The effect of hydraulic retention time on stabilisation unit in anaerobic – contact stabilisation (A-CST) for treating palm oil mill effluent

Abstract

The increased use of palm oil in Indonesia has triggered an increase in the quantity of Palm Oil Mill Effluent (POME). The contents of Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Suspended Solid (TSS), as well as oils and grease in palm oil mill effluent, need to be reprocessed, in accordance with the provisions of the Ministry of Environment Regulation No. 5 of 2014, concerning Wastewater Quality Standards, before being discharged into water bodies. In this study, a modification of the treatment unit involving the integration of suspended growth and attached growth in anaerobic and aerobic processes, known as Anaerobic – Contact Stabilisation (A-CST) unit, was conducted to reduce the high concentration of organic matter in POME. This modification can shorten the detention time and reduce the land usage for treatment. The objective of this research was to analyse the performance of the modified A-CST system, based on variations in the detention time and modelling the estimation of biokinetics under unsteady-state conditions, through numerical analysis, statistical tests, and model validation. The research focused on the stabilisation unit, with variations in Hydraulic Retention Time (HRT) of 6 hours, 5 hours, and 4 hours. The results of this study revealed that, the highest percentage of removal was obtained at an HRT variation of 6 hours, with a COD 88%.