Development of a filter system for roof water harvesting

Abstract

Roof top rainwater harvesting has enormous potential in solving the water scarcity of a region, especially the domestic requirement. Roof water needs adequate purification to separate the impurities getting into the rain water from the roof. Conventional filter used for the purpose, a sand and gravel filter, has the inherent limitations of hassle free cleaning and as a result the filter unit go clogged and the entire system become dysfunctional very quickly. To tide over this issue, an M.Tech research work has been taken up with the objective of developing a simple and easy to clean filter system. Under the study, an existing micro mesh filter has been evaluated thoroughly under actual rainfall conditions. Two additional filters viz. sand and charcoal were also developed as secondary filters and connected to the outlet of the mesh filter to improve the purification efficiency. As rainfall was insufficient to test the performance of the sand and charcoal filter combinations with the mesh filter, synthetic roof water was prepared and test was carried out. The study also included testing the roof water quality from different roofs such as clay tiled, RCC paved with terracotta tiles, clay tiled, old RCC and new RCC. The results showed that pH values of the roof water were not varying with respect to roof materials and their values were very close to 7. EC was varying with respect to roofs and rainfall events but there were no consistency in their variation, also, their values were within the permissible limit of potability. Turbidity and suspended solids were also showing variation with respect to roof and rainfall events, their concentration was higher than the permissible limit. After the filtration, the turbidity and suspended solids concentration reduced by 81% for mesh filter alone and 85% when secondary filter combinations of sand or charcoal were used. All the filter combinations were also capable of reducing the EC values of the roof water significantly. BOD 5 test of the inflow and outflow water also showed considerable reduction in BOD 5 in the outflow water. Coliform test revealed that roof water washaving coliform bacteria, but after the filtration, the presence of coliform bacteria was negligible. The study has proved that the micro mesh filter and the filter combinations with sand and charcoal are very effective in the purification of roof water and they are also very user friendly from the point of view of cleaning.