Abstract
Biogas upgrading to biomethane with microbial electrosynthesis (MES) is receiving much attention due to increasing biomethane demands and surplus renewable energy. Research has demonstrated the feasibility of MES to increase methane yield by reducing CO2 in anaerobic digestion (AD). Such CO2 reduction occurs at the cathode and requires the supply of both protons and electrons. The most studied sources of protons and electrons are oxidation of organic substances and water, generated at the anode. These anodic reactions, however, also imply the production of CO2 and O2, respectively, both with negative implications for the AD process. A source of protons and electrons without CO2 and O2 as by-products would be beneficial for MES-enhanced biomethane production. This opinion article discusses the possibility of ammonium to serve as a sustainable proton and electron source.
Highlights
Anaerobic digestion (AD) produces biomethane from organic waste materials, possibly with the best carbon footprint of all biofuels, and has growing demand [1]
Anode : Electrochemical Process Oxidation of water and organics are the best-known anode reactions used in Microbial electrosynthesis (MES) [7,8,9], while using ammonium as anode p&e source has, to the best of our knowledge, not yet been investigated
The CO2 in biogas can be reduced to methane (Equation (1)) by p&e generated from ammonium oxidation
Summary
Anaerobic digestion (AD) produces biomethane from organic waste materials, possibly with the best carbon footprint of all biofuels, and has growing demand [1]. Microbial electrosynthesis (MES) is a promising technique, which has been demonstrated to enrich AD biogas up to 94% methane content [3]. In MES the oxidation of organic substances and water electrolysis reactions at the anode are known sources of protons and electrons (p&e) [7,8,9]. The types and availability of oxidable organics in the MES reactor determine the amounts of p&e that can be donated to the cathodic reaction. Higher carbon content substances, such as long-chain carboxylic acids or fats, can release more protons and electrons upon oxidation, which increases the methane production quantity, but the meStuhstaanineabicliotyn2t0e2n0,t1(2v, x/vFO%R)PrEeEmR aRiEnVsIEsWimilar since they all generate a significant fraction of2caorf b5on dioxide.
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