A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, school of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1980

A flow pattern investigation and two equations for predicting turbidity reduction in the horizontal prefilter are presented in this study. The turbidity removal of the artificial turbid influent which was prepared by mixing the tap water with Kaolin-Clay is affected by four parameters in this study. There are flow rate (Q) , size of filter coarse medium (d), length (L) and depth (D) of filter medium. The most predominant parameter of them affecting on turbidity removal through horizontal prefilter is length of filter medium (L), follow by flow rate (Q), size of filter coarse medium (d) and depth of filter medium (D) . The first empirical equation based on Reynold's Number can be expressed as follow: 2 3 p = 100 - Re + (Re) - (Re) 8.3 74 209 where p = turbidity reduction Re = Reynolds' Number in porous medium The second equation was derived from Hazen's (1904) concept indicating that turbidity reduction in filter was achieved by pores which are considered as a series of subdivisional. sedimentation units. It is presented as: -n p = 1 - (1+1 x v ) n D/ta where n = the number of subdivisional sedimentation units td = detention time And in the tracer study, real detention time was found approximately to be half of theoretical detention time, because of the short-circuiting and dead-zone in this filter.