A review of spatial distribution of typical antibiotic resistance genes in marine environment surrounding China.

Antibiotic resistance genes (ARGs) have been steadily increasing due to the extensive overuse of antibiotics in the marine environment. Currently, the research considering ARGs distribution in marine ecosystems gains more interest. As the coastal sea has been regarded as one of the most polluted areas by antibiotic contaminants in China. However, no comprehensive review of the spatial distribution of ARGs in marine environment surrounding China. The main objective of this review is to investigate the level, characteristic, and spatial distribution of ARGs in the marine environment (seawater and sediments) surrounding China. Key sea areas, such as Bohai Sea, Yellow Sea, East China Sea, and South China Sea were selected in this review. The marine environment was the reservoir of ARGs, and ARGs in seawater were generally 1 to 2 orders of magnitude higher than that in sediments. Total ARGs were more abundant in the Yellow Sea, followed by the Bohai Sea, the East China Sea, and the South China Sea. This study raises questions regarding the spread and distribution for antibiotic resistance in marine environments.

Tree-structured parzen estimator optimized-automated machine learning assisted by meta-analysis for predicting biochar-driven N2O mitigation effect in constructed wetlands.

Biochar is a carbon-neutral tool for combating climate change. Artificial intelligence applications to estimate the biochar mitigation effect on greenhouse gases (GHGs) can assist scientists in making more informed solutions. However, there is also evidence indicating that biochar promotes, rather than reduces, N2O emissions. Thus, the effect of biochar on N2O remains uncertain in constructed wetlands (CWs), and there is not a characterization metric for this effect, which increases the difficulty and inaccuracy of biochar-driven alleviation effect projections. Here, we provide new insight by utilizing machine learning-based, tree-structured Parzen Estimator (TPE) optimization assisted by a meta-analysis to estimate the potency of biochar-driven N2O mitigation. We first synthesized datasets that contained 80 studies on global biochar-amended CWs. The mitigation effect size was then calculated and further introduced as a new metric. TPE optimization was then applied to automatically tune the hyperparameters of the built extreme gradient boosting (XGBoost) and random forest (RF), and the optimum TPE-XGBoost obtained adequately achieved a satisfactory prediction accuracy for N2O flux (R2 = 91.90%, RPD = 3.57) and the effect size (R2 = 92.61%, RPD = 3.59). Results indicated that a high influent chemical oxygen demand/total nitrogen (COD/TN) ratio and the COD removal efficiency interpreted by the Shapley value significantly enhanced the effect size contribution. COD/TN ratio made the most and the second greatest positive contributions among 22 input variables to N2O flux and to the effect size that were up to 18% and 14%, respectively. By combining with a structural equation model analysis, NH4+-N removal rate had significant negative direct effects on the N2O flux. This study implied that the application of granulated biochar derived from C-rich feedstocks would maximize the net climate benefit of N2O mitigation driven by biochar for future biochar-based CWs.

Biofilm electrode reactor coupled manganese ore substrate up-flow microbial fuel cell-constructed wetland system: High removal efficiencies of antibiotic, zinc (II), and the corresponding antibiotic resistance genes.

A coupled system comprised of a biofilm electrode reactor (BER) and a manganese ore substrate microbial fuel cell-constructed wetland (MFC-CW) system was used to remove co-exposed antibiotic and Zn (II), as well as simultaneously reduce copies of antibiotic resistance genes (ARGs) in the current study. In this system, BER primarily reduced the concentrations of antibiotics and Zn (II), and the effluent was used as the input to the MFC-CW, thereby providing electricity to BER. Co-exposure to a high concentration of Zn (II) decreased the relative abundances (RAs) of ARGs in the BER effluent, whereas the remaining sub-lethal concentration of Zn (II) increased the RAs of ARGs in the MFC-CW effluent. Even though the absolute copies of ARGs in the effluents increased during co-exposure, the total number of target ARG copies in the effluent of MFC-CW was significantly lower than that of BER. Moreover, BER pre-treatment eliminated most of Zn (II), which improved the electrical power generation characteristic of the MFC-CW unit. Correspondingly, the bacterial community and the ARGs hosts were analyzed to demonstrate the mechanism. In conclusion, the coupled system demonstrates significant potential to reduce antibiotics, Zn (II) and environmental risks posed by ARGs.

