A New Polyelectrolyte Dosing Method: Injection into Deep Bed Filter Media

The aim of this paper was to investigate a novel method of polyelectrolyte injection into deep bed filter media. The raw water and the filter media used in the pilot filters were obtained from the Omerli Reservoir that supplies one million m3/day of water to the greater city of Istanbul. A cationic polyelectrolyte was injected at the entrance of the filter and at different depths of the sand bed. The effect of polyelectrolyte injection location and method was evaluated by measuring the effluent turbidity, effluent particle count, and the head losses at different locations of the sand media. It was observed that the simultaneous injection of the polyelectrolyte on top of the filter bed and at the center can lengthen the filter run time while achieving an effluent turbidity as low as 0.06 NTU (nephelometric turbidity unit) and 4 log (99.99%) particle removal. In this study, a polyelectrolyte injection method that has not been tried earlier was studied. The results showed that simultaneous polyelectrolyte additions to the entrance and into the midpoint of the filter media produced better effluent quality and longer filter run time compared to polyelectrolyte addition only to the inlet of the filter.