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

Understanding the sorption and biotransformation of organic micropollutants in innovative biological wastewater treatment technologies

New technologies for wastewater treatment have been developed in the last years based on the combination of biological reactors operating under different redox conditions. Their efficiency in the removal of organic micropollutants (OMPs) has not been clearly assessed yet. This review paper is focussed on understanding the sorption and biotransformation of a selected group of 17 OMPs, including pharmaceuticals, hormones and personal care products, during biological wastewater treatment processes. Apart from considering the role of “classical” operational parameters, new factors such as biomass conformation and particle size, upward velocity applied or the addition of adsorbents have been considered. It has been found that the OMP removal by sorption not only depends on their physico-chemical characteristics and other parameters, such as the biomass conformation and particle size, or some operational conditions also relevant. Membrane biological reactors (MBR), have shown to enhance sorption and biotransformation of some OMPs. The same applies to technologies bases on direct addition of activated carbon in bioreactors. The OMP biotransformation degree and pathway is mainly driven by the redox potential and the primary substrate activity. The combination of different redox potentials in hybrid reactor systems can significantly enhance the overall OMP removal efficiency. Sorption and biotransformation can be synergistically promoted in biological reactors by the addition of activated carbon. The deeper knowledge of the main parameters influencing OMP removal provided by this review will allow optimizing the biological processes in the futureThis research was supported by the Spanish Government (AEI) through the Projects COMETT (CTQ2016-80847-R) and HOLSIA (CTM2013-46750-R). The authors belong to the Galician Competitive Research Group GRC2013-032 and to the CRETUS Strategic Partnership (AGRUP2015/02)S

Trends in organic micropollutants removal in secondary treatment of sewage

This is a post-peer-review, pre-copyedit version of an article published in Reviews in Environmental Science and Bio/Technology volume. The final authenticated version is available online at: https://doi.org/10.1007/s11157-018-9472-3Organic micropollutants (OMPs) comprise a wide group of substances highly consumed in modern societies. There has been a growing social and scientific interest on OMPs in wastewaters in the twentyfirst century. This research paper has identified the evolution of the research trends in the period 2001–2017 on OMPs fate during secondary wastewater treatment. These trends have moved from a global perspective on the occurrence of OMPs in wastewaters to more specific research focussed on understanding their behaviour during advanced treatment processes. Based on a bibliometric analysis carried out using one of the leading scientific databases, pharmaceuticals have been identified as the main group of OMPs. An increasing number of publications have been released on the fate of pharmaceuticals in wastewater with a growing number of countries involved: from 38 publications belonging to 14 countries in first 5-year period analysed (2001–2005) up to 138 from 42 countries only in the last 2 years (2016–2017). The main operational conditions in wastewater treatment plants influencing the removal of OMPs, as well as the mechanisms involved depending on the physico-chemical characteristics of the substances are reviewed. The paper also considers the role of microbial populations, as well as technological and operational features in OMPs abatement. Finally, a specific section is dedicated to the metabolic and cometabolic biotransformations of some OMPs taking place under heterotrophic, nitrifying and anaerobic conditions, a more novel research trend explored more recentlyThis research was supported by the Ministerio de Economía y Competitividad (AEI) through the Project COMETT (CTQ2016-80847-R). The authors belong to the Galician Competitive Research Group GRC2013-032 and to the CRETUS Strategic Partnership (AGRUP2015/02). All these programs and project are co-funded by FEDER (UE)S

Integrating granular activated carbon in the post-treatment of membrane and settler effluents to improve organic micropollutants removal

Granular activated carbon (GAC) is applied as post-treatment technology in wastewater treatment plants (WWTPs) in order to increase the elimination of organic micropollutants (OMPs). However, the efficiency and life-time of GAC depend on several parameters, such as the quality of the effluent to be treated or the type of GAC. In the present paper, two types of GAC, based on bituminous carbon (BC-GAC) and coconut shell (CS-GAC), were assessed from a technical, economic and environmental point of view to further remove OMPs present in two secondary effluents, coming from integrated biological systems with a membrane or a settler, respectively. Although all GAC filters were efficient in removing selected OMPs, the quality of the secondary effluent had a strong influence on the lifespan of adsorbent material and the technical operability of the filtration systems. While GAC filters treating membrane effluent were highly effective to remove recalcitrant compounds, such as carbamazepine and diazepam (>80%), even after 430 d of operation (>30,800 BV), the efficiency of GAC filters treating settler effluent quickly lowered to 50% after 100 d of operation (<7200 BV). Both types of GAC showed similar adsorption capacities and only slight differences were found in terms of costs (2.4 €/kg vs 2.7 €/kg). However, CS-GAC has a lower carbon footprint than BC-GAC, mainly due to the more environmentally friendly production process of CS-GACThis research was supported by the Spanish Government (AEI – Spain) through the projects HOLSIA (CTM2013-46750-R) and COMETT (CTQ2016-80847-R). The authors belong to the Galician Competitive Research Group GRC ED431C2017/29 and to the CRETUS Strategic Partnership (AGRUP2015/02). All these programmes are co-funded by FEDER (EU)S

Influence of metabolism and microbiology on organic micropollutants biotransformation in anoxic heterotrophic reactors

