An important pillar on the way to greater sustainability and better environmental protection is the use and processing of food waste which is full of energy that can be used sustainably. If food waste is left to decompose on a landfill site, this energy is dissipated into the open air as methane gas that harms the environment. To avoid this, the City of Cardiff decided in 2012 that food waste should be collected from local residents and businesses in the City and in the surrounding county of Vale of Glamorgan to be used to produce biogas, green electricity, and organic fertilizer.
In April 2015, Anaergia was commissioned by Kelda Organic Energy Ltd, a subsidiary of the Kelda Group, to build a biogas plant with waste processing facilities on the site of Welsh Water‘s Cardiff Wastewater Treatment Works in Tremorfa (Cardiff, Wales). The plant, now owned by Welsh Water Organic Energy, can process up to 35,000 tons of food waste every year: kerbside food waste with <7% non-organic contamination and commercial food waste with <10% non-organic contamination. The food waste is prepared by removing all non-food contamination before it is processed in two fermentation tanks to produce biogas. The biogas is used to operate a combined heat and power (CHP) which produces 2 MWel and 2 MWth supplying clean electricity and heat to the plant and excess electricity to the neighboring wastewater treatment works or the public grid. The heat is used to heat the digesters and pasteurize the digestate on site.
In addition, the process produces 1,886 tons of solid digestate for compost production (20-25% dry matter) and 37,611 tons of liquid digestate for crop production (3-4% of dry matter) a year. These are impressive figures, showing what state-of-the-art waste processing technology is capable of.