Performance enhancement, membrane fouling mitigation and eco-friendly strategy by electric field coupled membrane bioreactor for treating mariculture wastewater.

An eco-friendly strategy for mariculture wastewater treatment using an electric field attached membrane bioreactor (E-MBR) was evaluated and compared with a conventional membrane bioreactor (C-MBR). The removal efficiencies of total nitrogen (TN) and chemical oxygen demand (COD) increased significantly and the membrane fouling rate reduced by 44.8% in the E-MBR. The underlying mechanisms included the enriched nitrifiers and denitrifiers, the enhanced salinity-resistance, the increased activities and upregulated genes of key enzymes involved in nitrification and denitrification for improving the performance of mariculture wastewater treatment, and the enriched extracellular polymeric substance (EPS)-degrading genera, the downregulated EPS biosynthesis genes, the repressed biofilm-forming bacteria, the enhanced zeta potential absolute value and the generated H2O2 for membrane fouling mitigation by electrical stimulation. Compared with the C-MBR, the energy consumption, carbon emissions, and nitrogen footprint were reduced. These findings provide novel insights into mariculture wastewater treatment using an applied electric field.

The responses of activated sludge to membrane cleaning reagent H2O2 and protection of extracellular polymeric substances.

Hydrogen peroxide (H2O2) is evaluated as a potential replacement for chlorine to control biofouling in membrane bioreactors (MBRs). However, H2O2 might diffuse into the mixed liquor and damage microorganisms during membrane cleaning. This study comprehensively analyzed the impacts of H2O2 on microbes. Key enzymes involved in phenol biodegradation were inhibited with H2O2 concentration increased, and thus phenol degradation efficiency was decreased. Increase of lactic dehydrogenase (LDH) and intracellular reactive oxygen species (ROS) indicated more severe cell rupture with H2O2 concentration increased. At the same H2O2 concentration, Extracellular polymeric substances (EPS) extraction further led to inhibiting the activity of key enzymes, decreasing phenol degradation efficiency, and enhancing LDH release and ROS production, demonstrating that the existence of EPS moderated the adverse impacts on microbes. Spectroscopic characterization revealed the increase of H2O2 decreased tryptophan protein-like substances, protein-associated bonds and polysaccharide-associated bonds. Hydroxyl and amide groups in EPS were attacked, which might lead to the consumption of H2O2, indicated EPS protect the microorganism through sacrificial reaction with H2O2.

Effect of Fe3O4 nanoparticles exposure on the treatment efficiency of phenol wastewater and community shifts in SBR system.

Increasing magnetic Fe3O4 nanoparticles (Fe3O4 NPs) application has aroused concern about its potential environmental toxicity. During acute and chronic exposure, key enzymes involved in phenol biodegradation were promoted at 0-600 mg/L Fe3O4 NPs, while were inhibited at 800 mg/L Fe3O4 NPs, correspondingly affected phenol degradation efficiency. Lactic dehydrogenase (LDH) increased when Fe3O4 NPs exceeded 600 mg/L, indicated the more severe cell rupture at high Fe3O4 NPs concentration. At the same Fe3O4 NPs concentration, the removal of EPS further inhibited key enzymes, decreased phenol degradation, and increased LDH, indicating that the existence of EPS relieved the adverse effects on microorganisms. Spectroscopic analysis showed that protein and polysaccharide associated bonds in EPS decreased at 0-600 mg/L Fe3O4 NPs, while increased when Fe3O4 NPs exceeded 600 mg/L, which was in accordance with EPS content. Biopolymer-degrading and phenol-degrading genera increased at 0-600 mg/L Fe3O4 NPs, while decreased at Fe3O4 NPs exceeded 600 mg/L, which conformed to EPS content and phenol degradation efficiency.

Enhanced treatment performance of phenol wastewater and membrane antifouling by biochar-assisted EMBR.

Biochar-assisted EMBR (BC-assisted EMBR) was built to enhance treatment performance of phenol wastewater and membrane antifouling. BC-assisted EMBR significantly increased phenol degradation efficiency, owing to combined effects of biodegradation, adsorption and electro-catalytic degradation. Meanwhile, BC-assisted EMBR obviously mitigated membrane fouling. The coupling effect of BC and voltage led to the lower N-acyl-homoserine lactones (AHLs) and bound extracellular polymeric substances (bound EPS) contents around and on membrane surface. Protein (PN)/polysaccharide (PS) in bound EPS was decreased, led to the increase of negative charge and decrease of hydrophobicity of sludge, which abated bound EPS adsorption on membrane surface. Microbial community analyses revealed that the coupling effect of BC and voltage could enrich phenol-degraders (e.g., Comamonas), electron transfer genus (Phaselicystis), and biopolymer-degraders (Phaselicystis and Tepidisphaera) in BC-assisted EMBR and on its membrane surface, while decrease biofilm-former (e.g., Acinetobacter) and bound EPS-producer (Devosia), which was beneficial to promote phenol treatment and mitigate membrane fouling.

Quorum quenching bacteria bioaugmented GO/PPy modified membrane in EMBR for membrane antifouling.