There is scarce information about the biotransformation of organic micropollutants (OMPs) under anoxic conditions. In this study, a heterotrophic denitrifying bioreactor was set up to study the fate of several OMPs from metabolic and microbiological points of view. Primary metabolic activity was increased by adding progressively higher nitrogen loading rates during the operation (from 0.075 to 0.4 g N-NO3- L−1 d−1), which resulted in an important shift in the microbial population from a specialized biomass to a more diverse community. Such a change provoked a significant increase in the removal efficiency of erythromycin (ERY), roxithromycin (ROX) and bisphenol-A (BPA), and some bacterial taxa, such as Rhodoplanes, were identified as possible indicators related to the biodegradation of these compounds. The increasing primary metabolic activity in the reactor did not enhance the OMP-specific removal rates, suggesting that the bacterial composition is more influential than cometabolismThis research was supported by the Spanish Research State Agency (AEI) through ANTARES (PID2019–110346RB-C21) project. M. Martinez-Quintela would also like to express his gratitude to the same agency for awarding a research scholarship (BES-2017–080503). All authors belong to the Galician Competitive Research Groups (GRC)_ ED431C-2021/37S

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

How should ecohazard of micropollutants in wastewater be gauged? Using bioassays to profile alternative tertiary treatments

The research on emerging pollutants in wastewater has become a worldwide issue of increasing environmental concern, especially considering the growing interest in wastewater reuse. However, the latter implies additional post-treatment after the conventional activated sludge processes, in order to produce a safer effluent. Our work aimed at determining the efficiency of reducing the toxicity associated with organic micropollutants (OMPs) in secondary wastewater effluents, using 3 different post-treatment technologies (granular activated carbon (GAC), sand biofiltration and UV irradiation): in particular, target chemical analysis of the OMPs most commonly founded in wastewater was coupled with effect-based assays (estrogenicity and mutagenicity). While chemical analysis assessed satisfactory performances for all 3 technologies in the abatement of selected OMPs, biological assays evidenced another perspective: both GAC and sand biofilters were significantly able to make the estrogenic load plummet; however, the UV system was ineffective in estrogenicity abatement, and its effluent exhibited also a slight mutagenicity, likely due to photo-transformation by-products. These results indicate that a synergistic combination of chemical analysis and biological assays can drive to a proper gauging of post-treatment technologies, taking into account not only the removal of OMPs, but also their overall toxicityThis work was conceived within a Short Term Scientific Mission (STSM) of the Water2020 Cost Action ES1202: Conceiving Wastewater Treatment in 2020 | Energetic, environmental and economic challenges. Authors from Universidade de Santiago de Compostela belong to the Galician Competitive Research Group GRC 2013-032 and to the CRETUS Strategic Partnership (AGRUP2015/02). All these programmes are co-funded by FEDER (UE)S

Impact of dissolved sulfide on a hybrid membrane bioreactor treating the effluent of a mainstream up-flow anaerobic sludge blanket

Despite being toxic to some microbes in wastewater treatment, sulfide can also promote nitrogen removal through sulfide-oxidizing bacteria. This study evaluates the dissolved sulfide impact on a hybrid MBR treating the effluent of a mainstream UASB. A UASB-MBR (176 L) was fed with synthetic domestic sewage and operated for 154 days. Two periods were distinguished, one without (Period I) and one with (Period II) sulfide dissolved in the UASB effluent. Dissolved methane, COD, nitrogen, and organic micropollutants (OMP)s removals accomplished in the MBR during both periods were compared. Initially, sulfide inhibited methane removal, but once fully oxidized into sulfate in the anoxic compartment, the efficiencies recovered to similar levels as without sulfide (>70%). Sulfide additions significantly enhanced the MBR denitrification potential through sulfide-oxidizing bacteria, with improved removals in Period II (63.4 TN Lfeed−1) compared to Period I (40 mg TN Lfeed−1). Most of the nitrogen removal occurred in the anoxic compartment of the MBR, however, up to 21% of the nitrogen was denitrified in the aerobic compartment within the biofilm carriers. Aerobic methane oxidation coupled with denitrification, heterotrophic denitrifiers, sulfide oxidation, and anammox processes were involved in the nitrogen removal. COD and OMPs removals were not affected by sulfideThis research was supported by the Ministry of Science, Innovation and Universities of Spain through the Antares project (PID2019-110346RB-C21). Tomás Allegue extends his appreciation to the Ministry of Economy and Competitiveness (Spain) for granting him a research scholarship (BES-2014-069114). The authors are part of the Galician Competitive Research Groups (GRC) ED431C-2021/37S

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

Cometabolic removal of organic micropollutants by enriched nitrite-dependent anaerobic methane oxidizing cultures

The innovative and recently discovered n-damo process, based on anaerobic methane oxidation with nitrite, was developed in a membrane-based bioreactor and evaluated in terms of organic micropollutants (OMPs) removal. The main singularity of this study consisted in the evaluation of organic micropollutants (OMPs) removal in the biological reactor. A strategy consisting on progressively increasing the nitrogen loading rate in order to increase the specific denitrification activity was followed to check if the selected OMPs were co-metabolically biotransformed. Significant nitrite removal rate (24.1 mg N L−1 d−1) was achieved after only 30 days of operation. A maximum specific removal of 186.3 mg N gVSS−1 d−1 was obtained at the end of the operation, which is one of the highest previously reported. A successfully n-damo bacteria enrichment was achieved, being Candidatus Methylomirabilis the predominant bacteria during the whole operation attaining a maximum relative abundance of about 40 %. The natural hormones (E1 and E2) were completely removed in the bioreactor. The specific removal rates of erythromycin (ERY), fluoxetine (FLX), roxithromycin (ROX) and sulfamethoxazole (SMX) were successfully correlated with the specific nitrite removal rates, suggesting a co-metabolic biotransformationThis research was carried out with the financial support received from Spanish Ministry of Economy and Competitiveness through the project COMETT (CTQ2016-80847-R), co-funded by FEDER. M. Martínez would also like to express his gratitude to the same Ministry for awarding a research scholarship (BES-2017-080503). The authors belong to the Galician Competitive Research Group GRC (ED431C 2017/29), programme co-funded by FEDER, and to CRETUS Strategic Partnership (ED431E 2018/01)2022-07-12S