Construction And Process Enhancement Mechanism Of An Airlift Bioelectrochemical System For Benzene-Series VOCs Treatment

Volatile organic compounds（VOCs）are important precursor for fine particulate matter(PM_2.5)and ozone（O₃）in ambient air,which is important cause of atmospheric composite pollution in China.Especially toluene,xylene,which generation O₃,SOA,the generation potential is significantly higher than other components,it is important that control benzene-series VOCs for both air quality control and social development.Biotechnology is a green and safety purification of benzene-series VOCs with the advantage of low carbon emission.However,the benzene-series VOCs degradation was limited by liquid-gas mass transfer and degradation rates in biotechnology,which made the long empty bed residence time and large unit size restraint the biotechnology in business.In this paper,we coupled the mass transfer enhancement of airlift reactor（ALR）with the reaction enhancement of bioelectrochemical system（BES）to construct an airlift microbial electrochemical system（AL-BES）to study the removal and mineralization of benzene pollutants.The airlift microbial electrolysis cell（AL-MEC）system was built by Microbial electrolysis cell（MEC）coupled with airlift reactor.Loading the benzene-series VOCs degrading bacteria on polypyrrole-sleeve electrode and got 81%removal efficiency of o-xylene at 2400 mg m^-3 inlet gas concentration.Investigated the purification load of AL-MEC at diffierent process conditions（potential,inlet oxygen concentration,empty bed residence time）,the removal efficiency of o-xylene achieved at 95%and 465.1 g m^-3 h^-1maximum purification load when the potential set on+0.3 V vs.SHE,21%（v/v）oxygen gas concentration and 80s empty bed residence time.The removal efficiency was remained at75%at the inlet o-xylene gas concentration of 3800 mg m^-3.The result of filed SEM was confirmed that the bacterium was grown on polypyrrole surface.The abundance nanowires was observed on electrode,it proved the effectiveness of the polypyrrole modification.The PCR result proved the Novosphingobium sp.、Dokdonella sp.、Sphingopyxis sp.were the dominant biodegradation bacteria,and the main electroactive bacteria were Bacteroidia sp.The BES system was switched to microbial fuel cell（MFC）,and constructed the airlift-microbial fuel cell（AL-MFC）system to operated continuously.Under the same experimental conditions as AL-MEC,AL-MFC obtained a higher removal efficiency（98%）and output voltage of 0.549 V,the o-xylene mineralization efficiency remained between 70and 80%.There was no significant effect on the output voltage when the oxygen concentration was increased from 10%to 21%;the output voltage of AL-MFC was increased to 0.606 V in the presence of external carbon source Na AC,but the removal efficiency of o-xylene was reduced to 74%.The intermediary’s transformation experiments and cyclic voltametric curves confirmed that the electron transfer between microorganisms and electrodes was mainly in the direct mode,and pigment proteins including Omc Z,Omc S,and Omc A on the cell membrane,which involved in the transmembrane electron transfer process.Furthermore,we investigated the degradation effect of AL-MFC on different VOCs components.The removal efficiency of single component ethyl acetate,toluene and o-xylene exhaust gas were remained at 99%,97%and 95%.When the three components were mixed,the removal rate of ethyl acetate did not decrease,while the removal efficiency of toluene and o-xylene decreased by 17%and 3%,respectively,the overall removal efficiency remained above 90%,it confirming that AL-MFC can stably clean multi-component VOCs exhaust gas.