MODELLING OF TURBIDITY IN RAPID SAND FILTER

Abstract

When water is passed through a filter medium, the mechanisms involved in removal of suspended solids are very complex. The dominant mechanism depend on the physical and chemical characteristics of the suspension and the medium, the rate of filtration and the chemical characteristics of water mechanisms which are mainly responsible for removal are transport mechanism and attachment mechanism. Residual turbidity of effluent when plotted with time gives two types of responses. In case-I, residual turbidity first decreases with time and reaches a minimum and then increases. In case-II residual turbidity continuously increases with time. Case-I is the most general case. This study presents a mathematical model on the most general case of turbidity - sand depth - time response. The model makes use of two parameters first describing turbidity attachment mechanisms and second describing detachment mechanisms. The model has, been fitted by extensive use of computer. The two parameters have been evaluated taking typical data of filtration curves given in Weber's book "Physico chemical Processes for Water Quality Control". The fitting of the mathematical model has been checked by comparing the observed and fitted curves.