Synergistic Degradation Of Landfill Leachate In A Hybrid Microbial Fuel Cell System With Algae Biofilm And Oxygen-Consuming Unit

Landfill leachate is a kind of natural exudation from garbage decomposition of landfill or landfill closure.It is one of the most difficult sewage to degrade due to its high organic matter and high ammonia nitrogen content,thus traditional landfill leachate treatment methods may cause secondary pollution and the cost of treatment is high.Therefore it is urgent to develop a green and low-cost landfill leachate treatment technology.Microbial fuel cells?MFCs?use microorganisms as biocatalysts to oxidize organic substrates and release electrons,with the potential for simultaneous wastewater treatment and power production.However,microbial fuel cells are more prone to degrade organic contaminants,and the efficiency of nitrogen removal in leachate is poor.In this paper,microalgae biofilm technology was introduced into single-chamber MFC,and microalgae can effectively absorb nutrients N and P in leachate for growth.MFC can provide the microalgae with the CO₂ required for photosynthesis,MFC simultaneously utilizes the in situ generated oxygen of microalgae photosynthesis as the electron acceptor of the MFC cathode.However,the O₂ generated by the microalgae can diffuse to the single-chamber MFC anode,which is not conducive to the survival of the microorganisms,and further reduce the electricity production performance of the MFC.Therefore,the oxygen-consuming unit was used to couple the microalgae biofilm with the single-chamber MFC in this paper,and leachate was used as the target pollutant to study the feasibility of degrading pollutants and energy recovery.The study includes the following sections:?1?The landfill leachate was degraded by AB-MFC system,AB-OCU-MFC system?The oxygen-consuming unit used carbon felt as a carrier,and was inoculated for a period of time after inoculation of sewage?,MFC system and AB system,and the feasibility of coupling system to recover electric energy and biomass energy was studied.The experimental results showed that AB-OCU-MFC achieved maximum COD and NH₄⁺-N removal efficiency of86.80%and 89.40%,the maximum voltage was 0.39V,and a algae biomass productivity of1.23 g·L^-1·d^-1 could be obtained simultaneously.The COD and NH₄⁺removal efficiency of AB-MFC were 73.90%and 77.70%,while the COD and NH₄⁺removal efficiency of AB were72.69%and 80.00%.The removal efficiency of organic matter and nitrogen was the lowest in the MFC system alone,69.30%and 30.30%,respectively.The algal biomass production of the AB-MFC,AB and the AB-OCU-MFC system was gradually increased,and the electric energy recovery efficiency of MFC,AB-MFC,AB-OCU-MFC was gradually reduced.The degrade effect of humic acid was the best in AB-OCU-MFC system,while it was relatively poor in other systems.?2?The effects of oxygen unit of different thicknesses in the AB-OCU-MFC system on pollutant degradation and energy recovery in leachate were explored.Experimental results found that with the increase of OCU thickness,the removal efficiency of COD and nitrogen was getting higher and higher.When the thickness of OCU was 0 cm,the final degradation efficiency of COD was 73.90%,and the maximum removal efficiency of NH₄⁺-N and TN were77.70%and 69.56%,respectively,which was the slowest degradation rate and the lowest efficiency.When the thickness of OCU was 1 cm and 2 cm,the maximum degradation efficiency can be achieved within 12 h.The degradation efficiencies of COD were 78.80%and 86.80%,respectively,and the degradation efficiencies of NH₄⁺-N were 84.40%and89.40%,respectively.Microalgal biomass production increased with increasing oxygen unit thickness,while electrical energy recovery efficiency decreased.?3?This study explored the effects of oxygen unit on the microbial community structure of anodes and cathodes in order to understand the mechanisms of power generation and pollutant removal.Analysis of the anode and cathode microbial community structures in the AB-OCU-MFC system and the AB-MFC system by high-throughput sequencing revealed:The microbial morphology on OCU was diverse,and the microbial abundance of different populations was similar.The proportion of the anaerobic bacteria Geobacter in the AB-OCU-MFC system was37.7%higher than that in the AB-MFC system,and a new electrogenic bacterium Rhodopseudomonas appeared.In addition,the most abundant microorganism of the cathode was Thauera,and the abundance was 24.7%,while the aerobic fungus Flavobacterium appeared in the anode of the AB-MFC system,and the Thauera on the cathode was only 2.6%,indicating that OCU could effectively block oxygen from entering the MFC cathode chamber,provide anaerobic environment for anode electroforming bacteria and promote cathodic nitrification and denitrification.