Perchlorate is a concern in drinking water because of its high solubility and mobility, its effects on thyroid hormone production, and treatment cost. The primary objectives of the project were to demonstrate: (1) a reliable, cost-effective treatment technology for removing perchlorate from drinking water, (2) removal of both perchlorate and trichloroethene (TCE) simultaneously, and (3) simple system operation and maintenance (O&M) with minimal monitoring.
This project demonstrated the application of granular activated carbon (GAC) tailored (TGAC) for the removal of perchlorate in drinking water. The tailoring process adsorbs surfactants with quaternary ammonium groups to GAC, which dramatically increases the perchlorate removal capacity of the GAC, while still allowing the GAC to remove volatile organic compounds (VOCs).
The demonstration site was an operating drinking water treatment plant in Fontana, CA, a city located in the Inland Empire region of southern California. The Inland Empire’s perchlorate plume is at least 6 miles long and impacts water supplies in four towns. Two field test installations were implemented; the first consisted of three vessels in series treating 38 gallons per minute (GPM) (0.14 m3/minute), and the second consisted of six smaller-scale treatment trains treating 1.5 GPM (0.0057 m3/minute).
The 38 GPM field-scale TGAC demonstration system operated nearly continuously for 318 days and treated over 16.2 million gallons of perchlorate-impacted groundwater. Six parallel pilotscale test beds were operated for approximately 6 months each, challenging the technology with varied influent conditions. These challenges included various added ions, pre-disinfection, and TCE as a co-contaminant. Field data were supplemented with 17 rapid small-scale column tests (RSSCTs) performed in the Pennsylvania State University (PSU) laboratory with Fontana groundwater. TGAC testing with Fontana groundwater showed a shorter bed life to initial perchlorate breakthrough than proportional-diffusivity-based RSSCTs predicted. Laboratory studies indicated that when using RSSCTs to predict perchlorate removal, the best fit to field-scale data relative to initial breakthrough can be obtained using a mathematical approach intermediate between proportional and constant diffusivity.
For these trials, an anthracite-based GAC was preloaded with cetylpyridinium chloride (CPC). Studies conducted after the completion of the Fontana field-scale work show that the anthracite-based GAC is inferior in performance to bituminous-based GAC because of differences in porosity structure. The CPC tailoring agent was selected for this field test based on previous data and for ease of permitting. However, other tailoring agents such as Arquad 2C-75 may provide better perchlorate selectivity over competing anions like nitrate. Based on results available to date, TGAC technology may be best suited for use on aerobic waters with low nitrate concentrations and with VOCs as co-contaminants. Additional research to optimize tailoring agents to particular groundwater chemistries may be warranted.
Regulatory requirements for TGAC technology may include a discharge permit (and possibly treatment) for disposal of backwash water and other process water, and permitting as required in the state of operation prior to use as a drinking water technology. Department of Transportation (DOT) and Resource Conservation and Recovery Act (RCRA) regulations apply to disposal of spent TGAC and potentially to spent particulate filters if VOCs are treated. From the end user’s perspective, perceived or potential limitations not found with other treatment technologies include (1) a lower perchlorate capacity than most IX resins, requiring more frequent changeouts and (2) a lower hydraulic loading rate or a longer contact time than IX, requiring more or larger vessels to treat a given flow rate of water, which increases capital cost and treatment system footprint. If applied to a mixed-contaminant water (e.g., perchlorate and VOCs), the contaminants may reach breakthrough at different times, which would require an early changeout, and thus a reduced capture efficiency for VOCs or perchlorate as compared to two separate media. Finally, TGAC may leach small concentrations of the tailoring agent into treated water, possibly requiring the addition of a “guard” bed to capture residual tailoring agent.