Effect of two-step bioaugmentation of an indigenous bacterial strain isolated from oily waste sludge on petroleum hydrocarbons biodegradation: Scaling-up from a liquid mineral medium to a two-stage composting process

Abstract The effects of two-step bioaugmentation of an indigenous strain on the efficacy of a two-stage composting system, scaled-up from a liquid mineral medium (LMM), for bioremediation of oily waste sludge (OWS) were surveyed. After isolating the bacterial strain (Acinetobacter radioresistens strain KA2) from OWS, its ability in biomass production and oil degradation in the LMM was evaluated. Then, it was added twice to the composting experiments containing multiple levels of final compost (FC). The process duration divided to the first 8 weeks as the primary composting (PC) and the final 8 weeks as the secondary composting (SC). Based on the results, the strain degraded 65.24, 76.14, 53.81, 31.84, and 25.21% of crude oil of concentrations of 1, 2, 3, 4, and 5%, respectively in the LMM. The total petroleum hydrocarbons (TPHs) removal of 67.64-89.56% reached over the two-stage process. In the composting experiments, the degradation of hydrocarbons proceeded according to the first-order kinetics. The computed values of half-lives and degradation rate constants verified the better performance of SC and the effectiveness of the second inoculation. The study confirmed the effective scaling-up of the LMM to the composting process for OWS bioremediation.