Below, we discuss whether biomass, biofuel, bioenergy, and biogas might be sustainable across several indicators.
Summary – Is Biomass, Biofuel, Bioenergy & Biogas Sustainable?
Overall
Biomass and bioenergy in particular are often referred to as being renewable.
However, what some of the data might show below is that although biomass derived energy sources have some sustainability features to them, they may not rate as particularly sustainable according to some other indicators.
A Note About Variation In Sustainability
The sustainability of biomass derived energy can change, depending on different variables and factors in producing and consuming energy in different geographic locations.
So, each biomass derived energy source needs to be assessed for sustainability separately.
Developments made in the bio energy industry in the future may also change sustainability ratings and outcomes of biomass derived energy.
Sustainability Of Biomass, Biofuel, Bioenergy, & Biogas Over Different Sustainability Indicators
How biomass, biofuel, bioenergy and biogas might rate across the different sustainability indicators might include:
Renewability/Scarcity
Biomass tends to be categorised as a renewable resource
It can be grown, harvested, and then re-grown again across relatively short time periods of time
Comparatively, other energy sources like fossil fuels tend to take very long time periods to form vs their consumption rate, and are considered as non renewable or scarce resources
Use Of Resources & Inputs
– How Much Resources Are Required For Production (Total Resource Use)
There’s a difference in the inputs/resources required for first generation edible food crop biomass, and later generations of biomass.
The same goes for dedicated biomass grown specifically for biomass derived applications, and biomass that is is produced as a co-product or bi-product.
But, there there can be a lot of resources required to produce dedicated biomass.
There’s the agricultural land itself (agricultural land in itself is a scarce resource, that also has an opportunity cost when it’s used for biomass over other land uses), along with water (especially irrigation), energy/fuel, and also agricultural inputs like fertilizer and pesticides.
Comparatively, second generation biomass feedstock in the form of non edible biomass like residues and waste, might have a lower resource footprint, because they come from the production of other goods or products.
Additionally, third generation biomass feedstock like algae don’t require the agricultural land like first generation feedstock does, but may need resources like water and energy for production.
So, resources required to produce biomass might be varied depending on the type of biomass.
– Efficiency Of Resource Use
theguardian.com indicates that ‘… bioenergy is an inefficient use of land [and water]’.
Also paraphrased and summarised from the rest of theguardian.com’s report:
They go on to explain how it’s inefficient, and the yield is poor, to turn the energy stored in plants and biomass (from photosynthesis) into useable energy, instead of using this biomass for other uses like food for example
They reference research that might suggest that there wouldn’t be enough plants (and therefore biomass) in production to meet the world’s total energy demand in the future.
They point out that solar converts sunlight to energy with greater efficiency and less water use than bioenergy, and provide stats that illustrate how solar PV systems can generate far more useable energy per hectare of land, and also how electric motors using solar as an energy source might be far more land efficient than internal combustion engines using biomass derived fuel
They might also indicate that fertile agricultural land might better be used for ‘food, timber, and carbon storage’, as opposed to biomass production
Pollution
– Biogas
Biogas in particular might have the ability to contribute to pollution with the use of anaerobic biodigesters
Some of this pollution may be concentrated in small or vulnerable communities
Biogas is also a by-product or co-product of some industries that might be some of the biggest polluters in the world
From vox.com:
RNG [has] local air [pollution] and water impacts [that] are concentrated in vulnerable communities
RNG exacerbates air pollution problems [because it’s chemically identical to natural gas, and] it has all the same effects when leaked or combusted
[Renewable natural gas] is reliant on a steady supply of landfills and factory farms, which produce the very sort of pollution that electrification eliminates.
Also from vox.com: ‘RNG is also produced by sources that are themselves big polluters [as] two biggest sources of biogas [in California] are landfills and manure from factory farms.’
– Biofuels
Biofuels emit air pollutants when they are burnt
Some reports indicate that they release more of some specific air pollutants compared to some fossil fuel based fuels, such as gasoline or diesel
Although, other reports indicate that biofuels have some features that help them burn cleaner
Biodiesel has significantly higher NOx emissions compared to ordinary diesel fuel because it has much more oxygen (forbes.com)
From eia.gov:
Ethanol and ethanol-gasoline mixtures burn cleaner and have higher octane levels than gasoline that does not contain ethanol, but they also have higher evaporative emissions [that contribute to ozone and smog air pollutants] from fuel tanks and dispensing equipment.
