Effect Of Salinity And Treatment Process On Alginate Secretion Of Activated Sludge System

With the continuous increase of excess sludge in sewage treatment plants,the proper disposal of sludge is an urgent problem to be solved.Extracting alginate from remaining sludge is the current research direction of sludge resource utilization with good development prospects.Some coastal urban sewage treatment plants that use seawater technology for large households will generate corresponding excess sludge.Due to the presence of seawater salinity will have a certain impact on the biological treatment system of sludge and the characteristics of sludge,the utilization of alginate for these excess sludge needs further study.In this study,six SBR reactors were used to treat artificial simulated domestic sewage containing 0%,10%,20%,50%,80%,and 100%seawater,the pollutant removal effect and the characteristics of sludge in the treatment system under different salinity conditions was investigated,the effect of salinity of different seawater ratio on the content and characteristics of sludge alginate in the system was emphatically investigated.The mechanism of the effect of different salinity on alginate secretion was explored from the aspects of microbial population structure and microbial signaling molecule(c-di-GMP).At the same time,the content and characteristics of alginate in the sludge of different treatment processes were compared,providing technical reference for the extraction of alginate from the surplus sludge of sewage treatment with large domestic seawater.The main findings are as follows:(1)Different proportions of seawater affect the biological wastewater treatment system.The sludge with a proportion of 0%,10%,20%,50%,and 80%seawater has good settling properties and biomass,and can effectively remove pollutants in sewage,with a removal rate of more than 94%.The sludge activity of 100%seawater ratio is low,the value of MLVSS/MLSS is only 0.60,the SVI value is 36.88 m L/g,and the average removal rate of pollutants is not higher than 90%.(2)The different proportions of seawater affect the content and characteristics of EPS and alginate.The proportion of seawater increased from 0%to 100%,and the total EPS increased from 248.96 to 347.37 mg/g VSS.The extraction amount of sludge alginate increased from 74.02 mg/g VSS to 114.41 mg/g VSS.According to infrared spectroscopy analysis,the properties of the six alginates are similar.From the separation of different blocks and the acetylation content,the higher the salinity,the greater the proportion of mannuronic acid(M),the higher the degree of acetylation,and the better the water retention and swelling properties of alginate.The activated sludge treatment system that treats 80%of the seawater can maintain a high pollutant removal effect and at the same time obtain a higher alginate content from the remaining sludge.(3)The different proportions of seawater affect the population structure of activated sludge.The increase in salinity reduces the species richness of sludge.The predominant populations in the 50%,80%,and 100%seawater sludge are Winogradskyella,Halomonas,and Ruegeria.The increase of salinity increases the content of c-di-GMP,and it also has a certain contribution to the secretion of alginate.(4)The alginate content and characteristics of different treatment processes are different.In A~2/O,the anoxic pool has the highest alginate content(82.36 mg/g VSS),the highest proportion of mannuronic acid(M)is the anoxic pool,and the highest guluronic acid(G)is the aerobic pool.The sedimentation tank is the one with the highest degree of acetylation;in the Oxidation ditch process,the alginate content in the anaerobic tank is the highest(78.71 mg/g VSS),the anaerobic tank is the highest in the M ratio,and the aerobic tank is the highest in the G,the highest acetylation level is the anaerobic tank;the MBR process has the highest alginate content(89.23 mg/g VSS),the highest M ratio is the anaerobic tank,the highest G is the aerobic tank,and the highest acetylation level is Anoxic pool.In general,the sludge of the MBR process can extract more alginate than the A~2/O and Oxidation ditch processes.(5)The content and characteristics of SBR(20%)sludge alginate and A~2/O,Oxidation ditch,MBR sedimentation tank sludge alginate are different.The alginate content of SBR(20%),the content of mannuronic acid(M)and the degree of acetylation in alginate were higher than those of the other three sludges.According to infrared spectroscopy analysis,the properties of the four alginates are similar.