Development of an automatic cleaning mechanism for roof water harvesting

Abstract

One of the easiest and efficient way of water conservation to solve drinking water scarcity is rooftop water harvesting. However, the technology has some limitations with regard to its purification system. The commonly used sand and gravel filter is very prone to clogging and its cleaning is not an easy job. At the same time, the alternative upward flow mesh filter needs further improvement in cleaning efficiency and some hassle free drain cum back washing mechanism. Hence, a study has been taken up on the upward flow filter system to improve its filtration efficiency and incorporate an automated drain cum back washing mechanism. The study also included the performance evaluation of a first flush system when attached to the inlet side of the micro mesh filter. To evaluate the performance of the filter and first flush, inflow and outflow of the rooftop water samples were analysed for pH, EC, TDS, SAL and TSS parameters. In general, the PH, electrical conductivity, and TDS of the roof water samples were within the drinking water standards and the filter system was found to reduce TDS values. In the case of TSS, mostly the impurities were organic in nature and concentration varied between 220 to 280 mg/l, a level much higher than WHO and BIS standards. The 3 micron mesh filter is removing 100% of the organic TSS impurities. The filtration rate of this filter is about 0.37 lps at a hydraulic head of 1.5 m and hence suites to rooftop rain water harvesting. First flush system showed better cleaning efficiency when attached to the inlet side of the coarser micro mesh filters. Automatic flush developed for the removal of stagnant water with impurities were performing well by removing all the stagnant water and about 92 % of the impurities. It can be concluded that 3 micron mesh filter with automatic flush can function as a near fool proof mechanism for filtering rooftop rain water.