Anaerobic membrane bioreactor (AnMBR) treatment of a simulated domestic wastewater was evaluated at psychrophilic temperatures of 15, 12, 9, 6, and 3 °C. Chemical oxygen demand (COD) removal >95% was ...achieved at temperatures as low as 6 °C, but fell to 86% at 3 °C. As temperature decreased, soluble COD in the bioreactor increased suggesting a reduction in suspended biomass activity. The high total COD removal was maintained via biological activity in the membrane biofilm, which resulted in significant dissolved methane oversaturation in the permeate. Sequencing of 16S rRNA suggested that the biofilm's metabolic diversity increased as temperature decreased in response to a greater flux of complex organics into the biofilm due to temperature-based suspended biomass inhibition. Hydrogenotrophic methanogenesis as opposed to aceticlastic methanogenesis was the preferred pathway in the biofilm, but not in the suspended biomass. This research demonstrated that AnMBR treatment of domestic wastewater at very low temperatures is feasible. However, it is important to develop technologies for dissolved methane recovery and to consider strategies to improve suspended biomass activity at low temperatures to decrease the reliance on biofilm treatment thereby decreasing dissolved methane oversaturation.
Aims
Interactions with water bacteria affect the incorporation of pathogens into biofilms and thus pathogen control in drinking water systems. This study was to examine the impact of static vs flow ...conditions on interactions between a pathogen and a water bacterium on pathogen biofilm formation under laboratory settings.
Methods and Results
A pathogen surrogate Escherichia coli and a drinking water isolate Stenotrophomonas maltophilia was selected for this study. Biofilm growth was examined under two distinct conditions, in flow cells with continuous medium supply vs in static microtitre plates with batch culture. E. coli biofilm was greatly stimulated (c. 2–1000 times faster) with the presence of S. maltophilia in flow cells, but surprisingly inhibited (c. 65–95% less biomass) in microtitre plates. These divergent effects were explained through various aspects including surface attachment, cellular growth, extracellular signals and autoaggregation.
Conclusions
Interactions with the same water bacterium resulted in different effects on E. coli biofilm formation when culture conditions changed from static to flow.
Significance and Impact of Study
This study highlights the complexity of species interactions on biofilm formation and suggests that environmental conditions such as the flow regime can be taken into consideration for the management of microbial contamination in drinking water systems.
Two-phase (acid-gas) anaerobic digestion can improve process performance relative to conventional, mesophilic, single-phase anaerobic digestion. However, few studies have considered the impact of ...phase separation on microbial community structure. We compared six full-scale, two-phase digestion (TPD) facilities and four conventional digestion (CD) facilities at municipal wastewater treatment plants by collecting performance data and evaluating microbial community structure via Illumina 16S rRNA gene sequencing. Sequence data indicated that nearly complete phase separation was achieved in all TPDs with few syntrophic bacteria or methanogens detected in acid phase digesters (APDs). Thermophilic methane phase digesters (MPDs) exhibited poor performance relative to mesophilic MPDs consistent with substantially lower relative abundances of syntrophic bacteria and methanogens in thermophilic MPDs. Although known syntrophic acetate oxidizers were only detected at very low levels in MPDs (0.11 ± 0.20%), the low abundance of aceticlastic methanogens observed suggests that syntrophic acetate oxidation plays a prominent role by yet to be described populations in TPD. TPDs exhibited greater microbial diversity than CDs, likely due to APDs supporting more diverse populations of hydrolytic and fermentative bacteria.
Membrane fouling was evaluated in a side stream anaerobic membrane bioreactor (AnMBR) operated for the treatment of swine manure. The AnMBR consisted of an external tubular polyethersulphone ...ultrafiltration membrane module (diameter = 12 mm) connected to a six-liter mixed bioreactor. The system was operated for 135 days without chemical membrane cleaning resulting in a membrane flux of 5–10 L/m
2 h. Membrane fouling was dominated by a loosely attached fouling layer, which could be removed by flushing the tubular membrane. Intensive chemical cleaning after the 135 days of continuous operation resulted in an irreversible resistance of 3×10
12 1/m, equivalent to 1.3 times the resistance of the new membrane. More frequent chemical membrane cleaning using HNO
3 could not prevent the development of irreversible fouling. Equilibrium calculations and scanning electron microscopy with energy dispersive spectroscopy demonstrated that inorganic precipitation contributed to fouling of the membrane surface and in the membrane pores.
