Anaerobic digestion of synthetic wastewater (acetate): effect of COD and C/N ratio in batch mode

This paper attempts to understand the effect of the main operating variables, find an optimized operating condition, and develop a model for biogas production from Palm Oil Mill Effluent (POME). However, POME is a complex substrate with mixed sources of carbon and nitrogen as well as other essential nutrients that makes it difficult to understand clearly how the C/N ratio and volatile fatty acid (VFA) affect the efficiency of the anaerobic digestion (AD) process. In order to clarify the effects of the main variables and be able to develop a deeper and more realistic mathematical model from focused/basic experimental data, the author chose to optimize the biogas production using a synthetic wastewater (acetate with nutrient supplements instead of POME) digested in batch mode. The effects of C/N ratio (for 10/1 to 50/1) and COD (in range of 1,000-12,000 mg/L) were studied in 1000 mL-reactors containing synthetic wastewater and inoculum (sludge of POME). The results of this study were as follows: the optimal for batch mode and COD (as acetate) was 1,000 mg/l of COD with gave %CH4 greater than 50, CH4 yield was 72.90 mg CH4/g CODremoval and 80.62% of CODremoval. The optimal C/N ratio was 30/1 with %CH4 around 35% and 44.49 of %COD removal. Moreover, all of the experiment data fitted well with both Gompertz and Monod models. Furthermore, it gave a corrected prediction of steady state performance of the biogas both qualitatively and quantitatively. In this work, a model to predict the composition of biogas production from the substrate composition was also preliminarily developed which predicted the biogas composition with a correct trend.