Comparing Filtration Efficiency of Six Natural Fibres Used in Rainwater Harvesting Systems

In this study, different natural fibres such as sisal, jute, hemp, coir, oil palm and banana were tested as filter media in rainwater harvesting systems. The superior one among the six fibre media was selected through adsorption studies based on its potential to adsorb nitrate (NO₃-) ions from storm water. The results revealed that the adsorption of NO₃- for coir, sisal, hemp and banana fibres, occurred mostly within the first 24 h, while the adsorption process took 18 h for oil palm and 6 h for jute fibre. The NO₃- ions’ adsorption properties could be adequately described by the Freundlich isotherm. The adsorption capacity of the coir filter medium was found to be higher, followed by oil palm. The sisal, hemp, jute and banana fibres stood in the third to sixth position, respectively, in the order of higher adsorption capacity. Irrespective of the fibres, pH and electrical conductivity (EC) of the water decreased during the first 6 h and remained constant afterwards. Based on the findings of column studies, it was observed that coir fibre performed best in removal of NO₃- ions (10.3% removal), followed by sisal (10.1%) and oil palm (7.7%). The high total solids (TS) removal efficiency of 88%, 83.5% and 77% were exhibited by the coir, oil palm and jute fibres, respectively. However, the sisal, oil palm and jute fibres performed well in reducing EC. By comparing sorption capacity and hydraulic performance of different fibres, coir fibre could be recommended as a better filter medium for removing nitrate ions. The findings of the study are useful for developing water filtration systems using bio-degradable fibre materials.