Handling Industrial Flows and High TDS in Water Reclamation Facilities

Handling Industrial Flows and High TDS in Water Reclamation Facilities

The demand for recycled water continues to grow as many businesses, municipalities, and utilities across the country search for ways to make their operations more resistant to drought and reduce their dependence on outside water sources. To keep up with demand, our industry is starting to innovate ways we can reuse water sources with higher levels of complexity. For example, the high total dissolved solids (TDS) concentrations and other constituents found in industrial wastewater that are not normally found in sanitary wastewater can limit the potential uses of recycled water, but facilities are finding ways to overcome this problem. 
 
This is exactly what we helped the City of Victorville, CA do. After implementing a major reuse project, the city realized that one of the industrial wastewater sources that was feeding into their new Integrated Wastewater Treatment Plant (IWWTP) was elevating the TDS in the effluent to the point where the plant’s final effluent was failing to meet the local power plant’s water quality criteria for water reuse in their cooling towers. We worked with the plant to find a short- and long-term solution that would keep the city in compliance with their discharge permit and provide Title 22 effluent that met the water quality requirements of cooling towers.

While dealing with high TDS concertation requires a plant-specific approach, I wanted to share with you the decisions we made when implementing Victorville’s short term and long-term treatment solutions to highlight some of the trade-offs among available treatment technologies.   

Short Term Solution: Ion Exchange 

The first solution needed to be implemented in six weeks or less.  With a time-frame this tight, our main concerns were whether the equipment would readily available, how the technology could integrate into the IWWTP with minimal impact to existing operations, and how the high TDS waste stream generated from each technology would be managed.

During initial screening of alternatives, electrodeionization (EDI) was eliminated from the evaluation due to the long lead time for vendors to fabricate and deliver the equipment, leaving reverse osmosis (RO) and ion exchange as the two technologies evaluated in detail. The RO option met all key criteria except that disposing of the concentrated brine waste generated (approximately 151 cubic meters or 40,000 gallons per day) was not feasible from a cost standpoint when considering a typical transportation and disposal cost of $0.15 to $0.20 per gallon. 

The ion exchange option could be implemented quickly and the mobile trailers containing ion exchange media could be sourced from a vendor with a local service center and media regeneration facility. The vendor could manage all the resins and regeneration and there would be no brine to dispose of. The mechanical and electrical modifications required to integrate the mobile ion exchange trailers into the existing WWTF were cost effective with minimal impact on operations. For these reasons, ion exchange was appropriate short-term solution. This solution was implemented in the summer of 2017 and has been successful in reducing TDS to the required levels since startup.

Long-Term Solution: Membrane Technologies 

Ion exchange is not considered a viable long-term solution due to the high operating costs, which required us to develop an additional long-term solution. Any long-term solution needed lower operating and life cycle costs; lower operational complexity, but higher operational flexibility and resiliency; and a manageable amount of reject concentration volume. To meet these needs, we explored membrane technology alternatives and established a treatment scheme consisting of four unit processes to meet the required TDS limit: primary TDS removal, concentrate softening, solids processing, and brine concentration, with the concentration brine stream sent to evaporation ponds that would be constructed local to the IWWTP. Below you will find the treatment schemes we explored in this project.

Scheme Letter  Primary TDS Removal  Softening Process  Brine Concentrator
 A  RO  Lime Softening with Microfiltration (MF)  Secondary RO
 Closed Circuit Desalination (CCD) Lime Softening with MF   Secondary CCD
 C  RO  Lime Softening with Clarification  Secondary RO
 D  CCD  Lime Softening with Clarification  Secondary CCD
 E  RO  Caustic Softening with MF  Forward Osmosis (FO)
 F  EDI or Radial Deionization  N/A  Mechanical Evaporators
                                                       

In the end, our analysis concluded that implementing TDS removal via RO or CCD with lime softening and MF (Scheme A or Scheme B) would provide reliability and performance at lower life-cycle costs than other comparable options. The MF membranes used in both treatment schemes have a long lifespan and the post-softening MF protects secondary RO from passed-through suspended solids. Both schemes send small volume of concentrated brine to evaporation ponds.

Finding creative ways to conserve California’s water supply is daunting task, but these challenges are giving us an unparalleled opportunity to dive into the possibilities surrounding water reuse. If you would like to learn more about this project, please read the white paper I wrote for WEF or reach out to me at : bsutter@woodardcurran.com

Author

Senior Project Manager
Industrial Wastewater

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