Cathode membrane fouling reduction and sludge property in membrane bioreactor integrating electrocoagulation and electrostatic repulsion

A novel reduced graphene oxide/polypyrrole conductive ceramic membrane enhanced electric field membrane bioreactor: Mariculture wastewater treatment performance and membrane fouling mitigation

A novel electric field membrane bioreactor (EMBR) for mariculture wastewater treatment utilizing reduced graphene oxide/polypyrrole ceramic membrane (rGO/PPy CM) was constructed and compared with MBRs using CM support and rGO/PPy CM. EMBR (rGO/PPy) obtained the highest pollutant removal rates (84.99% for TOC, 85.98% for NH₄⁺-N), the lowest average membrane fouling rate (2.42 kPa/d) and pollutant adhesion performance by characterization. Meanwhile, the specific fluxes of characteristic foulants in EMBR were enhanced, and the total resistances were reduced by 8.12% to 62.46%. The underlying mechanisms included reduced attraction energy and improved electrostatic repulsion between contaminants in EMBR and membrane by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, DLVO model and force analysis. Therefore, this study complemented the understanding of antifouling effect and mechanism in EMBR by interaction energy and force analysis of characteristic pollutants. These findings also provided new insights into the application of EMBR for mariculture wastewater treatment.

Experimental investigation of the performance of anaerobic membrane bioreactor with electrolytic regeneration (AMBER) for challenges and options in wastewater treatment

Significant changes in wastewater services are necessary for achieving the sustainable development goals (SDGs), by utilizing resource recovery, recycle, and reuse in urban wastewater-treatment plants. Based on recent experiences, to improve the filtration behavior of a membrane bioreactor, a hybrid system including an upgraded anaerobic baffled reactor coupled with an electrolysis process and a nanocomposite-membrane was developed. The system, called an anaerobic membrane bioreactor with electrolytic regeneration (AMBER), is a bio-electrochemical process that is expected to be simultaneously efficient in both biogas augmentation and fouling mitigation. The goals were to enhance the stability and efficiency of the anaerobic membrane bioreactor. The integration of the electrolytic process with the ABR (EABR) using a pair of iron electrodes enhanced the removal of contaminants in the ABR while successfully maintained pH in the optimum range for anaerobic digestion (6.8 to 7.2). Then, the performance of AMBER in pollutant removal, including organic load, suspended solids, and microbial load, were investigated over 240 days. The results showed that configuration considerably enhanced permeate flux, as it reduced the deposition of extracellular polymeric substances (EPS) on the surface of the nanocomposite membrane, leading to a reduction in membrane fouling. EPS was extracted and quantified to compare the effect of biogas backwash on the function of the membrane reactor. After 7 d of operation with a daily biogas backwash, the flux reduction was approximately 13 % for the conventional combination of the anaerobic baffled reactor and the membrane bioreactor (AMBR), while it was limited to 4 % in AMBER. After cleaning by the biogas, EPS formation decreased 63 % in AMBER when compared to the AMBR. The results revealed that AMBER can be considered an environmentally competitive bioenergy technology for wastewater treatment with the purpose of water recovery and reuse, employing optimized operational conditions, application of antifouling membranes, and electrically-based strategies.

Two-stage microbial fuel cell (MFC) and membrane bioreactor (MBR) system for enhancing wastewater treatment and resource recovery based on MFC as a biosensor

Lack of process control between the two stages of a combined microbial fuel cell-membrane bioreactor (MFC-MBR) system limits its application in wastewater treatment due to membrane fouling and high energy consumption. In this study, a two-stage MFC-MBR integrated system was established to investigate the impact of incorporating process control on petroleum refinery wastewater treatment. The results showed that chemical oxygen demand (COD) removal exhibits a linear relationship with the MFC voltage output (R² = 0.9821); therefore, the MFC was used as a biosensor to control the combined system. The removal efficiencies of COD, ammonium nitrogen (NH₄⁺-N), and total nitrogen (TN) were 96.3%, 92.4%, and 86.6%, respectively, in the MFC-MBR biosensor, whereas those in the control system were 74.7%, 71.2%, and 64.7% respectively. Furthermore，using the biosensor control system yielded a 50% reduction in the transmembrane pressure (1.01 kPa day^-1) and decreased membrane fouling in wastewater treatment. The maximum energy recovery of the biosensor system (0.00258 kWh m^-3) was five times higher than that of the control system, as determined by calculating the mass balance of the system. Thus, this study indicates that using the MFC as a biosensor for process control in an MFC-MBR system can improve overall system performance.