Impacts of draw solutes on the fate of tetracycline in an osmotic membrane bioreactor: Role of the combination between membrane fouling and microorganisms.

Osmotic membrane bioreactors (OMBRs) are considered a suitable technology for treating wastewater containing tetracycline due to their high rejection and biodegradation efficiency. However, the impact of membrane fouling layer (i.e., chemical composition, microbial composition, and formation) on the filtration and biodegradation of tetracycline is still unclear. Herein, the effects of draw solute concentration and type on the formation of a membrane fouling layer for tetracycline filtration and its relationship with microbial activity were investigated. The results showed that over 99% of tetracycline was retained on the feed side by membrane rejection, and the fouling layer played an important role in tetracycline filtration. Specifically, membrane foulants resulted in a more hydrophilic membrane facilitating tetracycline filtration, while the tetracycline-degrading genera from the fouled membrane promoted tetracycline degradation. The structure equation model showed that tetracycline filtration dominated by electrostatic repulsion between tetracycline and the fouled membrane was more important than tetracycline degradation for tetracycline removal (path coefficient of 0.655 vs. 0.395). This study provided insights into the combined effect of membrane foulants and microorganisms on tetracycline removal.

Enhanced removal of antibiotic and antibiotic resistance genes by coupling biofilm electrode reactor and manganese ore substrate up-flow microbial fuel cell constructed wetland system.

Manganese ore substrate up-flow microbial fuel cell constructed wetland (UCW-MFC(Mn)) as an innovative wastewater treatment technology for purifying antibiotics and electricity generation with few antibiotic resistance genes (ARGs) generation has attracted attention. However, antibiotic purifying effects should be further enhanced. In this study, a biofilm electrode reactor (BER) that needs direct current driving was powered by a Mn ore anode (UCW-MFC(Mn)) to form a coupled system without requiring direct-current source. Removal efficiencies of sulfadiazine (SDZ), ciprofloxacin (CIP) and the corresponding ARGs in the coupled system were compared with composite (BER was powered by direct-current source) and anaerobic systems (both of BER and UCW-MFC were in open circuit mode). The result showed that higher antibiotic removal efficiency (94% for SDZ and 99.1% for CIP) in the coupled system was achieved than the anaerobic system (88.5% for SDZ and 98.2% for CIP). Moreover, electrical stimulation reduced antibiotic selective pressure and horizontal gene transfer potential in BER, and UCW-MFC further reduced ARG abundances by strengthening the electro-adsorption of ARG hosts determined by Network analysis. Bacterial community diversity continuously decreased in BER while it increased in UCW-MFC, indicating that BER mitigated the toxicity of antibiotic. Degree of modularity, some functional bacteria (antibiotic degrading bacteria, fermentative bacteria and EAB), and P450 enzyme related to antibiotic and xenobiotics biodegradation genes were enriched in electric field existing UCW-MFC, accounting for the higher degradation efficiency. In conclusion, this study provided an effective strategy for removing antibiotics and ARGs in wastewater by operating a BER-UCW-MFC coupled system.

Towards bio-utilization and energy recovery potential exploration of membrane foulant from membrane bioreactor by using microbial fuel cell-centered technology.

The utilization of membrane foulant is expected to push forward the developments of membrane bioreactor (MBR). In this study, the combination of microbial fuel cell (MFC) with bio-electrochemical enhanced hydrolysis process was proposed, and three systems were conducted to utilize the membrane foulant and simultaneously harvest electricity. Polysaccharides (PS), proteins (PN) and humic acid (HA) concentration variations and the fluorescent compound changes in different chambers revealed the biodegradability of membrane foulant. Optimized HRT improved the hydrolysis of membrane foulant while allowing MFC to utilize the biodegradable components efficiently. MFC-MFC system had the highest voltage and satisfactory effluent quality at HRT of 1 d. Microbial community structure analysis indicated that Proteobacteria, Planctomycetes and Bacteroidetes were the majority phyla and network analysis further revealed that Proteobacteria played a key role in membrane foulant utilization. This study suggests that MFC hybrid systems has potential application for synchronous membrane foulant reuse and energy recovery.

