United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-93/066 June 1993
Project Summary
On-Site Engineering
Report of the Slurry-Phase
Biological Reactor for Pilot-Scale
Testing on Contaminated Soil
Majid Dosani, Judy Hessling, Michael L Smith, Alan Jones, and William R.
Mahaffey
The performance of pilot-scale
bioslurry treatment on creosote-con-
taminated soil was evaluated. The re-
sults of the bench-scale study were
used to optimize a pilot-scale bioreactor
system containing 66 L of slurry per
reactor. Five reactors were operated in
parallel and each reactor contained 30%
soil by weight. The soil was a sandy
soil with minor gravel content. The pi-
lot-scale phase utilized an inoculum of
indigenous polynuclear aromatic hydro-
carbon (PAH) degraders (9.3 x 107 per
g of soil), an inorganic nitrogen supple-
ment in the form of ammonia nitrogen,
and a media broth containing potas-
sium, phosphate, magnesium, calcium,
and iron to achieve an overall reduc-
tion of the PAH contaminants. The test
reactors were operated over a period
of 12 wk. During the testing of the soil,
levels of soil-bound and liquid-phase
PAHs, total petroleum hydrocarbons
(TPHs), nutrients, pH, dissolved oxy-
gen, temperature, toxicity, and micro-
bial activity were monitored. The re-
sults of analysis performed on post-
treated soil samples revealed that the
total percent reduction of soil bound
PAHs, after 12 wk, ranged from >66.8%
to >92.6%. Concentrations of PAHs in
the liquid samples after 12 wk were
very low.
This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the research project
that is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
This study was performed for the U.S.
Environmental Protection Agency to sup-
ply information as part of the data base
on Best Demonstrated Available Technolo-
gies for soil remediation. The data base
will be used to develop soil standards for
Land Disposal Restrictions.
The ultimate goal of biodegradation is
to convert organic wastes into biomass
and relatively harmless by-products of mi-
crobial metabolism such as carbon diox-
ide, methane, water, and inorganic salts.
As part of the effort to treat the PAHs in
the soil more effectively, biodegradation
studies using the pilot-scale slurry-phase
process were conducted. In this process,
the soil is suspended to obtain a pumpable
slurry, which is circulated in a large-ca-
pacity, continuously stirred tank reactor.
The reactor is then supplemented with
oxygen, nutrients, and, when necessary,
a specific inoculum of microorganisms to
enhance the biodegradation process. This
treatment method has several advantages
because the engineering and biotechnol-
ogy required to provide an optimal envi-
ronment for biodegradation of the organic
contaminants can be controlled with a high
degree of confidence. Biological reactions
can be accelerated in a slurry system
because of the increased contact efficiency
that can be achieved between contami-
nants and microorganisms and by suc-
cessfully maintaining high bacterial popu-
lations and an optimum concentration of
oxygen and nutrients.
Printed on Recycled Paper
-------
Procedure
Before initiating the pilot-scale slurry-
phase testing program, the soil was passed
through a 1/2-in. screen to remove any
debris and oversized material. Originally,
the soil was brown to black, fine-to-me-
dium grained sand with some minor gravel
content, and somewhat resilient and
greasy. Following initial screening of the
soil, it was mixed with water to form a
slurry. The water-to-soil ratio of the slurry
was 2.33 (on a weight basis). The slurry
was passed through a ball mill three times
to produce a slurry with a grain size distri-
bution suitable for charging the EIMCO
Biolift™' reactors. Five pilot reactors were
operated in parallel. Following milling, 66
L of the soil slurry was transferred into
each of the reactors. Figure 1 presents a
schematic diagram of the reactors used
throughout the study.
After charging the reactors with the soil
slurry, 666 ml of a concentrated inoculum
(three bacterial isolates: Pseudomonas
stutzeri, Pseudomonas fluorescens, and
Alcaligenes sp.) was added to the slurry
in each of the reactors. Based on the titer
of bacteria present in the inoculum, this
amounted to a total of 1.98 x 1012 bacteria
per reactor. Furthermore, because the
amount of free nitrogen, as measured by
ammonia nitrogen, in the soil slurry was
quite low for microbial activity, ammonia
supplementation was necessary to en-
hance activity for the microbes in the slurry.
Nutrient amendments added to the re-
actor included ammonia and phosphate
along with trace amendments of magne-
sium, calcium, iron, and ammonium mo-
lybdate.
Sampling and analysis activities per-
formed during the pilot-scale tests included
collection of composite samples from each
of the reactors for pre-treatment and post-
treatment analysis and throughout the
study to monitor system operation. During
the study, levels of soil-bound and liquid-
phase PAHs, TPHs, nutrients, pH, dis-
solved oxygen, temperature, toxicity, and
microbial activity were monitored. Com-
posite samples were collected from the
three sampling ports located along the
side of the reactor at three different verti-
cal locations (Figure 1). Concentrations of
organic contaminants in the off-gases were
also monitored. All parameters of the study
were monitored in accordance with the
sampling and analysis plan prepared for
the project.
