Identification And Quantification Of Natural Organic Matter In The Windhoek Operating Company Water Treatment Plant In Windhoek, Namibia

Abstract

Natural organic matter (NOM) is a generic term for a mixture of organic, slightly watersoluble components found in soil, sediment and natural waters, which represents severe challenges for the process control in water treatment plants as well as water distribution systems. The effective removal of NOM during drinking water treatment requires a good understanding of its character. The current study aimed to identify and quantify NOM present in the Windhoek Goreangab Operating Company (WINGOC) water treatment plant and to assess the efficiency of the plant in removing or reducing these organic matters. Water samples were collected at different points in the treatment plant starting with the raw ponds until the final treatment point once a week over a period of twelve months. Temperature, pH, organic content, nitrates, UV absorbance at 254 nm (UV254) and specific UV absorbance (SUVA) measurements were performed on the day of sampling. The molecular weight distribution of the organic fractions was determined using high pressure size exclusion chromatography (HPSEC) with fluorescence and UV detection methods. Raw water (ponds) had high dissolved organic matter, however this was greatly reduced after the dissolved air flotation, biological and granular activated carbon treatment processes. Dissolved organic carbon (DOC) removal efficiencies of up to 98% were achieved in some cases, which indicates that the treatment process employed at WINGOC treatment plant is effective in removing organic matter from the water. UV absorbance at 254 nm was found to be directly correlated to the organic content, decreasing gradually as the water is passing through different treatment stages.