High-performance diesel biodegradation using biogas digestate as microbial inoculum in lab-scale solid supported bioreactors

Abstract

Industrial anaerobic digestion (AD) produces biogas and a digestate that is usually applied as a biofertilizer. However, the study and application of this by-product in terms of its rich microbial diversity and high metabolic activity have been barely investigated. In this work, the digestate regarded as an inoculum—without any further manipulation—was faced to a target hydrocarbon (i.e., diesel oil) to explore its biodegradation capability and potential application in bioaugmentation strategies. Lab-scale single batch bioreactors with solid support (i.e., sand or gravel) embedded with the inoculum and diesel were used to improve bioaccessibility and biofilm formation. In addition, different experimental conditions were assayed varying the initial diesel concentration, microbial load, type of solid support, inoculum aging time, and presence or absence of oxygen. Remaining diesel concentration, dehydrogenase activity and microbial community structure were periodically determined. Remarkably, this low-cost consortium was capable of a significant reduction (>90%) in the concentration of diesel, within 14 days and when the initial load was as high as 6950 mg/kg dry solid support. Furthermore, a 10-fold increment in dehydrogenase activity, alongside an increase in the abundance of hydrocarbon-degrading bacterial groups, and the enrichment of genes for alkane monooxygenase and aromatic ring-hydroxylating dioxygenases, encourage further study of this consortium for bioremediation purposes.