Lessons Learned from an Experimental Campaign on Promoting Energy Content of Renewable Biogas by Injecting H2 during Anaerobic Digestion

Shiplu Sarker,Sander N Wijnsma,Kristian M Lien

doi:10.3390/en13143542

Abstract

Direct injection of H2 to an anaerobic reactor enables biological fixation of CO2 into CH4 (biomethanation) and consequently boosts methane content in the produced biogas. However, there has been only a small amount of literature reporting results on this technique in a continuous reactor framework to date. To fill this gap, the present study devoted an experimental work to direct H2 addition to a fed-batch semi-continuous reactor, where the injected H2 concentration increased gradually (~3–30 mmol), spanning a moderate operational period of about 70 days. As the results revealed, the reactor continued anaerobic operation for each level of H2 dosing and produced an average methane content in the biogas ranging between 65% and 72%. The exhibited biogas upgrading trend appeared to be under-developed, and thereby suggests the need for further research.

Highlights

Fossil fuel-based energy is predicted to become obsolete in the future, given the diminishing resources and increasing population
The H2 injection strategy together with the corresponding development of H2 :CO2, biogas amount, and methane content in the biogas are displayed in Table 3, while Figures 2 and 3 illustrate the effect of
~69%, pH of 7.2, and total volatile fatty acids (VFA) of 500 mg/L corresponding to a cumulative S:I of 2.5

Summary

Introduction

Fossil fuel-based energy is predicted to become obsolete in the future, given the diminishing resources and increasing population This has led to accelerated generation of renewable energy from all available sources, e.g., wind, solar, biomass, and geothermal, among others. Employing P2G, surplus electricity produced from seasonal renewable sources can be utilized to split water via electrolysis into H2 and O2 , and subsequently H2 synthesis into methane in the presence of CO2 in a catalytic chemical reaction (the so-called “Sabatier process”) This approach, is energy intensive, less efficient (η < 80%), and characterized by a high operating temperature (250–700 ◦ C), high pressure, and the use of a catalyst (e.g., nickel) [2,3]. The bio-Sabatier process (i.e., biomethanation), mediated by archaea (i.e., a domain of single-cell microorganisms), occurs at a relatively lower temperature and normal pressure according to Equation (1) [4]:

Objectives

Methods

Results

Conclusion