Using actual membrane wastewater as an example,this study explored the dynamic responses of methanogenesis and microbial communities in high-concentration organic nitrogen wastewater under ammonia stress,clarifying the ammonia inhibition threshold,inhibition form,inhibition mechanisms,and response strategies.The results indicate that the primary form of ammonia inhibition in anaerobic digestion(AD)treatment of high-concentration organic nitrogen wastewater is free ammonia(FA),with an inhibition threshold of(145±10)mg/L and a half-maximal inhibitory concentration of(244±10)mg/L.During AD treatment of high-concentration organic nitrogen wastewater,the key methanogenic microorganisms include Methanosaeta(acetotrophic methanogens),Methanomassiliicoccus and Methanomethylovorans(methylotrophic methanogens).The activities of Methanosaeta and Methanomethylovorans decline at ammonia nitrogen levels above 300mg/L and 900mg/L,respectively.Simultaneously,the functional microbes related to hydrogen and carbon dioxide production are inhibited when FA exceeds 140mg/L.This leads to the accumulation of small organic molecules with more than one carbon atom in the system,ultimately resulting in reduced chemical oxygen demand removal efficiency and incomplete release of ammonia nitrogen under high free ammonia(FA)conditions.After severe ammonia inhibition,recovery of the system can be achieved by adjusting the pH,but not through microbial acclimatization.
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