Laboratory-scale bioremediation experiments on hydrocarbon-contaminated soils

Successful application of bioremediation technology to contaminated soil requires knowledge of the characteristics of the site and the parameters that affect the microbial biodegradation of pollutants. Here, we propose a simple protocol for biotreatability assays in two phases. In the first phase of the assays we examined the type and metabolic activity of the indigenous microorganisms at the site, and the presence of possible inhibitors. The biodegradability of contaminants in soil slurries under optimal conditions was also tested. In the second phase several parameters, such as the influence of nutrients and the addition of surfactant and specialized inocula, were evaluated in microcosms with 2.5 kg soil. The application of this protocol to two hydrocarbon-contaminated soils is described. In the first phase of the protocol, the results obtained with the first soil indicated high metabolic activity of indigenous microbial populations and a total petroleum hydrocarbon (TPH) decrease of 46%. Assays of the second soil indicated low indigenous microbial metabolic activity and limited biodegradation of TPH. In the second phase of the protocol, which lasted 360 days, assay of microcosms showed that the first soil responded to several treatments with a large decrease in TPH, while none of the treatments applied to the second soil showed a reduction in TPH. The information obtained from the results in the first phase of the protocol indicates whether a biological treatment of contaminated soil is appropriate. In the second phase of the protocol, we attempted to identify the most appropriate treatment through the evaluation of various conditions and additives.