Shedding light on the transfer of tetracycline in forward osmosis through experimental investigation and machine learning modeling.

Tetracycline in wastewater can pose adverse impacts on the environment and human health. Forward osmosis (FO) is a promising method to reject antibiotics due to its low energy demand and high rejection rate. Tetracycline rejection during FO is a complicated process. Mechanistic models have been developed to describe antibiotic rejection by the FO membrane under ideal conditions but cannot be applied to real wastewater. Herein, the effects of draw concentration, pH, and solute type on the fate of tetracycline during FO were investigated by combining experimentation, factor analysis, and artificial neural network (ANN) modeling. High draw concentrations led to high convection that favored tetracycline diffusion. Low draw pH helped reject antibiotics potentially due to the decreased tortuosity and pore size of the FO membrane. When different draw solutes were tested, both convection and electrostatic interaction exerted effects on tetracycline retention on the FO membrane surface, and steric hindrance could further affect the amount of tetracycline in the draw solution. Exploratory factor analysis (EFA) showed that tetracycline rejection was a combined result of convection, steric hindrance, and electrostatic interactions. Path analysis revealed the significant roles of initial conductivity and draw pH in tetracycline rejection. Eight representative input variables were selected from 13 observed explanatory variables using redundancy analysis (RDA), based on which an ANN was trained and successfully predicted tetracycline diffusion and transfer through the FO membrane. These results have provided practical and predictive insights in the development of FO processes for efficient treatment of pharmaceutical wastewater.

Quantifying biochar-induced greenhouse gases emission reduction effects in constructed wetlands and its heterogeneity: A multi-level meta-analysis.

Zero-waste biochar is an emerging tool for carbon neutralization, but the role of biochar in reducing greenhouse gases (GHGs) emissions from CWs were controversy and uncertainty. Yet, no previous study has integrated multiple research systems to quantitatively examine biochar-mediated GHGs emission reduction potential in CWs. Here we synthesized 114 studies to quantify biochar-induced declines ability of GHGs in the CWs by using the multi-level meta-analysis, reveal the variation of GHGs emission effect in different biochar-CWs and its response relationship with biochar, and identify the moderating variables that had a strong explanatory effect on the emission reduction effect of biochar. We showed that biochar remarkably affect CO2 mitigation (p < 0.05), but has insignificant and heterogeneous effects on CH4 and N2O. Pyrolysis time, influent dissolved oxygen (DO), influent NO3--N concentration, hydraulic retention time (HRT) and wetland type can significantly affect the effect of biochar on CH4 emission reduction. Particularly, the importance of HRT and wetland type was 0.89 and 0.85, respectively. Specially, the surface batch CWs modified by biochar could significantly promote the emission of CH4 (p < 0.001), and the effect size was up to 89.59. For N2O, biochar diameter, biochar addition ratio, influent COD/TN ratio, plant name, and removal efficiency of NO3--N/TN/COD were significant moderators. Among them, influent COD/TN ratio and plant name showed a stronger explanation. Planting Cyperus alternifolius L. significantly enhanced the N2O emission reduction capacity by biochar (p < 0.001), and effect size was as low as -24.32. 700-900 °C biochar can promote CH4 flux but inhibit N2O flux. This study provides an important theoretical basis and valuable strategic guidance for more accurate estimation and improvement of synergistic emission reduction benefits between CH4 and N2O of biochar in CWs.

Electrochemical disinfection may increase the spread of antibiotic resistance genes by promoting conjugal plasmid transfer.

