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

Electrocatalytic coupled biofilter for treating cyclohexanone-containing wastewater: Degradation, mechanism and optimization

Electrocatalytic coupled biofilter (EBF) technology organically integrates the characteristics of electrochemistry and microbial redox, providing ideas for effectively improving biological treatment performance. In this study, an EBF system was developed for enhanced degradation of cyclohexanone in contaminated water. Experimental results show that the system can effectively remove cyclohexanone in contaminated water. Under the optimal parameters, the removal rates of cyclohexanone, TP, NH4+-N and TN were 97.61 ± 1.31%, 76.31 ± 1.67%, 94.14 ± 2.13% and 95.87 ± 1.01% respectively. Degradation kinetics studies found that electrolysis, adsorption, and biodegradation pathways play a major role in the degradation of cyclohexanone. Microbial community analysis indicates that voltage can affect the structure of the microbial community, with the dominant genera shifting from Acidovorax (0 V) to Brevundimonas (0.7 V). Additionally, Acidovorax, Cupriavidus, Ralstonia, and Hydrogenophaga have high abundance in the biofilm and can effectively metabolize cyclohexanone and its intermediates, facilitating the removal of cyclohexanone. In summary, this research can guide the development and construction of highly stable EBF systems and is expected to be used for advanced treatment of industrial wastewater containing cyclohexanone.

An overview of the recent advances and future prospects of three-dimensional particle electrode systems for treating wastewater

Three-dimensional (3D) electrochemical technology is considered a very effective industrial wastewater treatment method for its high treatment efficiency, high current efficiency, low energy consumption, and, especially, ability to completely mineralize nonbiodegradable organic contaminants. Particle electrodes, which are the fundamental components of 3D electrochemical technology, have multiple functions in the electrochemical reaction process. Various types of particle electrodes have been created and applied for wastewater treatment. Herein, we present a thorough analysis of the research and development of particle electrodes used for electrocatalyzing pollutants. Initially, reactor designs, factors affecting the removal efficiency of pollutants and degradation mechanisms are introduced. In particular, a detailed investigation is conducted into the selection of particle electrode materials and the roles they play in the 3D electrochemical treatment of wastewater. Subsequently, the degradation efficiency and energy consumption associated with 3D electrochemical technology for different pollutants are investigated. Finally, the directions and outlook for further studies on particle electrodes are discussed. We believe that this review will offer a useful perspective on the development and application of particle electrodes for wastewater purification.

Refractory degradable dissolved organic matter (R-DOM) driving nitrogen removal by the electric field coupled iron‑carbon biofilter (E-ICBF): Performance and microbial mechanisms

Researches on the advanced nitrogen (N) removal of municipal tailwater always overlooked the value of refractory degradable dissolved organic matter (R-DOM). In this study, a novel electric field coupled iron‑carbon biofilter (E-ICBF) was utilized to explore the performance and microbial changes with polyethylene glycol (PEG) as the representative R-DOM. Results demonstrated that the removal efficiencies of E-ICBF for nitrate nitrogen (NO3--N), ammonia nitrogen (NH4+-N), and total nitrogen (TN) improved by 28.76 %, 12.96 %, and 28.45 %, compared to quartz sand biofilter (SBF). Moreover, removal efficiencies of NO3--N and TN in E-ICBF with R-DOM went up by 12.11 % and 14.02 % compared to methanol. Additionally, both PEG and the electric field reduced the microbial richness and diversity. However, PEG promoted the increase of denitrifying bacteria abundance including unclassified_f_Comamonadaceae, Thauera, and unclassified_f_Gallionellaceae. The electric field improved the abundances of genes related to N removal (hao, nasC, nasA, nifH, nifD, nifK) and PEG further enhanced the effect. The abundances of key enzymes [EC:1.7.5.1], [EC:1.7.2.1], [EC:1.7.2.4], and [EC:1.7.2.5] decreased due to the addition of PEG and the electric field mitigated the negative influence. Additionally, the electric field changed relationships between microorganisms and pollutant removal, and improved interspecific relationships between denitrifying bacterial genera and other genera in E-ICBF.

