United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
Research and Development
EPA/600/S2-85/077 Aug. 1985
Project Summary
Anaerobic-Aerobic Treatment
Process for the Removal of
Priority Pollutants
Zahava Slonim, Li-Ta Lien, W. Wesley Eckenfelder, and John A. Roth
The removal of 4,6-dinitro-o-cresol
(DNOC), a phenolic priority pollutant,
and the removal kinetics were investi-
gated using an anaerobic recycle fluid-
ized bed reactor as a pretreatment stage
followed by an activated sludge reactor
as the aerobic treatment stage.
The DNOC was completely converted
during the anaerobic pretreatment stage
(anaerobic bed effluent DNOC concen-
tration
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nutrients. These anaerobic reactors were
monitored and analyzed for PH, ORP, SS,
VSS, COD, TOC, TOA, DNOC concentra-
tion, and sucrose concentration.
Anaerobic-Aerobic Continuous
Pilot System
The pilot plant consisted of an anaerobic
upflow sand filter and an activated sludge
unit, as shown in Figure 1. Pre-washed
sand, which was used as a matrix for the
attachment of microorganisms, was 3.0
feet high in the lower section. When
operating, the bed expanded about 30%
to a height of 4.0 feet. The temperature of
the column was maintained at 36.5°C.
The anaerobic upflow sand filter col-
umn was operated continuously with a
recycle flow rate maintained at about
3,000 I/day. Sodium chloride tracer tests
showed that the liquid phase was com-
pletely mixed. However, the biomass in
the fluidized bed was not uniformly
distributed. The microorganisms were
predominantly concentrated in the upper
22" ħ2" section of the sand. The activated
sludge tank was a conventional 19-liters
plexiglass unit. Effluent from the anaer-
obic upflow column was pumped directly
into the activated sludge unit as feed.
The anaerobic upflow sand filter col-
umn was initiated with several inocula-
tions of seed from a sludge digester from
a local municipal sewage treatment plant.
Operating parameters such as organic
loading, hydraulic retention time, loading
concentrations of DNOC and of sucrose
were carefully monitored.
The performance of the anaerobic
column was monitored by sampling the
effluent and analyzing for pH, alkalinity,
ORP, SS, VSS, COD, TOC, and DNOC
concentration. A sample was also ex-
tracted and analyzed for sucrose concen-
tration. When gas production was signif-
icant, the off-gas was analyzed and its
volume was measured.
The performance of the activated sludge
process in the treatment of the anaerobic/
degradation/products was monitored by
sampling its effluent and analyzing it for
pH, COD and TOC.
Results and Discussion
Preliminary shaker bottle results given
in Table 1, in which sucrose (3.0 g/l) was
used as a co-substrate clearly indicated
that DNOC was degradable under anaer-
obic conditions. Over a period of 7 days,
the original DNOC concentraton of 100
mg/l was reduced to 15 mg/l. Additional
results when filtered primary sludge was
used as co-substrate provided supporting
Off Gas
Anaerobic Effluent
Recycle
Activated Sludge Tank
'Effluent
Pump
Figure 1. Schematic of pilot plant apparatus.
Table 1.
Anaerobic Shaker Bottle Batch Test Results
Time
(days)
0
1
2
3
4
5
6
7
Sample*
S
D
S
D
S
D
S
D
S
D
S
D
S
D
S
D
pH
8.43
8.54
6.84
6.89
6.82
6.84
6.70
6.79
6.77
6.85
6.75
6.81
6.76
6.82
6.76
6.83
SS
(mg/l)
138
142
279
246
245
188
203
172
234
172
130
89.5
114
143
88.0
80.0
VSS
(mg/l)
64.0
69.0
197
153
177
123
145
115
156
114
111
68.5
93.0
86.5
73.5
56.5
TOA
(mg/l)
341
371
2150
1950
2210
2230
2310
2160
2700
2180
2170
2600
2260
CODs
(mg/l)
3130
3340
2550
2810
260O
2780
2630
2790
2560
2710
2850
2980
3100
324O
2790
2820
TOC
(mg/l)
1720
1780
1430
1610
1390
1530
1490
1780
1360
1400
1660
1660
1750
1810
1320
1390
DNOC
(mg/l)
100
78.6
61.2
39.8
21.9
18.0
15.5
14.6
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evidence that DNOC is anaerobically
degradable.
The continuously stirred batch reaction
results indicated that the degradation of
DNOC occurring under anaerobic condi-
tions was a result of the co-metabolism of
the nitroaromatic compound and depend-
ed upon the presence of a co-substrate. In
the presence of the co-substrate sucrose,
DNOC was anaerobically co-metabolized.
