Establishment Of Anaerobic-Bioelectrochemical System Hybrid Reactor And Its Performance In Dye Wastewater Treatment

Dye wastewater is the major part of the industrial wastewater and characterized by complex composition,varying effluent quality,recalcitrant to biodegradability,toxic and intense color.Discharging dye wastewater without adequate treatment would pose serious environmental problem,such as aesthetic problems and light penetration fade,especially the dyes would potentially cause carcinogenicity,teratogenicity and/or mutagenicity.Dye wastewater treatment is one of the major concern of the water pollution control.Biological method is the widely used technology for dye wastewater treatment in consideration of the large discharging quantity.However,it is inefficient and barely satisfied the stricter discharge standard.Bioelectrochemical system(BES)is a newly established and continuously developing technology for contamination remediation,which employs microbes as catalyst and possesses high efficiency in electron transfer and utilization.Nevertheless,study cases about scale-up and practice application of BES are scarce and require continuous research focus in the future.This study dedicated to solve the key issues of the BES application.Organic matters in domestic wastewater(DW)was demonstrated to efficiently drive BES for implementing the decolorization of azo dye as a cost-effective yet highly efficient electron donor source.A hybrid anaerobic reactor with built-in BES was developed and the electrodes material and position were optimized.A combined process system consisted of hybrid anaerobic reactor with built-in BES+aerobic biofilm reactor+denitrification filter+ chemical dephosphorization /advanced treatment was built to treat mixed dye wastewater.The operational parameters and chemicals dosage were optimized to satisfy the discharging and reusing standard.In order to decrease the operating cost,DW was employed as electron donor to decolorize azo dye.Compared to sodium acetate and glucose as electron donor,decolorization efficiency(DE)of BES fed with DW(RDW)was >99% and maximum decolorization rate reached 795.05±60.78 g/(m3?d).RDW presented highest electron utilization efficiency and only few electron lost in methanogenesis and microbial growth.DE kept at 94.91±1.55% when the influent DW diluted to 80 mg-COD/L(corresponding to reductant supply rate of 4.40 mol COD/mol azo bond).Besides,DW was proved to also provide some conductivity and buffer capacity.Accordingly,DE of RDW was less deteriorated to 93.52±0.74% when fully removing the external buffer salts.Microbial community structure analysis indicated that the species abundance and diversity were increased in RDW,biofilm structures from four electrodes were similar and not be altered by the polarity nor the position of electrodes.Desulfovibrio was the dominated genus,which was capable of bidirectional extracellular electron transfer and azo dye reduction.A hybrid anaerobic reactor with built-in BES was developed to overcome the uncertainty of sole BES application and accelerate the practical using of BES technology.Hybrid reactor obviously increased DE compared to sole anaerobic treatment.Compared to carbon fiber,granular graphite was efficient electrode material and DE increased by 6%(influent loading rate of 800 g/(m3?d)).DE increased by 8% when the granular graphite electrode installed above anaerobic sludge than under it.The hydraulic characteristics of hybrid reactors were depicted by residence time distribution and the results indicated the reactor that granular graphite electrode installed above anaerobic sludge well fitted with tanks-in series model,the characteristic value N=3.15.ANSYS Fluent was employed to visually characterize the flow regime,granular graphite electrode simplified to porous zone.Results illuminated that the pressure and resistance of the reactor were increased significantly.Textile printing and dyeing industries often cluster together in some parks,to deal with the low strength,recalcitrant and mixed dye wastewater from that parks,a combined process system consisted of hybrid anaerobic reactor with built-in BES+ aerobic biofilm reactor+ denitrification filter+chemical dephosphorization/advanced treatment was built.The mixed dye wastewater was consisted of 8 kinds dyes(from 3 categories)and real DW.The operating conditions were optimized as influent loading rate of 800 g/(m3?d),recycle ratio of 100%,extra electron donor source for denitrification was 1.35 times to theoretical value,5% poly aluminum chloride solution of 1.5 m L/L.The effluent color,COD,total nitrogen,ammonia nitrogen and total phosphorus were 48±4 times,75±18 mg/L,12.91±0.31 mg/L,3.02±1.80 mg/L and 0.37±0.05 mg/L,respectively,corresponding to removal efficiencies of 91.96±0.31%,85.58±2.60%,83.97±1.88%,95.18±0.51% and 94.20±0.80%,which can meet the discharge standard for dye wastewater.The sodium hypochlorite was added in the chemical phosphorous removal unit to improve effluent quality.Design-Expert provided the optimized dosage of sodium hypochlorite and poly aluminum chloride were 1.28 and 2 m L/L,respectively.In this study,coupling anaerobic digestion and BES as a hybrid reactor then built combined process system could successfully remedy mixed dye wastewater.This finding brings BES closer to the practice and provides a new concept to efficiently treating and reusing textile and dyeing industrial wastewater.