| Treated water used for backwashing a water utility's conventional or direct filtration process units can consume from 3 to 10 percent of a plant's total water production. This use of clean treated water for plant operations not only consumes a considerable quantity of a plant's total water production, but also generates an equally significant wastewater volume which must be managed. At present, this waste residual volume, termed Filter Backwash Water (FBWW), can be directly discharged without treatment to the source water, or recycled within the treatment plant. Although direct discharge to waterways of clarified wastewater is a widely practiced disposal method, recycling the generated wastewater is an attractive option for utilities governed by strict plant economics and increasingly stringent government discharge regulations. Diminishing water resources, rapid population growth and industrial development have also prompted new interest in the reclamation of municipal and industrial wastewaters.; Over the past ten years, the use of membrane technology for treating ground and surface water supplies has gained widespread acceptance. Recent research has focused on evaluating contaminant removal of membrane treated FBWW in terms of assessing this technology for recycling purposes. However, little, if any, research has evaluated the microbiological regrowth potential of utilizing membrane treated FBWW blended with filtered water. Therefore, the motivation for this study was to evaluate zero-discharge management strategies for waste residual streams generated in conventional filtration drinking water plants. Specifically, the main objective of this research project was to provide new information regarding the impacts of blending ultrafiltration (UF) membrane treated FBWW with plant filtered water in terms of microbiological regrowth and disinfectant by-product formation within a modeled distribution system. As well, the potential for metal post-precipitation to occur in the distribution system with the introduction of higher concentrations of colloidal and dissolved metals present in the UF FBWW was investigated. To obtain these objectives, UF treated FBWW was blended with filtered water in both batch and continuous bench-scale experiments and evaluated in terms of biostability and chemical quality. This research project also focused in part on evaluating potential new indirect integrity methodologies which may complement existing guidelines and policies for membrane integrity testing. In particular, innovative integrity tests were examined to assess methodologies that may provide a more comprehensive representation of membrane system performance under challenge conditions. |
