Note: Descriptions are shown in the official language in which they were submitted.
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1
Apparatus and Method for the Treatment of Water Containing Organic Pollutants
FIELD OF THE INVENTION
The present invention relates to an apparatus and method for the treatment of
contaminated
water by biodegradation. In particular, the apparatus and method are suited
for the
biodegradation of volatile organic compounds (VOC's) such as trichloroethylene
and
related conipounds or benzene and related compounds. The process employs an
immobilized soil bioreactor (ISBR) optionally having a headspace re-
circulation systeni.
BACKGROUND OF THE INVENTION
Groundwater contaminants frequently have high volatilities. Examples of
contaminants
include berizene, toluene, ethylbenzene, xylene (BTEX compounds) and related
compounds that result from gasoline spills or leaks as well as
trichloroethylene (TCE) and
related conipounds such as dichloroethylene which are the most frequently
encountered
groundwater contaminants.
In the evaluation of models and processes for groundwater treatment, TCE can
be used as a
model compound for the evaluation of the model and has been designated as a
priority
pollutant by the United States Environmental Protection Agency. TCE and
related
compounds are only weakly toxic aiid carcinogenic but their degradation
products
(especially the vinyl chloride formed under anaerobic conditions) may be
serious
carcinogens. Unlike BTEX compounds, clllorinated hydrocarbons often cannot
serve as
the sole source of carbon and energy for most microorganisms but co-metabolism
(i.e. co-
oxidation) is possible. Co-metabolism results froni the expression of
nonspecific enzyjnes
that degrade the primary substrate and involves the transformation of a
compound that
does not supply carbon or energy to the microorganism. Co-metabolism of
compounds
such as TCE has been found to occur with methane, toluene and NH4 degrading
microorganisms. Best results have been shown using methane. Unfortunately,
during co-
metabolisni by methanotrophs, methane acts as a competitive inhibitor of
methane
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2
monooxygenase, the enzyme responsible for TCE degradation. Therefore, methane
concentrations must be kept relatively low.
Biofilters are beds of peat, compost or other materials that can serve as
supports for
microorganisms while allowing a gas phase to pass through the bed. The
microorganisms
may then degrade organic or inorganic compounds in the gas phase. In
particular, the
microorganisms are used to treat easily degradable compounds such as BTEX and,
recently have been shown to have possible applications in TCE treatment.
Furthermore, past systems used in the degradation of VOC's have been limited
as a result
of the volatization of the VOC's, leading to unacceptable release of VOC's to
the
atmosphere. The loss of VOC's or pollutant in the gas exit stream is often a
result the
aeration required by many reactors. Accordingly, there has been a need for a
highly
effective process and apparatus for the biological degradation of both non-
volatile
pollutants such as pentachlorophenol (PCPO as well as volatile pollutants such
as TCE or
BTEX compounds in water and, in particular, a bioreactor which minimizes the
release of
VOC's to the atmosphere.
Still further, there has been a need for a system which enables the treatment
of volatile
products of anaerobic biodegradation processes and, in particular, the
effluent of an
anaerobic process. For example, it is known that perchloroethylene cannot be
readily
degraded aerobically but can be degraded to less chlorinated compounds such as
TCE and
dichloroetllane (DCE) anaerobically but that complete mineralization will not
take place
anaerobically.
SUMMAR Y OF THE INVENTION
In accordance with the invention, an apparatus for removing organic
contaminants froln
water is provided, the apparatus comprising:
an immobilized soil bioreactor (ISBR), the ISBR including a reaction chamber
including a top portion, a bottom portion, an aeration side and a non-aeration
side,
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the aeration and non-aeration sides segregated by a supported soil matrix, the
supported soil matrix including a microorganism culture adapted for the
biodegradation of the organic compounds, the supported soil matrix extending
substantially from the bottom portion to the top portion wherein the supported
soil
matrix allows a circulation of fluid around the supported soil matrix from the
aeration side to the non-aeration side; and,
a headspace re-circulation system operatively connected to the ISBR for
circulating
fluid around the supported soil matrix, the headspace re-circulation system
including means for pumping gas phase in the top portion of the ISBR to the
bottom portion of the ISBR on the aeration side of the ISBR.
