The removal of suspended particles inside direct sand filters

摘要

Direct sand filtration experiments by using a small scale pilot plant were conducted to investigate the removal mechanism of kaolin particles coagulated with aluminum coagulants in deep bed filters. The measurements of size and zeta potential of the particles in sample waters extracted from three different filter levels indicate that the removal of the floc particles inside the filter starts int he order from particles having greater size and better-controlled zeta potential. Based on the filter impediment modulus with respect to filtration time and filter depths which was obtained by applying the direct sand sampling technique, some findings have been presented, among them being one that as the changing shape of the impediment modulus developed with the increase of deposited material inside filters, the mountain shape and descending shape predominated. The maximum impediment modulus in each experimental condition occurred in the top 0-5cm of the filter, and randed from 10.4x10~(-2) with a filtration rate of 120 m/d and alum dosage of 13 mg/1 to 16.2x10~(-2)cm~(-1) with 240 m/d and PAC 10mg/l.