Enhanced metronidazole removal in seawater using a single-chamber bioelectrochemical system

The aim of this study was to investigate the removal of metronidazole (MNZ) from seawater using a bioelectrochemical system (BES). Single-chamber BES (i.e., S-BES) and dual-chamber BES (i.e., D-BES) were constructed with carbon brush as the anode and cathode. With the inoculum of sea mud and 2 g/L of glucose as the substrate in seawater, S-BES and D-BES were acclimated to test the MNZ removal. Results showed that S-BES could remove almost 100 % of 200 mg/L MNZ within 120 h and remain stable within 10 cycles of operation (∼50 d) under the applied voltage of 0.8 V. The MNZ removal reached ∼100 % and 60.2 % in the cathodic and anodic chambers of D-BES fed by 100 mg/L MNZ under 0.8 V, respectively. The MNZ concentration of 200 mg/L significantly inhibited the sulfur metabolism, decreased the ratio of live to dead cells in the electrode biofilms, and thus reduced the SO42- removal in the S-BES. The MNZ degradation and S2- oxidation was mainly attributed to the cathodic and anodic biofilms of S-BES, respectively. Three degradation pathways of MNZ were proposed based on the identified intermediates and results of density functional theory calculations. The synergies among different genus species in the bacterial communities of biofilms, and between anodic and cathodic reactions could be responsible for the high performance of S-BES. Results from this study should be not only useful for the MNZ removal but also for effective MNZ inhibition of sulfate-reducing bacteria induced microbiologically influenced corrosion in seawater.

Advanced degradation of refractory organic compounds in electroplating wastewater by an in-situ electro-catalytic biological coupling reactor: Removal performance, microbial community and possible mechanism

A high-efficiency treatment system for advanced degradation of refractory organic compounds such as saccharin sodium (SS) and polyethylene glycol 6000 (PEG 6000) in electroplating wastewater was proposed, which coupled ion exchange, electrocatalysis, and microbial interactions through ion exchange particle electrode (IEPE) in a reactor, named in-situ electro-catalytic biological coupling reactor (i-SECBCR). A small-scale experimental test system was established and a feasibility investigation was conducted under the condition of 1.248 L/h continuous flow. The results revealed that (1) the i-SECBCR showed higher average removal rates of SS, PEG 6000, COD and NH4+-N, i.e. 88.48 %, 41.26 %, 66.81 % and 51.61 %,which meant an increase by 5.04 %, 12.05 %, 0.46 %, and 34.50 %, respectively, compared with BAF; (2) the optimal current intensity (CI) of i-SECBCR for simultaneous removal of SS, PEG 6000, COD and NH4+-N was 0.40 mA cm-2; (3) Rhodobacter, Defluviimonas, unclassified_f__Microscillaceae, Pseudoxanthomonas, Novosphingobium, and unclassified_f__Xanthobacteraccae accounted for the main bacterial community in i-SECBCR; (4) the possible degradation mechanism was attributed mainly to the synergistic effect of ion exchange, electrocatalytic oxidation and biology. Therefore, the i-SECBCR was suitable to simultaneously advanced remove SS, PEG 6000, COD and NH4+-N in electroplating wastewater.

Pyrolyzed sediment accelerates electron transfer and regulates rhodamine B biodegradation

Electron transfer efficiency is a key factor that determined the removal of environmental pollution through biodegradation. Electron shuttles exogenously addition is one of the measures to improve the electron transfer efficiency. In this study, the sediment was pyrolyzed at different temperature to investigate its properties of mediating electron transfer and removing of rhodamine B (RhB) in microbial electrochemical systems (MESs). Sediments pyrolyzed at 300 °C (PS300) and 600 °C (PS600) have promoted electron transfer which led to 16 % enhancement of power generation while the result is reversed at 900 °C (PS900). Although power output of PS300 and PS600 are similar, the removal efficiency of RhB is not consistent, which may be caused by the biofilm structure difference. Microbial community analysis revealed that the abundance of EAB and toxicity-degrading bacteria (TDB) in PS600 was 6 % higher than that in PS300. The differentiation of microbial community also affected the metabolic pathway, the amino synthesis and tricarboxylic acid cycle were primarily upregulated with PS600 addition, which enhanced the intracellular metabolism. However, a more active cellular anabolism occurred with PS300, which may have been triggered by RhB toxicity. This study showed that pyrolytic sediment exhibits an excellent ability to mediate electron transport and promote pollutant removal at 600 °C, which provides a techno-economically feasible scenario for the utilization of low-carbon-containing solid wastes.

