This paper describes the laboratory development of a microbial treatment for soil contaminated with oil hydrocarbon residues at a disused refinery site and the application of this technology in a pilot scale treatment bed in the field.
Micro-organisms isolated from the site capable of utilizing a number of normal and branched chain alkanes were tested in a series of soil microcosms, together with various permutations of commercially available surfactants and nutrients for stimulating the activities of hydrocarbon-utilizing micro-organisms. Amongst the most effective reagents were: (a) the fertiliser 'PurisolR' 110 (1 1 per cent N, 11 per cent P,O,, 11 per cent K,O, 'Chafer, Brit. Ag,' Ltd.), which in combination with other supplements resulted in reductions of total oil hydrocarbons and associated polar products (TOHP) from 24,100 to below 16,000 mg kg-' after five weeks (compared to 21,200 mg kg-' in the control); (b) a hexadecane degrading Acinetobacter sp., which in combination with nutrients, reduced T O H P from 21,400 to 13,200 mg kg-I, in seven weeks compared to 16,800 mg kg-' in the control and 15,100 mg kg-' in the treatment with nutrients only and; (c) brewer's yeast which in combination with other supplements reduced TOHP from 16,300 to 7,600 mg kg-' in 14 weeks.
These reagents, together with other supplements were applied to a pilot-scale treatment bed consisting of 200 m3 of contaminated soil. Reductions in T O H P from 25,500 to 9,400 mg kg-' were achieved in 15 months. Corresponding reductions in total oil hydrocarbons (TOH) from 22,600 to 2,000 mg kg-' were achieved in the same period. After this time little further degradation was observed. The requirements for: (a) a critical evaluation of analytical methodology for assessing the bioremediation of oil contaminated soil, and; (b) considering the overall chemical stability of the asphaltene-like residue remaining after biodegradation of the primary oil has taken place when setting meaningful targets for restoration of oil-contaminated land, are highlighted in this study.