Effective bioremediation of soil from the Burgan oil field (Kuwait) using compost: A comprehensive hydrocarbon and DNA fingerprinting study

An innovative combination of metagenomic profiling of microbial communities and GC-MS & Pyrolysis-GC-MS fingerprinting methods were used to assess the biodegradation of contaminated soil from the Burgan oil field in Kuwait. The soil was treated with (sludge) compost in microcosms to evaluate the feasibility of this material for bioremediation purposes. The most favourable trial showed a > 80% decrease in TPH, thereby indicating strong potential for full-scale application using a cost-effective technology and thus in line with the principles of the circular economy. The microbial study showed that compost addition enhanced the organic matter and nutrient content of the soil. However, the microorganisms in the compost did not seem to play a relevant role in bioremediation, meaning that compost amendments serve as a biostimulation rather than a bioaugmentation approach. The chemical study of the distinct oil fractions revealed rapidly biodegraded compounds (alkanes, alkyl-aromatics, etc.) and others that were much more refractory (hopanes, benzohopanes, etc.). Of note, although heavy fractions are usually considered recalcitrant to biodegradation, we observed incipient degradation of the asphaltene fraction by means of double-shot thermodesorption and pyrolysis. Finally, chemical fingerprinting also revealed that the treated soil contained some of the compounds found in the compost, such as coprostanol, cholesterol, and plant sterols. This observation would support the use of these compounds as proxies to monitor the effects of compost and to adjust dosages in real-scale bioremediation treatments.