Molecular insights into the impacts of iron(III) ions on membrane fouling by alginate

Molecular mechanisms responsible for the filtration behaviors of sodium alginate (SA) in presence of different iron(III) ion concentration were explored in this study. It was found that specific filtration resistance (SFR) of alginate mixtures (1.0 gSA/L) firstly increased and then decreased to a trough with iron(III) concentration increase from 0 to 2.5 mM. Alginate mixture interacting with 0.1 mM iron(III) possessed an SFR as high as 1.65 × 10¹⁴ m kg^-1, which could be explained by Flory-Huggins lattice theory related with gel filtration. Optical observation showed significant morphology transition (from gel to granular solids) of foulant layers with iron(III) concentration increase. A series of characterizations indicated the change of microstructure, pH and surface charge of alginate mixture with iron(III) concentration. Density functional theory (DFT) simulation suggested that iron(III) ion preferentially forms coordination bonds with three terminal carboxyl groups of alginate chains, facilitating elongation and cross-linking of alginate chains. Such a coordination mode induces formation of a slime and homogeneous gel, corresponding to high SFR. Continuous increase in iron(III) concentration leads to non-terminal coordination, which makes alginate chains more clustered and coiled. This effect, together with effects of the reduced surface charge and electric double layer compression, significantly decrease SFR of alginate mixtures. This study provided deep molecular insights into effects of iron(III) ions on alginate fouling.

Filtration behaviors and fouling mechanisms of ultrafiltration process with polyacrylamide flocculation for water treatment

This study aims to investigate thermodynamic mechanisms of filtration behaviors of ultrafiltration (UF) process with polyacrylamide (PAM) flocculation for surface water treatment, which has not been investigated previously. It was interestingly found that, filtration of durably mixed sodium alginate (SA) solution corresponded to an extraordinarily high specific filtration resistance (SFR) (3.28 × 10¹⁴ m·kg^-1 without polyacrylamide addition) and a V-shaped profile of SFR characterized by a sharp fall followed by a correspondingly sharp rise along with the increase in PAM addition concentration. Experimental characterizations suggested that, membrane fouling was mainly caused by the gel layer formation rather than the pore clogging and cake/floc formation. Rather than the chemical composition change, the changes of the solution physicochemical properties (pH and zeta potential) and foulant morphology are associated with above-mentioned interesting filtration behaviors. Accordingly, the thermodynamic mechanisms of the filtration behaviors were proposed. It was proposed that, the thermodynamics of polymeric network described by the Flory-Huggins lattice theory were responsible for the extraordinarily high SFR of SA gel layer. Low dosage of PAM addition decreased the negative zeta potential and homogeneity of the gel system, causing the reduced SFR. In contrast, further PAM addition increased the negative zeta potential and homogeneity of the gel system, and then increased the SFR of the gel layer. These results reasonably explained the V-shaped profile of SFR. This study provided significant insights into the effects of PAM addition on ultrafiltration behaviors of alginate solution.

Feasibility of isolated novel facultative quorum quenching consortiums for fouling control in an AnMBR

