A methanogenic fluidized bed reactor (FBR) fed with lactate and tetrachloroethene (PCE) was operated for 14 months to study the effect of electron donor and PCE loading on chloroethene dechlorination rates. Lactate was fed continuously at 200 mg/L (2.2 mmol/L), and the influent PCE feed concentration was increased stepwise from 3.5 to 160 µmol/L. Vinyl chloride (VC) and ethene accounted for 80% and 20%, respectively, of the PCE dechlorination. Batch tests with various electron donors showed that H 2 , propionate, and lactate supported dechlorination of PCE, trichloroethene (TCE), cis-dichloroethene (c-DCE), and VC, whereas no dechlorination was observed with acetate or in the absence of an electron donor. Different short-term steady H 2 concentrations were obtained by adjusting the FBR influent lactate feed concentration, and the effect of H 2 concentration on the rate of chloroethene dechlorination was determined. Dechlorination rates for PCE, TCE, c-DCE, and VC showed a Michaelis-Menten relationship with H 2 partial pressure. The half-velocity coefficients for H 2 utilization by dechlorinators ranged from 12 to 28 ppm for the chloroethenes and are at least an order of magnitude lower than values reported for methanogens. This implies that dechlorinating bacteria can out-compete methanogens for H 2 utilization at low H 2 concentration.

The abundance and relevance of Accumulibacter phosphatis (presumed to be polyphosphate-accumulating organisms [PAOs]), Competibacter phosphatis (presumed to be glycogen-accumulating organisms [GAOs]), and tetrad-forming organisms (TFOs) to phosphorus removal performance at six full-scale enhanced biological phosphorus removal (EBPR) wastewater treatment plants were investigated. Coexistence of various levels of candidate PAOs and GAOs were found at these facilities. Accumulibacter were found to be 5 to 20% of the total bacterial population, and Competibacter were 0 to 20% of the total bacteria population. The TFO abundance varied from nondetectable to dominant. Anaerobic phosphorus (P) release to acetate uptake ratios (P rel /HAc up ) obtained from bench tests were correlated positively with the abundance ratio of Accumulibacter/(Competibacter 1TFOs) and negatively with the abundance of (Competibacter 1TFOs) for all plants except one, suggesting the relevance of these candidate organisms to EBPR processes. However, effluent phosphorus concentration, amount of phosphorus removed, and process stability in an EBPR system were not directly related to high PAO abundance or mutually exclusive with a high GAO fraction. The plant that had the lowest average effluent phosphorus and highest stability rating had the lowest P rel /HAc up and the most TFOs. Evaluation of full-scale EBPR performance data indicated that low effluent phosphorus concentration and high process stability are positively correlated with the influent readily biodegradable chemical oxygen demand-to-phosphorus ratio. A system-level carbon-distribution-based conceptual model is proposed for capturing the dynamic competition between PAOs and GAOs and their effect on an EBPR process, and the results from this study seem to support the model hypothesis. Water Environ. Res., 80, 688 (2008).

Methanosarcina species with a high maximum specific growth rate (l max ) and high half-saturation coefficient (K S ) and Methanosaeta species with a low l max and low K S are the only known aceticlastic methanogens. Because of Methanosaeta's low K S , the low acetate concentrations in conventional, mesophilic anaerobic digestion yield Methanosaeta dominance. However, Methanosarcina absorbs increases in acetate more efficiently and thus promotes more stable digestion. This paper tests the hypothesis that decreasing digester feeding frequencies can increase Methanosarcina predominance. Two acetate-fed reactors were established at a 17-day solids retention time. One reactor was fed hourly, and one was fed once daily. Microscopic and molecular methods were used to verify that the hourly fed reactor enriched for Methanosaeta, while the daily fed reactor enriched for Methanosarcina. Growth and substrate-use kinetics were measured for each reactor. A digester overload condition was simulated, and the Methanosarcina-enriched reactor was found to perform better than the Methanosaeta-enriched reactor. These findings indicate that Methanosarcina dominance can be achieved with infrequent feedings, leading to more stable digestion. Water Environ. Res., 78, 486 (2006).

Impacts of trace concentrations of estrogens on aquatic ecosystems are a serious environmental concern, with their primary source being wastewater treatment facility effluents. Increased removal of 17alpha-ethinylestradiol (EE2) has been reported for activated sludge treatment with long enough solids retention time for nitrification. Previous work based on batch tests with Nitrosomonas europaea and nitrifying activated sludge at high EE2 concentrations (>300 000 ng/L) and high NH4-N concentrations (>200 mg/L) has led to the hypothesis that ammonia oxidizing bacteria cometabolically degrade EE2. This work investigated EE2 transformation with N. europaea and Nitrosospira multiformis at environmentally relevant EE2 concentrations and LC-MS-MS to observe transformation products. Degradation of EE2 was not observed in batch tests with no NH4-N addition or with 10 mg/L NH4-N fed daily. At increased NH4-N concentrations (200-500 mg/L) EE2 transformation was observed, but the only detected products were nitrated EE2. Abiotic assays with growth medium confirmed EE2 removal by nitration, which is enhanced at low pH and high NO2-N concentrations. These results suggest that EE2 removal at low concentrations found in municipal treatment activated sludge systems is not due to cometabolic degradation by ammonia oxidizing bacteria, or to abiotic nitration, but most likely due to heterotrophic bacteria.

Fats, oils and greases (FOG) are energy-dense wastes that can be added to anaerobic digesters to substantially increase biomethane recovery via their conversion through long-chain fatty acids (LCFAs). However, a better understanding of the ecophysiology of syntrophic LCFA-degrading microbial communities in anaerobic digesters is needed to develop operating strategies that mitigate inhibitory LCFA accumulation from FOG. In this research, DNA stable isotope probing (SIP) was coupled with metagenomic sequencing for a genome-centric comparison of oleate (C18:1)-degrading populations in two anaerobic codigesters operated with either a pulse feeding or continuous-feeding strategy. The pulse-fed codigester microcosms converted oleate into methane at over 20% higher rates than the continuous-fed codigester microcosms. Differential coverage binning was demonstrated for the first time to recover population genome bins (GBs) from DNA-SIP metagenomes. About 70% of the 13C-enriched GBs were taxonomically assigned to the Syntrophomonas genus, thus substantiating the importance of Syntrophomonas species to LCFA degradation in anaerobic digesters. Phylogenetic comparisons of 13C-enriched GBs showed that phylogenetically distinct Syntrophomonas GBs were unique to each codigester. Overall, these results suggest that syntrophic populations in anaerobic digesters can have different adaptive capacities, and that selection for divergent populations may be achieved by adjusting reactor operating conditions to maximize biomethane recovery.