The results presented in Figure 2 demon-
strate that the metabolic process occurs.
The microorganisms cannot utilize the
200 r
DNOC as its sole source of carbon and
energy. When there is no sucrose present,
the concentration of DNOC remained
unchanged. This also resulted in a drastic
inhibition of biomass growth; i.e., no
change in VSS concentratoin was ob-
served over time. The DNOC itself does
not degrade by the anaerobic microorga-
nisms when a readily biodegradable co-
substrate is not available.
DNOC was treated in the anaerobic-
aerobic flow system over influent concen-
tration range of 10 mg/l to 750 mg/l.
Initial Concentrations
Symbols
DNOC
A
/ss
0
A
a
DNOC
(mg/l)
0
100
1OO
Sucrose
(a/I)
3.0
3.0
0
150
S
o
o
to
§
O
1
too
DNOC was not detected in the anaerobic
column effluet with DNOC concentrations
as high as 600 mg/l, when the sucrose
concentration in the influent was main-
tained at 3.0 g/l and the hydraulic
retention time (HRT) at 3 days.
Gas analyses were performed when
gas production exceeded 3 liters/day.
Based on limited data, the gas composi-
tion was 82 to 85% CO2, 15to17%N2and
less than 1% ChU. These data indicate
that acid-producing bacteria dominated
the microorganism population in the
anaerobic column. The production of
nitrogen gas also indicates that a denitri-
fication process occurred in the anaerobic
column. Thus, the denitrifying micro-
organisms are responsible for the reduc-
tion of the DNOC molecule nitro groups to
nitrogen gas.
Although the DNOC is degraded or
converted under anaerobic conditions in
the presence of sucrose as co-substrate,
this degradation was not associated with
an appreciable decrease in soluble COD.
One of the early batch tests resulted in
DNOC removal of 85% over a period of 7
days. The removal of DNOC in the anaer-
obic column was determined using influ-
ent DNOC concentrations of 250 and 500
mg/l. The influent sucrose concentration
was gradually reduced at fixed hydraulic
residence time. These results are shown
in Figures 3 and 4.
i/50
I
1/25
O
o
Q 75
I
50
I
o
.u
9)
to
Influent DNOC Cone. = 250 mg/l
HRT = O.47 Days
1234567
Anaerobic Column Influent
8 9
Sucrose Cone./
1
DNOC Cone.
Im9 1 J^3\
. \i / 1 )
Figure 2. The effect of sucrose concentration on the co-metabolism of DNOC in the
continuously stirred batch test.
Figure 3. The effect of sucrose/DNOC
concentration ratio on the re-
moval of DNOC in the anaerobic
column.
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I
c
S 125
8 100
<3
8 75
Q
Iğ
25
<3
Influent DNOC Cone. = 500 mg/l
HRT = 3.0 Days
01234567
Anaerobic Column Influent
Sucrose Cone.
Img I mg\
'( 1 I 1 )
Figure 4.
DNOC Cone.
The effect of sucrose/DNOC
concentration ratio on the re-
moval of DNOC in the anaerobic
column.
The performance of the anaerobic
column was highly dependent on the
influent concentration of the co-substrate
sucrose. An influent sucrose to DNOC
ratio of 2:1 or higher resulted in 95-100%
removal (or conversion) of DNOC in the
anaerobic process. However when influ-
ent sucrose to DNOC ratio was less than
2:1, the anaerobic microoganisms failed
to co-metabolize DNOC.
The degradation of the DNOC molecule
in the anaerobic process was not associ-
ated with an appreciable decrease in
soluble COD. Preliminary data indicated
in one case that over a period of 7 days a
DNOC removal of 85% was associated
with 16% decrease in TOA. In another
case a removal of 99.8% of DNOC was
associated with only an 11 % decrease in
soluble COD, while the TOA level in-
creased by 700%. These data demonstrate
that in the presence of sucrose, the
anaerobic microorganisms co-metabolize
the DNOC molecule changing the initial
structure in or around its benzene
nucleus. The two main processes which
took place in the anaerobic system were:
the co-substrate sucrose was degraded to
organic acids resulting in a large increase
in TOA concentratoin and an insignificant
decrease in soluble COD; and the struc-
tural conversion of the DNOC molecule
via co-metabolism by the anaerobic bac-
teria which were dependent on the
presence of the co-substrate sucrose.