Sampling and analyses of the soil slurry
samples from the bioreactors were contin-
ued for a total of 12 wk. In the 9th wk of
operation, however, four of the bioreactors
were reinoculated with an additional 125
ml of the inoculum to stimulate the PAHs
degradation process. Details regarding
sampling locations, the method and fre-
quency of sampling and constituents that
were analyzed are presented in the Onsite
Engineering Report (OER) prepared for
this study.
Results
Table 1 presents a summary of the re-
sults of analysis for the PAHs in the pre-
treatment soil samples at the start of test-
ing (Week To). The concentrations of these
contaminants in the soil samples ranged
from 5.5 to 840 mg/kg. Table 2 presents
the results for the posttreatment soil
samples at the end of testing (Week T12).
The data indicate that the PAHs in the soil
matrix were significantly reduced in each
Diffuser Air Supply
Rotary Valve
of the reactors. The total percent reduc-
tion of PAHs after Week T ranged from
>66.8% to >92.6%.
With regard to the liquid samples, the
concentration of PAHs in the pretreatment
samples ranged from 0.006 to 18 mg/L.
The concentration of PAHs in the post-
treatment liquid samples after 9 wk of
treatment ranged from 0.013 to 0.14 mg/
L Only the more recalcitrant complex
PAHs remained.
Results of the analysis for the semi-
volatile organics in the off-gas samples
indicated that some of the PAHs (i.e.,
naphthalene, 2-methylnaphthalene,
acenaphthylene, acenaphthene, dibenzo-
furan, fluorene, phenanthrene, and an-
thracene) were detected during the first 4
days of sampling. Beginning with the sixth
day of operation, however, very small
quantities (at or below detection) of these
semivolatile organics were found.
Rake Drive Shaft -
Support Bearings
Impeller Drive Shaft
Support Bearings
Airlift
Discharge (2)
Airlifts (2)
Sample and
Drain Valves
Aeration Diffuser
(Partially Shown)
Rake Blades (5)
Rake Drive
Gearmotor
Impeller Drive
Gearmotor
Airlift Air Supply
Block Valve
Airlift Water Flush
Connection
Airlift
Check Valve
Impeller Drive Shaft
Impeller
Rake Drive Shaft
Rake Arms
Mention of trade names or commercial products does
not constitute endorsement or recommendation for
use.
Figure 1. EIMCO Biolift™ Reactor.
-------
Table 1. Concentration of Critical Semivolatile Organic Contaminants in Pretreatment Soil Samples
(Week TJ, mg/kg
Contaminant
Naphthalene
2-Methylnaphthalene
Acenaphthylene
Acenaphthene
Dibenzofuran
Fluorene
Phenanthrene
Anthracene
Fluoranthene
Pyrene
Benzo(a)anthracene
Chrysene
Benzo(b)fluoranthene
Benzo(a)pyrene
lndeno(1 ,2, 3-cd)pyrene
Dibenzo(a,h)anthracene
Benzo(g,h,i)perylene
Total
1
600
220
39
240
190
330
680
410
570
360
140
140
130
70
<40
<40
<40
4119
2
360
130
18
130
100
150
460
300
330
210
80
85
37
33
<40
<40
<40
2423
Reactor No.
3
40
16
5.5
46
34
57
150
92
130
68
24
27
28
11
<40
<40
<40
728.5
4
540
210
44
320
230
380
840
520
660
500
180
210
190
96
<40
<40
<40
4920
5
64
28
9.6
95
67
110
300
140
180
150
47
54
49
22
<40
<40
<40
1315.6
Table 2. Concentration of Critical Semivolatile Organic Contaminants in Posttreatment Soil Samples
(Week T,2), mg/kg'
Reactor No.
