The pre-acidification gas impact on upgrading the biogas produced in expanded granular sludge bed reactor

Abstract

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 pre-acidified 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 the 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 a higher temperature range has a significant impact on energy yield in a digester. One of the important findings was the amount of the PA gas injected into the EGSB reactor should be less than 50% of the theoretically calculated hydrogen gas based on ethanol substrate assumption.

Keywords:

• Upgraded biogas
• anaerobic digestion
• pre-acidification gas
• renewable energy

Acknowledgment

The authors would like to gratefully mention The Higher Committee of Education Development (HCED) for their financial help. We would like to thank the Chemical and Biochemical Engineering Dept./Missouri University of Science and Technology, Missouri State, USA for their support. Special thanks to Dr. Darrell P. Ownby and Nina Ownby for their technical editing support.

Disclosure statement

No potential conflict of interest was reported by the authors.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.