Comparative pilot-scale investigation into uprating the performance of percolating filters by partial medium replacement

A pilot-scale investigation was carried out to ascertain whether the loading to conventional single-pass percolating filters could be increased by partially replacing mineral medium with a random plastic medium. The treatment efficiency of a mixed-media filter (1.2m 3 blast furnace slag topped by 0.8 m 3 Flocor RC plastic medium) was compared over 26 months with the treatment efficiencies of two single-medium filters containing 2 m 3 blast furnace slag and 2 m 3 Flocor RC respectively. Two hydraulic loadings, 1.68 and 3.37 m 3 m −3 d −1, average organic loadings 0.28 and 0.63 kg BOD m −3 d −1, were used for consecutive periods of 13 months. Medium replacement has been shown to be a viable system for uprating conventional filters. The mixed filter was more versatile and was also markedly more efficient than the slag filter at the higher hydraulic loading. It is estimated that at this loading the mixed filter could treat a 30% greater organic load than the slag filter.