Selenium reduction by a denitrifying consortium

A denitrifying bacterial consortium obtained from the Pullman, Washington wastewater treatment facility was enriched under denitrifying conditions and its ability to reduce selenite and selenate was studied. Replicate experiments at two different experimental conditions were performed. All experiments were performed under electron-acceptor limiting conditions, with acetate as the carbon source and nitrate the electron acceptor. In the first set of experiments, selenite was present, whereas, in the second set, selenate was added. A significant lag period of approximately 150 h was necessary before selenite or selenate reduction was observed. During this lag period, nitrate and nitrite use was observed. Once selenite or selenate reduction had started, nitrate and nitrite reduction was concomitant with selenium species reduction. Trace amounts of selenite were detected during the selenate reduction study. Analysis of the data indicates that, once selenium species reduction was induced, the rate of reduction was proportional to the selenium species concentration and to the biomass concentration. Furthermore, at similar biomass and contaminant concentrations, selenite reduction is approximately four times faster than selenate reduction. Copyright 1999 John Wiley & Sons, Inc.     

Anaerobic transformation of 1,1,1-trichloroethane by municipal digester sludge

Anaerobic transformations of 1,1,1-trichloroethane (TCA), 1,1-dichloroethane (DCA), and chloroethane (CA) were studied with sludge from a lab-scale, municipal wastewater sludge digester. TCA was biologically transformed to DCA and CA and further to ethane by reductive dechlorination. TCA was also converted to acetic acid and 1,1-dichloroethene (11DCE) by cell-free extract. 11DCE was further biologically converted to ethene. This pathway was confirmed by transformation tests of TCA, DCA and CA, by tests with cell-free extract, and by chloride release during TCA degradation. With cell-free extract, acetic acid accounted for approximately 90% of the TCA transformed; tests with live cells indicate that the fraction of TCA transformed by this pathway decreased with lower biomass. The dechlorination of DCA to CA and CA to ethane was not stoichiometric. A high rate of TCA removal was observed under the experimental conditions. The results indicate that removal of TCA in anaerobic digestion should be complete, but DCA and CA could persist in a normally operating digester.     

Complete transformation of 1,1,1-trichloroethane to chloroethane by a methanogenic mixed population

A methanogenic mixed population in a packed-bed reactor completely transformed 1,1,1-trichloroethane (10 μM) to chloroethane by a cometabolic process. Chloroethane was not further transformed. Acetate and methanol served as electron donors. Complete transformation of 1,1,1-trichloroethane to chloroethane only occurred when sufficient electron donor was fed into the reactor. Otherwise, besides chloroethane, 1,1-dichloroethane was also found as a product. The products of 1,1,1-trichloroethane transformation also depended on the type of electron donor present. With acetate, the degree of dechlorination was higher, i.e. more 1,1,1-trichloroethane was transformed to chloroethane than with methanol. In an enrichment culture obtained from the reactor contents, 1,1,1-trichloroethane was only transformed to 1,1-dichloroethane and was not further metabolized. Methanol, acetate, formate, ethanol, 2-propanol, trimethylamine and H₂, but not dimethylamine and methylamine, served as electron donors for 1,1,1-trichloroethane transformation by this enrichment culture. Both nitrate and nitrite inhibited 1,1,1-trichloroethane transformation; while nitrate completely inhibited 1,1,1-trichloroethane dechlorination, some conversion did occur in the presence of nitrite. The product(s) of this conversion remain unknown, since no chlorinated hydrocarbons were detected. Received: 19 June 1998 / Received revision: 14 September 1998 / Accepted: 17 September 1998     

Biotransformation of 1,1,1-trichloroethane, trichloromethane, and tetrachloromethane by a Clostridium sp

