Using the Landfarming Technique to Remediate Soils Contaminated with Hexachlorocyclohexane Isomers

Abstract

Landfarming is a bioremediation technology in which contaminated soil is mixed with nutrients and amendments, and the material is periodically tilled for aeration. Contaminants are degraded, transformed and immobilised by means of biotic and abiotic reactions. In this study, a soil heavily contaminated (>5000 mg kg−1) with hexachlorocyclohexane (HCH) isomers derived from lindane production was treated using this technique. The combination of the physical disruption of HCH aggregates together with the biological degradation which is favoured by the improvement in the soil’s physical and chemical conditions, both contributed to a significant decrease of the α- and γ-HCH isomers (up to 89 and 82% of the initial concentration, respectively) at the end of the 11 month long experiment. In contrast, the most persistent β-isomer remained essentially unaffected. Flooded conditions did not improve HCH degradation. Degradation of α- and γ-HCH was quite rapid initially. Pentachlorocyclohexene (PCCH) and tetrachlorocyclohexene (TCCH) were identified as the main metabolites during the treatment period. The main variables that affected the process were: moisture content, temperature and especially the distribution and size of HCH aggregates, which limits HCH bioavailability. Aerobic landfarming appears to be an interesting and cost effective bioremediation treatment for soils contaminated with α- and γ-HCH isomers. However, complete sanitation of soil (total HCH < 2 mg kg−1), especially in the case of β-HCH, would require the application of other techniques, for example slurry system under anaerobic conditions.