Three-dimensional Biofilm Electrode Reactors Research Articles

Enhanced denitrification by graphene oxide–modified cathode for the secondary effluent of wastewater treatment plants in three-dimensional biofilm electrode reactors

ABSTRACT In this study, a novel three-dimensional biofilm electrode reactor (3D-BER) with a graphene oxide (GO)–modified cathode was developed to enhance the denitrification performance of secondary effluent from wastewater treatment plants (SEWTPs). The effects of different hydraulic retention times (HRTs) and currents on the 3D-BER were explored. The results indicated that at the optimal HRT of 4 h and current of 350 mA/m2, the 3D-BER with GO-modified cathode had a higher denitrification rate (2.40 ± 0.1 mg TN/L/h) and less accumulation of intermediate products, especially with 3.34% total nitrogen (TN) molar conversion to N2O. The GO-modified cathode offered a large biocompatible specific surface area and enhanced the conductivity, which favored microbial growth and increased electron transfer efficiency and extracellular enzyme activities. Moreover, the activity of nitrite reductase increased more than that of nitrate reductase to accelerate nitrite reduction, thus facilitating the denitrification process. The proposed 3D-BER provided an effective solution to elevate tertiary denitrification in the SEWTP.

Denitrification reaction performance in three-dimensional biofilm electrode reactors using self-releasing carbon biofilm electrodes

Agricultural waste, corncobs, and sponge iron were used to develop a self-releasing carbon biofilm electrode (SRC-BE) and utilized for denitrification experiments in three-dimensional biofilm electrode reactors (3D-BERs). Fe2+ was released to enhance the extracellular electron transfer. Following an alkali treatment, SRC-BE were introduced into 3D-BERs of the electrode group (EG), with iron serving as the anode-cathode plate in the EG. Under a current density of 0.1 mA/cm2, hydraulic retention time of 2 h, and dissolved oxygen control at 0.5–1.0 mg/L, the removal rates were as follows: the highest removal rates were 71.09 % for total nitrogen, 40.26 % for NH4+-N, and 84.34 % for NO3−-N, with a stable 96.87 % removal rate for total phosphate. The effluent chemical oxygen demand in the EG remained stable at approximately 12 mg/L during the stable phase, thus reducing the risk of secondary pollution. The enrichment of electroactive microorganisms and functional genes related to C and N also verified their denitrification efficacy.

Enhanced nitrogen removal in low-carbon saline wastewater by adding functional bacteria into Sesuvium portulacastrum constructed wetlands

Functional bacterial communities (FBC) have members of different taxonomic biochemical groups, such as N2-fixation, nitrification and denitrification. This study explored the mechanism of the FBC from an upflow three-dimensional biofilm electrode reactor on enhancing the nitrogen removal efficiencies in a Sesuvium potulacastum (S. potulacastum) constructed wetland. There were high abundances of denitrifying bacteria detected in the FBC, and they had potential metabolic processes for nitrogen reduction. In the constructed wetland, cellular nitrogen compounds of S. potulacastum were enriched by overexpressed differentially expressed genes (DEGs), and the napA, narG, nirK, nirS, qnorB, and NosZ genes related to the denitrification process had more copies under FBC treatment. Nitrogen metabolism in root bacterial communities (RBCs) was activated in the FBC group compared with the control group without FBC. Finally, these FBCs improved the removal efficiencies of DTN (dissolved total nitrogen), NO3¯­N, NO2¯­N, and NH4+-N by 84.37 %, 87.42 %, 67.51 %, and 92.57 %, respectively, and their final concentrations met the emission standards of China. These findings indicate that adding FBC into S. potulacastum-constructed wetlands would result in high nitrogen removal efficiencies from wastewater and have large potential applications in further water treatment technology.

