Enhanced Coagulation Of Luanhe River Water By Multiple Coagulants

Tanggu Water Treatment Plant is responsible for the drinking water supply of the entire Tanggu District, Luan River is its exclusive source heretofore. The source water quality of Luan River fluctuates greatly with variation of seasons, which brings great impact on the conventional treating process of Tanggu Water Treatment Plant, and the working conditions of various steps of water treatment also fluctuate, that is, the operating conditions of water treatment system are non-stable.According to the existing problems of the Tanggu Water Treatment Plant, and beginning with improve the coagulants, study is conducted to improve the effluent quality and enhance the impact resistance of traditional process to the water quality changes, which is based on the conventional treating process and obsolete treatment units/equipments.Through synthetically analyzing the source water quality indexes of calendar year, this paper chooses temperature, turbidity and algae as the main water quality indexes, the Luan River source water is divided into three phases: low temperature and turbidity-laden period, high temperature and algae-laden period and transition period.By beaker stiring experiments in the laboratory, the process and the optimum conditions of enhanced coagulation by combination of coagulants are systematically researched in different periods and water quality stages, which is also compared with the coagulation process using single FeCl₃ in the same source water period. The results showed that: under the customary treating operation conditions of Tanggu Water Treatment Plant (stirring for 3min at 200r/min, stirring for 2min at 40r/min and settling for 10min), the best combination way for enhanced coagulation by combination of coagulants of high temperature and algae source water is adding PAFC (or PAC) first while fast mixing following with FeCl₃ 5s～20s (or 10s～40s) later, then adding HCA with the concentration of 0.2～0.3mg/L about 1 minute later. The best mass ratio of PAFC(or PAC)/FeCl₃ is 1:3～1:2; the best combination way for enhanced coagulation by combination of coagulants of low temperature and turbidity source water is adding PAFC first while fast mixing following with FeCl₃ 5s～20s later without coagulant aid HCA, the best mass ratio of PAFC/FeCl₃ is 1:1.