Efficiency Improvement And Its Mechanism Of Bioaugmentation To Alleviate Ammonia Inhibition In Anaerobic Digestion

Ammonia nitrogen produced by nitrogen-rich organic substrates decomposition is the main toxicant to the AD process,causing process imbalance and decrease of methane production.Adding the ammonia tolerant consortia to alleviate the ammonia inhibition does not require additional infrastructures,dilution,or longer hydraulic retention time.However,the bioaugmentation is vulnerable to ammonia shock load and its performance remains to be further promoted.Moreover,methanogens are impractical to transfer and store due to its environmental sensitivity,slow growing rate and short shelf time,which also limits the application of this novel technology.This thesis systematically investigated the efficiency enhancement strategies of bioaugmentation to alleviate ammonia inhibition in anaerobic process.The specific research works and results are as follows:（1）The effects of adding 60 m L ammonia tolerant methanogenic consortia gel（biogel）,2g L^-1 biochar and the mixture of biogel and biochar to alleviate 4.5 g NH₄⁺-N L^-1ammonia inhibition were compared.Compared with the control group,the methane production yield increased by 10.6%,22.6%and 35.0%by adding biogel,biochar and their combination,respectively.The novel bioaugmentation strategy with the combination of biochar and biogel improved the methane yield to 90.9%of the uninhibited state.The microbial community and its network analysis showed that Methanoculleus thermophilus and Syntrophic acetate-oxidising bacteria（e.g.Syntrophicus）introduced into reactors contributed to the rapid recovery of methanogenic efficiency.Biochar promoted the ammonia resistance of Methanosarcina spp.Biogel and biochar had obvious synergistic interaction on alleviating ammonia inhibition.The hydrogenotrophic species Methanoculleus thermophilus was the only strain with significant positive correlation to methanogenic efficiency under high ammonia levels,and was identified as the"crucial species"for methanogenic efficiency under ammonia stress.（2）The long-term performance and stability of ammonia inhibition alleviating strategies were evaluated under ammonia shock loads.The results showed that the reactor bioaugmented with both biogel and biochar was minimally affected by ammonia shocks of 5.5,6.5 and 7.5 g NH₄⁺-N L^-1.Its methane yield was 91.1%,65.3%and 25.3%of that uninhibited state,respectively,which was 28.6%,48.8%and 23.9%higher than the reactor bioaugmented only with biogel.Biochar significantly improved the long-term efficacy of biogel to alleviate ammonia inhibition under ammonia shock loads.The microbial community analysis showed that the addition of biochar significantly improved the stability of microbial community structure under ammonia shock loads.The bioaugmentation with biogel and biochar significantly boosted the“crucial species”Methanoculleus thermophilus with relative abundance increased from 48.0%to 95.7%.（3）The ammonia tolerant consortia were lyophilized and used for bioaugmentation to alleviate 5.0 g NH₄⁺-N L^-1ammonia inhibition after both 180 days and 365 days storage.The results showed that compared with the control group,the methane production increased by 28.9%and 15.2%with the addition of lyophilized powder stored for 180 and 365 days,respectively.The microbial community analysis showed that the Methanosarcina sp.was the dominant methanogenic species in reactors added with lyophilized powder.It was also found that Geobacillus Hydrogenibaillus,the direct interspecific electron transport partner of Methanosarcina sp.had an average relative abundance of 11.3%in the reactors where the lyophilized powder（stored 180 days）was added.However,it was not detected in the reactors where the lyophilized powder（stored 365 days）was added.This species played an important role in the bioaugmentation performance of the lyophilized ammonia tolerant consortia after long-term storage.（4）The effects of adding potassium chloride,magnesium chloride and glycine betaine to alleviate ammonia inhibition were assessed.The results showed that:methane yield increased by 16.0%,12.8%and 23.6%due to the addition of 20 mg L^-1 potassium chloride,20mg L^-1magnesium chloride and 50 mg L^-1 glycine betaine,which were equivalent to 67.2%,78.0%and 70.4%before inhibition,respectively.With doubled concentrations of the three osmoprotectants,the methane yield in reactors added with potassium chloride and magnesium chloride had no significant change,however,it increased to 88.6%of uninhibited state in the glycine betaine addition reactor.The microbial community analysis showed that the relative abundance of hydrogenotrophic methanogenic genus Methanoculleus was increased in all reactors added with osmoprotectants,specifically,glycine betaine significantly promoted relative abundance of the“crucial species”Methanoculleus thermophilus from 2.3%to 48.2%.The results of this study could provide a theoretical basis and technical support for improving the efficiency of bioaugmentation on alleviating ammonia inhibition in anaerobic digestion systems.