr =2.34 MW
- 43 -
-------
HMt
Raoetion Trantfcr
Vassal Fluid
Cantarlina insuloted
Tubular
Housing
Watar Reaction
Divider VmmI
Tub* Housing
Hsct
Tramftr
Fl aid
Heot
Tranifar
Fluid
Wi
m
wau
Bora
Rock Formation
Ca mant
"TSltll
Mill I
Fig. 6.2-1. VRV Cross-Sectional Schematic
- 44 -
-------
ENERGY INPUT
2.87 MWatts (9.8 MM BTU/hr.)
Oxidation
£3 MW
1185%)
Heat Transfer Fluid
134 MW (81i°/.l
ENERGY OUTPUT
2.87 MWafts (9.8 MM BTU/hr.)
Rush Out
147 MW (StOV.)
Loss to Rock
UO MW (49.0%]
Fig. 6.2-2 Non-Autogenous Energy Balance
- 45 -
-------
Effluent Flush-out Losses
(55,500 lb/hr) i [1 Btu/lb°F) X (150°F - 60°F)
= 5,000,000 Btu/hr = 1.47 MW
Rock Losses
By Difference:
Rock Loss = Heat Transfer Fluid + Heat Reaction - Flush-out
= 2.34 + 0.53 - 1.47 MW = 1.40 MW Rock Losses
6.2.3 Autogenous Operation
Autogenous operation is the point at which the heat generated from
the exothermic oxidation reaction is at least equal to the sum of the heat
losses to the rock and heat flushed out in the effluent stream. During
autogenous operation, the system is self-sustaining; no external heat
input is necessary.
In Longmont, the reaction vessel was operated autogenously from
February 1985 to August 1985. During March and April, sludge was hauled
in from neighboring communities to provide the additional fuel needed.
Afterward the WWTP stored sludge while the system was not operating. A
typical energy balance for autogenous operation is shown in Figure 6.2-3.
Energy input, entirely from the heat of reaction, was 1.50 MW. Energy was
lost to the rock (0.94 MW) and to the effluent (0.56 MW).
Flush-out and rock heat losses during autogenous operation are
less than the* losses experienced during non-autogenous operation. Since
the heat transfer fluid was no longer needed to heat the VRV, the losses
across the insulated tubular were effectively eliminated, reducing
temperature differences from influent to effluent. Heat losses to the
rock during autogenous operation were only 60-70% of those experienced
during non-autogenous operation. The improved insulated tubular design
will reduce heat losses during start-up and acid wash operation to the
level experienced during autogenous operation.
CALCULATIONS:
Heat of Reaction
(1,210 lb siudge/hr) X (.7 lb reacted/lb feed) X (6,000 Btu/lb)
= 5,100,000 Btu/hr =1.51 MW
Effluent Flush-out Losses
(63,400 lb/hr) X (1 Btu/lb°F) X (90°F - 60°F)
= 1,900,000 Btu/hr =0.56 MW
Rock Losses
Rock Loss = Heat of Reaction - Flush-out
= 1.51 - 0.56 = 0.94 MW Rock Losses
- 45 -
-------
ENERGY INPUT
1.50 MWafts (5.1 MM BTU/hr.}
Oxidation
ISO MW I10C.0V.)
ENERGY OUTPUT
1.50 MWalts (5.1 MM BTU/hr.)
Rush Out
0.54 MW (37.3V.)
6.2-3 Autogenous Energy Balance
- 47 -
-------
6.2.4 Heat Recovery
Heat recovery was necessary when the heat produced from the
exothermic oxidation reaction was greater than the flush-out heat and heat
loss to the rock. If heat was not removed from the reaction vessel by the
heat transfer fluid, the effluent temperature would have increased and
fluid in the upcomer would begin to boil.
By flowing the heat transfer fluid in the opposite direction from
start-up, heat was recovered from downhole. The heat transfer fluid
flowed co-currently with the aqueous downcomer, removing heat from the
downcomer across the heat transfer fluid housing. When the heat transfer
fluid reached the bottom, it returned in the insulated tubular, retaining
the high downhole temperature. The heat transfer fluid can be used to
generate steam or hot water in conventional equipment above ground.
A small 0.37 MW air-cooled exchanger was used to waste any excess
heat to the atmosphere. A typical energy balance for autogenous operation
with heat removal is shown in Figure 6.2-4. Energy input from the
oxidation reaction was 1.87 MW. Energy lost to the rock totaled 0.94 MW.
The other half of the energy was lost to the effluent (0.56 MW) and wasted
in the surface exchanger (0.37 MW).
Calculations are similar to those in Section 6.2.3, except that
more sludge was processed to generate additional heat. The amount of
sludge which can be processed is limited by the two-phase flow
characteristics and by the heat exchanger size.
6.3 CHEMICAL OXYGEN DEMAND TOTAL (CODT)
6.3.1 CODT Reduction as a Function of Temperature
Reduction of CODT in the VRV is dependent on many different
parameters, of which the most important are residence time and
temperature. In Longmont, the residence time can be changed in the vessel
by varying the liquid and gas flow rates. The Longmont demonstration
vessel was designed for an approximate one-hour residence time, with the
pump sizing restricting the possible flow rates and residence times
through the vessel. Because of these restrictions, the residence time
could not be varied enough to determine its influence on CODT reduction.
Any influence of residence time on CODT reduction is negligible in the
current reaction vessel design.
The influence of bottomhole temperature on the CODT reduction is
shown in Figure 6.3-1. CODT reduction increases with increasing
temperature. This figure represents 369 data points taken during
intensive sampling periods while operating autogenously. The average CODT
reduction over the entire temperature range (227-280°C) was 76.3%. Note
the large variation in reductions obtained for each of the temperature
values tested. The variation of +10% from the straight line curve fit is
- 48 -
-------
ENERGY INPUT
1.87 MWaits (635 MM BTU.hr.}
Oxidation
1.87 MW (100.0%)
ENERGY OUTPUT
187 MWatts (6J5MM BTU/hr.)
Heat
Transfer
Ruri '
Remval
0.37 MW IW.fiVo)
Flush Ouf
0i6 MW (30.0%]
Fig. 6.2-4 Autogenous Energy Balance with Heat Removal
- 49 -
-------
00-
Q3-
00"
03"
00-
73-
70"
69-
00
33"
50"
45-
40
33
30
25
20
13
io-
3"
0
Operating Conditions
AvaragQ Rango
C1ow-hIgh)
~ COD Influent. mg/L 21.400 5,000 - 40.500
COD Effluent, mg/L 5.030 1. 400 - 19,400
COD Reduction X 76. 3 32.3 - 92.1
Bottomhola Tamp, C
267.
5
22B -
282
Sludge Load. Ib/hr
1200.
0
0 -
1. 030
Liquid Flow, gpm
10B.
8
65 -
145
Air Flow. Ib/mln
3.
4
0 -
24. 0
Oxygen Flow, lb/tnln
17.
2
9. 5 -
25. 4
1 1 1 1 1 1 1 1 1 1 1 1 h-
3 223 230 233 240 243 230 253 280 2B3 270 273 280 2BS
Bottomhole Temperature (C)
Fig. 6.3-1 CODT Reduction vs Bottomhole Temperature
-------
due to other variables, such as liquid and gas flow rates, the overall
temperature profile and influent concentration. Reductions greater than
80% were routinely obtained while operating the VRV -under- normal
conditions.
6.3.2 CODT Reduction as a Function of Concentration
Figure 6.3-2 shows the dependency of CODT reduction on the inlet
concentration. These data include all of the composite sampling done by
J&A Associates over the course of the project. Most of the data points
are at lower concentrations before autogenous operation started. The high
concentrations represent average CODT reductions obtained while operating
autogenously. The data are fit to a curve represented by the general
equation which represents the response of a first order system to a step
change:
CODT Reduction = A x [1 - exp( - Influent CODT/tau)]
In the case of CODT reduction, the curve levels out at 77.4%
reduction above 12,400 mg/L influent CODT concentration. This reduction
is slightly lower than what would be achieved operating at ideal
conditions. The scatter indicates the influence of other variables such
as temperature on the concentration dependency.
6.3.3 Effect Of Recycle On CODT Reduction
The raw sludge feed was normally diluted with clarifier effluent
to the desired influent flow rate. Recycled VRV effluent was also used
for this purpose. During autogenous operating periods, a fraction of the
reaction vessel effluent was recycled to the inlet and reprocessed. Table
6.3-1 summarizes average results for CODT reductions with and without
effluent recycle. More detailed data are presented in Tables 6.7-1,
6.7-2, 6.7-5, and 6.7-6, where BODT recycle is also discussed.
TABLE 6.3-1
CODT REDUCTIONS WITH AND WITHOUT EFFLUENT RECYCLE
kg CODT Consumed kg CODT Consumed
kg CODT Influent kg CODT Processed
Without Recycle 0.791 0.791
With Recycle 0.737 0.847
As shown, CODT reductions across the reaction vessel itself
decreased from 79.1% without recycle to 73.7% with recycle, but overall
CODT reduction based on total CODT processed increased from 79.1% without
recycle to 84.7% with recycle. This difference can be attributed to the
accumulation of refractory compounds such as low molecular weight organic
acids. These components, which are more resistant to oxidation, undergo
further oxidation through recycling.
- 51 -
-------
100-
03"
00-
es-
80-
73"
70-
B5-
oo-
33"
30-
43-
40
93-
3CT
23-
20-
13
JO
s-
0
+
+¦
+
~
=n
o
~
>8
TT
~
Br
JJL
~
=a=
~
~
COO Influent,
COD Effluent.
mg/L
mg/L
COO Reduction X
Bottomhole Tamp, C
Sludga Load, lb/hr
Liquid Flow, gpm
Air Flow, lb/mln
Oxygon Flow. Ib/min
Heat Trans Fluid, lb/mln
\ 1 1 1 H
10. 320
2. 430
66. 6
~
~
Operating Conditions
Average
Range
(low-high)
230 - 32. 400
800 - 10. 900
45 - 83. 9
265. 0
241 -
279
560. 0
150 -
1. 500
112. 0
93 -
136
12. 5
0 -
22. 9
13. 1
0 -
22. 0
350. 0
0 -
470
+
+
+
+
+
H
2000 4000 BQOO B000 10000 12000 14000 18000 10000 20000 22000 24000 26000 28000 30000 32000 34000
Influent COD (mg/1)
Fig. 6.3-2 CODT Reduction vs Influent CODT Concentration
-------
6.3.4 Effect of Oxygen Consumption on CODT Reduction
Oxygen consumption during sludge processing was determined by CODT
analysis of VRV influent and effluent. An on-line gas chromatograph {GC)
was used to monitor oxygen, nitrogen, carbon dioxide and carbon monoxide
concentrations in the VRV off-gas every 15 minutes.
Several oxygen balances were performed during intensive sampling
periods for quality control checks of analytical CODT data and process
instrumentation. A sample oxygen . balance during oxygen-enriched air
operation is presented in Table 6.3-2. The average O2/CODT ratio was
1.014 indicating excellent agreement.
