AWWA MTC57627

While most water treatment facilities are most concerned with the finished water quality produced, reverse osmosis (RO) facilities are also concerned with the quality of their concentrate. The City of Vero Beach, Florida has successfully operated their RO facility for the past 11 years with the originally installed membrane elements. In recent years, membrane performance has decreased and feed pressures have increased significantly. Chemically cleaning the elements provided an effective short-term solution to the performance problems; however, the membranes returned to their pre-cleaning condition in less than three months. Based upon the rapid decline in the membrane performance and age of the membranes, the City elected to replace the membrane elements. Three manufacturers of 8-1/2 inch thin film composite membranes were tested side by side on the identical feed water quality. The design of the membrane skid allows for a full-scale demonstration of seven 8-1/2 inch membrane elements to be loaded into full-length pressure vessels. The full-scale test evaluated both the physical operating parameters and water quality produced from the condition feedwater, permeate, and concentrate stream. This paper focuses on the concentrate water quality produced by the three membranes tested. The City of Vero Beach currently disposes of concentrate water from the RO facility into the Main Canal downstream of a tidal salinity barrier. The quality of the concentrate water is critical in maintaining this method of disposal for this facility. The current regulatory permit for the National Pollutant Discharge Elimination System (NPDES) for their concentrate is discussed and compared to the data collected during the demonstration pilot test. Membrane performance is evaluated based upon meeting the NPDES permit criteria. The membranes are compared based upon the results of acute and chronic toxicity testing that were performed on the concentrate of each individual element. The concentrate has been analyzed for a variety of parameters ranging from acute toxicity to ion concentrations. The final membrane selection is based not only on permeate quality but also concentrate quality. Comparisons between membrane performance focusing on permeate quality and concentrate quality is made. Includes 3 references, tables, figures.