The use of organic coagulants for turbid water clarification

Summary

The results of studies of the coagulating ability of domestic organic coagulants of well-known brands for the treatment of turbid waters with color not exceeding the water quality target, depending on the characteristics of the coagulants, water turbidity and process parameters of coagulation and sedimentation are presented. The efficiency of using organic coagulants VPK-402, Kaustamin-15 and Biopag to reduce the turbidity of water caused by fine-grained clay particles with a hydraulic size of less than 0.01 mm/s is considered. It was found that VPK-402 coagulant characterized by the highest molecular weight, possessed the greatest coagulating ability. It was shown that the dose of the coagulant did not exceed 0.4 mg/l with an increase in the turbidity of the source water to 750 mg/l. The maximum reduction in water turbidity by sedimentation with the use of organic coagulants is observed with a flocculation time of 20 minutes, where 83–84% of the resulting flocs have a hydraulic size of more than 0.8 mm/s.

Key words

settling , turbidity , flocculation , hydraulic size , organic coagulants , water clarification

Reducing color of natural water with the use of organic coagulants

Summary

The results of studies of the effectiveness of reducing color of low-turbid natural water by filtration with the use of organic coagulants of domestic trademarks: VPK-402, Kaustamin-15 and Biopag are presented. It is shown that the decrease in color of natural waters with organic coagulants occurs mainly due to coagulation processes at low alkalinity close to zero, and chemical interactions of the polyanion of humic acids with the coagulant polycation with alkalinity more than 1.2 mmol-eq/l. It was determined that the optimal doses of organic coagulants increase with a decrease in molecular weight in the series VPK-402 < Kaustamine-15 < Biopag and an increase in alkalinity of the treated water; whereas with an increase in hardness – decrease. In the alkalinity range of 1.2–2 mmol-eq/l the specific consumption of coagulants VPK-402 and Kaustamin-15 increases from 0.04–0.06 to 0.12 mg per degree of initial color while low-molecular Biopag coagulant practically does not change and is 0.09 mg/degree. The dispersion of the formed particles of the suspension increases with a decrease in the hardness of the treated water, an increase in alkalinity and the concentration of low molecular weight fractions of humic acids in water being purified which is accompanied by an increase in color of the purified filtered water. It is shown that the standard decrease in water color below 20 degrees is achieved by removing coagulated particles with a size of more than 0.3 microns in the process of filtration.

Key words

turbidity , chromaticity , coagulation , natural water , filtration , hardness , alkalinity , organic coagulants

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