(568b) The Pre-Acidification Gas Impact on Upgrading the Biogas Produced in Expanded Granular Sludge Bed Reactor

Two-stage anaerobic reactors are being widely used in the organic waste management industry. In these reactors, up to one-third of the chemical oxygen demand (COD) content is naturally preacidified in a first stage pre-acidification (PA) and then fed to a second stage digester for conversion to methane. Traditionally, all the generated gases from the PA tank will be vented to the atmosphere. Hydrogen and carbon dioxide are the main gases generated in the PA tank. A pilot scale of two-stage anaerobic expanded granular sludge bed reactor was fabricated and used to investigate the impact of the PA gas injection into the second stage. The gas from the PA reactor was captured and stored in storage tank. The tests were run under two temperature ranges and five organic loading rates (~2, 3, 4, 5, and 6 g COD/L.day). For mesophilic range, the biogas production and energy yield increased by 10-90% and 40-130%, respectively, from without PA gas injection case compared to with PA injection case. For thermophilic range, the biogas production and energy yield increased by 12-40% and 90-140%, respectively, from without PA gas injection compared

to with PA injection case. For each OLR, the gas production and energy yield were 90 to 160% more in thermophilic range than the mesophilic range for the cases with and without the PA gas injection. This implies that higher temperature range has a significant impact on energy yield in a digester. One of the important finding was the amount of the PA gas injected into the EGSB reactor should be less than 50% of the theoretical calculated hydrogen gas based on ethanol substrate assumption.