ASSESSMENT OF THE EFFICACY OF SOLAR RADIATION AS A DISINFECTION METHOD FOR WELL WATER IN A SLUM IN IBADAN

Abstract

Lack of safe drinking water is a serious problem in many urban centers in Nigeria. The limited water available for low income communities is contaminated with human wastes and is responsible for many water-borne diseases. This study is aimed at developing a cheap method of water disinfection using solar radiation in Koloko-Aiyekale communities in Ibadan North East Local Government. These communities are low income and live in unplanned, high-density areas. They are also characterised by narrow roads, open drains and shallow wells. The study is descriptive and analytical in nature. A random sampling method was used to select respondents for the study. All the houses in the area were surveyed and the PHC numbers used in random selection. Thus 324 households were selected and the senior woman was interviewed using a structured questionnaire. A guideline was developed and the items of information sought included demographic characteristics, source of water, water treatment practices, knowledge, attitude and practice of water use and related health risks, personal hygiene and sanitary features of wells. In addition 78 water samples were analyzed to determine physical, chemical and bacteriological quality. Solar radiation disinfection, was standardized in the laboratory using various parameters such as type of container, cover, colour of container and cover, volume of water, turbidity and number of hours of exposure to sunlight. Furthermore, a solar radiation chamber was designed, fabricated and used to determine its efficacy in disinfecting water in polythene sachets. The results showed that 96 (29.5%) interviewed had no formal education, 82 (25.3%) had primary education 52 (16.1) had secondary education, 15(1.5%) had tertiary education. Most of the women interviewed (91.1%) were married and belonged to the Muslim faith. The women had a mean monthly income of #1,253 and 13 (3.7%) were unemployed. 43 (13.6%) of the women also had vocational training in tailoring, hair dressing, cloth weaving and dyeing. Shallow well water was their main source of water with 78.9% of the households using it in rainy season and 92.4% in the dry season. They used the water for drinking and other domestic needs. About the sanitary features of the well 137 (42.3%) of the wells were unlined or poorly lined with many of them lacking parapet, apron, cover or a permanent bucket About 199 (61.4%) had animal excreta around the wells. The depths of the wells ranged from 0.178m to 37.93m and the water depths ranged from 0.06m to 18.29m About the treatment of water, 46 (8.29%) of the respondents said they chlorinate their wells 211 (38%) boil, 257 (46.3%) treat using other methods like alum treatment and salt addition About 41 (7.4%) gave no treatment When asked whether they will like to use solar radiation as a method of water disinfection, 292 (93%) indicated their willingness. Regarding the quality of well waters the following mean values were recorded during rainy season (mg/l): Total solids, 383.1; Suspended solids, 78.1; Total Alkalinity, 54.3 ; Total hardness, 86.3; Calcium, 28.7; Magnesium, 12.4 and Chlorides, 70.1; the mean coliform count was 2685 MPN/100ml. The dry season values recorded were (mg/l): Total solids, 443.6; Suspended solids, Not done; Total Alkalinity, 68.0; Total hardness, 67.6; Calcium, 15.6; Magnesium, 7.8 and Chlorides, 11.06; The mean coliform count was 833.7 MPN /100ml. These results indicate that the well waters are polluted and needed effective disinfection. Solar radiation experiments in the laboratory indicated that the disinfection process is effective when 51 samples were taken in a plastic bowl. The degree of disinfection is relatively higher when the colour of the container was while or black Blue, green and brown showed relatively lower disinfection efficiencies. Similarly when the bowls were covered with plastic cover, white and black showed higher efficiency than other colours. The optimal exposure time was found to be 7 to 8 hours. When the days were cloudy or rainy, the solar disinfection process was not significantly affected as long as the samples had 5 hours of sunshine. During the solar radiation process the ambient temperature varied between 23°C and 46.5°C, and the water temperature ranged between 25°C and 45°C. It was shown that solar radiation had a definite effect on the coliform reduction as compared to the heat effect. This study on regrowth of coliforms after storage of water indicated that when the water samples were properly disinfected, there were no regrowths after storage. Increasing turbidity beyond 40 mg/l had a slightly reducing effect on the disinfection efficiency. There was a negative correlation between the thickness of container and the efficacy of solar disinfection. The trials with selected community members also showed that solar disinfection process is satisfactory and viable. A solar radiation chamber was designed and fabricated using plywood, plain glass and a mirror. This chamber was found to be efficient in disinfecting small quantities of water (500ml) which are commonly sold in the market as "pure water". The disinfected sachets did not show any regrowth even after storage for about a day. These results are significant in that the solar radiation disinfection method is economical as people can adopt this technology with minimal skills and little expenditure. Based on these results, certain recommendations were made to the communities and policy makers to encourage the use of solar radiation technology as a water disinfection method.