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The Future is Now: Desalination and Concentrate Minimization are Changing the Face of Water Supply and Management

Authors: Abhishek Manikonda, PhD; Tom Seacord, PE; Brandon Yallaly, PE

Currents: Volume 4, 2022

Currents CRG 25 Years

The Carollo Research Group (CRG) has been instrumental in securing Carollo’s position as the national leader in this growing and challenging field…bringing ideas from scientific concepts to practical solutions. This is showcased by the projects completed by Carollo over the past 25 years as shown on the timeline:

Rapid urban growth, climate change, as well as supply challenges due to limited amounts of freshwater and salinity buildup have been key drivers for communities and industries across the US in adopting desalination as a means of diversifying their water supply. Some examples include: (1) Use of more saline waters once considered expensive to treat (e.g., seawater), (2) Advanced treatment to recycle both fabrication waste from
semiconductor manufacturing and cooling tower blowdown water from data centers, and (3) Potable reuse. Although, desalination has recently become more efficient and cost-competitive, managing waste products like reverse osmosis (RO) concentrate remains a challenge. Strict environmental regulation, a need for higher water recovery, and/or extraction of valuable minerals are leading to global growth of RO concentrate volume minimization and zero liquid discharge (ZLD) technologies. During the last decade, there has been a significant development of concentrate minimization and ZLD systems, particularly in the US, with the market for ZLD construction projected to reach $8.1 billion by 2023.

CRG’s Pellet Softening Pilot

Characteristically, RO concentrate is supersaturated with salt. One way to maximize the water recovery from a desalination process and reduce the volume of concentrate that requires disposal is to remove these salts from RO concentrate by precipitative softening. Although pellet-softening treatment processes have been used throughout Europe for decades, it was not practiced in the US until 2008. That year, recognizing the potential of pellet-softening with the added benefit of making high-purity calcium carbonate pellets, CRG pilot-tested pellet softening at the Arlington Desalter in Riverside County, CA. The pilot demonstrated that pellet softening could be used to maximize RO recovery and reduce the maintenance required in the Inland Empire Brine Pipeline (IEBL), where these salts would precipitate and plug the pipeline. CRG’s successful testing at the Arlington Desalter led to the world’s first full-scale concentrate treatment plant at the Chino II Desalter using this technology.

Chino Concentrate Reduction Facility

The Chino Concentrate Reduction Facility (CRF) best demonstrates how the CRG laid the groundwork to make Carollo the industry leader in concentrate management and treatment. The CRF uses pelletized softening, solids contact softening, media filtration, and RO to remove hardness and silica to allow for additional water recovery and a reduction in concentrate disposal. The heart of the CRF design is the high-rate pellet softening and solids contact clarifier system to remove the limiting foulants (specifically calcium and silica) from the primary RO concentrate. Seeded calcium carbonate precipitation occurs in the fluidized pellet reactors, where hard and durable pellets are generated. The produced pellets are a value-added product that can be used in a variety of industrial applications, thus converting a waste stream of the Chino process into a usable commodity.

Due to the turbid nature of the pellet reactor effluent solids, contact clarification is required to remove magnesium solids that are formed in the pellet reactors and carry over due to their lower density. After the fouling compounds are reduced in the pellet reactor and the clarifier, the softened primary RO concentrate is polished with dual media filters. The filtered effluent is sent as feed to a secondary RO (SRO) system where the concentrate volume is further reduced. SRO treated water is blended with the primary RO permeate from the Chino II Desalter, and SRO concentrate is disposed to the IEBL. Using this approach, total water recovery from the RO system at the Chino II Desalter is increased from 83.5 to 95 percent, substantially reducing the volume of concentrate disposed, while increasing permeate production.

Low Energy Record for Seawater Desalination

CRG’s work with the Affordable Desalination Collaboration (ADC) demonstrated that, with a combination of proven technologies, seawater RO (SWRO) can be used to produce water at an affordable cost compared to other supply alternatives. In March 2006, ADC’s demonstration-scale SWRO plant completed over 6 months of testing at the US Navy’s Seawater Desalination Test Facility in Port Hueneme, CA. The results of this study drew attention from all over the world and helped establish Carollo as a US leader and innovator in seawater desalination. The concepts demonstrated through the ADC’s testing were applied in our recent design of the Florida Keys Aqueduct Authority’s (FKAA) Stock Island Seawater RO Treatment Plant.

Read more of this issue of Currents: Currents: Volume 4, 2022