Bio-degradation of ammonium perchlorate, nitrate, hydrolysates and other energetic materials

A method and system for carrying out the bio-degradation of perchlorates, nitrates, hydrolysates and other energetic materials from wastewater, including process groundwater, ion exchange effluent brines, hydrolyzed energetics, drinking water and soil wash waters, which utilizes at least one microaerobic reactor having a controlled microaerobic environment and containing a mixed bacterial culture. By the method of the present invention, perchlorates, nitrates, hydrolysates and other energetics can be reduced to non-detectable concentrations, in a safe and cost effective manner, using readily available non-toxic low cost nutrients. The treatment of significantly higher concentrations of perchlorate, nitrate, etc. (<1.5 wt %) than was previously contemplated is made possible.

The present invention is directed to the treatment of explosive laden and 
associated industrial wastewaters, groundwater, and drinking water and, in 
particular, waters which are contaminated with ammonium perchlorate, 
nitrate, hydrolysates and other energetic materials. 
BACKGROUND OF THE INVENTION 
Present inventories of solid rocket motor (SRM) propellant slated for 
disposal are over 164 million pounds and increasing due to the imminent 
disposal requirements of the Strategic Arms Reduction Treaty. 
Additionally, almost 7 million pounds of waste propellant are generated 
annually in the U.S. as a by-product of manufacturing. Over 500,000 tons 
of ordnance items are stockpiled and awaiting disposal. These propellants 
and explosives are hazardous waste due to their inherent reactive and 
toxic natures. 
Because these materials are complex cross-linked composites, with 
components that are partially or completely soluble in water, they are 
difficult to reclaim and reuse. Historically, open burning (OB) and open 
detonation (OD) have been used to dispose of these materials. However, 
under Resource Conservation and Recovery Act (RCRA), OB/OD has been 
severely limited and, in some cases, totally prohibited. 
Ammonium perchlorate is the primary ingredient in most rocket propellants 
and is also present in lesser quantities in many ordnance items. The U.S. 
Environmental Protection Act (EPA) recently established a provisional 
reference dose for perchlorate of 32 parts-per-billion (ppb). This has 
caused the California Department of Health Services to close 23 drinking 
water wells in southern and northern California. 
Separation or concentration of perchlorate in drinking water and disposal 
by biodegradation is one possible solution to the problem. Safe ways of 
containing and destroying energetic materials and wastewater generated 
from disposal and production activities is critically important to 
continued use of these materials in our nation's weapon systems. 
In addition to treating perchlorate in the presence of salts and other 
energetic materials, other energetics themselves (nitramines, 
nitroglycerin, nitrates, nitroaromatics, etc.) must be destroyed. 
Processes to treat energetic materials must be robust, predictable, and 
cost-effective. 
A method for treatment of such contaminated wastewater is disclosed in U.S. 
Pat. No. 5,302,285. The method involves reduction of perchlorate to 
chloride in a first stage anaerobic reactor, using a specific 
microorganism in mixed culture, followed by treatment of the organics 
produced in the first reactor in a second stage aerobic reactor. The 
specific microorganism is designated as HAP1 and was classified as being 
strictly anaerobic. 
It was recently discovered that the bacterium Wolinella succinogenes can 
effectively reduce perchlorate (Wallace, W., Ward, T., Breen, A., Attaway, 
H. 1996 "Identification of an Anaerobic Bacterium Which Reduces 
Perchlorate and Chlorate as Wolinella succinogenes". Journal of Industrial 
Microbiology, 16:pp. 68-72). Although originally categorized as being an 
anaerobe in Bergey's Manual of Systematic Bacteriology, Vol. 1, Wolinella 
sp. is in fact capable of respiring with oxygen. It has also been 
subsequently recognized as a H.sub.2 and formate requiring microaerophile 
(Bergey's Manual of Determinative Bacteriology, Ninth Edition, 1994). 
