Determination of potential methane production capacity of a granular sludge from a pilot-scale upflow anaerobic sludge blanket reactor using a specific methanogenic activity test

A 450 dm³ pilot-scale upflow anaerobic sludge blanket (UASB) reactor was used for the treatment of a fermentation-based pharmaceutical wastewater. The UASB reactor performed well up to an organic loading rate (OLR) of 10.7 kg COD m^-3 d^-1 at which point 94% COD removal efficiency was achieved. This high treatment efficiency did not continue, however and the UASB reactor was then operated at lower OLRs for the remainder of the study. Specific methanogenic activity (SMA) tests were, therefore, carried out to determine the potential loading capacity of the UASB reactor. For this purpose, the SMA tests were carried out at four different initial acetate concentrations, namely 500 mg dm^-3, 1000 mg dm^-3, 1500 mg dm^-3 and 2000 mg dm^-3 so that substrate limitation could not occur. The results showed that the sludge sample taken from the UASB reactor (OLR of 6.1 kg COD m^-3 d^-1) had a potential acetoclastic methane production (PMP) rate of 72 cm³ CH₄ g^-1 VSS d^-1. When the PMP rate was compared with the actual methane production rate (AMP) of 67 cm³ CH₄ g^-1 VSS d^-1 obtained from the UASB reactor, the AMP/PMP ratio was found to be 0.94 which ensured that the UASB reactor was operated using its maximum potential acetoclastic methanogenic capacity. In order to achive higher OLRs with desired COD removal efficiencies it was recommended that the UASB reactor should be loaded with suitable OLRs pre-determined by SMA tests.