Contaminant
Naphthalene
2-Methylnaphthalene
Acenaphthylene
Acenaphthene
Dibenzofuran
Fluorene
Phenanthrene
Anthracene
Fluoranthene
Pyrene
Benzo(a)anthracene
Chrysene
Benzo(b)fluoranthene
Benzo(a)pyrene
lndeno( 1 ,2, 3-cd)pyrene
D/benzo(a,h)anthracene
Benzo(g,h, i)perylene
Total
1
5.4
<25.0
<0.89
<25.0
<9.0
<2.5
5.7
4.3J
11.0
8.5
<2.4
9.0J
170.0
95.0
56.0
19.0
39.0
<487.69
2
<2.3
<25.0
<0.89
<25.0
<9.0
<2.5
2.1J
<8.1
3.3
<5.7
<2.4
<14.0
32.0
17.0
<2.9
<1.8
<25.0
< 178. 99
3
2.Ub
<25.0
<0.89
<25.0
<9.0
<2.5
2.9J
<8.1
4.8
<5.7
<2.4
<14.0
62.0
39.0
12.0
<1.8
<25.0
<242.19
4
<2.3
<25.0
<0.89
<25.0
<9.0
<2.5
6.6
4.1J
12.0
<5.7
<2.4
7.3J
120.0
78.0
39.0
<1.8
29.0
<370.59
5
3.4
<25.0
<0.89
1.2J
<9.0
<2.5
<3.8
3.7 J
<1.3
<5.7
<2.4
<14.0
95.0
60.0
25.0
<1.8
19.0J
<273.69
MDLs3
2.3
25.0
0.89
25.0
9.0
2.5
3.8
8.1
1.3
5.7
2.4
14.0
9.4
13.0
2.9
1.8
25.0
3 MDLs = Method Detection Limits.
bj = Estimated value of compound detected below specified detection limit.
'These results are slightly different from the Week TJ2 results given in Table 6-6 of the full report
because the samples were reanalyzed. This did not affect the final conclusions.
Conclusions
The pilot-scale biodegradation demon-
stration achieved significant reduction of
PAHs in the soil matrix. Results of the
analysis revealed that, on average, >87.6%
(range, >68.7% to >96.7%) and >83.8%
(range, >66.8% to >92.6) of total PAHs
were degraded over all five operating re-
actors after the 9th and 12th wk of the
study, respectively. These results indicate
that the additional spiking of microbes dur-
ing Week 9 did not assist in further degra-
dation of the complex PAHs. One reason
for the increase in contamination during
Week 12 may have been that the addi-
tional spiking may have allowed for further
degradation of the less complex hydrocar-
bons in the soil; this additional degrada-
tion could have cleaned up the soil by
removing interferences that may have af-
fected earlier analysis. The cleaner matrix
would have allowed lower detection limits,
as evidenced by Week 12 analysis, and
thus allowed better detection of contami-
nants present in the soil.
The range in percent removal for the five
reactors (example: >66.8% to >92.6 % after
12 wk) indicates that there was considerable
variation in PAH removal between reactors.
This is also seen in Table 1 which shows
significant variation between reactors for indi-
vidual contaminant concentrations. Although
some variation is expected for biological sys-
tems with high creosote concentration, one is
reminded to view the data from this study
with caution.
With regard to the various PAH iso-
mers, degradation rates (mg/kg/wk) for 2-
and 3-ring PAHs were appreciably higher
than they were for 4- to 6-ring PAHs. The
more rapid degradation of the lower-mo-
lecular-weight PAHs reflects the prefer-
ence of the bacterial populations for these
PAHs over the higher weight PAHs. The
slower degradation of the higher weight
PAHs also could reflect that they were
more tightly bound into the soil. The re-
sults of analysis on posttreatrnent samples
show that the more complex PAHs, such
as benzo(b)fluoranthene and benzo(a)pyrene
were more recalcitrant to the biological activ-
ity than were the less complex PAHs such as
naphthalene and acenaphthene.
During the off-gas sampling, low con-
centrations of volatiles (toluene, benzene,
xylene) and low concentrations of lower 2-
and 3-ring semivolatiles (naphthalene,
fluorene, phenanthrene) were detected for
the first few days of operation. All of these
contaminants diminished to concentrations
that were below the detection limit after 5
days of operation. The lower-molecular-
weight, posttreatrnent volatile compounds
were probably products of degradation of
the higher molecular weight compounds
because the volatile compounds were be-
low the detection limit in the pretreatment
soil samples. Volatile organics degrade
very rapidly within the reactor, and this is
why they were not detected in the off-gas
after the first few days of sampling.
The full report was submitted in fulfill-
ment of Contract No. 68-C9-0036, Work
Assignment No. 2-69, by IT Corporation,
under the sponsorship of the U.S. Envi-
ronmental Protection Agency.
'U.S. Government Printing Office: 1993 — 750-071/60243
-------
Majid Dosani, Judy Hessling, and Michael L. Smith are with IT Environmental
Programs, Inc., Cincinnati, OH 45246, and Alan Jones and William R.
Mahaffey are with EVOCA Corporation, Redmond, WA 98052.
Richard P. Lauch is the EPA Project Officer (see below).
The complete report, entitled "On-Site Engineering Report of the Slurry-Phase
Biological Reactor for Pilot-Scale Testing on Contaminated Soil," (Order No.
PB93-178 259/AS; Cost: $27.00, 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:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-93/066
------- |