LAUSR

Within this study different biochars (BC) with widely varying characteristics have been tested as materials for the adsorption of hexachlorocyclohexane's (HCH) isomers (α, β, γ and δ) from water. Three BCs produced from digestate (700 °C), greenhouse tomato waste (550 °C) and durian shell (400 °C) were tested. The BCs demonstrated variable physico-chemical characteristics, especially with respect to surface area, with CO2-surface area ranging from 5.4 to 328.6 m2 g-1 and iron content ranging from 0.0733 to 11.17 g kg-1. Isotherm tests were carried out to understand which mechanisms drive HCH uptake to BC, to assess whether stereochemistry affects adsorption and to assess whether competitive sorption occurs. Log KF values ranged from 3.7 to 5.8 (μg kg-1) (μg L-1)-n for the various isomers on the three biochars. No competition (t-test, P < 0.0001) was observed between α-, β-, γ- and δ-HCH. Freundlich adsorption constants of α-, γ- and δ-HCH followed the order: BC digestate > BC greenhouse tomato waste > BC durian shell, in contrast to β-HCH which followed the order: BC durian shell > BC greenhouse tomato waste > BC digestate. In addition to stereochemistry, sorption coefficients were affected most strongly by BC surface area and iron content, in addition to specific HCH/BC matrix interactions. In this study the iron content of a carbonaceous material has been investigated, for the first time, as a factor that can affect the sorption of HCHs.