Prior to the present invention the use of such a microorganism in the 
treatment of perchlorate contaminated wastewater had only been carried out 
in a two stage anaerobic-aerobic process. Such a process was capable of 
reducing perchlorate wastewater concentrations of 7750 mg per liter. 
It has been surprisingly found, however, that wastewater contaminated with 
perchlorate, and other energetic materials, including hydrolysate products 
of energetic compounds, can be more effectively treated using a controlled 
microaerobic environment. 
By the use of the present invention and the use of a controlled 
microaerobic environment as opposed to a strictly anaerobic, aerobic or 
anoxic environment, certain advantages over the prior art are realized. In 
particular, the invention is (1) capable of reducing higher perchlorate 
concentrations, greater than 9000 mg/l in a single stage reactor system 
and greater than 15,000 mg/l in a multi-stage system; (2) capable of 
higher reduction rates than previously reported, greater than 0.7 g/l per 
hour; (3) capable of reducing anions (ClO.sub.4.sup.-, ClO.sub.3.sup.-, 
NO.sub.3.sup.-, NO.sub.2.sup.-) in the presence of high salt 
concentrations (&gt;3.4% total dissolved solids); (4) capable of reducing 
perchlorate and alkaline hydrolyzed energetics simultaneously; (5) capable 
of reducing greater than 18,000mg/l of nitrate (NO.sub.3.sup.-) in a 
single stage system; (6) capable of maintaining anion (ClO.sub.4.sup.-, 
ClO.sub.3.sup.-, NO.sub.3.sup.-, NO.sub.2.sup.-) reducing capability over 
extended periods (&gt;2 weeks), without anions present; (6) capable of 
maintaining ClO.sub.4.sup.- reduction capability at ClO.sub.4.sup.- 
concentrations of &lt;1.5 ppm; (7) capable of effectively using low-cost 
nutrients (e.g., cheese whey, whole yeast, milk and brewery waste and 
sugar/starch-based carbohydrate wastes, etc.,) and combinations of 
low-cost nutrients; (8) capable of effectively treating contaminated 
ground water with or without a preliminary concentration step; (9) capable 
of reducing anions (ClO.sub.4.sup.-, ClO.sub.3.sup.-, NO.sub.3.sup.-, 
NO.sub.2.sup.-)in NaCl brine from ion exchange concentration processes; 
and (10) capable of effectively reducing chromium VI to relatively 
insoluble chromium III compounds. 
It is therefore an object of the present invention to provide a method for 
effectively treating wastewaters contaminated with perchlorate, nitrate, 
hydrolysates and other energetic materials. 
It is another object of the present invention to provide a method for 
reducing perchlorate, nitrate, hydrolysates and other energetic materials 
present in wastewaters using a specific bacterium, Wolinella succinogenes, 
in a mixed culture and in a controlled microaerobic environment. 
It is a further object of the present invention to provide a method for 
effectively and easily maintaining a microaerobic environment. 
It is also an object of the present invention to treat wastewaters with 
high concentrations of perchlorate, nitrate, hydrolysates and other 
energetic materials and at high perchlorate reduction rates, in a simple 
and cost effective manner. 
These and other objects of the present invention will become apparent from 
the detailed description and examples which follow. 
SUMMARY OF THE INVENTION 
In accordance with one embodiment, the present invention provides a method 
for the treatment of wastewaters and the like, suspected of being 
contaminated with perchlorates, nitrates, hydrolysates and other energetic 
materials, comprising: 
(a) providing at least one microaerobic reactor containing a mixed 
bacterial culture capable of reducing perchlorates, nitrates, hydrolysates 
and other energetic materials; 
(b) feeding wastewater, suspected of being contaminated, to the at least 
one microaerobic reactor; 
(c) maintaining a microaerobic environment in the microaerobic reactor by 
at least one method selected from the group consisting of (i) mixing air 
and nitrogen gas and sparging or purging the reactor with the gas mixture; 
(ii) using a nitrogen membrane separator to provide a low 
oxygen-containing nitrogen gas to the reactor for sparging or purging; 
(iii) adding air to the reactor for sparging or purging to maintain a 
target dissolved oxygen concentration or a target oxygen concentration in 
head space gas present in the reactor; and (iv) maintaining chlorate, 
nitrate and perchlorate concentration in the feed; and 
(d) maintaining suitable nutrient and environmental conditions in the 
microaerobic reactor. 