A gram-positive, strictly anaerobic, motile, endospore-forming rod, tentatively identified as a proteolytic Clostridium sp., was isolated from the effluent of an anaerobic suspended-growth bioreactor. The organism was able to biotransform 1,1,1-trichloroethane, trichloromethane, and tetrachloromethane. 1,1,1-Trichloroethane was completely transformed (greater than or equal to 99.5%) by reductive dehalogenation to 1,1-dichloroethane (30 to 40%) and, presumably by other mechanisms, to acetic acid (7%) and unidentified products. The reductive dehalogenation of tetrachloromethane led to the intermediate trichloromethane, which was further transformed to dichloromethane (8%) and unidentified products. The biotransformation occurred during the exponential growth phase, as well as during the stationary phase. Tetrachlorethene, trichloroethene, 1,1-dichloroethene, chloroethane, 1,1-dichloroethane, and dichloromethane were not biotransformed significantly by the organism.     

Biodegradation of polyalcohol ethoxylate by a wastewater microbial consortium

Polyalcohol ethoxylate (PAE), an anionic surfactant, is the primary component in most laundry and dish wash detergents and is therefore highly loaded in domestic wastewater. Its biodegradation results in the formation of several metabolites and the fate of these metabolites through wastewater treatment plants, graywater recycling processes, and in the environment must be clearly understood. Biodegradation pathways for PAE were investigated in this project with a municipal wastewater microbial consortium. A microtiter-based oxygen sensor system was utilized to determine the preferential use of potential biodegradation products. Results show that while polyethylene glycols (PEGs) were readily degraded by PAE acclimated microorganisms, most of the carboxylic acids tested were not degraded. Biodegradation of PEGs suggests that hydrophobe–hydrophile scission was the dominant pathway for PAE biodegradation in this wastewater community. Ethylene glycol (EG) and diethylene glycol (DEG) were not utilized by microbial populations capable of degrading higher molecular weight EGs. It is possible that EG and DEG may accumulate. The microtiter-based oxygen sensor system was successfully utilized to elucidate information on PAE biodegradation pathways and could be applied to study biodegradation pathways for other important contaminants.     

Transformation of 1,1,1-trichloroethane in an anaerobic packed-bed reactor at various concentrations of 1,1,1-trichloroethane, acetate and sulfate

Biotransformation of 1,1,1-trichloroethane (CH₃CCl₃) was observed in an anaerobic packed-bed reactor under conditions of both sulfate reduction and methanogenesis. Acetate (1 mM) served as an electron donor. CH₃CCl₃ was completely converted up to the highest investigated concentration of 10 μM. 1,1-Dichloroethane and chloroethane were found to be the main transformation products. A fraction of the CH₃CCl₃ was completely dechlorinated via an unknown pathway. The rate of transformation and the transformation products formed depended on the concentrations of CH₃CCl₃, acetate and sulfate. With an increase in sulfate and CH₃CCl₃ concentrations and a decrease in acetate concentration, the degree of CH₃CCl₃ dechlorination decreased. Both packed-bed reactor studies and batch experiments with bromoethanesulfonic acid, an inhibitor of methanogenesis, demonstrated the involvement of methanogens in CH₃CCl₃ transformation. Batch experiments with molybdate showed that sulfate-reducing bacteria in the packed-bed reactor were also able to transform CH₃CCl₃. However, packed-bed reactor experiments indicated that sulfate reducers only had a minor contribution to the overall transformation in the packed-bed reactor. Received: 22 January 1997 / Received revision: 12 May 1997 / Accepted: 19 May 1997     

Biotransformation of 1,1,1-trichloroethane, trichloromethane, and tetrachloromethane by a Clostridium sp.

A gram-positive, strictly anaerobic, motile, endospore-forming rod, tentatively identified as a proteolytic Clostridium sp., was isolated from the effluent of an anaerobic suspended-growth bioreactor. The organism was able to biotransform 1,1,1-trichloroethane, trichloromethane, and tetrachloromethane. 1,1,1-Trichloroethane was completely transformed (greater than or equal to 99.5%) by reductive dehalogenation to 1,1-dichloroethane (30 to 40%) and, presumably by other mechanisms, to acetic acid (7%) and unidentified products. The reductive dehalogenation of tetrachloromethane led to the intermediate trichloromethane, which was further transformed to dichloromethane (8%) and unidentified products. The biotransformation occurred during the exponential growth phase, as well as during the stationary phase. Tetrachlorethene, trichloroethene, 1,1-dichloroethene, chloroethane, 1,1-dichloroethane, and dichloromethane were not biotransformed significantly by the organism.     