In further embodiments, the ISBR includes any one of or a combination of means
for
introducing a solution containing contaminant into the ISBR, means for
introducing a
microorganism nutrient solution into the ISBR, means for introducing oxygen
into the
ISBR, means for introducing a co-metabolism compound into the ISBR and/or
means for
removing aqueous phase from the ISBR.
In a still fi.irther embodiment, the system includes biofilter operatively
connected to the gas
phase in the top portion of the ISBR, the biofilter including immobilized
biomass for
biodegradation of pollutant within the gas phase
In a more specific embodiment, the immobilized soil contains a microbial
culture adapted
for the biodegradation of trichlorooethylene (TCE) or other pollutant to be
treated.
The invention also provides a process for the biodegradation of organic
compounds in
water in an immobilized soil bioreactor (ISBR), the immobilized soil
bioreactor including
a reaction chamber including a top portion, a bottom portion, an aeration side
and a non-
aeration side, the aeration and non-aeration sides segregated by a supported
soil matrix, the
supported soil matrix including a microorganism culture adapted for the
biodegradation of
the organic compounds, the supported soil matrix extending substantially from
the bottom
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portion to the top portion wherein the supported soil matrix allows a
circulation of fluici
around the supported soil matrix from the aeration side to the non-aeration
side, the
process comprising the steps of:
a) introducing a contaminated water stream containing any one of or a
combination
of organic and/or volatile organic compounds into the ISBR; and,
b) circulating the contaminated water stream within the ISBR through aeration
of
the aeration side.
In a more specific embodiment, gas phase is collected from the top portion of
the ISBR.
and is re-circulated to the bottom portion of the aeration side to effect
fluid circulation
around the supported soil matrix.
In further embodiments of the process, the process may include any of or a
combination of
introducin;; a nutrient solution, dissolved oxygen solution, and/or a co-
metabolism solution
into the ISBR and/or removing aqueous phase from the ISBR.
In a more specific embodiment of the process, the process includes introducing
a micrabial
culture adapted for biodegradation of trichloroethylene or other pollutants to
be treated.
Still further, the process may include subjecting the gas phase collected from
the top
portion of the ISBR to a downstream biofiltration process and/or operation of
the device in
series with. at least another ISBR.
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BRIEF DESCRIPTION OF THE DRA WINGS
These and other features of the invention will be more apparent from the
following
descriptioni in which reference is made to the appended drawings wherein:
5 Figure 1 is a schematic process diagram of a laboratory scale reactor in
accordance with
the invention;
Figure 1A is a schematic process diagram of an industrial scale reactor in
accordance with
the invention;
Figure 2 is a graph of Experiment A showing TCE concentration vs. time;
Figure 3 is a graph of Experiment B showing TCE concentration vs. time;
Figure 4 is a graph showing TCE concentration vs. time for an experiment using
the IF'BR
without geotextile and with sparging;
Figure 5 is a graph showing TCE concentration vs. time for an experiment using
the
IFBR, initially without geotextile and without sparging.
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DETAILED DESCRIPTION OF THE INVENTION
With reference to Figures 1 and 1 Aõ laboratory and industrial scale reactor
systems having
an immobilized soil bioreactor (ISBR) are shown. With reference to Figure 1,
the system
includes an ISBR reactor 12, a co-metabolism system 14, a contaminant supply
system
5 16 and a headspace re-circulation system 18. Generally, the ISBR reactor 12
supports a
microorganism culture which is capable of mineralizing a volatile or non-
volatile pollutant
delivered from the contaminant supply system 16, the contaminant supply system
containing the contaminant as well as the nutrients and oxygen required to
support the
microorganism culture. A co-metabolism system 1.4 may be required where the
10 microorganism culture requires additional compounds, such as methane,
toluene or
anunonium to facilitate the biodegradation efficiency.
The reactor 12 is preferably a cylindrical chamber which is centrally divided
into an
aeration side 20 and a non-aeration side 22 by an immobilized soil region 24
described in
"Soil Immobilization: New Concept for Biotreatment of Soil Contaminants,
Karamanev et
al., Biotecl:mology and Bioengineering, Vol 57, No. 4, (1998)" and which is
incorporated
herein by reference. The immobilized soil region 24 preferably includes a
geotextile
supporting matrix which entrains soil within the reactor against the matrix.
