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For several years, the Guadalupe-Blanco River Authority (GBRA) has actively pursuedthe implementation of a surface water supply system to meet the increasing demands of aTexas area dependent on limited groundwater. To achieve water quality goals andfundamental project objectives, the GBRA is building a 10 MGD microfiltration (MF)plant with a unique application of in-line coagulation pretreatment. Coagulant doses ashigh as 60 ppm may be added to remove disinfection byproduct (DBP) precursors priorto membrane filtration without pre-settling to comply with the requirements of the Stage1 D/DBP Rule.Like many new or expanded water treatment plants (WTPs), the water quality andtreatment objectives for the GBRA are primarily driven by the need to supply safe andaesthetically pleasing drinking water. However, the development of this WTP had someunusual project drivers. Because water from the new treatment plant will largely bewholesaled to other agencies, the project demanded the utmost sensitivity to taste andodor issues as well as seamless blending with existing chlorinated water supplies.Ultimately, the project required free chlorine to be used as the secondary disinfectant in a40-mile transmission line. Subsequent bench tests indicated that removal of DBPprecursors is required either upstream or downstream of the membranes to meet existingand future DBP regulations. Membrane filtration with in-line coagulation was theselected treatment process to meet water quality goals.Bench and preliminary pilot testing over the past two years indicates that a ferric sulfatedose of approximately 60 ppm (equating to an average total organic carbon (TOC)removal of 30 to 35 percent) is required to remove enough organic material from the rawwater to control the formation of DBPs in the transmission and customer distributionsystems. The GBRA evaluated pretreatment alternatives including conventionalflocculation/sedimentation, in-pipe flocculation, and in-line coagulation for treatmentfeasibility and cost-effectiveness. Seven membrane manufacturers were initially solicitedfor piloting, but due to in-line coagulation requirements, only two were responsive.During initial pilot testing, both membrane manufacturers (Pall and Zenon) were able tosustain operation with coagulated feed while meeting minimum cleaning intervalrequirements. However, interesting operational differences were observed between thetwo types of membrane systems; for example, pre-settling affects fluxes differently foreach system. Based on bench and pilot information, the GBRA proceeded with in-linecoagulation followed by a short flocculation period and direct application to the MF/UFmembrane filters. While pilot results indicate that the systems could potentially operateIn-Line Coagulation with Microfiltrationat higher fluxes with optimized mixing and flocculation, a conservative flux wasspecified in the procurement documents due to the membrane industry's lack of full-scaleoperating experience with the treatment strategy. Includes tables, figures.

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Edition: Vol. - No. Published: 03/05/2003 Number of Pages: 15File Size: 1 file , 2.6 MB