Enhanced Performance Of Coupled Bio-Electrochemical System-anaerobic Sludge Process For Chloronitrobenzene Contained Wastewater Treatment

Chloronitrobenzenes(CINBs)as a kind of halogenated aromatic compounds,have been listed in the’priority pollutant list’by many countries due to the teratogenic,carcinogenic and mutagenic characteristics.Enhanced pollutant decontamination by coupled process based on bioelectrochemical system(BES)and anaerobic bioreactor is one of the research hotspots.However,the research about the biotoxicity of pollutant to bioelectrode,the effects of key parameters on the stability of the coupled process for CINBs contained wastewater treatment as well as potential mechanism for the enahnced performance of the coupled process are limited.This thesis was aimed to cultivate bioanode tolerance to biotoxicity of 2,4-dichloronitrobenzene and improve the BES performance by optimzing the structural paramters,including bioelectrode interval,size and immersion proportion.At the same time,the effects of external voltage,salinity and pollutant concentration on the performance of the coupled BES-upflow anaerobic sludge blanket(UASB)process were investigated and intermittent voltage supply was proposed to reduce energy input.Furthermore,the mechanism for the enhanced performance of the coupled process for DCINB contained wastewater treatment was discussed.The main results are as follows:1.BES without ion exchange membrane(IEM)was developed and bioanode was cultivated by gradient DClNB strategy.The proportion of live cells in the anode biofilm increased from 47.3%to 66.1%after cultivation,making the anode high electrochemical active in the presence of high pollutant concentration which was important for the establishment of IEM-free BES.Compared with the traditional IEM-equipped BES,charge transfer resistance of the IEM-free one decreased from 244.6 to 49.9 Q,leading to the increase of DCINB removal efficiency from 73.3%to 91.3%.Partial DCINB could be removed through anaerobic biological pathway in the IEM-free BES,leading to the increase of total removal efficiency.2.Coupled BES-anaerobic sludge process was constructed and operated in batch assay to investigate the effects of bioelectrode interval,size(reactor volume/electrode size ratio)and immersion proportion(the proportion of electrodes immerged in the sludge)on the performance of the coupled process.The results indicated that immersion proportion had the most significant influence on reactor performance.Specifically,biofilm on the electrode surface with proper thickness(40 μm)was achieved,leading to the decrease in resistance from 240.5 to 138.3 Ω and increase in current and DCINB removal efficiency from 4.4 mA and 56.1%to 6.6 mA and 75.5%.The optimal conditions for electrode interval,reactor volume/electrode size ratio and immersion proportion were 2.3 cm,40 and 40%,respetively.DCINB removal rate was 1.822±0.04 mg L-1 h-1 and △Cl-reached 11.89±0.18 mg L-1 under the optimal condition.3.Coupled BES-UASB process was developed and continuously operated to investigate the effects of external voltage,DCINB concentration and salinity on reactor performance.The results indicated that the coupled process was more stable than the UASB.Performance of the coupled process increased with voltage(0-1.5 V),while inhibition could be observed with an overhigh voltage(2.0 V).More extracellular polymeric substrances(EPS)secretion and higher dehydrogenase activity were achieved in the coupled process,contributing to better stability when the process parameter fluctuated.The results of coupled BES-UASB process with intermittent voltage supply indicated that maximum aniline production rate of the system reached 12.1 g m-3 d-1 which was comparable to that of the continuous one with a pollutant loading of 150 gDCINB m-3 d-1.It should be mentioned that power consumption of 0.02 kWh g-1 AN for the intermittent system was 50%lower than that of the continuous one.Moreover,Syntrophomonas and Dehalobacter genera,responsible for electron transfer and reductive dechlorination were enriched in the coupled process.Specifically,the abundances of Syntrophomonas and Dehalobacter in sludge samples from the coupled process with intermittent voltage supply were 8.2%and 2.6%while the corresponding values in the continuous one were 6.4%and 3.3%.The abundances of Syntrophomonas and Dehalobacter in cathode biofilm samples from the coupled process with intermittent voltage supply were 4.7%and 3.3%while the corresponding values in the continuous one were 6.4%and 8.4%.In this study,long-term stable treatment of DCINB contained wastewater could be achieved in the coupled BES-UASB process.Intermittent voltage supply will be an alternative due to lower power consumption and good performance,providing a new concept for CINBs contained wastewater treatment.