Study On Stirring Effects On Sludge Flocs And Dewatering Performance Under Aluminum,Iron Salts Conditioning

The quantity of wastewater treatment plant is increasing in our country.The sewage quantity is becoming larger and larger, so production of the sludge from sewage also increases. It is important to reduce the volume of sludge.At present,we dispose sludge after early conditioning,then,we process dehydration. But at the stage, conditioning methods are ineffective and in need of high drug consumption and energy consumption.It is limited to improve sludge dewatering effect.Therefore,we need further study on the inner characteristics of sludge.We also need 0ptimization of conditioning reagents and best kinetic control parameters to improve sludge conditioning mechanism.This study was supported by the National Natural Science Foundation of China 51278143E0804.The project studies stirring parameters’ effects on sludge characteristics and dewatering property,based on sludge conditioning by PAC and Fe Cl3.This passage also clarify the changes of floc structures and moisture transfer during sludge conditioning process. At last,it establishes correlation model of sludge nature indexes、dewatering performance indexes with stirring parameters and dosage.The study investigated the effects of the first stirring intensity and time、the second stirring intensity and time on sludge characteristics and dewatering、settling property by single factor experiment. It showed that four stirring parameters all could have significant impacts on floc structure and moisture with PAC and Fe Cl3.The first stirring intensity and the second stirring intensity had similar influence on physicochemical properties and dewatering performance.With stirring intensity increased,floc particle size was gradually increased to the maximum.Then the particle size became smaller.The free water content firstly increased and then became smaller.CST and SVI both firstly decreased and then increased.So each stirring intensity has its best value,too large or too small stirring intensity are not conducive to the sludge flocculation and settling. With the first stirring time and the second stirring time increased,the floc particle size was increasing, and free water content increased,CST and SVI decreased.When each level of time reached a certain level and still increased,sludge flocculation worsened,resulting in decreasing floc particle size and free water content.Besides,CST and SVI increased.PAC and Fe Cl3 conditioning could improve sludge dewatering, sedimentation performance.PAC conditioning under optimal stirring parameters,sludge dewatering performance indicator CST reduced 50.14% than the original sludge,SVI reduced9.39%,particle size increased 338.39%, free water content increased 2.47%.Fe Cl3 conditioning under optimal stirring parameters,sludge dewatering performance indicator CST reduced 37.48% than the original sludge,SVI reduced 10.21%,particle sizeincreased 68.85%, free water content increased 2.26%.So PAC conditioning had better effects on improving sludge dewatering performance and floc agglomeration,but settling performance was slightly lower than Fe Cl3.RSM was used to study PAC and Fe Cl3 conditioning sludge.We established regression model of CST、SVI and four stirring parameters.When conditioned by PAC and Fe Cl3 at optimal dosage,the importance of every stirring parameters contributed to CST and SVI was similar:the first stirring intensity>the first stirring time>the second stirring intensity ≈ the second stirring time.The optimum stirring parameters of PAC conditioning were:the first stirring intensity 200 rpm,the first stirring time 40 s,the second stirring intensity 60 rpm,the second stirring time 9min.The optimum stirring parameters of Fe Cl3 conditioning were:the first stirring intensity 250 rpm,the first stirring time 90 s,the second stirring intensity 100 rpm,the second stirring time 3min.It was found in the experiment that LB-EPS substantially lower than the TB layer.LB layer proteins had an important influence on sludge dewatering performance.The lower LB-EPS was,the better dewatering and settling performance were.The paper established regression models of drug dosage,sludge physical and chemical properties,dewatering and settling performance.The nature indexes of sludge included:viscosity,free water content, particle size.The dewatering performance indexes of sludge included:CST,SVI.When PAC conditioning,correlations between viscosity,free water content, particle size, CST, cake moisture content, SVI and dosage were strong. Analysis of a number of indicators,the optimal dosage of PAC was0.36g/L.When Fe Cl3 conditioning,correlations between viscosity, free water content,particle size, CST, cake moisture content and dosage were strong,but the correlation between SVI and dosage was poor. Analysis of those indicators,the optimal dosage of Fe Cl3 was 1.5g/L.When PAC conditioning,correlations between CST,SVI and viscosity,free water content, particle size were strong.When Fe Cl3 conditioning,correlations between CST and viscosity, free water content, particle size were strong,but correlations between SVI and viscosity, free water content, particle size were weak.The results of the passage explored the change of sludge flocculation and moisture migration.The paper established regression relationship between stirring parameters and dewatering, settling properties.At the same time,it established regression relationship between drug dosage and physico-chemical properties,dewatering, settling properties. The optimal dosage was found.It also gave the agent optimization for Songhuajiang River water sewage treatment plant.It is important to improve sludge dewatering property and reduce drug consumption.It provides a theoretical basis for the sludge reduction treatment in the future.