Harish Arora and Saqib Karori

OBJECTIVES:

The primary goal of this project was to evaluate two adsorption media--ArsenX^np and Adsorbsia GTO--under full-scale conditions at very small drinking water systems. Specific objectives of the project were to (1) develop operational data for the media, (2) evaluate various hazardous properties of exhausted media, (3) compare performance of regenerated media with that of virgin media, and (4) determine the impact of water quality parameters that may hinder the treatment processes.

BACKGROUND:

The major issues associated with very small water supply systems adopting technologies for compliance with the Arsenic Rule include lack of funds and other resources. There is a need to implement technologies that are cost effective, simpler to operate, and produce minimum amount of residuals. Non-treatment options can be economical but are generally not feasible or practical. The project evaluated two new adsorption media (one regenerable) for their application in very small water systems.

HIGHLIGHTS:

Adsorption technology may be the cost effective way to achieve compliance with the Arsenic Rule for very small water systems and was evaluated for this project. Highlights of findings from this project are included below:

1. Properly designed adsorption treatment systems were operated successfully at two very small water systems.

2. Adsorption media performance is site specific and is impacted by source water characteristics.

3. An economic analysis is recommended before enhancing treatment (e.g., pH adjustment versus increased media performance) or adopting a different treatment strategy.

APPROACH:

The adsorption media were tested at full-scale at two very small public water systems. The Triple G Dairy Water System utilized Adsorbsia GTO in a prefabricated, fiber-reinforced plastic vessel 30-inch in diameter and 72-inches in height capable of treating 30 gallons per minute (gpm). The Camp Verde Water System utilized AsX and consisted of steel adsorption vessel 24-inches in diameter and 72-inches in height, capable of treating 20 gpm. To evaluate adsorption media performance, collected samples were analyzed for field and laboratory water quality parameters using standard methods. To evaluate hazardous properties, the spent media were analyzed using the Toxicity Characteristics Leaching Procedure. Spent AsX media was regenerated at an off-site facility, and its treatment performance was compared with the virgin media.

RESULTS/FINDINGS:

The Triple G arsenic treatment facility with Adsorbsia GTO treated 99,430 gallons of water at variable flowrate. The influent arsenic ranged from 13 to 18 ppb, and the effluent arsenic level reached 11 ppb in 125 days of operation, or 1,325 bed volumes (BVs) treated. The observed Adsorbsia GTO performance was much lower than that observed in other studies, and was attributed to high source water pH (average of 9.2) and competition from other water constituents such as vanadium. The Camp Verde ATF treated 1.6 million gallons of water resulting in 31,800 BVs at effluent arsenic level of 12 ppb. The average arsenic concentration in the source water at Camp Verde was 23 ppb. Spent AsX media was regenerated at an off site facility, and installed in the contactor to compare its treatment effectiveness with virgin AsX. At an effluent arsenic level of 10 ppb, regenerated media treated 26 percent fewer BVs (19,900) when compared to virgin media (26,800 BVs). Both ATFs could be operated without any major problems. Both media were analyzed to be non-hazardous and could be disposed of in a sanitary landfill.

IMPACT:

The project developed performance and operations information for control of arsenic by two new adsorption media at two very small water systems. A regenerable adsorption media was evaluated at one water system but a substantial loss of capacity was observed after one regeneration. Both ATFs operated as designed with minimum operator attention. High pH impacted adsorption performance at one water system, but pH adjustment requirement may result in additional costs for a very small water system. Spent adsorption media were non hazardous and can be disposed of in a sanitary landfill. Adsorption appears to be an applicable arsenic control technology for very small water systems. Procedures developed under this project may be adopted by a water system in selecting appropriate media for arsenic control.

RESEARCH PARTNER:

This study was jointly funded by the Water Research Foundation and the U.S. Department of Energy through the Arsenic Water Technology Partnership. The report will also be published by WERC (a Consortium for Environmental Education and Technology Development at New Mexico State University).

PARTICIPANTS:

Two North American utilities, the Triple G Dairy Water System and Camp Verde Water System, participated in this project. SolometeX (a Layne Christensen Company) and the Dow Chemical Company provided the adsorption media.