AWWA WQTC58894

The practice of recycling filter backwash water (FBWW) has become common in many North American water treatment plants. Although direct discharge to waterways of clarified waste streams is a widely practiced disposal method, recycling the generated wastewater is an attractive option for utilities governed by strict plant economics and increasing government discharge regulations. Backwashing a plant's conventional or direct filtration process units can consume up to 3-10 % of the treated water produced, and generates an equally significant volume of wastewater, termed as filter backwash water (FBWW) that must be managed. Filter backwash water consists of metal-hydroxides, concentrated microorganisms and dissolved organic and inorganic contaminants. FBWW and clarifier sludge generally comprise the majority of the waste residual volume generated, and in relative terms can be collectively referred to as combined filter backwash water (CFBWW). As a result of pathogen outbreaks attributed to inadequate clarification of backwash water, utilities are considering more advanced treatment methods for these waste residual streams. The objective of this study was to evaluate the impact of blending treated water with FBWW that had been treated with a submersed ultrafiltration (UF) system. In particular, this study examined water distribution issues concerning microbiological regrowth and the formation of chlorinated disinfection byproducts (DBPs) originating from disinfection with free chlorine, chlorine dioxide or chloramines on water that received a 10% blend of UF treated CFBWW. Includes 3 references, tables, figure.