The geotextile
is an appropriate membrane having a pore size sufficient to trap soil
circulating within the
reactor while also permitting a degree of water circulation through the
entrapped soil.
As indicated above, the reactor inch-ides an aeration side 20 and a non-
aeration side 22.
During operation, an aerating gas 26 is released at the bottom of the reactor
whereupon it
rises to the surface of the aerating side 20. The rising gas lowers the
density of fluids on
the aeratio:n side 20 allowing a circulation of fluid to occur between the
aeration 20 anci
non-aeration sides of the reactor. In order to facilitate the movement of
fluid between the
two sides, it is preferable that the inimobilized soil region 24 provides a
space 24a at the
bottom of the reactor and another space 24b at the top of the reactor 12 to
permit a
consistent circulation of fluid between the two sides.
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A nutrient solution containing microorganism nutrients and dissolved oxygen is
also
introduced into the reactor 12. In the embodiment shown in Figure 1, the
nutrient solution
is introduced with the contaminant and dissolved oxygen by pump 16a.
Furthermore, a co-metabolism solution may also be introduced into the reactor,
if
necessary to maximize the efficiency of the specific microorgansims within the
reactor. In
the embodiment shown in Figure 1, methane is dissolved in a nutrient solution
and
introduced into the reactor 12 by pump 14a.
A decontaminated product stream 28 of spent nutrient and water is withdrawn
from the
reactor 12 to maintain a steady voluine of fluid in the reactor 12.
Gases released at the surface of the liquid phase of the reactor are collected
and pumped
by pump 18a through the headspace recirculation system 18 and returned to the
bottom of
the reactor 12 as the aerating gas 26.. Accordingly, any VOC's released to the
gas phase are
collected and re-circulated through the reactor 12.
With refere:nce to Figure 1 A, a field scale water treatment system 100 is
shown as a typical
installation for the treatment of contaminated groundwater. A tank 102 has
leaked a
quantity of a pollutant 104, for exaniple TCE, to the groundwater 106. The
pollutant 104 is
shown below the water table and above any bedrock 110 which may be present in
the
formation. A well 112 is drilled to enable the contaminated groundwater to be
pumped to
the surface by pump 114. The pump 114 delivers contaminated groundwater to an
ISBR
116 as described above. Furthermore, a headspace recirculation system 118 is
provided
through wl--ich headspace gas is collected and recirculated to the base of the
reactor 116.
Addition of an aerating gas, oxygen and possibly a co-metabolism compound may
be
introduced through pipe 120 into the headspace recirculaton system as required
or,
alternatively, directly into the reactor 116 through a separate inlet system
(not shown).
Decontaminated water is re-introduced to the ground through pipe 121 from the
reactox
116.
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In addition to the ISBR reactor 116, the system may be provided with a
biofilter system
122 for the further decontamination of volatized pollutant released to the
headspace 118a.
The biofilter 122 utilizes a bed of compost or other suitable materials to
support to
microorganisms to further facilitate the biodegradation of volatile pollutants
from the
gaseous phase. Accordingly, gas from the headspace 118a is passed through the
biofilterl22 along with additional air and/or cometabolism compounds (pipe
124), if
necessary, to continue the biodegradation of the pollutant. Decontaminated gas
phase may
be released to the atmosphere through pipe 126.
The ISBR i-eactor and biofilter may be operated in series to effect
biodegradation where
desired results and system parameters warrant.
Examples
The following examples are illustrative of the effectiveness of the system in
the
decontamiriation of water. In these examples, TCE was used as a model compound
for the
development and study of the invention because it is one of the most commonly
found
groundwater contaminants, is highly volatile and is relatively difficult to
biodegrade.
Some of its relevant characteristics are given in Table 1.
