Comparison of the effectiveness of mineral and mixed coagulants in the lightening of water from a surface source

Abstract

The results of experimental studies of the coagulation treatment of the Sura River water in the autumn period and during high water with the use of mixed coagulants based on aluminum sulfate (AS), polyaluminum chloride “AQUA-AURAT 18” (PACl) and organic coagulant FL 4540 are presented. When treating river water with a low temperature, the use of mixed organic and mineral coagulants allows for a more significant reduction in the turbidity of the settled water compared to mineral coagulants AS and PACl at the same doses. Mixed coagulants with a weight ratio of FL 4540: AS (or FL 4540: PACl) equal to 1:4 have a greater efficiency of action compared to coagulants with a ratio of organic and mineral parts equal to 1:1. When treating low-turbidity water with a low temperature in the autumn period, the highest effect of clarification by settling was obtained using mixed coagulants based on PACl and FL 4540. At a standard mixing time of the initial river water with coagulants of 2 min, the use of a mixed coagulant K3 based on PACl and FL 4540 allows getting the same lightening effect as when using only PACl, but with doses lower by 30%. Experimental data on the coagulation treatment of the source water with low alkalinity and increased turbidity during the flood showed the greatest effectiveness of the mixed coagulant K1 based on AS and FL 4540, the use of which, with a mixing time of 2 minutes with the source water, reduces the dose of AS by 10% with the same settling effect. Increasing the mixing time with water to 15 minutes increases the effectiveness of the mixed coagulants, which in this case can reduce the doses of AS and PACl by 1.6-2 times without compromising the quality of clarified water by settling.