Biofilm Reactor Research Articles

Sulfamethoxazole removal in nitrifying membrane aerated biofilms: Physiological responses and antibiotic resistance genes.

Efficient removal of ammonia nitrogen and sulfamethoxazole (SMX) from wastewater has become increasingly critical due to their detrimental effects on aquatic ecosystems and public health. This study aimed to investigate the nitrogen transformation and SMX removal in a membrane aerated biofilm reactor (MABR) under different SMX concentrations (0 ∼ 200 μg·L-1) with a nitrifying membrane bioreactor (MBR) as a control. Results suggested that SMX removal in MABR was better than that of MBR with SMX addition (50 ∼ 200 μg·L-1). Membrane aerated biofilms tended to secrete more extracellular polymeric substances (EPS) and generate less antioxidant enzymes in response to SMX stress when compared with nitrifying sludge in MBR. Metagenomic analysis indicated that distinct succession of microbial community was observed in both systems after SMX addition, and the relative abundance of nitrifying bacteria (Nitrosomonas, Nitrospira, and Nitrobacter) evidently decreased under SMX concentration of 200 μg·L-1. The proliferation of predominant antibiotic resistance gene (ARG) sul2 was suppressed more obviously in MABR than that in MBR. Thus, this study provided extensive insights into the advantages of nitrifying MABR in simultaneous removal of ammonium and antibiotics with less risk of associated ARGs spread.

Sulfate Leached from Phosphogypsum Is Transformed in a Hydrogen-Based Membrane Biofilm Reactor

Sulfate Leached from Phosphogypsum Is Transformed in a Hydrogen-Based Membrane Biofilm Reactor

Factorial experiment to identify two-way interactions between temperature, harvesting period, hydraulic retention time, and light intensity that influence the biomass productivity and phosphorus removal efficiency of a microalgae–bacteria biofilm

ABSTRACT This study evaluated the two-way interaction and main effects of four factors on biomass productivity and phosphorus removal efficiency of a microalgae–bacteria biofilm grown in municipal anaerobic digester centrate, with factor levels and operating conditions selected to mimic a pilot rotating algae biofilm reactor (RABR) at a water resource recovery facility (WRRF) in Utah. The two-way interactions of harvesting period × light intensity (LI), harvesting period × temperature, and LI × hydraulic retention time (HRT) had significant effects on biomass productivity: At high temperature and at low LI, highest biomass productivity was achieved with a 14-day harvesting period (25.5 and 10.9 g AFDW/m2/day, respectively), but at medium temperature and at high LI, highest biomass productivity was achieved with a 7-day harvesting period (16.1 and 16.4 g AFDW/m2/day, respectively). At high HRT, highest biomass productivity occurred at low LI (11.9 g AFDW/m2/day), but at low HRT, highest biomass productivity occurred at high LI (19.3 g AFDW/m2/day). Phosphorus removal was strongly influenced by LI (>70% removal at 1,600 μmol/m2/s) and occurred most rapidly during the first 2 days HRT (e.g. 2,270 TP/m2/day for days 0–2 vs. 217 mg TP/m2/day for days 2–4), which, in combination with chemical equilibrium modeling, suggests precipitation contributed significantly to phosphorus removal in this study.

Fabrication of a PETG-Based Biocarrier Using Additive Manufacturing for Moving Bed Biofilm Reactor (MBBR) Applications

The moving bed biofilm reactor (MBBR) has been identified as a promising method for reducing water pollution. Biocarriers are important in MBBR treatment processes because they provide surface area for biofilm attachment and improve treatment efficiency. These biocarriers use decomposing microorganisms attached to their surface and have been developed in a variety of shapes, materials, and procedures. This study aims to create a biocarrier using an additive manufacturing process and a PETG (Polyethylene Terephthalate Glycol) filament as its material. The biocarrier's pore size plays a crucial role in determining its effectiveness for biofilm attachment and treatment efficiency. By modifying the net diameter of the biocarrier's design, we aimed to investigate the impact of different pore sizes on these factors. We experimented with fabricating three different sizes of the biocarrier's pore by modifying three different sizes of the net diameter of the biocarrier's design: type 1 is 1.8 ± 0.22 mm, type 2 is 1.0 ± 0.29 mm, and type 3 is 0.8 ± 0.27 mm. This research provides insights for the next step: evaluating biofilms' attachment efficiency on each type of biocarrier and comparing their performance.

