TREATMENT EQUITY: CAN CONVENTIONAL TREATMENT MAKE THE GRADE WHEN MEMBRANE FILTRATION JOINS THE WATER SYSTEM?

摘要

The use of low pressure membranes in lieu of conventional treatment is oftentimes perceived to provide higher quality, state-of-the-art treatment than granular media filtration. In a public water system that employs conventional and membrane filtration processes, consumers commonly assume that the differing systems result in a disparity of drinking water quality whereby customers of the conventional treatment facility receive an inferior finished product. The objective of this study was twofold: 1) to compare the filtration processes and resultant water quality of a conventional treatment and membrane filtration plant to quantify any potential treatment inequity and 2) to employ the LT2ESWTR Microbial Toolbox to capitalize on current treatment performance and identify process improvement alternatives to provide a comparable degree of treatment at the conventional filtration facility without the application of advanced treatment processes, such as low pressure membranes or ultraviolet disinfection. For this analysis, Cryptosporidium removal was selected as the most appropriate means of comparing the performance of each facility because Cryptosporidium control is primarily achieved by physical exclusion and removal processes (i.e., filtration) rather than inactivation. Furthermore, Cryptosporidium is the smallest protozoa (3-5 μm) that are removed by both low pressure membranes and conventional treatment. Turbidity removal was assessed and used as a surrogate for Cryptosporidium removal in accordance with the design and operational criteria set forth in the Toolbox. The findings of this study demonstrate that opportunities frequently exist within the Toolbox options to augment the removal credit of a conventional treatment plant with nominal improvements or alterations to the current treatment processes and operational strategies. The establishment of treatment equity affirms the efficacy and reliability of conventional treatment with respect to membrane processes and will likely promote consumer confidence and satisfaction.