Long-term attenuation of petroleum hydrocarbons in continuous-flow soil columns using alginate/gellan-encapsulated indigenous microbial consortia under contrasting oxygen conditions

This study evaluated the attenuation of total petroleum hydrocarbons (TPHs) in contaminated aquifer materials using alginate/gellan gum microbeads encapsulating an indigenous bacterial consortium (EIMs) under continuous-flow soil column conditions. Four-column systems were operated under contrasting dissolved oxygen conditions to compare the effects of microbial encapsulation and oxygen availability on TPH attenuation. Compared with the suspended-cell treatment, the EIM treatment increased net TPH removal by 30.8 percentage points under oxygen-limited conditions. Oxygen supplementation further enhanced treatment performance, and the EIM+O 2 column achieved the highest effluent TPH removal (80.0 ± 2.3%) and operationally defined system-level unrecovered TPH fraction based on mass balance (89.3 ± 6.1%), along with the lowest residual soil TPH concentration (20.1 ± 1.3 mg/kg) and higher endpoint ATP levels. Microbial community analysis showed endpoint enrichment of genera previously associated with aerobic hydrocarbon transformation, including Pseudomonas and Bacillus , in the oxygen-supplemented EIM treatment. Overall, the results indicate that encapsulation and oxygen supply were associated with improved treatment performance in this continuous-flow system. These findings provide comparative experimental evidence supporting the potential of encapsulated indigenous consortia for hydrocarbon bioremediation under flow-through subsurface conditions, while further work is needed to clarify transport behavior, redox dynamics, measurement uncertainty, and field-scale applicability.