Enhanced nitrogen and phosphorus removal by a novel ecological floating bed integrated with three-dimensional biofilm electrode system

The ecological floating bed (EFB) has been used extensively for the purification of eutrophication water. However, the traditional EFB (T-EFB) often exhibits a decline in nitrogen and phosphorus removal because of the limited adsorption capacity of fillers and inadequate electron donors. In the present study, a series of electrolysis-ecological floating beds (EC-EFBs) were constructed to investigate the decontamination performance of conventional pollutants. EC-EFB outperformed T-EFB in terms of nitrogen and phosphorus removal. Its removal efficiency of total nitrogen and total phosphorus was 20.51-32.95% and 45.06-96.20%, which were higher than that in T-EFB.. Moreover, the plants in EC-EFB demonstrated higher metabolic activity than those in T-EFB. Under the electrolysis condition of 0.51 mA/cm2 for 24 h, the malondialdehyde content and superoxide dismutase activity in EC-EFB were 6.08 nmol/g and 22.61 U/g, which were significantly lower compared to T-EFB (38.65 nmol/g and 26.13 U/g). And the soluble protein content of plant leaves increased from 3.31 mg/g to 5.72 mg/g in EC-EFB. Microbial analysis revealed that electrolysis could significantly change the microbial community and facilitate the proliferation of nitrogen-functional microbes, such as Thermomonas, Hydrogenophaga, Deinococcus, and Zoogloea. It is important to highlight that the hydrogen evolution reaction at the cathode area facilitated phosphorus removal in EC-EFB, thereby inhibiting phosphorus leaching. This study provides a promising and innovative technology for the purification of eutrophic water.

Enhanced thyroxine removal from micro-polluted drinking water resources in a bio-electrochemical reactor amended with TiO2@GAC particles: Efficiency, mechanism and energy consumption

A three-dimensional bioelectrochemical system (3D-BES) with both electrocatalytic and biodegradation functions was designed and developed to enhance iodine-containing hormone removal from micro-polluted oligotrophic drinking water sources and to reduce energy consumption. Thyroxine (T4) removal efficiency was 99.0% in the 3D-BES amendment with TiO2@GAC as the particle electrodes, which was 20.5% higher than the total efficiency of single biodegradation (28.7%) plus electrochemical decomposition (49.8%). The high T4 removal efficiency was a result of biochemical synergistic degradation, enhancement of electron transfer and utilization, enrichment of functional microorganisms, and the expression of dehalogenation functional genes. The electron transfer was increased by 1.63 times in 3D-BES compared to the 2D-BES, which contributed to: (i) ∼17.8% enhancement of dehalogenation, (ii) 2.35 times enhancement of the attenuation rate, and (iii) 60% reduction in energy consumption. Moreover, the aggregation of microorganisms and the hydrophobic T4 onto TiO2@GAC shortened the transfer distance of matter and energy, which induced the degradation steps to be shortened and the toxic decay to be accelerated from T4 and its metabolites. These comprehensive functions also enhanced the 31.8% ATPase activity, 7.3% abundance of the functional reductive dehalogenation genera, and 52.3% dehalogenation genes expression for Pseudomonas, Ancylobacter, and Dehalogenimonas, which contributed to an increase in T4 removal. This work provides an environmental-friendly biochemical synergistic method for the detoxification of T4 polluted water.

The aggregated biofilm dominated by Delftia tsuruhatensis enhances the removal efficiency of 2,4-dichlorophenol in a bioelectrochemical system

Bioelectrochemical system is a prospective strategy in organic-contaminated groundwater treatment, while few studies clearly distinguish the mechanisms of adsorption or biodegradation in this process, especially when dense biofilm is formed. This study employed a single chamber microbial electrolysis cell (MEC) with two three-dimensional electrodes for removing a typical organic contaminant, 2,4-dichlorophenol (DCP) from groundwater, which inoculated with anaerobic bacteria derived from sewage treatment plant. Compared with the single biodegradation system without electrodes, the three-dimensional electrodes with a high surface enabled an increase of alpha diversity of the microbial community (increased by 52.6% in Shannon index), and provided adaptive ecological niche for more bacteria. The application of weak voltage (0.6 V) furtherly optimized the microbial community structure, and promoted the aggregation of microorganisms with the formation of dense biofilm. Desorption experiment proved that the contaminants were removed from the groundwater mainly via adsorption by the biofilm rather than biodegradation, and compared with the reactor without electricity, the bioelectrochemical system increased the adsorption capacity from 50.0% to 74.5%. The aggregated bacteria on the surface of electrodes were mainly dominated by Delftia tsuruhatensis (85.0%), which could secrete extracellular polymers and has a high adsorption capacity (0.30 mg/g electrode material) for the contaminants. We found that a bioelectrochemical system with a three-dimensional electrode could stimulate the formation of dense biofilm and remove the organic contaminants as well as their possible more toxic degradation intermediates via adsorption. This study provides important guidance for applying bioelectrochemical system in groundwater or wastewater treatment.

