Bioremediation of Petroleum-Contaminated Acid Soil by a Constructed Bacterial Consortium Immobilized on Sawdust: Influences of Multiple Factors

Bioremediation has been widely applied to decontaminate petroleum-contaminated sites. However, successful bioremediation remains challenging due to complicated environmental factors that are present in petroleum-contaminated soil. Hence, in this study, we used a constructed bacterial consortium immobilized on sawdust through a series of microcosm experiments to identify the main factors affecting decontamination and the optimal conditions for the bioremediation of heavily petroleum-contaminated acid soil. The acid soil collected from a refinery was first improved with an ameliorant made from an industry residue. Then, an orthogonal experimental design (OED, L9 (3(4))) was employed to evaluate the effects of the main factors (total inoculum size, inoculation addition protocol, amounts of mixed surfactants, and amount of inorganic fertilizer) on the soil bioremediation. The removal of total petroleum hydrocarbons (TPH) reached the highest level (60 %) after 60 days under the optimal conditions of 2 % (w/w) of the immobilized consortium, delivered in three increments and 6 % (v/w) of SDS/TritonX-100 (a molar ratio of 2: 1). The most significant negative factor was the inorganic fertilizer. The size and addition protocol of inoculant were positive factors, while the amounts of surfactants had a minimal impact. The addition of inorganic fertilizer could have caused excessive soil salinity and reduced the bioremediation effectiveness. Repeated applications of incremental doses are recommended, rather than a single bolus dose, to optimize the bioremediation of the contaminated sites.