Continuous oxygen monitoring in the off-gas determined the effect
of excess oxygen on efficiency of CODT removal. Figure 6.3-3 shows that
increasing excess oxygen in the off-gas had no effect on process CODT
reductions. Excellent reductions at stoichiometric oxygen addition can be
attributed to excellent mass transfer of oxygen into solution during
oxidation.
6.3.5 Solids Reduction Related to CODT Reduction
This section presents the results of reduction of TVSS, TVS, and
TSS as related to CODT reduction in the VRV. Graphs show results obtained
from the City of Longmont daily analyses, as well as a similar plot drawn
from the composite analyses of J & A Associates.
Figures 6.3-4 and 6.3-5 present the results of TVSS Reduction.
Even at low CODT reductions of 50%, volatile suspended solids reduction
was greater than 75%. Section 6.4 provides more TVSS results. Figures
6.3-6 and 6.3-7 give results of total volatile solids reductions. TVS
reduction is about 15% greater than CODT reduction. Figures 6.3-8 and
6.3-9 present results for total suspended solids reductions. TSS
reduction closely follows CODT reduction.
Note that the pairs of graphs presented for each of the parameters
investigated agree closely, indicating that although the analytical and
sampling techniques discussed in Section 4 differed between the Longmont
City Laboratory and J & A Associates, the results were very similar.
6.4 TOTAL VOLATILE SUSPENDED SOLIDS (TVSS)
6.4.1 TVSS Reduction as a Function of Temperature
Figure 6.4-1 shows the influence of bottomhole temperature on TVSS
reduction in the reaction vessel. The temperature dependency on TVSS is cle
ar. Volatile suspended solids destruction is nearly complete in the VRV at
high temperatures.
During the entire operating period, composite samples analyzed for
TVSS indicated an average reduction of 92.3%, with a maximum of 98.4%. An
average TVSS reduction of 96.5% was achieved during autogenous -operation.
- 53 -
-------
Table 6.3-2 OXYGEN BALANCE
GAS
CHROMATOGRAPH DATA
INTENSIVE SAMPLING DATA
TIME
% h2
J 02
t coz
% CO
* OTHER
LOOT In
mg/L
COOT Out
mg/L
1 RED.
13:00
46.99
4.89
41.96
3.11
3.05
10710
2360
78.0
13:15
47.72
4.88-
42.51
3.09
1.80
9840
2250
77.1
13:31
47.95
3.56
43.49
2.90
2.10
9920
2170
78.1
13:46
47.79
3.55
43.75
2.46
2.45
10240
2160
78.9
14:01
47.15
4.22
44.14
2.09
2.40
10240
2090
79.6
14:16
47.33
4.37
43.99
2.02
2.24
9740
2150
77.9
14:32
46.98
6.45
42.23
2.09
2.25
11470
2090
91.8
14:47
47.06
6.51
42.02
2.18
2.23
10640
2110
80.2
Average
47.37
4.80
43.01
2.49
2.32
10350
2173
78.9
Std.Dev.
0.37
1.08
0.86
0.44
0.36
537
86
1.4
OXYGEN BALANCE
02 In
kg/hr
02 Out
kg/hr
COOT RED.
kg/hr
0» RED.
kg/hr
o2/codt
Closure t
241.0
18>. 6
225.4
222.4
98.6
241.0
18.3
204.9
222.7
108.7
241.0
13.3
209.2
227.7
108.8
241.0
13.3
218.1
227.7
104.4
241.0
16.0
220.0
225.0
102.2
241.0
16.5
204.9
224.4
109.5
241.0
24.6
253.2
216.4
85.4
241.0
24.8
230.3
216.2
93.9
241.0
18.2
220.8
222.8
101.4
0.0
4.5
16.1
4.5
7.9
-------
90-T
80" "
B6-1-
8-4-r
_~ D
66-"
B4T
B2-"
~ ~
10
15
20
25
30
Mole Percent Oxygen in Off Gas
Fig. 6.3-3 CODT Reduction vs Oxygen in Off-Gas
- 55 -
-------
COD Raductlon X
Fig. 6.3-4 TVSS vs CODT - J & A Data
-------
to- -
oH 1 1 1 1 1 1 1 1 1 1 1 \ 1 1 1 1 1 1 1 r
o b io is eo eo so sa 40 4S bo bb so sb 70 78 eo m so bb ioo
COD Reduction x
Fig. 6.3-5
TVSS vs CODT - City of Longmont Data
-------
100-
os-
00-
03'
BO
73*
70"
03-
00-
33-
30-
43
40
33
30
25'
20
J3
io-
3"
0
CD
10
15
20
25
30
39
40
49
SO
99
89
70
73
eo
es
eo
05
100
COD Reduction X
Fig. 6.3-6 TVS vs CODT
• J I A Data
-------
too-
oo-
BO
70"
60
BO
40
90
BO
to-
0
i 1 i r ¦ ¦ i i 1 i 1 1 1 1 1 1 1 1 1 r
4S 80 SO SO 95 40 40 00 BO 00 00 70 70 00 00 00 00 100
COO Reduction X
Fig. 6.3-7 TVS vs CODT - City of Longmont Data
-------
COD Reduction X
Fig. 6.3-8 TSS vs CODT - J & A Data
-------
100"
90-
BO"
70*
80-
50
40
30
20-
10
0
~
~
~
£
~
~
~ r*Tir|
p g%
[ft? ~ C Da
f
>"b n
^ %
~
to in bo aa so 33 40 40 oo bo so as 70 70 ao bo ao so too
COD Reduction X
Fig. 6.3-9 TSS vs CODT - City of Longmont Data
-------
oa-
03"
QG-
85"
00-
73-
70"
as
60
53
SO
43
40
33
30
23
20
IS
10
—I-
240
243
Gporating ConditIons
Averago
COD Influent,
COD Effluent,
mg/L
mg/L
COD Reduction %
Bottomhole Tamp, C
Sludge Load, lb/hr
Liquid Flow, gpm
Air Flaw, lb/mln
Oxygen Flow, lb/mln
Heat Trans Fluid, lb/mln
—I 1 1 f-
230 2SS 260 ZBS
Bottomhole Temperature
TVSS Reduction vs Bottomhole Temperature
Range
(1ow-hi gh>
12. 700
2. 200 -
32. 400
2. 700
goo -
10. 900
69. 0
50 -
83. 9
267. 0
247 -
280
700. 0
150 -
1. 500
111.0
93 -
136
11. 7
0 -
20. 2
8. 7
0 -
22. 0
310. 0
¦
0 -
t
470
•
1
270
I
273
1
200
s
Fig. 6.4-1
-------
6.4.2 TVSS Reduction as a Function of Concentration
TVSS reduction dependency on concentration is shown in Figure
6.4-2 For influent TVSS concentrations greater than 3400 mg/L, there is
virtually no influence of feed concentration on TVSS reduction. This
curve suggests that reductions will level out at approximately 95.74 TVSS
reduction, regardless of influent concentration. Greater reductions are
obtained by increasing the bottomhole temperature and the residence time.
6.4.3 Effect of Demonstration Facility on longmont WWTP TVSS
City of Longmont TVSS data were collected daily for each stage of
operation from December 1984 to September 1985. TVSS values were also
averaged over the entire period with results given in Table 6.4-1
Average percent removals for TVSS from WWTP influent to effluent with the
VRV System operating were 86.0% and without the VRV system operating were
85.64. As shown, system operation had no significant effect on overall
TVSS removals in the WWTP.
TABLE 6.4-1
TSS/TVSS AVERAGE FOR LONGMONT WWTP
DECEMBER 1984 - SEPTEMBER 1985
Influent
Equalization
Effluent Basin
Primary Clarifier
Effluent
Trickling Filter
Influent
Trickling Filter
Effluent
Rotating Biological
Contactor Effluent
Final Clarifier
Effluent
Avg.4 Removal
WWTP OPERATING
WITHOUT VERTECH
(mg/L)
TV5T
TS5
145
307
111
131
129
149
27
81 .44
125
236
89
102
102
106
18
85.6%
WWTP OPERATING
WITH VERTECH
(mq/L)
755
T75T
151
342
122
154
156
178
27
82.14
129
250
99
109
112
119
18
86.04
- 63 -
-------
oo-
03-
00-
B3-
oo-
73-
70"
B3-
BO'
33'
30
43-
40-
33
30'
33-
zo-
13'
ID-
S'
0
~~
~
Operating Conditions
Avaraga Range
(low-high)
COD Influent. mg/L 12.700 2.200 - 32,400
COO Effluent. mg/L 2.700 900 - 10.900
COD Reduction X 69.0 50 - 93. 9
Bottomhole Tamp. C 267.0 247 - 200
Sludge Load, lb/hr 700.0 150 - 1.500
Liquid Flow, gpm 111.0 93 - 136
Air Flow. Ib/mln 11.7 0 - 20.2
Oxygen Flow, Ib/mln 9.7 0 - 22.0
Heat Trans Fluid. Ib/itiln 310.0 0 - 470
—I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1000 2000 3000 4000 3000 6000 7000 B000 0000 10000 11000 12000 13000 14000 1SOOO 18000 17000 IBOOO
Influent TVSS
-------
6.5 TOTAL VOLATILE SOLIDS (TVS)
6.5.1 TVS Reduction as a Function of Temperature
Figure 6.5-1 illustrates total volatile solids reductions obtained
at various bottomhole temperatures. Each point represents a composite
sampling period at various operating conditions. The linear regression
curve fit indicates an increasing TVS reduction with increasing
temperature.
During the entire operating period, composite samples showed an
average TVS reduction of 83.7%, with a maximum reduction of 97.5%. The
average TVS reduction during autogenous operation was 93.9%.
6.5.2 TVS Reduction as a Function of Concentration
TVS reduction dependency on reaction vessel influent concentration
is shown in Figure 6.5-2. TVS reduction levels out at 93.3% at
concentrations greater than 9100 mg/1.
6.6 TOTAL SUSPENDED SOLIDS (TSS)
6.6.1 TSS Reduction as a Function of Temperature
The influence of bottomhole temperature on suspended solids
reduction is presented in Figure 6.6-1. The curve fit suggests increasing
TSS reduction with increasing tenperature, as expected. The wide scatter
illustrates the fact that high temperatures alone will not insure high
reduction. For a constant bottomhole temperature, the high reductions are
obtained at generally higher TSS concentrations, while the low reductions
are at lower TSS concentration.
TSS reductions averaged 69.8% based on composite sampling for the
entire operating period, with a high of 91.5%. During autogenous
operation, TSS reductions averaged 78.72.
6.6.2 TSS Reduction as a Function of Concentration
TSS reductions ranged from 45-91? and are shown in Figure 6.5-2.
As illustrated by the curve fit, reductions increased with increasing
concentration up to 7400 mg/1, at which point the TSS reduction leveled
out at 79.0%.
6.6.3 Effect of the Demonstration Facility on WWTP TSS Removal
Longmont TSS data were collected daily for each operating stage
from December 1984 to September 1985. TSS values were averaged over the
entire period with results shown previously in Table 6.4-1. Average
percent removals for TSS from WWTP influent to effluent were 82.1% with
the VRV System operating and 81.4% with VRV system shutdown. VRV System
- 65 -
-------
oo-
03-
00-
09-
90"
73-
70"
63-
80*
33"
SO"
43-
40
33
30-
25-
20
13
10'
3-
0
~
~
~
Oporat1ng Condit1one
Avoraga Rango
(1ow-hi gh>
COD Influent. mg/L
COD Effluent. mg/L
COD Reduction 7.
