Modeling desorption kinetics of a persistent organic pollutant from field aged sediment using a bi-disperse particle size distribution

Abstract

Purpose With the predicted climate change, it is expected that the chances of river flooding increase. During flood events, sediments will resuspend and when sediments are polluted, contaminants can be transferred to the surrounding water. In this paper we discuss a numerical intraparticle diffusion model that simulates desorption of dieldrin from a suspension of contaminated porous sediment particles with a well-characterized particle size distribution. The objective of this study was to understand the desorption rate (flux) of dieldrin from a suspension of field-aged sediment at different hydraulic retention times (HRT) of the aqueous phase and to elaborate the effect of particle-size distribution on mass transfer. Materials and methods Desorption kinetics of dieldrin, a persistent organic pollutant (POP), were experimentally measured and described in a separate paper using fieldcontaminated sediment. A radial diffusion model, accommodating intraparticle reversible sorption kinetics, aqueous phase pore diffusion, and a sink term for bulk aqueous phase refreshment was used to describe the experimental data. Results and discussion We observed rapid equilibrium of contaminants between small particles (10 μm) and the surrounding water even though the sorption affinity of dieldrin towards organic matter was high. On the contrary, for the larger particles (84 μm), calculations show that desorption was limited by intraparticle diffusion. Combining small and larger particles in our radial diffusion model resulted in the biphasic desorption behavior often observed even when using a linear isotherm. Conclusions Flood events will result in an increase of desorption rate of POPs from sediments to the surrounding water. HRT and the particle-size distribution determine the desorption rate. We conclude that nonstationary diffusion within organic matter is the main process of mass transfer. Particle size distributions are very valuable to understand the phenomenology related to mass transfer limitations often described as limited bioavailability and can be used as basis to develop engineering options to limit contaminant mass fluxes into the environment.

In situ remediation of contaminated sediments using carbonaceous materials

“…Hydrophobic organic compounds (HOCs) such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), chlorinated pesticides, dioxins, methylmercury, and brominated flame retardants are of particular concern because of their high persistence and toxicity. Although these compounds adsorb strongly to particulate matter, sediment may become a source of pollution by chemical desorption or particle ingestion by biota and thus may have a considerable impact on the quality of aquatic ecosystems 3–7.…”

Partition kinetics of chlorobenzenes in a sediment-water system

“…Rapid desorption of CBs in this study (0 -12 hours) followed by relatively steady concentrations (12 -48 hours) (Fig. 2) can be associated with partition from small particles in the rapid phase and partition from large particles in the steady phase (Smit et al, 2010).…”

Spatial Distribution and Location of Natural Organic Matter on Sediment Particles by Scanning Electron Microscopic Analysis and the Development of a New Persistent Organic Pollutant–Sediment Kinetic Desorption Model

“…More recent investigations have failed to identify some key characteristics of the relationship between NOM and POPs. A later investigation by Smit et al (2010) described the release of dieldrin from field‐aged sediment as a bi‐disperse particle size distribution process. Kukkonen et al (2003) failed to observe a linear correlation between labile desorption rate constants and NOM content using literature data from a variety of sources and experimental techniques.…”