Every year, Britons throw away around 270,000 tonnes of food during the Christmas season. But we can use those leftover mince pies, roast vegetables and turkeys to generate a renewable form of energy: biogas. The Christmas season alone could be used to generate up to 300 gigawatt-hours. That is enough to heat 25,000 homes. It would also cut carbon dioxide emissions by 236,000 tonnes, says the UK National Grid operator.

In fact, British households, caterers, food manufacturers, retailers and wholesalers are estimated to throw away 10 million tonnes of food per year. As a result, we lose or waste approximately 30 per cent of food produced each year worldwide. What is more, each day, a 1,000-pound dairy cow produces an average of 80 pounds of manure.

Greenhouse gas emissions: Carbon dioxide vs methane

All of these types of waste release methane gas as they naturally decompose. That is a huge problem for the planet. That is because methane is a greenhouse gas that is far worse than carbon dioxide. Indeed, scientists say that methane can be 90 times worse for global warming than carbon dioxide over 20 years.

Exploiting this naturally produced fuel could be part of the solution to tackle climate change. Capturing gases produced by decomposing organic material is a renewable form of energy. But, critics say that it is also part of the problem. That is because using biogas will continue to heat up the planet. This article explores many of the issues surrounding this fuel.

What is biogas?

Biogas is a type of fuel. It is released when bacteria naturally break down dead organic matter, otherwise known as biomass. Biomass can decompose naturally or at an industrial scale in an anaerobic digester. In that sense, biomass is the raw material, and biogas is the end product. It can also be known as bio-methane, marsh gas, sewer gas, compost gas and swamp gas in the United States. The gas occurs naturally and is a renewable source of energy because it comes from breaking down organic waste.

Biogas consists mostly of methane and carbon dioxide. It can also include small amounts of hydrogen sulphide, siloxanes and some moisture. The mixture varies depending on the composition of the biomass that is decomposing. 

Inside a biogas plant in Alberta, Canada

Inside the Himark biogas plant in Alberta, Canada

Biogas production: Anaerobic digestion

We produce biogas by allowing dead organic materials, such as plant, animal and human waste, to decompose naturally or in an industrial unit. At a special plant, bacteria break down the organic waste materials in a process called anaerobic digestion. The resulting gas is used as energy or as a raw material for other products. We can use organic materials, such as human food waste, landfill waste, animal manure, dead plant material and even sewage, in biogas plants.

There are 118 biogas plants currently operating in the UK. The country built its first plant in 2011. In 2020, Biocow in Somerset, England, became the first to feed its biomethane into the national gas network.

Australia’s capacity to produce biogas

The industry is also emerging slowly in Australia. In 2016-2017, electricity generation from biogas was about 1,200-gigawatt hours, or 0.5 per cent of total electricity generated. The government estimates that up to 90,000 biogas producing plants could be built in the country.

In the US, there are currently 2,200 sites. China, however, is the world’s largest producer of biogas. An estimated 50 million Chinese households use the fuel, mostly in rural areas, using small-scale home and village plants. 

Potential for biogas

Some say that biogas’ potential is huge. 103 trillion kilowatt-hours of electricity could be produced each year through this renewable energy source, some claim. Moreover, capturing the emissions from all the waste would be equivalent to removing an estimated 117 million passenger vehicles from the road.

Australia has the potential to remove around nine million tonnes of carbon dioxide emissions every year. The country’s renewable energy department says that its potential is around 103 terawatt-hours of energy. This is the same as the current biogas production in Germany.

New York’s approach to mitigating greenhouse gas emissions

New York, for example, generates around 13 million tonnes of waste each year. The city spends almost USD $400 million per year just moving that waste – by rail, barge or trucks – to incinerators or landfills. All of this generates even more carbon dioxide. However, treating that waste by turning it into biogas instead could save emissions and create a sustainable energy supply.

But, there are concerns that increasing demand for biogas is encouraging farmers to grow corn destined for such plants. Some plants use specially grown biomass material rather than waste. There may not be enough waste in the world to generate sufficiently large amounts of biogas to replace fossil fuels.

What are biogas’ uses?

Biogas has a lot of uses. It can heat buildings and homes or even the processing plant itself. It can also generate electricity using a combustion engine, fuel cell or gas turbine. In that sense, it works like any other type of fossil fuel or renewable energy source.

It can also be a replacement for natural gas. From there, it can be a fuel for vehicles, used for cooking and heating up homes, or deployed as a raw material to produce products like plastics. However, it is important to note that biogas is not exactly the same as natural gas. It can just be purified and upgraded to resemble natural gas. 

The creation of biogas also leaves liquid and solid organic materials behind. The liquid form is a highly nutritious material that can be a plant fertiliser. Left-over solids are frequently used as compost with minimal processing.

For example, a dairy farm in Indiana, US, produces 1.2 million cubic feet of biogas each day using manure from its 9,000 dairy cows. The company turns some of it into compressed natural gas (CNG) and uses it to power its transport for delivering milk. This way, it reduces its use of diesel fuel by 1.5 million gallons per year.

In Australia, home biogas systems and appliances are becoming increasingly popular. The technology is particularly used within its relatively large farming sector.

Furthermore, in 2020, Australia built its first biomethane-to-gas project. The project uses wastewater from Sydney’s Malabar treatment plant to power thousands of homes and businesses in New South Wales.

Biogas plant in Alberta, Canada

Himark Biogas plant in Alberta, Canada

What are the benefits and problems associated with biogas?

Benefits of biogas

The benefits of biogas are clear. As already mentioned, an estimated 10 million tonnes of food waste is produced each year in the UK alone. This food waste alone could heat up 830,000 homes each year if turned into biogas at industrial plants. It would also cut emissions by 8.8 million tonnes of CO2 equivalent greenhouse gases, says the national electricity grid operator. If this were to be replicated worldwide, the impact could be enormous. 

Other types of organic materials, such as animal and plant waste material, can also produce biogas. It saves us from sending that material to landfills. 

Biogas can also be a replacement for natural gas – a fossil fuel that is harmful to the planet. The production of natural gas also emits methane, which heats up the atmosphere. Using biogas as a substitute would cut these emissions.

Problems with biogas

While biogas is a useful technology, many warn against relying excessively on it as a solution to the climate crisis. The most obvious problem with biogas is that it contains high concentrations of methane, and burning it releases carbon dioxide into the air. In other words, biogas is not emissions-free, like solar and wind energy, for example. Countries should be moving away from natural gas heating and cooking, and looking towards electricity-based appliances. However, using biogas allows people to carry on using gas instead of cleaner electricity options

Renewable energy or food waste?

One big criticism is that growing demand is incentivising farmers to grow foods, especially for biomass. In Britain, corn for biogas plants grows across thousands of hectares of land. Subsidies are creating a similar problem in Germany. The Guardian’s George Monbiot says that the demand for this renewable energy is creating incentives for the industry to trash the food supply and the soil, all in the name of protecting the planet.

Biogas can be part of the solution when it is just used to naturally treat organic waste. But, turning it into a large industry as a solution to global warming can cause more harm than intended.