Comparison of Single and Dual Media Filters Efficiency in Direct Filtration

In recent years, according to water shortage, non-optimal of energy and high cost of water treatment, usage of dual media filters (DMF) and direct filtration have paied more attention. On the other hand, filtration is known as heart of water treatment plant (WTP) and takes about 20% of total capital cost of WTP, Therefore, optimal design in the economical scope is very important.This research tries to evaluate direct filtration through DMF (Anthracite Coal and Sand) and single media filter (SMF) and applied this method for raw water with low turbidity (below15-20NTU) for the first time in Iran with natural water (taken from reservoir of Karaj Dam) in Kan WTP (Tehran No. Two water treatment plant).In the first experiment direct filtration was carried out in pilot scale by injection of 1 ppm FeCl3 and 2 ppm lime into the raw water with a turbidity of 8.3-15.5NTU. Runing time and average effluent turbidity were 32 hr, 1.31 NTU for SMF and 48hr, 1.11 NTU for DMF respectively.The second experiment carried out with 2.2ppm lime (Without FeCl3) led to run time and average effluent turbidity of 37.5, 2.15NTU for SMF and 58.3hr, 2.06NTU for DMF respectively.Pilot results indicated direct filtration with DMF in conjunction with low amount of coagulants can be used for the seasons of years in which the turbidity of raw water is less than 15-20 NTU.