Studies On Effects Of Different Organic Matters In Source Water On Coagulation Process And Residual Aluminum

Aluminum is the important metal pollutant in drinking water, its presence could make people poisoned if its concentration is high. The drinking water standards in China for aluminum is 0.2mg/L. Therefore, how to decrease the residual aluminum in drinking water is important to the safety of drinking water. In this study, residual aluminum in drinking water was studied based on the properties of organic matters.The details of the study and results are listed below?The source water of a water treatment plant chosen in this study was various. In order to study the relationship between organic matters and residual aluminum, the third phase of the water treatment plant(A(3A), B(3B)) was chosen. In this study, the turbidity for water sample, the amount of particles in the process of coagulation, the organic matters and the molecular weight(MW) distribution of residual aluminum were investigated. The results indicated that different source water have different kinds of organic matters. The turbidity decreased after the coagulation process, and the removal efficiency for the turbidity could reduce the concentration of the particle aluminum effectively. When the turbidity was low, it could result in the reduction of the particle collision and the increasing of the concentration of the particle aluminum.The higher concentration of dissolved aluminum in the finished water whose MW is smaller than 1500 Da is one of the main reasons for the higher concentration of residual aluminum. Organic matters whose MW is smaller than 1500 Da had significant effects on the residual Aluminum.In order to furtherly investigate the effects of different organic matters on the coagulation performances and residual aluminum, the residual aluminum produced inHA or BSA solution and flocs formed in different coagulation conditions were studied.The results are listed below.(1)Different organic matters had different effects on residual Aluminum, and there would be more residual Aluminum in HA solution than in BSA solution under the same DOC concentration and solution pH.(2)In HA solution, the concentration of residual Aluminum increased with increasing the concentration of DOC under the same solution pH. There would be less residual Aluminum and dissolved residual Aluminum in the weak acid solution.(3)The influence of the concentration of HA on the residual Aluminum would not be changed with the change of aluminum form in the coagulants.The HA molecules had more effects on residual Aluminum.(4)When the pH of BSA solution was 6.0, the concentration of the total residual Aluminum and the total dissolve residual Aluminum reached the lowest.(5)When the solution pH was larger than 7.0(the concentration of DOC larger than 4.0 mg/L), the proportion of total dissolved residual Aluminum was larger than 90%, and solution pH had no significant effects on total dissolved residual Aluminum.(6)It was found that floc breakage and regrowth were intensely affected by stirring rate. When the stirring rate was increased to 100 rpm, a significant drop in floc size could be observed immediately.(7)The flocs formed by AlCl3 had larger strength factor, and the flocs formed by PACI-Al13 had larger recovery factor.(8)When there were BSA molecules in the HA solution, the strength factor and the recovery factor of the flocs would became larger.(9)At the same time, the concentration of dissolved residual Aluminum would became lower.The concentration of residual Aluminum would reach the lowest point when the radio of HA/BSA was close to 1:1.