Research On Alkaloid Enhancing Anaerobic Digestion Of Sewage Sludge And Methane Production

Anaerobic digestion(AD)of sewage sludge is widely used in industry because of its low cost,simple operation and high resource utilization.However,there are still problems needed to be conquered,such as long operating cycle,low methane producing efficiency and so on.For the aim of promoting methane production efficiency of AD for sewage sludge,this study focused on alkaloid enhancing AD and methane production(MP).Results are showed as followed:In alkaloid optimization experiments,choline,atropine and matrine were studied.Results showed that choline not only improved MP,but also accelerated the process of methanogenesis.In contrast,atropine and matrine showed no improvement on MP from AD.In choline’s dosage optimization experiments,batch tests were carried out to investigate sludge degradation,MP and enzyme activities.The results showed that 0.3 g/L choline addition performed the best with methane yield of 225.7 m L/g volatile solids,30.0% higher than the control.Dynamic fitting results showed that choline increased maximum methane potential by37.0%(under Cone model)and reduced lag-time of methanogenesis by32.8%.Also,choline addition improved the hydrolysis rate and maximum methane production rate of AD from sludge.In the mechanism part,choline’s metabolism pathway was done first.Results showed that in the AD of sludge,choline would be immediately transformed into a more stable intermediate 2-(2-Hydroxyethoxy)-N,N,Ntrimethylethanaminium(HTMA),which presented a positive effect on glucose degradation,acidification acceleration and hydrogen production.Meanwhile,choline increased conductivity(+7.0%)and electronic exchange capacity(+13.3%)at the beginning period of AD.When furtherly investigated choline’s influence on methanogenesis pathways and microbes,big changes of the distribution for methanogenesis pathways(acetoclastic methanogenesis(AM)and hydrogenotrophic methanogenesis(HM))in AD of sludge were found after choline addition:AM was the major pathway in the control,while HM became the dominant pathway by choline addition,made up for 58.3% of MP.On the contrary,when 2000 mg/L acetate acted as substrate,choline application enhanced AM for 17.0%,instead of HM.Meanwhile,the enrichment of Methanobacterium(+2.8%),Methanobacterium(+13.4%),Methanobrevibacter(+129.2%),and Methanosarcina(+202.7%)verified the promotion of HM during the AD process,also indicating an increased microbial adaptability and stabilization.The investigation of choline’s intermediates also revealed a stimulation of acidification and hydrogen production,still an evidence for choline’s good performance on AD.