Effects of anode materials on nitrate reduction and microbial community in a three-dimensional electrode biofilm reactor with sulfate

Graphite rod corrosion and peeling are serious problems in three-dimensional electrode biofilm reactors (3D-BERs). In this study, titanium rods, titanium suboxide-coated titanium rods and graphite rods were used as anodes to investigate the effect of anodic materials on the electrochemical and bioelectrochemical reduction of nitrate and sulfate. The results showed that the reactor with the titanium suboxide-coated titanium rod anode (3D-ER-T) exhibited a stable NO3--N removal efficiency (46%-95%) with a current range of 160-320 mA in the electrochemical reduction process. In the bioelectrochemical reduction, the removal efficiencies of NO3--N and SO42- and nitrogen selectivity in the 3D-BER with titanium suboxide-coated titanium rod anode (3D-BER-T) were higher than those in the 3D-BER with titanium suboxide-coated graphite rod anode (3D-BER-G). The removal efficiencies of NO3--N and SO42- and nitrogen selectivity were 92%, 43% and 86%, respectively, in 3D-BER-T under 320 mA and HRT 12 h. Anode materials affected the microbial community. Hydrogenophaga and Dethiobacter were the dominant bacteria in 3D-BER-T, while OPB41 and Sulfurospirillum were dominant in 3D-BER-G. Nitrate and sulfate were effectively removed in 3D-BER-T by the synergistic work of electrochemical reduction, bioelectrochemical reduction and indirect electrochemical reduction. The resupply/reserve mode of the electron donor promoted the load of shock resistance of 3D-BER-T via the sulfur cycle. Titanium suboxide coating could significantly enhance the anti-corrosion ability of matrix anodes.

Fabrication of a P-Si/ZnO heterojunction based on galvanic cell driven and the complete degradation of RhB via fast charge transfer

Semiconductor heterojunctions can significantly enhance photocatalytic degradation efficiency by facilitating rapid interfacial charge transfer. This article is based on the galvanic-cell driven principle; porous silicon (P-Si) was prepared by the carbon-catalytic etching method, and ZnO was loaded on its surface via electroless chemical deposition technology to form a P-Si/ZnO heterojunction, which was applied to the degradation of Rhodamine B (RhB). At a deposition temperature of 90 °C, a flawless 1D hexagonal prism structure of ZnO was formed, allowing the P-Si/ZnO heterojunction to completely degrade RhB within 2 hours with a degradation rate of 100%. Compared with a single P-Si material, the degradation performance is improved by 1.7 times. The formation of the built-in electric field and the rapid charge transfer at the heterojunction interface realized the complete degradation of RhB organic pollutants. After 20 cycles of use, the photocatalytic degradation rate remains above 70%, demonstrating excellent stability and recyclability.

An overview of recent advances and future prospects of three-dimensional biofilm electrode reactors (3D-BERs)

Three-dimensional biofilm electrode reactors (3D-BERs) have attracted extensive attention in recent years due to their wide application range, high efficiency and energy saving. On the basis of traditional bio-electrochemical reactor, 3D-BERs are filled with particle electrodes, also known as the third electrodes, which can not only be used as a carrier for microbial growth, but also improve the electron transfer rate of the whole system. This paper reviews the constitution, advantages and basic principles of 3D-BERs as well as current research status and progress of 3D-BERs in recent years. The selection of electrode materials, including cathode, anode and particle electrode are listed and analyzed. Different constructions of reactors, like 3D-unipolar extended reactor and coupled 3D-BERs are introduced and discussed. Various contaminants degraded by 3D-BERs including nitrogen, azo dyes, antibiotics and the others are calculated and the corresponding degradation effects are described. The influencing factors and mechanisms are also introduced. At the same time, according to the research advances of 3D-BERs, the shortcomings and weakness of this technology in the current research process are analyzed, and the future research direction of this technology is prospected. This review aims to summarize recent studies of 3D-BERs in bio-electrochemical reaction and open a bright window to this booming research theme.

