Performance And Mechanisms Of An Electrochemical Biofilter (EBF) For Gaseous VOCs Removal

The performances and mechanisms of an electrochemical biofilter(EBF)was studied in this research,to investigate different current and nutrient salt's effects on removal performances and biomass control,along with investigations on electrochemical mechanisms and microbial community structure changes caused by changes of parameters.The EBF was integrated a graphite anode and a stainless-steel cathode,filled with polyurethane packing media inoculated with activated sludge.The first part of the study is the investigation of optimal current intensity,a 60 d continuous study of four current intensities:0 mA,20 mA,50 mA and 80mA,each for 15 d was carried out.Removal efficiency of toluene,mineralization rate,biomass and microbial activity are measured in each session.Results concluded that 50 mA(0.42 mA/m~2)with toluene removal efficiency of 66.5%and 48%biomass growth rate decrease,with highest microbial metabolic ability and activity,is an overall optimal current intensity for EBF operation considering its outstanding enhancements.Investigation for optimal nutrient salt was studied,parameters identical to previous current study with optimal 50 mA intensities for investigation of two ammonium salts:ammonium chloride and ammonium sulfate,their performances were monitored and compared with parts of the previous current study which used nitrate salt,for comparisons of these three salts and their sensitivity to EBF system.Results showed that nutrient with ammonium chloride as nitrogen source was the most effective for EBF system,with removal efficiency increase of 9.6%and biomass growth rate reduction of 62%,along with enhanced microbial metabolic activities and abilities.Investigation on EBF's effects on system performances for degradation of four VOCs:n-hexane,styrene,dichloromethane and diisobutylene was carried out.Results showed that EBF have enhancement effects on n-hexane,styrene and dichloromethane but not diisobutylene.Increases in VOCs removal are 30.7%,48.7%,35.7%and-10.6%for n-hexane,styrene,dichloromethane and diisobutylene respectively,with reduction of biomass growth rate of 31.9%,62.2%,21.2%and-2.1%respectively.A simulated system with electrodes submerged directly in nutrient solution used for spray feeding was constructed and studied with identical concentration and current/voltage intensities.Aiming for detection of four oxidants:sodium hypochlorite,hydrogen peroxide,hydroxyl radical and superoxide dismutase.0.24 mg/m~3 free chlorine was detected in ammonium chloride after 20 min of 50 mA electrification whereas 0.05mg/m~3 was detected in sodium nitrate and ammonium sulfate.Hydrogen peroxide was present in all samples after 30 min electrification at 1700 mA,with concentrations of approximately 2 mg/L.Hydroxyl radical was detected as over 1.5 mg/L in ammonium salts after 20 min electrification at 1700 mA.Superoxide dismutase showed an inhibition rates of over 0.6%in all samples.Investigation on the effects of electrical current on microbial community structure provide insights for better understanding of the mechanisms of EBF.Results showed that Actinobacteria has lower current tolerance whereas Proteobacteria and Bacteroidetes generally increase in population with the increase of current,indicating higher tolerance in EBF.The dominant genus Rhodococcus responsible for degradation of aromatic compounds decreased as current increased.Nitrifying bacteria were inhibited in EBF,lowering competition of nitrogen source for degrading bacteria,possibly explaining the enhanced performances.Xantomonadaceae family showed increase in n-hexane sample,Acidobacterium and Mycobacterium increased slightly in dichloromethane samples and Nitrosomonas showed decrease in samples of ammonium salts.