A circular economy approach in which vegetable residues are turned into biogas covers up to 40% of the energy used by frozen vegetables, herbs and fruit producer Ardo in Ardooie, Belgium.
Over 70,000t of vegetable by-products, 8,000t of maize, and wastewater are used to produce 24,000MW/h per year in a process which also yields organic fertiliser and clear water.
No manure or animal by-products are used at the two Digrom Energy plants in Ardooie. The project is a cooperation between Ardo, and environmental companies Trevi and BiogasTec.
Biogas production
The technologies of an industrial biogas plant and anaerobic wastewater treatment are combined to produce biogas which is transformed into green electricity and heat, CEO of BiogasTec, Wouter Platteau said.
He explained that the different waste is fermented and mixed in a heated tank where microorganisms use the organic part of the waste to feed themselves and produce biogas.
While post treatment is undertaken after the fermentation process, due to an excess of nutrients including nitrogen in the Flanders region, he said it is a legal requirement to treat and to export them.
In the region ammonia emissions from agriculture are the main source (74%) of atmospheric nitrogen deposited to sensitive ecosystems, including Natura 2000 sites, the European Environment Agency said.
The digestate is separated into a solid fraction which is used as an organic fertiliser in France, while the liquid fraction is treated and the nitrogen content changes and becomes odourless.
A total of 20,000t of organic fertiliser is produced every year containing 9g of nitrogen (N)/kg; 7g of phosphorus (P)/kg; and 5g of potash (K)/kg, according to recent BiogasTec analysis.
The BiogasTec CEO explained that the carbon dioxide (CO2) emitted during the biogas combustion process is different as it originates from plants and not from fossil fuels.
Circular economy
The green energy is used to store the vegetables, while green steam produced with the waste heat from the engines is used for steaming and blanching directly at the Ardo plant.
To minimise water consumption, the water used for vegetable processing is collected and purified, and then used a second time for washing the vegetables coming from the field.
The remaining water is stored in a 150 million litre reservoir. Through an irrigation network and 22km pipes farmers can use the water for irrigation, regional director for Benelux and Germany at Ardo, Tijl Goens said.
At the site vegetables, herbs and fruit are stored at -21°. When producing cold, residual heat is inevitably created which is then captured and used to make hot cleaning water, Ardo said.
This recuperated heat is being used to heat Ardo’s workplace when it is cold outside. During hot weather recycled cold from the cold stores is used to cool the work spaces.
Sustainability programme
In 2014 Ardo started the Minimum Impact, Maximum Output, Sustainable Agriculture (MIMOSA) project with the ambition of minimising the impact of its growing activities on the environment, whilst achieving optimal yields.
Optimising the use of all resources, including seeds, herbicides and pesticides, fertilisers, and irrigation water is a priority for the agri business. 76% of the total volume of all the crops grown by Ardo have no residue of plant protection products.
The company comprises 3,500 growers producing 947,000t of up to 100 different crops on 50,000ha across Portugal, Spain, France, Belgium, Denmark, the Netherlands, the UK, Austria and Costa Rica.
