Scan of water treatment processes to achieve desirable chlorine stability in water supply systems

Abstract

Abstract Removal of natural organic matter (NOM) is increasingly important in production and distribution of drinking water complying with health and aesthetic guidelines. The impact of treatment is often investigated using the resulting dissolved organic carbon (DOC) concentration and trihalomethane formation potential. Water treatment processes of ferric and alum coagulation with and without pre-oxidation by ozone and permanganate were scanned for their ability to treat synthetic raw water from peat extract. To compare the efficiency of the treatment methods the dissolved organic carbon (DOC) concentration and chlorine decay and trihalomethane (THM) formation tests — the important parameters needed in practice were used. A high level of DOC removal (>80%) was achieved with all the treatments. A significant difference was observed in chlorine decay rates and THM production. Pre-oxidation with 2 mg/L of O3 and coagulation with 45 mg/L of ferric sulphate produced the most chlorine stable water followed by water treated with 80 mg/L of ferric sulphate. Chlorine decay test was found to be a more sensitive indicator of a successful treatment than DOC. The optimisation of the ozone dose is likely to identify the best water quality and chemical cost combination which is not likely achievable by the coagulation alone.