Evaluation of the performance of natural fabric protected slow sand filters

In the developed world Non-Woven synthetic fabrics (NWF) are put on top surface of Slow Sand Filtration (SSF) units the aim being to increase the filter run times and concentration of most of the treatment process in the fabric layer (S). hence reducing the frequency of filter cleaning and resanding. The aim of this research was to investigateto what extent a natural fabric can protect the SSF unit especially the Household SSF. The fabric used was Luffa cylindrical commonly known as vegetable sponge (or Nadodoki in Kiswahili). During this study, laboratory and field tests were conducted at a filtration rate of about 0.1 m/h. laboratory tests were conducted on inlet water and filtrates from the Household SSF units for water quality determination. Parameters monitored included: head loss, temperature, pH, turbidity, Bacteriological quality, conductivity, Total Dissolved Solids (TDS), Dissolved Oxygen (D.O.) and apparent colour. In the study it was formed that it is possible to use Luffa cylindrical to protect the Household SSF. It was also found that very low rates of head loss development could be achieved by optimization of thickness of Luffa cylindrical fabric. As a result of this filter run time extension by a factor of up to 1.6 was attained. It was also found that it is possible to concentrate the majority of impurities in the Luffa cylindrical multi-layers such that routine maintenance involves cleaning of the fabrics only at the end of the filter runs. It was also found that although Luffa cylindrical multi-layer can capture a large majority of impurities as demonstrated by turbidity and bacteriological removal, but because the filtrate quality of conventional SSF is usually of excellent quality the additional treatment performance of SSF is not very significantly improved by the use of Luffa cylindrical fabric on top of the SSF sand beds. It is recommended that for further research a preliminary treatment of the fibres with a detergent should be done for the fabrics to become less adhesive to water. It is also recommended that lower and higher filtration rates than 0.1 m/h be used in order to investigate the effect of filtration rates on the rate of head loss development. It was further recommended that parameters like Taste and odour of the filtrates from the SSF units be monitored.