Physicochemical and Microbiological Characteristics and Organic Amendments of Oil Contaminated Site of an Abandoned Artisanal Refinery in Obi-Ayagha of Ughelli South, Delta State, Nigeria

Soil, a vital non-renewable natural resource, plays a fundamental role in supporting plant growth, providing essential nutrients, and detoxifying environmental pollutants. The aim of this paper was to evaluate the physicochemical and microbiological characteristics, and organic amendments of the oil-contaminated site of an abandoned artisanal refinery in Obi-Ayagha of Ughelli South, Delta State, Nigeria using appropriate standard procedures. Data obtained reveals that he pH of the soil sample (Control and Impacted) ranged between 6.7 and 7.4. EDX result showed 69.10% of Carbon that could be credited to the plant extract, total heterotrophic bacterial count revealed notable variations across different treatments over the study period (1–84 days). For natural attenuation (control), the THBC ranged from 31.33±1.53 to 119.00±9.64. In the biostimulation setup using carbon dots, the initial concentrations showed the following results: it was observed that CFU/g counts were generally higher in polluted soils compared to unpolluted ones. The compost, with a pH of 8.00, was stable and alkaline, whereas the NPK amendment was acidic, with a pH of 6.25. Conductivity measurements showed values of 13,830 µS/cm for compost and 20,800 µS/cm NPK. The temperature of both amendments was in a similar range (27.9°C–27.0°C). Nitrate content (mg/kg), compost exhibited 309.93, while NPK showed only 17.73. Total organic carbon was significantly higher in compost (118.08 mg/kg) compared to NPK (16.73 mg/kg). Moisture content for compost was 1.70, while for NPK, it was 9.60. Macronutrients like nitrogen (N), phosphorus (P), potassium (K), alongside micronutrients such as iron (Fe) and zinc (Zn), are indispensable for plant growth, contributing to biochemical processes and structural development.