CONSIDERATIONS ON THE RELATIVE EFFICACY OF ALUMINUM SULPHATE VERSUS POLYALUMINUM CHLORIDE FOR IMPROVING DRINKING WATER QUALITY

Abstract

This study presents the evolution of specific parameters of raw water quality from the Strâmtori-Firiza Lake, which is the raw water source of the water plant in Baia Mare town, Romania. Parameters such as temperature, turbidity, oxidability were recorded over a four years’ period. A comprehensive database on the evolution of these water parameters was thus created showing the tendency of these parameters across time. The possible correlations among the parameters were investigated. Positive correlations were found for oxidability and Al content and also for turbidity and oxidability. Temperature and turbidity were found to be highly variable (2-17°C, 3-53 NTU) across seasons. In order to improve the turbidity of treated water, two coagulants were tested: basic polyaluminum chloride (PAC) and aluminum sulphate (SA) evaluating the efficiency of the two treatment methods. While the traditionally used aluminum sulphate was found to be effective only when the temperature and turbidity were high: temperature >10ºC, turbidity >10 NTU (nephelometric turbidity unit), PAC emerged as an efficient clarifying agent even at low temperature and turbidity.