Biodegradation of propanol and isopropanol by a mixed microbial consortium

The aerobic biodegradation of high concentrations of 1-propanol and 2-propanol (IPA) by a mixed microbial consortium was investigated. Solvent concentrations were one order of magnitude greater than any previously reported in the literature. The consortium utilized these solvents as their sole carbon source to a maximum cell density of 2.4 × 10⁹ cells ml⁻¹. Enrichment experiments with propanol or IPA as carbon sources were carried out in batch culture and maximum specific growth rates (μ_max) calculated. At 20 °C, μ _max values were calculated to be 0.0305 h⁻¹ and 0.1093 h⁻¹ on 1% (v/v) IPA and 1-propanol, respectively. Growth on propanol and IPA was carried out between temperatures of 10 °C and 45 °C. Temperature shock responses by the microbial consortium at temperatures above 45 °C were demonstrated by considerable cell flocculation. An increase in propanol substrate concentration from 1% (v/v) to 2% (v/v) decreased the μ _max from 0.1093 h⁻¹ to 0.0715 h⁻¹. Maximum achievable biodegradation rates of propanol and IPA were 6.11 × 10⁻³% (v/v) h⁻¹ and 2.72 × 10⁻³% (v/v) h⁻¹, respectively. Generation of acetone during IPA biodegradation commenced at 264 h and reached a maximum concentration of 0.4% (v/v). The results demonstrate the potential of mixed microbial consortia in the bioremediation of solvent-containing waste streams. Received: 14 December 1999 / Received revision: 3 April 2000 / Accepted: 7 April 2000     

Biodegradation of polycyclic aromatic hydrocarbons by a halophilic microbial consortium

In this study we investigated the phenanthrene degradation by a halophilic consortium obtained from a saline soil sample. This consortium, named Qphe, could efficiently utilize phenanthrene in a wide range of NaCl concentrations, from 1% to 17% (w/v). Since none of the purified isolates could degrade phenanthrene, serial dilutions were performed and resulted in a simple polycyclic aromatic hydrocarbon (PAH)-degrading culture named Qphe-SubIV which was shown to contain one culturable Halomonas strain and one unculturable strain belonging to the genus Marinobacter. Qphe-SubIV was shown to grow on phenanthrene at salinities as high as 15% NaCl (w/v) and similarly to Qphe, at the optimal NaCl concentration of 5% (w/v), could degrade more than 90% of the amended phenanthrene in 6 days. The comparison of the substrate range of the two consortiums showed that the simplified culture had lost the ability to degrade chrysene but still could grow on other polyaromatic substrates utilized by Qphe. Metabolite analysis by HPLC and GC–MS showed that 2-hydroxy 1-naphthoic acid and 2-naphthol were among the major metabolites accumulated in the Qphe-SubIV culture media, indicating that an initial dioxygenation step might proceed at C1 and C2 positions. By investigating the growth ability on various substrates along with the detection of catechol dioxygenase gene, it was postulated that the uncultured Marinobacter strain had the central role in phenanthrene degradation and the Halomonas strain played an auxiliary role in the culture by utilizing phenanthrene metabolites whose accumulation in the media could be toxic.     

