Surface Characteristics And Thermodynamic Analysis Of Filamentous Bulking Microbial Aggregates Of Activated Sludge

Since its inception,the activated sludge process has become the most widely used wastewater biological treatment process in the world.However,the sludge bulking problem has severely restricted the application and development of the activated sludge process,and is an important issue to be solved in the field of sewage.At present,there are many researches on sludge bulking mechanism,but most of them are based on the process level,the process of sludge bulking is revealed and simulated from the perspective of kinetics.The bulking mechanism of filamentous bacteria is not directly revealed from the microscopic level.Therefore,this study uses the main line of "SBR reactor start-up and operation-sludge bulking induced-different swelling degree sludge surface physical and chemical properties analysis-sludge bulking mechanism”,analysis surface Physicochemical properties and microscopic composition of different expansion degree of activated sludge floc,combined with XDLVO theoretical coupling thermodynamic mechanism to reveal the mechanism of sludge bulking,and explore the changes of bacterial alginate to explain its impact on microbial aggregation behavior.The main findings are as follows:(1)The flocculation sedimentation performance and surface physicochemical properties of activated sludge with different degrees of expansion were monitored.The results show that the flocculation sedimentation performance of activated sludge is closely related to the surface Zeta potential and the relative hydrophobicity.With the increase of SVI value,the higher the absolute value of Zeta potential,the lower the relative hydrophobicity,the worse the flocculation and sedimentation performance.At the same time,the content and composition analysis of extracellular polymer(EPS)of different bulking slludge floc showed that the total amount of EPS,polysaccharide content and protein content were negatively correlated with SVI value.with the increase of sludge expansion degree,the total amount of EPS,polysaccharide content and protein content decreased.The zeta potential on the sludge surface is positively correlated with EPS and PN.The protein content in EPS is a key factor affecting the zeta potential value.(2)By analyzing the alginate(ALE)content and composition of different bulking sludge floc,it was found that the content of alginate and its different block(GG,MG,MM)decreased With the increase of SVI value,results in a decrease in the alginate gel formed with the metal cations,thereby weakening the sludge floc structure performance.Further,UV-visible spectroscopy and infrared spectroscopy were used to confirm that the alginate extract was similar to the sodium alginate standard.The GG block was the main component of bacterial alginate and played an important role in the formation of alginate gel.(3)Further analysis the mechanism of sludge bulking by XDLVO theoretical coupling surface thermodynamic analysis,it is showed that the absolute values of WA,WR and WAB were decreasing as the sludge bulking,that is,Their contribution to the total potential of the XDLVO in system is decreasing.And the repulsion barrier of the sludge system is increasing,that is,the flocculation and weighing performance of the sludge is continuously decreasing.In this study,the surface characteristics of microbial in the process of filamentous bacteria bulk were examined and analyzed,and the mechanism of the effect of bacterial alginate on sludge bulking was revealed.From the thermodynamic point of view,the mechanism of sludge bulking was analyzed by XDLVO theory.