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 andthe Mill Creek. The YVRWFF will provide an additional source of drinking water for the YVWD, whichcurrently relies on groundwater to meet the water demand. Microfiltration has been selected as thefiltration process because it provides a physical barrier that removes turbidity and bacteria withoutchemical pretreatment. MF can operate on waters with varying quality and produce water that meets theturbidity and Protozoa Cysts (Giardia and Cryptosporidium) requirements of the Surface WaterTreatment Rule and its subsequent iterations.The Yucaipa Valley Water District currently has approximately 40 wells producing potable water. Thewell water is low in TOC and YVWD uses free chlorine in the distribution system to maintain asecondary disinfection residual. The State Project Water contains moderate amounts (2 to 4 mg/L) ofTOC. TOC constituents, when combined with disinfectants such as free chlorine, form DisinfectionByproducts (DBP's). Disinfection By-Products include two groups of compounds known astrihalomethanes (THM's) and haloacetic Acids (HAA's). Microfiltration is not very effective at reducingTOC and other species that can contribute to DBP's. Therefore, YVWD has examined ways to reduce theformation of DBP's of the treated surface water. One alternative would be to use chloramine versus freechlorine in the distribution system to maintain a secondary disinfection residual. Chloramine is a weakerdisinfectant, and will not form DBP's at the same rate as free chlorine. In order to convert from freechlorine to chloramine, the District would have to construct and maintain an ammonia feed system at eachwell site. A second option is to utilize nanofiltration (NF) membranes to treat a portion of the MF filtratewater. NF membranes will remove the TOC from the water and allow the District to maintain a freechlorine residual in the distribution system.Today's NF membranes have excellent TOC removal rates, operate at fairly low pressure and do notremove a substantial amount of monovalent ions. Therefore, an NF system operating on MF treated waterhas the potential to economically produce water that is both low in hardness and low in DBP formationpotential. NF membranes will only be required to treat a portion of the MF filtrate, in order to produce awater 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 waterquality.A previous Bench Scale Nanofiltration study identified which commercially available NF membraneswere appropriate to treat State Project Water for the YVRWFF. The nanofiltration pilot study consistedof collecting data required for full-scale design using three previously identified membranes. Themembranes 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 properblend 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 operatingon YVWD MF filtrate;determine how the nanofiltration hydraulics and permeate water quality vary with a change inthe membrane flux rate; and,further characterize three nanofiltration membranes that were previously tested anddetermined to be appropriate for operation on Yucaipa's microfiltered water. Includes tables, figures.

Product Details

Edition:

Vol. - No.

Published:

03/01/2007

Number of Pages:

13

File Size:

1 file , 480 KB