Enrichment of nitrite-dependent anaerobic methane oxidizing bacteria in a membrane bioreactor

The use of nitrite-dependent anaerobic methane oxidation (n-damo) processes could represent an innovative technology in order to minimize the environmental impact of anaerobic sewage effluents at low temperatures, since these biological processes are able to simultaneously remove nitrite and dissolved methane in anaerobic conditions. Nevertheless, n-damo bacteria are well-known by their reported low activity and slow doubling times which hinders a practical application. On this study, the enrichment on these bacteria was successfully achieved in a membrane bioreactor system at 28 °C. Despite biomass accumulation was not detected, a high apparent specific n-damo activity of 95.5 mg NO2−-N g−1 MLVSS d−1 was achieved after 388 days of operation, being one of the highest nitrite removal rates reported in the literature for n-damo cultures to date. Additionally a slow doubling time of 11.5 d was estimated. 16S rRNA gene amplicon sequencing analysis indicated that Candidatus Methylomirabilis became the most abundant bacterial organism by day 344 with a relative abundance of 50.2%. During the entire experiment ammonium was continuously added to the system as an alternative nitrogen source, to avoid biomass growth limitations. Finally, a relation between permeate nitrite concentrations and nitrous oxide production was found, which allows to optimize the process in terms of the minimization of both nitrogen species. The nitrous oxide emissions represented between 0 and 3.7% of the denitrified nitrogenThe authors acknowledge the financial support received from Spanish Ministry of Economy and Competitiveness through the projects HOLSIA and COMETT (CTM2013-46750-R & CTQ2016-80847-R), both co-funded by FEDER. T. Allegue would also like to express his gratitude to the same Ministry for awarding a research scholarship (BES-2014-069114). The authors belong to the Galician Competitive Research Group GRC 2013-032, programme co-funded by FEDER, and to CRETUS (AGRUP2015/02)S

An innovative wastewater treatment technology based on UASB and IFAS for cost-efficient macro and micropollutant removal

An innovative process based on the combination of a UASB reactor and an IFAS system is proposed in order to combine different redox conditions and biomass conformations to promote a high microbial diversity. The objective of this configuration is to enhance the biological removal of organic micropollutants (OMPs) as well as to achieve the abatement of nitrogen by using the dissolved methane as an inexpensive electron donor. Results showed high removals of COD (93%) and dissolved methane present in the UASB effluent (up to 85%) was biodegraded by a consortium of aerobic methanotrophs and heterotrophic denitrifiers. Total nitrogen removal decreased slightly along the operation (from 44 to 33%), depending on the availability of electron donor, biomass concentration, and configuration (floccules and biofilm). A high removal was achieved in the hybrid system (>80%) for 6 of the studied OMPs. Sulfamethoxazole, trimethoprim, naproxen, and estradiol were readily biotransformed under anaerobic conditions, whereas ibuprofen or bisphenol A were removed in the anoxic-aerobic compartment. Evidence of the cometabolic biotransformation of OMPs has been found, such as the influence of nitrification activity on the removal of bisphenol A, and of the denitrification activity on ethinylestradiol removalThis research was supported by the Spanish Government (AEI) through the Project COMETT (CTQ2016-80847-R). The authors belong to the Galician Competitive Research GroupGRC-ED431C 2017/29 and to the CRETUS Strategic Partnership (AGRUP2015/02). All these programs and project are co-funded by FEDER (UE)S

Simultaneous nitrogen and dissolved methane removal from an upflow anaerobic sludge blanket reactor effluent using an integrated fixed-film activated sludge system

One of the main drawbacks of upflow anaerobic sludge blanket (UASB) reactors that treat low-strength sewage at room temperature is related to the low quality of their effluents in terms of dissolved methane, organic matter, and nitrogen content. The present study aims to evaluate the feasibility of using an integrated fixed-film activated sludge (IFAS) system as an alternative post-treatment technology to mitigate the environmental impact of such effluents. For this purpose, a pilot plant composed of a UASB (120 L) followed by an IFAS (66 L) system was operated for 407 days. Special attention was paid to the suspended biomass retention capacity and the dissolved methane and nitrogen removal potential of the IFAS post-treatment system. Furthermore, the role of carriers on denitrification and nitrification processes and the microbial communities present in the biofilm were also analyzed. Average total chemical oxygen demand (CODT) and ammonium removal efficiencies of 92 ± 3% and around 57 ± 16% were attained throughout the entire operation, respectively. During a first period in which biomass was maintained in both biofilms and suspension, and nitrite was the main electron acceptor, maximum nitrogen removal and methane removal efficiencies of 32.5 mg TN L-1 and 93% were observed in the IFAS system, respectively. However, throughout the second period, in which suspended biomass was completely washed out from the IFAS system, and nitrate became the main electron acceptor, these values decreased to 18 ± 4 mg TN Lfeed-1 and 77 ± 12%, respectively. Surprisingly, throughout the entire operation, it was observed that around 50 and 41% of the total nitrogen and methane removals observed in the IFAS system, respectively, were carried out in the aerobic compartment. Aerobic methane oxidizers and anammox were detected with significant relative abundances in the biofilm carriers used in the anoxic and aerobic compartments using 16S rRNA gene amplicon sequencing analysis. Therefore, the use of an IFAS system could be suited to diminish greenhouse gas emissions and nutrients concentration for those sewage treatment plants that used UASB systems, especially in countries with temperate and warm climatesThis research was supported by the Ministry of Economy and Competitiveness of Spain through the COMETT project (CTQ2016-80847-R) and by the Ministry of Education and Science of Spain through the Red Novedar project (CTQ2014-51693-REDC). T. Allegue would also like to express his gratitude to the Ministry of Economy and Competitiveness of Spain for awarding a research scholarship (BES-2014-069114). The authors belong to the Galician Network of Environmental Technologies (ED341D R2016/033) and to the CRETUS Strategic Partnership (ED431E 2018/01), financed by the Galician GovernmentS

Operating strategies to optimize a membrane bioreactor enriched in nitrite-dependent anaerobic methane-oxidizing bacteria

The use of N-damo bacteria, which can simultaneously remove nitrite and dissolved methane, could represent a cost-effective and sustainable alternative to minimize the environmental impact of effluents from methanogenic reactors treating domestic sewage. The operation of N-damo bacteria reactors is often not stable, and their activity decrease with no proven reason over time. This study aims to optimize the nitrite removal capacity of a lab-scale MBR by using different operating strategies for 878 days. The reactor was operated in continuous mode and with biomass highly enriched in these microbes. It was found that adjustments in the mineral medium concentration (reduction of Ca, P, and K) and composition (EDTA addition, increasing the Cu and Fe bioavailability), contributed to achieving remarkable and prolonged nitrite removal rates of up to 285.7 mg NO2–-N/L/d. N-damo bacteria dominated the culture, up to 57 %. To the best of our knowledge, the rates attained are the highest reported in an N-damo bacteria enrichmentThe authors acknowledge the financial support received from the Spanish Ministry of Science and Innovation through the project ANTARES (PID2019-110346RB-C21), co-funded by FEDER. T. Allegue would also like to express his gratitude to the same Ministry for awarding a research scholarship (BES-2014-069114). The authors belong to the Galician Competitive Research Groups (GRC) ED431C-2021/37, a program co-funded by FEDERS