Current in the milliampere range can be used for electrochemical inactivation of bacteria. Yet, bacteria-including antibiotic resistant bacteria (ARB) may be subjected to sublethal conditions due to imperfect mixing or energy savings measures during electrochemical disinfection. It is not known whether such sublethal current intensities have the potential to stimulate plasmid transfer from ARB. In this study, conjugal transfer of plasmid pKJK5 was investigated between Pseudomonas putida strains under conditions reflecting electrochemical disinfection. Although the abundance of culturable and membrane-intact donor and recipient cells decreased with applied current (0-60 mA), both transconjugant density and transconjugant frequency increased. Both active chlorine and superoxide radicals were generated electrolytically, and ROS generation was induced. In addition, we detected significant over expression of a core oxidative stress defense gene (ahpCF) with current. Expression of selected conjugation related genes (traE, traI, trbJ, and trbL) also significantly correlated with current intensity. ROS accumulation, SOS response and subsequent derepression of conjugation are therefore the plausible consequence of sublethal current exposure. These findings suggest that sublethal intensities of current can enhance conjugal plasmid transfer, and that it is essential that conditions of electrochemical disinfection (applied voltage, current density, time and mixing) are carefully controlled to avoid conjugal ARG transmission.

Insight into the role of microbial community interactions on nitrogen removal facilitated by a bioelectrochemical system in an osmotic membrane bioreactor.

Insufficient nitrogen removal is a key challenge for the application of an osmotic membrane bioreactor (OMBR). The integration of a bioelectrochemical system (BES) and an OMBR was constructed to enhance nitrogen removal.To optimize the operation, five aeration intensities and three draw solutes (DSs) were applied in the proposed system. The results showed that the proposed system obtained the highest nitrogen removal efficiency of 77.36 ± 3.55 % with an aeration intensity of 0.6 L/min, and it was further increased to 94.99 ± 2.83 % and 99.92 ± 0.14 %with the NaOAc DS and the glucose DS, respectively.The analysis ofmetabolic pathways implied that species interactions existed,andthe following different mechanisms of enhanced nitrogen removal for the two organic DSs were proposed. The growth of denitrifying bacteria was enhanced by using reverse-fluxed organic NaOAc DS as a carbon source;glucoseDS stimulated electron transfer system activity to accelerate denitrification.

Enhanced removal of antibiotics and antibiotic resistance genes in a soil microbial fuel cell via in situ remediation of agricultural soils with multiple antibiotics.

Soil microbial fuel cells (MFCs) have been applied for the in situ remediation of soils polluted by single antibiotics. However, the investigation of only single antibiotic pollution has hindered MFC application in real-world soil remediation, where the effects of multiple antibiotics with similar chemical structures on the fate of antibiotics and their corresponding antibiotic resistance genes (ARGs) remain unknown. In this study, antibiotic removal rates, microbial community compositions, metabolite compositions, and ARG abundances were investigated in soil MFCs by adding two commonly used antibiotics (sulfadiazine, SDZ, and sulfamethoxazole, SMX), and comparing them with the addition of only a single antibiotic (SDZ). The antibiotic removal rate was higher in the soil MFC with addition of mixed antibiotics compared to the single antibiotic due to enhanced biodegradation efficiency in both the upper (57.24% of the initial antibiotic concentration) and lower layers (57.07% of the initial concentration) of the antibiotic-polluted soils. Bacterial community diversity in the mixed antibiotic conditions increased, and this likely resulted from the decreased toxicity of intermediates produced during antibiotic biodegradation. Moreover, the addition of mixed antibiotics led to lower risks of ARG release into soil environments, as reflected by higher abundances of host bacteria in the single antibiotic treatment. These results encourage the further development of soil MFC technology for in situ remediation of antibiotic-polluted soils.

Simultaneous removal of antibiotic resistant bacteria and antibiotic resistance genes by molybdenum carbide assisted electrochemical disinfection.

