Biogas & Biomethane

Biogas is a promising bioenergy alternative to be recovered from organic waste/wastewater in the context of environmental sustainability & circular economy [SD, 2022].  After biogas purification processes, methane is isolated, achieving concentrations of 90% or greater, product known as “biomethane”, an important biofuel for transportation.  Figure 1 shows biogas & biomethane production flow.

​

Biogas

  

Biogas is a renewable energy source composed of a mixture of gases, mainly methane (45-75%), but also contaminants, such as CO2 and H2S (gas composition depends on the type of feedstock & production pathway.

  

It is produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, wastewater, and food waste by anaerobic digestion of organic matter in an oxygen-free environment, a proven way & efficient method.

  

A biogas system is typically made up of a biodigester, which are airtight systems (thru the use of containers or tanks) in which organic material, diluted in water, is broken down by naturally occurring micro‑organisms.  In addition to biodigesters, landfill gas recovery systems & wastewater treatment plants are also used to produce biogas.

  

Materials & devices used in the construction of biodigesters include coats for gas-holder, piping systems (pipes, valves & accessories), and pumps.  The piping system has to be reliably gas-tight during the life-span of the biogas unit.  Galvanized steel or PVC pipes are most commonly used for this purpose.

  

Almost 2/3 of biogas production in 2018 was used to generate electricity & heat, with an approximately equal split between electricity-only facilities and co‑generation facilities (Figure 2).  In Europe, most biogas production today comes from municipal wastewater; and in the U.S., from crops (Figure 3). [IEA, 2022].

​

Biomethane

  

One possible use of biogas is in the form of biomethane, a.k.a, renewable (or sustainable) natural gas (RNG).  The methane (CH4) content of biogas typically ranges from 45% to 75% by volume, with most of the remainder being CO2.  Biomethane is obtained by upgrading biogas, which could be a major source of future growth (around 90% of today’s biomethane production is from upgrading biogas).

 

Although most of the biomethane production comes from upgrading biogas (using feedstocks described above), the gasification route to biomethane can use woody biomass (in addition to MSW & agricultural residues) as a feedstock, which consists of residues from forest management and wood processing.  Most biomethane production today is in Europe and the U.S., although these regions upgrade only a small share of their overall biogas output [IEA, 2022].

  

Only biomethane is considered suitable for use in the transport sector.  The U.S. is also leading the way globally in the use of biomethane in the transport sector, as a result of both state and federal support [IEA, 2022].

  

Takeaways

  

The rise of biogas has been shaped by two main factors: Policy support and feedstock availability [IEA, 2022].  Biogas & biomethane today account for less than 3% of total bioenergy demand, and represent an even smaller 0.3% share of total primary energy.  In Brazil, Raízen (RAIZ4) plans to build biogas units in all its sugar & alcohol plants (nearly 40) by 2030 (w/ a budget of BRL 300 mi per biogas unit), where the (bio) gas will be produced from sugar-cane waste (vinasse & filter cake) [PH, 2022].

  

Biogas & biomethane can play an important part in waste management, improving overall resource efficiency.  Where it displaces gas transported or imported over long distances, biogas and biomethane also yield energy security benefits.

  

There are also broader non‑energy considerations, such as nutrient recycling, rural job creation or reductions in the time spent in low-income communities collecting firewood.  Both biogas and biomethane can also be developed at scale thru partnerships btw energy & agricultural industries.