United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-114 Aug. 1981
Project Summary
Pilot-Scale Anaerobic Filter
Treatment of
Heat Treatment Liquor
Eugene Donovan
Using the anaerobic filter to treat
liquor waste resulting from heat treat-
ment of raw sludge in municipal sew-
age treatment plants was demonstrated.
The liquor, which contains high con-
centrations of soluble wastes, is often
returned to the head end of a plant
where it can impose an additional load
on the plant's operation and reduce its
efficiency.
Operational data from a laboratory
and two pilot anaerobic filter columns,
operated over an 18-month period,
demonstrated high levels of BOD and
COD removals from the raw heat
treatment liquor (HTL). The generated
gas contained 65% to 70% methane.
Based on the pilot column studies, a
suggested design and costs for an
anaerobic filter unit were developed.
These costs were compared with
costs of other means of treatment
such as the aerobic alternative. The
anaerobic filter process had lower
capital and operating costs than other
modes of treatment. The gas produced
would be sufficient to maintain the
temperature of the filter at 35° C and
provide additional fuel for other plant
uses. These calculations show a net
profit in operating costs. Further
investigations to optimize design con-
figurations are suggested.
This Project Summary was devel-
oped by EPA's Municipal Environmen-
tal Research Laboratory. Cincinnati,
OH. to announce key findings of the
research project that is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
A pilot plant study was conducted on
the anaerobic filter treatment of HTL
from the heat treatment of si udge from a
municipal sewage plant.
The anaerobic filter's capability of
removing large amounts of soluble
organic matter with no oxygen required,
at relatively low hydraulic detention
times and low solids production, can
result in distinct advantages for the
pretreatment of high strength organic
wastes.
Although the concept of the anaerobic
filter has been studied for 15 or more
years, most of the work has been on
laboratory scale systems, with little pilot
or full-scale information developed. The
potential cost benefits of this process,
however, have increased because of its
low energy requirement when compared
with aerobic systems typically applied to
soluble organic wastes. Consequently,
operation on a pilot scale to verify
kinetic data, develop practical operating
and control schemes, and uncover
scale-up problems was clearly appro-
priate.
Heat Treatment Liquor (HTL)
Heat treatment of municipal primary
and secondary sludge is practiced at
over 100 plants. The liquor from de-
watering the treated sludge contains a
high concentration of organicssolubilized
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in the process. This load can contribute
up to 30% of the raw waste load of the
plant and requires either pretreatment
or significant additional capacity in the
treatment plant.
The anaerobic filter was proposed as
a cost effective way to pretreat this
waste. To develop design parameters
and provide data for a cost comparison
with alternative aerobic treatment, an
anaerobic filter laboratory and full-scale
pilot plants were operated on a typical
municipal HTLfrom a sewage treatment
plant. The characteristics of HTL are
shown in Table 1.
Pilot Plant Studies
The laboratory column was 5 cm in
diameter and contained 1.25 m of 1.6-
cm plastic Pall Rings media, porosity
85%. The two full-scale pilot columns
were each 60 cm square by 3.5 m high
and contained 1.85 m of 9-cm plastic
Pall Rings, porosity 95%. Temperature
was maintained at about 35° C for these
studies.
Table 1. Characteristics of HTL from a Sewage Treatment Plant
Constituent
pH
Alkalinity. mg/L
Total Solids. mg/L
Volatile Solids. %
COD. mg/L
BOD. mg/L
TKN. mg/L
NH3-N. mg/L
Volatile Acids, mg/L
Range
4.9-5.8
600-1560
7390-8460
55-83
10160-1 1540
3830-6100
840-990
270-390
1970-2230
Average
5.2
1075
7735
71
10750
4965
920
295
2085
Loading Conditions
Column 1 was operated at a constant
load throughout the study; the loadings
to column 2 and the laboratory column
were increased in several increments
during the study. Tables 2 and 3 present
summarized operational data, collected
after an initial acclimation period, for
the pilot units. Figure 1 illustrates the
removal of BOD and COD with time for
the pilot units.
The primary gases produced in
anaerobic treatment are carbon dioxide
and methane. During the study, the
methane and carbon dioxide contents of
the gas samples were measured, versus
soluble COD removed (CODR). The
following relationships were developed.
m3 Total Gas Produced = 0.50/kg
CODR 100%
m3 Methane Produced - 0.34/kg
CODR 68%
m3 C02 Produced = 0.15/kg
CODR 29%
Time
Loading
100
90
80
^
1 70
s »
2
^ 50
§
0
£ 40
**^
V
/
/
0
. /
?
