Rainwater Harvesting with Subsequent First Flush: Water Quality Performance for Non-Potable Purpose

Abstract

In the framework of enhancing water resource management, the Rainwater Harvesting (RWH) system has been recognized as one of the potential solution to mitigate water crisis issues. This paper aimed to study the water quality analysis of RWH system with subsequent flushes devices; in terms of its efficiency and practicality for non-potable purposes such as irrigation and toilet flushing. The project is also meant to identify the ideal volume among the five (5) FF devices installed; to be flushed away in order for the harvested rainwater to be usable for non-potable activities (i.e. irrigation, industry and toilet flushing). A RWH model were mounted on a wall of an existing store building at Universiti Teknologi PETRONAS (UTP), Perak. A total of eight (8) rain events (set of readings) were analysed. The nine (9) parameters monitored are: pH, turbidity, dissolved oxygen (DO), total suspended solids (TSS), total coliforms (TC), chemical oxygen demand (COD), total nitrogen (TN), ammonia and nitrate. For physical water quality parameters; pH, turbidity, DO and TSS, the final reading ranges were 4.60~8.37, 0.41~1.52 NTU, 7.60~9.44 mg/L and 0~40 mg/L, respectively. Chemical parameters such as COD, TN, ammonia and nitrate were in the ranges of 0~32 mg/L, 4~12 mg/L, 0.11~0.95 mg/L and 0~1.4 mg/L, respectively. Meanwhile the biological parameter which is the TC was in the range between 0~358.5 MPN. Based on the calculations, it is deduced that a minimum of 1.02 mm of rainfall of total 10.5 mL from FF1 to FF3 is needed to be flushed away; ensuring only better quality of rainwater being stored. The FF method is very important in the application of RWH system because it diverted the first flow of rainfall that is expected to be the most contaminated. The RWH system with subsequent FF devices is suitable for non-potable purpose. Upon further treatment and model modification, the harvested rainwater shall fit for potable use.