Coupling Technology Of Nitrogen Removal And Electricity Generation Of Halomonas Microbial Fuel Cell Under High Salt Condition

Microbial fuel cell is a device that uses the biocatalysis of electrochemically active microorganisms to directly convert chemical energy stored in organic matter into electrical energy.The coupling of MFC power generation and wastewater purification technology has the advantages of energy recovery,wastewater purification and recycling,and sludge reduction.Wastewater discharged from industries such as food processing,textiles,leather,petrochemicals,and marine aquaculture are usually high-salt nitrogen-containing wastewater.High salt content can improve the ionic strength of MFC matrix,thus improving the conductivity and proton transfer ability,reducing the internal resistance of MFC and improving the power output.When the salinity in the wastewater exceeds the threshold that the electricity-producing bacteria can withstand,its growth and metabolic activity will be inhibited,resulting in a reduction in the performance of the MFC’s coupled operation of electricity generation and denitrification.For high-salt nitrogen-containing wastewater,finding microorganisms that can tolerate high-salt and have high-efficiency denitrification performance is one of the best solutions.The use of Halomonas to study the coupled operation of electricity production and denitrification of MFC under high salinity has important theoretical and practical significance.In this thesis,a moderately halophilic bacterium Halomonas venusta DSM 4743^T,capable of salt-tolerant growth and capable of SND denitrification and electricity generation,was selected as the coupled operation strain of MFC denitrification and electricity generation.The growth characteristics of H.venusta DSM 4743^T were investigated.It can grow salt-tolerant at a concentration of 30-150 g/L Na Cl.The maximum yield of Ectoine was686.53 mg/L at 60 g/L Na Cl concentration,and the highest Ectoine secretion rate was 81.59%at 30 g/L Na Cl concentration.The SND denitrification conditions of H.venusta DSM 4743^T are optimized.The optimized conditions are:sodium succinate as carbon source,C/N of 5,p H 9,and Na Cl 30g/L.Under optimized conditions,from 0 to 168 hours,and the SND denitrification rate was94.33%.Single-chamber MFC was constructed with H.venusta DSM 4743^T as the electricity-producing bacteria,and the electricity-producing conditions of the MFC were optimized.The optimized conditions of the matrix are sodium acetate as the carbon source,50μM riboflavin,p H 9,30 g/L Na Cl,and 100%seawater.Under optimized conditions,the maximum output voltage is 402 m V;the maximum power density is 167.21 m W/m²,which is317%higher than before optimization.The SND denitrification method of H.venusta DSM 4743^T in a single-chamber MFC was investigated.In MFC,the strain oxidized NH₄⁺-N and nitrated to produce intermediate NO₂^--N and NO₃^--N,which were then removed by denitrification to generate gaseous nitrogen.At the same time,the electrons generated by anodic oxidation of organic matter reach the cathode through the external circuit to participate in the cathodic reduction reaction,and complete the synchronous denitrification and electricity generation process.The maximum AMO,NAR and NIR activities of H.venusta DSM 4743^T in the SND denitrification process were 10.30 U,7.52 U and 4.49 U,respectively.The amo A,nar H and nir D genes encoding H.venusta DSM 4743^T denitrification-related enzymes were cloned.The denitrification mechanism of strain SND was revealed from enzymology and molecular biology respectively.H.venusta DSM 4743^T operates under high-salt MFC with seawater as a substrate for nitrogen removal and electricity generation.The maximum output voltage is 287 m V,and the maximum power density is 84.27 m W/m².The NH₄⁺-N and TN removal rates of MFC at 72 h were 95.73%and 94.50%,respectively.The results show that H.venusta DSM 4743^T,as an electricity-generating bacteria,has a good effect on denitrification and electricity generation by MFC under high salinity.