General method for determining anaerobic biodegradation potential

Different types of sludge granules in UASB reactors treating acidified wastewaters

The influence of a high energy substrate, i.e. sucrose, on the granular sludge yield and the development of different types of granular sludge was investigated by using Upflow Anaerobic Sludge Bed (UASB) reactors fed with synthetic wastewater. The feed COD was a mixture of volatile fatty acids (VFA) i.e., 20, 40, and 40% of the COD as C2-, C3-, and C4-VFA, respectively. Furthermore, experiments were carried out in which 10 and 30% of the VFA COD was substituted with sucrose. The following distinctly different types of granules were observed in each testrun: in the reactor fed with solely VFA, black (B) and white (W) granules developed; in the reactor fed with a mixture of 90% VFA and 10% sucrose, three types of granules i.e., B, W, and grey (G) granules could be seen; in the reactor fed with 70% VFA and 30% sucrose, only W and G granules were found. The granular sludge yield increased proportional to the amount of sucrose COD. At steady-state performance of the reactors, specific acidogenic (SAA) and methanogenic (SMA) activity tests on these granules revealed that B granules had the highest SMA with low SAA. The W granules had very high SMA with low SAA. G granules gave the highest SAA with a considerable SMA. Measurement of coenzyme F420 revealed that B granules consist mainly of acetoclastic methanogens. The fore-mentioned tests were supplemented with analyses of the wash-out cells present in the reactor effluent and the results suggested that acidogens, if present, prevail at the granule surface. The B granules were particularly rich in Ca, Mn, and Zn minerals. The size distribution analysis showed that the granule diameter increased in the following order: B < W < G granules. The biogas bubbles tended to adhere to the B and W granules but not so strongly to the G granules.

Anaerobic biodegradation potentials in digested sludge, a freshwater swamp and a marine sediment

An anaerobic gas production test was used for determining the potential biodegradation of 22 organic chemicals under methanogenic conditions. Nine of the examined chemicals were extensively mineralized (> 75%) both in sewage sludge and in a freshwater swamp indicating good agreement between biodegradation potentials in these habitats. Samples from a marine sediment showed a less extensive mineralization of most of the test chemicals, and lag periods of several weeks often preceded net gas production. As marine sediments usually contain sulfate at the time of collection, the assessment of biodegradation potentials in such environments is probably more reliable when using a method based on sulfate reduction instead of methanogenic gas production. The results of the tests indicate that the commonly recommended washing of sludge solids can be eliminated by applying a more diluted inoculum.

Testing and classification methods for the biodegradabilities of organic compounds under anaerobic conditions

Biodegradability is one of the most important characteristics of an organic compound for predicting its fate and life in the environment and its application in biological wastewater treatment. But there is no general testing method for biodegradability under anaerobic conditions. The biodegradabilities of thirteen principal organic compounds was investigated in a batch test using vials under various conditions, such as the concentration of an organic compound, the cultivation method and the concentration of anaerobic bacteria for seeding. Two test methods in the standard concentration and the low concentration were developed. A new method to classify the biodegradabilities of organic compounds into thirteen ranks was proposed by considering inhibition, complete biodegradation and first step biodegradation.

Bacteria obtained from a sequencing batch reactor that are capable of growth on dehydroabietic acid

Eleven isolates capable of growth on the resin acid dehydroabietic acid (DhA) were obtained from a sequencing batch reactor designed to treat a high-strength process stream from a paper mill. The isolates belonged to two groups, represented by strains DhA-33 and DhA-35, which were characterized. In the bioreactor, bacteria like DhA-35 were more abundant than those like DhA-33. The population in the bioreactor of organisms capable of growth on DhA was estimated to be 1.1 x 10(6) propagules per ml, based on a most-probable-number determination. Analysis of small-subunit rRNA partial sequences indicated that DhA-33 was most closely related to Sphingomonas yanoikuyae (Sab = 0.875) and that DhA-35 was most closely related to Zoogloea ramigera (Sab = 0.849). Both isolates additionally grew on other abietanes, i.e., abietic and palustric acids, but not on the pimaranes, pimaric and isopimaric acids. For DhA-33 and DhA-35 with DhA as the sole organic substrate, doubling times were 2.7 and 2.2 h, respectively, and growth yields were 0.30 and 0.25 g of protein per g of DhA, respectively. Glucose as a cosubstrate stimulated growth of DhA-33 on DhA and stimulated DhA degradation by the culture. Pyruvate as a cosubstrate did not stimulate growth of DhA-35 on DhA and reduced the specific rate of DhA degradation of the culture. DhA induced DhA and abietic acid degradation activities in both strains, and these activities were heat labile. Cell suspensions of both strains consumed DhA at a rate of 6 mumol mg of protein-1 h-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaerobic biodegradability testing of surfactants

