Sorbent-Based Technology for Mercury Remediation in a Freshwater Aquatic System

The persistent geochemistry of mercury renders cleanup efforts challenging across a vast number of mercury-contaminated sites globally. Of particular concern is the existence of diffuse mercury sources that complicate technology development efforts for mercury remediation in freshwater stream systems, such as the East fork Poplar Creek (EFPC), Oak Ridge, Tennessee (EFPC). As a case study, the EFPC ecosystem received large point-source discharges during the 1950s. Although upstream mercury discharges to EFPC have declined, mercury releases still persist from point sources within the industrial facility where mercury was used and from diffuse downstream sources, such as contaminated bank soils. Mercury fate and transport within EFPC ecosystem are constrained by the strong interaction of aqueous mercury with dissolved organic matter (DOM, at ~3 mg/L), which renders mercury binding to sorbents and removal from water column by strong reductant problematic. Furthermore, DOM can outcompete mercury for sorption sites on amendment materials (e.g. GAC, biochar etc.), thus, decreasing the overall effectiveness of these materials for mercury sequestration. Despite ubiquitous use of amendments for in-situ sequestration of organic contaminants, large-scale application of mercury sorbents is uncommon due to cost and fouling problems of sorbents that can potentially leach constituents and particles into waterbodies, thereby severely limiting their applications. In this study key variables controlling adsorption and release of mercury by a suite of select sorbent materials were evaluated under environmental conditions representative of EFPC ecosystem. Batch sorption experiments were performed to understand the factors promoting mercury retention and release by single or mixed sorbent media. The impact of varying mercury concentration, sorbent dosages and varying liquid-to-solid ratios on mercury adsorptive properties of these sorbents were investigated. Understanding the fate of mercury in the presence of a suite of sorbent media is an important first step in predicting production organomercury species (MeHg) in contaminated ecosystems. Key results will be discussed in details during this presentation.