Modelling of two stage anaerobic digestion process for palm oil mill wastewater

Abstract

One accident occurred in palm oil mill effluent (POME) treatment plant when the wastewater from a latex factory bypassed its digesters and mixed together with palm-oil-mill wastewater ponds under due to shortage of space in the existing latex wastewater ponds under water flooding during heavy raining. VFA climbed up and exceeded the upper limit, causing the system failure which took around two months for system recovery. The incidence suggested that predictive models for directing the system adjustment was urgently needed. So, we decided to develop a model which was based on ADM1 to simulate a scencario similar to the incident and compared with the data obtained during that period. OpenModelica was used to implement the model and simulate the failure scenario in terms of biogas production rate, COD degradation and toxic substances occurred during the complex co-digestion process. This mathematical model was used to descrie the behaviour of two-stage anaerobic digestion process and the parameter variation which affected the efficiency in biogas production and COD reduction. Insightful understanding of kinetics of two-stage anaerobic digestion was obtained and may be used as a design bases, operation and control the system to achieve optimal performance. The results indicated that the ADM1 model could simulate biogas flow and COD degradation for various feed concentrations with extra source of substrate in the co-digestion process. The prediction of the model for such scenario was in agreement with the actual data from the incident which occurred during November 2014. Although the model prediction was rather imprecise and only gave a correc trend as what actually occured. This discrepancy was due to the difficulty in estimating many process parameters. Finally, the model demonstrated the usefulness of the ASM1 in describing behaviour of an anaerobic wastewater treatment system from palm oil mill industrial and can be used for the purpose of future design and operating the existing plant.