The effect of the hydraulic retention
time (HRT) in the anaerobic column on the
removal of soluble COD was studied
under influent sucrose and DNOC con-
centrations of 2.0 g/l and 250 mg/l,
respectively. The HRT in the anaerobic
column was varied from 0.16 days to 3.0
days and the soluble COD removal in the
anaerobic column varied from 26% to 3%,
respectively. The soluble COD removal
achieved in the subsequent activated
sludge reactor varied from 24% to 87%
resulting in an overall soluble COD re-
moval of 50% and 70% removal respec-
tively, while a HRT of 0.43 days and
longer resulted in overall COD removals
of about 90%.
Figures 5 and 6 show the effect of
influent sucrose concentratoin on the
removal of soluble COD through the
anaerobic-aerobic system. When the ratio
of influent sucrose concentration to in-
fluent DNOC concentration was main-
tained at 2:1 or higher, the degradation
(or conversion) of DNOC in the anaerobic
column was between 92% and 100%.
However, even when provided with ade-
quate supply of co-substrate sucrose to
achieve more than 90% conversion of
DNOC, the anaerobic microorganisms
were unable to decrease the soluble COD
by more than 23% in the first set of
conditions and 30% in the second set of
conditions. The subsequent aerobic stage
achieved removals that ranged from 54 to
71 % under the first set of conditions and
from 48 to 63% under the second set of
conditions.
The performance of the activated sludge
process was adversely affected when the
ratio of sucrose:DNOC in the anaerobic
column influent was less than 2:1 and
reflects the inability of the anaerobic
microorganisms to satisfactorily co-
metabolize DNOC.
Conclusions
The effectiveness of the anaerobic-
aerobic system in the treatment of DNOC
is demonstrated. In contrast to the inabil-
ity of conventional activated sludge to
remove DNOC, the DNOC was completely
100
o
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Operational Condition:
Influent DNOC = 500 mg/l
HRT = 3.0 Days
125
% of COD Removal fAC + AS)
A % of COD Removal (AC)
O AC Effluent DNOC Concentration
Total COD Removed by Activated Sludge
Total COD Removed by
Anaerobic Column
Figure 6.
1.0 1.5 2.0
Influent Sucrose Concentration fg/IJ
The effect of influent sucrose concentration on COD removal by the system at high
HRT.
converted during the anaerobic pretreat-
ment stage. The anaerobic bed effluent
DNOC concentration was less than 1
mg/l, with a DNOC concentration in the
influent up to 600 mg/l. It was also found
that while 100% conversion of DNOC
occurred during the anaerobic pretreat-
ment stage, there was less than 25%
removal of COD during that stage. In the
activated sludge process most of the COD
was removed resulting n 80-90% overall
COD removal.
The initial breakdown of DNOC in the
anaerobic pretreatment stage was due to
co-metabolism. The DNOC itself does not
degrade by anaerobic microorganisms if
no other, readily biodegradable, co-
substrate was available to them. DNOC
cannot be, therefore, used as a sole
carbon source by the anaerobic bacteria.
Sucrose was used as the co-substrate in
this study. The data suggest that there is a
relationship between influent sucrose
concentration and the performance of the
anaerobic pretreatment stage of the
conversion of DNOC. The ratio of sucrose
to DNOC of 2:1 or higher resulted in a
95-100% conversion of DNOC in the
anaerobic pretreatment stage. The anaer-
obic microorganisms failedto co-metabo-
lize DNOC when the sucrose to DNOC
influent concentration ratio was less than
2:1.
DNOC can be regarded as a model
compound representing other degrada-
tion-resistant aromatic compounds
which, due to their recalcitrancy, present
the need for an innovative treatment
process for their removal from waste-
water. The higher removal rates of DNOC
achieved in this treatment process indi-
cated that this treatment process should
be evaluated for other recalcitrant phe-
nolic or nitroaromatic priority pollutants.
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Zahava Slonim, Li-Ta Lien, W. Wesley Eckent'elder, and John A. Roth are with
Vandervilt University, Nashville, TN 37235.
Thomas £. Short is the EPA Project Officer (see below}.
The complete report, entitled "Anaerobic-Aerobic Treatment Process for the
Removal of Priority Pollutants," (Order No. PB 85-226 900/AS; Cost: $13.00,
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:
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
P.O. Box 1198
Ada, OK 74820
&U. S. GOVFJttlMENT PRINTING OFFICE: 1985/559-111/20665
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Environmental Protection
Agency
Center for Environmental Research
Information
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Official Business
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