Treating palm oil mill effluent (POME): Opportunities, challenges, and sustainable practices

Palm oil mill effluent (POME) remains a major environmental challenge in the palm-oil industry due to its high organic load, nutrient content, recalcitrant compounds, and methane emissions associated with conventional treatment and disposal. This review synthesizes two decades of scientific, technological, and policy developments to assess pathways for cleaner, resource-efficient POME management. Conventional treatment systems mainly open ponding—offer low-cost stabilization but can generate high greenhouse-gas emissions. Engineered biological reactors and membrane-based polishing units can achieve high organic-matter removal (COD and BOD removal often >80% in pilot- to full-scale treatment trains), although performance depends on influent strength and operating conditions. Nature-based solutions (NBS), including microalgae, floating macrophytes, and constructed wetlands, provide low-energy alternatives with strong nutrient removal and biomass valorization potential, though performance remains sensitive to hydraulic and climatic variability. Resource-recovery routes such as biogas, struvite precipitation, biochar production, polyhydroxyalkanoate formation, and single-cell protein generation highlight opportunities for circular-bioeconomy integration at the mill scale. Comparative policy analysis across major producer regions indicates persistent disparities in discharge limits, enforcement capacity, and methane-capture requirements, which influence technology adoption and sustainability certification. By integrating treatment efficiency, resource-recovery potential, technology readiness, and governance context within a structured decision framework, this review advances a systems-level roadmap for selecting and upgrading POME treatment pathways. Key research needs include improving NBS resilience, integrating digital monitoring and AI-based optimization, expanding techno-economic and life-cycle assessments, and harmonizing regulatory frameworks. Overall, this review identifies technical, ecological, economic, and governance strategies that can transform POME from an environmental liability into a low-carbon, resource-positive stream aligned with cleaner production objectives. • POME treatment remains a major bottleneck in sustainable palm oil processing • Anaerobic digestion with biogas recovery is the most mature POME valorization route • Hybrid systems improve effluent quality, energy recovery and operational stability • Nature-based solutions enable low-energy polishing but require resilience optimization