Study On Ammonia Nitrogen Inhibition Mechanism And Mitigation Methods In Anaerobic Digestion Of Livestock Wastewater

In the study of high concentration of ammonia nitrogen to inhibit anaerobic fermentation,some research groups examined effects of various nitrogen sources and different concentrations.There are different thresholds of ammonia concentration cause inhibition due to differences in nitrogen sources,inocula and substrate.In most of the previous studies,ammonium chloride was used as the external nitrogen source.In real anaerobic digestion,the decomposition of urea,protein and nucleic acids produces ammonia nitrogen.Many studies have found that free ammonia（FAN）is considered to be a key parameter affecting the stability and efficiency of the anaerobic digestion process,but the FAN inhibition results by different anaerobic fermentation substrates are not the same.Real anaerobic digestion process of livestock manure wastewater is complicated,the concentration of FAN is affected by acid production,p H value during the hydrolysis stage,the effect of urea and ammonia chloride on the anaerobic digestion of real wastewater is not clear.So it is necessary to use the real livestock manure wastewater as a substrate to study the inhibition of urea and ammonium chloride on anaerobic digestion for get the mechanism of ammonia nitrogen inhibition,Through preliminary experiments,Zero-valent iron（ZVI）was added to the anaerobic reactor to mitigating the inhibition of high ammonia nitrogen anaerobic fermentation.Explore the role and mechanism of zero-valent iron in high ammonia nitrogen anaerobic fermentation.The research contents and results were listed as follows:（1）Urea and ammonium chloride were used as additional nitrogen sources for anaerobic fermentation of livestock wastewater.The produced concentration of free ammonia nitrogen,volatile fatty acids（VFAs）and p H with urea as external nitrogen sources were significantly higher than ammonia chloride in the anaerobic fermentation process of swine manure wastewater,but their total ammonia nitrogen（TAN）concentration is similar.Urea as the nitrogen source(TAN≤500mg·L^-1)and ammonium chloride as the nitrogen source(TAN≤1500mg·L^-1)can promote methane production of anaerobic fermentation of swine manure wastewater.But exceeding this concentration,the effect of ammonia inhibition was arised.Ammonia inhibitory thresholds of urea on anaerobic fermentation of swine waste water(TAN>500 mg·L^-1)is much lower than that of ammonium chloride(TAN>1500mg·L^-1),and urea as nitrogen source has stronger ammonia inhibition on anaerobic fermentation of swine manure wastewater.It provides a theoretical basis for selection of nitrogen source for high ammonia nitrogen inhibition of anaerobic fermentation.（2）The concentration of TAN is less than 1500 mg·L^-1,and Lactobacillus relative abundance increases with the increase of FAN concentration with urea as the added nitrogen source.Lactobacillus can hydrolyze organic by producing extracellular enzymes,which can promote the hydrolysis process of anaerobic fermentation.The concentrations of s COD and VFAs in the urea-added group are higher than the control.The hydrogenotrophic methanogen Methanobrevibacter is more resistant to high ammonia nitrogen than the aceticlastic methanogen Methanosarcina.Using urea as an additional nitrogen source,Methanosarcina was inhibited,and Methane production was also inhibited.The cumulative methane production of anaerobic fermentation with TAN=500mg·L^-1 was the same as the control,but the peak of methane production was delayed by16 days.Methanosarcina adapted high ammonia nitrogen TAN=1500 mg·L^-1 on the 56th day of anaerobic fermentation,the relative abundance increased,the cumulative methane production increased by 58.35%compared with the control,but the peak of methane production was delayed by 52d.（3）Adding ZVI to anaerobic fermentation of high ammonia nitrogen pig manure wastewater,aceticlastic methanogen methanosarcina relative abundance increased,methanosphaera,methanobrevibacter,methanocorpusculum,and methaobacterium that were reported to be hydrogenotrophic methanogen relative abundance were decreased,and cumulative methane production increased by 31.16%compared with the control.Adding ZVI can enhance the Methanosarcina produce methane metabolism pathway and effectively increase the methanogenesis of anaerobic fermentation of high ammonia nitrogen pig manure wastewater.