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University of Nairobi (2018)

Water use practices, water quality and performance of a continuous solar water disinfection system in Isiolo County, Kenya

Abok, Elisha O

Titre : Water use practices, water quality and performance of a continuous solar water disinfection system in Isiolo County, Kenya

Auteur : Abok, Elisha O

Université de soutenance : University of Nairobi

Grade : Master of Science in Food Science and Technology 2018

Potable water scarcity is a major challenge faced by most developing nations of the world. Moreover, Arid and semi-arid lands of Kenya endure unbearable living conditions due to water pollution and limited number of water sources. Renewable energy can be tapped for use in treatment of water for use in households. The objective of this study was to determine the Water use practices, water quality and performance of a Continuous Solar Water Disinfection System in Isiolo County Kenya. Purposive sample of 165 respondents were interviewed using a semi-structured questionnaire. In the second phase, 44 purposive water samples were collected from water sources in the study area and analysed for microbiological and physico-chemical attributes using ISO procedures. In the last phase, a continuous solar water disinfection (SODIS) system was designed using two flat plate solar collectors (each 2.34 m2), a shell and tube heat exchanger, a solar photovoltaic pumping system and two water tanks. The system was tested under different conditions. The solar intensity and temperatures were measured using a pyranometer and digital temperature sensors respectively. Results show that 26.5 % of the respondents use borehole water, 21.8 % use river water while 16.9 % use spring water for drinking and processing in Leparua sub-location. Urban treated water is used by 14.5 % of the respondents based in Wabera and Kulamawe location. Pans and rain water are used during rains by 3.6 % of the respondents. Boiling was the main water disinfection method used by 66.7 % of the respondents while 21.7 % used chlorination. Solar water disinfection was new to the population and used by none of the respondents. Highest mean log Clostridium pafrigens counts in ground and surface water were 3.16 Cfu/ml and 3.53 Cfu/ml respectively. The mean log Staphylococcus aureus counts were 2.87 Cfu/ml and 3.12 Cfu/ml in surface water and ground water respectively. Escherichia coli and total coliforms contamination was 29.88 % and xviii 88.2 % respectively. Microbial counts in the water sources differed significantly (p≤0.05). Total coliforms had a significant negative relationship (r = -0.76) with residual chlorine. Highest and lowest total hardness values were 638.5 mg/l and 138.5 mg/l for borehole and tap water respectively. Calcium and magnesium ions mean values were 33.92 mg/l and 68.43 mg/l respectively. Borehole water had the lowest turbidity of 0.8 NTU. Mean value range for electrical conductivity and color were 139 μS/cm to 454 μS/cm and 13 TCU to 280 TCU respectively. Physico-chemical properties significantly differed (p≤0.05) across the water sources. Results show a significant positive (r =0.87) logarithmic change in solar radiation with time of the day. Temperature of disinfected water significantly differed with time of the day (p≤0.05). The SODIS system achieved mean log reduction for coliforms, Escherichia coli, Staphylococcus aureus and total viable counts of 3.08, 2.071, 1.368 and 3.474 respectively. Despite the difference in temperatures of the day the disinfection effect insignificantly differed (p≤0.05) for most times of the day. Flow rate was a significant exponential function of disinfection temperature (r = 0.9738). Isiolo County has adequate insolation and effective solar water disinfection can be enhanced extensively through optimized flow rates, disinfection temperature, holding time and solar radiation intensity. Key words : Solar water treatment ; Disinfection system ; Water quality ; Solar collectors ; Food processing


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