5.1 Design Considerations of Floating PlasticMedia Pre-Filter for Removal of Particles from Surface Water with High Turbidity Level

摘要

This study was conducted to determine design criteria of floating plastic media bed used for pretreatment of surface water with high turbidity level. It was performed by using synthetic raw water with constant turbidity of 80 NTU. From the jar test, poly aluminum chloride was found to be the best coagulant with an optimum dose of 15 mg/l. Filtration test using floating plastic media bed with different media size of 3,6,8 mm and bed depth of 0.4, 0.6, 0.8 m at filtration rate of 5, 7.5 and 10 m~3/m~2.h was examined. Highest particle removal efficiency was achieved when the system was operated using 6 mm media size and 0.6 m bed depth at 5 m~3/m~2.h filtration rate. The size of particles released from the filter increased with time. Proposed criteria to achieve 80% turbidity removal in this floating plastic media pre-filter were L/d of 100 or more, bed depth of 0.6 m or more with filtration rate between 5 and 10m~3/m~2.h. The system was then applied at a water treatment plant in Bangkok where raw water turbidity fluctuated between 75-166 NTU. Average turbidity in treated water from floating plastic media filter was 7.5 and 28.1 NTU at the filtration rates of 5 and 10m~3/m~2.h.