Considering conventional disinfection methods are not effective in simultaneously removing ARB and ARGs, a novel electrochemical disinfection (ED) process assisted by molybdenum carbide (Mo2C) electrodes was developed in this study. The established ED process was proved to effectively inactivate multi-resistant ARB (i.e. Escherichia coli K-12 LE392 with resistance to kanamycin, ampicillin, and tetracycline) and to degrade ARGs (including tetA and blaTEM in the form of both intracellular (iARGs) and extracellular ARGs (eARGs)). Specifically, within 15 min treatment by the Mo2C-assisted ED under 2.0 V, a 5-log ARB removal was realized, without any ARB regrowth observed, indicating a permanent inactivation of ARB by the process. Moreover, degradation of the iARGs (0.4-log reduction of the blaTEM and 3.1-log reduction of the tetA) and the eARGs (4.2-log reduction of the blaTEM and 1.1-log reduction of the tetA) were achieved within 60 min, further underpinning the viability of the Mo2C-based ED. While e-, H2O2, and •O2- played leading roles in the entire process of ED, H+ and •OH contributed to bacterial inactivation in the early and late stages of ED, respectively. The reactive species induced by electrolysis posed pressure to the ARB strains, which enhanced oxidative stress response, triggered higher reactive oxygen species generation, induced membrane damage and changed cellular structure. Collectively, the Mo2C-assisted ED demonstrated in the present study represents an attractive alternative to the traditional disinfection methods in combating the spread of antibiotic resistance.

Increase of antibiotic resistance genes via horizontal transfer in single- and two-chamber microbial electrolysis cells.

Microbial electrolysis cells (MECs) have been applied for antibiotic degradation but simultaneously induced antibiotic resistance genes (ARGs), thus representing a risk to disseminate antibiotic resistance. However, few studies were on the potential and risk of ARGs transmission in the MECs. This work assessed conjugative transfer of ARGs under three tested conditions (voltages, cell concentration, and donor/recipient ratio) in both single- and two-chamber MECs. The results indicated that voltages (> 0.9 V) facilitated the horizontal frequency of ARGs in the single-chamber MECs and anode chamber of two-chamber MECs. The donor cell number (donor/recipient ratio was 2:1) increased the transfer frequency of ARGs. Furthermore, voltages ranged from 0.9 to 2.5 V increased reactive oxygen species (ROS) production and cell membrane permeability in MECs. These findings offer new insights into the roles of ARG transfer under different applied voltages in the MECs, which should not be ignored for horizontal transfer of antibiotic resistance.

Antibiotic removal and antibiotic resistance genes fate by regulating bioelectrochemical characteristics in microbial fuel cells.

Antibiotics removal and ARGs control in microbial fuel cell (MFC) has received extensive attention. In particular, the critical role of bioelectrochemical characteristics deserves further study. Bioelectrochemical characteristics significantly affected sulfamethoxazole (SMX) removal and ARGs fate, in which the current intensity played a more critical role than anode potential. High-concentration SMX (2 mg/L and 10 mg/L) facilitated the anode potential tend to be close, and thus, the strengthening effect of current on the system was highlighted. However, the SMX degradation pathway under different bioelectrochemical characteristics was not affected. Furthermore, the higher current intensity was preferable to antibiotic removal, but unfavorable for ARGs control might be due to the oxidative stress on microorganisms. Low-concentration SMX (0.5 mg/L) contributed to improving higher electricity generation because of Geobacter enrichement. This study suggested that appropriate bioelectrochemical characteristics regulation in MFCs was essential in removing antibiotics and controlling ARGs.

Effects of voltage on the emergence and spread of antibiotic resistance genes in microbial electrolysis cells: From mutation to horizontal gene transfer.

Microbial electrolysis cells (MECs) are widely considered as promising alternatives for degrading antibiotics. As one of the major operating parameters in MECs, voltage might affect the spread of antibiotic resistance genes (ARGs) given it can affect the physiological characteristics of bacteria. However, little is known about the impacts of voltage on the acceleration of bacterial mutation and the promotion of ARG dissemination via horizontal transfer in MECs. In this study, two voltages (0.9 V and 1.5 V) were applied to identify if electrical stimulation could increase bacterial mutation frequency. Three voltages (0.9 V, 1.5 V, and 2.5 V) were used to evaluate the conjugative transfer frequency of plasmid-encoded the ARGs from the donor (E. coli K-12) to the recipient (E. coli HB101) in MECs. After repeating subculture in MECs for 10 days, the mutation frequency of E. coli K-12 was promoted, consequently, the generated mutants became more resistant against tetracycline. When the voltage was higher than 0.9 V, conjugative ARG transfer frequency was significantly increased in the anode chamber (p < 0.05). The over-production of reactive oxygen species (ROS) (voltage >0.9 V) and cell membrane permeability (voltage >1.5 V) were significantly enhanced under electrical stimulations (p < 0.05). Genome-wide RNA sequencing indicated that the expressions of genes related to oxidative stress and cell membrane were upregulated with exposure to electrical stimulation. Electrical stimulations induced oxidative reactions, which triggered ROS over-production, SOS response, and enhancement of cell membrane permeability for both donor and recipient in the MECs. These findings provide insights into the potential role of voltage in the generation and spread of ARGs in MECs.

