Effect of Substrate and Granules/Inocula Sizes on Biochemical Methane Potential and Methane Kinetics

Abstract

This study aimed to evaluate the Biochemical Methane Potential (BMP) of different types of wastewaters and sizes of granules. The granules (CS: from a cassava, SS: a seafood, and PS: a palm oil factory) and wastewaters initial Chemical Oxygen Demand (COD) were 18,800, 4,200 and 100,000 mg/l respectively). Modified Gompertz equation was used to compare the data from the experiments. Wastewater from a cassava factory gave the highest BMP when used with only granules from its own source (CS). Wastewater from seafood factory had the highest nitrogen content thus, represented the most imbalance nutrient source. In this case, mix- granules (SS+CS) gave highest BMP. Palm oil mill effluent did not match COD: N ratio criterion and had too high COD level which caused substrate inhibition. Here the mix-granules (PS+CS) gave highest BMP. In general, the larger granule size and the nutrient balance could improve the efficiency and hence increase the biogas production rate. The initial COD or different substrate has a strong effect on BMP and the maximum specific methane rates whereas the different sizes of granule have an effect on the length of lag phase period. In most cases, it was sufficient to represent the experimental data with traditional modified Gompertz equation and Monod models.