Microbial Dynamics of Soil Impacted by Palm Oil Mill Effluent in Umuapu, Imo State, Nigeria

The indiscriminate discharge of untreated Palm Oil Mill Effluent (POME) a dark, organic-rich wastewater poses serious threats to soil integrity and ecological health. This study investigates the microbial dynamics of POME-contaminated soils in Umuapu, Imo State, Nigeria. A total of eight (8) soil samples were collected from two depths (0–15 cm and 15–30 cm) using an soil auger from POME-contaminated sites. Microbial isolation was conducted using five standard culture media: Nutrient Agar, MacConkey Agar, Salmonella-Shigella Agar (SSA), Mannitol Salt Agar (MSA), and Sabouraud Dextrose Agar (SDA). Standard serial dilution and plate count techniques were employed to enumerate total heterotrophic bacteria and fungi. Bacterial isolates were purified and identified via Gram staining and biochemical profiling, while fungal species were characterized morphologically and microscopically. Results revealed Total Heterotrophic Bacterial Counts (THBC) ranging from 1.8 × 10⁵ to 6.0 × 10⁶ CFU/g, with Akano recording the highest and Ihie the lowest. Fungal counts ranged from 3.0 × 10⁵ to 6.0 × 10⁵ CFU/g, following a similar spatial pattern. Bacillus spp. emerged as the predominant bacterial genus (41.2%), followed by Escherichia coli and Staphylococcus spp. (each 23.5%), and Salmonella spp. (11.8%). Among fungi, Aspergillus spp. dominated (60%), followed by Mucor (30%) and Penicillium spp. (10%). POME contamination significantly disrupts soil microbial ecology, promoting the proliferation of pathogenic and opportunistic microorganisms. Urgent implementation of bioremediation strategies and stricter effluent discharge regulations is essential. This study provides critical insight into microbial shifts in POME-impacted soils, offering a foundational basis for sustainable waste management and soil health restoration relevant both nationally and globally.