Effect of competition between petroleum-degrading bacteria and indigenous compost microorganisms on the efficiency of petroleum sludge bioremediation: Field application of mineral-based culture in the composting process

The effect of competition between isolated petroleum-degrading bacteria (PDB) and indigenous compost microorganisms (ICM) on the efficiency of composting process in bioremediation of petroleum waste sludge (PWS) was investigated. After isolating two native PDB (Acinetobacter radioresistens strain KA5 and Enterobacter hormaechei strain KA6) from PWS, their ability for growth and crude oil degradation was examined in the mineral-based culture (MBC). Then, the PDB isolate were inoculated into the composting experiments and operated for 12 weeks. The results showed that the PDB degraded 21.65-68.73% of crude oil (1-5%) in the MBC after 7 days. The PDB removed 84.30% of total petroleum hydrocarbon (TPHs) in the composting bioreactor containing the initial TPH level of 20 g kg^-1. Removal of petroleum hydrocarbons (PHCs) in the composting experiments proceeded according to the first-order kinetics. The computed values of degradation rate constants and half-lives showed a better performance of the PDB than ICM for TPHs removal. This finding suggests that simultaneous application of the PDB and ICM in the composting reactors resulted in a decline in the effectiveness of the PDB which is due to competition between them. The study also verified that the capability of PDB in degrading PHCs can be successfully scaled-up from MBC to composting process.

Biodegradation of high concentrations of petroleum compounds by using indigenous bacteria isolated from petroleum hydrocarbons-rich sludge: Effective scale-up from liquid medium to composting process

The scale-up of petroleum hydrocarbons-rich sludge (PHRS) bioremediation from liquid medium to a composting method bioaugmentated with two indigenous bacteria, capable of degrading high levels of crude oil, was surveyed. After isolating the strains (Sphingomonas olei strain KA1 and Acinetobacter radioresistens strain KA2) and determining their biomass production, emulsification index (E₂₄), bacterial adhesion to hydrocarbon (BATH), and crude oil degradation in liquid medium, they were inoculated into the composting experiments. In liquid medium, the removal rate of crude oil were 67.25, 70.86, 61.77, 42.13, and 27.92%, respectively for the initial oil levels of 1, 2, 3, 4, and 5% after 7 days. Degradation of 10, 20, 30, 40 and 50 g kg^-1 concentrations of total petroleum hydrocarbons (TPH) were also calculated to be 91.24, 87.23, 84.69, 74.08, and 60.14%, respectively after a composting duration of 12 weeks. The values of the rate constants (k) and half-lives (t_1/2) of petroleum hydrocarbons degradation were 0.083-0.212 day^-1 and 3.27-8.35 days for the first-order and 0.003-0.089 g kg^-1day^-1 and 1.12-6.67 days for the second-order model, respectively. This study verified the suitability of the isolated strains for PHRS bioremediation. Successful scale-up of PHRS bioremediation from a liquid medium to a composting process for degrading high amounts of TPH was also confirmed.