Table 1. Some Physical Properties of Trichloroethylene
Property Value
Molecular weight 131.39 g mol-'
Melting point - 84,8 C
Boiling point (760 mm Hg) 86.7 C
Aqueous solubility at 20 C 1000 mg L-'
Vapour pressur at 20 C 60 mm Hg
at 30 C 95.5 mm Hg
Henry's constant at 25 C 8.92 x 10-3 atm m3 mol-'
Density at 25 C 1.460 g ml-'
K ,,, (log) 2.42
K. (log) 2.10
Source : Perry et al., (1997) et Merck Index (1996)
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In all the following examples the operational conditions were as follows
unless otherwise
indicated.
Chemicals and stock solutions
For radioactive labelling14C was used. The [14C]TCE (Sigma Chemicals, St-
Louis, MI)
used had a purity greater than 98 % and a specific activity of 5.4 mCi/mM. A
nutrient
stock solution was prepared in deionized water with NaNO3 (2 mM), phosphate
buffer (2
mM) (KHZ]?O4 (3.9 mM) and NaZHPO4(6.0)), MgSO4=7H2O (50 M) and FeSO4=7H2O
('80
M) (Anachemia, Montreal, Quebec). The TCE and the hexane (laboratory grade)
came
from Anachemia. The methane and air mixture (air:C02 (20 % of COZ v/v)) came
from
Air liquid (:anada.
Laboratory-scale reactor system
As described above and as shown in Figure 1, the laboratory-scale system
incorporated
three separate sub-systems: 1) a contaminant supply unit for the addition of
TCE, nutrient
and dissolved oxygen; 2) a co-metabolism system (methanator) for the addition
of
methane; and, 3) an immobilized soil bioreactor.
During large-scale use of the system, it may not be necessary to use the co-
metabolism
sub-system as co-metabolism compounds and air can be added as a gas directly
into the
bottom of the reactor as in a typical air-lift reactor. For the purpose of
laboratory
investigations, the co-metabolism system was used at a laboratory-scale
facilitate accurate
analysis of oxygen and methane usage.
The unit for the addition of TCE ancl nutrient was composed of a TedlarT"' bag
(20.3 L)
(Cole Parmer, Vernon Hills, IL) and a water tank. The TedlarTM bag was used to
contain
TCE and nutrient solution. The bag was utilized to avoid the TCE
volatilization. A 23 L
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water tank was used to add dissolveci oxygen in the reactor. The methanator
was
composed of a TeflonT'' (polytetrafluoroethylene) bag (4.7 L) (Cole Parmer)
filled with
methane and an aspirator bottle (V = 1 L) (VWR Canlab, Mississauga, Ont.) on a
stirring
plate. The mass transfer of methane was executed inside the bottle. All the
tubing inside
5 the methanator was stainless steel (316-SS, O.D. = 3.18 mm) and the tubing
which
connected the reactor with the methanator was in TygonTM SE-200 (I.D. = 3.18
mm and
O.D. = 6.35 mm). The immobilized soil bioreactor was a 2 L cylinder glass
reactor sealed
with a rubber stopper (size : interior dia. = 77 mm, exterior dia. = 90 mm,
thickness = 40
mm). Inside the reactor a geotextile (H = 36.4 cm, L = 7.8 cm t = 0.5 cm)
contain the
10 immobilized soil (2.55 g). The temperature inside (T = 29.5 C -30.8 C)
was controlled
by thermal exchange with a tubing (U form) through which cool water was
passed. All
tubing insicte the reactor was in stainless steel. The agitation and
circulation of the liquid
phase interior the bioreactor was performed by recirculating the headspace gas
using a
pump.
Measurement of Dissolved Oxygen
Dissolved oxygen (DO) concentration was measured with a Model YSI-5739 oxygen
meter (Yellow Spring Instruments iric., Yellow Spring, OH) that had been
calibrated in air-
saturated water (9.09 mg L-' at 20 C).
Measurement of Dissolved Methaile
Measurement of dissolved methane concentration was determined by headspace
analysis.
10 ml of liquid for methane analysis was injected with a glass syringe (model
1010,
Hamilton) into an evacuated 12 ml glass vial (Wheaton) with a butyl rubber
seal. The
pressure was equilibrated with atmospheric air. The vial was shaken vigorously
by hand
for 30 seconds. 50 L of the gas phase was removed with a 250 L gas-tight
syringe, then
injected into a Hewlett-Packard model 5890 (column HP-1, 15 m x 0.53 m x 0.15
m)
with a flame ionization detector (FII)). The temperature for the oven was
increased from
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60 C to 9() C at a rate of 15 C/min and 90 C to 120 C at a rate of 10
C/min.
