Study On The Promotion Of Anaerobic Digestion Of Waste Activated Sludge By Sodium Lauroyl Sarcosinate

The activated sludge technology is widely used to treat wastewater around the world,resulting in production of a large amount of waste activated sludge(WAS),which has become an increasingly serious problem faced by countries all over the world today.Anaerobic digestion(AD)is one of the effective technologies to achieve WAS reduction and resource utilization(recover energy such as short-chain fatty acids(SCFAs)and methane).Due to the low energy input,adding additives in the anaerobic digestion process of WAS is considered to be a promising method to promote anaerobic digestion,and surfactants are one of the good additives.In this paper,the use of sodium lauryl sarcosine(SLS)to promote anaerobic digestion of WAS was studied,the methane production characteristics of different doses of sodium lauryl sarcosine were explored with batch tests,the influence of sodium lauryl sarcosine on various aspects of WAS anaerobic digestion process was analyzed,and the protein and polysaccharides content were monitored.The composition and structure of dissolved organic matter(DOM)was analyzed by Three-dimensional fluorescence(3D-EEM)technology.Meanwhile,the profile of short-chain fatty acids and the activities of key enzymes were analyzed.The contribution of degraded sodium lauryl sarcosine to methane production was revealed,and the underlying cause of the prolonged lag period was dug out.The microorganism composition and structure involved in the process were analyzed.This study aims to provide a theoretical basis for the addition of sodium lauryl sarcosine to promote the anaerobic digestion process of WAS,and the main conclusions are as follows:(1)Methane production rate and maximum accumulative methane production increased with the increase of sodium lauryl sarcosine dosage,indicating that the addition of sodium lauryl sarcosine could enhance methane production.A delay effect was observed in both cumulative methane production curve and daily methane production curve,but the time required to reach the maximum cumulative methane production was nearly the same.In addition,no lag effect was observed in the reactor with a 10 mg/g TSS dosage.(2)3D-EEM showed that the fluorescence intensity of soluble microbial byproducts and humic acids were enhanced after the addition of sodium lauryl sarcosine,and the contents of soluble polysaccharides and proteins also increased with the increase of sodium lauryl sarcosine dosage.These changes were related to the reduced surface tension and solubilization effect resulting from sodium lauryl sarcosine.(3)As the dosage of sodium lauryl sarcosine increase,the concentration of total SCFAs also increase,which indicates that the dosage of sodium lauryl sarcosine is conducive to the formation of calculations.The key enzyme activity analysis showed that the activity of α-amylase and protease was increased,and the activity of acetate kinase seldom showed change at the presence of sodium lauryl sarcosine.However,high sodium lauryl sarcosine dosage(≥20 mg/g TSS)seems to inhibit the activity of Coenzyme F420.(4)Sodium lauryl sarcosine can be degraded into lauric acid(LA)and corresponding amino acid,and then further be degraded into SCFAs,and be converted into methane eventually.The degradation of sodium lauryl sarcosine is relatively easy,but the degradation of lauric acid is relatively slow,and the degradation time required is four-folds more than that of sodium lauryl sarcosine.Moreover,lauric acid may be the real cause of the prolonged lag period.(5)In the reactor of adding sodium lauryl sarcosine,the genera of utilizing amino acids(Leptolinea),oxidizing propionic acid(Longilinea),and degrading long chain fatty acids(LCFAs)(Syntrophomona)were both enriched.In addition,the advantages of archaea genera was more obvious,and the degree of enrichment of hydrogenotrophic methanogens is higher than that of acetic acid-trophic methanogens.