Although there is already a wide application of biogas technologies around the world, the industry is still in the early stages of development. This article, based on the World Biogas Association (WBA)’s report Global Potential of Biogas, draws attention to the capabilities presented by the use of biogas technologies and actions needed to achieve the best results.
According to the WBA’s report, the industry is already leading in reducing greenhouse gas (GHG) emissions by capturing the methane that would otherwise have entered the atmosphere from rotting food waste, sewage, farm wastes and agri-industrial process wastes. Capturing this methane and transforming it into electricity, heat or fuel are processes that have matured and are rolled out in many countries on both a small and large scale. However, there is even more potential for it to absorb uncontrolled GHGs as well as reduce reliance on fossil fuels to produce energy.
The report states that the biogas industry is currently capturing approximately 2% of the global potential. While making these contributions, the biogas industry can also help provide food security, manage waste, protect water bodies, restore soil health, improve air quality, promote health and sanitation as well as provide employment.
The biogas industry can be analysed in three broad categories: micro digesters using biogas, scale digesters generating electricity, and scale digesters producing biomethane.
Micro digesters play an important role in rural areas, where they are an integral part of farming, waste management and energy security. There are close to 50 million microscale digesters operating around the globe with 42 million operating in China and another 4.9 million in India. 700,000 biogas plants are estimated to have been installed in the rest of Asia, Africa and South America. Biogas is a form of micro-scale digesters is most often used in stoves for cooking or heating, displacing solid, high emission fuels like firewood and charcoal.
Scale digesters generating electricity: Generation of electricity from biogas is an established technology, widely implemented around the globe. This is most commonly done with a combined heat and power (CHP) engine. A CHP engine can be linked to any operating anaerobic digester. Operators of biogas plants are trying to maximise efficiency and income streams by increasing the utilisation of heat. There is also a growing interest in trigeneration, which generates electricity, heat, and cooling when needed. It is estimated that there is a total of around 132,000 small-, medium- or large-scale digesters operating in the world. The biogas industry is growing globally. IRENA statistics on global electricity generation from biogas show that it has grown from 46,108GWh in 2010 to 87,500GWh in 2016. That is 90% growth in just six years.
Medium to large scale digesters producing biomethane: Upgrading of biogas to biomethane is a relatively new but now proven technology. While some plants upgrade biogas to be used as vehicle fuel, others inject it into the local or national grids. Plants are also beginning to capture CO2 to be used in greenhouses and the food and drinks industry. There are over 540 upgrading plants operating in Europe, about 50 in the US, 25 in China, 20 in Canada, and a few in Japan, South Korea, Brazil and India. Based on available data, it is estimated that there are 700 plants that upgrade from biogas to biomethane globally.
Having presented a picture of the industry as it stands at present, WBA’s report looks at the potential contribution that the anaerobic digestion technology can give to energy and food security and GHG abatement at a global level, first by feedstock and then collectively.
Livestock manure: some key findings
If all ‘available’ livestock manure from cattle, buffaloes, pigs and chickens were to be collected and anaerobically digested, it has the potential to generate 2,600 to 3,800TWh of energy globally, which can be used in the form of electricity and heat. It can meet the electricity demand of 330 to 490 million people. If upgraded to biomethane, there is a potential for 250 to 370bcm biomethane to meet the natural gas demand of China and India combined. The energy generated from the treated livestock manure has the potential to meet 100% of the energy needs of world agriculture: 2,400TWh including electricity, coal, fuel oil, liquefied petroleum gas, motor gasoline, gas-diesel oil, and energy for power irrigation. It can contribute significantly to the energy security of farms, which are often off the grid.
To achieve the potential held in livestock manure as a biogas feedstock, government should mandate digestion of slurry for farms over a certain size. Also, incentivise energy generation and use from livestock manure via targeted policies such as specific rural schemes in developing countries for micro-scale digestion that result in energy security and independence, reduced use of solid fuels for domestic cooking and heating, and reduced deforestation. It will be essential to include operation and maintenance training, health and safety training, regular maintenance and safety checks, and specifically include women in the economy of managing animal manures.
Sewage: some key findings
If all available sewage generated by the entire world population is collected and treated via anaerobic digestion, there is a potential to generate 210 to 300TWh of energy, which can be utilised as heat and electricity or 22 to 32bcm biomethane. The electricity can meet the needs of 27 to 38 million people around the globe or the natural gas needs of Ukraine.
Anaerobic digestion of sewage generated by people can mitigate 75 to 100Mt CO2 eq. of GHG per annum, equivalent to the emissions of Israel. If all sewage is collected and all sludge digested it could produce enough to provide fertilisers for 30 million hectares of arable land replacing about 0.4 to 3% of global inorganic fertiliser used. However, to achieve this potential, much work lies ahead in terms of policy to ensure the availability of sanitation facilities for all and building centralised sewage collection and treatment infrastructure. Connecting decentralised sanitation facilities or community toilets to micro- or small-scale digesters must be a priority and promotion of anaerobic digestion of sewage sludge as the preferred method of treatment.
Food waste/loss: some key findings
If ‘all available’ food waste/loss were to be collected and recycled via anaerobic digestion, there is a potential to generate 880 to 1,100TWh of energy, which can be utilised as electricity and heat. The electricity generated can meet the electricity needs of 112 to 135 million people. If upgraded into biomethane, the 85 to 100bcm biomethane generated can replace the natural gas consumed by Germany.
To achieve this potential, awareness among individuals on the ill-effects of food wastage and how they can prevent it must be raised. Local governments of cities over a certain population should be required to provide separate food waste collection facilities to citizens. Implementing regulations, standards and certifications for safe trading and use of digestate will add to making food waste an energy resource.
Energy crops: a key finding
If energy crops were grown effectively and sustainably on 7% of agricultural land, as a part of annual, double, cover and rotational cropping schemes, there is a potential to generate 3,350 to 5,000TWh of energy, which can be utilised as heat and electricity, equivalent to the electricity consumed in India.
Crop residues: some key findings
This waste stream has a high untapped potential for energy generation and GHG mitigation. Using all sustainably recoverable residues from the current global production of crops suitable for anaerobic digestion – rice, wheat, maize, rye, barley, oats, rapeseed, sugar beets, sugarcane, and sorghum – there is a potential to generate 3,080 to 3,920TWh or 300 to 380bcm biomethane per year. It takes into account ploughing in and diversion of a part of the residues to feeding animals.
In conclusion, the application of biogas has the benefit of displacing fossil fuel-based energy with low carbon, renewable energy and also abatement of GHG emissions. The report assumes that all conditions of sustainable recovery and growth discussed with regard to each feedstock are met and all feedstock then made available is used via anaerobic digestion.
The WBA is a non-profit association dedicated to the development of biogas globally. The Global Potential of Biogas report’s lead author is Dr Sarika Jain and contributors are David Newman, Ange Nzihou, Harmen Dekker, Pharoah Le Feuvre, Hannah Richter, Frederic Gobe, Charlotte Morton, and Rebecca Thompson.