Anionic and nonionic surfactants (5-50 mg C/g solids/L medium) were screened for anaerobic microbial decomposition to methane in an automated pressure transducer serum bottle assay system at 35C using municipal digester solids as a source of anaerobic bacteria. Analysis of the headspace gas recovered from tests with linear primary alcohol sulfates (A45S and A24S) and a linear alcohol ethoxylate (LAE-8) showed that these compounds were readily degraded (60-85% of the theoretical methane, TM) after a 15-30 day lag period at 50 ppm C. The extent of degradation of a branched alkyl phenol ethoxylate (NPE-9) was lower (30-40% TM). A survey of intact nonionic and anionic surfactants present in municipal digester sludges in the U.S. showed that these materials were present at levels of 0.5-8 mg CTAS or MBAS/g dry solids. A surfactant which was slower to biodegrade (NPE-9) at 50 ppm C was readily metabolized to methane when tested at 5 and 10 mg C/g solids/L. The pressure transducer serum bottle method described may be used to test biodegradability and inhibitory effects on methanogenesis at surfactant concentrations (e.g. 5 ppm C/g solids) typically present in digesters.

Enhanced biodegradation of aromatic pollutants in cocultures of anaerobic and aerobic bacterial consortia

Toxic aromatic pollutants, concentrated in industrial wastes and contaminated sites, can potentially be eliminated by low cost bioremediation systems. Most commonly, the goal of these treatment systems is directed at providing optimum environmental conditions for the mineralization of the pollutants by naturally occurring microflora. Electrophilic aromatic pollutants with multiple chloro, nitro and azo groups have proven to be persistent to biodegradation by aerobic bacteria. These compounds are readily reduced by anaerobic consortia to lower chlorinated aromatics or aromatic amines but are not mineralized further. The reduction increases the susceptibility of the aromatic molecule for oxygenolytic attack. Sequencing anaerobic and and aerobic biotreatment steps provide enhanced mineralization of many electrophilic aromatic pollutants. The combined activity of anaerobic and aerobic bacteria can also be obtained in a single treatment step if the bacteria are immobilized in particulate matrices (e.g. biofilm, soil aggregate, etc.). Due to the rapid uptake of oxygen by aerobes and facultative bacteria compared to the slow diffusion of oxygen, oxygen penetration into active biofilms seldom exceeds several hundred micrometers. The anaerobic microniches established inside the biofilms can be applied to the reduction of electron withdrawing functional groups in order to prepare recalcitrant aromatic compounds for further mineralization in the aerobic outer layer of the biofilm. Aside from mineralization, polyhydroxylated and chlorinated phenols as well as nitroaromatics and aromatic amines are susceptible to polymerization in aerobic environments. Consequently an alternative approach for bioremediation systems can be directed towards incorporating these aromatic pollutants into detoxified humic-like substances. The activation of aromatic pollutants for polymerization can potentially be encouraged by an anaerobic pretreatment step prior to oxidation. Anaerobic bacteria can modify aromatic pollutants by demethylating methoxy groups and reducing nitro groups. The resulting phenols and aromatic amines are readily polymerized in a subsequent aerobic step.