Anaerobic membrane bioreactor (AnMBR) technology is being recognized as an appealing strategy for wastewater treatment, however, severity of membrane fouling inhibits its widespread implementations. This study engineered novel facultative quorum quenching consortiums (FQQs) coping with membrane fouling in AnMBRs with preliminary analysis for their quorum quenching (QQ) performances. Herein, Acyl-homoserine lactones (AHLs)-based quorum sensing (QS) in a lab-scale AnMBR initially revealed that N-Hexanoyl-dl-homoserine lactone (C6-HSL), N-Octanoyl-dl-homoserine lactone (C8-HSL) and N-Decanoyl-dl-homoserine lactone (C10-HSL) were the dominant AHLs in AnMBRs in this study. Three FQQs, namely, FQQ-C6, FQQ-C8 and FQQ-C10, were harvested after anaerobic screening of aerobic QQ consortiums (AeQQs) which were isolated by enrichment culture, aiming to degrade C6-HSL, C8-HSL and C10-HSL, respectively. Growth of FQQ-C6 and FQQ-C10 using AHLs as carbon source under anaerobic condition was significantly faster than those using acetate, congruously suggesting that their QQ performance will not be compromised in AnMBRs. All FQQs degraded a wide range of AHLs pinpointing their extensive QQ ability. FQQ-C6, FQQ-C8 and FQQ-C10 remarkably alleviated extracellular polymeric substances (EPS) production in a lab-scale AnMBR by 72.46%, 35.89% and 65.88%, respectively, and FQQ-C6 retarded membrane fouling of the AnMBR by 2 times. Bioinformatics analysis indicated that there was a major shift in dominant species from AeQQs to FQQs where Comamonas sp., Klebsiella sp., Stenotrophomonas sp. and Ochrobactrum sp. survived after anaerobic screening and were the majority in FQQs. High growth rate utilizing AHLs under anaerobic condition and enormous EPS retardation efficiency in FQQ-C6 and FQQ-C10 could be attributed to Comamonas sp.. These findings demonstrated that FQQs could be leveraged for QQ under anaerobic systems. We believe that this was the first work proposing a bacterial pool of facultative QQ candidates holding biotechnological promises for membrane fouling control in AnMBRs.

On the performance of electrocoagulation-assisted biological treatment processes: a review on the state of the art

The combined treatment systems have become a potential alternative to treat highly polluted industrial wastewater to achieve high-quality treated effluents. The current review focuses on the treatment systems compromising electrocoagulation (EC) as a pretreatment step followed by a biological treatment step. The reasons for applying EC as a pretreatment process were mainly to (1) detoxify the wastewater by removing inhibitors of the biotreatment step or (2) to remove the major part of the COD or (3) the dissolved materials that could cause fouling to membrane bioreactors or (4) to increase the activity of the microorganisms. This combination represents a new and promising application characterized by higher performance and removal efficiency. The main published findings related to this application are presented and analyzed. Besides, the statistical models used to optimize the process variables and the kinetics of microorganism growth rate are discussed herein. Most of the previous investigations were conducted in a laboratory-scale level with biologically treated water as a feed to the EC process. Only a few works applied a hybrid system consisting of the biological step and the EC step. In all studies, improved performance and higher removal efficiencies of the combined process were achieved particularly when applying aluminum electrodes, providing more than 95% removal efficiency. Many researchers have reported that they had faced a significant problem in the operation of the electrocoagulation process associated with the reduction of electrodes' efficiency caused by deposits of the coagulation complex. This problem needs to be effectively resolved.

Biofouling effects on the performance of microbial fuel cells and recent advances in biotechnological and chemical strategies for mitigation

The occurrence of biofouling in MFC can cause severe problems such as hindering proton transfer and increasing the ohmic and charge transfer resistance of cathodes, which results in a rapid decline in performance of MFC. This is one of the main reasons why scaling-up of MFCs has not yet been successfully accomplished. The present review article is a wide-ranging attempt to provide insights to the biofouling mechanisms on surfaces of MFC, mainly on proton exchange membranes and cathodes, and their effects on performance of MFC based on theoretical and practical evidence. Various biofouling mitigation techniques for membranes are discussed, including preparation of antifouling composite membranes, modification of the physical and chemical properties of existing membranes, and coating with antifouling agents. For cathodes of MFC, use of Ag nanoparticles, Ag-based composite nanoparticles, and antifouling chemicals is outlined in considerable detail. Finally, prospective techniques for mitigation of biofouling are discussed, which have not been given much previous attention in the field of MFC research. This article will help to enhance understanding of the severity of biofouling issues in MFCs and provides up-to-date solutions. It will be beneficial for scientific communities for further strengthening MFC research and will also help in progressing this cutting-edge technology to scale-up, using the most efficient methods as described here.

