United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-85/019 Aug. 1985
Project Summary
Biological Treatability of KRW
Energy Systems Gasifier PDU
Wastewaters
Frank J. Castaldi
Bench-scale biological treatability
tests with wastewaters produced from
the KRW Energy Systems gasifier pro-
cess development unit (KRW-PDU)
were conducted to assess the bio-
treatability of these aqueous wastes
and to develop data for correlations
that establish a basis for designing a
biooxidation process. An autotrophic
activated sludge process was devel-
oped that utilized a mixed culture of ni-
trifying and sulfur-oxidizing bacteria for
simultaneous thiocyanate biodegrada-
tion and nitrification. An ammonia-
nitrogen concentration of greater than
250 mg/L and a thiocyanate concentra-
tion of 150 mg/L were biooxidized at a
hydraulic residence time of 24 hours
and at sludge ages between 60 and 150
days. Experimental testing at bioreac-
tor temperatures below 20°C indicated
that the nitrifying bacteria were
severely impacted at a bioreactor tem-
perature of 10°C, while the observed
thiocyanate removal efficiency deterio-
rated at a mixed liquor temperature of
6°C. Elevated concentrations of chlo-
ride, fluoride, and boron in experimen-
tal wastewaters did not inhibit either
nitrifying or sulfur-oxidizing bacteria in
the activated sludge process. However,
heavy metals were concentrated in the
activated sludges: this was thought to
be a consequence of the long sludge
ages of the experimental process.
This Project Summary was devel-
oped by EPA's Air and Energy Engineer-
ing Research Laboratory, Research Tri-
angle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report or-
dering information at back).
Introduction
Biological treatability studies were
conducted on wastewaters from the
KRW Energy Systems gasifier, formerly
called the Westinghouse gasifier, pro-
cess development unit (PDU) as part of
a characterization program to develop
design and environmental data for syn-
thetic fuels plants based on KRW-type
coal gasification technology. This report
gives results of the biooxidation study,
conducted through the cooperative ef-
forts of Radian Corporation and
Engineering-Science, Inc., to provide
engineering and environmental data for
designing wastewater treatment sys-
tems for this and other similar coal gasi-
fication technologies.
In 1982 the Department of Energy's
Morgantown Energy Technology Cen-
ter (METC), the Gas Research Institute
(GRI), and the Environmental Protection
Agency (EPA/AEERL) recognized the
need for a program to provide waste-
water treatment process design data for
a ash-agglomerating fluidized-bed gasi-
fication process. In response to this
need, METC, GRI, and EPA entered into
a joint program to develop wastewater
treatment performance data, design pa-
rameters, and environmental character-
ization data from a series of bench-scale
treatability tests with wastewaters from
the KRW-PDU coal gasification process.
The program produced a series of
wastewater characterization and treata-
bility documents which established the
basis of design data for several waste-
water treatment and reuse unit opera-
tions/processes:
• coagulation/clarification for re-
moval of small diameter (<2 jim)
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carbon particles (fines) present in
the wastewaters after bulk
settling of dense solids suspensions
found in the PDU quench li-
quors/gas cooling condensates;
• chemical conversion and fixation of
cyanide to less toxic forms;
• steam stripping for removal of dis-
solved acid gases and ammonia;
• activated sludge for ammonia, thio-
cyanate, and organic carbon re-
moval; and
• concentration of treated effluents
by low- and high-temperature evap-
oration processes.
This report is the basis-of-design doc-
ument for an autotrophic activated
sludge process, developed to treat pro-
cess wastewaters from an ash-
agglomerating fluidized-bed gasifica-
tion process. The technology, also gen-
erally applicable to the treatment of pro-
cess wastewaters from entrained-bed
gasifiers, should be viewed as a tech-
nology innovation for treatment of low
tar, oil, and phenol coal gasification
quench liquors and gas cooling conden-
sates.
Objectives
The biological treatability tests were
performed using wastewater from the
KRW gasifier PDU. Primary objectives
of the study were:
• To determine the feasibility of bio-
logical treatment of KRW-type gasi-
fier wastewaters using mixed popu-
lations of heterotrophic and
obligate autotrophic bacteria for
degradation of organic carbon, am-
monia, and thiocyanates.
• To obtain data for the determination
of preliminary design parameters
for an activated sludge process to
treat KRW-type gasifier wastewater.
Bench-scale laboratory studies using
continuous-flow bioreactors were con-
ducted with the KRW wastewater. The
studies were preceded by an initial pe-
riod of activated sludge acclimation that
established a representative microbial
population for treatability testing. The
continuous-flow biooxidation reactors
were operated at different biological
solids retention times and substrate
loadings in order to establish the bioki-
netics of the activated sludge process.
The impact of any toxic or inhibitory
substances that may have been present
in the KRW wastewater was investi-
gated during treatability testing.