The drinking water exposome Vikesland, P. J; Raskin, L
Environmental science water research & technology,
01/2016, Letnik:
2, Številka:
4
Journal Article
Recenzirano
Guest editors Peter Vikesland and Lutgarde Raskin introduce the Drinking Water Exposome themed issue of
Environmental Science: Water Research & Technology
.
To evaluate the role of Methanosaeta spp. in a variety of anaerobic environments, small-subunit rRNA targeted oligonucleotide hybridization probes were developed and experimentally characterized. The ...probes were designed to be genus specific for Methanosaeta and species specific for Methanosaeta concilii and Methanosaeta thermophila. The temperature of dissociation was determined for each probe. Probe specificities were determined using a diverse collection of Archaea and through an evaluation of probe nesting using samples from a variety of anaerobic bioreactors. Cell fixation and hybridization conditions for fluorescence in situ hybridizations were also evaluated. Although permeability of methanogens was variable, M. concilii cells could be permeabilized using a range of paraformaldehyde and ethanol based fixation conditions. Using the newly designed probes together with previously designed probes for methanogens, it was determined that Methanosaeta spp. were the dominant aceticlastic methanogens in a variety of anaerobic bioreactors when acetate concentrations were low. Their levels were higher in bioreactors with granular sludge than in those with flocculent sludge. In lab-scale upflow anaerobic sludge blanket reactors, the levels of M. concilii rRNA were as high as 30% of the total rRNA.
The microbial processes involved in two-phase anaerobic digestion were investigated by operating a laboratory-scale acid-phase (AP) reactor and analyzing two full-scale, two-phase anaerobic digesters ...operated under mesophilic (35 °C) conditions. The digesters received a blend of primary sludge and waste activated sludge (WAS). Methane levels of 20% in the laboratory-scale reactor indicated the presence of methanogenic activity in the AP. A phylogenetic analysis of an archaeal 16S rRNA gene clone library of one of the full-scale AP digesters showed that 82% and 5% of the clones were affiliated with the orders Methanobacteriales and Methanosarcinales, respectively. These results indicate that substantial levels of aceticlastic methanogens (order Methanosarcinales) were not maintained at the low solids retention times and acidic conditions (pH 5.2-5.5) of the AP, and that methanogenesis was carried out by hydrogen-utilizing methanogens of the order Methanobacteriales. Approximately 43, 31, and 9% of the archaeal clones from the methanogenic phase (MP) digester were affiliated with the orders Methanosarcinales, Methanomicrobiales, and Methanobacteriales, respectively. A phylogenetic analysis of a bacterial 16S rRNA gene clone library suggested the presence of acetate-oxidizing bacteria (close relatives of Thermacetogenium phaeum, 'Syntrophaceticus schinkii,' and Clostridium ultunense). The high abundance of hydrogen consuming methanogens and the presence of known acetate-oxidizing bacteria suggest that acetate utilization by acetate oxidizing bacteria in syntrophic interaction with hydrogen-utilizing methanogens was an important pathway in the second-stage of the two-phase digestion, which was operated at high ammonium-N concentrations (1.0 and 1.4 g/L). A modified version of the IWA Anaerobic Digestion Model No. 1 (ADM1) with extensions for syntrophic acetate oxidation and weak-acid inhibition adequately described the dynamic profiles of volatile acid production/degradation and methane generation observed in the laboratory-scale AP reactor. The model was validated with historical data from the full-scale digesters.
A multi-compartment anaerobic bioreactor, designated the anaerobic migrating blanket reactor (AMBR), did not perform well in terms of chemical oxygen demand (COD) removal after an increase in sulfate ...load, compared to a conventional upflow anaerobic sludge blanket (UASB) reactor. The trophic structures of the bioreactors were characterized by analyzing the electron flows, formation and consumption of fermentation intermediates and terminal product (methane and hydrogen sulfide) formation. Critical performance parameters were linked to operational perturbations such as increase in sulfate load and changes in flow reversal schemes in the AMBR. Both of these manipulations affected the microbial communities, which were monitored by terminal restriction fragment length polymorphism (T-RFLP) analysis targeting the bacterial and archaeal domains. The less stable AMBR did not produce granular biomass, and in response to increased sulfate concentrations, experienced a reversal in the distribution of hydrogenotrophic methanogens that correlated with a shift in electron flow from butyrate to propionate. As this shift occurred, bacterial populations such as butyrate-producing clostridia, became predominant, thus leading to reactor imbalance. The stable UASB reactor developed and retained granules and maintained a relatively stable archaeal community. Sulfate perturbation led to the selection of a novel bacterial group (
Thermotogaceae), which was most likely well adapted to the increasingly sulfidogenic conditions in the bioreactor.
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