Three-Dimensional Biofilm Electrode Reactors with a Triple-Layer Particle Electrode for Highly Efficient Treatment of Micro-Polluted Water Sources

Micro-polluted water, which is widespread in rural areas, poses a serious health risk. To address this issue, we propose a three-dimensional biofilm electrode reactor with triple-layer particle electrodes (TL-BERs) for the decentralized and small-scale treatment of micro-polluted water. The first and second layers of the electrode, granular activated carbon (GAC) and biological ceramsite (BC), respectively, are responsible for electric field oxidation and microbial degradation, respectively, while the third, quartz sand (QS), is responsible for further improving turbidity and pollutant removal. Our tests indicated that the TL-BER-treated effluent met the drinking water quality standards of China. At 10 V, the average turbidity, CODMn, NH4+-N, and UV254 removal rates of the TL-BERs system were 97.66%, 61.11%, 91.67%, and 72.94%, respectively. Furthermore, the intensities of the main fluorescence peaks, A, B, C, and D, of the raw water sample, decreased by 36.67%, 66.22%, 67.08%, and 69.76%, respectively, after treatment, indicating that tryptophan-like proteins, fulvic acid, and humic acid were also effectively removed. High-throughput sequencing analysis showed the enrichment of microorganisms, such as Proteobacteria, Bacteroidota, and Actinobacteriota, which play important roles in the removal of various pollutants. Therefore, the application of this strategy will enable the practical treatment of micro-polluted water.

Nano α-Fe2O3 Self-Assembled Hybrid Biofilm Boosts Hydrogen Autotrophic Denitrification in a Three-Dimensional Biofilm Electrode Reactor

The performance of three-dimensional biofilm electrode reactors (3D-BERs) in hydrogen autotrophic denitrification is determined by electroactive biofilms. Herein, a self-assembled hybrid biofilm (SAHB) is developed on granular activated carbon particle electrodes by incorporating nano α-Fe2O3. The influences of operating parameters such as current, influent concentration, and hydraulic retention time (HRT) on denitrification are investigated as well as the mechanisms of SAHB-improved denitrification. The results indicate that SAHB achieves a high autotrophic denitrification rate of 4.20 mg TN/L/h under 40 mA current, 100 mg/L nitrate, and 26 h HRT, outperforming the naturally formed biofilm by 23.53%. SAHB contains more microorganisms than naturally formed biofilms, revealing that nano α-Fe2O3 is conducive to trapping free microorganisms on particle electrodes. SAHB enriches denitrification-related genes and increases corresponding enzyme activities (particularly nitrite reductase). According to metagenomic sequencing, nano α-Fe2O3 addition at a current level of 40 mA appears to favor denitrification via the nirS-dependent pathway probably due to its high affinity for cytochrome C. Metagenomic binning reveals that the microorganism associated with Zoogloeaceae (Rhodocyclales order) in SAHB may play a pivotal role in hydrogen autotrophic denitrification. This work develops a novel denitrification system, furthering our understanding of hydrogen autotrophic denitrification in 3D-BERs.

Study of a three-dimensional biofilm-electrode reactor (3D-BER) that combined heterotrophic and autotrophic denitrification (HAD) to remove nitrate from water.

A three-dimensional biofilm-electrode reactor (3D-BER) that combined heterotrophic and autotrophic denitrification (HAD) was developed to remove nitrate. The denitrification performance of the 3D-BER was evaluated under different experimental conditions, including current intensities (0-80 mA), COD/N ratios (0.5-5), and hydraulic retention times (2-12 h). The results showed that excessive current limited the nitrate removal efficiency. However, a longer hydraulic retention time was not required to achieve a better denitrification effect in the 3D-BER. Moreover, the nitrate could be effectively reduced over a broad range of COD/Ns (1-2.5), and its removal rate peaked at 89% at I = 40 mA, HRT = 8 h, and COD/N = 2. Although the current reduced the diversity of microorganisms in the system, it promoted the growth of dominant species. Nitrification microorganisms were enriched in the reactor, especially Thauera and Hydrogenophaga, which were crucial to the denitrification process. Thus, the combination of autotrophic denitrification and heterotrophic denitrification was promoted by the 3D-BER system to increase the efficiency of nitrogen removal.

