Removal of Aluminium in Filter Backwash Water: A Treatment Optimization Case Study

Abstract

This is a study of filter backwash water handling methods and the development of an optimization strategy for the current treatment process at a water treatment plant in Nova Scotia. The aluminum concentration at the point of regulation was found to always exceed the guideline of 184 μg/L with an average discharge of 669471 μg/L. Tracer studies showed significant short-circuiting with a minimum retention time of five hours and forty-nine minutes for the entire treatment system. The treatment lagoons were modeled using fluid dynamics and different baffle placements were compared; two evenly spaced longitudinal baffles displayed the biggest improvement in retention time. Bench-scale settling tests determined an optimal polymer dose of 5 mg/L using a cationic medium molecular weight polymer with a settling time of 1.5 hours, which is representative of the initial discharge of the two baffle CFD model. The aluminum concentration with this combination of improvements was reduced to 101 μg/L.