Microbial Electrolysis Cell For Treatment Of Post-hydrothermal Liquefaction Wastewater And Hydrogen Generation

Hydrothermal liquefaction(HTL)is a thermal-chemical technology which could convert high moisture content biomass into biocrude oil under high temperatures and pressures.Most of the studies on HTL focused on the improvement of biocrude yield and quality.However,the treatment of post-hydrothermal liquefaction wastewater(PHWW)has seldom been investigated.This kind of wastewater contains complex and toxic organic compounds with high concentration,such as oxygen and nitrogen heterocyclic compounds,etc.Currently,the traditional wastewater treatment technologies did not have good performance on the PHWW treatment,and the COD removal was merely 40-60%.Based on above,in this study,we built a MEC platform and explored the feasibility of MEC treatment on two typical PHWW and hydrogen production.Furthermore,the effects of different environmental factors(applied voltages,organic loading rates,hydraulic retention times)on the performance of MEC were revealed,and the mechanism of organic matter removal and simultaneously total nitrogen removal from PHWW via MEC was analyzed.The main results were as follows:The feasibility experiments indicated that the design and performance of the MEC platform were fine.It could realize the treatment of two typical PHWW and simultaneous hydrogen production.MEC cathode had absolute advantage in hydrogen production,when swine manure PHWW with high ammonia nitrogen content was used as the substrate,the maximum H2 generation rate and content were 75.36 mL/L/d and 61.77%,respectively.When cornstalk PHWW with low ammonia nitrogen content was used as the substrate of MEC,the maximum H2 generation rate and content were 25.49 mL/L/d and 55.45%,respectively.Therefore,MEC was a feasible way for PHWW treatment,it had great potential for intense research.The research of the MEC performance based on different environmental factors suggested that the organic pollutants in the PHWW were degraded to a great extent and produced hydrogen with high efficiency after MEC treatment.The highest COD removal rate was 97.87%under lower initial substrate concentrations.When swine manure PHWW with high ammonia nitrogen content was used as the substrate,the maximum H2 generation rate and yield were 168.01 mL/L/d and 5.14 mmol/kg COD,respectively.In this case,the hydrogen produced by MEC can basically meet the requirement of hydrogen for biocrude upgrading,so as to realize good coupling of HTL and MEC.MEC treatment also showed better performances on TKN removal(>80%),while NH3-N removal(36.66%-76.53%)was not so well as TKN.Therefore,MEC is suitable for heterocyclic organic nitrogen removal,not good for the high concentration of NH3-N removal.The analysis of microbial community structure in the anode and the organic degradation relationship found that bacteria were dominant in MEC anode and most of them were bacilli.The bacterial diversity in sludge was significantly higher than that in MEC anode biofilm,and the bacteria on MEC biofilm was more specific.In Phylum level,the Proteobacteria,Bacteroidetes,Chlorobi,Actinobacteria,Firmicutes,Chloroflexi constituted over 80%of the total bacteria in the MEC anode.Recalcitrant macromolecular organic compounds such as dimethyl phthalate and diethyl phthalate,were also significantly degraded,and the removal rate were 95.3%and 79.3%,respectively.The degradation of dimethyl phthalate was related to Xanthobacter on the anode biofilm.