Study of the technologies of wash water treatment from contact clarifiers

Summary

The results of the laboratory studies of twelve flocculant kinds used for wash water treatment from contact clarifiers are presented. The optimal dosages of flocculant were determined. Two of the flocculants studied were selected that could ensure the maximum degree of water clarification at the minimum concentration of residual aluminium, residual polyacrylamide and suspended solids in water. It was stated that the sludge generated during water clarification had 99.9% moisture content. It was proved that Flopam FO 4240 PWG and Маgnafloc LT-22S flocculants ensured good sedimentation of pollutants present in wash water. Possible use of chemical and chemical free filtration in «Fil’tr Polimernyi» manufactured by «Samenviro» LLC as well as of membrane filtration in UNA-620A hollow fiber module (based on Microza^® pressure membranes) in a pilot plant rendered by «Pall Evrasia» LLC was considered.

Key words

turbidity , flocculant , wash water , contact clarifier , residual aluminium , residual polyacrylamide , optimal dosage of chemical

Providing for the efficiency of contact clarifiers under conditions of reduced design filtration rate

Summary

An analysis of methods of providing for the efficiency of contact clarifiers under conditions of reduced design filtration rates is presented. Under actual operating conditions of contact clarifiers with a lower than design capacity after the introduction of a coagulant (aluminum sulfate), the estimated residence time of the coagulant in the water is 5.3 minutes before contact filtration starts. Furthermore, the motion speed of the flow being two to three times lower than the design value, is approximately 0.02 m/s, which is typical for the floc formation conditions. As a result, an undesirable coagulation process occurs in the free volume, so that previously formed aluminum hydroxide flocs disperse to form colloidal aluminum hydroxide. The formation of colloidal aluminum hydroxide in the free volume under contact coagulation conditions may worsen rather than improve water purification processes; in particular, the rate of pressure loss in the granular filter bed may increase. The results of pilot tests at the Kolpino Water Treatment Plant operated by SUE «Vodokanal of St. Petersburg» are presented, followed by the introduction of the best technical solutions.

Key words

contact clarifier , contact coagulation , particle size distribution of the filter media , mixed chemicals

Development of Contact Clarification Technology for Low Turbid Water Treatment

Summary

The enhancement of a single-stage flow chart of treatment of low turbid water of the Saratov Reservoir (the Volga) in contact clarifiers at the treatment facilities of the city of Samara is considered. The experience of the operation of contact clarifiers in Samara under conditions of low turbid colour water treatment shows the high efficiency of water clarification and decolouration at simultaneous reduction of the cost of construction and operation of treatment facilities in comparison with the two-stage water treatment. The process of contact coagulation progresses faster than the usual coagulation in the free volume. A doze of coagulant at water clarification in contact clarifiers is smaller than in the course of two-stage treatment. The temperature of the water has almost no influence on the process of contact coagulation.

Key words

disinfection , surface water source , water supply plant , contact clarifier , loading material