Phosphorus recycling to enable sustainable use of raw materials
Phosphorus is a vital element which, along with nitrogen and potassium, is one of the most important components of the body's cells and bones. Human DNA – the carrier of genetic information – also contains phosphoric acid. Phosphorus fuels plant growth: one hectare of wheat requires 60kg of the nutrient each season, and all agricultural fertilisers have phosphorus as their main component. Large quantities of residues are produced at wastewater treatment plants and plants to treat waste from meat processing and the disposal of animal carcasses. Large amounts of phosphorus can be recovered from these residues.
Starting in 2026, phosphorus must be recovered from wastewater, sewage sludge or sewage sludge ash and recycled, for example as fertiliser. This will enable domestic agriculture to meet its requirements for this valuable mineral using local sources and without having to import mineral fertilisers from problematic sources or containing harmful heavy metals. Phosphorus recycling also closes an important material cycle and conserves primary phosphate reserves.
Phosphorus management in Switzerland
Wastewater is the principal phosphorus-rich waste. Around 6,500 tonnes of phosphorus are lost annually in Switzerland in this waste stream. Today, phosphorus can be recovered from wastewater, sewage sludge and the ash of sewage sludge. Sewage sludge must always be thermally treated in accordance with the ban on direct spreading of sewage sludge in agriculture. Animal by-products are the second major phosphorus-rich waste stream. Around 1,200 tonnes of phosphorus are lost annually via this waste in Switzerland's waste management sector. Compared to sewage sludge, animal by-products have high phosphorus concentrations and low levels of impurities. This makes the phosphorus in animal by-products comparatively easy to recycle from a technical perspective.
Phosphorus fertiliser imports
Switzerland must import phosphorus from abroad in order to cover its current requirements, in particular the demand for phosphorus fertiliser. There are no primary phosphorus deposits in Switzerland and the direct application of sewage sludge containing phosphorus onto agricultural land has been banned since 2006. Net phosphorus imports amount to just under 15,000 tonnes each year. This dependence is a cause for concern. Although sufficient phosphate ores are available in the medium term, the deposits are concentrated in a small number of countries and geopolitically unstable regions. Phosphorus fertilisers produced from primary deposits also contain high levels of cadmium and uranium. In the case of cadmium, these sometimes exceed the applicable limits.
The Federal Act on the Protection of the Environment (EPA, SR 814.01), the Federal Act on the Protection of Waters (WPA, SR 814.20), and the Ordinance on the Prevention and Disposal of Waste (ADWO, SR 814.600) contain the key regulations for the environmentally sound handling of waste.
In accordance with Article 15 paragraph 1 ADWO, phosphorus must be recovered from municipal wastewater, from sewage sludge from central wastewater treatment plants (WWTPs) and from the ash produced by the incineration of such sewage sludge. It must then be recycled. The same applies to the phosphorus in animal and bone meal that is not used as animal feed (Art. 15 para. 2 ADWO).
The Federal Council has stipulated in Article 51 ADWO that this requirement to recover phosphorus will apply from 1 January 2026. Recovery must be carried out according to the state of the art (Art. 12 para. 2 ADWO).
Possibilities and requirements of phosphorus recovery
Phosphorus recovery from wastewater, sewage sludge, the ash resulting from the thermal treatment of sewage sludge, and animal and bone meal is a new branch of technology. For this reason, the state of the art in phosphorus recovery cannot yet be described on the basis of empirical values from large-scale plants. Meaningful quantitative and qualitative requirements which describe the current state of the art were derived from various research and development activities as well as the existing legal requirements.
In principle, as much phosphorus should be recovered from the respective waste stream as is feasible according to the state of the art. In the long term, at least as much phosphorus should be recovered in Switzerland as is currently imported via mineral fertilisers and chemical products. A recovery rate is required in order for this goal to be achieved. The enforcement aid on phosphorus-rich waste provides the cantons and affected business organisations with a framework to ensure that phosphorous recovery processes are as uniform as possible. The guide explains the legal requirements and the state of the art in phosphorus recovery.