Author: Christopher E. Hortert
Accelerated Remediation Catalysis (ARC) – An Emerging Water Treatment Technology for the Treatment of a Wide Range of Dissolved Phase Organic and Inorganic Contaminants
The Accelerated Remediation Catalysis (ARC) system is a process that can be applied to reduction or oxidation. For reduction, hydrogen gas and an inexpensive, proprietary catalyst are used to perform a chemical reduction of appropriate contaminants. The application of shear forces that can be achieved by using certain pumps is also a feature that dramatically accelerates reaction times.
On the reduction side, there is data supporting the degradation of 1,4-dioxane (1,4-D), perfluorocarbons (PFCs), chlorinated hydrocarbons, and oxyanions (nitrate and perchlorate). With respect to metals and metalloids such as selenium, these species are precipitated and collected for disposal. ARC is also applicable to oxidative processes for appropriate organics like petroleum hydrocarbons, as well as metals/metalloids that precipitate under high redox conditions. In this application, the oxygen is provided by dilute hydrogen peroxide or peracetic acid with a different catalyst.
To help reduce start-up costs, the ex-situ process uses common tankage, pumps, valves, and process controls that can be obtained from standard vendors. If the process handles low levels of contaminants, it can be constructed of common thermoplastics such as polyvinyl chloride (PVC), polyethylene, and fiberglass.
ARC can operate in either batch or continuous mode. In batch mode, the reaction tank is filled at start-up and the total reaction time is allowed to reach the predetermined level to assure destruction of the constituents of concern (COCs). After this point has been achieved, the process switches to continuous mode, and the reaction tank functions as a single-stage plug flow reactor. The process can be made to be continuous at start-up by simply filling the reactor tank with clean water. The overall retention time for completion of most reactions has been on the order of 10 to 15 minutes. Using reduction, hydrogen used in the catalyst vessel is generated electrochemically at the site, reducing the need to handle compressed gas. Depending on the COC, the reaction will either cause manageable gas evolution, or precipitate out of the water and be recovered by a variety of methods. The insoluble catalyst can be recovered by filtration and recycled back to the reactor vessel.
Case studies where ARC has been used for chemical reduction include:
- The conversion of 1,4-dioxane to ethanol. Water with 100 μg/l of 1,4-dioxane was reduced to <1 μg/l.
- The complete destruction of perfluorocarbons to non-detectable concentrations with a fluorine residue of low concentration, as the initial concentrations of perfluorocarbons are generally low.
- Chlorinated ethenes are easily reduced to ethene and ethane.
- Trihalomethanes have been reduced from a typical 80 μg/l level to <10 μg/l in 10-15 minutes.
- Perchlorate levels as high as 100 mg/l are reduced to chloride.
- Nitrate is reduced to nitrogen gas.
- Selenium in the form of selenate can be reduced to selenite and removed as a precipitate. Selenate was reduced from 200 mg/l to <1 mg/l.
- Chlorobenzene at ppm levels is reduced to benzene that is then collected on the low-cost catalyst.
The ARC system can be designed for a wide range of process flow rates. Design of the system is only limited by the required retention time for the reaction. In essence, the system was brought into focus because of the emerging contaminants issue, and it is applied to pump-and-treat systems. This is important because the nature of 1,4-dioxane and PFCs makes in-situ treatment challenging. It is expected that there will be both an increase in the use of pump-and-treat systems and a need for more efficient water treatment technologies, especially since conventional methods of treatment (such as those that use carbon) are limited.
Additionally, because of the low concentrations of reactants in the process, there is typically no detectable heat gain in the reaction vessel. Therefore, cooling of the process is generally not required prior to releasing the treated effluent. Then there are other applications in traditional wastewater treatment, such as removal of selenium from scrub water at coal-fired power plants. The ARC system’s inherent simplicity allows it to be easily scaled so that dealing with the large flow rates encountered in industrial settings is feasible. While the endpoint for ARC treated water is generally to be discharged, a supplementary feature called Advanced Regenerative Process (ARP) can be added as a further polishing step so that beneficial reuse, including human consumption, is an option.
ARC targets those applications where more complicated and expensive systems, such as conventional Advanced Oxidation Processes (AOP), are being used. The chemical usage, energy, and safety features of AOP systems, combined with their operational footprint, suggest they will eventually be replaced by better remedial options like ARC. There are other developing technologies that have similar objectives to displace AOP systems, such as resin-based operations, but ARC presents distinct advantages in cost, efficacy, physical layout, and scalability.
For additional information, please contact Chris Hortert at (800) 365-2324 (firstname.lastname@example.org); Steve Koenigsberg at (949) 262-3265 (email@example.com); or Thom Zugates at (602) 644-2163 (firstname.lastname@example.org).