Gasoline requires extra processing to reduce evaporative emissions before blending with ethanol
[In terms of biodiesel] oxygen present in the biodiesel may improve combustion thereby reducing particulate emissions, carbon monoxide and hydrocarbon (azocleantech.com)
Environmental Degradation
However, dedicated biomass crops may have some environmental concerns common to agriculture, with erosion of agricultural land and soil being one example.
The environmental degradation effects of newer generations of biomass may not be as significant, depending on how they are sourced and produced.
Greenhouse Gas Emissions
– Understanding The Different Carbon Cycles Of Biomass vs Fossil Fuels
A difference between biomass derived energy sources and fossil fuels might be:
Fossil fuels are mined from under the ground.
Burning fossil fuels takes carbon that was stored under the ground, and releases it into the atmosphere.
Some systems like CCS may capture carbon, but might generally not be included in calculations
With biomass on the other hand, carbon dioxide starts in the atmosphere, is then absorbed by biomass, and is then released again into the atmosphere when biomass derived energy sources are converted or combusted.
So, greenhouse gases are cycled back into the air, as opposed to taking it from the ground and adding more to the atmosphere.
New biomass may then absorb CO2 again in the used biomass’ place
– Debate & Nuance Relating To Calculations & Assumptions Made About Emissions
Greenhouse gas emissions from biomass derived energy sources might be the subject of debate and nuance.
How calculations are done, and assumptions made in calculations and studies can impact the results of emissions data.
The physicsworld.com guide listed in the ‘sources’ list at the bottom of this post does a good job of explaining how the differences in calculations and assumptions can change the carbon emissions footprint of biomass derived goods and products
theguardian.com also discusses how calculations impact emissions footprint results
Our paraphrased summary of some important points from physicsworld.com include:
[Factors that can impact the CO2 footprint of biomass and biomass energy can include the type of biomass used (such as waste and residue vs dedicated biomass), how biomass is transported to biomass plants, assumptions on whether carbon is recaptured immediately by new biomass growth, whether biomass that is burned would have release carbon dioxide naturally when it rots down in nature, & other factors]
[The carbon debt payback time of different biomass feedstock types is also debated. It can depend for example on variables relating to how biomass is grown, managed and eventually processed]
[In the UK, some biomass power plants have emitted more CO2 than coal plants they’ve replaced, but, there’s also a combined heat and power generation plant in Denmark that pays back it’s carbon debt quicker, due to different feedstock, locally sourcing feedstock, and maximizing the energy produced]
From theguardian.com:
… most calculations claiming that bioenergy reduces greenhouse gas emissions relative to burning fossil fuels exclude the carbon dioxide released when biomass is burned [based …] on the assumption that this release of carbon dioxide is matched and implicitly offset by the carbon dioxide absorbed by the plants growing the biomass
Yet if those plants were going to grow anyway, simply diverting them to bioenergy does not remove any additional carbon from the atmosphere and therefore does not offset the emissions from burning that biomass.
Furthermore, when natural forests are felled to generate bioenergy or to replace the farm fields that were diverted to growing biofuels, greenhouse gas emissions go up.
– Variables In Feedstock & Production That Impact Emissions
Each calculation is different because each energy project has different variables.
From the type of feedstock used, to the energy conversion or production method used, to other factors – these variables all impact emissions footprints.
vox.com: ‘[For the use of biomethane in buildings … The carbon emissions from biomethane depend on the feedstock used and other circumstances’
From azocleantech.com:
[Whether or not ethanol as a biofuel has lower emissions than gasoline depends on the feedstock used, and the production processes used]
[Ethanol can have lower CO2 emissions per litre compared to conventional gasoline if certain crops are used, and if] bagasse is used to provide power and heat …]
[There’s also other instances where ethanol might produce less CO2 per litre compared to gasoline]
– Clearing Forests & Vegetation Can Also Impact Carbon Footprint
When forests or grassland have to be cleared to grow biomass, more carbon can be released in the process than what biomass will sequester.
Soil’s ability to store carbon may also be impacted.
… studies have found that clearing forests to grow biomass results in a carbon penalty that takes decades to recoup, so it is best if biomass is grown on previously cleared land, such as under-utilized farmland (nrel.gov)
[Clearing forests also impacts the soil and the soil’s ability to store carbon and impact the carbon cycle] (physicsworld.com)
– Emissions During Combustion/Burning
Some reports indicate that the carbon emissions from biofuels, biogas, and bioenergy might not be as low as other reports may indicate.
