Sweden: Biowaste Recycling Energy and Valuable Products Created from Fruit Waste
Waste from the citrus industry can provide biogas and valuable products for a range of industries. This has been shown by Lukitawesa, who recently defended his doctoral thesis at the Department of Resource Recovery and Building Technology at the University of Borås, Sweden.
Borås/Sweden — Climate change has increased the need for resource recycling and a circular economy. What to do with waste is one such challenge; more environmentally friendly alternatives are needed when it comes to recycling and producing materials and energy from things humans discard. This is the starting point of Lukitawesa's doctoral thesis Methane and Volatile Fatty Acid Production from Toxic Substrates, which focuses on waste from citrus fruits.
“In my home town of Yogyakarta in Indonesia alone, the amount of waste in the Gemah Ripah Fruits and Vegetables Wholesale Market is between one and two tonnes – every day. From a single market. So you can imagine how much there is globally,” says Lukitawesa, who has the aim of contributing to improvements. He points out that the entire industry is a significant environmental problem. The citrus industry creates 40 and 60 % of the total citrus mass with the world's total citrus production being 132 million tonnes of fruit per year.
Anaerobic Digestion and Valuable Fatty Acids
Lukitawesa's research aims to develop methods for how citrus waste can be made into methane/biogas and building block chemical for biocomposite of plastic. This is a major challenge, as the waste contains toxic citrus peel oil and thus becomes difficult to use in anaerobic (non-oxygen demanding) digestion. However, the study shows that it is, in fact, possible.
Toxic organic waste such as fruit waste has traditionally been disposed of in landfills. But anaerobic digestion can be used to produce biogas or fatty acids — all for the sake of the environment and the climate. The solution that Lukitawesa highlights is anaerobic digestion in two steps, using a membrane.
In the first part of the doctoral thesis, biogas production from citrus waste was studied. This is something that can reduce environmental destruction and increase the production of renewable energy. Afterwards, he realised that even the direct product of the first stage of digestion, fatty acids, is valuable. The second half of his doctoral thesis deals with how bioreactors can produce volatile fatty acids when loaded with a large amount of citrus waste. Previous research in the field has focused primarily on loading a smaller amount of citrus waste.
Volatile fatty acids today have a wide range of uses within industry and are included in a wide variety of products: from medicines and food to paints and plastics. But the volatile fatty acids that are normally used industrially are fossil-base. Fruit waste would offer a climate-friendly alternative.