New insights into the role of molecular structures on the fate and behavior of antibiotics in an osmotic membrane bioreactor.

Osmotic membrane bioreactors (OMBRs) have been applied to enhance removal of antibiotics, however, information on the effects of molecular structures on the behavior of antibiotics is still lacking. Herein, adsorption kinetics, transformation pathways, and membrane rejection mechanisms of OMBRs were investigated by adding two typical antibiotics (i.e., sulfadiazine, SDZ, and tetracycline hydrochloride, TC-HCl). 80.70-91.12% of TC-HCl was removed by adsorption and biodegradation, while 17.50-75.14% of SDZ was removed by membrane rejection; this depended on its concentration due to reduced electrostatic interactions and hydrophobic adsorption. The adsorption capacity of TC-HCl (i.e., 1.34±0.01 mg/g) was significantly higher than that of SDZ (i.e., 0.18±0.03 mg/g) due to enhanced π-π interactions, hydrogen bonding and improved electrostatic interactions. The abundant production of polysaccharide-like substances from TC-HCl biodegradation contributed to microbial metabolism and thus enhanced microbial function during TC-HCl biotransformation. The primary degradation pathways were determined by microbial function analysis, and the primary intermediates from TC-HCl degradation were less toxic than those from SDZ degradation due to the different reactions of amino groups. These results and the corresponding mechanism provide a theoretical foundation for the further development of OMBR technology for highly efficient treatment of antibiotic wastewater.

Quinones contained in wastewater as redox mediators for the synergistic removal of azo dye in microbial fuel cells.

The present paper aimed to investigate the roles of quinones contained in wastewater and the enhanced effects on microbial fuel cells (MFCs) under different redox conditions. The feasibility of using wastewater rich in quinones to act as co-substrate and redox mediators (RMs) library to strengthen the synergistic removal of azo dye in MFCs was evaluated. The results demonstrated that quinones achieved enhanced effects on electricity generation and COD removal of MFC better at higher current intensity. The addition of pure quinone decreased electron transfer resistance (Rct) of MFCs from 4.76 Ω to 2.13 Ω under 1000 Ω resistance and 1.16 Ω-0.75 Ω under 50 Ω resistance. Meanwhile, higher coulombic efficiency was achieved. Compared with sodium acetate, using quinone-rich traditional Chinese medicine (TCM) wastewater as the co-substrate enhanced the synergistic removal of reactive red 2 (RR2) in MFCs from 79.58% to 92.45% during 24 h. RR2 was also degraded more thoroughly due to the accelerated electron transfer process mediated by RMs. Microbial community analysis demonstrated that the presence of quinone in TCM wastewater can enrich different exoelectrogens under varied redox conditions and thus influenced the enhanced effects on MFC. Metagenomic functional prediction results further indicated that the abundance of functional genes involved in carbohydrate metabolism, membrane transport metabolism, biofilm formation, and stress tolerance increased significantly in presence of RMs. Redundancy analyses revealed that RMs addition was the more important factor driving the variation of the microorganism community. This study revealed the potential effect of quinones as redox mediators on the bioelectrochemical system for pollutants removal.

Biological detoxification and decolorization enhancement of azo dye by introducing natural electron mediators in MFCs.

