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Managing Brackish RO Concentrates Case Study: Precipitative Softening Pilot Study in South Florida

Managing Brackish RO Concentrates Case Study: Precipitative Softening Pilot Study in South Florida

Sethi, S., Ph.D., P.E., MacNevin, D., Ph.D., Munce, L. P.E., Akpoji, Ph.D., P.E., Elsner, M., P.E., An, J., Ph.D., P.E.
Published In: 
AMTA Solutions,  
September 2010

Carollo evaluated concentrate minimization technologies for their suitability for increasing RO recovery in South Florida. The first part of the study evaluated 14 of the 31 RO WTPs in the South Florida Water Management District, including North Miami Beach’s WTP, by:

  • Source water modeling and identification of recovery-limiting salts by site.
  • Characterization of existing treatment by site.
  • Review of four concentrate minimization technologies.
  • Examination of technical, permitting, and implementation factors for each site/technology combination.
  • Estimation of capital and O&M costs for each site/technology combination.

Concentrate minimization technologies evaluated included:

  • Dual RO system with intermediate chemical precipitation.
  • Brine concentrator and evaporation ponds.
  • Brine concentrator and crystallizer.
  • Salt recovery and extraction.

A dual RO system with intermediate chemical softening and media filtration was pilot tested at the City of North Miami Beach’s Norwood WTP in August 2009 and was completed in November 2009. The pilot plant demonstrated stable performance, effectively increasing the overall system recovery from 75 to 88 percent under conservative operating conditions for the secondary RO. The secondary RO process demonstrated excellent removal of dissolved solids, organics, hardness, and pathogens, with removals for all these parameters ranging from about 90 to 99 percent.

This study was an important first step in understanding and reclaiming brackish RO concentrates throughout South Florida. North Miami Beach pilot tested a concentrate treatment system that cut concentrate waste in half, increasing recovery from 75 percent to 88 percent. At full-scale, this would make an additional 1 mgd of water available to the City. For the entire SFWMD, an increase in recovery from the current average, 75 percent, to a higher 95 percent will make 140 mgd of additional water available.

Sethi, S., Ph.D., P.E., MacNevin, D., Ph.D., Munce, L. P.E., Akpoji, Ph.D., P.E., Elsner, M., P.E., An, J., Ph.D., P.E. “Managing Brackish RO Concentrates Case Study: Precipitative Softening Pilot Study in South Florida.” in AMTA Solutions, American Membrane Technology Association. Fall 2010. pp. 1, 5-8.