Transforming Food Waste into Bioenergy

Food waste is one of the many environmental problems caused by modern agriculture. Biotechnology innovations may help us tackle it by turning waste into energy.

For decades now, bioenergy has been posited as a renewable and clean source of energy. Biomass, particularly from forestry, is the largest source of renewable energy in the UK. However, recent research suggests that forestry bioenergy isn’t always carbon neutral. Trees and plants are renewable, but burning them releases large amounts of carbon in the atmosphere at once, and growing equivalent forests takes decades, if not years. 

Therefore, to produce truly clean bioenergy, a more sustainable alternative is to use food and agriculture waste.

The food and agriculture sectors have a massive environmental footprint. It starts with the massive amounts of land and water required and the use of synthetic agrochemicals, as well as things as seemingly innocuous as methane-emitting cows. Food waste along the long supply chains contributes to further emissions. While developed countries have lower supply chain losses as compared to the developing ones, they also produce a greater amount of waste within households. Just when you think things couldn’t get any more environmentally unfriendly, as food waste decomposes in landfills it releases methane and pushes toxic metals and pathogens into the surrounding environment.

Several companies have identified food waste as a potential source of bioenergy. This helps the environment in two ways. Firstly, it takes food waste away from landfills. Secondly, it offers clean energy, reducing our dependence on fossil fuels.

Digesting food waste to produce energy

Anaerobic digesters are airtight containers that produce methane from food waste in a process that’s very similar to what happens when food waste is dumped in landfills. The four-step process is driven by a community of bacteria that thrive in the absence of oxygen and break down the organic matter into simpler molecules, including methane. 

ReFood is a British food waste recycler that uses anaerobic digestion to produce biomethane for the UK’s National Grid. Over a month-long process, bacteria convert the blended organic matter into methane. 

“All food waste streams are suitable for the ReFood process – from fruit and vegetables to meat, fish, bread, cakes, biscuits, pasta, and more,” said Philip Simpson, Commercial Director at ReFood. “We collect plate scrapings, bones, fat, gristle, out-of-date produce, processing residues, and waste beverages. Thanks to our state-of-the-art depackaging equipment, we even welcome food still in its original packaging – a hugely valuable service, especially for grocery retailers.”

Amur is another British company working in this area. In addition to running its own facilities, the firm also provides a rapid analysis of the food waste going into the process to its customers, in order to quantify the energy-producing potential for all kinds of food waste.

“All feedstocks received by the site undergo strict analysis to ensure that firstly, they are suitable for feeding and are not contaminated in any way, and secondly that the material gives good biogas yield. The material is then blended, based on its nutritional profile, into the overall feed mixture to achieve the target carbon to nitrogen ratio,” Christine Parry, Head of Development and Innovation for Amur, told me.

“We take the same approach to feedstocks as we do towards our animal feeds: ensuring that the microbes in our system receive the correct nutritional profile. Just as in a ruminant diet, you should not feed too much fat or sugar, and the protein content needs to be carefully controlled to ensure you maximize your outputs.”

Other food waste to bioenergy technologies

While anaerobic digestion works regardless of the type of food waste, it is not very efficient and generally needs industrial-scale setups for it to be economically viable. Consequently, biotech researchers and startups are advancing other technologies to transform food waste into energy.

Researchers at the National Technical University of Athens are working with microbial fuel cells to convert food waste into bioelectricity. The fuel cell contains electrogenic bacteria that consume food waste collected from local households and transform the resulting energy into an electric current.

Another approach is pyrolysis, which uses temperatures above 300°C to decompose organic matter. In a recent study, researchers at Ajou University in South Korea are studying the co-pyrolysis of food waste and wood bark as a sustainable means of producing hydrogen. Other physical techniques that are gaining traction include gasification and liquefaction.

Plant-derived biofuels have often run into the controversy of utilizing available land for producing biodiesel when the land could be used to grow food. As part of a growing trend, companies and researchers are refashioning the techniques commonly used for biofuel production, such as transesterification and alcoholic fermentation, to apply them to food waste. For instance, the high carbon content of food processing waste makes it suitable to produce biobutanol, which is used as gasoline as well as an industrial solvent.

Food-to-waste in the bioeconomy

Transforming food waste into bioenergy will play a key role in developing the bioeconomy. In the future, these technologies will likely be combined with other processes, including water purification as well as using byproducts to generate a range of other products such as feed, fertilizers, and specialty chemicals. 

For instance, ReFood uses its anaerobic digestion technology to produce a high-quality sustainable biofertilizer. “Produced from digestate, a by-product of the anaerobic digestion process, the liquid fertilizer is used by local farmers to maximize crop growth. It is rich in major plant nutrients, contains no fossil fuels, and meets the requirements of the UK for quality, consistency, and safety. The perfect alternative to more traditional chemical fertilizers,” Simpson added.

So far, there have been few studies on the bioenergy potential of food waste or even how much food waste could actually be diverted to bioenergy solutions. Since food waste deteriorates quickly, it needs to be converted into energy as soon as possible. Any delay changes the nutritional profile and, subsequently, alters the chemical composition of byproducts. Efficient waste collection methods are needed to fully capitalize on the benefits of food waste valorization.

Another approach would be to take the technology to the end-users, such as households or restaurants. Swedish biotech Biofrigas serves that niche with a biomethane unit. Jonas Stålhandske, CEO of Biofrigas, told me that “the new thing here is that the methane is purified and converted into a liquid for fuel for heavy transport.” Additionally, the unit is designed to be small enough to be used by small farms.

Just as not all biomass is equally environmentally friendly, some food waste valorization techniques are more sustainable than others. The sustainability of the technique usually depends on the actual composition of the organic matter in agriculture and food waste, as well as the targeted products. Going forward, biotech companies working in this area will need to perform a full life-cycle assessment to compare the environmental costs of each technology and come up with the best possible solutions to produce energy sustainably.

Cover image from Elena Resko