Effect of ozone pre‐treatment of colored upland water on some biological parameters of sand filters

A pilot treatment plant for potable water, consisting of an ozonating unit followed by slow sand filters, was built in order to determine the relationship between filter biomass and performance following ozonation of colored feed water of upland origin. The color is due largely to the presence of humic substances, being most prevalent after heavy rainfall in the catchment. Ozone improves color by breaking down large humic molecules to smaller organic species, thus providing more bioavailable material in the water. Slow sand filtration, applied after ozonation, removes some of this material at the expense of more rapid clogging of the filters. This study on the schmutzdecke showed that the overall biomass of ozonated filters after clogging was significantly greater compared to non‐ozonated filters. Results revealed an increase in the heterotrophic biomass, but no significant change in the autotrophic community biomass, in slow sand filters receiving pre‐ozonated water.