Three-Dimensional Biofilm Electrode Reactors with Polyurethane Sponge Carrier for Highly Efficient Treatment of Pharmaceuticals Wastewater Containing Tetrahydrofuran

Three-dimensional biofilm electrode reactors (3D-BERs) exhibit efficacy in the removal of refractory wastewater of pharmaceuticals due to the resistance of pharmaceutical wastewater to biodegradation. In this paper, a new 3D-BER with a polyurethane sponge carrier was applied to the treatment of pharmaceutical wastewater containing tetrahydrofuran (THF) with an objective of exploring the removal efficiency, degradation pathway and main functions of microorganisms of 3D-BERs for wastewater containing THF. The results indicate that when the voltage is 10 V, the highest CODCr removal efficiency is (95.9 ± 1.6)%. Compared to the control group, the removal rate was increased by 21.97 ± 4.69%. The main intermediates of THF, γ-butyrolactone and 4-hydroxybutyric acid, were detected, respectively, by Gas Chromatography–Mass Spectrometry (GC–MS), indicating that 3D-BERs contribute to the degradation of THF with electro-oxidation as well as microbial synergism. Microorganisms, such as Proteobacteria with extracellular electron transfer capacity, Bacteroidetes capable of degrading complex carbon sources and parthenogenic anaerobic bacteria Firmicutes, were found to be enriched by high-throughput sequencing analysis in 3D-BERs, which were conducive to the degradation of refractory pollutants. At the genus level, Chryseobacterium, Brevundimonas, Erysipelothrix, and Desulfovibrio were the main functional genera, whose degradation of THF intermediates was found by functional prediction, mainly through chemoheterotrophy, aerobic chemoheterotrophy, etc. It is to be hoped that this study will provide a solution to the practical treatment of pharmaceutical wastewater containing THF via this new 3D-BER system with a polyurethane sponge carrier.

Deciphering the effects of antibiotics on nitrogen removal and bacterial communities of autotrophic denitrification systems in a three-dimensional biofilm electrode reactor

In this study, three-dimensional biofilm electrode reactors (3D-BERs) were constructed, and the effects of metronidazole (MNZ) on the nitrogen removal performance and bacterial communities of autotrophic denitrification systems were evaluated. The results showed that nitrogen removal decreased slightly as the MNZ concentration increased. Specifically, nitrate-nitrogen removal efficiency decreased from 97.98% to 89.39%, 86.93%, 82.64%, and 82.77% within 12 h after the addition of 1, 3, 5, and 10 mg/L MNZ, respectively. The 3D-BERs showed excellent MNZ degradation ability, especially at a concentration of 10 mg/L. The MNZ removal efficiency could be as high as 94.38% within 6 h, and the average removal rate increased as the MNZ concentration increased. High-throughput sequencing results showed significant changes in the bacterial community under different MNZ concentrations. As the antibiotic concentration increased, the relative abundances of Hydrogenophaga and Silanimonas increased, from only 0.09% and 0.01% without antibiotics to 3.55% and 2.35%, respectively, at an antibiotic concentration of 10 mg/L. Changes in antibiotic concentration altered the abundances of genes involved in nitrogen metabolism. Redundancy analysis showed that MNZ removal efficiency was positively correlated with SBR1031, SC-I-84, Hydrogenophaga, Silanimonas and Denitratesoma, whereas the removal efficiencies of nitrate-nitrogen and total nitrogen were negatively correlated with these genera. The results of this study provide a theoretical basis for studying the toxic effects of antibiotics on the denitrification process and also provide guidance for the control of antibiotics and nitrogen pollution in ecosystems.