Combining nonthermal N2 plasma with a denitrifying biofilm reactor for PFAS-contaminated wastewater remediation

Perfluoroalkyl and polyfluoroalkyl substances (PFAS), commonly known as ’forever chemicals,’ pose significant environmental threats to water bodies due to their persistence and toxicity. Traditional remediation methods are often ineffective or costly. In response, this study presents a novel two-step solution combining nonthermal nitrogen (N2) plasma degradation with a denitrifying biofilm reactor to treat PFAS-contaminated wastewater efficiently. Treatment by N2 plasma resulted into PFOA and PFDA degradation efficiencies up to 45% and 60%, respectively. The low cost of N2 gas makes N2 plasma more favorable (compared to e.g. Ar plasma) for practical applications. The biofilm reactor, inoculated with activated sludge and packed by expanded clay aggregates (ECA), could efficiently remove the inorganic nitrogen produced by N2 plasma. CH3COONa was utilized as a carbon source to supply energy for denitrifying bacteria. The total nitrogen (TN) removal efficiency was up to 90% at a C/N ratio of 4.0. Also, UV254 (40–50%), turbidity (80–90%) and COD (80–90%) were removed in the biofilm reactor. Due to the non-biodegradability of PFAS, their removal (initially up to 60–90%) in the biofilm reactor was attributed to ad- or absorption on sludge and ECA. The bioreactor offers a cost-effective solution to the issue of secondary inorganic nitrogen pollution caused by N2-containing plasma. This is beneficial for broadening the practical use of both N2 plasma and air plasma. The two-step process is not only applicable for treating PFAS-contaminated wastewater but can also be applied to various fields suitable for N2 and air plasma applications.

Effects of Zn(II) on the simultaneous nitrification and denitrification (SND) process: performance and microbial community

Simultaneous nitrification and denitrification (SND) is considered an attractive alternative to traditionally biological nitrogen removal technology. Knowing the effects of heavy metals on the SND process is essential for engineering. In this study, the responses of SND performance to Zn(II) exposure were investigated in a biofilm reactor. The results indicated that Zn(II) at low concentration (≤ 2 mg·L−1) had negligible effects on the removal of nitrogen and COD in the SND process compared to that without Zn(II), while the removal of ammonium and COD was strongly inhibited with an increasing in the concentration of Zn(II) at 5 or 10 mg·L−1. Large amounts of EPS, especially PN, were secreted to protect microorganisms from the increasing Zn(II) damage. High-throughput sequencing analysis indicated that Zn(II) exposure could significantly reduce the microbial diversity and change the structure of microbial community. The RDA analysis further confirmed that Azoarcus-Thauera-cluster was the dominant genus in response to low exposure of Zn(II) from 1 to 2 mg·L−1, while the genus Klebsiella and Enterobacter indicated their adaptability to the presence of elevated Zn(II). According to PICRUSt, the abundance of key genes encoding ammonia monooxygenase (EC: 1.14.99.39) was obviously reduced after exposure to Zn(II), suggesting that the influence of Zn(II) on nitrification was greater than that of denitrification, leading to a decrease in ammonium removal of SND system. This study provides a theoretical foundation for understanding the influence of Zn(II) on the SND process in a biofilm system, which should be a source of great concern.

