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Small System Use of a Solid Arsenic Oxidizing Media in Place of Chemical Oxidation to Enhance Arsenic Removals
Citation:
SORG, T. J., A. Chen, AND L. Wang. Small System Use of a Solid Arsenic Oxidizing Media in Place of Chemical Oxidation to Enhance Arsenic Removals. Presented at OH AWWA Annual Conference, Cincinnati, OH, September 20 - 23, 2011.
Impact/Purpose:
To inform the public.
Description:
As part of the USEPA Arsenic Demonstration Program, an arsenic removal adsorptive media treatment system (10 gpm) was installed at Head Start School in Buckeye Lake, Ohio on June 28, 2006. The source water (ground water) contained around 20 µg/L of arsenic, existing predominately as soluble As(III). The source water was temporarily stored in a 120-gal pressure tank, softened through a water softener, chlorinated with a sodium hypochorite (NaOCl) solution, and retained in a 120-gal contact tank; all of which existed prior to the installation of the arsenic removal system. The new arsenic treatment system that was install following the existing contact tank and consisted of two, 18-in × 65-in, adsorption vessels in series, each loaded with 4.5 ft3 of ARM 200, an iron oxide/iron hydroxide media The system operated from June 28, 2006, to February 24, 2010, treating approximately 303,200 gal (or 9,000 bed volumes [BV]) of water for an average daily use rate 450 gallons. During the almost 4 years of operation, the highest arsenic concentration measured after treatment was 1.4 µg/L indicating that the treatment system was very effective in removing arsenic. Shortly after the installation of the arsenic removal system, the OHEPA reported elevated total trihalomethanes (TTHM) and haloacetic acids (HAA5) in the effluent from the new system. Examination of system operating conditions and disinfectant byproduct (DBP) data revealed that the high levels (80 -240 THMs) coincided with elevated chlorine residuals levels at or above 4.4 mg/L (as Cl2). The results of laboratory column studies suggested that ARM 200 media may have promoted TTHM and HAA5 formation. The TOC level in the source water was around 2 mg/L. Extensive laboratory studies did not reproduce the same increases in TTHM or HAA5 as observed onsite. Therefore, the results of neither the column studies, nor on-site studies, did not totally explain the elevated DBP concentrations observed onsite. During March, 2010, the Head Start School school connected up to a newly constructed Buckeye Lake, OH water treatment system. At the request of the Head Start school, the arsenic treatment system was removed and at the request of the OHEPA the system (which was very successful in remoing arsenic) was moved to the Plainview Christian School, Plainview, OH. This school also had an arsenic problem (15-20 ug/l ) and was under an efforcement action by the OHEPA. The Buckeye Lake arsenic removal system was installed at the Plainview Christian School in September, 2010. Because the arsenic at this location was also predominately As III, oxidation of As III to As V was also determined to be necessary to enhance arsenic removal. Historically, the School did not add chlorine to their source water, and therfore, was not interested in adding chlorine if another option was available. In addition, the use of chlorine would also require DBP monitoring which would add to the operational cost of using chlorine. Consequently, The school was very acceptable to a proposal by USEPA to using an non-chemical oxidation process for As III oxidation, Filox. USEPA had good experience in using Filox as an As III oxidant and OHEPA was willing to approve it use at this site to minimized operational issues and cost. With approval of the new system design, the adsorptive media system was installed using Filox as an arsenic oxidizing media. Monitoring of the system for six months of operation has shown the Filox to be effective in oxidizing As III to As V and the arsenic in the effluent water for the treatment system has been less than 2 ug/L. This presentation will discuss the TTHM and HAA5 issues that were found with the Buckeye Lake treament system. The presentation will also describe the changes made to the Buckeye lake treatment system particularly the pretreatment Filox system and present the treament data collected from the system since the time of installation at the Plainview Christian School . The data will show the effectiveness of Filox as an solid oxidizing media and the effectiveness of the adsorptive media system for the removal of arsenic. The presentation will conclude with a discussion of the advantages of using an solid oxidizing media by small drinking water systems.