Injector and detector temperature were maintained at 90 C and 220 C,
respectively. The
carrier gas was helium (134 kPa). A integrator (HP-3396 A) was coupled with
the GC to
analyze the constituent of the gas phase. Quantification of the unknown sample
was
achieved by a calibration curve (con-elation coefficient of 0.99) for the
methane. This
method gave the gaseous methane concentration. The dissolved methane
concentration
was calculated using equation 1.
r [CH4]g B
LC'~4l L v
L (1)
TCE Degradation
TCE degradation was determined by syringe extractions in hexane
(sample:hexane, 1:1
(v/v)) followed by gas chromatography (capillary column HP-5, 25 m x 0.2 mm x
0.33
m) with an electron capture detector (ECD) analysis using 1,2-dibromoethane
(EDB) as
an internal standard. A 1 L sample of the extract was injected automatically
(Hewlett-
Packard model HP-7673) into the GC. The program temperature for the oven was
increased fi-om 45 C to 150 C at a rate of 15 C/min, held at 150 C for one
minute
followed by a 150 C to 120 C decrease at a rate of 10 C/min. Injector and
detector
temperature were maintained at 150 C and 250 (:, respectively. The retention
time
obtained for TCE and 1,2-dibromoethane was 2.89 min. and 4.15 min.,
respectively.
Quantification of the unknown sample was achieved by injecting standards that
had been
treated like samples and comparing the relative areas with an integrator (HP-
3396 A)
(correlatior.t coefficient of 0.99).
['aC]TCE inineralization
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12
The study of mineralization was performed in serological bottles (120 ml)
which contained
60 ml of nutrient, 20 ml of aqueous phase from the reactor (or 10 g of solid
phase from the
biofilter with no added nutrient solution), a COZ trap (1 ml KOH 1 M), a
mixture of gas
CH4:air (1:1 v/v) and with various radioactive TCE concentrations (1 to 15
ppm). Abiotic
control sannples were prepared for each TCE concentration by using NaN3 (0.2 %
m/v).
Microcosms were incubated in the dark at room temperature. Mineralization was
determined by measuring the evolution of"CO2 from [14C]TCE. Radioactive CO2
was
trapped in 1. ml of 1 M KOH. Another 1 ml of KOH to rinse the trap. The 2 ml
samples
were added to 10 ml of liquid scintillation counter fluid and mixed
vigorously. 14C02
levels were determined with a liquid scintillation counter (model LSC 1409,
Wallac
Scintillatioa Products, England).
Soil was added to an aerated ISBR which had previously contained no soil. The
optical.
density (660 nm) of the medium immediately increased to about 1.1 but after 46
h it had
returned to the original optical density indicating that the soil was almost
totally
immobilized.
Two experiments were carried out tc- assess the ability of the ISBR to degrade
TCE. In
these experiments, the reactor was loaded with soil as described above and
supplied with
methane to develop a methanotrophic bacterial population. The soil was
collected from
the aerobic,lanaerobic interface of a swamp to provide the desired
microorganisms and, in
particular, methanotrophs. TCE was then fed at various feed rates, different
amounts of
methane supplied and the hydraulic residence time was varied to produce the
results shown
in Figures 2 and 3. These figures show raw data that demonstrates the TCE
degradation.
efficiency of the ISBR operated under methanotrophic conditions. In general
the amount
of TCE degraded (difference between the circles (TCE in the feed) and the
squares (TCE
leaving the reactor) increased with the amount of TCE fed and with the
residence time.
Results wei-e compared with the results previously obtained with other
reactors by other
researchers. These comparisons are shown in Table 2 and show that the system
of the
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13
invention vvas much more efficient at TCE biodegradation than previous stirred
tank
reactor systems at similar residence times and TCE outlet (ie. reactor)
concentrations.
Table 2 Comparison of the results of TCE biodegradation in a methanotrophic
IFBR with
other published reports of reactor-based TCE degradation.