Dual application of lotus stem in fabricating a bioreactor for the remediation of nitrate, plumbum, and carbamazepine in industrial wastewater

Addressing the treatment of complex industrial wastewater continues to be a substantial challenge within the realm of water treatment. A biofilm reactor was engineered, integrating lotus stem biochar, lotus stem biological filler, and the ZW5 strain for enhanced wastewater treatment. The removal efficiencies of nitrate (NO3--N), calcium (Ca2+), chemical oxygen demand (COD), phosphorus (PO43--P), plumbum (Pb2+), and carbamazepine (CBZ) were 98.46, 81.08, 91.79, 96.63, 97.75, and 99.26% when HRT was 3 h, pH was 7.0, Pb2+, CBZ, and influent salinity contents were 15.0, 3.0, and 1500 mg L-1. The reactor effectively fixed the microorganisms and provided a good microenvironment and niche, which was conducive to the adsorption of Pb2+ and CBZ by microorganisms and biominerals. Furthermore, the modified biochar in the reactor filler facilitated microbial metabolism and enabled indirect electron transfer. Microorganisms altered their dominant community structure in response to Pb2+ and CBZ exposure. Microorganisms maintained efficient activity through synergy and direct electron transfer through nanowires. The reactor serves as a model for pollutant removal from complex industrial wastewater, leveraging the multifaceted use of lotus stems and microbial-induced calcium precipitation.

Effect of long-term ammonia deficiency on nitrification performance and microbial dynamics in downflow sponge biofilm reactor

The downflow sponge biofilm (DSB) reactor has a promising nitrification capacity for ammonium (NH4+-N)-polluted raw water treatment. However, the highly fluctuating NH4+-N levels in raw water may pose a challenge to a stable nitrification process. It is unclear how the DSB reactor contends with NH4+-N deficiency. This study evaluated the robustness of a DSB reactor under long-term NH4+-N abundant and NH4+-N deficient conditions. Four NH4+-N deficient periods were investigated, comprising two 14-day partial NH4+-N deficient phases, one 56-day phase involving both partial and complete NH4+-N deficient, and one 90-day complete NH4+-N deficient phase. Repeated 14-day partial NH4+-N deficient phases had no impact on nitrification performance. However, shifting from partial to complete NH4+-N deficient condition resulted in a delay in NOx−-N production when NH4+-N was replenished. Following an additional 90 days of NH4+-N deficient phase, NH4+-N removal performance recovered faster than nitrite (NO2−-N) removal performance, which took 5 and 29 days, respectively. Furthermore, long-term NH4+-N deficiency resulted in a nominal loss of biomass in the DSB reactor. These findings suggested that the nitrification capacity of the DSB reactor is robust when subjected to long-term NH4+-N deficient conditions. The 16S rRNA amplicon sequencing results revealed that the growth of Nitrosomonas was suppressed, but Candidatus Nitrosotenuis predominated in NH4+-N deficient conditions, while Nitrospira persisted throughout the study. The observed persistence of Nitrospira may be attributed to their diverse metabolic capabilities, which include mixotrophy and complete ammonia oxidation metabolisms. Collectively, the co-existence of Ca. Nitrosotenius, Nitrosomonas, and Nitrospira contributed to stable NH4+-N removal performance in the robust DSB reactor. The DSB reactor shows promise for use in raw water treatment with highly fluctuating NH4+-N availability.

Performance of a pilot-scale microbial electrolysis cell coupled with biofilm-based reactor for household wastewater treatment: simultaneous pollutant removal and hydrogen production.