Bioelectrochemical systems for enhanced nitrogen removal with minimal greenhouse gas emission from carbon-deficient wastewater: A review

Nitrogen pollution and the rising amount of wastewater generation are calling for advanced wastewater treatments, which is particularly necessary for carbon-deficient wastewater that contains multi-species inorganic nitrogen, since conventional heterotrophic denitrification processes cannot remove nitrogen completely when carbon sources are insufficient. For that, bioelectrochemical systems (BES) have been recently developed because they can simultaneously produce electricity and remove resistant nitrogen from the carbon-deficient wastewater. However, the simultaneous removal of multi-species inorganic nitrogen cannot be achieved by electroautotrophic denitrification using BES alone. Moreover, the efficiency of nitrogen removal and power generation has been thwarted by the low energy output, high internal resistance of the device, and electron competition in non-denitrification pathways. This review article discusses the latest developments for nitrogen removal through BES-enhanced denitrification and elucidates multiple coupled BES-based denitrification pathways to remove multi-species inorganic nitrogen simultaneously. Focus points of the research area include coupling BES technologies with emerged methods, electron transfer enhancement, and avoiding electron competition that improves performance with less cost. The prospect of reducing emissions of greenhouse gases is also critically reviewed, in the hope of reducing potential intermediate products of denitrification, such as nitrous oxide (a potent greenhouse gas), through multi-factor regulation. We imply that BES is a good choice for future scale-up applications of MFC coupled with MEC to treat carbon-deficient wastewater. Overall, this review will provide useful information for the development of advanced technologies to treat carbon-deficient wastewater with less emission of greenhouse gases.

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.

Nano-α-Fe2 O3 for enhanced denitrification in a heterotrophic/biofilm-electrode autotrophic denitrification reactor

In this study, a heterotrophic/biofilm-electrode autotrophic denitrification reactor (HAD-BER) was constructed and nano-ɑ-Fe₂ O₃ was coated on granular activated carbon (GAC) as a third electrode to enhance the nitrate removal performance. The introduction of nano-ɑ-Fe₂ O₃ could stimulate microorganisms to secrete more extracellular polymeric substances (EPS), accelerating the electron transfer. Moreover, more denitrification bacteria were enriched on the particle electrodes, especially Pseudomonas and Thermomonas, which played a significant role in denitrification. The denitrification performance at different COD/N ratios (0.65-3.23) and current intensities (0-150 mA) was investigated in depth. When the nitrate concentration of the influent was 60 mg/L, nitrate was almost completely removed at the optimal current intensity (60 mA) and COD/N ratio (1.29). At the same time, there was almost no nitrite (<0.10 mg/L) and ammonia nitrogen (0 mg/L) accumulation in the effluent. This study provided a new direction for the advancement of HAD-BER and accelerated its implementation. PRACTITIONER POINTS: By introducing nano-a-Fe2O3 into HAD-BER, more denitrification bacteria were enriched on the particle electrodes. The increased contents of polysaccharide and protein content could accelerate the electron transfer. Almost completely denitrification could be achieved at current = 60 mA and COD/N = 1.29. The study provided a new direction for the further development of HAD-BERs.

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.

A mini review on bio-electrochemical systems for the treatment of azo dye wastewater: State-of-the-art and future prospects

Azo dyes are typical toxic and refractory organic pollutants widely used in the textile industry. Bio-electrochemical systems (BESs) have great potential for the treatment of azo dyes with the help of microorganisms as biocatalysts and have advanced significantly in recent years. However, the latest and significant advancement and achievements of BESs treating azo dyes have not been reviewed since 8 years ago. This review thus focuses on the recent investigations of BESs treating azo dyes from the year of 2013-2020 in order to broaden the knowledge and deepen the understanding in this field. In this review, azo dyes degradation mechanisms of BESs are first elaborated, followed by the introduction of BES configurations with the emphasis on the novelties. The azo dye degradation performance of BESs is then presented to demonstrate their effectiveness in azo dye removal. Effects of various operating parameters on the overall performance of BESs are comprehensively elucidated, including electrode materials, external resistances and applied potentials, initial concentrations of azo dyes, and co-substrates. Predominant microorganisms responsible for degradation of azo dyes in BESs are highlighted in details. Furthermore, the combination of BESs with other processes to further improve the azo dye removal are discussed. Finally, an outlook on the future research directions and challenges is provided from the viewpoint of realistic applications of the technology.

