Dear Pennytodollar,

Good to see you agai, Thanks for posting.

 Let me try to clarify what RNG is.

 RNG (renewable natural gas) is produced from the upgrading (or cleaning up) of methane gas that is naturally produced by bacteria in a landfill site or a dedicated bioreactor (or digester). Basically, nature is working for us converting kitchen waste, manure, wastewater treatment sludge and all kinds of compostable waste into a methane rich biogas.

Methane is the main molecule that is found in “natural gas”. Now, natural gas is somewhat of a misnomer, because it is a fossil fuel resulting from the same digestion process at play here but in that case, it took millions of years to produce instead of a few days in the case of biogas. RNG and biogas are considered renewable because you can always produce them from the waste we produce every day rather than taking it out of the ground where it has been sitting for millions of years. (As a side note, syngas is not involved here and is something completely different, produced by a thermochemical,(high temperature, process.

 In the upgrading process, biogas is cleaned up of its contaminants to concentrate the methane: sulfur, nitrogen, VOCs, siloxanes, oxygen and, yes, CO2, although in small volumes. This upgraded biogas, referred to as renewable natural gas or RNG is fed onto the regular natural gas pipeline where it can be used indistinctly from the standard natural gas.

Regarding the CO2 that got extracted from the biogas, it is today generally rejected to the atmosphere. We could envision in the future that this CO2 could be collected in some way or another and valorized or sequestered.

So…to finally answer your question: It is true that there is production of CO2 and methane during the fermentation of organic materials. However, biogas is considered CO2 neutral, since the methane and CO2 are absorbed during plant growth. They are therefore reused. This is why biogas is considered a renewable source of energy and that its use does not contribute to the increase of greenhouse gases.

Hope That Helps

Peter