12. 700
.2. 700
69. 0
2. 200 -
900 -
50 -
32. 400
10. 900
83. 9
Bottomhole Temp, C
Sludge Load, lb/hr
Liquid Flow, gpm
287. 0
700. 0
111.0
247 -
150 -
93 -
290
1. 500
136
Air Flow, lb/mln
Oxygen Flow, lb/mln
Heat Trans Fluid, lb/mln
i i i
11. 7
8. 7
310. 0
I
0 -
0 -
0 -
1
20. 2
22. 0
470
1
1 1 I
233 2BO 203
270
I
273
1
200
Bottomhole Temperature (C)
F1g. 6.5-1 TVS Reduction vs Bottomhole Temperature
-------
00-
03"
eo-
B3-
BO-
73"
70"
oa-
60
S3"
50
43'
40'
33'
30
23'
za
IS
ID-
S'
0
~
~
~
—f—
2000
Operating Conditions
Average
COD Influent.
COD Effluent,
COD Reduction
mg/L
mg/L
X
Bottomhole Temp, C
Sludge Load. Ib/hr
Liquid Flow, gpm
Air Flow, lb/mln
Oxygen Flow, lb/mln
Heat Trans Fluid, lb/mln
H 1 h
Rango
(low-high)
12, 700
2. 200 -
32. 400
2. 700
goo -
10. SOO
eg. o
50 -
83. 0
267. 0
247 -
200
700. 0
150 -
1. 500
111.0
93 -
136
11.7
0 -
20. 2
B. 7
0 -
22.0
310. 0
0 -
470
1—
24000
4000
aooo
8000
10000
12000
14000
i aooo
leaoo
20000
22000
26000
Influent TVS (mg/1)
Fig. 6.5-1 TVS Reduction vs Bottomhole Temperature
-------
100- -
83" "
80" "
0S- -
80"
75"
70"
B3- -
80"
33"
R
Q
d
U 50-
c
t
i
o
n as- -
45
40
X
30
23- .
20- -
13
10- "
s-
o-
233
~
240
243
Fig. 6.6-1
~
CD ~
~
~
Operating Conditions
Avaraga
COO Influent, mg/L
COD Effluent. mg/L
COD Raductlon X
12. 700
2. 700
69. 0
Range
2. 200 - 32. 400
900 - 10. 900
50 - 83. 9
—f-
230
Bottomhola Tamp. C 267. 0
Sludge Load. Ib/hr 700.0
Liquid Flow, gpm 111.0
Air Flow, lb/mln 11.7
Oxygon Flow, lb/mln 8.7
Heat Trans Fluid, lb/mln 310.0
1 1 1-
—I-
270
247 -
150 -
93 -
0 -
0 -
0 -
-I-
280
1. 500
136
20. 2
22. 0
470
1
2SS
273
Bottomhole Temperature (C)
TSS Reduction vs Bottomhole Temperature
-------
00-
05-
oo-
B3-
00-
73*
70"
09-
flO-
55
so-
43
40-
33
30
23-
20
13
to
s-
0
C
~
~
~
~
Operating Conditions
Avaraga Range
-------
operation had no significant effect on overall TSS removal in the WWTP.
The Longmont WWTP was able to produce a final effluent TSS within its
NPDES Discharge Permit Limitations of 30 ng/L,. whether or not the VRY
System was operating.
6.7 BIOCHEMICAL OXYGEN DEMAND TOTAL (BOOT)
6.7.1 Effect of VRV Recycle on BOOT Reduction
During autogenous operating periods in March and April 1985,
composite samples of reaction vessel influent and effluent were analyzed
for CODT and carbonaceous BOD5 to determine the" effect of recycling VRV
effluent.
Removal rates based on concentrations of VRV influent and effluent
(mg/L) from 12 tests with no recycle (Table 6.7-1) and 5 tests with
varying amounts of recycle (Table 6.7-2) show that a 51 decrease in CODT
and BODT reductions occurred when recycling. However, removal rates based
on actual mass of sludge processed show that recycling provides an
additional 104 reduction in BODT (Tables 6.7-3 and 6.7-4), and a 61
reduction in CODT (Tables 6.7-5 and 6.7-6).
TABLE 6.7-1
LONGMONT C0DT/B0DT REDUCTIONS
AUTOGENOUS WITHOUT RECYCLE
CODT
CODT % 1
Reduction
BODT
BODT
% Reduction
S-3
S-4
CODT
S-3
S-4
BODT
(mg/L)
(mg/L) S
-3 to S-4
(mg/L)
(mg/L)
S-3 to S-4
15,920
3,930
75.0
...
25,720
4,590
81.8
7,450
3,000
59.7
20,530
4,240
79.3
6,500
2,980
54.2
15,250
3,240
78.8
5,640
2,250
60.1
18,410
4,370
76.3
5,650
3,230
43.9
23,590
5,020
78.7
9,000
3,650
59.4
16,040
3,220
79.9
5,720
2,230
61.0
31,860
6,480
80.0
9,200
4,620
49.8
24,300
4,550
81.3
7,050
2,950
58.2
16,110
3,160
80.4
5,430
2,230
58.9
19,640
3,470
82.3
6,400
2,640
58.8
19,670
3,970
79.5
6,130
2,780
54.6
Average
78.7
Average 56.2
- 70 -
-------
TABLE 6.7-2
LONGMONT CODT/BODT REDUCTIONS
AUTOGENOUS WITH RECYCLE
CODT
CODT
% Reduction
BODT
BODT
% Reduction
S-3
S-4
CODT
S-3
S-4
BODT
(mg/L)
(mg/L)
S-3 to S-4
(mg/L)
(mg/L)
S-3 to S-4
18,930
6,060
68.0
24,780
5,790
76.6
8,520
4,210
50.6
19,230
5,230
72.8
7,860
3,690
53.0
20,010
5,300
73.5
6,790
4,020
40.8
20,950
4,740
77 A
8,220
3,180
61.3
Average 73.7
Average 51.4
TABLE 6.7-3
LONGMONT BODT REDUCTIONS
AUTOGENOUS WITHOUT RECYCLE
BODT/HOUR BODT/HOUR AVERAGE
FED
kg
(S-3)
(lb)
DISCHARGEE
kg
1 (S-4)
(lb)
kg BODT CONSUMED
kg BUDT FED
TEMPERATURE
°C (°F)
170.5
(376)
71.2
(157)
0.582
272
(523)
175.0
(386)
82.9
(183)
0.526
277
(531 )
156.9
(346)
64.8
(143)
0.587
276
(529)
159.2
(351)
92.0
(203)
0.422
268
(515)
234.5
(517)
98.4
(217)
0.580
274
(526)
140.1
(309)
56.7
(125)
0.596
275
(527)
193.6
(427)
101.6
(224)
0.475
274
(525)
148.7
(328)
64.8
(143)
0.764
279
(535)
122.9
(271)
52.6
(116)
0.572
269
(516)
155.1
(342)
66.2
(146)
0.573
276
(528)
147.4
(325)
69.4
(153)
0.529
270
(518)
Average 0.546
- 71 -
-------
TABLE 6.7-
-4
LONGMONT BODT REDUCTIONS
AUTOGENOUS WITH
RECYCLE
BODT/HR
BODT/HR
BODT/HR
BODT/HR
BODT
S-l
S-2
TO VRV
S-4
CONSUMED
TEMP.
kg (lb)
kg (lb)
kg (lb)
kg (lb)
BODT S-l
°C
(°F)
— —
— —
— —
— —
—
264
(507)
— —
—
— —
— - —
—
252
(485)
159.7 (352)
39.1 (86.2)
198.7 (438)
108.1 (225)
0.605
277
(530)
170.1 (375)
43.5 (95.8)
213.6 (471)
103.9 (229)
0.645
268
(514)
130.6 (288)
59.9(132.0)
190.5 (420)
116.6 (257)
0.566
274
(526)
154.7 (341 )
44.7 (98.5)
199.6 (440)
79.9 (176)
0.774
273
(524)
Average
0.648
Assumes S-2 (recycle) concentrations are equal to S-4 concentrations.
TABLE 6.7-5
LONGMONT CODT REDUCTIONS
AUTOGENOUS WITHOUT RECYCLE
CODT/HR
FED (S-3)
kg (lb)
CODT/HR
DISCHARGED (S-4)
kg (lb)
kg CODT CONSUMED
kg CODT FEED
AVERAGE
TEMPERATURE
°C (°F)
383.0
(844)
99.3
(219)
0.740
257
(495)*
578.8
(1,276)
109.3
(241)
0.811
272
(523)
553.8
(1,221)
118.4
(261)
0.786
277
(531)
525.5
(938)
92.9
(205)
0.781
276
(529)
509.4
(1 ,123)
124.7
(275)
0.755
268
(515)
615.1
(1,356)
135.6
(299)
0.779
274
(525)
392.4
(865)
81.6
(180)
0.792
275
(527)
671 .3
(1,480)
142.4
(314)
0.788
274
(525)
512.1
(1 ,129)
99.8
(220)
0.805
279
(535)
365.1
(805)
74.4
(164)
0.796
269
(516)
476.7
(1,051)
87.1
(192)
0.817
276
(529)
472.6
(1,042)
98.9
(218)
0.791
270
(518)
Average 0.791
*Low temperature not included in average.
- 72 -
-------
TABLE 6.7-6
LONGMONT CODT REDUCTIONS
AUTOGENOUS WITH RECYCLE
CODT/HR
CODT/HR
CODT/HR
CODT/HR
CODT
S-l
S-2
TO VRV
S-4
CONSUMED
TEMP.
kg (lb)
kg (lb)
kg (lb)
kg (lb)
CODT S-l
•c
(°F)
367.4 (810)
104.3 (230)
471.7 (1040)
156.5 (345)
0.858
264
(507)
263.1 (580)
76.2 (168)
339.3 (748)
134.7 (297)
0.778*
252
(485)
524.4 (1156)
54.0 (119)
578.3 (1275)
140.2 (309)
0.836
277
(530)
461.3 (1017)
61.7 (136)
523.0 (1153)
147.0 (324)
0.815
268
(514)
483.1 (1061 )
79.4 (175)
562.5 (1240)
153.8 (339)
0.846
274
(525)
441.4 (973)
66.7 (147)
508.0 (1120)
119.3 (263)
0.881
524
(524)
Average
0.847
*Low temperature not included in average.
Assumes S-2 (recycle) concentrations are equal to S-4 (effluent)
concentrations.
6.7.2 Effect of VRV System Operation on the BODT in Longmont WWTP
Figure 6.7-1 illustrates the overall Longmont WWTP flow diagram
and the point at which the VRV System's effluent was returned upstream of
the trickling filter. Daily composite samples were collected and analyzed
for BODT and BODS during the test program.