Fouling Mitigation and Wastewater Treatment Enhancement through the Application of an Electro Moving Bed Membrane Bioreactor (eMB-MBR)

High operational cost due to membrane fouling propensity remains a major drawback for the widespread application of membrane bioreactor (MBR) technology. As a result, studies on membrane fouling mitigation through the application of integrated processes have been widely explored. In this work, the combined application of electrochemical processes and moving bed biofilm reactor (MBBR) technology within an MBR at laboratory scale was performed by applying an intermittent voltage of 3 V/cm to a reactor filled with 30% carriers. The treatment efficiency of the electro moving bed membrane bioreactor (eMB-MBR) technology in terms of ammonium nitrogen (NH₄-N) and orthophosphate (PO₄-P) removal significantly improved from 49.8% and 76.7% in the moving bed membrane bioreactor (MB-MBR) control system to 55% and 98.7% in the eMB-MBR, respectively. Additionally, concentrations of known fouling precursors and membrane fouling rate were noticeably lower in the eMB-MBR system as compared to the control system. Hence, this study successfully demonstrated an innovative and effective technology (i.e., eMB-MBR) to improve MBR performance in terms of both conventional contaminant removal and fouling mitigation.

Critical review of fouling mitigation strategies in membrane bioreactors treating water and wastewater

The current research was an effort to critically review all approaches used for membrane fouling control in the membrane bioreactors treating water and wastewater. The first generation of antifouling methods tried to optimize operational conditions, or used chemical agents to control membrane fouling. Despite their positive impacts on the fouling mitigation, these methods did not provide a sustainable solution for the problem. Moreover, chemical agents may affect microorganisms in bioreactors and has some environmental drawbacks. The improved knowledge of membrane fouling mechanism and effective factors has directed the attention of researchers to novel methods that focus on disrupting fouling mechanism through affecting fouling causing bacteria. Employing nanomaterials, cell entrapment, biologically- and electrically-based methods are the latest efforts. The results of this review indicate that sustainable control of membrane fouling requires employing more than one single approach. Large scale application of fouling mitigation strategies should be the focus of future studies.

Mechanistic insights into alginate fouling caused by calcium ions based on terahertz time-domain spectra analyses and DFT calculations

Fouling mechanisms underlying the filtration behaviors of alginate solution caused by calcium addition were investigated by Terahertz time-domain spectroscopy (THz-TDS) and density functional theory (DFT) techniques. Filtration tests showed that specific filtration resistance (SFR) of alginate solution (0.75 g L^-1) monotonously increased with calcium addition at a relatively low range of calcium concentration (0-1.0 mM), and SFR (2.61 × 10¹⁵ m kg^-1) of alginate solution with 1.0 mM calcium addition was extremely high as compared with sludge suspension. Characterizations by X-ray photoelectric spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis (TGA) showed that the composition of functional groups, elements and thermal stability of alginate was not apparently affected by calcium concentration. Howbeit, THz-TDS spectra showed that calcium addition caused structural variation of alginate polymer in solution. DTF calculation results showed that initial binding of alginate chains induced by calcium ions preferentially occurred in intermolecular other than intramolecular, and moreover, the two alginate chains bridged by a calcium atom tend to stretch in a tetrahedron structure (cross to each other) other than parallel to each other. According to these results, "chemical potential gap" depicted by Flory-Huggins theory was suggested to be responsible for the filtration behaviors of alginate solution caused by calcium addition. This study provided the mechanistic insights into membrane fouling.

Tuning anti-adhesion ability of membrane for a membrane bioreactor by thermodynamic analysis

Developing strategies that allow tuning anti-adhesion ability of membranes in membrane bioreactors (MBRs) is of primary interest in membrane fouling research. In this study, interaction energies between foulants and membrane in three different interaction scenarios were systematically assessed based on thermodynamic methods. It was found that, membrane surface electron donor tension (γ(-)) rather than surface hydrophilicity was a more reliable indicator to predict adsorptive fouling. The interaction energy would be continuously repulsive in the initial range of separation distance when membrane γ(-) is higher than a critical value, suggesting that designing membrane with γ(-) higher than a critical value would confer membrane with high anti-adhesion ability. It was also found that, zeta potential on the membrane surface exerted certain effects on adsorptive fouling. This study proposed a novel strategy regarding adjusting membrane γ(-) to tune anti-adhesion ability of membrane, and also offered a thermodynamic theoretical background to this strategy.