Effects of Phosphates on Coagulation and Sedimentation of Turbid Waters

Abstract

The increased consumption of synthetic detergents in recent years has prompted research into the effects of these substances on conventional water treatment processes. Operational difficulties have been attributed to the presence of synthetic detergent compounds in treatment plant influents, and considerable research has been undertaken to establish what effects synthetic detergent components have on treatment processes, principally coagulation, sedimentation, and filtration. The major components of present‐day commercial synthetic detergents are surface‐active agents and builder compounds. The most important compounds among the builders are the condensed phosphates, sodium tripolyphosphate (STP), and tetrasodium pyrophosphate (TSPP). The purpose of this investigation was to evaluate the effects of STP and TSPP on the clarification of hard, turbid water under conditions of continuous flow in a pilot‐scale treatment plant. Results show that STP and TSPP, in relatively high concentrations, are capable of interfering with the coagulation and sedimentation of hard, turbid waters. The effects of TSPP and STP appear to be equal. The magnitude of the interference is reduced by reasonable increases in the coagulant dosage, improvement of mixing and flocculation characteristics, and by an increase in settling time.

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