In accordance with a second embodiment, the present invention provides a 
single-stage or a multi-stage microaerobic system comprising: 
at least one microaerobic reactor for treatment of contaminated wastewater 
and the like and containing a mixed bacterial culture capable of reducing 
perchlorates, nitrates, hydrolysates and other energetic materials; 
feed stream means for feeding contaminated wastewater or the like into the 
at least one microaerobic reactor; 
a microaerobic environment control means for controlling the environment in 
the at least one microaerobic reactor; and 
a treated wastewater discharge system. 
In accordance with a third embodiment, the present invention provides a 
method for reducing perchlorates, nitrates, hydrolysates and other 
energetic materials in a microaerobic bio-degradation system, the method 
comprising: 
(a) feeding wastewater or the like suspected of being contaminated with 
perchlorate, nitrate, hydrolysates and other energetic materials into a 
microaerobic reactor containing a mixed culture of bacterium and 
maintaining a suitable microaerobic environment in the microaerobic 
reactor so as to effectively biodegrade perchlorates, nitrates, 
hydrolysates and other energetic materials present in the reactor; 
(b) optionally feeding the microaerobically treated wastewater or the like 
from step (a) to at least one other reactor or series of other reactors 
selected from the group consisting of suspended growth 
continuously-stirred-tank reactors (CSTR), fixed-film reactors, sludge-bed 
reactors and activated sludge reactors; 
(c) feeding the treated wastewater and the like from step (a) and/or step 
(b) into a clarifier, and 
(d) recycling the treated and clarified wastewater from step (c) back to 
the microaerobic reactor. 
By the above method(s), treated wastewaters can be discharged for treatment 
directly to conventional sewage treatment systems.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The microorganism which reduces perchlorate, nitrate, hydrolysates and 
other energetic materials, Wollinena succinogenes, has the characteristics 
set forth in Bergey's Manual of Determinative Bacteriology, Ninth Edition, 
expressly incorporated herein by reference, as if individually set forth. 
A mixed culture of Wollinena succinogenes is deposited with the American 
Type Culture Collection Patent Depository, 12301 Parklawn Drive, Rockville 
Md. 20852 and has been given ATCC Number 29543. 
With reference to FIG. 1, contaminated wastewater and the like (hereinafter 
"wastewater") enters the system via inlet 1, along with a dilution stream 
2, e.g. water or other suitable media for dilution as required, a pH 
adjustment stream 3, e.g. containing acid, caustic soda or other suitable 
media for controlling pH, and a nutrient stream 4. The use of 
independently controlled multiple feed streams for each of wastewater 1, 
water 2, pH adjustment 3 and nutrients 4 is preferred and has several 
advantages, which are as follows: (1) saturated brine effluents containing 
greater than 27% salts can be fed directly to the bioreactor system; (2) 
saturated perchlorate, nitrate and hydrolysate effluents containing 
greater than 12% perchlorate can be fed directly into the bioreactor 
system; (3) brine effluents and concentrated perchlorate effluents can be 
fed simultaneously through independent feed streams without salt 
precipitation; (4) brine and concentrated perchlorate, nitrate and 
hydrolysate effluents can be mixed and diluted to concentrations which 
optimize process performance and cost; and (5) nutrient consumption can be 
optimized for performance and cost. The mix, which may have been 
optionally pre-treated depending on the concentrations of perchlorates 
etc., is fed to a microaerobic reactor 5 wherein the perchlorates, 
nitrates, hydrolysates and other energetic materials are reduced by the 
mixed culture containing the bacterium, Wolinella sp. which is present in 
the reactor 5. In a single stage reactor system, perchlorate 
concentrations as high as 9,000 mg/l, can be treated. In a multi-stage 
reactor system, perchlorate concentrations as high as 15,000 mg/l, can be 
treated. This concentration is based on the total wastewater feed stream 
entering the reactor. 
