Activated biochars reduce the exposure of polycyclic aromatic hydrocarbons in industrially contaminated soils

Abstract

Immobilisation of organic contaminants using biochar is becoming increasingly common. However, biochar is less effective than activated carbon in immobilising contaminants. To increase the efficiency of contaminant binding by biochar, an alternative method of biochar activation that leads to an increase in surface area is proposed. Herein, we improve the biochar by subjection to a range of activation techniques using microwaves, carbon dioxide or superheated steam. To test their effectiveness, the untreated and activated biochars were added at 5% w/w into three different industrially contaminated soils sampled from areas around a coal plant (KOK and KB) and a bitumen processing plant (POPI).The surface area (SSA) of biochar subjected to the activation techniques increased significantly. The SSA of the original biochar was 11m2/g, while those of the activated biochars was 443m2/g (microwave), 512m2/g (CO2) and 841m2/g (superheated steam). The addition of activated biochar reduced the freely dissolved PAHs (Cfree) in the KOK and POPI soils by up to 86% (from 153 to 22ng/L and from 172 to 24ng/L, respectively) and in the KB soil by up to 70% (from 52 to 16ng/L) compared to the untreated soils. Even more pronounced reductions were observed in the concentration of bioaccessible PAHs (Cbioacc). The activated biochars reduced Cbioacc in all soils by almost 100% (from 1.39 to 0.03 for KOK, from 1.92 to 0.01 for POPI and from 1.16 to 0.04mg/kg for KB) compared with the untreated soil. This research shows that biochar activation by different methods leads to significant enhancements in contaminant binding and thus is a promising method for increasing the potential use of biochar in soil remediation.