Turn food waste into fertiliser

When food waste leaves the kitchen, it goes through various treatments before it can and may be used as fertiliser.

Firstly, it is sorted and pulped, i.e. ground into a 'porridge'. In this process, the bags in which the waste has been collected are separated. It also removes other unwanted content, such as glass and metal, caused by incorrect sorting.

Once the food waste has been pulped, it will typically be degassed in a biogas plant. It is good resource utilisation to first make green energy from the waste before the nutrients return to the soil. During its stay in the biogas plant, the waste is also hygienised before the 'biogas slurry' is transported to farmers who use it as fertiliser.

Organic farmers are required by law to use organic fertiliser for their fields. This can be manure from livestock or fertiliser made from plant material. It should preferably be organic, but if there is not enough organic fertiliser, the organic farmer can also use certain types of non-organic fertilisers. Recycled fertilisers and manure digested in biogas plants are favoured in the organic rules because they contribute to circular production in line with the organic cycle principle. This is why organic farmers can use processed food waste, even though it may come from conventionally grown food. The nutrient content of the fertiliser is on par with cattle manure.

If the organic area is to double - and this is the ambition in Denmark as well as in the EU - organic farmers must have access to more fertiliser. Residues are important sources of fertiliser. In addition to food waste, these include composted garden and park waste and residual products from the food industry. In order to be used as fertiliser by organic farmers, they must be produced without the use of GMOs and be on the list of permitted fertilisers for organic farming.

Reusing and recycling reduces waste and is therefore a way to utilise natural resources more responsibly. Leftovers and waste should be recycled as high up in the 'waste hierarchy' as possible. Until now, much food waste has been incinerated and used for heat and electricity production. This results in the loss or destruction of nutrients, which cannot be recycled into new food, but must be replaced by energy-intensive fertilisers or minerals extracted through mining. It is therefore a climate and environmental advantage to recycle organic household waste. If we also produce green energy from the waste in a biogas plant during the process, the climate profile is even better.

Most municipalities have chosen to collect food waste in regular plastic bags, and you might be wondering why. Experience shows that regular plastic bags are the easiest to separate in the pre-treatment plant because they do not break as easily as paper or biodegradable plastic bags. This way, we get a cleaner fertiliser on the field.
Read more: Does plastic disappear when it ends up in the field?