Abstract:
Direct filtration is a water purification process used to remove colloidal particulates from the water. This process is a combination between coagulation and filtration. By utilizing the direct filtration in a water treatment system, sedimentation is not needed any more. This results in the reduction of water production cost. However, the disadvantage of this system is the limited level of turbidity in the raw water allowed to enter the filtration system. According to experimental results obtained during the direct filtration of synthetic water utilizing alum as a coagulant, the best performance of the pilot plant was obtained under the following condition : filtration rate 10 m³/m²-hr, raw water turbidity 10 NTU, alum dosage 5-7.5 mg/l. Daily backwash of the pilot filter was required. When applying to the high-turbidity raw water, more alum was required and consequently, the turbidity breakthrough occurred very quickly. The filtration cycle was short and frequent backwash of filter was necessary. Experimental results tended to indicate that filtrate turbidity varied directly with raw water turbidity and filtration rate but inversely with alum dose. While the loss of head seemed to vary with raw water turbidity, filtration rate and alum dose. In addition, efficiency of turbidity removal had inversely relationship to raw water turbidity.