Filter backwash water treatment options

Filtration acts as the final step in the removal of suspended matter and protozoa. The accumulated residue is removed during the backwash process and any subsequent recycling of filter backwash water could potentially re-introduce these contaminants into the main treatment process. By separating the filter backwash water from the main treatment process, factors that could interfere with the integrity of the primary treatment barriers, will be eliminated. Treatment and recovery of the filter backwash water would be beneficial in terms of water reuse, by replacing a proportion of the freshwater demand. The aim of this study was to investigate possible treatment options for the filter backwash water at Rand Water. Treatment options for filter backwash water treatment plants usually consist of a solids removal process and a disinfection process. Three solid removal processes for filter backwash water from Rand Water's filtration systems were selected for testing on an experimental basis: (1) sedimentation without flocculation, (2) sedimentation with flocculation, and (3) dissolved air flotation with flocculation. Flocculation with sedimentation produced the best results when compared to the other two treatment options evaluated. It is a simple and effective option for the treatment of filter backwash water.