Physicochemical analysis of roof runoff in the Obuasi area

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May 2008
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Life is dependent on water. Water exists in nature in many forms- clouds, rain, snow, ice, and fog; however, strictly speaking, chemically pure water does not exist for any appreciable length of time in nature. These impurities may give water a bad taste, color, odor, or cloudy appearance (turbidity), and cause hardness, corrosiveness, staining, or frothing. Quality of Water in the Obuasi area has been questioned due to the mining activities as well as ore treatment methods being used in the area. Residents are in dire need of other fresh water alternatives and roof runoffs harvesting has become very common. There is therefore the need to ascertain the quality of this alternative in order not to create another problem in trying to solve one. In this work, 75 roof runoffs samples from three selected areas (Wawasi, Ramia and Antobuasi) in the Obuasi area were sampled during five raining events between May and August 2007 from Aluminium, Aluzinc, Asbestos, Clay tiles and one collected from the skies to serve as control. The samples were analysed for physical parameters such as; pH, Alkalinity, Electrical conductivity, Total Dissolved Solids, Total Suspended Solids, Turbidity. Anions such as; Sulphates, Chlorides, Nitrites, Phosphates were also analysed. For each of the samples collected Six trace metals were determined. Metals were fractionated into dissolved and particulate fractions. Metals analysed include; Iron, Lead, Zinc, Aluminium, Chromium and Cadmium using Varian 220 Atomic Absorption Spectrophotometer. It was observed that the general quality of the water sampled from roofing material were seriously affected by the kind of roofing material being used with respect to the sampling area. It was also observed that most of the metals were particulate in nature and it contributed to over 60% of the total metal concentration. Except for pH, Pb Turbidity and Chromium all the parameters recorded values that were below the WHO guidelines for drinking water. The pH had a good correlation between Iron and Zinc but had a poor correlation with Lead, Aluminium, Chromium and Cadmium. Generally roof runoff can be recommended for washing utensils, flushing toilets laundry but not drinking and possibly cooking.
A Thesis Submitted to the Department of Chemistry, Kwame Nkrumah University of Science and Technology In partial fulfillment of the requirements for the Degree of Master of Science (Environmental Chemistry),