Simultaneous denitrification and antibiotic degradation of low-C/N-ratio wastewater by a three-dimensional biofilm-electrode reactor: Performance and microbial response

Three-dimensional biofilm-electrode reactors (3D-BERs) were fabricated and used to simultaneously remove nitrate and metronidazole (MNZ) from low-C/N-ratio wastewater. The results showed that 1 mg/L MNZ significantly promoted nitrate removal. After MNZ was added to the reactor, the removal efficiencies of total nitrogen (TN) and NO3–-N increased significantly from 18.97% and 52.09% to 71.63% and 99.98% within 6 h, respectively. The MNZ-removal kinetics conformed to a pseudo-first-order model, and the removal rate constant reached a maximum value of 0.853 h−1, which was 4.1 and 2.8 times higher than that of pure microorganisms and pure electrochemical reactors, respectively. This indicated that the 3D-BERs constructed in this study were capable of simultaneous MNZ degradation and denitrification. In the presence of nitrate, six MNZ-degradation intermediates were identified, and four MNZ transformation pathways were proposed, including cleavage of hydroxyethyl groups, reduction of nitro groups, N-denitration, and deprotonation of side-chain hydroxyl groups. High-throughput sequencing revealed that the reactor was rich in various MNZ-degraders and denitrifiers, such as Hydrogenophaga, Methylomonas, Crenohrix, Dechloromonas, and Methylophilus. A function prediction analysis of nitrogen metabolism showed that the 3D-BER reactor with MNZ had higher denitrification activity than the other reactors tested. It was speculated that the intermediates produced by MNZ could act as carbon sources allowing denitrifying bacteria to perform denitrification, which made a nonnegligible contribution to the removal of nitrogen.

Efficient degradation of naproxen in a three dimensional biofilm electrode magnetism reactor (3DBEMR): Removal performance and microbial community

A three-dimensional biofilm electrode magnetism reactor (3DBEMR) was constructed to removal naproxen (NPX). This study evaluated 3DBEMR performance in removal of refractory NPX, while also discussing the effect of the electro-magnetic superposition on microbial community by high throughput sequencing. Results indicated that 3DBEMR’s average removal rate for NPX stood at 88.36%, representing an increase by 75.24%, 65.03% and 12.36%, respectively, compared to 3DBR (Three-Dimensional Biofilm Reactor), 3DBMR (Three-Dimensional Biofilm Magnetism Reactor) and 3DBER (Three-Dimensional Biofilm Electrode Reactor). This was attributed to the influence of electro-magnetic adsorption, electro-oxidaton/catalysis, and electro-magnetic biodegradation. Another major contributing factor to NPX removal was the presence in 3DBEMR of high-abundance genera such as Rhodobacter, Porphyrobacter, Methyloversatilis, Sphingopyxis,Bosea, Singulisphaera, Sphingomonas. Therefore, the 3DBEMR was successfully demonstrated to be a flexible and effective technique in NPX degradation, which would help to better understand the effect of superposition of electric and magnetic fields on microbial community.

An integrated biological-electrocatalytic process for highly-efficient treatment of coking wastewater

Coking wastewater is typically refractory, mainly due to its biological toxicity and complex composition. In this study, a novel integrated biological-electrocatalytic process consisting of two three-dimensional electrochemical reactors (3DERs), two biological aerated filters (BAFs), and a three-dimensional biofilm electrode reactor (3DBER) is developed for the advanced treatment of coking wastewater. 73.21% of chemical oxygen demand (COD), 38.02% of ammonium nitrogen (NH4+-N) and 91.46% of nitrate nitrogen (NO3–-N) are removed by 3DERs. BAFs mainly convert NH4+-N to NO3–-N through microbial nitrification. The 3DBER removes the residual NO3–-N by bio-electrochemical denitrification. The integrated system can eliminate 74.72–83.27% of COD, 99.38–99.74% of NH4+-N, and 69.64–99.83% of total nitrogen from coking wastewater during the continuous operation, as well as significantly reducing the toxicity of the wastewater. The superiorities of the integrated 3DERs/BAFs/3DBER system recommend the application of such biological-electrocatalytic technology in the treatment of highly toxic wastewater.

