AWWA MTC64587

The City of Natchitoches, Louisiana uses the water from Sibley Lake for their potable water supply. The water from the Lake is high in Total Organic Carbon which is the source of precursors to disinfection byproducts. The City has had a history of regulatory noncompliance for haloacetic acids. The objective of this Integrated Membrane System (IMS) pilot study was to determine the most effective and efficient process for upgrade of the existing treatment plant using membrane technology. A bench scale procedure was conducted first to screen the membrane types and removal capabilities needed for the larger scale pilot plants. The large scale (20 GPM) pilot plants treated water from both raw lake water and clarified water using alum and lime. Hollow Fiber Ultrafiltration membranes followed by Spiral Wound Nanofiltration membranes were evaluated on both feed water sources. In addition, the use of Spiral Wound Nanofiltration membranes on the existing plant's finished water was evaluated. The study points out the need for pretreatment in order to protect and extend the life of membranes. Molecular weight cut-off is a critical consideration for selection of membranes from a standpoint of variations in make-up of different source waters. Variations in compound sizes can play a major role in selection of membrane types for the most effective treatment of a particular water source. All operational parameters used for system evaluation and design considerations are presented. The advantages of membrane technology versus conventional treatment methods include: reduced operational and maintenance requirements by way of highly automated process equipment; high efficient removal of unwanted compounds; and, added bonuses such as reduction in unregulated parameters: taste, color, and odor. Through the promulgation of new more stringent water quality standards, membrane treatment is becoming a feasible alternative for water treatment due to the nature of this process. The paper includes pilot plant data, process evaluation and feasibility. A detailed engineering evaluation and cost estimate with the intent toward facility design and construction is presented. Includes 4 references, tables, figures.