The anode is more beneficial to the advanced treatment of wastewater containing antibiotics by three-dimensional electro-biofilm reactor: Degradation, mechanism and optimization

The three-dimensional electrode biological aerated filter (3DE-BAF) has the potential to overcome inherent limitations of conventional electrochemical and biofilm methods. Electrochemical means could enhance the performance and sustainability of biofilm technologies and stimulate the spread of new applications in (waste) water treatment. This paper describes the construction and performance of 3DE-BAF in the treatment of simulated wastewater represented by tetracycline (TC). This is followed by a discussion of electrode performance, the electron transport mechanism and the electrode's effect on the biological community of 3D-EBAF. Given the gap between experimental studies and practical applications, the enlarged anode 3DE-BAF named 3DEAE-BAF reactor was applied with good results to duck farm wastewater. This study could provide guidance as to developing new methods to construct a highly stable 3DE-BAF. The paper concludes that improved 3DE-BAF technology is promising for advanced treatment of livestock wastewater containing antibiotics.

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.

Electro/magnetic superposition effects on diclofenac degradation: Removal performance, kinetics, community structure and synergistic mechanism

Electric and magnetic fields characterized by high efficiency, low consumption and environment-friendly performance have recently generated interest as a possible measure to enhance the performance of the biological treatment process used to remove refractory organics. Few studies have been carried out to-date regarding the simultaneous application of electric and magnetic fields on biofilm process to degrade diclofenac. In this study, 3DEM-BAF was designed to evaluate the electrio-magnetic superposition effect on diclofenac removal performance, kinetics, community structure and synergistic mechanism. The results show that 3DEM-BAF could significantly increase the average removal rate of diclofenac by 65.30 %, 57.46 %, 9.48 % as compared with that of BAF, 3DM-BAF, 3DE-BAF, respectively. The diclofenac degradation kinetic constants and dehydrogenase activity of 3DEM-BAF were almost 6.72 and 2.53 times higher than those of BAF. Microorganisms of 3DEM-BAF in the Methylophilus and Methyloversatilis genera were distinctively enriched, which was attributed to the screening function of electric field and propagation effect of magnetic field. Moreover, three processes were found to contribute to diclofenac degradation, namely electro-magnetic-adsorption, electro-chemical oxidation and electro-magnetic-biodegradation. Thus, the simultaneous application of electric and magnetic fields on biofilm process was demonstrated to be a promising technique as well as a viable alternative in diclofenac degradation enhancement.

Three-dimensional biofilm electrode reactors (3D-BERs) for wastewater treatment

Three-dimensional biofilm electrode reactors (3D-BERs) are highly efficient in refractory wastewater treatment. In comparison to conventional bio-electrochemical systems, the filled particle electrodes act as both electrodes and microbial carriers in 3D-BERs. This article reviews the conception and basic mechanisms of 3D-BERs, as well as their current development. The advantages of 3D-BERs are illustrated with an emphasis on the synergy of electricity and microorganisms. Electrode materials utilized in 3D-BERs are systematically summarized, especially the critical particle electrodes. The configurations of 3D-BERs and their integration with wastewater treatment reactors are introduced. Operational parameters and the adaptation of 3D-BERs to varieties of wastewater are discussed. The prospects and challenges of 3D-BERs for wastewater treatment are then presented, and the future research directions are proposed. We believe that this timely review will help to attract more attentions on 3D-BERs investigation, thus promoting the potential application of 3D-BERs in wastewater treatment.

Production of an electro-biological particle electrode (EBPE) from lithium slag and its removal performance to salicylic acid in a three-dimensional electrocatalytic biological coupling reactor (3D-EBCR)

Electro-biological particle electrode (EBPE) prepared by lithium slag was used to remove salicylic acid in a three-dimensional electrocatalytic biological coupling reactor (3D-EBCR). The physical and chemical properties of the EBPE, the removal performance of salicylic acid and the degradation mechanism were studied. Results revealed as follows: (1) the EBPE prepared by lithium slag contained effective catalytic components including Fe₂O₃, SnO₂, ZnO, MnO, Rb₂O and TiO₂, with stable structure and good adsorption performance; (2) the 3D-EBCR with EBPE had strong adaptability to the current intensity in the range of 0.25-0.40 A, and the removal rates of COD and salicylic acid were maintained above 87.1% and 85.2% respectively; (3) salicylic acid was removed through the synergistic action of adsorption, electrochemical oxidation and biological action.

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.

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 SO₄^2- was 150 mg/L, the removal efficiency of NO₃^--N and SO₄^2- 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.

