Mid Sweden University

Oil-based drilling cuttings comprise a large andhazardous waste stream generated by oil and gas wellsdrilling operations. Oil-based cuttings are muddy materialswith high contents of salts and hydrocarbons. Compostingstrategies have shown to be effective in the biodegradationof petroleum hydrocarbons, and it offers numerousadvantages in comparison with other bioremediationmethods. In order to assess the effectiveness of drillingcuttings bioremediation by composting with food andgarden wastes, an experiment was conducted in 60-Lreactors for 151 days. Four treatments were carried out:only oil-based cuttings, two proportions (in a volume basis)of organic wastes to drilling cuttings (33 and 75 %) andonly organic wastes (as a traditional composting reference),with pine-tree woodchips as bulking agent. High degradation percentages of total hydrocarbons (&82 %), n-alkanes(&96 %) and the 16 USEPA-listed polycyclic aromatichydrocarbons (&93 %) were reached in the treatment with75 % of organic wastes, and applying 33 % of organicwastes was not more effective than not applying organicwastes for the drilling cuttings hydrocarbons biodegradation. Furthermore, in the treatment with 75 % of organicwastes, alkanes half-life and polycyclic aromatic hydrocarbons half-life were about 10 times and four times lower,respectively, than those in the treatment with 33 % oforganic wastes. Possibly, lower hydrocarbons and saltsinitial concentrations (i.e., lower toxicity), higher microbialcounts, adequate nutrient proportions and water contentsupported a high biological activity with a consequentelevated biodegradation rate in the treatment with 75 % oforganic wastes.