The septic tank is the most commonly used decentralized wastewater treatment systems for household wastewater treatment in on-site applications. The removal rate of various pollutants is lower in different septic tank configurations. The integration of a microbial electrolysis cells (MEC) into septic tank or biofilm-based reactors can be a green and sustainable technology for household wastewater treatment and energy production. In this study, a 50-L septic tank was converted into a 50-L MEC coupled with biofilm-based reactor for simultaneous household wastewater treatment and hydrogen production. The biofilm-based reactor was integrated by an anaerobic packed-bed biofilm reactor (APBBR) and an aerobic moving bed biofilm reactor (aeMBBR). The MEC/APBBR/aeMBBR was evaluated at different organic loading rates (OLRs) by applying voltage of 0.7 and 1.0V. Result showed that the increase of OLRs from 0.2 to 0.44kg COD/m3 d did not affect organic matter removals. Nutrient and solids removal decreased with increasing OLR up to 0.44kg COD/m3 d. Global removal of chemical oxygen demand (COD), biochemical oxygen demand (BOD), total nitrogen (TN), ammoniacal nitrogen (NH4+), total phosphorus (TP) and total suspended solids (TSS) removal ranged from 81 to 84%, 84 to 85%, 53 to 68%, 88 to 98%, 11 to 30% and 76 to 88% respectively, was obtained in this study. The current density generated in the MEC from 0 to 0.41 A/m2 contributed to an increase in hydrogen production and pollutants removal. The maximum volumetric hydrogen production rate obtained in the MEC was 0.007 L/L.d (0.072 L/d). The integration of the MEC into biofilm-based reactors applying a voltage of 1.0V generated different bioelectrochemical nitrogen and phosphorus transformations within the MEC, allowing a simultaneous denitrification-nitrification process with phosphorus removal.

Performance study of the bioreactor for the biodegradation of methyl orange dye by luffa immobilized Stenotrophomonas maltophilia and kinetic studies: A sustainable approach

The biodegradation of methyl orange dye was examined in a biofilm reactor with luffa immobilized Stenotrophomonas maltophilia ((HE963840.1), low-cost packing material. The bacteria were isolated from the sludge collected from a common effluent treatment plant at IOCL refinery Mathura, Uttar Pradesh. The bacteria were characterized using 16rRNA. The reactor performance was studied at 30 ± 5 oC temperatures over a period of thirty days. The reactor was operated with the flow rates of 60 mL/h, 90 mL/h, 240 mL/h, 360 mL/h and 432 mL/h. The pollutant load ranges from 151.6 mg/(L-day) to 1091 mg/(L-day) and the pH of the dye solution was maintained at 7.0 ± 0.4 during the study. The maximum removal efficiency (RE) and elimination capacity (EC) at steady state were determined as 90.2 % and 658.1 mg/(L-day) respectively. The rate of utilization of the methyl orange dye is described by modified stover-kincannon model with kinetic parameters- maximum utilization rate (Umax) and saturation constant (KB) to be 2.70 g/(L-day) and 2.34 g/(L-day) respectively. The toxicity studies confirm the non-toxic nature of the biodegraded products.

Metabolism of nitrogen and sulfamethoxazole, performance recovery mechanism, and antibiotic resistance genes (ARGs) behaviors in membrane aerated biofilm reactor (MABR)

The limited information on micro-mechanism of sulfamethoxazole (SMX) metabolism and antibiotics resistance genes (ARGs) behaviors within membrane-aerated biofilm reactor (MABR) blocked the application of MABR in treating antibiotics containing wastewater. In this work, SMX metabolism and the changes of ARGs were investigated in MABR during 0.0-0.7 mg/L SMX. The system achieved a 92.3% SMX removal at 0.7 mg/LSMX, leading to the formation of 17 lower toxic metabolites, which indicated the robust SMX biodegradation capability of MABR. The metabolic pathways of SMX in MABR were first elucidated, revealing key processes including isoxazole ring opening (primarily in anaerobic zones), aniline hydroxylation, and cleavage of the S-N bond in the sulfonyl group. Microbial analysis revealed the involvement of multiple microbes in SMX biodegradation, and among these, sulfate-reducing bacteria (SRB; Desulfovibrio, Desulforhopalus, Desulfomicrobium) facilitated the isoxazole ring opening in the anaerobic zone, while Rhizobium and Chryseobacterium contributed to ipso-hydroxylation and cleavage of the -C-S-N bond in SMX, respectively. Furthermore, the slower accumulation of ARGs under SMX conditions was primarily attributed to the enhanced efflux pump activity, antibiotic target replacement mechanisms, and secretion of extracellular polymeric substances (EPS), suggesting the potential of MABR to inhibit ARG proliferation. Our research filled the knowledge gap in the micro-mechanism of SMX metabolism and ARGs fate within MABR processing SMX-containing wastewater, laying a theoretical foundation for the broader application of MABR in practical engineering.