Combined effects of electrical current and nonsteroidal antiinflammatory drugs (NSAIDs) on microbial community in a three-dimensional electrode biological aerated filter (3DE-BAF)

Three-dimensional electrode biological aerated filter (3DE-BAF) with particulate bioelectrode from lithium slag was used to simultaneously remove diclofenac and clofibric acid from the synthetic domestic sewage, and the combined effects of electrical current and nonsteroidal antiinflammatory drugs (NSAIDs) on microbial community was analyzed. The results indicated that (1) the average diclofenac and clofibric acid removal efficiency in the 3DE-BAF firstly increased, attained the peak of 79.40 ± 6.74% and 69.50 ± 6.26% at 0.35 A, and then decreased to 71.82 ± 4.90% and 55.92 ± 5.17% at 0.40 A, respectively; (2) the concentration of the diclofenac and clofibric acid in 3DE-BAF gradually decreased with the increase of reactor height; (3) the current intensity and space position affected the microbial structure at the different level; (4) at the optimum current intensity, Thiothrix, Flavobacteriaceae, Halothiobacillaceae, Hydrogenophaga, and Comamonadaceae accounted for the main bacterial community for removal diclofenac and clofibric acid in the 3DE-BAF.

Three-dimensional electrodes enhance electricity generation and nitrogen removal of microbial fuel cells

One of the critical problems for practical application of microbial fuel cells (MFCs) is the poor electron transfer between microbial cells and anode. Hence, good biocompatibility and high specific surface area of electrodes are indispensable for MFC scale-up. In this study, three-dimensional electrode MFC (3DEMFC) was developed by filling biochar between anode and cathode. Three types of biochar electrodes (biochar, biochar and zeolite mixture, and MgO-modified biochar) were employed, and the performance of 3DEMFCs treating nitrogen in wastewater was investigated. The results showed that the highest power density of MFCs was 4.45 ± 0.21 W m^-3 achieved by 3DEMFC filled with MgO-modified biochar, and the overall power generation of 3DEMFCs (2.40 ± 0.28 ~ 4.45 ± 0.21 W m^-3) was higher than that of MFC without biochar (1.31 ± 0.24 W m^-3). The linear sweep voltammetry (LSV) results also demonstrated biochar addition to MFC was conducive to electron transfer between microbes and anode and MgO-modified biochar presented the highest coulombs transfer ability. Moreover, the highest removal efficiencies of ammonium, total nitrogen, and COD (93.6 ± 3.2%, 84.8 ± 2%, and 91.6 ± 1.3%, respectively) were achieved by 3DEMFC containing MgO-modified biochar, and simultaneous short-cut nitrification and denitrification were observed in MFCs. Furthermore, the SEM images displayed the bacteria adhesion on biochar and the biofilm dry weights of MgO-modified biochar after experiment was the highest of 103 ± 4 mg g^-1 among three kinds of biochar electrodes. Therefore, the power generation and nitrogen removal conspicuously enhanced in 3DEMFCs and biochar exhibited excellent biocompatibility and distinct electrochemical performance for MFC practical applications in wastewater treatment.

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 1.29 kWh 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.

Fabrication and Characterization of a Novel Composite Magnetic Photocatalyst β-Bi2O3/BiVO4/MnxZn1-xFe2O4 for Rhodamine B Degradation under Visible Light

β-Bi₂O₃/BiVO₄/Mn_xZn_1−xFe₂O₄ (BV/MZF) composite magnetic photocatalyst was first synthesized using the hydrothermal and calcination method. BV/MZF was a mesoporous material with most probable pore size and specific surface area of 18 nm and 17.84 m²/g, respectively. Due to its high saturation magnetization (2.67 emu/g), the BV/MZF composite can be easily separated and recovered from solution under an external magnetic field. The results of photo-decomposition experiments show that the decomposition rate of Rhodamine B (RhB) by BV/MZF can reach 92.6% in 3 h under visible light. After three cycles, BV/MZF can still maintain structural stability and excellent pollutant degradation effect. In addition, analysis of the photocatalytic mechanism of BV/MZF for RhB shows that the p-n heterojunction formed in BV/MZF plays a vital role in its photocatalytic performance. This work has potential application in the future for solving environmental pollution.

A pilot-scale three-dimensional electrochemical reactor combined with anaerobic-anoxic-oxic system for advanced treatment of coking wastewater

Coking wastewater is highly concentrated and extremely toxic, greatly challenging the treatment technologies. Conventional biological technology such as anaerobic-anoxic-oxic (A²O) system is inefficient, since various biological reactions are inhibited by toxicants in coking wastewater. In this work, a pilot-scale three-dimensional electrochemical reactor (3DER) is integrated into the A²O system as a pretreatment unit to improve the treatment efficiency of coking wastewater. The results indicate that 3DER pretreatment increased the biodegradability of coking wastewater, promoting the degradation of coking wastewater in A²O system. The integrated 3DER-A²O system can remove 94.4% of COD and 76.2% of TN from coking wastewater, and the energy consumption was only 0.22 kWh/kg COD and 4.69 kWh/kg TN. The components of coking wastewater were significantly simplified and the acute toxicity was reduced from 99% to 12% after the treatment. The integrated 3DER-A²O system provides a new solution for coking wastewater treatment, showing a promising application potential.

