Characterization of Organic Matter in Water Treatment Plants

Organic matter is perceived to be one of the most important contaminant to water and wastewater treatment plants. Incomplete removal of the organic matter may result in impairment of the water quality. Hence, it is desirable to reduce the concentration of organic matter in water treatment plants to enhance water quality. Generally, organic matter strongly impacts on colour and odour of water, it also affects filter fouling and coagulant doses, and act as precursors to disinfection by-product formation.  In addition, synthetic organic micro-pollutants are more toxic to life and are not effectively removed from WTPs and WWTPs following the conventional processes. More studies are currently geared towards enhancing organic matter removal from the water treatment plants and automation of coagulation processes. In some cases water treatment trains with Activated carbon followed by chemical coagulation, or advanced oxidation followed by chemical coagulation have been applied but these increase the cost of the treatment process.

In Kenya, little has been done with regard to characterization of the natural organic matter in the source waters to the treatment plants. In this study an attempt was made to characterize organic compounds found in water and wastewater from Kabete and Ruai in order to provide baseline information on the composition of organic matter in the water. This information is vital and can be used to improve of optimize water treatment processes. Water was collected from the inlet, midway and outlets of the water treatment plants including after coagulation and sedimentation processes (for drinking water). For the wastewater treatment plant, water was collected from the inlet and the outlet streams to determine the presence of the organic matter.

Water physico-chemical parameters such as TDS, Turbidity, pH and conductivity were measured using portable meters. Further experiments were conducted using Lambda 25 UV/Vis spectrophotometer to determine the natural organic matter (NOM), and Gas chromatography coupled to mass spectrophotometer (GC-MS) to identify the types of synthetic organic matter in the water at different stages of the treatment train. For analysis of micro-oraganic pollutants, water was extracted by solvent/solvent extraction method using dichloromethane, whereas sediments were extracted by Soxhlet method using hexane/acetone mixture and analysed by GC-MS.

The results revealed the presence of high levels of organic matter and micro-organic pollutants in wastewater compared to drinking water sources. In Kabete, TDS was found to increase after coagulation and sedimentation processes signifying residual dissolved solids from the chemicals added. The report provide detailed concentrations and chemicals structures and spectra of identified chemicals. The results show the need for further studies to delineate the composition of organic matter in all water sources and to collect water during different seasons to understand the dynamics of water sources and the treatment processes across the year.

Key words: Water treatment, wastewater, natural organic matter, micro-organic pollutants

Documentation :