Biogas has been used as an energy source for centuries, to warm bathwater or light streetlamps, for example. But it is our slate of 21st-century socioenvironmental challenges that have sparked greater interest in biogas production and technology — especially the conversion of waste into biogas.
Organic waste disposal, a huge problem due to modern society’s soaring consumption patterns, could prove to be both an attractive and low-cost renewable alternative energy source and solution.
In fact, biogas systems may potentially meet a variety of energy needs worldwide, while reducing waste streams and providing biofertiliser as a by-product.
Some analysts now even suggest this win-win form of bioenergy could make a significant contribution to achieving the UN’s 17 Sustainable Development Goals, and also help nations hit their emissions targets under the Paris climate agreement.
What is a biodigester?
Anaerobic digesters, or biodigesters, produce biogas much like the human digestion system.
When biodigesters are fed organic material — food waste, agricultural residues, and animal or human manure — it is decomposed by microorganisms in the absence of oxygen and turned into biogas, which can then be used for heating, cooking, transportation and other needs.
Biodigesters can be designed in small, medium or large sizes to suit domestic, industrial or municipal uses.
Biogas produced from waste (also known as renewable natural gas) contains a mixture of gases, mostly carbon dioxide and combustible methane — both of which are potent greenhouse gases (GHG).
But waste conversion technologies capture GHG emissions that would otherwise be released into the atmosphere, and instead put them to work, saving energy. Biogas, as a result, can accomplish significant emission reductions, according to a 2018 World Resource Institute (WRI) paper.
Importantly, however, this form of bioenergy only generates climate benefits if it comes from waste and if it effectively reduces net methane emissions and replaces the use of fossil fuels.
The adoption of this innovative technology is increasingly showing promising results in urban and rural settings across the Global North and South, despite obstacles to the sector’s growth.
Global biogas production increased about 4 per cent per year between 2010 and 2018, which means the sector has grown approximately 40 per cent in the last decade.
There are currently more than 130,000 small-, medium- and large-scale biodigesters operating worldwide, mostly in Europe, China and the United States. Although biogas consumption only represents 0.3 per cent of the global energy mix today, that figure is projected to more than double by 2040.
Domestic biogas systems
It’s estimated that 3 billion people, 40 per cent of the world’s population, lack access to clean fuels for cooking. Likewise, 2.4 billion people, or one-third of the world, lack access to sanitation and waste management facilities, especially in poor and remote areas.
Small-scale biogas technology could help service these needs, enabling households to produce clean cooking gas — replacing wood, charcoal and coal — while sustainably managing domestic organic waste.
HomeBiogas is a company created with that purpose. Founded in 2012 by three Israelis, the firm first tested a domestic biogas system in underserved Bedouin and Palestinian households. Today, an upgraded, field-tested version of the system, packaged to include a biodigester and biogas stove, has been installed in homes in more than 90 countries.
A HomeBiogas biodigester converts food scraps, animal manure and/or human waste into biogas sufficient for up to two hours of household cooking per day. The smallest version costs $749 and can meet the cooking gas needs of a small family of two or three.
For Samuel Alexander, an Australian who has used a domestic biodigester for more than three years, the technology enabled his family to disconnect from the gas grid, reducing their energy expenses and environmental footprint. “It still amazes me to this day that we’re cooking our meals on gas produced from food waste,” he remarked.
HomeBiogas claims that each household system installed avoids about 6 tonnes of carbon dioxide emissions annually — approximately the yearly emissions of a typical passenger vehicle.
While the company has not commented on how it calculates this, analysts say the big benefit of domestic biogas systems isn’t only emission cuts.
“Adding up all these biodigesters [currently in use by households], perhaps the carbon reduction is not so great, but it can lead to a better quality of life for rural or marginalised populations,” says Leidiane Ferronato Mariani, a Ph.D. in energy systems planning with a focus on biogas from the University of Campinas, Brazil.
Domestic biodigesters do generate significant socioeconomic benefits, agrees Mariani, who is also affiliated with the Network for Biodigesters in Latin America and the Caribbean (RedBioLAC).
One example: the “brushland biodigesters” made by the NGO Diaconia and used in rural Brazil. The technology has enabled families in that nation’s semiarid northeast region — an area with low levels of development and high levels of poverty — to become self-sufficient in clean fuel for cooking and to cut gas expenses (about 10 per cent of monthly minimum wages).
Domestic biogas systems offer a clean alternative to dirty fuels traditionally used for cooking, including wood, charcoal or liquefied petroleum gas (LPG). The switch can reduce deforestation and GHG emissions, while improving health, by reducing inhalation of dangerous kitchen smoke, according to WWF.
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Because mains gas [in many areas] is almost always already connected [to homes]. People sometimes just choose the easiest path, even if it isn’t the cheapest or most sustainable.
Samuel Alexander, lecturer, University of Melbourne
A Nepali study found that household biogas use, besides contributing to reductions in forest cover loss, allowed users to save time and devote themselves to important tasks other than collecting firewood, such as agriculture and education.