Anaerobic biodegradability of cellulose and hemicellulose in excavated refuse samples using a biochemical methane potential assay

Improved techniques are needed to predict potential methane generation from refuse buried in landfills. The Biochemical Methane Potential (BMP) test was used to measure the methane potential of ten refuse samples excavated from a Berkeley, CA, landfill. The test was conducted in 125-ml serum bottles containing phosphate-buffered medium and inoculated with anaerobically digested sewage sludge. Comparison of the measured BMP to the theoretical BMP calculated from measured cellulose and hemicellulose concentrations indicated that cellulose plus hemicellulose is not well correlated with the measured BMP. The average of the measured to theoretical BMP was 19.1% (range 0-53%, s.d. = 16.9%). Measured sulfate concentrations showed that sulfate was an insignificant electron sink in the samples tested. Once methane production from the refuse was complete, 0.072 g of Whatman no. 1 filter paper was added to two of the four serum bottles incubated for each sample. An average of 84.9% (s.d. = 2.5%) of the added filter paper was recovered as methane, suggesting that some cellulose and hemicellulose present in refuse is recalcitrant or otherwise not bioavailable.

Effects of Polychlorinated Biphenyl Congener Concentration and Sediment Supplementation on Rates of Methanogenesis and 2,3,6-Trichlorobiphenyl Dechlorination in an Anaerobic Enrichment

We have employed a method of enrichment that allows us to significantly increase the rate of reductive polychlorinated biphenyl (PCB) dechlorination. This method shortens the time required to investigate the effects that culture conditions have on dechlorination and provides an estimate of the potential activity of the PCB-dechlorinating anaerobes. The periodic supplementation of sterile sediment and PCB produced an enhanced, measurable, and sustained rate of dechlorination. We observed volumetric rates of the dechlorination of 2,3,6-trichlorobiphenyl (2,3,6-CB) to 2,6-dichlorobiphenyl (2,6-CB) of more than 300 μmol liter -1 day -1 when the cultures were supplemented daily. A calculation of this activity that is based on an estimate of the number of dechlorinating anaerobes present indicates that 1.13 pmol of 2,3,6-CB was dechlorinated to 2,6-CB day -1 bacterial cell -1 . This rate is similar to that of the reductive dechlorination of 3-chlorobenzoate by Desulfomonile tiedjei. Methanogenesis declined from 585.3 to 125.9 μmol of CH 4 liter -1 day -1 , while dechlorination increased from 8.2 to 346.0 μmol of 2,3,6-CB dechlorinated to 2,6-CB liter -1 day -1 .

Role of electron-donating cosubstrates in the anaerobic biotransformation of chlorophenoxyacetates to chlorophenols by a bacterial consortium enriched on phenoxyacetate

A bacterial consortium that anaerobically mineralized phenoxyacetate, with transient production of phenol as an intermediate, was obtained from a methanogenic aquifer site near the Norman, OK municipal landfill. This consortium was able to convert the eight halogenated chlorophenoxyacetates tested to the corresponding chlorophenols. The chlorophenols were not subsequently metabolized. The addition of reduced substrates increased the rate of degradation of all chlorophenoxyacetates, with 78% of mono- and di-chlorinated substrates being transformed to chlorophenols in butyrate-amended cultures, compared to less than 37% transformed in unsupplemented cultures. Butyrate increased the transformation of 2,4,5-trichlorophenoxyacetate from 10% to 20%. An experiment evaluating the effects of several compounds on the side-chain cleavage reaction of 3-chlorophenoxyacetate showed that addition of compounds which readily act as hydrogen donors (butyrate, crotonate, ethanol, propionate, and hydrogen) resulted in 2 to 5 times the amount of 3-chlorophenoxyacetate transformed compared to controls with no amendment, formate had a slight stimulatory effect, and acetate and methanol had no effect. Butyrate addition also increased the rate of phenoxyacetate degradation, resulting in transient phenol accumulation not observed in butyrate-unamended controls. These results support the hypothesis that the side-chain cleavage of phenoxyacetate is a reductive process that is stimulated by the oxidation of reduced cosubstrates.

Subculturing of a polychlorinated biphenyl-dechlorinating anaerobic enrichment on solid media

An anaerobic culture capable of dechlorinating polychlorinated biphenyls was subcultured under strict anaerobic conditions on solid media containing sterilized river sediment. The dechlorination activity was transferred as a bacterial colony on a solid medium three times. After two transfers on solid medium, the culture was no longer methanogenic but still dechlorinated a mixture of tri- and tetrachlorobiphenyls. This demonstrates that anaerobic bacteria are responsible for the polychlorinated biphenyl dechlorination and can be grown without polychlorinated biphenyl on solid media.

