Biogas & Biomethane
The power of biochemical processes
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 is a renewable energy source composed of a mixture of gases, mainly methane (45-75%), but also contaminants, such as CO2 & 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.
Biogas in Europe and the U.S.
Europe is the largest producer of biogas today: Germany is by far the largest market, home to two-thirds of Europe’s biogas plant capacity. Energy crops were the primary choice of feedstock that underpinned the growth of Germany’s biogas industry, but policy has recently shifted more towards the use of crop residues, sequential crops, livestock waste, and the capture of methane from landfill sites. Denmark, France, Italy, and the Netherlands have actively promoted biogas production [IEA, 2023].
In the U.S., the primary pathway for biogas has been through landfill gas collection, which today accounts for nearly 90% of its biogas production. There is also growing interest in biogas production from agricultural waste, since domestic livestock markets are responsible for almost one-third of methane emissions in the U.S. (USDA, 2016). The country 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, 2023].
Almost 2/3 of biogas production in 2018 was used for electricity & heat, with an approximately equal split between electricity-only facilities and co‑generation facilities (Figure 2). And, in short, in Europe most biogas production today comes from crops; and in the U.S., from municipal wastewater (Figure 3).
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 &federal support [IEA, 2022].
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 million per biogas unit), where the (bio) gas will be produced from sugar-cane waste (vinasse & filter cake) [PH, 2022].
Brazil's biogas sector ended 2021 with nearly 700 plants, up from 670 in 2020. The country has the potential to produce up to 120mn m³/d of biogas and is on track to reach 30mn m³/d by 2030, according to Abiogas [AM, 2023].
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 & 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.
Figure 1: Biogas & biomethane production flow
Figure 2: Biogas applications
Figure 3: Biogas production by region & feedstock