However, results vary, as optimal biogas production depends on optimal conditions, including the type, frequency and amount of waste fed into a biodigester.
“Some households may not be able to produce a lot of gas from their own food waste,” Alexander notes. In his case, he relies on two neighbors who contribute their food waste to produce enough gas for his family’s cooking needs. And it’s also more work: “Compared to turning on the mains gas, there are slightly more things to do with biogas; collect waste, feed the unit and disperse the output liquids a few times a week,” he explained.
Climate also limits biogas efficiency, as anaerobic digestion requires temperatures higher than 20° Celsius (68° Fahrenheit).
Alexander, who lives in the subtropics, built a greenhouse around his biodigester to keep it warmer. “For about 8 months of the year we can cook every day on the system, often twice,” he said. “In winter, we cook on it three or four times a week. On occasions when there is no biogas, we use our electric stove.”
Considering the many benefits, the question arises as to why biogas hasn’t been widely adopted worldwide. Alexander, a lecturer at the University of Melbourne’s Office for Environmental Programs, suggests why: “Because mains gas [in many areas] is almost always already connected [to homes]. People sometimes just choose the easiest path, even if it isn’t the cheapest or most sustainable.”
Unsupportive government policies are another problem. Where regulations favor biogas development, it is more frequently utilised.
In Brazil, for example, municipal schools are a major user of biodigesters. That’s because municipal secretaries back the technology through financial incentives as part of environmental education programs, said Giovanna Faifer, a spokesperson from BioMovement, a Brazilian HomeBiogas distributor.
Urban residents interested in sustainability also form a large part of the firm’s clientele, Faifer says. Other customers include companies, hotels, hospitals, and kennels (which also appreciate the biofertilizer byproduct). But, she adds, national legislation to encourage biogas use is still lacking in Brazil, which is slowing expansion.
Agricultural biogas systems
Food production generates 26 per cent of global GHG emissions. However, about 1.3 billion tonnes, or one-third of all food produced, is lost or wasted globally, every year. This not only increases GHG emissions, but also wastes resources, including water, energy and fertilizer. Biogas technology can reduce this sector’s environmental footprint, while benefiting farmers and consumers.
Sistema.bio is a social enterprise engaged in that mission. Founded in 2010 in Mexico, the company’s biodigesters are already installed on more than 17,000 farms on five continents.
The firm works with medium-sized, small and subsistence farmers, said Sistema.bio communications director Xunaxi Cruz. To make the technology accessible to lower income farmers, and promote wide-scale adoption, the company partners with grant makers including governments, NGOs and foundations.
Sistema.bio’s biodigesters, which are bigger than domestic versions, are currently used most on livestock farms to process manure and power farm activities. The firm estimates that its technology has already contributed to the treatment of more than 13 million tonnes of agricultural waste and the mitigation of more than 250,000 tonnes of CO2 emissions.
According to researcher Mariani from RedBioLAC, biodigesters installed on farms can significantly reduce emissions from intensive agricultural processes. That’s especially true with livestock operations, as animal manure emits large amounts of methane, a powerful greenhouse gas.
But it’s not just environmental gains. Biogas technology helps promote energy and economic resilience on farms, suggests the US Environmental Protection Agency. Sistema.bio’s Cruz says that farmers using the company’s system save money on both energy and agricultural inputs, and some have even achieved economic security.
As a bonus, biodigesters produce “digestate” as by-product, a biofertiliser suitable for organic farming. Rich in macro- and micronutrients, including nitrogen, phosphorus and potassium, this biofertilizer can be used in agriculture as an alternative to synthetic petrochemical fertilisers, which are costly and energy intensive to make. Its use generally increases soil fertility and crop yields, and contributes to soil carbon sequestration.
However, digestate should go through an aerobic composting process before being used on crops, advises the Zero Waste International Alliance. Otherwise, if applied directly to the soil, it may release fugitive emissions of methane and ammonia, and leak nitrogen, which can undermine the system’s environmental benefits.
Although biodigesters don’t require advanced technical skills to operate, they do require responsible management to avoid gas leakage — key because leaks increase GHG emissions.
To ensure farmers use biodigesters responsibly, Sistema.bio begins by assessing which system is best for a particular farm. “It’s the same technology, but we have 11 sizes,” Cruz said. “It depends on the energy demand the farmer has, the quantity of waste [they produce] and how to make this balance.”
The biogas sector is improving efficiency, Mariani adds, making equipment easier to install and operate. This comes with the challenge of making scientific and technological knowledge more accessible and adapted to varied decision-makers, she explains.
“In different countries, the level of understanding about biogas is very different,” Cruz says. In India and Kenya, for example, there’s a high level of public awareness of biogas technology benefits, along with government implementation incentives. Whereas in Latin America, biogas is a lesser-known energy source compared to solar and wind. Much work needs to be done to create widespread awareness and demand. “Even though we started in Mexico, we are growing faster in other regions of the world,” Cruz explains.