Reductive debromination of the commercial polybrominated biphenyl mixture firemaster BP6 by anaerobic microorganisms from sediments

Anaerobic microorganisms eluted from three sediments, one contaminated with polybrominated biphenyls (PBBs) and two contaminated with polychlorinated biphenyls, were compared for their ability to debrominate the commercial PBB mixture Firemaster. These microorganisms were incubated with reduced anaerobic mineral medium and noncontaminated sediment amended with Firemaster. Firemaster averages six bromines per biphenyl molecule; four of the bromines are substituted in the meta or para position. The inocula from all three sources were able to debrominate the meta and para positions. Microorganisms from the Pine River (St. Louis, Mich.) contaminated with Firemaster, the Hudson River (Hudson Falls, N.Y.) contaminated with Aroclor 1242, and Silver Lake (Pittsfield, Mass.) contaminated with Aroclor 1260 removed 32, 12, and 3% of the meta plus para bromines, respectively, after 32 weeks of incubation. This suggests that previous environmental exposure to PBBs enhances the debromination capability of the sediment microbial community through selection for different strains of microorganisms. The Pine River inoculum removed an average of 1.25 bromines per biphenyl molecule during a 32-week incubation period, resulting in a mixture potentially more accessible to aerobic degradation processes. No ortho bromine removal was observed. However, when Firemaster was incubated with Hudson River microorganisms that had been repeatedly transferred on a pyruvate medium amended with Aroclor 1242, 17% of the meta and para bromines were removed after 16 weeks of incubation and additional debromination products, including 2-bromobiphenyl and biphenyl, were detected. This suggests the possibility for ortho debromination, since all components of the Firemaster mixture have at least one ortho-substituted bromine.(ABSTRACT TRUNCATED AT 250 WORDS)

Microbial reductive dehalogenation

A wide variety of compounds can be biodegraded via reductive removal of halogen substituents. This process can degrade toxic pollutants, some of which are not known to be biodegraded by any other means. Reductive dehalogenation of aromatic compounds has been found primarily in undefined, syntrophic anaerobic communities. We discuss ecological and physiological principles which appear to be important in these communities and evaluate how widely applicable these principles are. Anaerobic communities that catalyze reductive dehalogenation appear to differ in many respects. A large number of pure cultures which catalyze reductive dehalogenation of aliphatic compounds are known, in contrast to only a few organisms which catalyze reductive dehalogenation of aromatic compounds. Desulfomonile tiedjei DCB-1 is an anaerobe which dehalogenates aromatic compounds and is physiologically and morphologically unusual in a number of respects, including the ability to exploit reductive dehalogenation for energy metabolism. When possible, we use D. tiedjei as a model to understand dehalogenating organisms in the above-mentioned undefined systems. Aerobes use reductive dehalogenation for substrates which are resistant to known mechanisms of oxidative attack. Reductive dehalogenation, especially of aliphatic compounds, has recently been found in cell-free systems. These systems give us an insight into how and why microorganisms catalyze this activity. In some cases transition metal complexes serve as catalysts, whereas in other cases, particularly with aromatic substrates, the catalysts appear to be enzymes.

