Abstract:
Raw water was synthesized to have theoretical colloid sizes of equal to or smaller than one micron and 50 NTU turbidity. The turbidity particles were destabilized by poly aluminum chloride in a rapid mixing unit and different polymers such as anionic, nonionic and cationic polymer were added as coagulant aid. The doses of poly aluminum chloride were set at concentration of 0, 1 and 3 mg./l while those of anionic and nonionic polymer were 0.05, 0.10 and 0.30 mg./l, and cationic polymer were 0.30 mg./l. Each experiment was tested at up flow velocities of 40 and 60 cm. /min for six hours, with samplings being taken every hour. Effluent turbidity, pH, size and settling velocity of pellet floc at levels 0, 50, 100 and 130 cm. were determined for comparison. Quantities of dissolved aluminum and suspended solids at steady state were also tested. Experimental results led to the following conclusions: 1. Anionic polymer and nonionic polymer were suitable as coagulant aid in the process. 2. In The cationic polymer case, no conclusion was drawn, due to the fact that the steady state was not reached. 3. At steady state, effluent turbidity increased when up flow velocity in the pelletizer was increased but decreased when dose and molecular weight of anionic and nonionic polymer were increased. The product water was less than 5 NTU. 4. Effluent dissolved aluminum content increased with doses of poly aluminum chloride, but the residual aluminum was still below the 0.2 mg. /l standard.