The microaerobic reactor 5 is preferably a sludge bed reactor and its 
microaerobic environment is controlled by one of four methods, (1) feeding 
a mixture of air and nitrogen gas and sparging or purging the reactor 5 
with this mixture as appropriate; (2) using a nitrogen membrane separator 
to provide a low-oxygen containing nitrogen gas to the reactor 5; (3) 
adding air to the reactor 5 for sparging and purging as appropriate and 
(4) maintaining a chlorate, nitrate and perchlorate concentration in the 
feed. Each of these methods used alone, or separately, maintain a target 
dissolved oxygen concentration in the liquid present in the reactor 5 or a 
target oxygen concentration in head space gas. The sparging and purging 
gas control means 10 may be any type of control mechanism, electronic or 
pneumatic. For example, in a nitrogen membrane system manual adjustment of 
pressure and flow rates controls the nitrogen purity. The same control 
means may also control the environment in other reactors which may be 
present in the system. 
The operating conditions for perchlorate reduction in the microaerobic 
reactor 5 may vary depending on the nature and composition of the 
wastwater/effluent being treated. With this in mind, the temperature is 
preferably maintained between about 10-42.degree. C., most preferably 
between about 20-35.degree. C. The residence time (RT) for the wastewater 
or effluent being treated in the reactor 5 is preferably between about 
2-48 hours, most preferably between about 6-18 hours. The perchlorate feed 
concentrations may be anywhere between about &lt;1-&gt;15,000 mg/l. Preferably 
the feed concentrations are between about &lt;1-9,000 mg/l when a 
single-stage system is used and between about &lt;1-15,000 mg/l when a 
multi-stage system is used. The nitrogen feed concentration can be 
approximately &gt;18,000 mg/l for a single-stage system. The nutrient feed 
ratio, if ClO.sub.4.sup.- is greater than 100 mg/l, is preferably between 
about 1:1-10:1 g(nutrient):g(ClO.sub.4-). The nutrient feed concentration 
is preferably between about 1-32 g/l. The amount of total dissolved solids 
in the reactor 5 is preferably between about 1-34 g/l. The pH within the 
reactor 5 is preferably maintained between about 6.5-7.6. The oxygen 
concentration in the sparge gas is preferably maintained between about 
0.1-4.0 vol %. 
Following treatment in the microaerobic reactor 5, the treated 
wastewater/effluent may be fed to a primary clarifier 6, which is 
optional, depending on the nature and composition of the effluent being 
treated and the nutrients used. The primary clarifier concentrates 
nutrients and microbial biomass. Specifically, the use of such enables the 
nutrients to be completely digested to soluble components, recycling back 
to the microaerobic reactor, and the microbial biomass to be concentrated 
in sludge-bed reactors. This also enables the efficient utilization of low 
cost, partially insoluble nutrients and results in very high reactor 
activity. Such also enables fixed-film reactors to be used in subsequent 
stage of a multi-stage system, which would have ordinarily required 
soluble nutrients i.e., partially insoluble nutrients are useable in 
fixed-film reactors. 
If a primary clarifier is used, the clarified effluent may be recycled back 
into the microaerobic reactor 5. The treated effluent, whether clarified 
or not, may also be fed to a series of optional reactors 11, 12 and 13, 
for further treatment, in a multi-stage reactor system. When such optional 
reactors are not used the system is referred to as a single stage system. 
Secondary clarifiers may also be optionally used, as shown in FIG. 1. 
Optional reactors 11, 12 and 13 may be suspended growth continuously 
stirred tank reactors (CSTR), fixed film reactors operated in anaerobic, 
microaerobic or aerobic modes or sludge bed reactors. Whether such 
optional reactors are used and what modes they are run under depends on 
the nature and composition of the effluent being treated. 