Microbial reductive dehalogenation

A wide variety of compounds can be biodegraded via reductive removal of halogen substituents. This process can degrade toxic pollutants, some of which are not known to be biodegraded by any other means. Reductive dehalogenation of aromatic compounds has been found primarily in undefined, syntrophic anaerobic communities. We discuss ecological and physiological principles which appear to be important in these communities and evaluate how widely applicable these principles are. Anaerobic communities that catalyze reductive dehalogenation appear to differ in many respects. A large number of pure cultures which catalyze reductive dehalogenation of aliphatic compounds are known, in contrast to only a few organisms which catalyze reductive dehalogenation of aromatic compounds. Desulfomonile tiedjei DCB-1 is an anaerobe which dehalogenates aromatic compounds and is physiologically and morphologically unusual in a number of respects, including the ability to exploit reductive dehalogenation for energy metabolism. When possible, we use D. tiedjei as a model to understand dehalogenating organisms in the above-mentioned undefined systems. Aerobes use reductive dehalogenation for substrates which are resistant to known mechanisms of oxidative attack. Reductive dehalogenation, especially of aliphatic compounds, has recently been found in cell-free systems. These systems give us an insight into how and why microorganisms catalyze this activity. In some cases transition metal complexes serve as catalysts, whereas in other cases, particularly with aromatic substrates, the catalysts appear to be enzymes.

Microbiology of vadose zone paleosols in south-central Washington State

Three unsaturated subsurface paleosols influenced by moisture recharge, including a highly developed calcic paleosol, were studied to investigate the microbiology of paleosols. Two near-surface paleosols, one impacted by moisture recharge and the other beyond the influence of recharge, were also sampled to directly assess the effect of moisture recharge on the activity and composition of the microbial community associated with paleosols. The highly developed paleosol had a higher population of culturable heterotrophs, a greater glucose mineralization potential, a higher microbial diversity based on colony morphology, and a more than 20-fold higher concentration of ATP than the two weakly developed paleosols. The recharged near-surface paleosol, as compared to the near-surface paleosol unaffected by recharge, had a lower population of culturable heterotrophs, smaller mineralization rate constant, and lower richness based on colony morphology. The recharged paleosols contained predominantly gram-negative isolates, whereas the paleosol unaffected by recharge contained predominantly gram-positive isolates. Storage at 4°C of subsurface and near-surface paleosol samples containing high water potential increased the population of culturable aerobic heterotrophs, decreased diversity in colony morphology, and increased first-order rate constants and decreased lag times for glucose mineralization. These results indicate that aerobic heterotrophs are present in deep vadose zone paleosols and that there is potential for stimulation of their in situ growth and activity.

Anaerobic dechlorination of polychlorobiphenyls (Aroclor 1242) by pasteurized and ethanol-treated microorganisms from sediments

A polychlorobiphenyl (PCB)-dechlorinating inoculum eluted from upper Hudson River sediments was treated with either heat or ethanol or both. The treated cultures retained the ability to dechlorinate PCBs (Aroclor 1242) under strictly anaerobic conditions. The dechlorination activity was maintained in serial cultures inoculated with transfers of 1% inoculum when the transferred inoculum was treated each time in the same manner. No methane production was detected in any treated culture, although dechlorination of PCBs in the untreated cultures was always accompanied by methane production. All treated cultures preferentially removed meta chlorines, yielding a dechlorination pattern characterized by accumulation of certain ortho- and para-subsituted congeners such as 2-4-chlorobiphenyl (2-4-CB), 2,4-2-CB, and 2,4-4-CB. In contrast, the untreated cultures showed more extensive dechlorination activities, which almost completely removed both meta and para chlorines from Aroclor 1242. These results suggest that microorganisms responsible for the dechlorination of PCBs in the upper Hudson River sediments can be grouped into two populations according to their responses to the heat and ethanol treatments. Microorganisms surviving the heat and ethanol treatments preferentially remove meta chlorines, while microorganisms lost from the enrichment mainly contribute to the para dechlorination activity. These results indicate that anaerobic sporeformers are at least one of the physiological groups responsible for the reductive dechlorination of PCBs. The selection of a dechlorinating population by such treatments may be an important step in isolation of PCB-dechlorinating microorganisms.