A novel integrated system with quorum quenching (QQ) bacterium Burkholderia sp. ssn-2 bioaugmented graphene oxide/polypyrrole (GO/PPy) conductive polymercomposite membrane (CPM) in MBR with electric field (EMBR) was established. The integrated system exhibited the highest degradation efficiency for phenol (100%) and COD (93.2%-99.9%) during the 120 days operation. Membrane fouling in the integrated system was notably mitigated by the coupling effect of CPM + voltage and QQ bacterium ssn-2. The hydrophilicity and antibacterial activity of CPM inhibited the hydrophobic protein foulants adsorption, bacteria colonization and attachment on the CPM surface. Extracellular polymeric substances (EPS) content was positively correlated with N-acyl-homoserine lactones (AHLs) concentration, and decreased with AHLs degradation by QQ bacterium ssn-2. The increased negative charge of EPS on the CPM surface augmented the electrostatic repulsion between the EPS and cathode CPM in the integrated system. Moreover, the coupling effect altered the microbial communities. A decreased AHLs concentration had a significantly negative correlation with QQ bacterium ssn-2 enrichment, which exhibited the dual effects of degrading phenol and AHLs, and enriching biopolymer-degrading genera Clostridium sensu strict and Acidovorax in the integrated system and on the CPM surface. This can lead to a decrease in the EPS content.

Impacts of long-term electric field applied on the membrane fouling mitigation and shifts of microbial communities in EMBR for treating phenol wastewater.

The membrane antifouling and shifts of microbial communities of long-term electric field applied in MBR (EMBR) for treating phenol wastewater was systematically investigated. The increased voltage increased the phenol degradation rate and slowed down the TMP increase rate in EMBR (G1-G4: 1.65 × 10-3-8.40 × 10-4 Mpa/d), indicated the enhancement of phenol treatment and mitigation of membrane fouling. Decrease of protein (PN)/polysaccharide (PS) in EPS increased the negative charge and decreased the hydrophobicity of sludge, thus abated its adsorption on membrane surface. The decrease of AHLs concentration attributed to the electrolysis of AHLs by the electro-generated H2O2. Besides, the AHLs had significantly negative correlation with QQ bacteria Rhodococcus and Stenotrophomonas enrichment and positive correlation with QS bacteria Aeromonas decrease in EMBRs, suggesting that coupling effects of voltage and QQ bacteria degraded AHLs, thus decreased EPS content which was positively correlated with AHLs concentration. Biopolymer-degrading genera (Clostridium sensu strict etc.) increased in EMBR and on membrane surface, while biofilm-forming genera (Pseudomonas etc.) decreased on membrane surface. These resulted in EPS content decrease and membrane antifouling.

Effects of biochar on the phenol treatment performance and microbial communities shift in sequencing batch reactors.

The extensive application of biochar (BC) attracts concerns regarding its environmental effect. Wastewater treatment systems are potential BC recipients; however, the impacts of BC on these systems are still unclear. In this study, effects of BC on the phenol treatment performance and shift in microbial communities in sequencing batch reactor (SBR) were investigated. The phenol degradation rates were enhanced in all BC-treated SBRs during the whole operation due to promotion of key enzymes involved in phenol degradation. The decrease in abundance of intracellular reactive oxygen species (ROS) in SBRs indicated that BC protected microorganisms by ameliorating phenol toxicity, leading to a decrease in the secretion of extracellular polymeric substances (EPS). The functional groups, protein (C=O, -CO-NH), polysaccharide (C-OH, C-O-C, C-O), and nucleic acids (O-P-O) associated bonds of EPS decreased or disappeared in BC-treated SBRs. Miseq sequencing revealed significant decrease in bacterial diversity and remarkable changes in the bacterial community structure in BC-treated SBRs. Abundances of Comamonas and Cupriavidus increased significantly upon BC exposure, which contributed to phenol degradation. Treatment with relatively high BC dosage exhibited considerable inhibition on Thauera. Canonical correspondence analysis (CCA) indicated that the shift in abundances of these genera was closely associated with BC dosage. This study suggested that BC exerted protective effects on sludge microbes of phenol wastewater treatment systems, while it affected the bacterial community structure and diversity at test concentrations. Thus, this study elucidates the comprehensive effects of BC on wastewater treatment process.

Impacts of applied voltage on EMBR treating phenol wastewater: Performance and membrane antifouling mechanism.

The impacts of electric field applied in MBR (EMBR) for treating phenol wastewater and membrane antifouling mechanism were systematically investigated. Phenol degradation rate increased from 0 to 0.8 V/cm, while decreased from 0.8 to 1.75 V/cm, which significantly positively correlated with key enzymes. The membrane fouling rate of EMBR gradually slowed down with voltage increasing. The applied voltage significantly reduced EPS contents, and altered its compositions probably due to H2O2 oxidation, which were the major reasons for membrane antifouling. Red shift in UV-Vis spectrum at 210-220 nm and reduction of fluorescence emission intensity from tryptophan protein-like substances in EPS reduced the energy requirement for electrons transition of electron-donating groups with voltage increasing. Positively charged bond NH2 decreased and negatively charged bond COO increased in EPS with voltage increasing, which led to the increase of absolute value of zeta potential and then remarkable augmented of electrostatic repulsion between sludge and membrane.