The co-application of earthworms (Dendrobaena veneta) and compost to increase hydrocarbon losses from diesel contaminated soils

The feasibility of using composted civic waste for the remediation of a soil contaminated with petroleum hydrocarbons (extractable petroleum hydrocarbons (EPH) 10 ± 1.8 g kg- 1 and total 16 USEPA PAH 1.62 ± 0.5 g kg- 1) was assessed. The effects of compost to soil ratio, in combination with and without earthworm presence (Dendrobaena veneta), upon the loss of contaminants were determined for EPH (GC-FID) and PAH (GC-MS), respectively. Increasing the ratio of compost substrate to hydrocarbon impacted soil (1:0.5, 1:1, 1:2 and 1:4 (soil:compost wt/wt)) in the absence of earthworms resulted in significantly (p < 0.05) greater losses of both EPH and SPAH after an 84 d incubation period, when compared to the soil only control. Where earthworms were present without compost, EPH losses were significantly (p < 0.05) enhanced in the soil only treatment (33.4 ± 5.3% residual) compared to the soil only control (54.4 ± 5.3% residual). However, PAH loss in the soil only treatment (with-earthworm presence) were only slightly enhanced (65.3 ± 9.3% residual), with respect to the soil only control (69.2 ± 6.4% residual). Synergistic benefits of both earthworm and compost presence were most significant for PAHs (p < 0.05), and less so for EPH. 14C-respirometer studies, to establish catabolic competence in terms of microbial mineralisation of key hydrocarbons, complemented the hydrocarbon analysis.