AWWA MTC61140

Greater Cincinnati Water Works evaluated membrane softening technologies (i.e., nanofiltration, reverse osmosis, and electrodialysis reversal) and conventional softening technologies (i.e., lime/soda softening and ion exchange) for use at the City of Mason Water Treatment Plant. The basis for evaluation included maximizing system recovery, minimizing residuals production to reduce or eliminate sewer use fees, making use of the existing plant as a pretreatment, or supplement, to the recommended softening alternative, and optimization of finished water chemistry to minimize corrosion in the distribution system. Nanofiltration, electrodialysis reversal, and lime/soda softening are able to meet the water quality goals established by Greater Cincinnati Water Works. Ion exchange is capable of meeting the finished water hardness goals established, but corrosion parameters and increases in finished water sodium concentrations are a concern. Residuals handling and disposal significantly impacted the operations costs. In this instance, it is necessary to dispose of concentrate from the membrane softening technologies, as well as the spent regenerant from the ion exchange process, to the sanitary sewer resulting in significant sewer use fees. Lime softening sludge can be land applied at much lower costs. Finally, groundwater is provided by a limited yield aquifer and the limited recovery of the membrane alternatives (because of the nature of the foulants present) represents a significant hurdle to implementation of these technologies for the City of Mason supply. Includes tables, figures.