Potential of Roof Rain Water Harvesting at an Industrial Setup

Abstract

This study examined the Roof Rain Water Harvesting (RRWH) prospective at textile mill alongside with the assessment of legal framework on RWH. The following information was analyzed:  Decadal rainfall variability, Rainfall probability, Rainwater quality (pH, Total Suspended Solids (TSS), hardness, Iron, Manganese and Lead). The metals were analyzed by Atomic Absorption Spectrophotometer, the rest of the parameters were analysed according to APHA (1997).  Volume of rainwater tank was chosen using Rapid Depletion Method.  Topographical survey of the site was done using standard Spot Height method. The Weibull formula was applied for plotting positions. The Hydrological Vertical Electrical Survey of the site was conducted with Standard Terresmeter. The average monthly rainfall was found at 91mm, which is higher than 50 mm recommended by Kenya Rainwater Association. Jointly with rainfall probability of 66% it was concluded that RWH was feasible. All the rainwater test results were within the stipulated standards, with exception of TSS, which exceeded the standard by 294%. To address this issue the study designed First flush off system and three layer Roughing filter. The payback period was found reasonably attractive - 5.6 years, thus the study recommended RRWH reinforced concrete system as a supplementary source of water at the mill with economic profit due to reduction of water utility bill. In addition environmental benefits can be obtained, such as control of storm water and decrease of vector borne diseases, e.g. malaria, which was not quantified.  Specific recommendations were made in order to promote and scale up RWH in Kenya.

Keywords: Roof Rainwater Harvesting, industry.