Abstract

This report documents the results of year-long sampling and analysis at two ion exchange plants (referred to as Plants A and B) and two activated alumina plants (referred to as Plants C and D), with capacities of 800 to 3,000 gallons per day. The objective of sampling and analysis was to evaluate the performance of the full-scale water treatment plants to consistently remove arsenic from source water. In addition, data were collected to evaluate the chemical characteristics of the residuals produced by the treatment processes.

The study was divided into three phases:

• Source water sampling – conducted to evaluate source water characteristics at each plant
• Preliminary sampling – initiated in August 1998; consisted of four sampling events conducted at each facility either weekly or biweekly to refine procedures for subsequent events during the third phase
• Long-term evaluation – consisted of weekly or biweekly sampling at each facility from September 1998 to September 1999

Samples from resin regeneration were collected at Plant A from March to June 1999. Spent activated alumina samples were collected at Plants C and D during the media change-out events in December 1998 and May 1999, respectively.

Results from the long-term evaluation demonstrated that both the ion exchange and activated alumina systems are capable of achieving arsenic levels of less than 5 micrograms per liter (µg/L) in the treated water, provided that the ion exchange resin was regenerated or the activated alumina medium was changed out before arsenic breakthrough occurred.

The two ion exchange systems had inlet arsenic concentrations (primarily arsenic [V]) between 45 and 65 µg/L. When Plant A was operated beyond 3,000 to 3,200 bed volumes (BV) of water, arsenic chromatographic peaking occurred. Arsenic breakthrough was not observed at Plant B, where an average 97 percent of removal efficiency was achieved, leaving only 0.8 to 4.5 µg/L arsenic in the finished water.

Both activated alumina systems consisted of two parallel treatment trains with a roughing activated alumina column followed by a polishing column in each train. The systems operated on a media-throwaway basis. The average arsenic removal efficiencies achieved at Plants C and D were 87 percent and 98 percent, respectively. The raw water at Plant C (34 to 76 µg/L total arsenic) contained approximately 0.3 to 28.8 µg/L arsenic (III), which was nearly completely removed even though no oxidation treatment was provided. The water at Plant D contained slightly higher total arsenic concentrations (53.3 to 87 µg/L) (but no arsenic [III]), which was consistently removed to less than 5 µg/L in the finished water. The activated alumina media in the roughing tanks was exhausted and disposed of every 1 to 1.5 years after treating approximately 9,600 BV at Plant C and 5,260 BV at Plant D. The regeneration process at Plant A recovered from 67 to 86 percent of arsenic from the spent brine. The spent activated alumina at Plants C and D passed the Toxicity Characteristic Leaching Procedure (TCLP) test for metals including arsenic and, therefore, was disposed of as nonhazardous waste.

Contact

Thomas J. Sorg

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