Particle electrode materials dependent tetrabromobisphenol A degradation in three-dimensional biofilm electrode reactors

The completely biological degradation of Tetrabromobisphenol A (TBBPA) contaminant is challenging. Bio-electrochemical systems are efficient to promote electrons transfer between microbes and pollutants to improve the degradation of refractory contaminants. In particular, three-dimensional biofilm electrode reactors (3DBERs), integrating the biofilm with particle electrodes, represent a novel bio-electrochemical technology with superior treatment performances. In this study, the electroactive biofilm is cultured and acclimated on two types of particle electrodes, granular activated carbon (GAC) and granular zeolite (GZ), to degrade the target pollutant TBBPA in 3DBERs. Compared to GZ, GAC materials are more favorable for biofilm formation in terms of high specific surface area and good conductivity. The genus of Thauera is efficiently enriched on both GAC and GZ particles, whose growth is promoted by the electricity. By applying 5 V voltage, TBBPA can be removed by over 95% in 120 min whether packing GAC or GZ particle electrodes in 3DBERs. The synergy of electricity and biofilm in TBBPA degradation was more significant in GAC packed 3DBER, because the improved microbial activity by electrical stimulation accelerates debromination rate and hence the decomposition of TBBPA. Applying electricity also promotes TBBPA degradation in GZ packed 3DBER mainly due to the enhanced electrochemical effects. Roles of particle electrode materials in TBBPA removal are distinguished in this work, bringing new insights into refractory wastewater treatment by 3DBERs.

Study on degradation of reactive brilliant red X-3B by three-dimensional biofilm electrode reactor

The treatment of azo dyes by three-dimensional biofilm electrode reactor (3D-BER) has the characteristics of fast decolorization, high mineralization efficiency and less sludge production and has broad application prospects. The 3D-BER was constructed by filling granular activated carbon (GAC) as a third bipolar electrode in the cathode chamber of conventional BER, and it greatly improved the degradation property of reactive brilliant red (RBR) X-3B. The effects of dye concentration, operating voltage, hydraulic retention time (HRT) and nitrate content on the stability of the experiment were investigated. The results reveal that azo dyes were first decomposed into aromatic amines such as aniline at the cathode, however, the amine substance was difficult to be biodegraded in the anaerobic cathode area, and then the decomposition products of aromatic amines reached the anode region and were further metabolized. Moreover, the water samples were analysed by FTIR and UV-Vis analysis. It was noted that the double bond of the azo dye was broken and degraded into aromatic amines, which were further effectively degraded.

Simultaneous removal of nitrate and sulfate using an up-flow three-dimensional biofilm electrode reactor: Performance and microbial response

Nitrate removal from low carbon water is a problem in the water treatment, especially in the presence of high sulfate. In this work, an up-flow three-dimensional biofilm electrode reactor (3D-BER) was established to remove nitrate and sulfate from low organic carbon water. Results indicated that sulfate negatively affected nitrate removal. Moreover, high electric current and short hydraulic retention time deteriorated the performance of nitrate and sulfate removal. When the influent of SO42− was 150 mg/L, the removal efficiency of NO3−-N and SO42− was 88.49 ± 4.5% and 29.35 ± 5.5%, respectively. The high-throughput sequencing revealed that denitrifying bacteria dominated in the lower part of the reactor while sulfate reducing bacteria dominated in the upper part of the reactor. It was speculated that oxidation products of sulfide could serve as supplementary electron donors to enhance nitrate removal in the 3D-BER.

Tertiary denitrification and organic matter variations of secondary effluent from wastewater treatment plant by the 3D-BER system

