Effects of backwashing on biological filters

Abstract

A pilot study identifies concerns and strategies for successful performance of biological filters.The success of biological filtration depends on careful control and maintenance of the amount of biomass on the media during the maturation period and backwashing as well as during sudden changes in hydraulic loading. Various backwashing strategies and hydraulic transients were studied to determine how they affected filtration performance of biofilters in terms of effluent quality and head loss. Biological filters backwashed with a combination of air plus subfluidization water flow at collapse pulsing, followed by water wash with 25 percent bed expansion, can produce a water low in assimilable organic carbon (AOC). Compared with air‐scoured filters, water‐washed filters produced lower initial peaks during ripening and similar effluent AOC. Chlorinated backwash affects biological activity. Under the conditions of these experiments, chlorinated backwash produced higher AOC and nonpurgeable organic carbon in the filter effluent. A sudden 30 percent increase in hydraulic loading had a greater effect on biological filtration performance than on conventional filtration, accelerating filter breakthrough and causing poorer effluent quality.