Feasibility of Concurrent Treatment of Arsenic and Molybdenum through Co-Precipitation and Adsorption with Case Study and Cost Analysis

Feasibility of Concurrent Treatment of Arsenic and Molybdenum through Co-Precipitation and Adsorption with Case Study and Cost Analysis

Grand Rapids, Michigan

Feasibility of Concurrent Treatment of Arsenic and Molybdenum through Co-Precipitation and Adsorption with Case Study and Cost Analysis Authors Mrs. Prachi Jain - United States - Haley & Aldrich, Inc. Mr. Brian Colonnese - United States - Haley & Aldrich, Inc. Dr. Jacob Chu - United States - Haley & Aldrich Inc. Abstract Molybdenum and arsenic are among the Appendix IV constituents required to be monitored under the coal combustion residuals (CCR) Rule. At some CCR sites, arsenic and molybdenum in CCR-impacted groundwater were found concurrently at a level above their groundwater protection standards. In the environment, molybdenum is highly soluble in water, usually present in the form of an oxyanion, and relatively weak in terms of sorption onto geological media with a low organic content. In contrast, while arsenic is also typically soluble and present in the form of oxyanions in groundwater, arsenic generally has a higher tendency to be adsorbed onto geological media in comparison to molybdenum. Therefore, arsenic transport in groundwater is typically slower than molybdenum. In pursuit of the most efficient and effective groundwater remedies for CCR sites, ideally remedies can concurrently treat multiple site-specific CCR constituents that exceed the groundwater protection standards. In this presentation, we will present review site-specific treatability test data where molybdenum and arsenic are the primary constituents of concern in groundwater. The treatability studies were designed to investigate the effects of ferric iron in aerobic conditions and the ability to promote co-precipitation and adsorption removal of arsenic and molybdenum concurrently to the levels below their respective groundwater protection standards (10 µg/L for arsenic and 100 µg/L for molybdenum). Preliminary laboratory treatability testing results indicate that the concurrent treatment can be achieved at a pH range between 5 and 5.5, with a ferric iron dose higher than 30 mg/L. In this same context, the results of preliminary remedial cost assessments will be presented for an ex-situ treatment system case study that utilizes optimal conditions with ferric iron enhancements to remove molybdenum and arsenic at three different treatment capacities (30 gallons per minute [gpm], 100 gpm, and 500 gpm).