Effect of Organic Loading Rate (OLR) on Biogas Yield Using a Single and Three-Stages Continuous Anaerobic Digestion Reactors

Abstract

The rate at which feedstock is added to the anaerobic digester (AD) reactor has to be adjusted for the growth rate of methanogens bacteria. Increase in biogas yield is as a result of improved mathanogens forming bacteria. Under loading and over loading of feedstock in the AD reactor has effect on methanogens forming bacteria. If more feedstock is added than the bacteria are able to degrade, the process will become acidic. Feedstock has to been fed to the reactor at a uniform rate and volume. If feeding pattern has to change, this must be done gradually so that bacteria can adapt to the new conditions. For optimum biogas yield, required amount of feedstock must be added to the AD reactor. The aim of this research work is to determine the effect of organic loading rate (OLR) on biogas yield from food waste, water hyacinth, cow dung, waste water from abattoir, poultry dropping and pig dung. The experimental set up comprises of single stage and three-stage continuous AD reactors. The same quantity and composition of feedstock were used and this was subjected to a variation of OLR 0.5 kg/m3(1.5 kg/m3, 2 kg/m3, 2.5 kg/m3, and 3 kg/m3). The experiment was conducted within a mesophilic temperature range of 36°C-37°C, percentage total solid (%TS) of 9.98% and percentage volatile solid (%VS) of 78%. pH meter was used to monitored the daily pH reading of the slurry. It was observed that the quantity of biogas yield from the feedstock increases with increasing organic load rate to the optimum value of 1.5 kg/m3and started decreasing above the optimum value for a single stage AD reactor but this was not the case for the three-stages continuous AD reactors that experienced continuous increase in biogas yield with a successive increase in OLR from 1-5 kg/m3-3.0 kg/m3.