Modified Activated Carbon: An Israeli Approach to Industrial Water Recycling

Metal Surfaces Incorporated (MSI) is one of the largest precision plating shops in North America, specializing in the aviation, aerospace, electronic, interconnect and automotive fields. MSI’s operations include a wide range of water intensive reel-to-reel plating and other metal finishing processes, including cyanide, silver, gold, cadmium, chromium, nickel, electroless nickel, zinc, tin and more.

In the past, MSI relied heavily on conventional wastewater treatment for regulatory compliance and environmental safety. Problematic wastewater streams such as hexavalent chromium and cyanide-complexed metals were separated and treated using standard industry chemicals like sodium bisulfite and sodium hypochlorite. The resulting trivalent chromium- and cyanide-free wastewater was then combined with general wastewater from the plant before undergoing traditional pH adjustment, settling, neutralization and discharge to the local sewer.

While MSI’s system complied with wastewater discharge permits, it was inefficient in chemical consumption and generated high-salinity wastewater that was impossible to reuse. With California entering its fifth year of drought, MSI was actively looking for new technologies to recycle water and improve the operational efficiency of its wastewater treatment plant (WWTP). ToxSorb’s experience with zero-liquid-discharge solutions, combined with its unique adsorption and reduction filtration, was a perfect fit.

ToxSorb worked with Metal Surfaces Incorporated to design a filtration system that incorporated ToxSorb’s proprietary Modified Activated Carbon (MAC) media, capable of handling a mixed wastewater stream.

Performance Meets Efficiency

In late 2015, ToxSorb began working with MSI to design a filtration system capable of handling a mixed wastewater stream, including all hexavalent chromium and cyanide-complexed rinses from the factory. This included a steady flow of wastewater ranging from 15,000 to 20,000 gallons per day (GPD), including periodic spikes in concentration from weekly bleeding of concentrated chromium and cyanide drag-out solutions.

The proposed treatment system incorporated ToxSorb’s proprietary Modified Activated Carbon (MAC) media, capable of reducing hexavalent chromium and oxidizing cyanide inside the filter without the use of chemicals. The effluent from the system would need to meet the highest quality in the metal finishing industry, necessary for military plating applications (<50 μS/cm). The final treated product would need to be free of chromium and cyanide so that it could be reused throughout the factory in a zero-liquid-discharge regime.

The only waste stream produced from the system would come from the periodic regeneration of the filters, estimated at 1,500-2,500 gallons of non-toxic regeneration solution each week, <3 percent of the treated flow. Since this solution contained high concentrations of valuable metals, ToxSorb and MSI decided to incorporate an on-site precipitation and settling process to capture these residuals separately from the rest of the WWTP. Once separated, the resulting supernatant would be blended back into MSI’s general wastewater stream, pre-neutralization.

ToxSorb’s treatment system incorporated two basic elements into the process:

1. Central Treatment System: A centralized treatment system incorporating a series of five media columns with 140 ft3 of specialized MAC media designed for chromium reduction, cyanide oxidation and subsequent deionization <50 μS/cm.
2. Polish Treatment System: A single media column designed to remove any remaining hexavalent chromium or cyanide in the regeneration solution before discharging to MSI’s general wastewater stream.

Most importantly, the system was designed for simplicity in operation, meaning all of the processes can be remotely monitored and controlled from Israel. ToxSorb worked hand-in-hand with MSI’s operational personnel throughout the running-in process, ensuring a smooth transition to steady-state operations.

Benefits of the system include:

• Water Savings: 20,000 GPD saved in fresh water purchase and wastewater discharge.
• Chemical Reduction: Elimination of NaHSO3 and NaClO and a reduction in NaOH downstream in the general WWTP.
• Sludge Reduction: Less sludge production through reduction in chemicals and partial elimination of city water.
• Improved Water Quality: Higher quality rinsing water (<50 μS/cm).
• Water Independence: Lower impact from supply and demand of water.

The Future Is Reuse

Today, the chromium and cyanide reuse system at MSI is fully operational, far exceeding its design target for water quality. ToxSorb and MSI are currently evaluating other streams for treatment and reuse, including their nickel and general acidic alkaline rinses.

ToxSorb is an Israeli water technology company specializing in the design, construction and operation of customized filtration systems using its proprietary Modified Activated Carbon (MAC) media, engineered to remove specific contaminants from water. To learn more about ToxSorb, visit www.toxsorb.net.