One report indicates that for bioenergy specifically, biomass like wood is less efficient than coal.
Also, methane has a high GWP, and biomethane may emit methane when it’s combusted.
When biofuels are burned, they emit roughly the same the amount of CO2 per unit of energy as petroleum fuels (theconversation.com)
From vox.com:
[For the use of biomethane in buildings] … the carbon emissions might not be as …] low-carbon as the industry claims …
[RNG is methane, so when it’s burnt, it’s it emits GHGs like methane]
… burning biomass directly emits a bit more carbon dioxide than fossil fuels for the same amount of generated energy (theguardian.com)
Combustion and processing efficiencies for wood are less than coal – [this means each megawatt hour of electricity produced by wood produces more CO2 than coal] (physicsworld.com)
– Emissions At Other Stages Of The Lifecycle
Apart from the combustion stage, there can be emissions at other stages of the energy lifecycle of biomass energy sources to consider.
Examples include leakages at anaerobic digesters, and also at leakages at pipelines for biomethane or RNG.
These emissions may not always be included in emissions footprint calculations.
From vox.com: ‘[For biomethane …] Anaerobic digesters … leak methane, at a rate of between 2 and 3 percent, adding to their lifecycle GHGs in a way that is rarely captured in models’
From vox.com:
[For transportation …]
Switching from diesel to [biomethane i.e. renewable natural gas] RNG [negates climate benefits because of gas pipeline leakage rates]
Even if there were no leakage, the combustion of methane in a vehicle emits carbon dioxide, carbon monoxide, and nitrogen oxides.
– General Statements On The Emission Friendliness Of Biomass Derived Energy
Several reports indicate that both biogas and bioenergy technology aren’t as effective for achieving carbon goals in some cities or regions as some other reports might claim
At the very least, they may not be a sole solution or primary solution to decarbinization
… in a temperate climate like California, RNG is not a viable alternative for decarbonizing buildings (vox.com)
[Some reports go as far to say that bioenergy isn’t carbon neutral on a timeline that is quick enough to achieve climate change goals] (physicsworld.com)
– Being Complementary/Supplementary To Other Energy Sources To Lower Carbon Footprint
In some cases RNG might be complementary or supplementary to the functions natural gas, and help lower the carbon footprint of these functions.
From vox.com:
RNG could work in the background [of some regions] to lower the carbon intensity of natural gas
– Considering The Concept Of ‘Paying Back The Carbon Debt’
physicsworld.com also discusses the concept of ‘paying back the carbon debt’ of an energy source
The more front loaded the carbon debt is for an energy project, and the more carbon intensive the energy or fuel is, the longer the carbon debt takes to pay off
So, analysing the carbon debt of biomass related energy sources might be important when comparing energy sources
– The ‘Health’ Of Different Energy Sources
Other renewable energy sources might be ‘healthier’ than RNG
[But,] The sun and wind are healthier sources of energy [than RNG] … (vox.com)
Second & Third Generation Biomass
Second and third generation biomass could increase energy yield and decrease carbon footprint, as there’s no need to cultivate crops and organic matter with them.
They could present new possibilities, and benefits and drawbacks compared to edible food and crop biomass grown as dedicated biomass
Practical, Economic & Other Considerations For Biomass Derived Energy
We’ve put together a separate guide where we discuss other considerations relating to biomass, biofuels, bioenergy, and also biogas, such as cost, performance, and practical considerations.
Sources
1. https://www.vox.com/energy-and-environment/2020/2/14/21131109/california-natural-gas-renewable-socalgas
2. https://www.azocleantech.com/article.aspx?ArticleID=337
3. https://climate.mit.edu/ask-mit/why-arent-biofuels-more-prevalent
4. https://www.theguardian.com/environment/2015/jan/29/biofuels-are-not-the-green-alternative-to-fossil-fuels-they-are-sold-as
5. https://www.nrel.gov/research/re-biomass.html
6. https://physicsworld.com/a/biomass-energy-green-or-dirty/
7. https://www.forbes.com/sites/judeclemente/2015/06/17/why-biofuels-cant-replace-oil/?sh=4daad4c1f60f
8. https://www.eia.gov/energyexplained/biofuels/biofuels-and-the-environment.php
9. https://theconversation.com/biofuels-turn-out-to-be-a-climate-mistake-heres-why-64463
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