Pre-treatment plant for food waste
Sysav has built a facility to process food waste into biogas and biofertilisers. Each year 25,000–30,000 tonnes of food waste from the region’s households, restaurants and food processing companies will be processed into a pumpable slurry in order to produce biogas, for cars and buses – and move society one step closer to a sustainable society with renewable transportation fuels. Sysav’s plant came into service in 2009. The technology for pre-treating food waste is still very much in its infancy, and several of the technical solutions at the plant cannot be found anywhere else. There is a huge potential of reducing emissions once this pre-treatment technique is fully developed.
Waste must be treated in such a way that the maximum environmental and social benefits are achieved, thus contributing to a more sustainable society. In a sustainable society, it is first and foremost important to minimise the production of waste. This is regulated within the European Union by the framework directive for waste, which requires member states to take measures to prevent the generation of waste. Member states are required to develop a waste reduction plan with the aim of reducing waste by 2020.
Waste management is prioritised according to a five-stage waste hierarchy: 1) Waste prevention, 2) Reuse, 3) Material recycling, 4) Recovery – for example energy recovery through combustion, and finally 5) Disposal. The European Union’s decisions establish the framework for Swedish waste management. One national environmental objective is that by the end of 2018 at the latest, a minimum of 50% of food waste from households, restaurants, catering kitchens and stores must be recycled through biological treatment. In 2011, 14,9% of the food waste in Sweden was treated biologically in various compost and biogas plants. That corresponds to 650,300 tonnes or 68,6 kg/person, and indicates an increase of 4,3% compared to 2010.
In order to meet this environmental objective, Sysav built a facility for receiving and processing food waste to produce biogas and biofertilisers. Each year 25,000–30,000 tonnes of food waste from the region’s households, restaurants, and food processing companies will be processed into a pumpable slurry in order to produce both biofertilisers to be used on farming land and biogas, for cars and buses – and move society one step closer to a sustainable society with renewable transportation fuels.
Sysav’s plant came into service in 2009. The technology for pre-treating food waste is still very much in its infancy, and several of the technical solutions at the plant cannot be found anywhere else. Sysav’s plant can receive three main types of food waste: pumpable liquid food waste (e.g. waste from disposal grinders and fat separation sludge), pre-packed liquid food waste (e.g. milk and juice in cartons), and separated solid food waste (standard, separated food waste from households, restaurants and large-scale kitchens).
The pre-treatment plant was designed with three treatment lines and is monitored and controlled from a control room. There are two operators on site to manage and monitor the pre-treatment plant. The pre-treated food waste then leaves Sysav in the form of pumpable slurry. This slurry is transported to a biogas plant where both biofertilisers and a renewable transportation fuel, biogas, is produced through digestion.
Barriers and drivers
One of the key drivers of this eco-innovation is Sweden's national environmental objective saying that at least 50% of all food waste need to be recycled through biological treatment by the end of 2018. This objective, based on the fact that society needs to reduce its dependence on fossil fuels in order to cut emissions and to secure a longterm energy supply, has pushed the development forward. In addtion, Sysav's overall goal is to recycle as much waste as possible (either as material or energy) in order not to let it go to landfill.
By reusing already existing materials locally (in this case food waste) instead of extracting fossil fuels far away, both material and transport costs go down. However, the total cost for biogas does not necessary go down since one needs more biogas than fossil fuels in order to extract the same amount of energy.
Three main positive impacts can be identified. First, producing biogas from food waste reduce our dependence on finite resources and therefore contributes to secure a longterm energy supply. Second, reduced emissions from traffic greatly improves the air quality in the local environment in cities and other trafficed areas. Third, most people's wellbeing increase when knowing that the food waste produced is not wasted, but reused effectively. A potential negative impact might be that traffic will increase as a result of people driving more when they no longer use fossil fuels and therefore consider driving to be environmentally friendly.
An increased use of biogas as a fuel reduces our dependence on oil, which is important both for the environment and for securing the energy supply in the long term. If 35% (322,000 tonnes) of Swedish food waste from households were to be used as substrates for biogas production (anaerobic digestion), 34 million litres (0.3 TWh) of gasoline could be replaced. This corresponds to the annual consumption of about 28,000 cars and a reduction of 164,000 tonnes of carbon dioxide emissions (0.3% of carbon dioxide emissions in Sweden). Today, only 6% of the food waste from households (about 55,000 tonnes of food waste), is utilised for biogas production. The potential is much higher and is estimated to be 11 TWh of biogas, which can replace over 12% of the fossil transportation fuels. Estimates show that replacing fossil transportation fuels by biogas reduces the carbon dioxide emissions per unit of energy by 90%. Moreover, the end residue from the pre-treatment process is used to produce electricity and district heating.
The production of biofertilisers gives environmental benefits too. Biofetilisers, which contain micro-organisms and humus, can replace the use of commencial fertilisers that are negative for the soil and the ecosystem.
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