Bioelectrochemical System For The Enhancement Of Methane Production By Anaerobic Digestion Of Sludge

Large amount of waste activated sludge(WAS)is produced in urban sewage treatment plant and timely treatment and disposal are needed.The WAS,if not well utilized,would be wasted and contaminate the environment.Anaerobic digestion(AD)can recover methane while removing pollutants at the same time,which would be the developing direction of sludge treatment technology.However,the traditional anaerobic digestion has some disadvantages such as long anaerobic digestion time,low substrate utilization efficiency,and sensitivity to toxic and harmful substances,which has become a major factor restricting the efficiency of AD systems.Microbial electrolysis cell(MEC)system can shorten the time of anaerobic digestion and break the bottleneck that inefficient utilization of proteins in anaerobic digestion.We have adopted a new technology called microbial electrolytsis cell-anaerobic digestion(MEC-AD)to treat WAS.We discussed the effect of MEC on anaerobic digestion processes.Here,we first reported the effect of alkaline pretreatment on anaerobic digestion.Experimental results showed alkaline pretreatment can effectively promote the dissolution of organic matters contained in the sludge.After 24 h alkaline pretreatment,the SCOD increased from 185 mg/L to 2981 mg/L,which was 16 times than that of the control.Alkaline pretreatment also improved the methane production.The maximum methane yield of alkaline pretreatment was 0.22 m L/(m L reactor.d),while the maximum methane yield of untreated sludge was only 0.13 m L/(m L reactor.d),cumulative methane production increased by 50%.Compared with the untreated group,the microbial community structure was significantly different.In the alkaline pretreatment group,Euryarchaeota reduced by 4.5%,while Firmicutes increased by 10.4%.Batch experiments were conducted to study bioelectrochemical enhancement of the anaerobic digestion of alkaline pretreated sludge with different applied voltage and with different Phosphate Buffer Solution(PBS).Experimental results showed bioelectrochemical method could be combined with alkaline pretreatment to enhance anaerobic digestion of sludge.The anaerobic digestion time was shortened by 6 days when applied voltage.The maximum methane yields of 0.8 V,0.5 V,and the control were 0.26,0.22 and 0.21 m L CH4/(m L reactor·d),respectively.The methane production of alkaline pretreated sludge increased by 37% and 42% when applied voltage was 0.5 V and 0.8 V.The optimal applied voltage was determined as 0.8 V.The influence of PBS on MEC-AD was also studied,experimental results showed that the maximum methane yield was 0.195 m L CH4 /(m L reactor·d)when mixed with PBS,while the control was 0.18 m L CH4/(m L reactor·d).The cumulative methane production in the MEC-AD reactor was 1.45 times than that of the control without PBS.Therefore,the PBS addition to the MEC-AD reactor is also helpful to the methanogenesis process.From the perspective of microbial community structure,the microbial electrochemical system strongly promoted the growth of Euryarchaeota.The proportion of Euryarchaeota increased from 20.3%(0V)to 50.4%(0.5V)and 27.5%(0.8V),respectively.The abundance of Euryarchaeota increased by 30.1%(0.5V)and 7.2%(0.8V)respectively.With applied voltage,the microbial community was selectively enriched with Euryarchaeota,and the enrichment of Euryarchaeota would facilitate the anaerobic digestion of methanogens.In this anaerobic digestion system,the dominant community of methane archaea was Methanosaeta and Methanobacterium.When applied voltage,the abundance of Methanosaeta and Methanobacterium increased.The abundance of Methanosaeta increased from 8.4%(0V)to 28%(0.5V)and 14.6%(0.8V),Methanobacterium increased from 8.4%(0V)to 20.5%(0.5V)and 12.3%(0.8V).