Biodegradation of naphthalene by enriched marine denitrifying bacteria

Numerous studies have been investigated on the PAHs biodegradation in aerobic and anaerobic environments; however, the biodegradation of PAHs under anoxic conditions, especially denitrifying conditions, has drawn less attention. In this study, four series of batch experiments were conducted to investigate the effect of temperature, pH, naphthalene concentration and nitrate concentration on the naphthalene degradation under denitrification condition. Our results showed that the degradation of naphthalene was most favorable at pH 7 and 25 °C. Results also indicated that 30 mg/l naphthalene inhibited the biodegradation and the removal efficiency was only 20.2%. Significant degradation (91.7% and 96.3%) of naphthalene occurred when nitrate concentrations were 1.0 and 5.0 mM. Moreover, the maximum degradation rates were 0.13 and 0.18 mg-NAP/(l h) depending on the concentration of nitrate. Based on 16S rDNA analysis, the denitrifying enriched culture was mainly composed of ??-Proteobacteria (19 clones out of a total of 23 clones) and Actinobacteria (4 clones). Using a primer set specific for naphthalene degrading functional gene nahAc, two operational taxonomy units were obtained in the clone library of nahAc. Both of them were closely related to nahAc genes of known species of Pseudomonas. Quantitative polymerase chain reaction (qPCR) was employed to quantify the change of naphthalene-degrading population during the degradation of naphthalene using nahAc gene as the biomarker. The maximum degradation rate and removal efficiency were strongly correlated with nahAc gene copy number, with R² of 0.69 and 0.79, respectively.     

Kinetics of biotransformation of 1,1,1-trichloroethane by Clostridium sp. strain TCAIIB

Batch experiments were conducted to examine the effects of high concentrations of 1,1,1-trichloroethane (TCA) on the biotransformation of TCA by Clostridium sp. strain TCAIIB. The biotic dehalogenation of TCA to 1,1-dichloroethane by nongrowing cells was measured at 35 degrees C, and the data were used to obtain the kinetic parameters of the Monod relationship half-velocity coefficient Ks (31 microM) and the coefficient of maximum rate of TCA biotransformation (kTCA; 0.28 mumol per mg per day). The yield of biomass decreased with an increase in the TCA concentration, although TCA concentrations up to 750 microM did not completely inhibit bacterial growth. Also, kTCA was higher in the presence of high concentrations of TCA. A mathematical model based on a modified Monod equation was used to describe the biotransformation of TCA. The abiotic transformation of TCA to 1,1-dichloroethene was measured at 35 degrees C, and the first-order formation rate coefficient for 1,1-dichloroethene (ke) was determined to be 0.86 per year.     

Chronic cardiac toxicity after inhalation of 1,1,1-trichloroethane.

Two patients showed evidence of chronic cardiac toxicity after repeated exposure to 1,1,1-trichloroethane. In both cases there was circumstantial evidence of a deterioration after routine anaesthetic use of the related compound halothane. An adolescent boy who sniffed trichloroethane presented with multiple ventricular arrhythmias during tonsillectomy. Follow up showed mild chronic left ventricular impairment. A 54 year old man had repeated industrial exposure to trichloroethane and deteriorated from mild stable cardiac failure to end stage cardiac failure after halothane anaesthesia for herniorrhaphy. Chronic cardiac toxicity is a previously unreported feature of this type of solvent exposure. Related compounds such as halothane may have a toxic interaction after exposure to trichloroethane.     

Biodegradation of aromatic compounds and TCE by a filamentous bacteria-dominated consortium

The Michaelis-Menten biodegradation kinetics (k and Ks) of aromatic compounds and trichloroethene (TCE) by an aerobic enrichment culture grown on phenol and dominated by a unique filamentous bacterium were measured. The average k and Ks values for phenol, benzene (B), toluene (T), ethylbenzene (E), o-xylene (oX), p-xylene (pX), naphthalene and TCE in g per g VSS-d and mg L-1 were 5.72 and 0.34, 1.20 and 0.51, 2.09 and 0.47, 0.77 and 0.23, 0.61 and 0.16, 0.73 and 0.23, 0.17 and 0.18, and 0.16 and 0.18, respectively. Significant variability in these measured kinetics was noted between tests conducted over the 5-month period during which the fed-batch culture with a 5-day solids retention time was maintained; the coefficient of variation of the k and Ks values ranged from 11–43% and 4–50%, respectively. This variation was significantly greater than the method measurement error on a given date. Degradation of BTEoXpX mixtures could be described by a basic competitive inhibition model.Batch tests during which the culture was fed individual BTEX compounds showed the culture grew poorly on the xylenes and had poor subsequent xylene degradation rates. This work indicates the potential to simultaneously treat a mixture of volatile organic compounds using this consortium, and the ability to predict the mixture biodegradation rates on the basis of the individual compound biodegradation kinetics.     