Average BODT and BODS concentrations are presented in Table 6.7-7
for each WWTP process with and without the VRV System operating during the
period from December 1984 to September 1985. This is the same period used
for the analysis in Table 6.4-1. An average increase of 38 mg/L BODT and
25 mg/L BODS was found at the trickling filter influent where YRV effluent
was returned. When the VRV System did not operate, Longmont sludge was
sent to the digesters. Digester supernatant was land applied and not
returned for secondary treatment. Therefore, when the reaction vessel was
operating, secondary treatment was able to handle the increased load due
to the VRV effluent. Increased loading to the WWTP shows a slightly
decreased overall efficiency in BODT and BODS removals.
Percent removals for each stage of the secondary treatnent process
for the period of December 1984 to September 1985 are presented in Table
6.7-8.
Percent removals calculated for BODT show VRV System operation had
little effect on the primary clarifier. The removal rates through the
trickling filter were much better with the system operating even though
- 73 -
-------
Land Application
WWTP Feed
Digester
Primary
Clarifler
Thickener
VRV Effluent
VRV Recycle
Ash
WWTP Effluent
WWTP Recycle
VRV
System
Trickling
Filler
Final
Clarifler
RBC
Equalizer
Fig. 6.7-1 longmont WWTP Flow Diagram
-------
TABLE 6.7-7
8OD5 CONCENTRATION FOR LOMGMONT WWTP
December 1984 - September 1985
WITHOUT VRV SYSTEM WITH VRV SYSTEM
109 DATA DAYS 116 DATA DAYS
BOOT mg/L BODS mg/L EWPT mg/L BODS mg/L
Influent 185 73 181 75
Equalization Basin Effluent 260 69 265 66
Primary Clarifier Effluent 131 57 134 56
Trickling Filter Influent 136 55 174 80
Trickling Filter Effluent 109 35 126 49
Rotating Biological Contactor
Effluent 87 21 102 30
Final Clarifier Effluent 21 13* 30 17*
Average Percent Removal 88.7% 82.Z% 83.41 77.3%
* BODS average is from December 1984 to May 1985 only.
TABLE 6.7-8
BOD PERCENT REMOVAL
FOR LONGMONT WWTP
December 1984 - September 1985
% REMOVAL
WITHOUT VftV SYSTEM HITh VRV SVsT^M
109 DATA DAYS 116 DATA DAYS
B5UT BUDS BODY BOUT
Primary Clarifier 49.6 17.4 49.4 15.2
Trickling Filter 19.9 36.4 27.6 38.8
Rotating Biological Contactor 20.2 40.0 19.1 38.8
Final Clarifier 75.9 38.1 70.1 43.3
Trickling Filter Influent to
Final Clarifier Effluent 84.6 76.4 82.8 78.8
- 75 -
-------
approximately 38 mg/L BODT was added from the VRV effluent return. The
rotating biological contactor efficiency for BODT removal was about the
same with the VRV System operating. A decrease in BODT removal was seen
at the final clarifier. A drop in removal efficiency through the final
clarifier with the VRV System operating can be attributed to additional
loading placed on an undersized clarifier.
Percent removal was calculated from daily BODT analyses from
January through April 1984, before VRV System start-up. These values were
compared with BODT analyses and percent removals for January through April
1985 while the system operated nearly every day.- This analysis, presented
in Table 6.7-9, determines the effect of the VRV System operation on the
efficiency of the WWTP processes. The average percent removals during
1985 are consistently higher than corresponding values in 1984 for all
WWTP processes. This Indicates that an Increased BODT removal rate was
accomplished through the WWTP with the VRV System operating. Increased
biomass in the trickling filter probably accounts for the increased
efficiency during 1985.
TABLE 6.7-9
WWTP MONTHLY AVERAGE BODT
ROTATING
PRIMARY BIOLOGICAL
CLARIFIER TRICKLING FILTER CONTACTOR FINAL CLARIFIER
Effluent Influent Effluent 2 Effluent ? Effluent ?
DATE mg/L mg/L mg/L Removal mg/L Removal mg/L Removal
1984
JAN
153
153
125
18.3
112
10.4
31
72.3
FEB
140
140
116
17.1
101
12.9
26
74.3
MAR
137
137
118
13.9
101
14.4
25
75.3
APR
123
123
109
11.4
91
16.5
27
70.3
1985
JAN
137
158
123
22.2
93
24.4
24
74.2
FEB
148
154
127
17.5
108
15.0
24
77.8
MAR
148
181
146
19.3
123
15.8
26
78.9
APR
138
174
140
19.5
115
17.9
30
73.9
- 76 -
-------
To smooth out the dally variation in BODT influent loading and
present the results graphically, daily BODT loading on the WWTP influent
-during January to-April- 1984 -a^nd- 1985 -was--p-lotted for each day of the
week, Figures 6.7-2 through 6.7-8. Table 6.7-10 gives a statistical
analysis of the daily and arithmetic mean values. The least scatter in
data was observed for Friday data points, Figure 6.7-7. Using Friday data
only, and an average of 0.2 kg BODT returned per kg sludge processed,
percent removal was calculated and compared to the average percent removal
without the VRV System operating. Figures 6.7-9, 6.7-10, and 6.7-11 show
the average percent removal of BODT for Fridays for each of the secondary
processes. Each of the squares on the plot represents a percent removal
at a specific sludge feed rate to the VRV. The double line is a best-fit
through these squares. Figure 6.7-9 shows an increase in percent removal
of BODT in the trickling filter with the VRV System operating and also
shows steady removal at high reaction vessel feed rates. Figure 6.7-10
shows slightly lower percent removals in the RBC with the system
operating. Figure 6.7-11 shows a small decrease in the final clarifier
effluent removal with VRV operating.
Based on these analyses, VRV System's effluent return to the WWTP
improved the efficiency of the secondary processes and maintained an
effluent quality that met the NPDES Specifications. The improved
secondary BODT removal efficiencies allowed the WWTP to process returned
effluent when the VRV System treated up to 18,000 kg/day (20 TPD) of
sludge.
TABLE 6.7-10
STATISTICAL ANALYSIS OF L0NGM0NT WWTP
INFLUENT BODT LOADING BY DAY
(BODT lb/day Influent)
AVERAGE
STANDARD
DEVIATION
MAXIMUM
MINIMUM
RANGE
DAILY
10,750
2,210
17,390
4,400
12,990
Sunday
10,140
2,440
16,340
5,690
10,660
Monday
ro
00
o
2,110
15,870
8,010
7,850
Tuesday
10,760
2,340
15,510
4,400
11,110
Wednesday
11,090
2,570
17,390
5,690
11,700
Thursday
10,290
1,880
13,490
6,910
6,580
Friday
10,800
1,710
15,370
7,000
8,370
Saturday
10,860
2,290
16,680
7,010
9,670
- 77 -
-------
24000*
22000-
20000'
10000-
16000'
14000
12000'
10000
8000
eooo
4000
2000
O'
Jar
~
~
~
~
~ ~
~
~
~
~
~
~
~
~
~
~
~
~
~
~
o
~
~
~
~
1 1 1 1 1 1 l-a-
Fob 64 Hor 84 Apr 64 Jan 85 Fob 03 Mar 85 Apr 83
Fig. 6.7-2 Influent Plant BOOT Load
Sundays Only
-------
23000--
24000-"
23000"
22000--
21000"~
B
0 20000--
D
Ioooo-"
1BOOO--
0
a 17000--
d
1
n
g
10000"-
15000--
I 4000--
J 3000-
12000-
-P
1
b
/
d
a nooo--
y
' 10000--
9000--
BDOO-j-
7000-
6000
~
~
~
~
~
~
~ D ~
~ ~
~
~
~
~
~
~
~
~
~
~
~
~
~
~
~ ~
Jan B4
-|
Fob 04
1
Apr B4
1
Jan B3
Fob B5
Nor B5
1
Apr B9
F1g. 6.7-3 Influent Plant BOOT Load
Mondays Only
-------
24000-
22000""
B
0
D
20000--
leooo--
L
0
a
d
1
n
g
i
b
/
d
a
y
~
~
I 4000--
izooo-
iooao-<
0000-
eooo--
~
°
~
~
~
O
~
~
~
~
~
~ ~ ~
D
~
~ ~
~
4000--
2000-
Jari 04
Fob G4
Har 6 4
1
Apr 04
Jan 05
—I—
Fab S3
Har S3
Apr BS
Fig. 6.7-4 Influent Plant BODT Load
Tuesdays Only
-------
24000" "
22D00-"
20000--
B
0
D
L
0
a
d
1
n
g
i
b
/
d
a
y
ISooo-
16000-"
I 4000-"
12000'
10000-
eooo-¦
eooo--
~
~
~
~
~
~
D
~
~
~
~
~
~
~
~
~
~
~ D ~
~
~
4000-
2000-
Jon 84
Feb B4
Mar* 04
—I—
Apr 04
-a—a—|-
Jan 05
—I—
Fab SS
Hor OS
1
Apr OS
Fig. 6.7-5 Influent Plant BODT Load
Wednesdays Only
-------
24000"
22000'
20000
leooo
16000
14000
12000'
10000
BOOO
6000'
4000
2000
o
~ ~
~ ~
~
~
~
~
~
~
Qd ~
~
n
~ ~
~ ~ ~
~
~ ~ u
~
~
84
—I—
Fab 64
+
Mar B4
H-
Apr 84
+
Jan 05
Fab B3
Mar 03
Apr BS
Fig. 6.7-6 Influent Plant BODT Load
Thursdays Only
-------
B
0
D
L
0
a
d
1
n
g
i
b
/
d
a
y
24000"-
22000"-
20000
18000--
leooo--
14000--
10000
eooo
6000--
4000--
2000
~
~ ~
~
~
~ ~
~
~
~
~
~
~
~
~
~
~
~
~
~
~ ~
~
~
+
—R—
Apr 04
Jon 64
Feb B4
Mar 84
Jan OS
Fob 03
Mar 05
Apr 05
Fig. 6.7-7 Influent Plant BOOT Load
Fridays Only
-------
24000-
22000'
20000"
10000-
IB000-
14000
1 2000'
10000
0000
0000
4000
2000
0
~
~
~
~
D ~ D
~
~ ~
~
~
~
~
~
o
~
~
~
~
~
~ D
~
~
~
~
64
Fob 84
Mar- 04
1
Apr 04
Jan B5
Fab 95
Mar 05
Apr BS
Fig. 6.7-8 Influent Plant BODT Load
Saturdays Only
-------
70-
65"
00-
35-
50-
45"
40-
35"
30
23
20
IS
10
5
0
~
~
~
~
~
~
~
U U
~ ~
Removal without
VRV Operatingi
12. 57.
~
n
12000
2B0Q0
Total Solids Processed by VRV, lbs/day
Fig. 6.7-9 Trickling Filter Efficiency
Friday Operation Only
-------
70-r
BS~ -
00* -
53-
Removal without
VRV Operating
IB. 7X
40- -
23-
AODO 7000 B000 0000 10000 I 1000 12000 13000 14000 13000 10000 17000 IBOOO 10000 20000 21000 22000 23000 24000 23000 20000 27000 26000
Total Solids Processed by VRV, lbe/day
F1g. 6.7-10 Rotating Biological Contactor Efficiency
Friday Operation Only
-------
JOO-r
Romovol without
VRV Operating!
