Research On Intensifying High-concentration Petrochemical Wastewater Methane Production Through Anaerobic Digestion Reactor Assisted Bioelectrochemical System

Anaerobic digestion(AD)can simultaneously realize sewage treatment and resource recovery.However,traditional anaerobic digestion treatment has many disadvantages such as low substrate utilization and low methane production,which restrict the development of anaerobic digestion treatment.Bioelectrochemical system(BES)assisted anaerobic digestion technology could improve the metabolic activity of microorganisms by enhancing electron transfer efficiency,thereby improving substrate utilization efficiency and methane production.In this study,BES was applied in anaerobic digestion system,supplied with an applied voltage of-0.8 V,to construct a high-efficiency anaerobic methanogenesis reactor capable of treating petrochemical wastewater.The main research findings are as follows:In this study,an electrochemically assisted anaerobic digestion reactor(BEAD)was constructed,and BEAD was compared with the traditional AD during the long-term operation to discuss the enhancement effect of BES on methane production.During 140 days of operation,BEAD exhibited excellent methanogenesis performance.Compared with the control group,the methane production rate was higher,reaching a maximum of 397.2 m L/d.The methanogenesis rate of AD was just 137.5 m L/d.At the same time,BEAD showed excellent water treatment effect,and the COD removal rate reached as high as 95%.By comparing the activity of coenzyme F420,it was found that the electrode biofilm > the suspended sludge in the BEAD reactor > the suspended sludge in the AD reactor.The activity of coenzyme F420 was enhanced by BES,thereby the methanogenesis of microorganisms was promoted.The reactor was then applied to treat the petrochemical wastewater.In the face of complex petrochemical wastewater,the COD removal efficiency of BEAD was 85%,and the effluent COD was stable at 360±24 mg/L.The COD removal rate of AD was less than 60%,which indicated that BES can improve the treatment efficiency of petrochemical wastewater.The methane yield of BEAD was 490 m L/d,and the proportion of methane accounted for 95.6 %,and AD did not detect methane.This may because the addition of petrochemical wastewater inhibited the methanogenesis of AD,while BES can promote the degradation of refractory substances in petrochemical wastewater.At the same time,petrochemical wastewater contains a large amounts of alcohols(such as methanol,ethanol),which could be directly converted into methane by methyl-type methanogens,hence further improving the production of methane.Finally,through the analysis of the microbial community structure,the hydrogen-type methanogens Methanolinea and Methanogula were selectively enriched in BEAD.The results indicated that BES can promote the enrichment of hydrogen type methanogens.During the whole operation process,the hydrogenotrophic methanogens were always the main methanogens of BEAD.After the addition of petrochemical wastewater,the main bacteria in AD changed from Methanobacterium to methylotrophic methanogens Methanomassiliicoccus.In conclusion,BES had greatly improved the methane production efficiency of anaerobic digestion while exhibiting high water treatment capacity.BEAD could maintain good treatment efficiency even when dealing with complex petrochemical wastewater.The results proved the feasibility of BES to enhance anaerobic digestion of high-concentration petrochemical wastewater to produce methane.