Effects Of Salinity And Sludge Morphology On The Secretion Characteristics Of Extracellular Enzymes In SBR Wastewater Biological Treatment Syste

Extracellular hydrolysis plays an important role in wastewater biological treatment.Many macromolecular particulate pollutants need to be metabolized by extracellular enzymes before entering the cells,which is the initial rate-limiting step of biological treatment.Therefore,it is necessary to study the secretion characteristics of extracellular enzymes.Since extracellular enzymes mainly exist in the extracellular polymeric substances（EPS）of sludge,salinity and sludge morphology are two important factors affecting the secretion of EPS.Therefore,in this study,the typical extracellular enzymes protease,α-amylase and alkaline phosphatase in the biological wastewater treatment system were used as the objects to analyze the secretion properties of the three enzymes,and the effects of salinity and sludge morphology on their activity and distribution characteristics in EPS were investigated.The specific research results are as follows:（1）Extracellular protease,α-amylase and alkaline phosphatase were detected in the activated sludge of simulated domestic sewage SBR biological treatment system without protein,starch and organic phosphorus as substrates,and their activities were14.22μmol/(min.g VSS^-1),67.27μmol/(min.g VSS^-1)and 7.08μmol/(min.g VSS^-1),respectively.It can be seen that these three extracellular enzymes are extracellular enzymes of microorganisms,and protease andα-amylase are mainly concentrated in the TB-EPS layer.Alkaline phosphatase was mainly distributed in the LB-EPS layer.（2）In the study of the effect of salinity on the secretion characteristics of these three extracellular enzymes,it was found that when the salinity increased from 0g/L to 30g/L（calculated as Na Cl）,the activity ofα-amylase increased first and then decreased.When the salinity increased from 0g/L to 10g/L,the activity increased from 61.97μmol/(min.g VSS^-1)to80.32μmol/(min.g VSS^-1),and then decreased to 44.55μmol/(min.g VSS^-1)with the increase of salinity.The protease activity decreased from 14.43μmol/(min.g VSS^-1)to9.40μmol/(min.g VSS^-1),and the phosphatase activity decreased from 7.09μmol/(min.g VSS^-1)to 3.74μmol/(min.g VSS^-1).It can be seen that the extracellular enzyme activity is inhibited under high salt environment.（3）When the salinity was 30g/L,the impact of starch and phenol could promote the activity of these three kinds of sludge extracellular enzymes,but had different effects on the distribution of extracellular enzymes in EPS.When 0.2g/L starch was added,the activity ofα-amylase increased from 44.55μmol/(min.g VSS^-1)to 61.94μmol/(min.g VSS^-1),and the activities of protease and phosphatase were 13.47μmol/(min.g VSS^-1)and2.78μmol/(min.g VSS^-1),respectively.The main distribution position of these three enzymes and their proportion in total enzyme activity wereα-amylase 38%（slimg-EPS）,protease51.67%（TB-EPS）and phosphatase 39.20%（TB-EPS）.Under the toxic stress of phenol（0.3g/L）,the activity ofα-amylase,protease and phosphatase increased.Among them,α-amylase and phosphatase were still mainly distributed in the TB-EPS layer,while the main distribution position of protease was changed from TB-EPS layer to LB-EPS.（4）In the study of the effect of sludge morphology on these three extracellular enzymes,it was found that with the formation of aerobic granular sludge,the EPS content increased from 109.75mg/g VSS to 226.39mg/g VSS,and the activities of protease,α-amylase and phosphatase in the stable period of granular sludge were 18.71μmol/(min.g VSS^-1),92.05μmol/(min.g VSS^-1)and 12.39μmol/(min.g VSS^-1),respectively.The protease activity(17.18μmol/(min.g VSS^-1))and phosphatase activity(8.68μmol/(min.g VSS^-1))in granular sludge were higher than those in floc sludge,but lower than the activity ofα-amylase(97.34μmol/(min.g VSS^-1)).Granular sludge could promote the secretion of protease and phosphatase more than floc sludge,but had little effect on the distribution of extracellular enzymes in EPS.Among the three enzymes,protease andα-amylase were distributed in the TB-EPS layer in aerobic granular sludge and floc sludge,while phosphatase was relatively evenly distributed in each layer of EPS.