AWWA MTC64589

The Yucaipa Valley Water District (YVWD) is currently constructing a 12 mgd Microfiltration (MF) - Nanofiltration (NF) Treatment Facility. This Yucaipa Valley Regional Water Filtration Facility (YVRWFF) will treat State Project Water but can be augmented by water from the Santa Ana River and the Mill Creek. The YVRWFF will provide an additional source of drinking water for the YVWD, which currently relies on groundwater to meet the water demand. Microfiltration has been selected as the filtration process because it provides a physical barrier that removes turbidity and bacteria without chemical pretreatment. MF can operate on waters with varying quality and produce water that meets the turbidity and Protozoa Cysts (Giardia and Cryptosporidium) requirements of the Surface Water Treatment Rule and its subsequent iterations. The Yucaipa Valley Water District currently has approximately 40 wells producing potable water. The well water is low in TOC and YVWD uses free chlorine in the distribution system to maintain a secondary disinfection residual. The State Project Water contains moderate amounts (2 to 4 mg/L) of TOC. TOC constituents, when combined with disinfectants such as free chlorine, form Disinfection Byproducts (DBP's). Disinfection By-Products include two groups of compounds known as trihalomethanes (THM's) and haloacetic Acids (HAA's). Microfiltration is not very effective at reducing TOC and other species that can contribute to DBP's. Therefore, YVWD has examined ways to reduce the formation of DBP's of the treated surface water. One alternative would be to use chloramine versus free chlorine in the distribution system to maintain a secondary disinfection residual. Chloramine is a weaker disinfectant, and will not form DBP's at the same rate as free chlorine. In order to convert from free chlorine to chloramine, the District would have to construct and maintain an ammonia feed system at each well site. A second option is to utilize nanofiltration (NF) membranes to treat a portion of the MF filtrate water. NF membranes will remove the TOC from the water and allow the District to maintain a free chlorine residual in the distribution system. Today's NF membranes have excellent TOC removal rates, operate at fairly low pressure and do not remove a substantial amount of monovalent ions. Therefore, an NF system operating on MF treated water has the potential to economically produce water that is both low in hardness and low in DBP formation potential. NF membranes will only be required to treat a portion of the MF filtrate, in order to produce a water that is of high quality and meets the regulatory requirements for DBP's. In addition, in the future, an NF system could be retrofitted with revere osmosis membranes to further improve drinking water quality. A previous Bench Scale Nanofiltration study identified which commercially available NF membranes were appropriate to treat State Project Water for the YVRWFF. The nanofiltration pilot study consisted of collecting data required for full-scale design using three previously identified membranes. The membranes selected for this study include: Filmtec NF-270; Koch - Fluid Systems SR2; and, TriSep XN45. The objectives of the Nanofiltration Pilot Testing were to: build a database of water quality (THM) data that will enable identification of the proper blend ratio or ratio of NF permeate to MF Filtrate that will meet the Stage 2 Disinfection Byproducts Rule; develop engineering data necessary for full-scale design of a nanofiltration system operating on YVWD MF filtrate; determine how the nanofiltration hydraulics and permeate water quality vary with a change in the membrane flux rate; and, further characterize three nanofiltration membranes that were previously tested and determined to be appropriate for operation on Yucaipa's microfiltered water. Includes tables, figures.