*
_ Reseeded
I 1 \ 1 I I \ \ \ I I I I
Column 2
2.9 2.6 1.9 1.0 0.7
1 1
3.7 4.2 5.0 9.0 9.4
' '
" A,
^x*
- -p^>v
f '***" S&
/ * x^*
A / ^
X
/v
X >-COD
/
/*
_/* Reseeded
[\ll\\l\ll\\l
Lab Column
0.7 0.6
6.9 12 to 20
BOD ++
J * * ^X*X
_ ^ 5^
/^*^
^ A
-'^T'
coo
^
_
1 1 1 1 1 1 1 1 1 1 1 1 1
10 30 50 70 90 110 130 10 30 50 70 90 110 130 10 30 50 70 90 110 130 15
Time from Start-Up (days)
Figure 1. BOD and COD removal from anaerobic filter study of HTL at 35°C.
2
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The average value of 0.5 m3 gas/kg
soluble COD removed is consistent with
typical gas production and with COD
correlations found in the literature and
in previous studies.
Summarizing the results, column 1 at
3.7 days detention achieved 80% to 85%
BOD removal and 65% to 70% COD
removal; column 2 at 1 day detention
achieved 65% to 75% BOD removal and
55% to 60% COD removal; and the
laboratory column at 0.6 day detention
achieved 80% to 95% BOD removal and
70% to 90% COD removal. The COD
removals reflect the nonbiodegradable
COD fraction, which was in the range of
10% to 20% of the HTL COD.
Loading Removal Relationships
For volumetric loading rates from 5 to
25 kg/COD/m3/d, the laboratory filter
consistently removed from 60% to 80%
of the COD. The pilot plant filters,
operated at 1 to 11 kg/COD/mVd,
exhibited lower removals and a decline
in removal with increased loading. This
decrease, however, was attributed to
the slow buildup of the anaerobic micro-
organisms on the larger media and their
poorer retention on the large media at
higher flow rates.
At the conclusion of the studies, the
filter media was removed and a deter-
mination of the solids, both attached
and suspended, was made. A high per-
centage of the solids in column 1 were
suspended in the bottom 60 cm. Column
2 had a fairly uniform distribution of
both attached and suspended solids
throughout the column. Over 90% of the
solids were attached in column 2 and
the laboratory column. The laboratory
Table 2. Summary of Operational Data for Laboratory Anaerobic Filter
Date
Day,
No.
29-33
49-55
57-60
71-75
92-96
113-120
120-131
141-147
Flow.
L/d
2.7
3.4
3.0
2.9
3.6
3.5
4.3
3.7
Deten.
Time,
days
0.8
0.6
0.7
0.7
0.6
0.6
0.5
0.6
Loading
Rate,
kg COD/m3/d
6.7
7.1
6.3
11.6
12.3
14.4
20.1
14.0
Gas
Prod.,
L/d
5.31
6.43
4.10
6.92
10.28
16.70
19.60
12.80
Gas,*
m3/kg
CODn
0.53
0.61
0.46
0.40
0.58
0.75
0.57
0.55
COD*
Removed,
%
71
70
68
70
68
74
81
79
BOD*
Removed,
%
85
92
92
87
88
93
95
96
*Based on influent total and effluent filtered; CODR is COD removed.
Table 3. Summary of Operational Data for Anaerobic Filters, Column 1 and Column 2
Date
Day,
No.
Flow,
L/d
Deten.
Time,
days
Loading
Rate.
kg COD/m3/d
Gas
Prod.,
m3/d
Gas,*
m3/kg
COD*
COD*
Removed,
%
BOD*
Removed,
%
42-51
52-61
62-71
72-81
82-91
92-102
103-112
113-122
123-133
134-143
144-148
174
165
107
124
184
179
178
180
190
203
180
Column 1
3.30
4.12
6.36
5.48
3.70
3.80
3.82
3.78
3.58
3.35
3.78
2.59
2.23
1.56
1.84
3.07
2.76
2.37
2.68
2.58
2.13
1.69
0.179
0.312
0.252
+
0.527
0.543
0.337
0.613
0.568
0.382
0.175
0.48
0.62
0.48
0.49
0.49
0.33
0.52
0.49
0.41
0.22
Column 2
21
33
49
53
52
59
63
65
66
64
68
60
66
67
83
77
80
86
85
42-51
52-61
62-71
72-81
82-91
92-102
103-112
113-122
125-139
140-148
350
284
210
170
268
263
245
272
717
988
1.94
2.39
3.24
4.00
2.54
2.59
2.78
2.50
0.95
0.69
5.21
3.85
3.06
2.53
4.47
4.06
3.25
4.05
8.75
9.39
0.187
0.241
0.402
0.314
0.592
0.729
0.451
0.735
1.230
1.360
0.31
0.24
0.51
0.42
0.41
0.46
0.39
0.57
0.40
0.39
17
39
38
43
47
58
52
47
52
55
45
57
56
74
74
66
78
*Based on influent total and effluent filtered; CODn is COD removed.
+Meter not operating.
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column had significantly more attached
growth in the bottom section of the
filter. On an average mass per unit
volume basis, the laboratory column
had about 3 to 3.5 times as much
attached growth as did either of the two
pilot columns.
For purposes of developing a removal
rate as a function of the mass of solids
retained in the filter (a first order kinetic
relationship), it was assumed that the
filters acted as completely mixed re-
actors. Removal rates were based on
the solids measured and removals being
achieved at the very end of the study.
