Colored Water Treatment Facility Technology Replacement and Expansion

Mesa Consolidated Water District, 

Colored Water Treatment Facility Technology Replacement and Expansion

2012 Outstanding Groundwater Project Award - National Ground Water Association
2011 Top Water and Wastewater Project - Water and Wastes Digest
Project Highlights: 
  • 3,000 ppd ozone capacity
  • 10 percent ozone concentration from LOX
  • Injectors and diffusers for contacting
  • Pre-qualification of ozone equipment supplier
  • Preparation of design/build plans and specifications
Mesa Colored WTP
Carollo prepared design/build documents and provided final design and construction-phase services for the 4-mgd project.

The Mesa Consolidated Water District’s (Mesa) original Colored Water Treatment Facility (CWTF) used ozone and biologically active carbon (BAC) to treat highly colored groundwater. Due to increasing groundwater color and bromide levels, which result in the production of bromate under ozonation, the original 4,000-gpm treatment capacity processes at the CWTF were unable to meet the desired treatment goals. In addition, recent modifications required by the Orange County Water District (OCWD) that dictated Mesa to install supply well packers or sleeves resulted in the need to draw water from deeper aquifers where color levels are higher, which would further stress the ozone treatment system. This, and elevated color levels, resulted in higher ozone doses and energy costs, and also increased downstream bromate control costs by more frequent carbon media replacement and higher ammonium chloride doses.

In April 2010, Carollo began parallel pilot testing and preliminary design of a new 6,000-gpm, state-of-the-art nanofiltration (NF) treatment plant for the treatment of highly colored groundwater to replace the existing treatment system under the CWTF Technology Replacement and Expansion project. The preliminary design phase was quickly followed by a compressed final design schedule so that the project could be out to bid in November 2010. The new NF system will use highly charged, sulfonated polyethersulfone (SPES) membranes manufactured by Hydranautics and marketed under the name HYDRACoRE. The plant will achieve recovery levels up to 98 percent when the primary and secondary NF systems will be used. The primary NF system will be a two-stage system with concentrate recycle that will allow for operation up to 95 percent recovery at a design flux rate of 16 gfd based on the recommendation from the manufacturer and also from successful pilot test results. The secondary NF system will use a single-stage array with concentrate recycle that allows for recovery levels up to 75 percent. Overall, the plant was designed to be expanded to 12,000 gpm capacity in the future.

Results of the pilot test indicated no operational issues at a system recovery of 95 percent and a flux rate of 16 gfd. Color removal was exceptional, with a reduction in color from 260 color units to 2 - 3 color units, and no indication of fouling or scaling. Color removal efficiency is not influenced by flux rate or recovery. Feed pressures were stable and preliminary data suggest that pressures are almost exclusively influenced by flux rate and not recovery, most likely because the SPES membranes do not reject salts well. Components of this project include hydrogen sulfide and methane removal using a CO2 system for pH suppression prior to a degasifier and scrubber system, new chemical feed systems, new well piping and well blowdown facilities, a new NF building and product water pump station, and extensive landscaping. The plant is currently under construction with start-up expected in April 2012.

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