Municipal biogas systems
Globally, more than 2 billion tonnes of municipal solid waste is generated annually, and at least 33 per cent is not safely managed, with today’s cities facing environmental and socioeconomic problems due to waste accumulation in landfills.
Landfills, besides leaching toxins into groundwater, release vast amounts of methane as organic waste decomposes — methane is 25 times more potent as a greenhouse gas than carbon dioxide.
This troublesome municipal waste could be transformed into a valuable energy resource using biogas technology.
This is “a great example of circular economy,” says Ole Hvelplund, CEO of Nature Energy. Nature Energy operates 11 biogas plants in Denmark and two abroad, and is one of the largest producers of this type of bioenergy in Europe.
“Nature Energy takes in biological waste and residues from different parts of [Danish] society, including industry, agriculture and households,” Hvelplund explained. “In this way we ensure a cost-effective, large production of biogas.”
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In Europe, for example, there are subsidy programs for generating electricity from biogas, precisely because it has a smaller carbon footprint than other sources.
Leidiane Ferronato Mariani, Ph.D. researcher, University of Campinas, Brazil
Biogas made from waste is upgraded to biomethane, which is then injected into the national gas grid, powering households, industry and vehicles. The company estimates that its annual production is now sufficient to heat 57,000 homes or fuel 8,000 trucks traveling 50,000 kilometres (30,000 miles) annually.
Nature Energy says it is responsible for a 4-million-tonne reduction in organic waste annually, and a reduction of more than 290,000 metric tonnes of CO2 emissions.
According to Mariani, life-cycle assessment studies indicate that the carbon footprint or emission factor for biogas is smaller than that of other energy sources (both nonrenewable and renewable). “In Europe, for example, there are subsidy programs for generating electricity from biogas, precisely because it has a smaller carbon footprint than other sources,” she said.
“One slight operational concern may be methane leaks from storage or piping,” said Enzo Favoino, a researcher at Scuola Agraria del Parco di Monza, Italy, and scientific coordinator for Zero Waste Europe (ZWE). So biogas plants must be properly designed and operated by utilities to ensure no GHGs escapes into the atmosphere, he explained.
Public officials must also oversee these plants to ensure that leaks are rapidly fixed; otherwise, leakage could undermine the climate benefits of this energy system.
Biomethane has a smaller environmental footprint than fossil fuels and other biofuels, including ethanol, traditionally used in transport. The International Energy Agency (IEA) reports that biogas-to-biomethane can contribute to the decarbonisation of the transport industry, which accounts for one-fifth of global CO2 emissions.
“Especially when it comes to heavy transport vehicles [such as trucks, buses and airplanes] and energy-intensive industry, biogas is considered one of the best CO2 neutral alternatives to fossil fuels like diesel and natural gas,” Hvelplund says. And it is cost-competitive to other transport fuels.
Another advantage: biogas can be stored and distributed over long distances through existing natural gas pipelines, making the shift from reliance on fossil fuels, including nonrenewable natural gas, easier. Nature Energy, in fact, recently started supplying biomethane to Shell Energy Europe, one of the world’s largest fossil fuel companies.
While biogas has many socioenvironmental and economic advantages, even compared to other renewable energy sources, it should not be pursued as a sole solution, experts caution. “We need to add all these [renewable] sources to have a sustainable energy mix and ensure inclusive access to energy,” Mariani says. The urgency of the climate crisis requires the pursuit of multiple decarbonisation routes.
“In Denmark, the climate target is to reduce the country’s CO2 emissions by 70 per cent in 2030 compared to 1990,” Hvelplund said. “Here, biogas is considered one of the key technologies to achieve this target, and we assess that biogas can play a vital role for other countries as well.”
Challenges ahead
Despite its potential, biogas and biomethane made from waste currently represent less than 1 per cent of the global energy mix. The sector is facing growth challenges, especially due to limiting government policies.
A key growth obstacle, Mariani says, is the lack of “a more harmonised agenda between government agencies and sector representatives.” Because biogas can be produced at different scales and for varied uses, regulatory processes are often complex and conflicting. Government incentives should also be better planned, she adds, to encourage not just production and use of biogas or biomethane, but innovative technological development as well.
ZWE’s Favoino says subsidies provided to grow crops used in biogas production should be discouraged. That’s because these subsidies could spur a switch to “energy crops,” rather than to the conversion of waste into biogas, creating more problems than it solves. WRI emphasises that biogas must be produced from waste to generate climate benefits.
Analysts believe biogas will play an important role over coming decades. It can, they say, also help create green jobs. In India, for example, 85,000 people are already employed in the sector.
The World Biogas Association (WBA) was formed to ensure policymakers are aware of the sustainable potential of this renewable energy source. The London-headquartered group intends to build momentum in the run-up to COP26, the UN climate summit in November.
“Our aim is to ensure countries integrate biogas into their Nationally Determined Contributions to the Paris Agreement,” said WBA spokesperson Jocelyne Bia.
This story was published with permission from Mongabay.com.
