Filtrate turbidity improvement of existing mono-media filters based on a pilot plant study

With the advancement of knowledge in drinking water and health impacts related to it, requirements for drinking water have progressively become more stringent. Removal of particulate matter causing turbidity has also been found to be an effective means for removal of microbial contaminants such as Giardia. The conventional treatment process most effective at removal of small particulates is filtration. Presented is a two-phase pilot-scale study used to select new filter media for the Rossdale Water Treatment Plant in Edmonton, Alberta. The study was necessitated by more stringent turbidity guidelines which existing filters would have difficulty achieving. The design and planning of the study had to consider constraints posed by upgrading of an existing filter facility which dictated the media depth and the allowable bed expansion during backwashing. Phase I involved a screening test of four types of media. Based on the phase I results, a crushed quartz and a dual-media consisting of anthracite and sand were selected for more detailed study in the second phase involving investigation of the effects of filtration rate (3.5–12.5 m/h). Filter performance was analyzed using different statistical methods. Factorial experimental concepts were used to study significant effects. Results from both phases indicated that crushed quartz consistently provided the best effluent quality, while the dual-media provided longer filter runs. Key words: water treatment, constant rate filtration, turbidity standards, filter media, crushed quartz, statistical analysis.