Researches On The Removal Of Perchlorate From Aqueous Solution By Combined Heterotrophic With Electrical Hydrogen Autotrophic Process

Perchlorate as an important pollutant in water has constantly reported in recent years mainly due to its high solublility and mobility in aqueous solution.Compared to physical-chemical process,biological treatment has the advantages of high removal efficiency and low operation cost.Heterotrophic reduction process has faster reaction rates than autotrophic process,and secondary pollution of residual organics has become of concern.Hydrogen autotrophic reduction process has advantages of high removal efficiency and harmless to drinking water,however,it is hard to storage and dangerous to control.The combined heterotrophic and hydrogen autotrophic process based on membrane electrolytic technology for the reduction of perchlorate from aqueous solution was explored in this research.The reactor could reduct perchlorate efficiently without secondary pollution of residual organics.1.The heterotrophic perchlorate reducing bacteria was inoculated by activated sludge obtained from the Wastewater Plant.The bacteria acclimation was conducted using acetate as electron donor in batch mode.Furthermore,the variations of microbial community during acclimation were investigated using High-throughput Sequencing method.During acclimation,the α-biodiversity of enriched mixed bacteria showed a decreasing tendency.The phylum of dominant perchlorate reducing bacteria in the mixed culture include: Proteobacteria,Bacteroidetes,Chlorofexi and Firmicutes.The Michaelis–Menten model described the perchlorate reduction kinetics well.The model parameters qmax and Ks were 4.03~6.27(mg ClO4-/gVSS h)and 7.69~14.30(mg/L),respectively.The optimal pH of reduction reaction was 7.0.The optimal CH3COO-/ClO4-ratio was 1.77 mgCH3COO-/mgClO4-.The enriched mixed bacteria could also use nitrate as electron accepter,and nitrate was more acceptable than perchlorate.2.In this study,perchlorate-reducing hydrogen autotrophic bacteria were acclimated by hydrogen aeration from activated sludge.High-throughput sequencing was applied to analyze changes in biodiversity and the dominant bacteria during acclimation process.The Michaelis-Menten model described the perchlorate reduction kinetics well.Microbial perchlorate reduction occurred across at pH range 5.0-11.0;removal was highest at pH 9.0.The predominant bacteria could use perchlorate,nitrate and sulfate as electron accepter,and the sequence of preference was: NO3-> ClO4-> SO42-.Compared to the feed culture,biodiversity decreased greatly during acclimation process,the microbial community structure gradually stabilized after 9 acclimation cycles.The Thauera genus related to Rhodocyclales was the dominated perchlorate reducing bacteria(PRB)in the mixed culture.3.A novel MBBR(Moving Bed Biological Reactor)based on membrane electrodialysis system for perchlorate removal was established in this study.The impact of applied current intensity and the microbial community structure was explored.In cathode chamber,bacteia utilized hydrogen as electron donor to transform perchlorate to chloride ion.And then the treated water influent from cathode chamber to anode chamber.In anode chamber,the chloride ion was oxidized to active chlorine.The result showed that when HRT(hydraulic retention time)was 4 h,the applied current was 6~20 mA,the cathode chamber could maintain an anaerobic condition.For 4.98 mg/L ClO4-in influent,when the applied current was 15 mA,the removal efficiency was higher than 98.75%.Besides,the transform of ClO4-→Cl-→Cl2 was verified in this system.Active chlorine could disinfect the water to improve effluent quality.The microbial community structure in this reactor is similar to directly hydrogen aeration.The Thauera genus was observed as the dominated perchlorate reducing bacteria.4.A combined heterotrophic and hydrogen autotrophic system was established to treat aquesous solution with perchlorate contamination(10 mg/L)in this research.The reactor was operated at the HRT 3.0 h.At the heterotrophic part,the acetate dosage was 5.90 mg/L,and the perchlorate removal efficiency was 12.13%.For the hydrogen autotrophic part(based on membrane electrolysis process),the applied current ranged from 70 mA to 190 mA.The increase of current could increase the supply of H2;the pH of cathode chamber would be increased consequently.When the pH was greater than 9.7,the activity of perchlorate reducing bacteria(PRB)in cathode chamber was reduced.In this study,the optimal current was 130 mA,with the removal efficiency could reach more than 98.08%.