Enhanced biotreatability of petroleum hydrocarbon-contaminated mining waste coupled with the attenuation of acid drainage production.

A biostimulation study was conducted on mining waste residue with nutrient (nitrogen and phosphorus) and/or liming agent (ash or CaCO3 ) amendment to assess petroleum hydrocarbon (PHC) biodegradation efficiency by indigenous microorganisms. Compounds accumulated and/or released by treated samples were also monitored to determine the potential for acid mine drainage production during biostimulation. The potential for natural attenuation (i.e., the biodegradation of PHC contamination) was initially low but increased significantly upon nutrient addition. The best results were obtained when nutrient addition was coupled with the addition of a liming agent, notably CaCO3 , which contributed to maintaining near-neutral pH values. In fact, during treatment without a liming agent, pH decreased due to the oxidation of sulfide minerals, resulting in acid mine drainage production with increased metals released into sample leachates. Sulfur- and iron-oxidizing bacteria were detected primarily in samples not amended with liming agents, and the predominant organisms were affiliated with Acidithiobacillus spp. and Acidiphilium spp. Overall, the results of the present study demonstrated that amendment with a liming agent when treating PHC-contaminated mining waste residue contributes to maintaining a pH close to neutrality, mitigates sulfate release, and reduces the release of metals without negatively affecting the activity of PHC degraders.