AWWA ACE59862

The United States Environmental Protection Agency has lowered the maximum contaminantlevel (MCL) for arsenic in potable water from 50 micrograms/liter (ug/L) to 10 ug/L. All watersystems are expected to comply with the new MCL by January 2006. Similar to many otherutilities in the United States, arsenic is of concern for System A. System A provides water to 30,000people, and operates and maintains four drinking water wells (Wells 6, 7, 8 and 9). Thesewells are the sole source of water for System A. The capacities of the wells vary from 900gallons per minute (gpm) to 1700 gpm, with approximately 7.5 million gallons per day of totalwell production capacity.Two of the wells (Wells 7 and 8) have high sulfate (400-500 mg/L) and hardness (400-450mg/L) levels. These wells are under the influence of a mine-tailing plume that resulted in thedeterioration of the water quality. The 400-500 mg/L of sulfate Wells 7 and 8 not only pose anaesthetic issue but may also cause public health issues (e.g., diarrhea in sensitive populations).System A initiated a planning study to develop strategies for arsenic removal from the four wells.The selection of arsenic mitigation strategies for Wells 7 and 8 is complicated by the presence ofsulfate and other ions. Several arsenic treatment technologies including ion exchange (IX),adsorption, reverse osmosis (RO) and coagulation-assisted microfiltration (CMF) were evaluatedfor their feasibility. The concentration of sulfate determines the achievable run lengths (forregeneration) for the IX process. Sulfate can scale the RO membrane, if proper anti-scalanttechniques are not used. There are no prior studies on the effect of high concentrations of sulfateon GIM and CMF treatment processes.Giving due consideration to water quality (arsenic and interfering ions concentrations), siteconstraints (availability of land, sewer and power), operational issues, residuals handling issuesand economic feasibility, this study developed alternative treatment alternatives. These treatmentalternatives considered granular iron media (GIM) adsorption for Wells 6 and 9 and GIMcoupled with IX or RO for Wells 7 and 8. The sequencing of GIM and IX/RO at Wells 7 and 8was developed in a manner to result in environmentally benign residuals.Site-specific recommendations for disposal of liquid and solid residuals were developed for eachcompliance alternative. Capital and operations and maintenance cost opinions were developedfor all compliance alternatives. This paper presents the findings of this study that will beuseful for all small and large water systems that are considering arsenic treatment for theirimpacted source waters. The paper presents the issues associated with selection of arsenictreatment strategies and assists water utility managers/operators in making some educated decisions for arsenic rule compliance. Includes reference, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

06/17/2004

Number of Pages:

20

File Size:

1 file , 790 KB