Comparison of different industrial scale palm oil mill effluent anaerobic systems in degradation of organic contaminants and kinetic performance

Palm oil mill effluent has been extensively researched via three different technologies, namely chemical, physicochemical and biological treatment methods. Biological treatment by anaerobic and aerobic means is currently the most commonly used method for palm oil mill effluent. However, the greatest challenge posed by them is the inconsistent biological oxygen demand of 20 mg/L for the final treated effluent. Large amount of investment for additional polishing plant prior to the final discharge has been utilised intentionally to further reduce the biochemical oxygen demand values, but the problem remains unresolved. The performance of current palm oil mill effluent treatment system deployed by the industry was evaluated by comparing two different types of anaerobic treatments: open ponding and covered lagoon systems (with hydraulic and gas mixing). The covered lagoon with hydraulic mixing achieved the highest chemical oxygen demand, total suspended solids, total volatile solids and lignin removal efficiencies of >80% compared to other systems which showed <50% removal. Sufficient hydraulic retention time, extended aeration system coupled with presence of pure aerobic microbial cells in the stabilisation pond were able to produce effluent that abided the final discharge limit of biochemical oxygen demand 20 mg/L. Stover-Kincannon, Monod Contois and Grau second-order kinetic models were applied to the chemical oxygen demand data obtained to gauge the performance of anaerobic treatment of covered lagoon system with hydraulic mixing. The modified Stover-Kincannon model was found to define the system most appropriately with R-2 of 0.9767. This work provided an up-to-date and representative palm oil mill effluent characteristics and contaminants degradation performance of the three commonly used palm oil mill effluent treatment methods in Malaysia. It helps in method selection and equipment sizing for palm oil mill effluent as well as other industrial-scale wastewater treatment and management. (C) 2020 Elsevier Ltd. All rights reserved.