Performance And Mechanism Of Waste Activated Sludge Decomposition Enhanced By The Combined Lysozyme And Rhamnolipid

Waste activated sludge has been increasing rapidly with the fast development of urban sewage treatment plants,the problem of how to appropriately treat and disposal waste activated sludge has become extremely urgent.Anaerobic fermentation has been proved to be an effective way to realize sludge reduction,stablizition,harmlessness and recycling.Hydrolysis was the first step of anaerobic digestion process and it was also confirmed to be the rate limiting step.Aimed at the problem of the slow and long-term hydrolysis of waste activated sludge,the efficient and environmentally friendly lysozyme was used to pretreat sludge to promote the hydrolysis and decomposition of sludge,and the combination of surfactant rhamnolipid(RL)and lysozyme was used to further improve the sustainable action time of lysozyme and the efficiency of hydrolysis and decomposition of sludge.The method of screening high-yield lysozyme producing strains in the sludge system was used to obtain lysozyme producing strains with high lysozyme activity and wide antibacterial spectrum,and the influence of environmental conditions on the production of lysozyme was investigated.The pretreatment of sludge with endogenous lysozyme was studied and so was the effect of different treatment conditions on sludge hydrolysis.The combination of endogenous lysozyme and RL was used to strengthen waste activated sludge hydrolysis and decomposition.The performance of lysozyme catalysis on waste activated sludge hydrolysis and decomposition indicated that lysozyme could promote the hydrolysis and disruption of waste activated sludge.Approximately 236.5 mg/L soluble chemical oxygen demand(SCOD),58.6 mg/L polysaccharide and 662.7 mg/L protein release within 240 min at the lysozyme dosage of 150 mg/g SS.Arising lysozyme dosages(from 0 to 150 mg/g SS step by step)could dramatically enhance the efficiency of the enzyme on waste activated sludge,and the optimum lysozyme dosage was 150 mg/g SS.The decomposition degree of bacteria and archaea reached 20.2% and 65.0%,respectively.Aimed at the problem of waste activated sludge was not dispersive enough and the lysozyme was easy to be captured by the complex organic matter in the sludge,this article evaluated the feasibility of the combined lysozyme and RL(Ly+RL)treatment on the hydrolysis of waste activated sludge.Results showed that lysozyme and RL combined treatment could significantly boost waste activated sludge hydrolysis and decomposition,improve the dispersibility of sludge and prolong the sustainable action time of lysozyme.An additional 1196.9 mg/L SCOD,792.5 mg/L protein and 133.5 mg/L polysaccharide were released compared with the sum of sole RL and sole lysozyme treatment at the RL dosage of 0.3 g/g SS.In the range of 0-0.5 g/g SS,increasing RL dosage could improve the hydrolysis efficiency of waste activated sludge,and the optimal RL dosage was 0.3 g/g SS.The decomposition degree of bacteria and archaea reached 45.3% and 84.5% respectively under this condition.Alkaline condition(p H7-11)was more conductive to the release of soluble organic matters,the improvement of sludge biodegradability and the reduction of sludge particle size than acid conditions(p H4-7),and the optimal p H was10.And 9591.6 mg/L SCOD,1612.0 mg/L protein and 1211.6 mg/L polysaccharide were released at p H10 after 12 h co-digestion.83.7% bacteria and 92.2% archaea were decomposed at p H10.Class Gammaproteobacteria(82.4%)was the predominant bacteria after treated by Ly+RL system.In view of the limited industrial lysozyme productivity,uneven lysozyme quality and narrow antimicrobial spectrum in China,four lysozyme producing strains Bacillus safensis,Bacillus amyloliquefaciens,Bacillus subtilis and Bacillus velezensis were screened from waste activated sludge,namely S1,S2,S4 and S5,respectively.The optimal temperature of enzyme production was found to be 30?,and the optimal p H of lysozyme production was p H8.5,p H7.5,p H7.0 and p H7.0,respectively.Results of the fermentation liquid of strains used as the lysozyme extracting liquid to hydrolyze sludge showed that the optimal lysozyme extracting liquid dosage was 15%(v/v).In the temperature range of 20-60?,the hydrolysis effect of lysozyme extracting liquid on sludge could be significantly improved by increasing the temperature.Under the conditions of 50? and 60?,the hydrolysis effect of lysozyme extracting liquid on sludge was much higher than other temperatures,and the optimal treatment temperature was 50?.Under this condition,the SCOD in the sludge pretreated with lysozyme produced by strains S1,S2,S4 and S5 was 1092.1,1579.1,1596.5 and 1522.6 mg/L respectively,and the protein was 407.0,581.9,513.1 and 596.5 mg/L respectively.p H played a vital role in the release of soluble organic matters within the lysozyme extraction solution pretreatment systems,and the alkaline condition was better than the acid condition in promoting the hydrolysis of sludge.p H10 was the optimal p H of sludge hydrolysis in the lysozyme pretreatment system of each screening strain,and the optimal sludge treatment time was 8 hours.Under this condition,the SCOD in the sludge after lysozyme pretreatment by strains S1,S2,S4 and S5 was 2185.6,2516.4,2280.3 and 2256.7 mg/L,protein was 972.4,1062.5,1117.4 and 1084.9 mg/L and polysaccharide 133.7,181.2,149.3 and 169.6 mg/L,respectively.The combined lysozyme extracting liquid and RL pretreatment system could significantly improve the hydrolysis and decomposition effect of waste activated sludge.In the range of 0-0.5g/g SS,increasing the dosage of RL could promote the release of soluble organic matters in sludge,and the optimal RL dosage was 0.3g/g SS.The SCOD of the sludge pretreated with RL and lysozyme produced by strains S1,S2,S4 and S5 after 8 h reached 6764.5,6513.2,7079.0 and 6852.3 mg/L respectively,the protein was 1892.7,1929.9,1965.8 and 2064.5 mg/L,the polysaccharide was 643.3,750.2,721.5 and783.3 mg/L,respectively.The pretreatment method of sludge with lysozyme extracting liquid and RL had a strong ability of sludge decomposition,which could cause the majority of microorganisms to break,and significantly reduce the relative abundance of gammaproteobacteria and the pathogenicity of sludge.After the combined treatment of RL and lysozyme produced by strains S1,S2,S4 and S5,betaproteobacteria became the most important class with the relative abundance of 60.5%,77.1%,76.5% and 76.8%.