New low-temperature applications of anaerobic wastewater treatment

Effect of low temperature and municipal wastewater organic loading on anaerobic granule reactor performance

Biogas production and municipal wastewater COD removal at low temperatures by granulated anaerobic biomass were investigated. Two anaerobic granule reactors were operated continuously for 1025 days by stepwise increase of organic loading from 1.3 to 15.2 g COD_dissolved·l^-1·d^-1 at 25, 16, 12, 8.5, 5.5, and 2.5 °C. The sustained reactor performance was evaluated by COD removal efficiency, methane production, and microbial community analysis. Stable COD removal of 50-70% were achieved at 25-8.5 °C and up to 15 g COD_dissolved·l^-1·d^-1, and no significant temperature effect was observed on specific methane production rate and yield. Below 8.5 °C, COD removal and methane yields reduced, but still significant methane formation was observed even at 2.5 °C. More than 90% of COD removed was converted to methane. Methanogenic archaea communities showed that temperature changes affected the major methane formation pathways, which explains temperature adaptability of the granules.

Influent wastewater microbiota and temperature influence anaerobic membrane bioreactor microbial community

Sustainable municipal wastewater recovery scenarios highlight benefits of anaerobic membrane bioreactors (AnMBRs). However, influences of continuous seeding by influent wastewater and temperature on attached-growth AnMBRs are not well understood. In this study, four bench-scale AnMBR operated at 10 and 25°C were fed synthetic (SPE) and then real (PE) primary effluent municipal wastewater. Illumina sequencing revealed different bacterial communities in each AnMBR in response to temperature and bioreactor configuration, whereas differences were not observed in archaeal communities. Activity assays revealed hydrogenotrophic methanogenesis was the dominant methanogenic pathway at 10°C. The significant relative abundance of Methanosaeta at 10°C concomitant with low acetoclastic methanogenic activity may indicate possible Methanosaeta-Geobacter direct interspecies electron transfer. When AnMBR feed was changed to PE, continual seeding with wastewater microbiota caused AnMBR microbial communities to shift, becoming more similar to PE microbiota. Therefore, influent wastewater microbiota, temperature and reactor configuration influenced the AnMBR microbial community.

Membrane biofilm development improves COD removal in anaerobic membrane bioreactor wastewater treatment

Membrane biofilm development was evaluated to improve psychrophilic (15°C) anaerobic membrane bioreactor (AnMBR) treatment of domestic wastewater. An AnMBR containing three replicate submerged membrane housings with separate permeate collection was operated at three levels of membrane fouling by independently controlling biogas sparging for each membrane unit. High membrane fouling significantly improved permeate quality, but resulted in dissolved methane in the permeate at a concentration two to three times the equilibrium concentration predicted by Henry's law. Illumina sequencing of 16S rRNA targeting Bacteria and Archaea and reverse transcription-quantitative polymerase chain reaction targeting the methyl coenzyme-M reductase (mcrA) gene in methanogens indicated that the membrane biofilm was enriched in highly active methanogens and syntrophic bacteria. Restoring fouled membranes to a transmembrane pressure (TMP) near zero by increasing biogas sparging did not disrupt the biofilm's treatment performance, suggesting that microbes in the foulant layer were tightly adhered and did not significantly contribute to TMP. Dissolved methane oversaturation persisted without high TMP, implying that methanogenesis in the biofilm, rather than high TMP, was the primary driving force in methane oversaturation. The results describe an attractive operational strategy to improve treatment performance in low-temperature AnMBR by supporting syntrophy and methanogenesis in the membrane biofilm through controlled membrane fouling.

Long-term (1,243 days), low-temperature (4-15 degrees C), anaerobic biotreatment of acidified wastewaters: bioprocess performance and physiological characteristics

The feasibility of long-term (>3 years), low-temperature (4-15 degrees C) and anaerobic bioreactor operation, for the treatment of acidified wastewater, was investigated. A hybrid, expanded granular sludge bed-anaerobic filter bioreactor was seeded with a mesophilic inoculum and employed for the mineralization of moderate-strength (3.75-10 kg chemical oxygen demand (COD)m(-3)) volatile fatty acid-based wastewaters at 4-15 degrees C. Bioprocess performance was assessed in terms of COD removal efficiency (CODRE), methane biogas concentration, and yield, and biomass retention. Batch specific methanogenic activity assays were performed to physiologically characterise reactor biomass. Despite transient disimprovements, CODRE and methane biogas concentrations exceeded 80% and 65%, respectively, at an applied organic loading rate (OLR) of 10 kgCODm(-3)d(-1) between 9.5 and 15 degrees C (sludge loading rate (SLR), 0.6 kgCOD kg[VSS](-1)d(-1)). Over 50% of the granular sludge bed was lost to disintegration during operation at 9.5 degrees C, warranting a reduction in the applied OLR to 3.75-5 kgCODm(-3)d(-1) (SLR, c. 0.4-0.5kgCOD kg[VSS](-1)d(-1)). From that point forward, remarkably stable and efficient performance was observed during operation at 4-10 degrees C, with respect to CODRE (>or=82%), methane biogas concentration (>70%) and methane yields (>4l(Methane)d(-1)), suggesting the adaptation of our mesophilic inoculum to psychrophilic operating conditions. Physiological activity assays indicated the development of psychroactive syntrophic and methanogenic populations, including the emergence of putatively psychrophilic propionate-oxidising and hydrogenotrophic methanogenic activity. The data suggest that mesophilic inocula can physiologically adapt to sub-optimal operational temperatures: treatment efficiencies and sludge loading rates at 4 degrees C (day, 1243) were comparable to those achieved at 15 degrees C (day 0). Furthermore, long-term, low-temperature bioreactor operation may act as a selective enrichment for psychrophilic methanogenic activity from mesophilic inocula. The observed efficient and stable bioprocess performance highlights the potential for long-term, low-temperature bioreactor operation.

Temporal microbial diversity changes in solvent-degrading anaerobic granular sludge from low-temperature (15°C) wastewater treatment bioreactors

Anaerobic sludge granules were obtained from laboratory-scale anaerobic bioreactors used to treat pharmaceutical-like (methanol-, acetone- and propanol-contaminated) wastewater under low-temperature conditions (15 degrees C). The microbial diversity and diversity changes of the sludge samples were ascertained by applying 16S rRNA gene cloning and terminal restriction fragment length polymorphism (TRFLP) analyses, respectively, and using sludge samples from the inoculum, throughout and at the conclusion of the bioreactor trial. Data from genetic fingerprinting correlated well with those from physiological activity assays of the reactor biomass. Specifically, for example, TRFLP profiles indicated the dominance of hydrogenotrophic methanogens within the archaeal community, thus supporting the findings of specific methanogenic activity measurements. TRFLP data supported the hypothesis that the deviation between the replicated reactors, in terms of treatment efficiency, was associated with succession within the microbial communities present, and indicated that community development was linked to both operating temperature and wastewater composition. Fluorescence in situ hybridization (FISH) was also applied, to quantitatively assess the abundance of selected microbial groups, and revealed the underestimation of the abundance Methanosarcina by gene cloning analysis and demonstrated the spatial arrangement of these organisms within the architecture of the low-temperature solvent-degrading anaerobic biofilms.