Effect of phenobarbital and 3-methylcholanthrene pretreatment on the hepatotoxicity of 1,1,1-trichloroethane and 1,1,2-trichloroethane

Pretreatment of rats with phenobarbital potentiated the hepatotoxicity of both 1,1,1- and 1,1,2-trichloroethane given by inhalation. The toxicity of the 1,1,2-isomer was increased to a greater extent than that of the 1,1,1-isomer. 3-Methylcholanthrene pretreatment did not result in increased hepatotoxicity.     

Kinetics of biotransformation of 1,1,1-trichloroethane by Clostridium sp. strain TCAIIB.

Batch experiments were conducted to examine the effects of high concentrations of 1,1,1-trichloroethane (TCA) on the biotransformation of TCA by Clostridium sp. strain TCAIIB. The biotic dehalogenation of TCA to 1,1-dichloroethane by nongrowing cells was measured at 35 degrees C, and the data were used to obtain the kinetic parameters of the Monod relationship half-velocity coefficient Ks (31 microM) and the coefficient of maximum rate of TCA biotransformation (kTCA; 0.28 mumol per mg per day). The yield of biomass decreased with an increase in the TCA concentration, although TCA concentrations up to 750 microM did not completely inhibit bacterial growth. Also, kTCA was higher in the presence of high concentrations of TCA. A mathematical model based on a modified Monod equation was used to describe the biotransformation of TCA. The abiotic transformation of TCA to 1,1-dichloroethene was measured at 35 degrees C, and the first-order formation rate coefficient for 1,1-dichloroethene (ke) was determined to be 0.86 per year.     

Degradation pathways of trichloroethylene and 1,1,1-trichloroethane by Mycobacterium sp. TA27

We analyzed the kinetics and metabolic pathways of trichloroethylene and 1,1,1-trichloroethane degradation by the ethane-utilizing Mycobacterium sp. TA27. The apparent Vmax and Km of trichloroethylene were 9.8 nmol min(-1) mg of cells(-1) and 61.9 microM, respectively. The apparent Vmax and Km of 1,1,1-trichloroethane were 0.11 nmol min(-1) mg of cells(-1) and 3.1 microM, respectively. 2,2,2-trichloroethanol, trichloroacetic acid, chloral, and dichloroacetic acid were detected as metabolites of trichloroethylene. 2,2,2-trichloroethanol, trichloroacetic acid, and dichloroacetic acid were also detected as metabolites of 1,1,1-trichloroethane. The amounts of 2,2,2-trichloroethanol, trichloroacetic acid, chloral, and dichloroacetic acid derived from the degradation of 3.60 micromol trichloroethylene were 0.16 micromol (4.4%), 0.11 micromol (3.1%), 0.02 micromol (0.6%), and 0.02 micromol (0.6%), respectively. The amounts of 2,2,2-trichloroethanol, trichloroacetic acid and dichloroacetic acid derived from the degradation of 1.73 micromol 1,1,1-trichloroethane were 1.48 micromol (85.5%), 0.22 micromol (12.7%), and 0.02 micromol (1.2%), respectively. More than 90% of theoretical total chloride was released in trichloroethylene degradation. Chloral and 2,2,2-trichloroethanol were transformed into each other, and were finally converted to trichloroacetic acid, and dichloroacetic acid. Trichloroacetic acid and dichloroacetic acid were not degraded by strain TA27.     

