Since 2012, the municipality-owned Tekniska verken has collected food waste in green plastic bags, which are handled together with the normal household waste. They are automatically sorted at Gärstad, and subsequently transported to the biogas facility.
Returning important nutrients“We receive nearly 100,000 tonnes of organic waste from the food industry and households every year. This is converted to biogas and biofertilizer, which return important nutrients such as phosphorus and nitrogen to neighbouring fields”, says Sören Nilsson Påledal, process engineer at Tekniska verken.
Photo credit Göran Billeson In addition, 20 GWh of biogas energy is produced each year from digesters at the municipal sewage treatment plant, part of the waste-water treatment system.
In the digestion chambers at Tekniska verken, the organic material is broken down in an oxygen-free environment at approximately 42 °C. The material remains in the digester for an average of 50-60 days. The gas, which consists of 65% methane and 35% carbon dioxide, is then passed to an upgrade facility where the carbon dioxide is removed, giving a gas with 97% methane.
This gas is distributed and sold by Svensk Biogas, a subsidiary to Tekniska verken. Svensk Biogas currently has 12 filling stations in the region, in Mjölby, Motala, Västervik, Norrköping and Linköping.
Liquid biogasThe board at Tekniska verken recently decided to build a facility for liquid biogas, which is particularly suitable for freight transport on land and at sea, and can be transported and stored more efficiently. This required an investment of SEK 68 million, where approximately SEK 30 million is a grant from Klimatklivet, an initiative from the Swedish Environmental Protection Agency.
The investment in biogas is characterised by political unity in Linköping, and its initial phase was made easier in that all the links in the chain – waste, water, heat and public transport – were under the responsibility of the municipality.
Translation George Farrants