Phosphorus recycling

Definition

Phosphorus recycling involves recovering the nutrient phosphorus from biological waste, sewage sludge, slaughterhouse waste or directly from human waste and reusing it. Some 15,000 tonnes of phosphorus are imported into Switzerland every year, primarily in animal feed and mineral fertilisers for agriculture as well as in plant-based foods. Every year, around 6500 tonnes are lost in wastewater and approximately 3700 tonnes in slaughterhouse waste.  

There are several methods for recovering phosphorus from these sources: Phosphorus can be precipitated directly from wastewater and sewage sludge using iron or aluminium. Phosphorus is dissolved from sewage sludge or meat and bone meal ash using strong acids. This produces technically pure phosphoric acid or triple superphosphate (TPS), high-quality raw materials that can be used for fertilisers and other chemicals. Finally, phosphorus and other nutrients can be separated directly from urine by means of biological or physical separation processes and used as solid fertiliser (struvite or calcium phosphate) or as liquid fertiliser. 

Current applications and opportunities 

According to the Ordinance on the Avoidance and the Disposal of Waste (ADWO) of 2016, mandatory phosphorus recovery from sewage sludge, sewage sludge ash and meat and bone meal will apply in Switzerland from 2026. However, as no facility is yet ready to enable this, the target will not be met. In contrast, the evaluation of three large-scale plants for recovery from phosphorus-rich ash in Zuchwil (Solothurn), Oftringen (Aargau) and Bazenheid (St. Gallen) is well advanced. The plant in Bazenheid is scheduled to go into operation in 2026, and the one in Zuchwil in 2030. 

An alternative approach is to recover phosphorus and other nutrients directly from human waste, a process also known as urine separation. Around half of the phosphorus in wastewater comes from human urine. In urine separation, separation would take place before the nutrients are diluted in the wastewater and washed away, for example in urine-diverting toilets. According to calculations by the Swiss Federal Institute of Aquatic Science and Technology (Eawag), separating 20 percent of the accumulated urine could recover 655 tonnes of phosphorus per year, replacing 15 percent of mineral fertiliser imports with recycled fertiliser. The process is being implemented in the NEST research and innovation building run by Empa and Eawag in Dübendorf – NEST stands for Next Evolution in Sustainable Building Technologies – as well as in several other office and laboratory buildings. The liquid fertiliser Aurin produced in this process has been marketed at cost price for ten years. 

Phosphorus recycling reduces dependence on imports of the finite raw material, which is mined in large phosphate mines, especially in Morocco, China and Russia, using processes that are sometimes harmful to the environment and hazardous to workers’ health.  

The technology makes an important contribution to a sustainable circular economy and strengthens the value chain in Switzerland. Recovery from sewage sludge and meat and bone meal ash yields a high-purity product that can be used in a variety of ways. Decentralised urine separation could be a useful addition to this large-scale method. It relieves the burden on wastewater and reduces the amount of nutrients entering natural waterways. Last but not least, the direct process removes other valuable nutrients such as nitrogen, potassium and sulphur from the urine in addition to phosphorus.  

Challenges 

Phosphorus recovery from wastewater, sewage sludge and ash is a new branch of technology whose development and large-scale application is primarily driven by legislation. The investment required for the construction and operation of the central facilities cannot yet be covered by the sale of the recycled product as it is not financially competitive with phosphorus extracted from mines. In addition, the regulatory and approval requirements for the resulting products (e.g. fertiliser approval) are extremely high, which further increases costs. 

The processes currently favoured in Switzerland for extracting phosphorus from sewage sludge and meat and bone meal ash have clear environmental benefits compared to phosphate mining, but require the use of large quantities of chemicals. The processes are energy-intensive and generate new production waste that pollutes the environment.  

The short- to medium-term implementation of urine separation is a controversial topic among wastewater experts in Switzerland, as 97 percent of households are connected to the conventional sewer system. Unlike existing sewage technology, however, urine separation can be implemented step by step using small-scale facilities and in a commercially viable manner, because the costs of the facilities are covered by the sale of the fertiliser. The marketing of the fertiliser requires close cooperation with fertiliser companies. 

Focus on industry 

Today, technology plays a marginal role in the private sector because disposal is heavily regulated as a public service. The three large-scale plants planned in Switzerland for the recovery of phosphorus-rich ash therefore offer only limited opportunities for SMEs and start-ups. The prospects are better in the area of urine separation, because planning offices and tradespeople operating in the sanitation sector could benefit from the necessary infrastructure adjustments. In addition, urine separation also offers prospects for plant builders and the machine industry, as the plants would have to be manufactured industrially and in series in order to be able to be installed in large numbers.  Scaling effects could quickly have a positive impact on the pricing structure in all areas. The large global demand for wastewater treatment plants without sewage systems is also worth mentioning. A market for export-oriented Swiss industry could develop here. 

In Switzerland, there is no specific training for employees in the field of phosphorus recycling. However, several universities of applied sciences offer courses on the nutrient cycle that promote knowledge and awareness of a sustainable circular economy. 

International perspective 

In the wastewater sector, Switzerland has traditionally been a pioneer in researching and developing new innovative processes. The nation is a leader in the field of phosphorus recovery from urine, for example. The political and regulatory framework, for example with regard to regulations or fertiliser approvals, is also favourable compared to other countries. The product Aurin, the world’s first fertiliser made from urine, was approved in Switzerland.  

However, Switzerland plays only a marginal role in the field of phosphorus recovery from municipal wastewater. Research and development for the large-scale plants planned in Switzerland for the recovery of phosphorus from sewage sludge and meat and bone meal ash was carried out mainly in other European countries, primarily in Spain and Germany.  

Future applications 

The large-scale implementation of phosphorus recovery from sewage sludge and meat and bone meal ash depends on political and economic conditions. Future applications of the products depend primarily on the optimisation and further development of the individual process steps. Phosphorus recycling could also become financially profitable if the external costs resulting from the extraction of primary phosphorus in the countries of origin and the environmental impact of excess phosphorus in wastewater can be internalised. 

The technology contributes to a sustainable circular economy and reduces dependence on phosphorus imports. At the same time as recovering phosphorus from wastewater, sewage sludge and human waste, all processes also filter out pollutants such as heavy metals or drug residues and reduce the amount of phosphorus and other nutrients entering surface waters and groundwater.