MATHEMATICAL MODELING OF EXISTING TWO STAGE ANAEROBIC DIGESTION PROCESS FOR PALM OIL MILL WASTEWATER

This work is an attempt to describe the dynamics of a two-stage industrial biogas plant using palm oil mill effluent (POME) and the mixture of POME with effluent from rubber factory (LTE), both at steady state and transient peroid before system failure accurred. One incident occurred in POME treatment plant when LFE bypassed its digesters and mixed together with palm-oil-mill wastewater due to no space in the existing latex wastewater ponds under water flooding during heavy raining period. The model was developed based on simplified ADM1 incorporating the effects of ALK/VFA and pH on the microbial growth. The model prediction for such scenario was in agreement with the actual data from the incident which occurred during November 2014. The Steady state simulation estimated that Ss reduced from 74,917 to 2856 mg/l at HRT 15 d which agreed well with the actual data. Dynamic simulation after adding LTE predicted that the Ss reduced to 20,300 at HRT 10.71 d which was the correct trend albeit rather imprecise. That was considered satisfactory for future operational purpose. This discrepancy was due to the difficulty in estimating many process parameters. In general the model demonstrates the usefulness of the ADM1 in describing behavior of an anaerobic wastewater treatment system from palm oil mill industry and can be used for the purpose of future design and operating of the existing plants.