76. 3X
AO
33- *
>o-| 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
60Q0 7000 eooo 0000 I ODOO 1 1000 12000 I 3000 I 4 000 1S000 18000 17000 10000 I eooo 20000 21000 22000 23000 24000 25C00 2«000 27000 28000
Total Solids Processed by VRV, lbs/doy
Fig. 6.7-11 Final Clarlfler Efficiency
Friday Operation Only
-------
6.8 ACID WASHES
6.8.1 Effect of Inorganic Scaling
Inorganic scale forms in the YRV. If present in the sludge feed,
elements such as calcium, magnesium, and aluminum form inorganic salts
which plate out on the VRY walls. The inverse solubility of these
components causes them to deposit at the higher temperature levels, near
the bottom. Because of the relatively low liquid velocity, deposits can
accumulate as thick as 1-2 cm before there is an appreciable pressure drop
associated with the scale.
Scale reduces heat transfer in the VRV. If the VRV is operated
for an extended period without an acid wash, scale build-up increases the
temperature difference between the downcomer and upcomer streams across
the divider tube.
6.8.2 Removing Inorganic Scale Materials
A proprietary procedure for scale removal was developed which
efficiently removed the scale from the VRV, restoring it to initial
conditions. A nitric acid solution is used to clean the VRV, removing all
of the scale and restoring the heat transfer capabilities. Table 6.8-1
summarizes the amount of acid solution used each month, and the amount of
scale removed. The acid solution was neutralized in the acid wash pits
before returning to the longmont WWTP.
TABLE 6.8-1
ACID WASHES
YEAR
MONTH
ACID SOLUTION
(Gallons)
SCALE REMOVED
(lbs)
1984 June
July
August
September
October
November
December
1,695
4,170
2,220
1,830
1,800
955
3,560
4,280
2,030
4,700
8,010
7,840
10,880
1985 January
February
March
April
May
August
September
2,160
1,410
3,060
4,390
2,070
700
920
8,280
7,290
4,120*
16,740*
8,050
3,080
3,690
*Total includes one acid wash with no scale removal data.
- 88 -
-------
6.9 AMMONIA
6.9.1 The Effect of. the VRV System on Anmonia/Nitrogen Discharge Levels
The operating conditions during aqueous-phase oxidation converted
the major portion of organically bound nitrogen in the biological sludge
to soluble TKN and ammonia.
6.9.2 Effluent Recycle Effects
As shown in Tables 6.9-1 and 6.9-2, lower ammonia concentrations
were observed during recycle. When recycling, an average of 0.026 kg
ammonia nitrogen per kg sludge processed was returned to the WWTP.
Effluent recycling increased overall organic nitrogen removal and reduced
the overall ammonia nitrogen returned to the WWTP by as much as 20%.
Table 6.9-2 presents NH3-N produced during autogenous operating periods
without oxidation effluent recycle. An average of 0.033 kg ammonia
nitrogen per kg sludge processed was returned back to the WWTP.
Average daily analyses of ammonia nitrogen in the Longmont WWTP
effluent are shown in Table 6.9-3 and 6.9-4. Increases of 6-7 mg/L
NH3-N during system operating periods correspond to an average of 0.035
kg NH3-N per kg sludge processed. This agrees well with the average
value of 0.033 kg NH3-N per kg sludge given in Table 6.9-2. Armenia
nitrogen produced is carried through the plant and discharged. Ammonia
removal was not addressed in the test program because ammonia limits were
not exceeded during system operation. If lower ammonia effluent
concentrations are required, steam stripping of the reaction vessel
effluent using available heat from the process will reduce effluent
concentrations to the lower levels necessary.
TABLE 6.9-1
AUTOGENOUS NH3-N RETURNED TO WWTP
WITH RECYCLE
kg NH3-N
Date
SLUDGE
FEED
NH3-N DISCHARGED
Returned per
Kg SIudge Fed
lb/hr
kg/hr
lb/hr
kg/hr
3/28/85
1466
666
28.7
13.0
0.020
3/31/85
1260
572
37.6
17.1
0.030
4/11/85
1085
493
30.7
13.9
0.028
Average
1270
577
32.3
14.7
0.026
- 89 -
-------
TABLE 6.9-2
AUTOGENOUS NH3-N RETURNED TO WWTP
WITHOUT RECYCLE
Date
SLUDGE
FEED
NH3-N DISCHARGED
kg NH3-N
Returned per
Kg Sludge Fed
lb/hr
kg/hr
lb/hr
kg/hr
3/26-27/85
1437
652
52.1
23.6
0.036
4/1/85
1263
573
40.1
18.2
0.032
4/1/85
1183
537
36.3
16.5
0.031
4/4/85
1198
544
42.0
19.1
0.035
4/5/85
904
410
29.0
13.2
0.032
4/7/85
1342
609
52.6
23.9
0.039
4/7/85
1294
587
35.9
16.3
0.028
4/8/85
832
378
24.8
11.2
0.030
4/10-11/85
1155
524
37.3
16.9
0.032
4/11-12/85
1245
565
39.8
18.1
0.032
Average
1185
538
39.0
17.7
0.033
MONTH/YEAR
TABLE 6.9-3
LONGMONT WWTP OPERATION
WITHOUT VRV SYSTEM
DATA
DAYS
EFFLUENT
(m^/hr)
WWTP AVERAGE
EFFLUENT
NH3-N(mg/L)
EFFLUENT—
NH3-N(kg/day)
December 1984
January 1985
February 1985
March 1985
April 1985
17
9
3
10
1
1025
1009
998
978
978
16
17
17
18
17
394
412
407
422
399
- 90 -
-------
TABLE 6.9-4
LONGMONT WWTP OPERATION
WITH VRV SYSTEM
AVERAGE
MONTH
DATA
DAYS
EFFLUENT
(nP/hr)
SLUDGE
(kg/day)
EFFLUENT
NH3-N
(mg/L) (kg/day)
NH3-N
INCREASE
(kg/day)
kg KIH3-KI
INCREASE PER
kg SLUDGE
PROCESSED
Dec.1984
14
1073
5176
22 567
173
0.033
Jan.1985
22
994
3450
23 549
137
0.040
Feb.1985
25
946
3178
23 522
115
0.036
Mar.1985
21
946
4903
25 568
146
0.030
Apr.1985
29
1025
6538
26 640
241
0.037
Average
0.035
6.70 OFF GAS
6.10.1 Major Components
Off-gases produced by the oxidation reaction can be divided into
two categories: major and trace components. Major components consisted of
carbon dioxide (CO2)> oxygen (O2), nitrogen (N2) and carbon monoxide
(CO). Relative percentages of these components were largely dependent on
whether compressed air or oxygen-enriched air was used. Table 6.10-1
shows off-gas analyses as determined by gas chromatograph sampling for
various oxygen concentrations.
TABLE 6.10-1
OFF-GAS ANALYSES - MAJOR COMPONENTS
OXYGEN CONCENTRATION
MAJOR
COMPONENTS
211
42%
63%
100%
N2
83.90
63.89
47.40
2.92
°2
8.6
5.65
4.80
2.86
co?
4.18
28.84
43.00
90.23
CO
.13
1 .62
2.50
3.97
- 91 -
-------
6.10.2 Trace Components
An Industrial Hygiene Survey (See Appendix A) was corrducted by
Stearns-Catalytic Inc. to determine the type and quantity of trace
compounds being emitted in the off-gas. Data presented in Table 6.10-2
were from high concentration oxygen testing. Table 6.10-2 lists chemical
compounds identified to any significant level.
TABLE 6.10-2
TRACE OFF-GAS COMPONENTS
MEASURED
ESTABLISHED
EXPOSURE LEVELS
TLV AND/OR
(ppm)
PEL (ppm)
Acetone
5 - 30
750
Furan
2 - 3
50
2-Butanone
3 - 4
200
2-Pentanone
1 - 2
200
1-Hexene
1 - 2
100
1-Heptene
1 - 2
400
Benzaldehyde
4.78
100
Furfural
0.34
2
Carbon Monoxide
5
50
All chemicals identified were in concentrations well below that of
established and recognized exposure levels. The carbon monoxide airborne
concentrations were not observed within the WWTP. Dispersion of carbon
monoxide was rapid and efficient with no detectable quantities outside the
VRV System battery limits (See Appendix A.). Sampling procedures and
other physical characteristics of the trace components are given in detail
in Appendix A.
6.11 ASH
6.11.1 Ash Content of Sludges Tested at Longmont
Several ash samples of Longmont sludge were collected and
analyzed. Analysis of crystalline compounds was obtained by X-ray
diffraction (XRD) and elemental composition by X-ray fluorescence (XRF).
Table 6.11-1 contains the elemental compound percentages found in two
different samples.
Sample No. 1 was obtained on June 27, 1984 while processing sludge
at 231 °C. Sample No. 2 was obtained on August 8, 1985 while processing
sludge at 245 °C. Compositions are similar with the exception of
phosphorus (P) and potassium (K).
- 92 -
-------
TABLE 6.11-1
ELEMENTAL ASH COMPOSITION (WT.%)
SAMPLE NO. 1
SAMPLE NO.2
ELEMENT
June 27, 1984
August 8, 1985
A1
16.85
10.7
P
16.43
5.8
Si
4.89
3.4
Ca
5.32
3.4
Fe
2.68
2.4
Mg
ND (1.51)
1.6
K
5.84
0.5
Cu
0.60
0.5
Ti
0.31
0.3
S
0.18
0.1
Zn
0.12
0.1
Sr
0.12
0.1
Ce
0.05
0.1
Sn
ND
0.04
Pb
ND
0.02
Ni
0.03
0.01
Na
ND (6%)
MD {8%}
TOTAL
53.42%
29.07%
ND = Mot detected.
6.11.2 Results of EP Toxicity Tests for Ash
Ash was analyzed for metals on a repeated basis for compliance
with EPA's EP Toxicity Test. At all times heavy metal concentrations were
lower than the acceptable limit set by EPA, usually by two orders of
magnitude. Representative analyses are shown in Table 6.11-2.
6.11.3 Ash Dewatering
Liquid/solids separation at the Longmont plant employed a Lamella
separator to concentrate the ash solids and return the clarified overflow
back to the Longmont WWTP. Underflow from the Lamella plate separator was
discharged into one of the three concrete pits. When a pit became full,
supernatant was drained off and the ash allowed to dry by evaporation.
A solid bowl centrifuge was field tested and produced results
given in Table 6.11-3. A clear centrate and a cake with 39-77% solids
was produced. These were only initial tests, and centrifuge operation
was not optimized. Figure 6.11-1 shows the relationship between
centrifuge feed rate and percent solids. Further tests would better
define the percent solids which would be obtained.
