Research On Morphology And Structure Of Excess Activated Sludge In Mulitistage Dewatering Process

In recent years,with the increase of the scale of the sewage treatment plant,the output of excess sludge is increasing gradually.The disposal of excess activated sludge has become one of the urgent problems to be solved.The mechanical dehydration of sludge is the most important step in the sludge treatment and disposal process.However,the research on the mechanical dehydration is mostly in the comparison of different dewatering equipment and the optimization of the operating parameters.There are few researches concerning about the changes of sludge morphology and microstructure in the dewatering process.In this study,the excess activated sludge from Wenchang Wastewater Treatment Plant was used as the research object to study the change of sludge cake in morphology and structure during the process of sludge dewatering.On this basis,the method of deep dewatering was proposed and the regression equation of sludge dewatering was established.The experiment examined the morphology of excess sludge and migration of water in primary regulation.The results show that the sludge can be used as a stable test material due to its stable physical and chemical properties in different seasons.The physical and chemical indexes of sludge were significantly correlated with the dehydration performance.The sludge concentration,viscosity and EPS content were positively correlated with the dewatering performance of sludge,and the pH and Zeta potential were negatively correlated with sludge dewatering performance.In the process of sludge settling,the floc morphology of the sludge is changing.At the stage of flocculation and sedimentation,the floc size of the sludge is increasing and the settling velocity reaches the maximum value of 0.16cm/min.At this stage,There is a certain amount of voids which is also beneficial to the transfer of water and enhanced the sedimentation and dewatering performance of excess activated sludge with CST value 20.5s.Duding PAC,FeCl+ and cationic PAM conditioning process,the distribution,migration and transformation of water in activated sludge were similar.After the conditioning,the content of free water was increased the content of bound water was reduced by the expansion method.In thermal drying method,the internal binding water content is unchanged and the surface water content has decreased.However,the free water and interstitial water content has increased.In contrast to the difference in moisture content measured by the expansion method and the thermal dying method,the addition of the agent reduces the binding energy of the water and the sludge during the sludge conditioning process.So part of the surface-bound water converted into interstitial water and free water and the original interstitial water convete into free water thereby enhancing the sludge dewatering performance.Through the filtration test,the resistance characteristics,microstructure,degree of homogenization and the content of bound water in the sludge cake were investigated.In the experiment,it was found that the filtration resistance increased during the filtration process,but the pressure growth rate of the filtration resistance is quite different.As the filtration pressure increases,the sludge floc is more easily broken into small particles to clog the filter cloth,and the filter cake with small voil is hard for water discharging.Under the pressure of 0.9MPa,the growth rate of filtration resistance is much greater than the growth rate of 0.7 MPa pressure filtration resistance.Under the condition of 0.9Mpa,the sludge has the best dehydration effect after the FeCl₃ treatment,and the water content of the cake is 60.1%.However,whether it is conditioned by PAC or FeCl₃,the water content of the sludge cake is 55% after tympanic membrane pressure.The maximum difference of transverse water content was 4.08% and the maximum difference was 1.8%,and the maximum difference of water content in longitudinal content is 1.8% in which the outer layer water content was lower than that of the inner layer.The water content of the sludge was higher than that of the inner layer,Uneven distribution of water content of sludge cake,hindered the dehydration process to further reduce the water content.Therefore,another tympanic membrane pressure filter after crushing and then mixing has been done to further reduce the sludge moisture content.In the test,the sludge cake moisture content dropped to below 50% after deep dewatering.Under the conditioning of PAC,the average water content reached 48.8%.Under the condition of FeCl₃,the average water content was 48.38%.With the decline of water content of sludge cake,the differcece of water content in sludge cake not more than 0.7% at different locations and not more than 0.5% at different layers.Sludge cake homogenization degree has greatly improved.Based on the filtration test,the key factors influencing the moisture content of the sludge cake were found by the correlation analysis.The regression equation was established by using the moisture content as the objective function and the physical and chemical properties of the excess activated sludge and pressure filter conditions as the independent variables.In the correlation analysis,Zeta potential,EPS content and its proportion of each component,pressure and pressure filtration time weres significantly related to sludge cake moisture content.In the establishment of the regression equation,the regression equation is established for both constant pressure and non-constant pressure.The moisture content of the sludge cake can be predicted according to the filter parameters and the sludge properties.The results of the study fill the blanks in the study of the sludge morphology and microstructure of the filtration process,clarify the reasons for the further improvement of the sludge dewatering performance,and provide a solution for the further improvement of the dehydration efficiency of the wastewater treatment plant The The establishment of the regression equation under different conditions will help to quickly establish the dosage of the conditioning process and the running parameters of the dehydration process,which greatly reduces the test time and cost,which will promote the social and economic benefits of the sewage treatment plant.The research results applied to the actual project.The sludge mechanical dehydration treatment costs 191.13 million / year,compared with the belt filter 7% savings.The effect is significant.