Optimizing anoxic/oxic intervals in intermittent aeration for STHP-AD filtrate treatment: Restoring partial nitrification and community dynamics in the SPNAD system

Currently, partial nitrification (PN) processes are commonly used to improve efficiency in high ammonia nitrogen wastewaters. However, initiating and restoring damaged PN performance is crucial for optimizing nitrogen removal efficiency without the use of chemical additives. In this study, a simultaneous partial nitrification and denitrification coupled with anammox (SPNAD) sequencing batch biofilm reactor was constructed to treat anaerobic digestion after sludge thermal hydrolysis pretreatment (STHP-AD) filtrate. The PN performance was successfully recovered through optimizing the operation mode of anoxic/oxic alternation within 120 days. Result showed that Nitrosomonas increased from 0.68 % to 3.43 %, while Nitrospira decreased to 0.06 %. The PN recovery also promoted anammox, with the only anammox bacterium of Candidatus Brocadia, detected in the mixing and biofilm sludge of 1.73 % and 1.41 %, respectively. The autotrophic denitrifying bacteria Thermomonas (increasing from 0.47 % to 23.85 %) and Truepera (rising from 2.31 % to 6.54 %) rapidly accumulated. After adjusting to the anoxic/oxic alternation ratio, the hydraulic retention time was shortened from 50 h to 37.5 h, and the oxic time was reduced to half of the initial operation. The PN recovery and anammox enrichment resulted in improving nitrogen removal approximately 20 %. Eventually, the SPNAD system realizes stable and efficient nitrogen removal with the influent nitrogen loading rate of 0.43 kgN/(m3·d), the ammonium removal efficiency of 94.73 ± 3.27 %, and the nitrogen removal efficiency of 72.98 ± 1.27 %. In this study, a new strategy using intermittent aeration while appropriately extending the oxic time was proposed to restore the system’s ability to treat STHP-AD filtrate after PN disruption.

Vanadium bioreduction in an ethane-based membrane biofilm reactor: Performance and mechanism

Vanadium (V(V)) contamination in groundwater poses a serious threat to human health. V(V) bioreduction is an effective method for vanadium contamination remediation. This study confirmed that ethane (C2H6) as an electron donor could realize efficient V(V) bioreduction. V(V) reduction by C2H6-based membrane biofilm reactor was enhanced with the increase of V(V) loading in the influent. Vanadium in the biofilm was mainly present as V(IV) precipitation. The C2H6-oxidizing bacteria Mycobacterium and Methylocystis used alkane 1-monooxygenase, alcohol dehydrogenase, and aldehyde dehydrogenase to generate metabolic intermediates, such as ethanol, acetaldehyde, and acetic acid, with the participation of O2, which were then utilized by V(V)-reducing bacteria Geothrix and Rudaea to reduce V(V) to V(IV) intracellularly and extracellularly under nicotinamide adenine dinucleotide (NADH) and cytochrome-c oxidase. This result could promote the application of C2H6 in the ex-situ remediation of V(V)-contamination groundwater.

Impact of carbon/nitrogen ratio on sequencing batch biofilm reactors initiated with different seed sludges for treating actual mariculture effluents

Impact of carbon/nitrogen ratio on sequencing batch biofilm reactors initiated with different seed sludges for treating actual mariculture effluents

Achieving efficient autotrophic nitrogen removal in anaerobic membrane bioreactor plus membrane aerated biofilm reactor by regulating nutrient ratios.