The effects of temperature and non-
substrate ions on microbial activity
were investigated using biooxidation
test reactors and activated sludges ac-
climated during continuous-flow test-
ing. Alkalinity and pH considerations
also were investigated during
continuous-flow testing.
These data were used to develop a
basis-of-design for an activated sludge
process to treat KRW-type gasifier
wastewater.
Results and Conclusions
Biological oxidation treatability stud-
ies on KRW-PDU wastewaters were
conducted to obtain data for the deter-
mination of design parameters for the
treatment of contaminated quench
liquors and gas condensates produced
during coal gasification. The character-
istics of the KRW-PDU wastewater were
such that biological oxidation of nitro-
gen species (i.e., ammonia and thio-
cyanates) is the most important consid-
eration because the organic pollutant
content of the wastewater is low. The
study involved examining aerobic
chemoautotrophic cultures which were
utilized for the biodegradation of am-
monia and thiocyanate. The principal
functions of the treatability study were
to ascertain the degree of biodegrada-
tion possible by conventional activated
sludge processes and to develop the
basic criteria which would establish
proper operation of an autotrophic bio-
logical treatment facility.
Coefficients to mathematical models
which establish basic operation criteria
were determined by operating bench-
scale biological reactors at various sub-
strate loadings and evaluating each sys-
tem for substrate removal, sludge pro-
duction, and oxygen requirements.
Sludge settleability and thickening tests
were performed throughout the treata-
bility study to determine surface load-
ing rates on secondary clarifiers which
would provide both effective clarifica-
tion and thickening during normal acti-
vated sludge process operation.
The treatment efficiency associated
with the operation of a test bioreactor is
indicated by the data presented in
Table 1. The continuously fed, com-
pletely mixed bioreactor was evaluated
at water temperatures of between 22
and 23°C. The steady-state period was
generally characterized by excellent
pollutant removal, with comparable ef-
fluent values observed for all test reac-
tors with respect to ammonia, thio-
cyanate, TOC, COD, and BOD20. Trace
element data for the bioreactors indi-
Table 1. Steady-State Bioreactor Aver-
age Treatment Performance
Parameter
Influent Effluent
(mg/L) (mg/L)
TOC
COD
BOD20
NHrN
NO3-N
NO2-N
SCN
Total CN
Total P
TDS
38
178
1163
253
<0.5
<0.1
130
1.19
4.95
294
2.7
18
5
<1
286
<0.1
<1
0.86
2.8
2,976
Alkalinity (as CaCO3) 57
36
cated little apparent difference between
the influent and effluent quality associ-
ated with biooxidation treatment be-
cause most of the trace elements were
present at low concentrations in the
KRW wastewaters. Sodium was present
in the bioreactor effluent at elevated
concentrations because of the addition
of sodium hydroxide to the test reactors
for pH control during biooxidation. Ele-
ments that were found at elevated con-
centrations in the sludge (relative to the
water phase) were aluminum, barium,
calcium, iron, potassium, magnesium,
phosphorus, silicon, and zinc. Cad-
mium, chromium, copper, manganese,
nickel, lead, and titanium were also
bioaccumulated, but to lower levels.
The presence of high concentrations of
iron, copper, and nickel in the biosludge
may indicate a potential for the accumu-
lation of complexed cyanides in the
sludge. These pollutants were at ele-
vated concentrations in the sludges be-
cause of the long operational sludge
ages of the autotrophic activated sludge
process.
The GC/MS results for biotreated
wastewaters indicated little apparent re-
duction during biooxidation of the low
levels of extractable/chromatograph-
able organics found in the KRW waste-
water. The data relative to biosludge
characteristics are inconclusive because
a new group of compounds were found
in the sludges that had not been de-
tected in the wastewater. This may have
resulted from the production of meta- I
bolic intermediates generated during
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the biodegradation of the low level of
organics in the wastewaters.
A series of tests were performed with
a continuously fed, completely mixed
bioreactor to identify the effects of oper-
ation at lower ambient temperatures on
substrate removal performance. These
tests were conducted at equilibrium
bioreactor temperatures of from 22 to
5.6°C. The effects of low temperature
operation on bioreactor effluent quality
are summarized in Table 2. These data
indicate an apparently severe impact on
removal efficiency at a mixed liquor
temperature of about 10°C. The results
presented show that nitrate formation
was strongly inhibited at temperatures
below 10°C under the conditions of the
experiments. The microbial washout
rate increased during this period, per-
haps due to cell lyse. At no time during
the study did nitrite build up in the
mixed liquor of the test bioreactor.
The observed thiocyanate removal ef-
ficiency deteriorated below a 6°C biore-
actor temperature. There was no appar-
ent reduction in thiocyanate biodegra-
dation: the temperature was reduced
until this temperature was reached, de-
spite elevated levels of ammonia in the
bioreactor.
