Experimental Validation of Roughing Filtration Theory for High Turbidity Water

Abstract

As an agricultural country Pakistan depends primarily on glacial melts and monsoon rains. Water from these sources flows down to rivers finding its way to Arabian Sea. The surface water thus collected is the chief source of drinking water in majority rural areas of Pakistan. However this water quality is objectionable. Typical problems regarding the use of surface water are presence of suspended solids, colloidal particles, turbidity, and agriculture runoff. Roughing filters are one of the economical solutions to remove the suspended particles from the surface water. Lab scale setup of three roughing filters was designed and operated using synthetic raw water of high turbidity, having turbidity up to 200 NTU. Turbidity of the influent water was maintained by intermittent manual mixing and flow rate of the influent water was maintained by using the pipe and valve assembly. Three filters were have different size of media and were operated at three different loading rates i-e., 1.1 m/hr, 1.5 m/hr and 1.9 m/hr. Best flow rate and media size was selected to operate the roughing filters at high turbid water. It is concluded from this study that 1.5 m/hr hydraulic loading rate and 8-12 mm media size is most appropriate to operate the roughing filter. Hypothesis of the study is that “rapid filtration theory can be applied to roughing filters”. It is concluded from this study that rapid filtration theory can be applied to roughing filtration. Comparison between two theories was carried out xvi i-e., rapid sand filtration theory and roughing filtration theory. Filtration theory was used to determine the transport coefficient, filtration coefficient and attachment coefficient for the validation of the roughing filtration theory. It is also concluded from this study that Tufenjiki theory is more precise that Yao’s theory to determine the transport as well as attachment coefficients.