Biodegradative Potentials of Pseudomonas and Bacillus species on Physicochemical Properties and Heavy Metal Levels in Palm Oil Mill Effluent collected from Mabolaje, Oyo State, Nigeria

Abstract

Palm oil mill effluent (POME) represents an environmental concern in oil-producing regions, characterised by high organic loads, heavy metal contamination, and physicochemical parameters exceeding regulatory discharge limits. Biological remediation using indigenous bacterial species offers a sustainable and cost-effective treatment alternative. Hence the objective of this paper was to evaluate the biodegradative potentials of Pseudomonas and Bacillus species on physicochemical properties and heavy metal levels in palm oil mill effluent (POME) collected from Mabolaje, Oyo State, Nigeria using appropriate standard methods. Indigenous bacterial isolates were characterised using morphological and biochemical methods. Biodegradation was monitored at 24 h, 72 h, and 144 h by measuring Total Dissolved Solids (TDS), Electrical Conductivity (EC), pH, temperature, Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD₅), and heavy metals (Pb, Cu, Zn). Fifty bacterial isolates were recovered, dominated by Bacillus spp. (56%) and Pseudomonas spp. (30%). Both genera demonstrated significant pollutant reduction.  TDS and EC each decreased by up to 61.3% at 72 h. pH increased progressively from 4.46 to 5.34, indicating alkalinization during degradation. Copper removal reached 100% by Pseudomonas sp., while zinc was reduced by up to 77.1%. Lead declined initially but showed partial re-mobilisation at 144 h. Viable bacterial counts declined from 10⁶ to 10⁵ CFU/mL, with Bacillus maintaining consistently higher populations. Pseudomonas and Bacillus species demonstrated substantial biodegradative capacity against POME pollutants, with Pseudomonas showing superior heavy metal removal and Bacillus exhibiting greater biomass resilience, supporting consortium-based bioremediation strategies for POME treatment.