Enhancing bioremediation in desert Soils: Comparative impacts of water- and sewage effluent-irrigation on oil degradation and microbial dynamics

This study investigates the efficiency of different bioremediation techniques in cleaning a desert soil sample saturated with crude oil. The soil was divided into three cores; two cores were regularly irrigated with either tap water or raw sewage effluent and mixed thoroughly, while the third core remained untreated as a control. Three parallel cores of pristine soil samples were also set for comparative analysis of microbial communities. The cores were exposed to natural environmental conditions for 10 months. The results of the study showed that bioremediation in the oil-saturated soil samples occurred via the activities of the indigenous bacteria, demonstrating self-cleaning. Oil-removal efficiency in the untreated soil samples reached 79.6 % after 10 months incubation. Water- and sewage effluent-irrigation along with soil mixing improved the environmental conditions in the polluted soil samples, thus enhancing the growth and propagation of hydrocabonoclastic bacteria, accelerating oil-biodegradation to 94 % and 97.4 %, respectively. Both culture-dependent and culture-independent analyses revealed significant shifts in bacterial community composition due to oil introduction and treatment type. The culture-independent method revealed TM7a, A4b, and Skermanella as the most abundant taxa. Conversely, the culture-dependent method identified Arthrobacter spp., Georgenia sediminis, Mycobacterium doricum, Pseudomonas spp., and Sinorhizobium meliloti as the predominant hydrocarbonoclastic indigenous bacteria in the untreated and water-irrigated soil. In the sewage effluent-irrigated soil, Aeromonas and Enterobacter dominated using the culture-dependent method, while JG30-KF-CM45 was the most abundant, with no coliform detection in the culture-independent method. The current study showed that self-cleaning of oil-saturated soils could be accelerated using cost-efficient methods.