Column 1 removal rate was quite low;
however, the laboratory column and
column 2 data showed fair agreement.
The reaction rate constant of 0.004 (kg
COD removed/d)/(kg column solids)/
(mg degradable COD/d)0.00056 on
kg column volatile solids basiswas
similar to that found by Mueller and
Mancini* in their evaluation of plug flow
anaerobic filter data. The low rate in
column 1 indicated a high concentration
of inert solids in the lower part of the
column. These inert solids were evi-
dently "washed out" of the laboratory
column and pilot plant column 2 by the
higher volumetric flow rates used in
these columns.
Anaerobic Filter Design
Differences in the development and
retention of methane forming organisms
is the apparent factor responsible for
the differences in removals seen be-
tween the laboratory unit and the pilot
columns. The greater solids concentra-
tion retained by the small media in the
laboratory column resulted in the greater
removals per unit of volume. The practical
consideration of media cost and solids
plugging tend to favor the use of the
larger media for a full-scale plant,
accepting somewhat lower removals
and lower volumetric loadings than with
the smaller lab-type media.
Based on the overall results of these
studies, and based on a HTL waste COD
concentration of 10,000 mg/L, a volu-
metric loading of 6.5 kg COD/mVd was
selected. This loading would result in
1.5 days detention. Assuming a total
solids concentration in the anaerobic
filter of 10 kg/m3, the loading on a solids
basis would be 0.65 kg COD/kg solids/d.
*J.A. Mueller and J.L. Mancini, "Anaerobic Filter
Kinetics and Application," Proceedings of the 30th
Industrial Waste Conference, May 6-8, 1975,
Purdue Univ , Lafayette, Indiana.
Applying the anaerobic filter to other
high strength soluble organic wastes
continues to appear promising in light of
these pilot plant results, as well as other
anaerobic filter studies. A preliminary
evaluation of potential economic bene-
fits, and treatability studies with labo-
ratory and pilot scale units, would be
recommended for sizing an anerobic
filter system for a particular application.
The full report was submitted in ful-
fillment of Contract No. 68-03-2484 by
Hydroscience, Inc., under the sponsor-
ship of the U.S. Environmental Protec-
tion Agency.
Removals in the range of 55% to 65%
COD and 75% to 85% BOD were pro-
jected for a full-scale installation. Ele-v
ments included in the anaerobic filter
include the digester, filter media, liquor
heating and cooling system, pump
station, and gas collection and burning
equipment. The heat treatment liquor at
about 60° C would require cooling in
summer; under severe winter condi-
tions, auxiliary fuel may be required to
maintain 35° C in the filter.
Cost Comparison
In a preliminary cost evaluation, the
cost of the anaerobic filter system is
compared with the incremental cost to
increase the treatment plant's aeration
system and with a separate aerobic
system for the HTL. Table 4 presents the
preliminary cost estimates. The incre-
mental cost of an aerobic treatment
plant was developed based on capacity
designed into a 15 MGD plant. Costs are
for the additional basin and aeration,
capacity in the heat treatment reactor,
sludge holding tank, and vacuum filter
required to handle the additional sludge
load of about 640 kg per day. Operation
and maintenance costs include costs for
power, maintenance, labor, and sludge
handling.
Summary
Pilot plant and laboratory studies
show that significant removal of soluble
organics from a high strength sludge
HTL can be achieved at hydraulic reten-
tion times of 0.5 to 2 days. The results of
using a laboratory filter containing
small media capable of retaining a much
higher solids concentration of attached
growth were compared with a full-scale
pilot plant utilizing typical larger media.
The identification of a possibly more
suitable cost effective media to result in
maximizing solids retention is an area
that requires further study. The eco-
nomics for anaerobic treatment of
sludge HTL compare quite favorably
with those for aerobic treatment.
Table 4. Estimated Costs (1978) for Anaerobic Filter Treatment of HTL Compared
with Those for Aerobic Filter Treatment (340 m3/d; 10.000 mg/L COD)
Filter Type
Anaerobic Filter
No Credit for Methane
Credit for Methane
Aerobic Filter
Incremental Plant Cost
Separate Pretreatment
Capital
Cost
$ 470.000
$ 470,000
$ 541,000
$1,036,000
Operating
Cost
$ 18,400
$-17.000
$ 53,200
$ 68,000
4
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Eugene Donovan is with Hydroscience, Inc., Westwood, NJ 07675.
B. Vincent Salotto is the EPA Project Officer (see below).
The complete report, entitled "Pilot-Scale Anaerobic Filter Treatment of Heat
Treatment Liquor," (Order No. PB 81-218 323; Cost: $11.00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U, S. Environmental Protection Agency
Cincinnati, OH 45268
<, US. GOVERNMENT PRINTING OFFICE: 1«61 -757-012/7268
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Environmental Protection
Agency
Center for Environmental Research
Information
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