Reactive red 2 (RR2) is a highly recalcitrant and toxic azo dye that can cause the collapse of biological treatment system. Although MFC can decolorize RR2 effectively, its performance is still inevitably affected by toxicity. Anthraquinone can enhance MFCs' performance through mediating electron transfer. In this study, an anthraquinone-rich natural plants (B.rheum (Rheum offcinale Baill)) was extracted and then added to MFCs. The optimal dosage was selected and the enhanced effects were investigated. The results showed that adding 5%(V/V) extract resulted in the optimal performance elevation of MFC. When 5% extract was added together with RR2, 15.63% and 1.33-fold improvement in RR2 decolorization efficiency and rate were achieved compared with the control group. Meanwhile, higher power density (2.75 W/m3), coulombic efficiency (6.45%), and lower internal resistance (233.69 Ω) were also observed when 5% B.rheum extract and RR2 were added. B.rheum extract in MFCs enhanced microbial activity and enriched the dye-degrading microorganisms, such as Enterobacter, Raoultella, Comamonas and Shinella. B.rheum extract acts as "antidote" in alleviating the biotoxicity of RR2 was firstly illustrated in this study. The results provided a new strategy for using plant-source electron mediators to simultaneously improve biological detoxification, bioelectricity generation and dye decolorization in bioelectrochemical system.

Minimizing salinity accumulation via regulating draw solute concentration in a bioelectrochemically assisted osmotic membrane bioreactor.

A suitable draw solute (DS) concentration in bioelectrochemically assisted osmotic membrane bioreactor (BEA-OMBR) can convert the "negative effect" of salinity accumulation into a "beneficial effect" by using the reverse-fluxed DS as a buffer agent or a carbon source supplement. Herein, the effect of DS concentration from acid buffer solution (i.e., ammonium chloride, NH4Cl), alkaline buffer solution (i.e., sodium bicarbonate, NaHCO3), and organic solution (i.e., sodium acetate, NaOAc) on salinity accumulation was systematically investigated. Salinity accumulation with NaHCO3 DS mainly derived from reversal fluxed sodium ion (Na+, major contributor with DS concentration ≤0.25 M) and bicarbonate ion (main contributor with DS concentration ≥0.50 M): Na+ accumulation could be mitigated by Na+ transport dominant by electrically driven migration (i.e., 21.3-62.1% of reverse-fluxed Na+), and bicarbonate accumulation could be reduced by buffer system. A medium-low concentration of 0.25 M NH4Cl DS had a better performance on current density of 165.0 ± 23.0 A m-3 and COD removal efficiency of 91.5 ± 3.4% by taking advantage that 77.7 ± 1.3% of reverse-fluxed ammonium could be removed by biological treatment and ammonium transport. A high NaOAc DS concentration (i.e., ≥0.05 M) exhibited a higher current density of 145.3-146.0 A m-3 but a lower COD removal efficiency due to the limited carbon source utilization capacity of anaerobic bacteria. Both concentration diffusion (20.9-28.3%) and electrically driven migration (29.5-39.4%) promoted reverse-fluxed Na+ transport to catholyte and thus mitigated Na+ accumulation in the feed/anolyte. These findings have provided an optimal DS concentration for BEA-OMBR operation and thus encourage its further development.

Effects of operating parameters on salinity accumulation in a bioelectrochemically-assisted osmotic membrane bioreactor.

Salinity accumulation in osmotic membrane bioreactors (OMBRs) is one of the key challenges, which can be mitigated in situ by reverse-fluxed solute transport through integration of bioelectrochemical systems (BES). The effects of several key operating parameters on salinity accumulation were investigated. Salinity accumulation depended on balance between reversal solute flux (RSF) and reverse-fluxed ammonium (RFA) transport, which was driven by electrical migration and concentration diffusion. DS concentration was the primary factor influencing RSF, and the lowest DS concentration exhibited the minimum solute leakage. Aeration played a vital role in RFA transport, and a higher aeration helped to enhance RFA transport. Increased current generation (i.e., influent flow rate of 0.5 mL min-1 and external resistance of 5.0 Ω) contributed to RFA migration. The lack of electrolyte addition in catholyte contributed to RFA diffusion. These optimal parameters encourage the further development of an effective strategy for salinity mitigation in BES-based OMBR technology.