Enhanced Oil Biodegradation Using Immobilised Rhodococcus-Dietzia Consortium on Agricultural Waste

Oil contamination of soils remains an acute environmental problem, particularly in oil-producing regions such as western Kazakhstan. In this study, we explored whether a microbial consortium - specifically Rhodococcus erythreus AT7 and Dietzia maris 22K - could work better when immobilised on agricultural waste like buckwheat and rice husks for cleaning up oil-contaminated soils. The adsorption immobilisation method was applied and compared with free cell systems over 45 days using model soils contaminated with crude oil from the Karazhanbas field. Our results showed that when we immobilised cells on buckwheat and rice husks, they achieved significantly higher TPH degradation (58.4 ±3.7) % and (52.1 ±4.2) %, respectively) compared to free cells. Kinetic modelling revealed first-order degradation kinetics (R² > 0.95) with rate constants of 0.0187 d^–1 for buckwheat husks, 0.0162 d^–1 for rice husks, and 0.0108 d^–1 for free cells, representing 73 % enhancement for buckwheat husk. Why did this work so well? We found several reasons: excellent cell retention (92.3 ±2.1) %, better moisture retention (55 % compared to just 38 % in controls), and - perhaps most interestingly - favourable chemical properties, especially higher antioxidant content. Under optimal conditions (10 % carrier ratio, 60 % - 70 % moisture, pH 7.0 - 7.5), projected cleanup timelines of 3-4 months are achievable. These findings suggest that agricultural waste carriers represent a promising and cost-effective approach for bioremediation of oil-contaminated soils.