The use of staging up to five reactors in series, as shown in FIG. 1, has 
several additional advantages to the single stage system. The 
concentrations of perchlorate in effluent fed to the reactor 5 can be as 
high as 15,000 mg/l, (or approximately 1.5 wt % of the total wastewater 
stream) which is much higher than previously demonstrated. Through 
sequential addition of nutrients and controlling the microaerobic 
environment, the perchlorate may be reduced to below detectable limits in 
the second and third reactors. Microaerobic reactors followed by aerobic 
reactors, as the second, third and fourth reactor stages, respectively, 
will first reduce the toxic inorganic anions and then aerobically oxidize 
organic energetics or energetic hydrosylate components and reduce the 
effluent biological oxygen demand (BOD) to a level that can be discharged 
into municipal sewage treatment plants. It has been found that the 
subsequent reactor stages can be independently configured to enable any 
combination of anaerobic, microaerobic or aerobic 
continuously-stirred-tank reactors, fixed-film reactors or sludge-bed 
reactors. Such is configured depending on the nature and composition of 
the effluent being treated and nutrient requirements. Effluents with high 
perchlorate and solids concentrations are best reduced in 
continuously-stirred-tank reactors or in sludge-bed reactors. Effluents 
with low perchlorate and solids concentrations are best reduced in 
fixed-film reactors. Mixing of reactor contents is carried out using 
mechanical stirrers 19 or by any suitable mixing process. 
Whether treated in a single stage reactor system or a multi-stage system, 
the treated effluent is fed to an activated sludge reactor 14 if further 
BOD reduction is required and is then fed to a secondary clarifier 15, 
which is required for an activated sludge process. The treated effluent 
may then be discharged directly to conventional sewage treatment systems 
16. The sludge may be recycled 17 either back into the activated sludge 
reactor 14 or is fed to a further sludge waste treatment system 18. 
Perchlorate contaminated wastewater and the like may concentrated using in 
an ion exchange process. The decontaminated wastewater and the like is 
returned to an appropriate water supply system or alternatively to an 
aquifier. The now concentrated perchlorate effluent is then fed to the 
microaerobic reactor system. If the perchlorate contaminated wastewater 
does not need to be concentrated, it may be fed directly to the 
microaerobic reactor and into the system illustrated in FIG. 1 whereby 
aerobic BOD reduction is carried out if necessary and is eventually 
discarded into a conventional sewage treatment system. 
The nutrient medium in the process of the present invention may be a low 
cost nutrient medium. This is an important advantage since the nutrient is 
a primary operating expense in the system. The nutrient medium according 
to the present invention can be one or any combination of the following 
nutrients; brewer's yeast, cheese whey, corn starch, corn liquors, corn 
syrups, sugars, acetate, alcohols, and food process wastes. Food process 
wastes are sugar and carbohydrate-based material that may include but are 
not limited to: brewery wastes; milk, cheese, and ice cream wastes; juice 
and soft drink bottling wastes; candy, cereal, and sweetened foodstuff 
wastes. 
Using food process wastes for nutrients substantially reduces the cost when 
compared to other conventional chemical and physical waste treatment 
processes. 
It has also been found that base hydrolysis pre-treatment of energetic 
materials, solids and sludges, removes the energetic nature of these 
materials and dissolves them so that they can be biodegraded. Base 
hydrolysis pre-treatment, typically carried out using sodium hydroxide or 
potassium hydroxide, although any similar base is contemplated, yields 
hydrosylate components such as formate, acetate, nitrite, nitrate, 
formaldehyde and glycerol that are biodegradable, and can provide a 
nutrient source for the microaerophillic mixed culture. By this means, 
degradation of any solid energetic material, by-product/sludge or aqueous 
effluent is possible. Both organic and typical inorganic anions (including 
perchlorate, chlorate, nitrate and nitrite compounds) are also reduced, in 
particular, after base hydrolysis (see Example 2). 
