Green-Synthesized Copper Nanoparticles from Azadirachta Indica for Antimicrobial Applications and Potential Visible-Light- Assisted Organic Load Reduction of POME

Objective: Palm Oil Mill Effluent (POME) is a high-strength agro-industrial wastewater of serious environmental concern due to its high organic load and microbial contamination. Methods: Copper nanoparticles (CuNPs) were synthesized using Azadirachta indica (neem) leaf extract and copper sulfate at different extract-to-metal salt ratios (1:1 and 2:1). The formation of CuNPs was confirmed by color change, FESEM, and EDX analyses. POME samples were collected from two treatment stages (raw and acidification ponds), and bacteria were isolated and identified using morphological, Gram staining, and biochemical tests. The antimicrobial activity of CuNPs at two concentrations (0.008 g and 0.016 g) was evaluated against isolated bacterial strains (Bacillus spp., Pseudomonas spp., and Stenotrophomonas spp.) using the agar well diffusion method. Results: The synthesized CuNPs ranged from 11–40 nm in size, confirming the presence of elemental copper with bioorganic capping. Antibacterial activity increased with CuNP loading, with the maximum inhibition zone (50 mm) observed for Bacillus spp. using CuNPs synthesized from a 0.1 M precursor solution and 0.016 g nanoparticle dose. At higher precursor concentrations (1.0 M), aggregation of nanoparticles occurred, leading to reduced antibacterial efficiency. Neem-CuNPs therefore demonstrated strong antimicrobial (disinfection) activity, while photocatalytic effects were observed as a secondary, light-assisted reduction of organic content rather than direct biodegradation. Conclusion: The green-synthesized CuNPs offer an eco-friendly and effective antimicrobial strategy for managing POME-associated bacteria. These findings provide a basis for future work combining CuNPs with biological systems to enhance wastewater remediation.