Mass transfer of nanobubble aeration and its effect on biofilm growth: Microbial activity and structural properties

It is necessary to improve the performance and reduce the aeration cost is of wastewater treatment by aerobic biofilm systems. Nanobubble aeration is supposed to be a promising method to achieve these goals. Compared with coarse bubbles, dissolved oxygen profiling showed that the nanobubbles provided more oxygen to biofilms, offering superior oxygen supply capacity and 1.5 times higher oxygen transfer efficiency. Nanobubble aeration accelerated the growth of the biofilm and achieved better removal efficiencies of chemical oxygen demand and ammonia, with as maximum as six times higher dehydrogenase activity, and more extracellular polymeric substance content than when using the traditional aeration mode. This is attributed to the enhancement of metabolism and the proliferation of microorganisms. Confocal laser-scanning microscopy imaging confirmed that nanobubble aeration affected the components of biofilm by shifting the microbial community and changing its metabolic pathways of biofilms, such as carbohydrate synthesis. Nanobubble aeration resulted in an energy saving of approximately 80%. The assessment of nanobubble aerated biofilm growth suggests that this technique can offer a rapid-initiation, high efficiency, and low-cost strategy for aerobic biofilm systems in wastewater treatment.

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.

Integrated effects of temperature and COD/N on an up-flow anaerobic filter-biological aerated filter: Performance, biofilm characteristics and microbial community

The integrated effects of temperature and COD/N ratio on performance, biofilm characteristics and microbial community in up-flow anaerobic filter-biological aerated filters (UAF-BAFs) were investigated. Results indicated that the UAF-BAF system could achieve excellent COD, NH₄⁺-N and TN removal, in which effluent quality well met the Class 1A standard. Biofilm physicochemical characteristics showed that the biomass, biofilm thickness and extracellular polymeric substance (EPS) content in the UAF-BAFs reduced with the decrease in COD/N ratio, but were enhanced under low temperature. The biofilm structure characterized by CLSM in the UAF-BAFs significantly shifted, which was closely correlated with operational conditions. Sequencing analysis revealed that Proteobacteria, Epsilonbacteraeota, Bacteroidetes and Firmicutes were dominant in the UAFs and the abundance of ammonium oxidizing bacteria (AOB) was responsible for nitrification performance in the BAFs. Functions analysis indicated that amino acid metabolism, carbohydrate metabolism, energy metabolism and lipid metabolism were clearly regulated by parameters changes.

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.

K2Ti6O13 hybridized graphene oxide: Effective enhancement in photodegradation of RhB and photoreduction of U(VI)

The environmental pollutions by organic pollutants and radionuclides have aroused great concern. Developing highly efficient elimination methods becomes an imperious demand. In this study, a nanocomposite of K₂Ti₆O₁₃ (KTO) nanobelts hybridized graphene oxide (GO) nanosheets (GO/KTO) was used to photodegrade RhB (dye) and photoreduce U(VI) (radionuclide), which was synthesized by a facile hydrothermal method. The adsorption capacity and the slope (k) of the curve -ln(C/C) versus time in photodegradation of RhB by GO/KTO were higher than that by GO and KTO. In the presence of different free radical scavengers, superoxide radical (·O₂^-) was found to play the most significant role in the reaction. The XPS experiment indicates U(VI) was successfully photoreduced to less toxic U(IV). The pH dependent photocatalytic experiments on RhB and U(VI) both showed the best performance at neutral pH value (from pH 6 to pH 8). To investigate the reason for the enhanced photocatalysis of GO/KTO, the morphology/microstructure, optical and photo-electrochemical properties were examined. The enhanced abilities of separation of photo electrons and holes and the adsorption of GO/KTO were ascribed to the structure of KTO nanobelts laying on the surface of GO nanosheets, which may maximize the contacting area between KTO and GO, and thus greatly reduce the surface related oxygen defects to enhance the electron interface transfer between KTO and GO and decrease the recombination efficiency of electrons and holes. These results showed the GO/KTO has great application potential in environmental treatment of organic pollutants and high valent heavy/radionuclide ions at neutral condition.

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.