- 93 -
-------
Table 6.11-2
RESULTS FROM EP TOXICITY TESTS FOR LONGMONT ASH (MG/L)
Test
EP Toxicity
Test Limit
09/10/84
F ONLY
11/10/84
F T
12/U/84
F T
12/15/84
T ONLY
12/22/84
F S
01/16/85
F S
01/22/84
F S
As
5.0
ND
ND
0.005
0.002
ND
0.003
0.004
0.009
0.055
0.007
0.008
0.040
0.004
0.004
0.032
0.001
Ag
5.0
0.41
0.17
0.15
0.08
0.02
0.08
0.08
0.02
0.04
0.03
0.07
0.025
0.1
0.1
0.01
0.01
0.1
0.02
Ba
100.0
0.46
2.6
2.1
1.0
1.0
0.42
0.52
1.0
1.0
1.0
0.43
1.0
1.5
0.75
1.0
1.0
0.72
1.0
Cd
1.0
0.08
0.5
0.4
0.09
0.01
0.05
0.05
0.01
0.01
0.01
0.05
0.01
0.04
0.05
0.01
0.01
0.04
0.01
Cr
5.0
0.46
2.3
0.2
0.55
0.02
0.25
0.24
0.2
0.2
0.2
0.43
0.2
0.26
0.25
0.2
0.2
0.14
0.2
Hg
0.2
ND
ND
0.002
0.001
ND
0.001
0.001
0.002
0.002
0.004
0.001
0.002
0.001
0.001
0.002
0.002
Pb
5.0
0.63
0.2
0.2
0.2
0.2
0.38
0.37
0.2
0.2
0.2
0.36
0.2
0.37
0.43
0.2
0.2
0,28
0.2
Se
1.0
ND
ND
0.001
0.001
ND
0.002
0.001
0.002
0.003
0.002
0.004
0.014
0.002
0.002
0.013
0.001
* Duplicate samples collected from pit.
F Filtrate (supernatant)
S Solids
T Total (solids & filtrate)
ND Hot Determined
-------
TABLE 6.11-3
DATA SUMMARY
LONGMONT CENTRIFUGE TESTS
DATE
TIME
CENTRIFUGE
FEED RATE
1/min (gpm)
POLYMER
FEED
MATERIAL
CAKE
SOLIDS
7/17/85
10:00
23
(6)
No
Ash Pits
47
7/17/85
10:30
95
(25)
No
Ash Pits
53
7/17/85
11:10
91
(24)
Yes
Ash Pits
51
7/17/85
14:24
38
(10)
Yes
Ash Pits
51
7/17/85
15:00
38
(10)
Yes
Ash Pits
42
7/17/85
15:10
19-25
(5-7)
Yes
Ash Pits
46
7/18/85
09:30
45
(12)
Yes
Ash Pits
70
7/18/85
09:50
45
(12)
Yes
Ash Pits
58
7/18/85
10:10
76
(20)
Yes
Ash Pits
60
7/26/85
10:50
38
(10)
Yes
L.U.
64
7/26/85
11:15
57
(15)
Yes
L.U.
65
7/26/85
11:45
87
(23)
Yes
Underflow
70
7/26/85
15:00
57
(15)
Yes
Under fl ow
69
8/01/85
38
(10)
Yes
Underflow
77
8/01 /85
19
(5)
Yes
Underflow
73
8/01/85
15:30
19
(5)
Yes
Underflow
64
8/23/85
12:00
57
(15)
No
Ash Pit
45
8/23/85
11:50
76
(20)
No
Ash Pit
61
8/23/85
11:30
95
(25)
No
Ash Pit
65
8/23/85
12:30
114
(30)
No
Ash Pit
39
L.U. - Lamella Underflow.
6.11.4 Ash Disposal Alternatives
Longmont ash residue met all the EP toxicity limits and was
disposed of in landfills- Other disposal alternatives which could have a
beneficial use of the ash product were reviewed. Laboratory tests were
conducted to determine the feasibility of utilizing ash as a filler
material in the manufacture of bricks. The tests concluded that additions
of 7-82, ash produced a product with improved physical properties. Details
of the test are reported in Appendix B.
- 95 -
-------
100-j
00-
80-
70-
ao-
50
40
30
20
10
0
~
~
~
~
~
~
~
xr
i
~
~
i
~
~
1 1 1 1 1 1 1 1 1 1 1 1 (-
a 10 12 14 IB IB 20 22 24 20 2B 30 32
Centrifuge Flow Rate (gpm)
F1g. 6.11-1 Solids Weight Percent vs. Centrifuge Flow Rate
-------
6.12 METALLURGY
High temperature aqlieous-phase oxidation of Longmont sludge
required the use of corrosion resistant materials. A duplex stainless
steel was chosen based on its resistance to stress corrosion cracking,
pitting and crevice corrosion. High strength was a necessity for downhole
tubulars and reasonable costs were also important factors in the selection.
During operation, corrosive conditions varied to some degree.
Operating temperature ranged up to 282 °C (540°F) with varying levels of
carbon dioxide, oxygen and chloride. Typical- chloride concentrations
averaged 100 mg/L. VRV tubulars were exposed to acid during scale removal.
Metal loss during sludge processing was not detectable indicating
little or no corrosion. After 15 months of successful operation, it was
decided to remove and inspect the inner reaction vessel tubulars to
determine the extent and type of corrosion experienced.
Upon removal, each length of pipe was checked for wall thickness
and visual defects to verify the actual corrosion. The wall thicknesses
of the 7-inch pipe are presented in Figure 6.12-1. It shows a general
corrosion from no loss at the surface to a loss of 0.2 MM (8 mils) at the
bottom.
Further inspection and laboratory analyses of the VRV tubulars
gave the following conclusions:
1. General corrosion is low and consistent with a 20-year
service life.
2. No pitting or crevice corrosion occurred on the pipe body.
3. No stress corrosion was found in the VRV tubulars.
4. No erosion was evident within the downhole system.
- 97 -
-------
1600-
e
«
u.
a
I J
k
s
I
I
1
sr
J
J
•I
••I
I
J
I
•: I
• I
: i
-+
jlL
200 220 240 260 280 300
Wall Thickness (Thousondths)
320 340 " 360 380 400
Fig. 6.12-1 Wall Thickness of 7" Pipe
- 98 -
-------
SECTION 7
OPERATING AND CAPITAL COSTS
7.1 VRV SYSTEM OPERATING COST
Operating costs for the VRV System demonstration plant do not
reflect the operating costs of a commercial unit. Operating costs for the
Longmont facility were higher due to the following:
0 Longmont did not operate at maximum capacity
° Chemical consumption was studied and not used at optimal rates
° Oxygen consumption was not optimized
° Maintenance costs were affected by modifications which would be
unnecessary in a commercial facility
The operating costs, however, can be accurately calculated based on
Longmont experience. Table 7.1-1 gives the operating costs for a Longmont
sized reaction vessel. Individual cost factors are discussed in the
following sections. It is seen that the operating and maintenance cost is
about $113/metric ton and a net operating cost of $9S/metric ton with an
energy credit.
7.1.1 Labor Cost
VerTech employed four operators to cover the operation twenty-four
hours a day, seven days a week. The supervisor covered one eight-hour shift
per week plus any sick leave and vacation shifts.
Labor costs can be reduced by more than 50% if the facility is
integrated into the Longmont WWTP. One operator will spend less than 50? of
his time operating the VRV System.
Table 7.1-1 assumed an operator salary of $22,000 per year and a
supervisor salary of $30,000 per year, plus 25% benefits.
Labor costs are calculated as follows:
Supervision 0.1 x $30,000/yr x 1.25 = $ 3,750/yr
Operators 2.1 x $22,000/yr x 1.25 = $57,75Q/yr
TOTAL LABOR $61,500/yr.
7.1.2 Utilities
Water: Final clarifier effluent has proven satisfactory for all
operations at Longmont. In addition, VerTech has used reaction vessel
effluent directly for dilution of the influent and demonstrated that it is
suitable; therefore the water costs are negligible.
- 99 -
-------
Fuel: The process generates excess heat, which can be exported as
steam, hot water or electricity. An energy credit of $171,400/year is
calculated in Table 7.1-2 based on 40£/Therm.
TABLE 7.1-1
OPERATING COST FOR PLANT
UTILIZING A 10" REACTION VESSEL
PLANT CAPACITY 9,100 metric tons, 10,000 short tons/year
PLANT AVAILABILITY 90S
UNIT COST
ANNUAL COST S/1000 kg
Labor
$ 61,500
6.80
Uti 1 i ti es
39,400
4.30
Oxygen
473,200
52.00
Chemicals
205,700
22.60
Maintenance
120,000
13.20
Ash Removal
125,000
13.70
TOTAL EXPENSES
$1,024,800
112.60
NET ENERGY CREDIT
$ (153,400)
(16.90)
TOTAL
$ 871 ,400
95.70
TABLE 7.1-2
ENERGY CREDIT
The total available usable energy
experience.
is calculated based on Longmont
Heat of Reaction
Flush Out
Heat Lost to Rock
Usable Energy
3.27 MW
(0.56) MW
(0.94) MW
1.77 MW
11.16 MM Btu/HR
(1.91) MM Btu/HR
(3.21) MM Btu/HR
6.04 MM Btu/HR
At an average cost of $4/MM Btu, 90% efficiency and
availability, the credit is $171 ,400/year, less start-up
requirements of $18,000/year gives a net credit of $153,400.
90%
fuel
- 100 -
-------
Electricity: The electrical consumption for a facility which will
produce an ash containing 50-70 wt % solids will be about 100 kW at
5^/kWhr. The annual electrical cost at 90% availabiVity is-$3-9<420/yr.
100 kW x 24 hr/day x 365/day/yr x 0.9 x $0.05/kWhr = $39,420/yr
7.1.3 Oxygen
At Longmont, liquid oxygen was supplied at about $100/1000kg for a
leased customer station. The ratio of TCOD/TS was between 1.0 and 1.1.
Thus, for an 80% COD reduction and TCOD/TS of 1.0, the cost was $80/1000
kg of TS.
0.8 kg02/kgTS x $100/1000 kg 02 = $80/1000 kgTS
Compressed oxygen can be generated from a leased unit including
backup for $65 to $90 per 1000 kg. A purchased unit can produce oxygen
for $33-40 per 1000 kg. At $65/1000 kg02, and 80% COD reduction, the
cost per 1000 kg of TS is
0.8 kg 02/kg TS x $65/1000kg 02 = $52.00/1000kg TS
7.1.4 Chemicals
The chemical consumption depends on the amount of scale components
in the original sludge. Longmont's WWTP added aluminum sulfate and
thereby increased the amount of scale in the reaction vessel. It has been
estimated that the chemical cost will be cut in half after the present
redesign of the .WWTP is completed. The costs reported are for the actual
test period which includes the addition of aluminum sulfate.
During the initial sustained autogenous operation in March 1985,
$46.60 per ton of solids were expended for chemicals. Further chemical
cost reductions were experienced at Longmont utilizing a new acid wash
procedure which reduced costs to $17.60 per ton for Longmont. Gulf Coast
chemical costs are 57% of Longmont's.
Chemical costs are:
$17.6/ton for wash chemicals
3.0/ton for polyelectrolytes
$20.6/ton solids
For a Longmont location, chemical cost is estimated at $20.60 per
ton solids, or $22.60/1000kg.
7.1.5 Maintenance
Maintenance costs given in Table 7.1-1 include the costs to remove
and inspect the VRV every 10 years.
- 101 -
-------
Maintenance costs are thus:
Labor $/year
Materials
Allowance for reactor removal
TOTAL $AEAR
45,000
45,000
30,000
120,000
7.1.6 Ash Disposal
At Longmont, the ash was deposited at the local landfill. The ash
was also transported to the local cement plant for use as a topping
material. Thus the costs were negligible. Costs for disposal of the asn
cake are typically $30/wet ton of ash. This results in a disposal cost of
$12.50 per ton of processed sludge solids ($13.70/1000 kg).
