AWWA ACE54388

The City of Abilene, Texas is expanding its water supply and treatment facilities to combat a dwindling fresh water supply. Abilene will be treating a brackish surface water supply (Lake O.H. Ivie, TDS ~ 1,200 mg/L, high barium sulfate scaling potential) which will require the use of an advanced treatment process to achieve acceptable finished water TDS levels. Based on the raw water quality, a dual membrane system (microfiltration or ultrafiltration followed by reverse osmosis) has been selected to accomplish the treatment goals. The Phase I capacity of the proposed water treatment facility is 8-mgd with future expansions possible to 24-mgd. This paper will discuss the development of the overall project, which includes the following: source water quality and removal requirements; treatment process selection; pretreatment requirements (iron, manganese, color, DOC); MF/UF pilot testing and selection criteria; reverse osmosis (RO) recovery optimization (including membrane performance projections and pilot testing with antiscalants/dispersants); RO bypass ratio/blending analysis; Post-treatment (disinfection, corrosion control); and, treatment challenges including biofilm control, iron/manganese/color removal, salinity reduction, turbidity control, and pathogen removal and/or inactivation from the surface water supply sources. Furthermore, the membrane-treated product water will be blended and must be compatible with water from existing supply and treatment facilities. Planned treatment includes upstream chloramine addition (biofilm control in the 50 mile raw water transmission pipeline and raw water storage tanks), potassium permanganate or chlorine dioxide addition (iron and manganese oxidation), ferric sulfate coagulant addition (color and DOC reduction), and dual-membrane processes (MF or UF for suspended solids and pathogen removal followed by reverse osmosis (RO) for dissolved solids reduction). Final treatment steps include disinfection (chloramines) and corrosion control (sodium hydroxide and corrosion inhibitor). A significant portion of the MF/UF product water will bypass the RO treatment and blend with RO permeate which serves to reduce the capacity of the RO part of the plant and lower overall costs. The technical information presented in this paper as well as description of the decision-making procedures used will be very useful for other utilities considering the use of alternative water sources and those considering membrane technology in Texas and elsewhere. Includes tables, figures.