It is feasible to integrate an anaerobic membrane bioreactor with a membrane aerated biofilm reactor to efficiently implement the sulfate reduction, simultaneous nitrification and autotrophic denitrification process. However, the effect of parameters on nutrient removal and environmental impacts of the process are unclear. In this study, the reactor performance was mainly influenced by the chemical oxygen demand to sulfate (COD/S) ratio and the ammonium to sulfate (N/S) ratio in long-term operation. Significant models were developed to optimize the two factors using the response surface methodology. Under optimal conditions (COD/S ratio of 2.5 and N/S ratio of 0.3), the system could remove above 86 % COD, 99 % ammonium, and 92 % total inorganic nitrogen. Moreover, this process could reduce energy consumption by 30 % and global warming potential by 50 % compared with traditional anaerobic/oxic activated sludge process. These findings provide guidance for the application of this technology in sulfate-containing municipal sewage treatment.

Influence of oxygen transfer performance on nitrogen metabolism and microbial community structure in an aerobic fluidized bed biofilm reactor under different aeration aperture

Influence of oxygen transfer performance on nitrogen metabolism and microbial community structure in an aerobic fluidized bed biofilm reactor under different aeration aperture

Insights into the efficiencies of different biological treatment systems for pharmaceuticals removal: A review.

This review presents a comprehensive analysis of current research on biological treatment processes for removing pharmaceutical compounds (PhCs) from wastewater. Unlike previous studies on this topic, our study specifically delves into the effectiveness and drawbacks of various treatment approaches such as traditional wastewater treatment facilities (WWTP), membrane bioreactors (MBRs), constructed wetlands (CW), and moving bed biofilm reactors (MBBR). Through the examination and synthesis of information gathered from more than 200 research studies, we have created a comprehensive database that delves into the effectiveness of eliminating 19 particular PhCs, including commonly studied compounds such as acetaminophen, ibuprofen, diclofenac, naproxen, ketoprofen, indomethacin, salicylic acid, codeine, and fenoprofen, amoxicillin, azithromycin, ciprofloxacin, ofloxacin, tetracycline, atenolol, propranolol, and metoprolol. This resource provides a depth and scope of information that was previously lacking in this area of study. Notably, among these pharmaceuticals, azithromycin demonstrated the highest removal rates across all examined treatment systems, with the exception of WWTPs, while carbamazepine consistently exhibited the lowest removal efficiencies across various systems. The analysis showcases the diverse results in removal efficiency impacted by factors such as system configuration, operation specifics, and environmental circumstances. The findings emphasize the critical need for continued innovation and research, specifically recommending the integration of advanced oxidation processes (AOPs) with existing biological treatment methods to improve the breakdown of recalcitrant compounds like carbamazepine. PRACTITIONER POINTS: Persistent pharmaceuticals harm aquatic ecosystems and human health. Biological systems show varying pharmaceutical removal efficiencies. Enhancing HRT and SRT improves removal but adds complexity and costs. Tailored treatment approaches needed based on contaminants and conditions.

Comammox Nitrospira was the dominant ammonia oxidizer in an acidic biofilm reactor at pH 5.5 and pH 5.

