Study On Enhancing Nitrous Oxide From Denitrification Treatment Of Incineration Leachate And Its Microflora Optimization

With the increasing of municipal solid waste production,a large amount of fresh leachate with high concentrations of both organic matter and nitrogen is generated before incineration.This incineration leachate is usually treated by biological methods.Anaerobic methanogenesis is usually applied to remove the high concentration of organic matter,while anoxic denitrification and oxic nitrification processes are usually applied to remove the high concentration of ammonia.N20 is generated and emited during these processes.N2O is a strong greenhouse gas,however,if properly captured it can also be used as a renewable energy source.Therefore,techniques that enhance nitrous oxide production during the water denitrification process should allow the recovery of more energy.In this study,a species with the capability of denitrification which was dominant in the microbial community in the leachate denitrification bioreactor was selected.And a nosZ-deficient strain of this strain was constructed by genetic engineering technologies.Experiments from pure cultrure and bioreactor suggest that,this nosZ-deficient strain was effective to enhance N2O production.By bioaugmentation of this strain into bioreactor treating incineration leachate,the production of N2O was significantly enhanced and the bioreactor was operated stably and efficienly.The effects of carbon source(acetate,methanol and glucose)and COD/N(1.5,2.5,3.5 and 5)on nitrous oxide production were investigated in this study to achieve high production efficiency of nitrous oxide.The results showed that carbon source and COD/N significantly affectedthe production of nitrous oxide.Higher nitrous oxide production rate was achieved when the reactor was fed leachate with acetate as the carbon source compared with the other two carbon sources,with a nitrous oxide conversion efficiency of 6.9%.Taking acetate as the carbon source and adjusting COD/N to 3.5,a highest nitrous oxide conversion efficiency was achieved as high as 15%.According to the microbial community analysis under the optimal conditions,the proportions of some genus with nitrous oxide as the terminal denitrification product were significantly increasedThe expression of nosZ gene in denitrifying bacteria is the main factor affecting Nos activity and N20 production.The nosZ gene of Pseudomonas aeruginosa was knocked out,so that the denitrification end product could only be N2O.During growth under denitrifying conditions,the nosZ-deficient strain was more highly transcribing other genes from the denitrification pathway(narG,nirS,and norB)than the wild-type strain.This strain could also convert 85%of NO2--N to N2O when it was grown with acetate compared to<0.6%by the wild-type strain.In order to make the successful production of N2O engineering bacteria enriched in thedenitrification system of the landfill leachate,a bioreactor treating synthetic wastewater was bioaugmented with this strain,the N2O conversion efficiencies were>73%and N20 comprised 73～81%of the biogas being generated.These results are significant and show that bioaugmentation of reactors during denitrification treatment processes with/nosZ-deficient strains of Pseudomonas or other core denitrifying bacteria might be an effective way to enhance N2O recovery.