A three-dimensional biofilm-electrode reactor (3D-BER) was constructed to facilitate the tertiary denitrification of the secondary effluent of wastewater treatment plants (SEWTP) under 12 mA and in the absence of a carbon source. The TN removal efficiency was 63.8%. The path of the formation and transformation of nitrogen, the relationship between the TN and COD removal rate and the relative concentration and composition of organic matter in the influent and effluent were analyzed to clarify the possible pathways of N and C transformation in the 3D-BER system. Under the action of an electric current, 4.4 mg NH4+-N·L−1 and 17.7 mg COD·L−1 accumulated in the 3D-BER system, and the removal rates of TN and COD were strongly and positively correlated (R2 = 0.9353). The microorganisms in the 3D-BER system under the action of electric current secreted organic matter, some of which (humic acid and microbial metabolites) could be further electrolyzed by microorganisms into bioavailable organic matter for heterotrophic denitrification. Partially dissolved organic matter (DOM, tryptophan aromatic protein, humic acid and microbial metabolites) in the SEWTP could be hydrolyzed under the action of the electric current in the 3D-BER system and consisted of bioavailable organic matter for heterotrophic denitrification. The contribution of heterotrophic denitrification to TN removal was greater than 11.7%. Therefore, the 3D-BER system removed a portion of DOM through microbial electrohydrolysis and promoted the coupling of hydrogen autotrophic denitrification and heterotrophic denitrification to enhance the effectiveness of nitrogen removal in SEWTP. Overall, this technique is effective for enhancing tertiary denitrification in SEWTP.

An integrated three-dimensional electrochemical system for efficient treatment of coking wastewater rich in ammonia nitrogen.

Coking wastewater is highly toxic and refractory industrial wastewater, and is thus extremely challenging to treat. Currently, most treatment technologies focus on degrading carbonaceous pollutants, while insufficient attention is placed on ammonium nitrogen (NH4+-N), the most important nitrogenous contaminant in coking wastewater and with a high biological toxicity. In the current study, we developed an integrated electrochemical system comprising two three-dimensional electrochemical reactors (3DERs), two three-dimensional biofilm electrode reactors (3DBERs) and one three-dimensional biofilm electrode reactor for denitrification (3DBER-De) to treat coking wastewater rich in NH4+-N. Our integrated system is able to remove 70.7% of total nitrogen (TN) at the low energy consumption of 1.29kWh m-3, and can reduce COD by 55.8%. The 3DERs primarily degrade NH4+-N, nitrate nitrogen (NO3--N), and COD by electrochemical redox reactions, while the 3DBERs convert residual NH4+-N to NO3--N by fusing biofilm and electricity. Moreover, the 3DBER-De further eliminates NO3--N by bio-electrochemical denitrification. The coking wastewater is purified as it flows through the integrated treatment system, with only a few hydrocarbon residuals detected that are able to be readily biodegraded by conventional biological treatments. The proposed 3DERs/3DBERs/3DBER-De system provides a new solution for coking wastewater with high concentrations of NH4+-N.

Effect of the coexposure of sulfadiazine, ciprofloxacin and zinc on the fate of antibiotic resistance genes, bacterial communities and functions in three-dimensional biofilm-electrode reactors

Three-dimensional biofilm electrode reactors (3D-BERs) with high treatment efficiency were constructed to treat wastewater containing sulfadiazine (SDZ) and ciprofloxacin (CIP) coexposure with Zinc (Zn). The results showed that coexposure to target antibiotics and Zn increased the absolute and relative abundances of target antibiotic resistance genes (ARGs). Additionally, the target ARG abundances were higher on cathode of 3D-BER compared with ordinary anaerobic reactor while the abundances of total ARGs were decreased in the effluent. Meanwhile, redundancy analysis results revealed that the composition of bacteria carrying ARGs was greatly influenced in the cathode by the accumulation of Zn and antibiotic, which dominated the changes of ARG abundances. Additionally, ARGs with their host bacteria revealed by network analysis were partially deposited on electrode substrates when being removed from wastewater. Thus, 3D-BER exhibits capability of simultaneously eliminating antibiotic and Zn, and greatly reduces the risks of ARGs spread.