Isolation of Clostridium propionicum strain 19acry3 and further characteristics of the species

Two mixed cultures able to ferment acrylate to equimolar acetate and propionate were enriched from anaerobic sediments. From one of these mixed cultures a pure culture of a Gram-positive, obligately anaerobic bacterium was isolated. This strain, designated 19acry3 (= DSM 6251) was identified as belonging to the species Clostridium propionicum. Only a narrow range of organic compounds supported growth, including acrylate and lactate. Acrylate and lactate were fermented to acetate and propionate in a 1:2 molar ratio. When co-cultured with the non-acrylate-fermenting "Campylobacter" sp. strain 19gly1 (DSM 6222), the fermentation balance shifted to almost equimolar acetate and propionate. Strain 19acry3 was compared with Clostridium propionicum type strain X2 (DSM 1682). The two strains displayed similar phenotypic properties. The mol% G + C of DNA isolated from both strains was 36-37 (by thermal denaturation). Both strains displayed a characteristic fluorescence when observed by fluorescence microscopy. Cell-free extracts of both strains were examined by spectrophotofluorimetry. In both strains, two excitation peaks were observed at 378 and 470 nm. Excitation at either of these wavelengths resulted in an emission maximum at 511 nm.

Reductive ortho and meta Dechlorination of a Polychlorinated Biphenyl Congener by Anaerobic Microorganisms

We used gas chromatography-mass spectrometry to study the metabolic fate of 2,3,5,6-tetrachlorobiphenyl (2356-CB) (350 muM) incubated with unacclimated methanogenic pond sediment. The 2356-CB was dechlorinated to 25-CB (21%), 26-CB (63%), and 236-CB (16%) in 37 weeks. This is the first experimental demonstration of ortho dechlorination of a polychlorinated biphenyl by anaerobic microorganisms.

Reductive dechlorination of dichlorophenols by nonadapted and adapted microbial communities in pond sediments

Fresh and dichlorophenol (DCP)-adapted sediments from two ponds near Athens, Georgia exhibited distinctly different dechlorinating activities. These differences centered on the relative rates of reductive dehlorination in both fresh and adapted sediments and on the substrate specificity of the adapted sediments. Fresh Cherokee Trailer Park Pond sediment dechlorinated 2,3-, 2,4-, and 2,6-DCP to monochlorophenols at a faster rate and after a shorter lag period than fresh Bolton's Pond sediment. Lag periods were not observed in either Cherokee or Bolton's sediments that had been adapted to dechlorinate either 2,3-, 2,4-or 2,6-DCP. Adapted Cherokee sediments exhibited faster dechlorinating rates and a broader substrate specificity than the adapted Bolton's sediments. The broad substrate specificity of each of the adapted Cherokee sediments contrasted sharply with the narrow specificity of the 2,6-DCP-adapted Bolton's sediment. The preference for reductive dechlorination wasortho>meta orpara in sediments from both ponds.

Dechlorination of Four Commercial Polychlorinated Biphenyl Mixtures (Aroclors) by Anaerobic Microorganisms from Sediments

The rate, extent, and pattern of dechlorination of four Aroclors by inocula prepared from two polychlorinated biphenyl (PCB)-contaminated sediments were compared. The four mixtures used, Aroclors 1242, 1248, 1254, and 1260, average approximately three, four, five, and six chlorines, respectively, per biphenyl molecule. All four Aroclors were dechlorinated with the loss of meta plus para chlorines ranging from 15 to 85%. Microorganisms from an Aroclor 1242-contaminated site in the upper Hudson River dechlorinated Aroclor 1242 to a greater extent than did microorganisms from Aroclor 1260-contaminated sediments from Silver Lake, Mass. The Silver Lake inoculum dechlorinated Aroclor 1260 more rapidly than the Hudson River inoculum did and showed a preferential removal of meta chlorines. For each inoculum the rate and extent of dechlorination tended to decrease as the degree of chlorination of the Aroclor increased, especially for Aroclor 1260. The maximal observed dechlorination rates were 0.3, 0.3, and 0.2 μg-atoms of Cl removed per g of sediment per week for Aroclors 1242, 1248, and 1254, respectively. The maximal observed dechlorination rates for Hudson River and Silver Lake organisms for Aroclor 1260 were 0.04 and 0.21 μg-atoms of Cl removed per g of sediment per week, respectively. The dechlorination patterns obtained suggested that the Hudson River microorganisms were more capable than the Silver Lake organisms of removing the last para chlorine. These results suggest that there are different PCB-dechlorinating microorganisms at different sites, with characteristic specificities for PCB dechlorination.

