Removal of Hydrophobic Contaminants from the Soil by Adsorption onto Carbon Materials and Microbial Degradation

The pollution of soil is a worldwide concern as it has harmful consequences on the environment and human health. With the continuous expansion of industry and agriculture, the content of hydrophobic organic pollutants in the soil has been increasing, which has caused serious pollution to the soil. The removal of hydrophobic organic contaminants from soil, aiming to recover environmental safety, is an urgent matter to guarantee sufficient food and water for populations. Adsorption has proven to be an effective and economically practicable method for removing organic contaminants. This paper summarizes the use of low-cost adsorbents, such as biochar and activated carbon, for removing hydrophobic organic contaminants from soil. Biochar is usually appropriate for the adsorption of organic contaminants via the adsorption mechanisms of electrostatic interaction, precipitation, and ion exchange. Biochar also has numerous benefits, such as being obtained from several kinds of raw materials, having low costs, recyclability, and potential for environmental treatment. This paper illustrates biochar’s adsorption mechanism for organic contaminants and discusses the microbial degradation of hydrophobic organic contaminants.

A Review of Empirical Models of Sorption Isotherms of Hydrophobic Contaminants

Renewed focus on empirical models of sorption isotherms of hydrophobic organic contaminants (HOCs) onto mineral surfaces and soil components is required because of the importance attached to numerous pollutants released into the environment. This examines the various models and isotherms with their assumptions by different scholars on the contribution of sorption of contaminants onto clay mineral sorbents and soil organic matter with the possible ways of prevention of environmental contamination by HOCs. Literature indicated that empirical models and isotherms have been used to ascertain several surfaces that can be sorbed by hydrophobic organic contaminants. These models also show that soils can retain HOCs even at low soil organic levels and the extent depends on the structure of the pollutant type and concentration of clay minerals in the sorbent. It also revealed the important role played by soil organic carbon in the sorption of contaminants onto soils and how it is strongly affected by the nature and structure of the organic soil matter. Contamination by different pollutants required a renewed approach in the context of the sorption of organic pollutants onto clay minerals from aqueous and non-aqueous solutions.

The influence of solid-phase organic carbon on the sorption of hydrophobic organic pollutants in landfill barriers, UK

The Oxford Clay from Bletchley, the Kimmeridge Clay from Kimmeridge Bay, Dorset, and Tertiary mud (Wittering Formation) from Whitecliff, Isle of Wight, United Kingdom were used as sorbent samples because of their distinctive organic material characteristics (Amorphous organic matter rich and/or phytoclast rich). Organic material was isolated for identification and analysis using a non-acid extraction method (heavy liquid) extraction and traditional methods involving HF digestion. These organic materials were then used to determine influences of extraction on hydrophobic organic contaminants, (toluene and naphthalene) sorption. Organic petrology classification was applied to identify the various types of isolated organic material. Amorphous organic matter from the Kimmeridge Clay displayed a higher sorption capacity (Sorption–desorption distribution coefficient (Kd), Kd = 6,481, 59, 670; for toluene and naphthalene, respectively) compared to literature values. Amorphous organic matter-rich sorbent extracts demonstrated a higher absorption capacity than the phytoclast-rich sorbents (e.g., Wittering Formation, Kd = 219, 10, 134; for toluene and naphthalene, respectively). Implications of results in landfill design/risk assessment and modelling are discussed.