Aerobic degradation of 1,1,1-trichloroethane by Mycobacterium spp. isolated from soil.

Two strains of 1,1,1-trichloroethane (TCA)-degrading bacteria, TA5 and TA27, were isolated from soil and identified as Mycobacterium spp. Strains TA5 and TA27 could degrade 25 and 75 mg. liter of TCA(-1) cometabolically in the presence of ethane as a carbon source, respectively. The compound 2,2,2-trichloroethanol was produced as a metabolite of the degradation process.     

Biodegradation of atrazine under denitrifying conditions

Anaerobic biodegradation of atrazine by the bacterial isolate M91-3 was characterized with respect to mineralization, metabolite formation, and denitrification. The ability of the isolate to enhance atrazine biodegradation in anaerobic sediment slurries was also investigated. The organism utilized atrazine as its sole source of carbon and nitrogen under anoxic conditions in fixed-film (glass beads) batch column systems. Results of HPLC and TLC radiochromatography suggested that anaerobic biotransformation of atrazine by microbial isolate M91-3 involved hydroxyatrazine formation. Ring cleavage was demonstrated by ¹⁴CO₂ evolution. Denitrification was confirmed by detection of ¹⁵N₂ in headspace samples of K¹⁵NO₃-amended anaerobic liquid cultures. In aquatic sediments, mineralization of uniformly ring-labeled [¹⁴C]atrazine occurred in both M91-3-inoculated and uninoculated sediment. Inoculation of sediments with M91-3 did not significantly enhance anaerobic mineralization of atrazine as compared to uninoculated sediment, which suggests the presence of indigenous organisms capable of anaerobic atrazine biodegradation. Results of this study suggest that the use of M91-3 in a fixed-film bioreactor may have applications in the anaerobic removal of atrazine and nitrate from aqueous media. Received: 3 September 1997 / Received revision: 4 December 1997 / Accepted: 2 January 1998     

Bio-reductive dechlorination of 1,1,1-trichloroethane and chloroform using a hydrogen-based membrane biofilm reactor

A H(2)-based, denitrifying and sulfate-reducing membrane biofilm reactor (MBfR) was effective for removing 1,1,1-trichloroethane (TCA) and chloroform (CF) by reductive dechlorination. When either TCA or CF was first added to the MBfR, reductive dechlorination took place immediately and then increased over 3 weeks, suggesting enrichment for TCA- or CF-dechlorinating bacteria. Increasing the H(2) pressure increased the dechlorination rates of TCA or CF, and it also increased the rate of sulfate reduction. Increased sulfate loading allowed more sulfate reduction, and this competed with reductive dechlorination, particularly the second steps. The acceptor flux normalized by effluent concentration can be an efficient indicator to gauge the intrinsic kinetics of the MBfR biofilms for the different reduction reactions. The analysis of normalized rates showed that the kinetics for reductive-dechlorination reactions were slowed by reduced H(2) bio-availability caused by a low H(2) pressure or competition from sulfate reduction.     

Functional consortium for denitrifying sulfide removal process

Denitrifying sulfide removal (DSR) process simultaneously converts sulfide, nitrate, and chemical oxygen demand from industrial wastewaters to elemental sulfur, nitrogen gas, and carbon dioxide, respectively. This investigation utilizes a dilution-to-extinction approach at 10⁻² to 10⁻⁶ dilutions to elucidate the correlation between the composition of the microbial community and the DSR performance. In the original suspension and in 10⁻² dilution, the strains Stenotrophomonas sp., Thauera sp., and Azoarcus sp. are the heterotrophic denitrifiers and the strains Paracoccus sp. and Pseudomonas sp. are the sulfide-oxidizing denitrifers. The 10⁻⁴ dilution is identified as the functional consortium for the present DSR system, which comprises two functional strains, Stenotrophomonas sp. strain Paracoccus sp. At 10⁻⁶ dilution, all DSR performance was lost. The functions of the constituent cells in the DSR granules were discussed based on data obtained using the dilution-to-extinction approach.