Municipal Wastewater Treatment By Bioelectrochemical Assisted-Osmosis Membrane Bioreactor

Forward osmosis(FO)is an emerging technology for water reuse and desalination,and has potential benefits of lower fouling propensity and lower energy consumption due to the absence of external hydraulic pressure.However,a key factor to obstain the application of FO system is to choose a suitable draw solute.In this study,a pH response draw solute(polyacrylic acid,PAA)was applied in FO system to achieve high water flux,low reversal salt flux,and resuse.Otherwise,the PAA draw solute was biodegradable and had the less effect on the activity of microbial due to the less salt accumulation in the feed solution,thus,it was applied to the osmosis membrane bioreactor with long-term operation.Microbial fuel cells(MFCs)are an emerging technology that can convert chemical energy in organic compounds to electrical energy through catalytic reactions of microorganisms under anaerobic conditions.In this study,the feed side of a FO was converted to an anode of a MFC and integrated as BES-OMBR system,where the pH response draw solute would recovery,and the possibility for membrane fouling reduced,which can be a promising candidate for wastewater treatment in an energy-efficient way.The specific objectives of this study were to(1)examine the the feasibility of poly acrylic acid PAA as DS in the term of osmosis performance and recovery efficiency;(2)evaluate the operation performance with PAA DS in FO system;(3)examine the operation performance with PAA DS in optimal FO system;(4)evaluate the operation performance with PAA DS in osmosis membrane bioreactor(OMBR)system;(5)examine the osmosis and current generation performance with PAA DS in BES-OMBR system.The results have important implications to further development of the BES-OMBR system with the following conclusions:Dynamic light scattering revealed that the hydrodynamic diameter of PAA increased with decreasing pH.The PAA-Na was in the polyelectrolytes state when the pH was over the pH response point,and that was in the aggregation state when the pH was lower the pH response point during the recovery process.Thus,the pH response point affected the acid and alkali dosage.The highest DS recovery efficiency by the combined pH + MF approach was 99.68%at pH of 4.35,resulting in relatively low PAA-Na concentration in the recovery water(60?67 mg/L).The water flux generated by the FO system using DI water as feeding solution was affected by the PAA-Na DS concentration and molecular weight(MW),and a higher concentration or lower MW had a higher water flux.The FO system achieved a high water flux of 18.0 ± 0.5 LMH,low reverse salt flux(RSF)of 0.11 ± 0.01 gMH,and the Js/Jw of 6.1 ± 0.3 mg/L with 25 wt%PAA-Na(2000 Da)as the DS,and the operation cost was estimated at 0.259 CNY/m3.The water flux generated by the optimal FO system using DI water as feeding solution was affected by the PAA-Na DS concentration during 170-h operation,and a higher concentration had a higher water flux.The FO system achieved a high water flux of 14.5 LMH,low reverse salt flux(RSF)of 0.18 gMH,and the DS concentration in the feed side of 132 mg/L with 30 wt%2000 PAA-Na as the DS.The water flux generated by the OMBR system using DI water as simulate wastewater was affected by the PAA-Na DS concentration during 110-h operation,and a higher concentration had a higher water flux.The FO system achieved a high water flux of 11.4 LMH,low reverse salt flux(RSF)of 0.18 gMH,the DS concentration in the feed side of 43 mg/L,and the COD concentration in the feed side of 56 mg/L with 30 wt%2000 PAA-Na as the DS.The maximum DS degradation rate in the feed solution was 6 mg/(d m3),and the maximum COD degradation rate in the feed solution was 63 mg/(d m3).The water flux generated by the OMBR system over 600-h operation using recovered PAA-Na DS with five-cycles decreased to 1.3%of that generated by original PAA-Na DS.There was no TOC and ammonia accumulation in the feed solution,and the the operation cost was estimated at 2.121?4.354 CNY/kg COD.The water flux generated by the BES-OMBR system using simulate wastewater as feeding solution was affected by the PAA-Na DS concentration and MW,and a higher concentration or lower MW had a higher water flux.The FO system achieved a high water flux of 12.6 ± 0.5 LMH,low reverse salt flux(RSF)of 0.05 ± 0.00 gMH with 32 wt%2000 PAA-Na as the DS.The water flux generated by the BES-OMBR system over 60-h operation using recovered PAA-Na DS with five-cycles decreased to 4.2?6.8%of that generated by original PAA-Na DS.The PAA loss due to RSF during operation was 3?20 mg/L,and the COD concentration in the feed side effluent was 65?71 mg/L.The highest DS recovery efficiency was 99.36?99.87%,resulting in the relatively low PAA-Na concentration in the recovered water(15?21 mg/L),and the the operation cost was estimated at 0.350 CNY/m3.The current density generated by the BES-OMBR system had the same trend with current density,and a higher concentration or lower MW had a higher current density.The FO system achieved a high current density of 159 ± 6 A/m3 with 32 wt%2000 PAA-Na as the DS.The highest current density of 175 A/m3 generated by recovered PAA-Na DS during first recovery process was higher that of original PAA-Na DS(175 A/m3),and it decreased during the following process.