H. David Stensel

A QSAR-based biodegradability model—A QSBR

A microbial biodegradability predictive model has been developed using groups and molecular indices as molecular descriptors. The model contains 12 variables. The model was calibrated and later validated with a data set developed from biodegradation studies of acclimated activated sludge metabolism. It also successfully predicted the biodegradation rate of several other substances with one exception within the limits established by a study of a second database. This latter study was designed to evaluate the expected scatter in acclimated biodegradation rate data. The nitro group, amines, halogens and heteroatoms severely decrease the rate as do structural complexity and electronic alterations created by most substituents. The carboxyl group markedly enhances the rate but the hydroxyl group has little effect. It appears that the hydroxyl group is significant in acclimation but not in degradation. A discussion of statistical methods and software is included in this work.

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.

PAH degradation and bioaugmentation by a marine methanotrophic enrichment

Abstract Methanotrophic bacteria were enriched from marine sediments and screened for their ability to biotransform polycyclic aromatic hydrocarbons (PAHs). Characterization of the methanotrophic enrichment showed that it was dominated by a Type I methanotroph, although significant amounts of 18:1 fatty acids were detected, suggesting the presence of Type II methanotrophs in marine systems. The methanotrophic enrichment degraded phenanthrene, anthracene, and fluorene to below detectable levels in 15 days. Partial transformation of fluoranthene occurred over 15 days, but pyrene was not transformed. Radiolabeled phenanthrene was oxidized to carbon dioxide with significant production of polar intermediates. The oxidation was inhibited by acetylene, an inhibitor of methane monooxygenase. The addition of the methanotrophic enrichment to a marine culture grown on PAHs as the sole carbon sources increased the transformation rate of phenanthrene, anthracene, and fluorene. The highest removal rates were obtained w...

Monitoring the dynamics of syntrophic β-oxidizing bacteria during anaerobic degradation of oleic acid by quantitative PCR

The ecophysiology of long-chain fatty acid-degrading syntrophic β-oxidizing bacteria has been poorly understood due to a lack of quantitative abundance data. Here, TaqMan quantitative PCR (qPCR) assays targeting the 16S rRNA gene of the known mesophilic syntrophic β-oxidizing bacterial genera Syntrophomonas and Syntrophus were developed and validated. Microbial community dynamics were followed using qPCR and Illumina-based high-throughput amplicon sequencing in triplicate methanogenic bioreactors subjected to five consecutive batch feedings of oleic acid. With repeated oleic acid feeding, the initial specific methane production rate significantly increased along with the relative abundances of Syntrophomonas and methanogenic archaea in the bioreactor communities. The novel qPCR assays showed that Syntrophomonas increased from 7 to 31% of the bacterial community 16S rRNA gene concentration, whereas that of Syntrophus decreased from 0.02 to less than 0.005%. High-throughput amplicon sequencing also revealed that Syntrophomonas became the dominant genus within the bioreactor microbiomes. These results suggest that increased specific mineralization rates of oleic acid were attributed to quantitative shifts within the microbial communities toward higher abundances of syntrophic β-oxidizing bacteria and methanogenic archaea. The novel qPCR assays targeting syntrophic β-oxidizing bacteria may thus serve as monitoring tools to indicate the fatty acid β-oxidization potential of anaerobic digester communities.

BTEX-Contaminated Gas Treatment in a Shallow, Sparged, Suspended-Growth Bioreactor

Abstract Treatment of a gas contaminated with a mixture of benzene, toluene, ethylbenzene, and o-xylene (BTEX) compounds in a 40-cm-deep laboratory-scale bioreactor containing suspended biomass was investigated. Gas treatment efficiency was not significantly impacted by different BTEX mixtures, and approximately 99% removal was achieved for volumetric loadings of 11 to 18 mg-BTEX/L-reactor volume/hr (specific biomass loadings of 0.27 to 0.83 g-BTEX/g-VSS/d; inlet concentrations of total BTEX of 2.3 to 4.3 mg/L) and operational solids retention times (SRTs) of 1.7, 2.7, and 9.2 days. Maximum specific biodegradation rates of the reactor biomass increased as the reactor SRTs decreased. Under specific loadings greater than 1 g-BTEX/g-VSS/d the gas treatment became biokinetically limited, such that BTEX and unidentified BTEX metabolites accumulated in the bioreactor liquid over time. BTEX gas-liquid mass transfer was sufficient in the 40-cm-deep sparged liquid reactor to provide high BTEX treatment efficiency.

DNA-SIP based genome-centric metagenomics identifies key long-chain fatty acid-degrading populations in anaerobic digesters with different feeding frequencies

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.

