Development of bioreactors for comparative study of natural attenuation, biostimulation, and bioaugmentation of petroleum-hydrocarbon contaminated soil

Bioremediation of soil and groundwater sites contaminated by petroleum hydrocarbons is known as a technically viable, cost-effective, and environmentally sustainable technology. The purpose of this study is to investigate laboratory-scale bioremediation of petroleum-hydrocarbon contaminated soil through development of eight bioreactors, two bioreactors for each bioremediation mode. The modes were: (1) natural attenuation (NA); (2) biostimulation (BS) with oxygen and nutrients; (3) bioaugmentation (BA) with hydrocarbon degrading isolates; (4) a combination of biostimulation and bioaugmentation (BS-BA). Total petroleum hydrocarbons (TPH) mass balance over the bioreactors showed about 2% of initial 20,000 mg kg-soil−1 TPH was removed by advection due to synthetic groundwater which was flowing through the soil, and the rest of decrease in TPH was caused by biodegradation. The BS-BA mode showed the highest TPH biodegradation percentage (89.7 ± 0.3%) compared to the NA (51.4 ± 0.6%), BS (81.9 ± 0.3%) and BA (62.9 ± 0.5%) modes. Furthermore, an increase in microbial population was another evidence of TPH biodegradation by microorganism. Reaction rate data from each bioremediation mode were fitted with a first-order reaction rate model. The Monod kinetic constants including maximum specific growth rate of microorganisms (μmax) and substrate concentration at half-velocity constant (Ks) were estimated for each bioremediation modes.