Nitrification is a vital process in the biological removal of inorganic nitrogen compounds. In order to ensure the stability and effectiveness of this process, buffer solutions should be added to the system to maintain neutral to slightly alkaline conditions. With a focus on the newly discovered comammox Nitrospira, this research investigates the transition of the nitrifying community within a biofilm reactor under different acidic levels (initiated at pH 6 and gradually decreased to pH 5). During the 305-day continuous operation experiment, it was observed that responsible ammonia oxidizers transitioned from ammonia-oxidizing bacteria (AOB) during the initial stages (setup stage and early stage of pH 6) to comammox Nitrospira under pH 5.5 and pH 5. Further analysis using next-generation sequencing targeting both the 16S rRNA region and amoA region revealed a shift in the dominant cluster of both Nitrospirae and comammox Nitrospira under varying pH conditions. Our study identified a distinct cluster of comammox Nitrospira that is phylogenetically closed to sequences found in acidic environments, but exhibits dissimilarity from known comammox Nitrospira isolates and the majority of environmental sequences. This cluster was found to be prevalent in the acidic biofilm reactor studied and thrived particularly well at pH 5. These findings underscore the potential significance of this distinct, uncultivated group of comammox Nitrospira in performing ammonia oxidation under acidic conditions. KEY POINTS: • Ammonia was effectively removed under pH 5.5 and 5 in the biofilm reactor • The dominant ammonia oxidizer was comammox Nitrospira when pH was 5.5 and 5 • A potential acidophilic cluster of comammox Nitrospira was identified in this acidic biofilm reactor.

Track of methylparaben in the bulk phase and on the extracellular matrix of dual-species biofilms: Biodegradation and bioaccumulation

Methylparaben (MP) is a preservative considered an environmental contaminant of emerging concern due to its persistence in water sources, including drinking water (DW). This study assesses the interaction between MP and dual-species biofilms of Acinetobacter calcoaceticus and Stenotrophomonas maltophilia. These biofilms were grown under realism-based conditions in a multiple-cylinder biofilm reactor on polypropylene (PPL) surfaces, for 7 days, and then exposed to MP at 0.5 mg/L for three consecutive days. S. maltophilia predominantly succeeds within these biofilms compared to A. calcoaceticus. Exposure to MP resulted in a 4-fold increase in the number of culturable cells and a 1.4-fold rise in polysaccharide content, suggesting that bacterial cells may utilize MP as a carbon source to enhance biofilm fitness. MP was found to adsorb to PPL with biofilms following a pseudo-second-order kinetic model. Circa 37 % of MP adsorbed to PPL after 3 days of exposure. Besides that, MP was biodegraded by biofilms following an apparent first-order kinetic model. Part (25 %) of the MP was biodegraded whereas only 0.02 % bioaccumulated on the biofilm matrix. Biodegradation was related to esterase and lipase activity. The results provide new insights into the interaction between MP with biofilms and materials used in DW industries.

Removal of selenate from wastewater using a bioelectrochemical reactor: The importance of measuring selenide and the role of competing anions

Removal of selenate (SeO42-) from selenate-contaminated wastewater is challenging due to the commonly co-existing and competing anions of sulfate (SO42-) and nitrate (NO3-). This study investigates SeO42− reduction to elemental selenium (Se0) in a cathode-based bioelectrochemical (BEC) reactor and a conventional biofilm reactor (i.e., an upflow anaerobic reactor). The simulated wastewater contained SeO42− at a typical concentration of 5 mg Se/L, SO42− at a typical concentration of 1000 mg S/L, and NO3− at concentrations that varied from 0 to 10 mg N/L. The impact of sulfate on the BEC reactor was much lower than that on the conventional reactor: The selenium removal, defined as (selenate in influent – dissolved selenium in effluent)/selenate in influent, was 99 % in the BEC reactor versus 69 % in the conventional biofilm reactor. The lower selenium removal in the conventional reactor was mainly due to the >10 times higher reduction of sulfate, which directly caused competition between sulfate and selenate for the common resources such as electrons. The more reduction of sulfate in the conventional reactor further led to 45 times higher production of selenide. Selenide is usually assumed to be minimal and therefore not measured in the literature. This simplification may significantly overestimate selenium removal when the influent sulfate concentration is very high. NO3- in the influent of the BEC reactor promoted selenium removal when it was less than 5.0 mg N/L but inhibited selenate removal when it was more than 7.5 mg N/L. This was supported by the microbial community analysis and intermediate (nitrite) analysis.