Development of granular indigenous microalgal-bacterial consortium (G-IMBC) technology for palm oil mill effluent treatment: Optimization, characterization, and microbial community dynamics

Palm oil mill effluent (POME) remains a major environmental concern due to its high organic load. This study presents a novel approach for the development and optimization of a Granular Indigenous Microalgal–Bacterial Consortium (G-IMBC) for effective POME treatment using a sequencing batch reactor (SBR). Response Surface Methodology (RSM) was employed to model and optimize key parameters, including wastewater concentration (380–760 mg COD/L), Ca²⁺ addition (40–100 mg/L), and granulation time (8–24 days). The optimized conditions 622 mg COD/L, 90 mg/L Ca²⁺, and 22 days—resulted in enhanced granule size (2.6 mm) and density (3.37 g/mL) with R² values of 0.93–0.97. The G-IMBC improved settleability and overall reactor performance. Morphological and elemental analyses confirmed the successful development of compact, dense granules dominated by carbon (42.77 %) and oxygen (33.54 %). Metagenomic analysis revealed a diverse microbial community, with Azotobacter and Coelastrum as the dominant bacterial and microalgal genera, respectively. Structural and microbial profiling providing insights into the granulation mechanism. The system demonstrated effective removal of major pollutants, with an average COD removal efficiency of 82.25 % ± 9.61, total nitrogen removal of 72.70 % ± 14.09, and Total Phosphorus removal of 71.68 % ± 21.20. These findings demonstrate that this technology can serve as an efficient strategy for POME treatment.