Experimental observation of trickling filter hydraulics

Abstract An open-face, plastic-sheet reactor design was tested to determine wastewater flow characteristics in cross-flow plastic media trickling filters. Flow characteristics were evaluated by routine visual inspection of the open-face reactor during its 40-day operating period and by 35-mm time lapse photography and video tape recording of impulse tracer dye applications. The experimental observations showed that the bulk of the trickling filter flow can be characterized as a vertical laminar liquid film flow over a majority of the biofilm surface that is interrupted at regular intervals by falling liquid drops, originating from irregularities or protrusions in the biofilm surface. A small portion of flow occurs by falling droplets and flow in 50–100-mm length, dispersed shallow channels. The liquid film appears to be mixed at the falling droplet impact location. The distance between these mixing locations, referred to as an uninterrupted flow path length, is determined by the location of biofilm surface protrusions. Although many biofilm surface protrusions are located near the nodes or crossing points of adjacent sheets of the medias surface, they are also found at other locations. Thus, it is not possible to specify the uninterrupted flow path distance from media geometry features alone. In addition, observed flow irregularities resulted in intermittent wetting of some biofilm surfaces with intermittent exposure directly to the reactor gas phase. This condition may have a significant effect on oxygen mass transfer rates to the biofilm.

Influence of bioselector processes on 17α-ethinylestradiol biodegradation in activated sludge wastewater treatment systems.

The removal of the potent endocrine-disrupting estrogen hormone, 17α-ethinylestradiol (EE2), in municipal wastewater treatment plant (WWTP) activated sludge (AS) processes can occur through biodegradation by heterotrophic bacteria growing on other organic wastewater substrates. Different kinetic and metabolic substrate utilization conditions created with AS bioselector processes can affect the heterotrophic population composition in AS. The primary goal of this research was to determine if these changes also affect specific EE2 biodegradation kinetics. A series of experiments were conducted with parallel bench-scale AS reactors treating municipal wastewater with estrogens at 100-300 ng/L concentrations to evaluate the effect of bioselector designs on pseudo first-order EE2 biodegradation kinetics normalized to mixed liquor volatile suspended solids (VSS). Kinetic rate coefficient (kb) values for EE2 biodegradation ranged from 5.0 to 18.9 L/g VSS/d at temperatures of 18 °C to 24 °C. EE2 kb values for aerobic biomass growth at low initial food to mass ratio feeding conditions (F/Mf) were 1.4 to 2.2 times greater than that from growth at high initial F/Mf. Anoxic/aerobic and anaerobic/aerobic metabolic bioselector reactors achieving biological nutrient removal had similar EE2 kb values, which were lower than that in aerobic AS reactors with biomass growth at low initial F/Mf. These results provide evidence that population selection with growth at low organic substrate concentrations can lead to improved EE2 biodegradation kinetics in AS treatment.

Bioaugmentation of sidestream nitrifying-denitrifying phosphorus-accumulating granules in a low-SRT activated sludge system at low temperature

Sidestream granular activated sludge grown on anaerobic digester dewatering centrate was bioaugmented and selectively retained to enable high nitrification performance of a 2.5-day aerobic SRT non-nitrifying flocculent activated sludge system at 12 °C. Sidestream-grown granules performed enhanced biological phosphorus removal (EBPR) and short-cut nitrogen removal via nitrite. After bioaugmentation, EBPR continued in the mainstream but ammonia oxidation was eventually to nitrate. Low effluent NH3-N concentrations from 0.6 to 1.7 mg/L were achieved with nitrification solely by granules, thus enabling denitrification and nitrogen removal. Molecular microbial analyses of flocs and granules also suggested that nitrifying organisms persisted on granules with minimal nitrifier loss to flocs. Mainstream granule mass at the end of bioaugmentation testing was 1.7 times the amount of sidestream granules added, indicating mainstream granular growth. Nitrite and nitrate availability during the unaerated feeding period encouraged significant growth of ordinary heterotrophs in mainstream granules, but nevertheless mainstream nitrification capacity was sustained.

Comparison of different aerobic granular sludge types for activated sludge nitrification bioaugmentation potential

Three types of nitrifying granules were grown on media simulating anaerobic digestion dewatering reject water and compared for their potential to increase nitrification capacity when added to mainstream flocculent activated sludge treatment. An advantage of nitrification bioaugmentation with sidestream granules instead of flocculent biomass is that the granules can be selectively maintained at longer retention times than flocs and thus provide higher nitrification capacity from bioaugmentation. The three granule types and feeding conditions were: nitrifying granules with aerobic feeding, nitrifying-denitrifying granules with anoxic feeding, and nitrifying-denitrifying/phosphate-accumulating (NDN-PAO) granules with anaerobic feeding. NDN-PAO granular sludge showed the highest potential for nitrification bioaugmentation due to its better treatment performance, granule physical characteristics, and much greater production of granular mass and nitrification capacity. Dechloromonas-associated organisms were dominant in these granules; Candidatus Accumulibacter-related organisms were also present. Nitrosomonas was the dominant ammonia-oxidizing bacteria, while Candidatus Nitrotoga was an abundant nitrite-oxidizer in all granule types.