RAINWATER HARVESTING AND THE ASSESSMENT OF GMELINA ARBOREA SAWDUST-CEMENT-BONDED TANK FOR STORAGE

Abstract

Safe water availability is a critical problem in the post - rainy season in Akure, humid Southwest Nigeria. The potential of rainwater as a sustainable option for solving the problem of seasonal water shortage was assessed. Also, the suitability of Gmelina arborea sawdustcement- bonded tank was assessed. Rainfall data for fourteen years (1980-1993) for Akure , Southwest Nigeria was collected from the International Institute for Tropical Agriculture (I1TA), Ibadan and used to determine the number and length of wet and dry days; the critical dry periods and the quantum of harvestable rainwater. The analysis of the fourteen years data (1980-1993) presents an average annual rainfall of 1462.2mm, harvestable rainwater of 92m3 per annum and average wet and dry days of 109 and 256 respectively. The period of scarcity remains November to February as it is in other areas of Southwest Nigeria. A Gmelina arborea sawdust-cement-bonded storage tank of model sizeO.006m3 was designed using three different mix ratios of cement: G. arborea sawdust (3.0: 1.0, 2.5: 1.0. 2.0:1.0). The evaluation of these mix ratios gave a tensile strength of IION/mm2 , 104N/mm2. , , 95N/mm2 and compressive strength of 5000KN, 3000KN and 2000KN respectively. The aging test conducted on the three mix ratios showed that the ratio 3.0: J.O became stronger as the compressive strength increased to 5500KN confirm that the mix ratio 3.0: 1.0 is the best ratio for constructing the tank. Rainwater was collected and tested to establish its quality. Some of the collected rainwater samples were stored in the three tanks produced from the three mix ratios of cement and sawdust and their quality was monitored every two weeks for two months. The physicochemical analysis results gives a pH of 6.85, Hardness - 220 Alkalinity determination - 0.7, vii Acidity determination - 0.7, Total suspended solid - 350 and dissolved free CO2- 0.4 for the rainwater sample before storage. The physico-chemical analysis result of the rainwater after storing for two months did not show significant difference compared to the one before storage and they fall within the acceptable limits of the World Health Organisation standard.