Biogas production from codigestion of palm oil milling effluent and cowdung: Performance evaluation and prediction modeling

Palm oil production are growing every day, by means of increasing the production but also providing more problems to the environment due to lack of waste management. In fact, Palm oil Mill Effluent (POME) are the most dangerous wastes due its highly water and soil pollution effect. Unfortunately, POME cannot be used solely as biogas substrates due its high nitrogen content. Actually, Biogas industries are mostly using Cowdung as main substrates. Cowdung associated to POME could be a solution to overcome the limitations of using POME as a unique substrate and provide a good solution to the local palm oil industries to reduce the environmental pollution. This work then aimed to determine the effect of POME-cowdung Ratios on biogas process performances (temperature, ph, pressure, volume) and to predict the usage of POME and Cowdung codigestion for palm oil industries. For this purpose the codigestion of POME and cowdung at four ratios [0:1 (control), 1:1, 1:0.5 and 0.5:1] was investigated in 20L bioreactor setup operating in batch mode. The hydraulic retention time was fixed at 25 days with an organic Loading Rate of 8 g VS/L. The codigestion process was made at a natural temperature condition (26°C-28°C). Four kinetic models (Exponential, Transference function, Logistic function and Modified Gompertz) were used and compared to predict the experimental data in this study. As results, the Ratio POME-COWDUNG 0.5:1 gave the highest biogas yield of 117.18L/kg VS, followed by the ratio 1:0.5 (61.69L/kg VS). The biogas temperature, ph and pressure were in the range 20°C to 42°C, 5 to 7.5 and 1 to 3.5 bars respectively whatever the ratio POME-cowdung. The highest methane percentage was ranging from 30.45% to 50.45% still observing with the ratio 0.5:1. The Modified Gompertz Model was the suitable one predicting the experimental data in this study with a coefficient of correlation R² closest to 1 and percent error less than 5% regardless the ratio POME-cowdung. The best ratio for codigestion for POME and cowdung is 0.5:1 followed by 1:0.5.