By the method of the present invention, complete reduction of energetic 
materials to their mineral component is obtainable. For example, 
ClO.sub.4.sup.-, ClO.sub.3.sup.-, NO.sub.3.sup.- and NO.sub.2.sup.- may 
be completely reduced by the method of the present invention, even in the 
presence of their associated cations such as, ammonia, sodium and 
potassium, and other cations. These anions are also reduced completely in 
the presence of high salt concentrations, in excess of 3.4% total 
dissolved solids (TDS) and in the presence of dissolved energetic 
components, such as nitroaromatics, nitramines and nitroglycerine (NG). 
In accordance with the present invention the term "wastewater" is given its 
meaning in the art and also means process groundwater, drinking water, ion 
exchange brines and soil wash water. The term "energetic materials" or 
"energetic products" means any energetic or explosive materials such as, 
nitramines, nitroaromatics, oxidizers, plasticizers, binders, 
nitroglycerine (NG), nitrocellulose (NC), ammonium perchlorates, nitrates, 
nitrites and hydrolysate products i.e., hydrolyzed energetic products. The 
term "microaerobic environment" means an environment having levels of 
oxygen lower than that used for aerobic environments, for example, oxygen 
levels, at least in the head space gas, of between approximately 0.1-4.0% 
oxygen. The term "oxygenated ions and/or molecules" means oxygenated ions 
such as NO.sub.3.sup.- ClO.sub.3.sup.-, PO.sub.4.sup.2-, SO.sub.4.sup.2-, 
acetate, formate and the like and/or oxygenated molecules such as 
alcohols, sugars, carbohydrates and the like. 
The invention will now be described by way of reference to the following 
examples which are not intended to limit the scope of the present 
invention. 
EXAMPLE 1 
The major constituents of a highly contaminated groundwater are shown in 
following table. 
TABLE 1 
______________________________________ 
Composition of a Highly Contaminated Groundwater 
Concen- 
Concentration, tration, 
Component mg/l Component mg/l 
______________________________________ 
Perchlorate, ClO.sub.4 .sup.- 
1200-1500 Calcium, Ca.sup.+2 
800 
Chlorate, ClO.sub.3 .sup.- 
3000-3500 Magnesium, Mg.sup.+2 
400 
Sulfate, SO.sub.4 .sup.- 
1700 Nitrate, NO.sub.3 .sup.- 
200 
Chloride, Cl.sup.- 
2000 Boron 14 
Sodium, Na.sup.+ 
1800 Chrome (VI) 9 
______________________________________ 
A carbohydrate, sugar and starch-based food waste nutrient was combined 
with the ground water in Table 1 and fed to a microaerobic reactor from a 
20-liter carboy. The nutrient concentration in the feed was adjusted to 6 
g/l (4:1 nutrient to perchlorate ratio). Ammonium hydroxide (.about.30% 
NH.sub.4 OH) was also added to the feed tank at rates from 0.1 to 1.0 ml/l 
to increase the feed pH, prevent unwanted microbial growth, and provide 
additional nitrogen. The feed mixture was agitated and pumped by means 
peristaltic pump into a nominal 7-liter continuously stirred tank reactor 
(CSTR) (5.75-liter working volume) at a rate of 6.0 ml/min. The hydraulic 
residence time (HRT) based on this feed rate is approximately 16 hours. 
The reactor temperature was maintained at 30.degree. C. The pH in the CSTR 
was controlled in a range from 6.5-7.6 by the automatic addition of NaOH 
or H.sub.3 PO.sub.4 as required. Reactor effluent was fed to a clarifier 
and sludge recycled and wasted at rates to maintain total suspended solids 
in the reactor between 5000 and 10,000 mg/l. Analysis by ion 
chromatography showed that nitrate and chlorate were reduced to 
non-detectable concentrations simultaneously with perchlorate. Perchlorate 
was reduced to non-detectable (&lt;4 ppb) concentrations. A chloride balance 
showed that &gt;97% of the chloride was accounted for and confirmed that the 
chlorate and perchlorate were being reduced to chloride and not being 
accumulated in the biomass. Chrome (VI) concentration was reduced to 0.2 
mg/l. 