Isolation and characterization of quinoline-degrading bacteria from subsurface sediments

Two gram-negative, motile bacteria isolated from deep subsurface sediments mineralized the nitrogen-containing polyaromatic hydrocarbon quinoline under aerobic conditions and transformed quinoline to soluble intermediates under anaerobic conditions. Many aromatic compounds were also able to serve as the sole source of carbon and energy under aerobic conditions. Rapid aerobic mineralization of quinoline at concentrations as low as 0.002 microgram ml-1 indicates that these organisms possess a high-affinity uptake and utilization system, which may reflect the oligotrophic nature of deep subsurface environments. Both bacteria harbored four plasmids of identical size, ranging from 50 to 440 kilobases.

Survey of the Anaerobic Biodegradation Potential of Organic Chemicals in Digesting Sludge

The degradation potential of 77 organic chemicals under methanogenic conditions was examined with an anaerobic digesting sludge from the United Kingdom. Degradation was assessed in terms of net total gas (CH 4 plus CO 2 ) produced, expressed as a percentage of the theoretical production (ThGP). The compounds tested were selected from various chemical groups and included substituted phenols and benzoates, pesticides, phthalic acid esters, homocyclic and heterocyclic ring compounds, glycols, and monosubstituted benzenes. The results obtained were in good agreement with published surveys of biodegradability in U.S. digesting sludges and other methanogenic environments. In general, the presence of chloro or nitro groups inhibited anaerobic gas production, while carboxyl and hydroxyl groups facilitated biodegradation. The relationship between substituent position and susceptibility to methanogenic degradation was compound dependent. The following chemicals were completely degraded (≥80% ThGP) at a concentration of 50 mg of carbon per liter: phenol, 2-aminophenol, 4-cresol, catechol, sodium benzoate, 4-aminobenzoic acid, 3-chlorobenzoic acid, phthalic acid, ethylene glycol, diethylene glycol, triethylene glycol, sodium stearate, and quinoline. 3-Cresol, 4-chlorobenzoic acid, dimethyl phthalate, and pyridine were partially degraded. Although the remaining chemicals tested were either persistent or toxic, their behavior may differ at more environmentally realistic chemical-to-biomass ratios. Our findings suggest that biodegradability assessments made with sludge from one source can be extrapolated to sludge from another source with a reasonable degree of confidence and should help in predicting the fate of an organic chemical during the anaerobic digestion of sewage sludge.

Reductive Dechlorination of Polychlorinated Biphenyls by Anaerobic Microorganisms from Sediments

Microorganisms from Hudson River sediments reductively dechlorinated most polychlorinated biphenyls (PCBs) in Aroclor 1242 under anaerobic conditions, thus demonstrating PCB dechlorination by anaerobic bacteria in the laboratory. The most rapid dechlorination was observed at the highest PCB concentration used; at 700 parts per million Aroclor, 53 percent of the total chlorine was removed in 16 weeks, and the proportion of mono- and dichlorobiphenyls increased from 9 to 88 percent. Dechlorination occurred primarily from the meta and para positions; congeners that were substituted only in the ortho position (or positions) accumulated. These dechlorination products are both less toxic and more readily degraded by aerobic bacteria. These results indicate that reductive dechlorination may be an important environmental fate of PCBs, and suggest that a sequential anaerobic-aerobic biological treatment system for PCBs may be feasible.

Anaerobic bacteria that dechlorinate perchloroethene

In this study, we identified specific cultures of anaerobic bacteria that dechlorinate perchlorethene (PCE). The bacteria that significantly dechlorinated PCE were strain DCB-1, an obligate anaerobe previously shown to dechlorinate chlorobenzoate, and two strains of Methanosarcina. The rate of PCE dechlorination by DCB-1 compared favorably with reported rates of trichloroethene bio-oxidation by methanotrophs. Even higher PCE dechlorination rates were achieved when DCB-1 was grown in a methanogenic consortium.

