Active capping technology: a new environmental remediation of contaminated sediment

Abstract

The management and treatment of contaminated sediment is a worldwide problem and poses major technical and economic challenges. Nowadays, various attempts have been committed to investigating a cost-effective way in contaminated sediment restoration. Among the remediation options, in situ capping turns out to be a less expensive, less disruptive, and more durable approach. However, by using the low adsorption capacity materials, traditional caps do not always fulfill the reduction of risks that can be destructive for human health, ecosystem, and even natural resources. Active caps, therefore, are designed to employ active materials (activated carbon, apatite, zeolite, organoclay, etc.) to strengthen their adsorption and degradation capacity. The active capping technology promises to be a permanent and cost-efficient solution to contaminated sediments. This paper provides a review on the types of active materials and the ways of these active materials employed in recent active capping studies. Cap design considerations including site-specific conditions, diffusion/advection, erosive forces, and active material selection that should be noticed in an eligible remediation project are also presented.

Contaminated Sediments

“…to strengthen their adsorption and degradation capacity. The active capping technology promises to be a permanent and cost-efficient solution to contaminated sediments (Zhang, Zhu et al 2016). Thin-layer capping with active carbon has shown promising results for reducing the bioavailability and leaching of organic contaminants .…”

“…The natural calcium-rich clay minerals sepiolite and attapulgite can effectively reduce both the mobile metal fraction and the bioavailability to benthic organisms in Pb and Cd polluted sediments (Yin and Zhu 2016). A review of active capping technology was performed in 2016 (Zhang, Zhu et al 2016) and a short overview of these results and new additional research is given below.…”

“…Apatite is the most abundant mineral of all phosphate bearing minerals, is readily available and has a low extraction cost. Apatite possesses a high cation exchange capacity suggesting it could be a binding agent to immobilize heavy metals (Singh, Ma et al 2001, Zhang, Zhu et al 2016. Hydroxyapatite has been shown to immobilize heavy metals such as Pb, Zn, Cd, Cu, Ni, and uranium (U) in water, soil and sediment (reviewed by Zhang et al 2016).…”

“…Apatite possesses a high cation exchange capacity suggesting it could be a binding agent to immobilize heavy metals (Singh, Ma et al 2001, Zhang, Zhu et al 2016. Hydroxyapatite has been shown to immobilize heavy metals such as Pb, Zn, Cd, Cu, Ni, and uranium (U) in water, soil and sediment (reviewed by Zhang et al 2016). The breakthrough of As, Cd, Co, Se, Pb, and Zn when using apatite as capping material in column studies was significantly delayed by apatite (Dixon and Knox 2012).…”

“…However, due to its nature, apatite can contain high concentrations of impurities (As, Cr, U) that may cause additional contamination when used for environmental remediation. Biologically formed apatite, like fish bone, has lower concentrations of impurities and higher solubility than mined and refined apatite (Zhang, Zhu et al 2016).…”