EXAMPLE 2 
The experimental apparatus for this example was the same as in example 1. 
Effluent from nitroglycerine (NG) production operation is hydrolyzed with 
NaOH at elevated temperature to produce a high nitrate effluent that is 
1-5% nitrate. In this example feed was prepared by adding a carbohydrate 
sugar/starch food waste to the feed carboy at a concentration of 15 g/l. 
Feed nitrate concentration was 12,050 mg/l, nitrite was 585 mg/l, and 
sulfate was 5500 mg/l. The total dissolved solid (TDS) was 3.2%. Caustic 
was not added to the feed, however, antifoam was added to prevent the 
foaming caused by nitrogen gas generation in the denitrification reaction. 
The CSTR was operated at an hydraulic residence time (HRT) of 24 hours, 
temperature maintained at 30.degree. C., and pH controlled at 6.5-7.6. In 
this example all of the nitrate and nitrite was reduced to nitrogen gas as 
confirmed by ion chromatography. 
EXAMPLE 3 
Brine from the regeneration of ion exchange resin contains perchlorate and 
other ions. Table 2 shows the composition of actual brine from an ion 
exchange demonstration in the San Gabriel Basin and surrogate brine with 
an elevated perchlorate concentration. 
TABLE 2 
______________________________________ 
San Gabriel Brine, 
Component Surrogate Brine, mg/l 
mg/l 
______________________________________ 
Total Dissolved Solids, 
34,000 (3.4%) .about.34,000 (3.4%) 
TDS 
Salt, NaCl 31,500 (3.15%) 
31,700 (3.17%) 
Sulfate 1260 1900 
Nitrate 360 350 
Perchlorate 90 1.4 
Carbonate 90 
Ca.sup.+2, Mg.sup.+2, K.sup.+ 
45 .about.50 
______________________________________ 
In this example the CSTR had a 2.5-liter hydraulic volume and a clarifier 
was not employed as a mechanism to concentrate and recycle biomass. The 
actual salt concentration of the regenerating brine was 7.0% NaCl. To 
ensure the high salt concentration would not inhibit perchlorate 
biodegradation, the actual brine was diluted with water to 45% of its 
original concentration which resulted in a 3.15% NaCl and 3.4% TDS feed 
material. The surrogate was prepared, using water softener salt. The 
reactor was operated at an HRT of 24 hours, temperature maintained at 
35.degree. C. and pH controlled between 6.5 and 7.6. In this example, both 
the nitrate and perchlorate were destroyed to non-detectable 
concentrations (&lt;4 ppb for ClO.sub.4-). 
EXAMPLE 4 
The effect of oxygen concentration on perchlorate concentration in a 
microaerobic reactor according to the present invention was investigated. 
Wastewater with a concentration of 5,000 mg/l perchlorate and was fed to a 
microaerobic reactor containing a mixed bacteria culture with bacterium of 
the species Wolinella succinogenes. Gas containing a mixture of nitrogen 
and air was sparged into the microaerobic reactor at various flow rates 
and various concentrations (vol %) over a 30 day period. Air and nitrogen 
were metered and mixed together to create a sparge gas with different 
oxygen concentrations. The sparge flow rate was varied in order to adjust 
the total rate at which oxygen was fed into the reactor. The other 
conditions in the reactor remained unchanged, wherein the temperature was 
maintained at 35.degree. C.; the nutrient feed ratio was maintained at 
2.4:1; the residence time was 18 hours and the pH was maintained between 
6.5-7.5. The nutrient used was BYF-100. The results are illustrated in 
FIG. 2. From the graph in FIG. 2 it can be seen that the reactor 
perchlorate concentration steadily decreased with an increase in oxygen 
concentration.