Publication [TCE]in [TCE]out Residence Maximal Efficiency
(mg L-') (mg L-') time (d) degradation rate (% TCE
(mg TCE L-' d-') removal)
Lanzaronne et al. 0.025 0.0185 0.02 0.33 26
1990
Arvin, 1991 1.2 0.924 0.2 1.38 23
Fennel et a.l. 1993 11.3 8.6 0.11 24.5 23.9
Aziz et al. 1995* 0.097 0.075 0.0065 3.38 22.7
This work 2.26 0.061 0.91 2.42 97.3
This work 18.12 8.46 0.042 230 53.3
* Bioreactor employing a pure methanotrophic strain
The lab-scale ISBR was usually operated without aeration, instead using
dissolved oxygen
in the incorning aqueous phase (water + medium) as the oxygen source. However,
in one
experiment, the ISBR was operated without geotextile (therefore no immobilized
soil so
little or no imicroorganisms) and with or without aeration by bubbling
(sparging). The
liquid residence time was 6 hours and the aeration rate (when aerated) was 0.5
L miri'. As
shown in Fig. 4 for an experiment without geotextile and with sparging, the
outlet TCI3
concentration in the aqueous stream never reaches the inlet concentration.
This shows
that a significant portion of the TCE (about 25 %) must have been transferred
to the gas
phase due to its volatility. Figure 5 shows the results of using the IFBR,
initially without
geotextile, but without sparging. The inlet and outlet TCE concentrations were
usually
very similar except at one point (as shown if Fig. 5) where geotextile support
was added
resulting in a small amount of TCE sorption to the geotextile.
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14
Headspace Recirculation
Operating 1:he system in a recirculation mode caused a steady decrease in the
TCE
concentration in both the aqueous and gaseous phases of the reactor.
Biofilter
In a large-scale mode of operation, the addition of co-metabolism compounds
and air
addition may require sparging wherein the reactor off-gases would contain
volatile
pollutant (in this case TCE). For this reason, the use of a downstream
biofilter was
investigated. Results of a series of rnethanotrophic biofiltration experiments
are given in
Tables 2, 3, 4, and 5.
A stainless steel biofilter with a diarneter of 0.097 m and 0.5 m in height
was used for the
biofiltration assays. The biofilter bed was composed of compost and perlite
(50 % w/w).
Biofiltration experiments showed a:linear relationship between TCE degradation
rate and
TCE concentration at the biofilter inlet. TCE inlet concentrations were varied
from 0.06
and 23 mg L'. The inlet CH4 concentration was relatively constant at 4 % v/v
and the
gaseous flow was 2.3 L miri'. TCE degradation rates of up to 43.5 g TCE m 3 h-
' (0.315
mol TCE ni 3 reacteur h-') were obtained. At initial CH4 concentrations lower
than 1,1 %
v/v, the cornpetition between CH4 and TCE was not detectable.
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Table 3: Operation of the biofilter at an initial CH4 concentration of 0.076
mmol L'
Entrance Exit
[CH4] (% v/v) 0.170 0.135
5 [CH4] (mmol L-') 0.076 0.060
[TCE] (mg L-') 1.82 0.76
[TCE] (mmol L-') 0.0140 0.0058
C/Co CH4 1 0.794
C/Co TCE 1 0.418
10 % CH4 consumption 20.59
% TCE degradation 58.24
Volume (L) 3.7
Flow rate (L miri') 2.529
Residence time (minutes) 1.463
15 Rate of CH4 consumption 0.643
(mol CH4 m 3 reactor h-')
Rate o:FTCE degradation 0.331
(mol TCE m 3 reactor h-')
Table 4: Operation of the biofilter at an initial CH4 concentration of 0.161
mmol L-' .
