Waste to energy

When waste is mentioned in regards to the coffee industry, many people think of discarded paper cups or used coffee grounds. Multiple programs and research projects worldwide have looked into how to reduce or recycle waste at consumer level. But waste occurs at all stages of the coffee supply chain. One form of waste that occurs at origin is water waste from cleaning and processing coffee beans. Dr. Claudio Avignone-Rossa, a Reader in Systems Microbiology at the University of Surrey in the United Kingdom, says that economically disadvantaged farmers in Colombia often have no choice but to return this waste water to larger water sources. This can cause serious environmental issues. “[Waste water] is a real pollutant. The level of oxygen in the water is decreased because of the organic matter carried over from washing coffee beans. This contributes to contamination, pollution, and bad smells as the organic matter rots,” he says. Avignone-Rossa’s team at the University of Surrey has partnered with Colombian researchers, including Dr. Lina Agudelo-Escobar from the University of Antioquia in Medellín, to develop a microbial fuel cell that could not only purify waste water, but generate energy too. A fuel cell is a device that can be continually fed with compounds that react and produce electricity. Chemical fuel cells, commonly found in trucks, buses, and other vehicles, use a chemical reaction to convert its feedstock, usually hydrogen, into energy. A microbial fuel cell, however, uses microbes, single-celled organisms such as bacteria, to convert its feedstock into electricity. “The idea was to utilise, or at least to test, if the waste coming from [this stage of] the coffee industry could be used to produce electricity. Our preliminary results have shown that it is possible,” Avignone-Rossa says. The University of Surrey project began when it received a grant from the UK-based Engineering and Physical Sciences Research Council, set up as an initiative for the sustainable generation of energy. “With my colleagues, we led a consortium of six universities in the UK devoted to developing microbial fuel cells which exploit the metabolic activity of microorganisms such as bacteria and fungi to degrade organic matter and produce electricity. One of the most organic-matter-rich feedstocks that you can find is waste water.” The possibility of partnering with Colombian scientists emerged when Agudelo-Escobar joined the Surrey lab for a six-month placement. “We decided ‘well, they have a lot of coffee there and we have knowledge of microbial cells, so why not combine those ideas into one?’” Avignone-Rossa says. The microbial fuel cell exploits the metabolic activity of bacteria to degrade organic matter and produce electricity. “There are some bacteria that are able to take electrons from organic matter and transfer those to an electrode. If you make these electrons circulate through a circuit, you get an electric current,” Avignone-Rossa says. “For a complex feedstock such as coffee waste water, one species of microbial bacteria is not enough to break down all its different elements. You need a consortium of microbes, so we went to different natural and artificial sources to find microbial communities, and tested them in our microbial cells.” Bacteria consume the organic matter and extract its energy to survive and grow. However, instead of the energy being used to grow the bacteria, it is collected by an electrode in the fuel cell. Following a successful laboratory-scale experiment, Avignone-Rossa says the team began work on how a larger scale system could be implemented at the farm level. “We are still in early stages of development. We need to do more tests and analysis to determine if this can be scaled up to match levels of production,” he says. “We were fortunate to receive a small grant from one of the research councils in the UK to try to use low cost materials to build these fuel cells.” Avignone-Rossa says one of the key considerations when scaling up the fuel cell is how the device could be constructed without lab equipment or expensive materials. “When we visited farms in Colombia, we identified a large number of materials that were just thrown away or discarded,” he says. “[The fuel cell] has to be something that anyone can build or repair, so we are using materials such as cardboard boxes, terracotta, and clay. “The goal is to be able to give the farmer a plan that they can follow to build [the fuel cell] very easily because it has nothing complex in it.” Although the electricity the fuel cell generates would not be sufficient to power a whole farm, Avignone-Rossa says it could at least provide light where there previously was none. “The electricity could also be used to power monitoring devices to track the state of the process. These monitors would not need a huge amount of energy, but it is still electricity that farmers would have to pay for, so it would help the cost of the farms to go down,” he says. “It could also continuously charge, so the farmers have access to reserve electricity if they need it.” Avignone-Rossa hopes that once the microbial cells are ready to be used on a wide scope, the units will be beneficial to not just the farmers but the wider community. “That waste water will come out much cleaner, and have a lower impact on the water bodies like streams, rivers, and lakes, which are being used to dump the water,” he says. “It will also help the farmer to set up a sustainable system for water that can continue to be used by the younger generation.” In November, the research project was awarded the UK-Colombia Newton Prize 2018. The prize recognises and funds UK research and innovation that supports Newton Fund partner countries, including nations in South America, Asia, and Africa. “We are very happy with this outcome as it will give support to our project and ideas, and will allow us to start building the prototype for installation in a farm in Colombia,” Avignone-Rossa says. “It will give us some idea of what is needed to go full scale.”

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