Metabolism of polyethylene glycol by two anaerobic bacteria, Desulfovibrio desulfuricans and a Bacteroides sp

Two anaerobic bacteria were isolated from polyethylene glycol (PEG)-degrading, methanogenic, enrichment cultures obtained from a municipal sludge digester. One isolate, identified as Desulfovibrio desulfuricans (strain DG2), metabolized oligomers ranging from ethylene glycol (EG) to tetraethylene glycol. The other isolate, identified as a Bacteroides sp. (strain PG1), metabolized diethylene glycol and polymers of PEG up to an average molecular mass of 20,000 g/mol [PEG 20000; HO-(CH2-CH2-O-)nH]. Both strains produced acetaldehyde as an intermediate, with acetate, ethanol, and hydrogen as end products. In coculture with a Methanobacterium sp., the end products were acetate and methane. Polypropylene glycol [HO-(CH2-CH2-CH2-O-)nH] was not metabolized by either bacterium, and methanogenic enrichments could not be obtained on this substrate. Cell extracts of both bacteria dehydrogenated EG, PEGs up to PEG 400 in size, acetaldehyde, and other mono- and dihydroxylated compounds. Extracts of Bacteroides strain PG1 could not dehydrogenate long polymers of PEG (greater than or equal to 1,000 g/mol), but the bacterium grew with PEG 1000 or PEG 20000 as a substrate and therefore possesses a mechanism for PEG depolymerization not present in cell extracts. In contrast, extracts of D. desulfuricans DG2 dehydrogenated long polymers of PEG, but whole cells did not grow with these polymers as substrates. This indicated that the bacterium could not convert PEG to a product suitable for uptake.

Extrapolation of biodegradation results to groundwater aquifers: reductive dehalogenation of aromatic compounds

The reductive biodegradation of a variety of haloaromatic substrates was monitored in samples from two sites within a shallow anoxic aquifer and was compared with freshwater sediment and sewage sludge. The metabolic capacity existing in methane-producing aquifer material was very similar to that in sediment in that three of four chlorobenzoates, five of seven chlorophenols, and one of two chlorophenoxyacetate herbicides were reductively dehalogenated in both types of incubations. The 2,4-dichlorophenoxyacetate was first converted to a dichlorophenol before dehalogenation occurred. Sewage sludge microorganisms dehalogenated four of seven chlorophenols tested and degraded both phenoxyacetate herbicides by first converting them to the corresponding chlorophenols, but the microorganisms did not transform the chlorobenzoates. In general, the same suite of initial metabolites were produced from a test substrate in all types of samples, as confirmed by cochromatography of the intermediates with authentic material. Aquifer microbiota from a sulfate-reducing site was unable to significantly degrade any of the haloaromatic substrates tested. Biological removal of the sulfate in samples from this site permitted dehalogenation of a model substrate, while stimulation of methanogenesis without removal of sulfate did not. These results demonstrate that dehalogenating microorganisms were present at this site but that their activity was at least partially inhibited by the high sulfate levels.

Kinetics of Phenol Biodegradation by an Immobilized Methanogenic Consortium

A phenol-degrading methanogenic enrichment was successfully immobilized in agar as shown by the stoichiometric conversion of phenol to CH 4 and CO 2 . The enrichment contained members of three physiological groups necessary for the syntrophic mineralization of phenol: a phenol-oxidizing bacterium, a Methanothrix -like bacterium, and an H 2 -utilizing methanogen. The immobilization technique resulted in the cells being embedded in a long, thin agar strand (1 mm in diameter by 2 to 50 cm in length) that resembled spaghetti. Immobilization had three effects as shown by a comparative kinetic analysis of phenol degradation by free versus immobilized cells. (i) The maximum rate of degradation was reduced from 14.8 to 10.0 μg of phenol per h; (ii) the apparent K m for the overall reaction was reduced from 90 to 46 μg of phenol per ml, probably because of the retention of acetate, H 2 and CO 2 in the proximity of immobilized methanogens; and (iii) the cells were protected from substrate inhibition caused by high concentrations of phenol, which increased the apparent K i value from 900 to 1,725 μg of phenol per ml. Estimates for the kinetic parameters K m , K i , and V max were used in a modified substrate inhibition model that simulated rates of phenol degradation for given phenol concentrations. The simulated rates were in close agreement with experimentally derived rates for both stimulatory and inhibitory concentrations of phenol.