A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering at the Asian Institute of Technology, Bangkok, Thailand.

Thesis (M.Eng.) - Asian Institute of Technology, 1976

A horizontal flow prefiltration system was developed using crushed stone as a filter medium for treating tropical surface waters. The main objective of the study was focussed on the reduction in turbidity and the factors affecting it. The multiple regression technique has been used to find the regression coefficients of the variable parameters. The influent turbidity, the depth of media, the length of media and the flow rate have been found to be the factors affecting the turbidity re duction in the horizontal flow filter. For raw water sources of low turbidity, about 35 JTU, the optimum flow rate was found to be 0.34 m3 /m2-h, and of high turbidity level about 150 JTU, it was 0.19 m3 /m2-h. There is no appreciable head loss noted in the laboratory scale study and thus this type of filter could function for longer duration without cleaning. A cost model has been developed for a pilot plant size horizontal flow prefilter unit and solved by Lagrange's function. It is concluded from this study that the horizontal flow filtration system using coarse media such as crushed stone is found to be very effective in removing suspended solids from tropical surface waters.