A thesis submitted in partial fulfi llment of the requirement for the degree of Master of Engineering, School of Environment, Resources, and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1995

A horizontal flow prefiltration system, a rotating drum filtration unit and a combination of prefilter and rotating drum units were developed for removing turbidity and algae from pond water. The main objectives of the study were to determine methods for the reduction of si1t and plankton turbidity and to harvest excess plankton from fish ponds at different flow rates and different turbidity concentrations. The inf1uent turbidity concentration, flow rates, fi1tering materials and sizes have been found to be factors affecting the turbidity reduction for both individual and combined media. For pond water sources 2 of high turbidity up to 252 NTU, the optimum flow rate was found to be 0.15 m /m - hr for 1. 7 - 12. 7 mm crushed stone as individual filter media. The optimum flow rate for 25 æm screen to remove algae waf 1. 15 m /m2 - hr as individual filter media. The combination of flow rates3 of 9.15 m /m -hr t through stone and synthetic material, and flow rate of 2.15 m / m - hr through micro screen were found optimum to remove plankton, and mixture of plankton and silt turbidity. It is concluded from this study that horizontal flow prefilter system using crus hed stone is found to be very effective in removing silt turbidity at minimum flow condition. The combined filter media of micro screen and coarse media of crushed stone and synthetic material are found very efficient in removing suspended solids of plankton, and si 1 t and plankton together at high and low flow rates from pond water