Pollutants which are common for
most fluidized- and entrained-bed gasi-
fier process wastewaters are chloride,
fluoride, and boron. These elements
may exist at elevated concentrations in
gasifier quench liquors and gas cooling
condensates and are considered a po-
tential source of problems for biological
treatment. A nonsubstrate ion toxicity
study was performed with bioreactor
activated sludges to document the im-
pacts of increased concentrations of
chloride, fluoride, and boron in the KRW
wastewater on biooxidation treatment
efficiency. A test bioreactor, operated at
3000 mg/L Cl~, 285 mg/L F~, and 150
mg/L BG>2~ (as boron), produced a
treated effluent quality comparable to
the effluent generated from a bioreactor
treating wastewaters with substantially
lower concentrations of these pollu-
tants. This indicated that the impact of
these elements on biological treatment
performance should be negligible.
Several conclusions can be drawn
from the information obtained during
steady-state and microbial stress test-
ing of activated sludges used for the
biooxidation of pollutants in the KRW-
PDU wastewater:
• KRW wastewaters pretreated by
steam stripping for ammonia reduc-
Table 2. Temperature Impact on Bioreactor Effluent Quality
Average Effluent Quality
Average
Temperature
(°C)
18
15
12
10
8
6
NH3-N
(mg/L)
0.12
0.07
0.08
209
252
278
N03-N
(mg/L)
269
284
270
68
3
2
NO2-N
(mg/L)
0.15
<0.1
0.16
0.22
<0.1
<0.1
SCN
(mg/L)
1.05
1.03
1.13
1.15
1.1
11
TOC
(mg/L)
4
5
4
3
2
6
COD
(mg/L)
13
23
30
27
33
23
tion and acid gas removal can be
successfully treated biologically
with the activated sludge process.
An ammonia-nitrogen concentra-
tion of 285 mg/L and a thiocyanate
concentration of 150 mg/L can be
biooxidized on a long-term basis at
neutral pH conditions with a mixed
culture of nitrifying and sulfur-
oxidizing bacteria.
Concentrations of 3000 mg/L chlo-
ride, 285 mg/L fluoride, and 150
mg/L boron in the KRW wastewater
did not inhibit either the nitrifying or
sulfur-oxidizing bacteria in the acti-
vated sludge process. The presence
of low levels of free and complexed
cyanide in the KRW wastewater did
not have an adverse impact on am-
monia or thiocyanate removal dur-
ing biooxidation. Consequently, an
autotrophic activated sludge pro-
cess can be used to treat similar
wastewaters derived from the gasi-
fication of different coals. The pro-
cess may also be applicable to the
treatment of wastewaters from
other fluid- and entrained-bed gasi-
fiers that produce aqueous wastes
with chemistries similar to the ex-
perimental wastewater composi-
tions.
A study of temperature effects on
the biodegradation of ammonia and
thiocyanate indicated that the nitri-
fying bacteria were severely im-
pacted at a bioreactor operational
temperature below 10°C. This effect
was thought to be largely the result
of substrate (ammonia) inhibition.
The observed thiocyanate removal
efficiency deteriorated at a bioreac-
tor operational temperature below
6°C. However, there was no appar-
ent reduction in thiocyanate bio-
degradation: the temperature was
reduced until this temperature was
reached, despite elevated levels of
ammonia in the test bioreactor.
• Although the settleabilities of the
activated sludges were generally
good, the apparent activated sludge
settling quality (measured by the
zone settling velocity and the
sludge volume index) showed a de-
terioration at higher bioreactor
sludge ages. Operational sludge
ages for the experimental biooxida-
tion process varied between 60 and
150 days. Generally, these sludge
ages were considered necessary to
maintain system stability for com-
plete nitrification and to minimize
sludge production.
• Heavy metals were concentrated in
the activated sludges during experi-
mental testing. However, the de-
gree of bioaccumulation associated
with the presence of metal-cyanide
complexes in the wastewater could
not be determined from the experi-
mental data. The removal during
biooxidation treatment of extract-
able/chromatographable organics
identified by GC/MS analysis was
inconclusive. The study did not de-
termine the fate of organics in the
autotrophic activated sludge pro-
.cess because of contradictory re-
sults regarding the nature of the or-
ganics in the aqueous and solid
phases of the process.
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F. J. Castaldi is with Radian Corp., Austin, TX 78766.
William J. Rhodes is the EPA Project Officer (see below).
The complete report, entitled "Biological Treatability of KRW Energy Systems
Gasifier PDU Wastewaters," (Order No. PB 85-199 685/AS; Cost: $17.50,
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:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S7-85/01 9
OCOC129 PS
n S CNVIR PROTECTION
•flU.S. GOVERNMENT PRINTING OFFICE: 1985—559-01b/271
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