A novel integrated system of three-dimensional electrochemical reactors (3DERs) and three-dimensional biofilm electrode reactors (3DBERs) for coking wastewater treatment

Treatment of coking wastewater is a great challenge due to their instinct characteristics of high concentration, complex composition and biological toxicity. In this work, a novel integrated system comprising three-dimensional electrochemical reactors (3DERs) and three-dimensional biofilm electrode reactors (3DBERs) in series is developed for coking wastewater treatment. Results indicate that 79.63% of COD as well as 76.30% of total nitrogen could be removed at the low energy consumption of 15.6 kWh/m3. 3DERs mainly contribute to COD and nitrogen removal through electrochemical oxidation/reduction, while 3DBERs are responsible for nitrification process by enriched functional microbes. After treating by the integrated system, only long-chain alkanes are left in the wastewater and the toxicity of effluent is significantly reduced. This integrated 3DERs-3DBERs system exhibits capability of simultaneously eliminating carbonaceous and nitrogenous contaminants in coking wastewater, and greatly saves the energy with synergy of electricity and biofilm.

Enhanced denitrification by nano ɑ-Fe2O3 induced self-assembled hybrid biofilm on particle electrodes of three-dimensional biofilm electrode reactors

Three-dimensional biofilm electrode reactors (3D-BERs) represent a novel technology for wastewater denitrification. Formation of mature electroactive biofilm on particle electrodes is crucial to realize successful denitrification in 3D-BERs. However, long start-up time and low electroactivity of the biofilm formed on particle electrodes limit the further application of 3D-BERs in wastewater treatment. In this work, self-assembled hybrid biofilms (SAHB) was cultivated on granular activate carbon particle electrodes of the 3D-BER by assembling nano ɑ-Fe2O3 into the biofilm. ɑ-Fe2O3 was selected due to its high affinity to bacterial outer-membrane cytochromes, an important mediator for microbial electron transfer. SAHB formed on particle electrodes were characterized and the denitrification performance of 3D-BERs was also investigated. Results indicate that nano ɑ-Fe2O3 plays positive roles in the start-up of 3D-BER, which captures more microbes into SAHB and constructs thick biofilm on particle electrodes. Special microorganisms with denitrification function related with genera of Hydrogenophaga and Opitutus are distinctively enriched in SAHB. Nano ɑ-Fe2O3 induced SAHB exhibit superior denitrification performance compared to natural biofilm. The average denitrification rate increases from 0.62 mg total nitrogen/L/h for natural biofilm to 1.73 mg total nitrogen/L/h for SAHB, mainly ascribed to accelerated nitrites reduction. Our work provides new technical solution to enhance nitrates removal in 3D-BERs and brings deep insights into application of bio-electrochemical system in wastewater treatment.

Synergistic effects of electricity and biofilm on Rhodamine B (RhB) degradation in three-dimensional biofilm electrode reactors (3D-BERs)

Three-dimensional biofilm electrode reactors (3D-BERs) represent an environmentally acceptable and cost effective technology for refractory wastewater treatment. Previous studies on 3D-BERs primarily focused on treatment performance, and little information is available about the microscopic mechanisms of contaminant degradation. The reactions occurred on particle electrodes, the core units of the 3D-BERs served as both electrodes and biofilm carriers, are still unclear. This study comprehensively elucidated the synergistic effects of electricity and biofilm on Rhodamine B (RhB) removal in 3D-BERs from both macroscopic and microcosmic aspects. Continuous-flow 3D-BERs were operated to evaluate overall treatment performance. Batch experiments were conducted to explore the kinetics of RhB degradation as well as the contributions of various physical, chemical, and biological processes to RhB removal. The biofilm formed on the particle electrodes was characterized by imaging and microbial analyses. The results indicated that applying voltage promoted degradation of RhB. Three processes, including electro-adsorption, electrochemical oxidation and electro-biodegradation, were identified to contribute to RhB degradation. Microorganisms in the Rhodanobacter and Thiomonas genera were distinctively enriched under acclimation voltage, which was attributed to the accumulation of intermediates generated by electrochemical oxidation. This study demonstrated that the synergistic effects of electricity and biofilm were dependent on applying voltage, that would be beneficial to comprehensively understand the contaminants removal process in 3D-BERs.