Entrance Exit
[CH4] ;% v/v) 0.36 0.31
[CH4] (mmol L-') 0.161 0.139
[TCE] (mg L-') 1.54 0.73
[TCE] (mmol L-') 0.0117 0.0056
C/Co CH4 1 0.861
C/Co TCE 1 0.474
% CH4 consumption 13.89
% TCE degradation 52.6
Volume (L) 3.7
Flow rate (L min') 2.393
Residence time (minutes) 1.546
Rate of CH4 consumption 0.872
(mol CH4 m 3 reactor h-')
TCE degradation rate 239
(mol TCE m 3 reactor h-')
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16
Table 5: Operation of the biofilter at an initial CH4 concentration of 0,500
mmol L-1 Entrance Exit
[CH4] ( % v/v) 1.1 1
[CH4] (mmol L-') 0.5 0.45
[TCE] (mg L-') 1.6 0.74
[TCE] (mmol L-') 0.0122 0.0056
C/Co CH4 1 0.909
C/Cp TCE 1 0.463
% CH4 consumption 9.09
% TCE, degradation 53.75
Volume (L) 3.7
Flow rate (L miri') 2.578
Residej:ice time (minutes) 1.435
Rate of CH4 consumption 1.906
(mol CH4 m 3 reactor h-')
TCE degradation rate 273
(mol TCE m 3 reactor W)
Table 6: Operation of the biofilter at an initial CH4 concentration of 2.15
mmol L-' .
Entrance Exit
[CH4] (1% v/v) 4.6 4.41
[CH4] (mmol L-') 2.15 2.06
[TCE] (mg L-') 1.02 0.7573
[TCE] (mmol L-') 0.078 0.0057
C/Co C:H4 1 0.959
C/Co TCE 1 0.735
% CH4 consumption 4.13
% TCE degradation 26.47
Volume (L) 3.7
Flow rate (L min') 2.505
Residence time (minutes) 1.477
Rate ofCH4 consumption 3.78
(mol CH4 m' reactor h')
TCE degradation rate 83
(mol TCE m 3 reactor h-')
The biofiltration experiments showed that a varied inlet concentration of
methane with a
relatively constant inlet concentration of TCE resulted in TCE degradation.
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17
TCE mineralization experiments were performed using either biomass from the
ISBR or
samples of the biofilter bed. Depending on the conditions, both usually
produced well in
excess of 50% of the theoretical CO2; production from the initial TCE showing
that
complete mineralization is possible with either the ISBR or the biofilter
biomass either
singularly or in combination.
The terms amd expressions which have been employed in this specification are
used as
terms of description and not of limitations, and there is no intention in the
use of such
terms and expressions to exclude any equivalents of the features shown and
described or
portions thereof, but it is recognized that various modifications are possible
within the
scope of the claims.
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18
References,
1. ARVIN, E. (1991). Biodegradation kinetics of clilorinated aliphatic
hydrocarbons with
methane oxidizing bacteria in an aerobic fixed biofilm reactor. Water Res 25 :
873-881.
2. AZIZ, C. E., FITCH, M. W., LINQUIST, L. K., PRESSMAN, J. G., GEORGIOU, G.
et
SPEITEL Jr, G. E. (1995). Methanotrophic biodegradation of trichloroethylene
in a hollow
fiber membrane bioreactor. Env Sci Technol, 29(10) : 2574-2583.
3. BOWMAN, J. P. et SAYLER, G. S. (1994). Optimization and maintenance of
soluble
methane m,Dnooxygenase activity in Methyl.osinus trichosporium OB3b.
Biodegradation,
5: 1-11.
4. FENNELL, D. E., NELSON, Y. r/1., UNDERHILL, S. E., WHITE, T. E. et JEWELL,
W. J. (199-3). TCE degradation in a methanotrophic attached-film bioreactor.
Biotechnol
Bioeng, 42: 859-872.
5. KARAIV[ANEV, D. G., CHAVARIE, C. et SAMSON, R. (1997). Soil immobilization:
a new concept for biotreatment of soil contaminants. Biotechnol Bioeng, 57:471-
476.
6. LANZARONE, N. A. et McCARTY, P. L. (1990). Column studies methanotrophic
degradatiori of trichloroethylene and 1,2-dichloroethane. Ground Water, 28(6)
: 910-919.
7. MERCK Index. (1996). An encyclopedia of chemicals, drugs and biologicals,
12th
edition, Merck and Co. inc., Whitehouse Station, New Jersey.
8. PERRY, Robert H., GREEN, Dori W. et MALONEY, James O. (1997). Perry's
Chemical Engineers Handbook, 7th ed., McGraw-Hill.