7.2 VRV SYSTEM CAPITAL COSTS
Final effluent discharge specifications determine the VRV System
capital costs. Typical capital costs will vary from $8-10 million for a
254 mm VRV System which will handle 30 TPD dry solids. A system similar to
Longmont, integrated into the WWTP, will be closer to $8 million. This cost
includes all equipment similar to that shown in Figure 1.4-2, except that
centrifuges will be used to dewater the ash instead of ash pits.
7.3 ECONOMIC ANALYSIS
Assuming $10 million capital for a complete system, straight line
depreciation over a 20-year period, and 6.5« financing on a 20-year loan,
capital costs will be below $100/tonne for a VRV System. Coupled with
operating costs below $100/tonne, the total project cost for a VRV System is
very competitive with other waste disposal methods.
The Municipality of Metropolitan Seattle completed an evaluation of
existing technologies in 1986. The current sludge management program in
Seattle produces a product used in silviculture, land reclamation, and
composting. Proposed technologies include composting, Carver-Greenfield,
Zimpro, and VerTech's aqueous-phase oxidation in a VRV System. The VRV
System is within a reasonable range of Seattle's current costs.
- 102 -
-------
REFERENCES
"Test Methods for Evaluating Solid Uaste," U.S. Environmental Protection
Agency, SW-846, 1980.
"Methods for Chemical Analysis of Water and Waste," U.S. Environmental
Protection Agency, EPA-600/4-7y-020, 1979.
"Standard Methods for the Examination of Water and Wastewater," 15th
Edition, American Public Health Association, American Water Works
Association, Water Pollution Control Federation, Washington, DC, 1980.
"NIOSH Manual of Analytical Methods," Taylor, D. G., Manual Coordinator,
2nd Edition, Volume 5, Method No. S-17, 1977.
"1980 Annual Book of ASTM Standards - Petroleum Products and Lubricants,
(II:D116)-D2896, American Society of Testing and Materials, Phi 1adelphi
PA, 1980.
- 103 -
-------
APPENDIX A
Stearns*S%.
Catalytrcgp
STEARNS CATALYTIC CORPORATION
March 10, 1986
VerTech Treatment Systems
12000 Pecos Street, Suite 3
Denver, Colorado 80234
Subject: Longmont Waste Water Treatment Plant
VerTech Process, Longmont, Colorado
Occupational (Off-gas Health Survey and Study)
Gentlemen:
The following is a summation of the Occupational Off-gas Health Survey and
Study performed for VerTech. The study considers the VerTech process operation
in conjunction with Longmont Waste Water Treatment Plant (LWWTP) activities.
It was concluded from the study that levels of contaminants identified were
well below established and recognized exposure levels listed by both American
Conference of Governmental Industrial Agencies and Federal Regulations and
Recommendations for toxic and/or irritant contaminants.
Specifically, those chemicals identified to any significant level were:
Established Evaluated
TLV and/or Exposure
PEL (ppm) Levels (ppm)
Acetone 750 5-30
Furan 50 2-3
2-Butanone 200 3-4
2-Pentanone 200 1-2
1-Hexene 100 1-2
1-Heptene 400 1-2
Benzaldehyde 100 4.78
Furfural 2 0.34
Carbon Monoxide 50 (20) <5
Numerous samples were collected from the VerTech facility, the Longmont Waste
Water Treatment Plant and from the breathing zones of plant personnel.
Analytical procedures used to evaluate these samples were gas chromatography-
mass spectrometry (GC/Hass Spec) and Girard-T reagent high pressure liquid
chromatography. Accuracy levels of the various analytic techniques were such
that air contaminant concentrations were detectable to less than one part per
million for activated charcoal tube collection (GC/MS evaluation),and two
parts per million for Girard-T reagent collection for aldehyde determination.
104
4500 Cherry Creek Drive, P 0 Box 5888, Denver, Colorado 80217, (303) 758-1122, TLX 45540, TWX 910-931-0453
-------
Normally, National Institute Occupational Safety and Health. Procedure- S-1J. is .
used for the determination of Furfural; however, because of its coraplexing
nature with other aldehydes, it was also used to determine total aldehyde
airborne concentrations. All other organic hydrocarbon collections were done
on activated charcoal and were desorbed in the laboratory prior to analyses.
The airborne sampling was done using approved EPA analytical procedures.
The analyses of samples taken outside the VerTech facility indicated only
trace amounts of organics. Spot check grab samples of transient vapor cloud
from the VerTech air separator (S-A unit) indicate concentrations in the range
of 3 to 5 ppm for short periods of exposure, under the worst atmospheric
conditions.
Airborne concentration levels of the components identified have never been
observed to approach nor exceed the earlier noted permissible exposure levels
and/or TLV's published by respective organizations. This includes
toxicological information of the effects characterized by these components at
lower evaluated levels than those published TLV's and/or PEL's.
Carbon monoxide airborne concentrations were not observed within the LWWTP.
Dispersion of any carbon monoxide generation was rapid and efficient with no
detectable quantities outside the VerTech facility. Atmospheric conditions
influenced dissipation of the heated, moisture laden off-§ases. Dispersion
was rapid with high local winds, slower during periods of low barometric
pressure.
As the data indicates, even accumulative effects of all of the above would be
diminished by the evidence of their extremely low or non-existent airborne
concentrations.
Very truly yours,
STEARNS CATALYTIC WORLD CORPORATION
l
Daniel S. Kinds
Assistant Manager of
and Health
Corporate Industrial
Corporate Safety
Hygienist
-------
APPENDIX B
Kenneth 0. Bradford
Manufacturing Consultant
7220 W. Jefferson Avenue, #350
Denver, Colorado 80235
September 28, 1984
Vertech Treatment Systems
2010 W. 120th
Westminster, Colorado 80234
Subject: Physical Testing of Vertech Waste Ash Combined with Clay
Brick Mixes.
I. Denver Brick Mix Tests.
Initially a dried sample of pit #4 ash was obtained, ground to
pass a 14M screen (retained moisture was 14.5%), additional water
added, and the material extruded in 1" x 1" bars. Several samples
were dried and fired above 2000°F. In each case, the bars melted.
Ash mixed with clay is stable however. Additional tests were run
mixing 16.7%, 8.3%, and 6.7% ash with a standard red brick mix
from Denver Brick Company. This mix is only semi-plastic. Since
the ash, although very fine, is a calcined material, it reduces
the mix plasticity and causes tearing at corners during
extrusion.
A second more plastic mix of Denver Brick (62T) was selected and
12.5% and 7.1% additive of ash were made. The 7.1% addition (Test
#14) extruded well, had .5% less dry shrinkage, .5% more fired
shrinkage, and equal absorption. This 7.1 percentage would be a
practical addition to this brick mix. Body color is darkened by
use of the ash. Further testing is necessary to determine if this
darkening is caused by sulfates migrating to the surface. If so
it can be controlled with Barium Carbonate in clear burned brick.
This would not be necessary with flashed or coated brick.
A seven-day efflorescence test, conducted according to ASTM C-67,
was made with sample #14 containing 7.1« ash, Denver Brick's #1
mix, #62T mix, and a #1 mix containing power plant fly ash. All
samples are classed as "No Efflorescence." Samples of #14 ash
test were subjected to compression and modulus of rupture tests
by CTL Thompson laboratory, along with #1 standard brick mix. A
formal report by CTL Thompson will be tendered next week.
IOC
-------
Vertech Treatment Systems
September 28, 1984
Page 2
Results:
#1 Brick Mix
it
77
14 (7.1% Ash)
Mix
Average Compression
7035 psi
6085 psi
Average M.O.R.
1877 psi
1314 psi
ASTM C-62 requires minimum 3000 psi compression to class brick as
S. W. (Severe Weathering), its highest classification. The ash
sample measures very well compared to the #1 mix and other brick
of the local area.
I conclude that waste ash additions up to 10% are safe additions
to brick mixes—no distortion or over vitrification. Drying of
brick will probably be improved because of lowered dry shrinkage.
Fired characteristics are equal or better than standard brick.
An important factor is weight reduction of fired brick. The #14
ash test indicated a reduction in fired weight of 5%. This would
be significant since shipping costs are of major concern to brick
manufacturers.
II. Colorado Brick Company Mix Tested.
A sample of Colorado Brick standard red mix was obtained and
sample bars extruded.
A second sample of ash was also obtained, ground, and mixed with
Colorado Red Mix--10% ash to 90% red mix. This level of ash
produced a lightly rougher edge in extrusion indicating that 7 to
8% ash addition would be more practical.
Physical results followed those found with Denver Brick mixes;
i.e., less dry shrinkage, more fired shrinkage, and 3% less fired
weight. Apsorption of the ash test was 1% higher than standard
mix but still quite low indicating that compression and modulus
of rupture should meet or exceed ASTM standards. A set of #15
(standard red mix) and #16 (10% ash) will be submitted to CTL
Thompson for compression and M.O.R.
Color of the ash test was again slightly darker. A sample of both
bars along with a copy of specification sheets will be given to
Jerry Gunning at Colorado Brick. I will recommend to him that the
ash is certainly usable and st be made.
KDB/ce
1G7
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APPENDIX C
MATERIAL SCIENCE CORF.
10381 E. Berry Drive
Englewood, CO 80111
President
P. E. Dempsey
OBSERVATIONS AND CORROSION REPORT
ON
PULLING THE LONGMONT REACTION VESSEL
December 3, 1985
100
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APPENDIX C
SUMMARY OF REACTION VESSEL CORROSION
Readings were taken by the UT thickness gauge to measure the extent
of corrosion observed in the reaction vessel tubulars. They were recorded
and averaged to give the wall thicknesses clotted in the attached graohs.
Corrosion of each individual joint could not be determined since the
original wall thickness was not known. It was however possible to measure
the wall thickness for several new unused joints of 5" and 7-5/3" available
at the site. Wall thickness for the as ordered .300" wall 7-5/8" oioe
averaged .310" and for the 5"-.253" wall DiDe averaged .263". Measurements
of new 5"-220" wall Dice was not obtainable since all of the suDDlied joints
were used in the reaction vessel string.
Based on the above averages for as suoolied new oiDe and actual
measurements of each joint removed from the system; it was acoarent that a
small degree of general corrosion did occur. Corrosion was not evident at
surface but increased with temperature and deDth. Corrosion on the 5"-.253"
wall DiDe varied from 0 to .003". As mentioned above corrosion for the
5"-.220" wall was not obtained. Measurements varied from .249" to .235"
which was considerable above the .220" wall ordered. Corrosion on the
7-5/8"-.300" wall DiDe varied from 0 at surface to .008" at deofi.
In both the 7-5/8" and the 5" DiDe, there was no evidence of stress
cracking, oitting or crevice corrosion.
109
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GLOSSARY
Anhydrite - A mineral substance containing no waters of
hydration; ie, CAS04 consisting of an anhydrous calcium sulfate that is
usually massive and white or slightly colored.
Autogenous - Plant operation where no external source of heat is
required to maintain process temperatures; self-generated; produced
without external influence.
