Remediation of Hydrocarbon-Polluted Soil Using Cassava Mill Effluent, Monitored by the Response of Soil Enzymes

Hydrocarbon pollution poses significant threats to soil health by disrupting microbial communities and enzyme activities essential for nutrient cycling. This study examined the potential of cassava mill effluent (CME), as a nutrient-rich organic waste, in enhancing bioremediation of petroleum hydrocarbon-degraded soil by monitoring its impact on the activities of specific soil enzymes such as urease, phosphatase and dehydrogenase. Clean soil (5 kg) was collected and weighed into containers and polluted with spent lubricating oil (SLO; 10 % w/w) to make a model of petroleum hydrocarbon polluted soil. The polluted soil was amended with CME (2.5 % v/w) at varying frequencies of single (PTN), monthly (PTM), weekly (PTW) and daily (PTD) treatments, but the control soil was not treated. Urease, phosphatase and dehydrogenase activities were monitored for six months. Soil samples were collected and analysed at the start of the study, 3 and 6 months after commencement of study. The results showed a significant (p < 0.05) increase of 79.19 % and 57.68 % in the activities of urease at 3 and 6 months respectively; acid phosphatase activity increased above 20 % in the daily and weekly amended at 3 months, while the highest increase of 81.52 % was observed in PTW in the activity of alkaline phosphatase but declined across all treatments at 6 months. Furthermore, dehydrogenase activity increased by 263.08 and 465.93 % in PTD at 3 and 6 months, respectively. The findings suggest that CME may serve as an effective biostimulant in the remediation of petroleumpolluted soils, offering a cost-effective and environmentally friendly solution for soil restoration.