Kinetic study of methanization process through mathematical modeling in biochemical methane potential assays from four different inoculants

Abstract

Biochemical methane potential (BMP) and specific methanogenic activity (SMA) tests are performed to assess sludges’ ability to degrade substrates anaerobically. Traditionally, the Modified Gompertz model is applied to estimate methane production and to describe methanization kinetics. However, technical literature reports other models that can be used for these purposes and may be equally or much suitable. This work aimed to determine the BMP and SMA of four types of anaerobic sludges, conduct a kinetic study of methane production, apply six mathematical models in BMP assays, and evaluate which one best describes the methanization bioprocess. The tests were carried out in batch reactors (50 mL reaction volume) maintained at mesophilic temperature (35 °C) and under agitation (150 rpm). Glucose and a volatile fatty acids solution were used as substrates. As inoculants, sanitary sludge, brewery sludge, and two sludges from the swine wastewater treatment (SWS) were used, one of which was previously adapted to microaerobic conditions. SWS degraded the substrates more quickly and returned the highest BMP, SMA, and methane concentration values in the biogas. Thus, in studies of methane production and energy recovery, the application of SWS can be advantageous. Mathematical models that describe exponential functions, mainly the Fitzhugh model, were the most adequate to describe methane production kinetics from readily biodegradable substrates.