Alkaline pH and enhanced catalase activity improve the in vitro bio-remediation of crude-oil polluted soil

Bioremediation effectiveness of crude oil-polluted soil can be monitored via bacterial enzyme activity. In this study, crude oil-polluted and non-polluted soil samples were used to prepare various treatment media, and petroleum hydrocarbon (PHC) degradation was assessed at different incubation periods and pH levels by measuring catalase activity. The stimulatory effects of kenaf-core combined with 95% rhamnolipid on in vitro PHC degradation were compared against bio-stimulation and bioaugmentation treatments. All treatments showed peak catalase activity on the 90th day of incubation. Among bio-augmented treatments, AZ1T6 (Azikoro-1) exhibited the highest catalase activity (20.19 mL KMnO4 g^-1h^-1), followed by OL1T6 (Ologbo-1) and OT1T6 (Otukpoti-1) (17.66 mL KMnO4 g^-1h^-1), with BN3T6 (Benin-3) showing the lowest (17.33 mL KMnO4 g^-1h^-1). In bio-stimulated treatments, media supplemented with kenaf-core and rhamnolipid (T4) demonstrated the highest catalase activity at day 90. All bio-stimulated treatments had significantly higher catalase activity compared to the negative control (T7) (P < 0.05), though their activity was statistically lower than in bio-augmented treatments (P < 0.05). Optimal degradation occurred at pH values between 6.0 and 8.0. The synergistic combination of kenaf-core and 95% rhamnolipid likely enhanced nutrient availability, stimulating indigenous microorganisms and catalase activity, thereby improving bioremediation efficiency beyond what either treatment achieved alone. The enhanced effectiveness observed when combining kenaf-core and rhamnolipid, relative to their separate use, provides evidence for a novel synergistic interaction.