Effect of Hydraulic Retention Time on Palm Oil Mill Effluent Treatment in a Cocoyam-Based Constructed Wetland

Palm oil mill effluent (POME) poses significant environmental threats to land and nearby water resources. Limited economic resources and a lack of awareness of sustainable wastewater treatment methods exacerbate the issue. Horizontal subsurface flow constructed wetlands (HSSFCWs) offers a proven, environmentally friendly, and cost-effective solution for wastewater treatment. This study investigated a greenhouse-scale HSSFCW using plastic containers as wetland cells filled with gravel (1-4 mm), sandy loam soil, and Xanthosoma spp. as a bioremediation agent. POME (0.9 L) was introduced to a controlled wetland and a research wetland, and effluent samples were analysed after 24, 48, and 72 hours of hydraulic retention time (HRT) using the flow rate monitoring method. In the research wetland, pH increased by 34% (from 5.55 to 7.41), BOD decreased by 75% (3.01 to 0.75 mg/L), COD by 76% (6.32 to 1.54 mg/L), while total nitrogen and phosphorus increased by 52.7% (4.27 to 6.52 mg/L) and 46.9% (2.46 to 3.61 mg/L), respectively. The significant differences in removal efficiencies between the control and research wetlands demonstrated the influence of Xanthosoma nutrient uptake on POME treatment. These results suggest that cocoyam-based HSSFCWs can effectively treat POME to meet environmental discharge standards. Future modelling studies could enhance the understanding of internal mechanisms, broadening the application of cocoyam-based HSSFCWs for sustainable POME management in the palm oil industry.