Biochemical Oxygen Demand (BOD) - A measure of the quantity of
oxygen utilized in the biochemical oxidation of organic matter in a
specified time and at a specific temperature. Commonly referred to as
Biological Oxygen Demand. All BOD measures are 5-day unless otherwise
noted.
Biochemical Oxygen Demand Total - A measure of the quantity of
oxygen utilized in the biochemical oxidation of organic matter, inorganic
matter such as sulfides and ferrous iron. It also measures the oxygen
used to oxidize reduced forms of nitrogen (nitrogenous demand). Commonly
referred to as Biological Oxygen Demand.
Biomass - The mass of biological material contained in a system,
consisting of the active biological population and inactive solids.
Biosystem - A treatment plant or system that uses biological
activity to remove BOD.
Bottomhole - Refers to the extreme bottom of the reaction vessel.
British Thermal Unit - Quantity of heat required to raise the
temperature of one pound of water 1°F-0.55°C equal to 0.95 kJ.
Carbonaceous Biochemical Oxygen Demand (COD) - A quantitative
measure of the amount of dissolved oxygen required for the biological
oxidation of carbon containing compounds in a sample. An inhibitor is
added to prevent oxidation of reduced forms of nitrogen.
Centrate - The liquid discharge from a plant or a piece of
equipment, such as a centrifuge.
Centrifuge - A mechanical device in which centrifugal force is
used to separate solids from liquids and/or to separate liquids of
different densities.
Chemical Oxygen Demand - A quantitative measure of the amount of
oxygen required for the chemical oxidation of carbonaceous (organic)
material in wastewater using inorganic dichromate or permanganate salts as
oxidants in a two-hour test.
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Chromatography - The generic name of a group of separation
processes that depend on the redistribution of the molecules of a mixture
between a gas or a liquid phase in contact with one or more bulk phases.
The several types of chromatography are: adsorption, column, gas, gel
liquid, ion, thin-layer and paper chromatography.
Colloids - Finely divided solids which will not settle but may
be removed from a liquid by coagulation or biochemical action as membrane
filtration. In general, particles of colloidal dimensions are
approximately 10 to 10,000 Angstroms in size.
Dewater - To extract a portion of the water present in a sludge
or slurry.
Diluent - An inert substance used to increase the volume of some
other substance or solution.
Dissolved Oxygen - Free elemental oxygen dissolved in water.
Dissolved Solids - Solids in solution that cannot be removed by
filtration.
Downcomer - A passageway in which a slurry or liquid is
conducted from the top of the reaction vessel or heat exchanger to the
bottom.
EP Toxicity Test - Extraction Procedure Toxicity (EP Toxicity);
an extraction procedure employing acetic acid at pH5 to determine
Teachable metals or hazardous organic compounds.
Effluent - A Discharge from a unit operation, such as the final
discharge stream from a waste treatment plant.
Electrolyte - A compound which forms charged species in
solution. Includes simple electrolytes (coagulants) and polyelectrolytes
(flocculants).
Exothermic - Indicating liberation of heat. Also know as
exoergic.
Filter Press - A plate and frame press operated mechanically to
produce a semi-solid cake from a slurry.
Floe - Collections of smaller particles agglomerated into larger
more easily settleable particles through chemical, physical or biological
treatment.
Flocculant - A water-soluble organic polyelectrolyte that is
used alone or in conjunction with inorganic coagulants, such as aluminum
or iron salts, to agglomerate solids present in water or wastewater to
form large, dense floe particles which settle rapidly.
- Ill -
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Flow Rate - A measure of the volume of water flowing through a
system over a period of time, i.e., gallons per day or liters per day.
Foul ants - Materials collecting in a system that tend to foul
it, causing reduced flow rates or increased pressure drop across the
system.
Gallons Per Day - The number of gallons in one day to pass
through a plant or system. One gallon is equal to 3.78 liters.
Gas Chromatography - A method of separating a mixture of
compounds into its constituents so they can be i-dentified. .The sample is
vaporized into a gas filled column, fractionated by being swept over a
solid absorbent, selectively eluted, and identified.
Gas Chromatography/Mass Spectrometry - The analysis of
constituents of water by gas chromatography/mass spectrometry involves
isolation and concentration of organics from a sample, separation of the
components on a gas chromatograph, and detection and quantification of the
compounds with a mass spectrometer.
Grab Sample - A sample taken from a process stream at one time,
not a composite sample.
Higher Heating Value - The heat released with the combustion of
a substance.
Horse Power - A unit of power equal in the U.S. to 746 Watts and
nearly equivalent to the English gravitational unit of the same name that
equals 550 foot-pounds of work per second.
Influent - Water, wastewater or other liquid flowing into a
treatment plant or treatment process.
Interphase - The interval between the end of one mitotic or
meiotic division and the beginning of another.
Kilogram - The basic metric unit of mass and weight equal to 2.2
pounds.
Lamella Solids Separator - A vessel containing inclined plates
used to separate solids from liquids and concentrate them. -
Mil - A unit of length equal to 0.001 inches or 0.0025
centimeters.
Millimeter - A unit of length equal to 0.001 meters.
Non-Autogenous - Plant operations utilizing an external source
of heat to maintain reaction temperatures.
- 112 -
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Non-Hazardous - Indicates a condition of no threat to life or
limb.
Percent Reduction - The percent of COD destruction in a waste
stream. It equals influent COD Minus effluent COD divided by the influent
COD.
pH - A measure of the hydrogen-ion concentration in a solution,
expressed as the logarithm (base ten) of the reciprocal of the
hydrogen-ions concentration in gram moles per liter.
Polyelectrolytes - Complex polymeric compounds, usually
comprised of synthetic macromolecules that form charged species (ions) in
solution. Water-soluble polyelectrolytes are used as flocculants;
insoluble polyelectrolytes are used as ion exchange resins.
Pressure Measurement Lines - Lines that extend deep into the
reactor and are purged with a low air flow.
Reaction Vessel - The concentric pipes that form the heat
exchanger, downcomer and upcomer in the reactor.
Recirculating - A closed loop circulation of a liquid through a
system.
Rotating Biological Contactor - A device for wastewater
treatment which is composed of large, closely spaced plastic discs that
rotate on a horizontal shaft. The discs alternately move through the
wastewater and the air, and develop a biological growth on their surfaces.
Sand Bed - A bed of sand through which water is passed to remove
fine suspended particles. Very common in water treatment plants; also
used in tertiary wastewater treatment plants and sludge drying beds.
Slurry - A thin, watery mud or any substance resembling it.
Soluble - Capable of being dissolved in a fluid.
Spectrophotometer - An instrument for measuring the amount of
electromagnetic radiation absorbed by a sample, as a function of wave
length.
Supernatant - The liquid remaining above a sediment or
precipitate after sedimentation.
Systeme International d'Units - It is the international system
of units of measurement, identified as SI in all languages. It is the
modernized metric system, a high refinement of the original metric system.
Total Dissolved Solids - The sum of all dissolved solids
(volatile and non-volatile) in a water or wastewater.
- 113 -
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Total Kjeldahl Nitrogen - The sum of ammonia nitrogen and
organic nitrogen in a sample.
Total Solids - The sum of dissolved and suspended solid
constituents in water or wastewater.
Total Suspended Solids - Insoluble solids that either float on
the surface of, or are in suspension in water.
Total Volatile Solids - Total materials, generally organic,
which can be driven off from a sample by heating, usually to 550°C.
Total Volatile Suspended Solids - That fraction of suspended .
solids, including organic matter and volatile inorganic salts which will
ignite and burn when placed in an electric muffle furnace at 550°C for 60
minutes.
Tubulars - The concentrically placed tubes that form the
reaction vessel.
Upcomer - A passageway in which a slurry is conducted from the
bottom of the reaction vessel or heat exchanger to the top.
Upflowing - The liquid in the reactor on its way up and out of
the reaction vessel.
Vertical Tube Reactor (VTR) - The early developmental stage of
the VerTech Treatment System reaction vessel.
Wet-Air Oxidation - A method of sludge disposal that involves
the oxidation of sludge solids in water suspension under high pressure and
temperature.
X-ray Diffraction - A method of identifying crystalline
substances by scattering of X-rays of the constituent atoms to form
characteristic patterns.
X-ray Florescence - A non-destructive physical method used for
chemical analysis of solids and liquids; the .specimen is irradiated by an
intense X-ray beam and the lines in the spectrum of the resulting X-ray
florescence are diffracted at various angles by a crystal with known
lattice spacing. The elements in the specimen are identified by the wave
lengths of their spectral lines, and their concentrations are determined
by the intensities of these lines.
- 114 -
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TFCHNICAL REPORT DATA
(Please read Instructions on rite rcierse before completing)
1 REPORT NO :
3 RECIPIENT S ACCESSION NO
4. TITLE AND SUBTITLE
Aqueous-Phase Oxidation of Sludge Usinq the Vertical
Reaction Vessel System
5 REPORT DATE
Januarv. 1987
6 PERFORMING ORGANIZATION CODE
7 AUTHOR(S)
The City of Longmont
B PERFORMING ORGANIZATION REPORT NO
9 PERFORMING ORGANIZATION NAME AND ADDRESS
The City of Longmont
Longmont, CO 80501
10 PROGRAM ELEMENT NO
11 CONTRACT/GRANT NO
CS-809337-01
12 SPONSORING AGENCY NAME AND ADORESS
Water Engineering Research Laboratory—Cincinnati, OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13 TYPE OF REPORT AND PERIOD COVERED
Final Report: 2/82-9/85
14 SPONSORING AGENCY COOE
EPA/600/14
15 SUPPLEMENTARY notes
Edward J. Opatken, (513)569-7855 Commercial or (513)684-7855 FTS
16 ABSTRACT
The overall objective of this study was to provide plant-scale operating data on
the wet-oxidation of municipal wastewater sludge utilizing the Vertical Reaction
Vessel System and the effect of the return flow from the wet-oxidation process on
the operation of the wastewater treatment plant.
The Vertical Reaction Vessel System consists of a series of long concentric
tubes placed in the earth using conventional oil field technology. Vertical
construction produces a high hydrostatic head at the bottom of the system. The high
pressure prevents boiling at temperatures of 250" or higher required for
wet-oxidation. By utilizing hydrostatic pressure, the only pumping required is that
to overcome frictional losses. Sludge is introduced along with air or oxygen into
the multiphase fluid downcomer, where it is heated by hot oxidized sludge rising in
the outermost concentric space within the vessel. At the center of the reaction
vessel is a tubular heat exchange system which can either extract excess heat or
provide heat for startup of the process.
At temperatures above 260°C total chemical oxygen demand reduction of about 80S
and total volatile solids reductions of over 90S were consistently achieved.
Returning the supernatant liquid from the process to the wastewater treatment system
did not significantly affect that system.
17 KEY WORDS AND DOCUMENT ANALYSIS
a DESCRIPTORS
b IDENTIFIERS/OPEN ENDED TERMS
c COS ATI r ield/Group
18. DISTRIBUTION STATEMENT
Release to Public
19 SECURITY CLASS (Tins Report)
Unclassified
21 NO OF PAGES
20 SECURITY CLASS (Tins page!
Unclassified
22 PRICE
EPA Form 2220-1 (Rev. i-77) PREVIOUS EDITION IS OBSOLETE
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