The characterisation of natural organic matter (NOM) in South African waters

Abstract

The removal of natural organic matter (NOM) from water is becoming increasingly important in order to prevent the formation of carcinogenic disinfection by-products (DBPs). The inadequate removal of NOM has a bearing on the capacity of other treatment processes to remove organic micro-pollutants or inorganic species that may be present in water. In order to effectively study the nature of South African water sources in terms of their NOM composition, water samples were collected from drinking water treatment plants in the five geographic water regions of South Africa. A raw water sample, an intermediate sample taken before sand filtration and a final sample after sand filtration were collected three times from these water treatment plants at two-month intervals and over three different seasons. Fluorescence excitation-emission matrices (FEEM), biodegradable dissolved organic carbon (BDOC), ultraviolet (UV) characterisation (200–900 nm) and dissolved organic carbon (DOC) analyses were used to characterise the NOM in the water samples. The FEEM and UV results revealed that the samples were composed mainly of non-humic substances with low UV-254 absorbance, while some samples had high humic substances with high UV-254 values. The samples' DOC results were within the range of 3.25–21.44 mg/L carbon, which was indicative of the varying nature of the NOM composition in the regions where samples were collected. The BDOC fraction of the NOM, on the other hand, ranged from 20 to 65%, depending on the geographical location of the sampling site.