Phosphor recycling

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. However, this nutrient is currently being lost from waste management systems.

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.

To create a stakeholder-inclusive process as a basis for participatory decision-making on phosphorus recycling in Switzerland, the Federal Office for the Environment (FOEN) began work on the SwissPhosphor platform in 2018.

Phosphorus fertiliser
©, gvl

Global reserves of primary phosphorus

Phosphorus (P) occurs almost exclusively in nature in oxidised form as a phosphate (P2O5). Phosphate mining is the extraction of rocks containing phosphates (phosphate ores). Most of these phosphate ores are of sedimentary marine origin, but there are also lesser phosphate deposits in igneous rocks. Although sufficient phosphate ores are available in the medium term, the deposits are concentrated in a small number of countries (e.g. Morocco, China, Russia) and geopolitically unstable regions. In addition, depending on the location, phosphorus extraction can have a serious impact on people and the environment.


Global reserves of primary phosphorus
© 2016 USGS, FOEN
A phosphate mine
© istockphoto | BrianBrownImages

Strict cadmium limits exacerbate import dependency

Marine sedimentary phosphate deposits have a higher phosphate content than igneous ore deposits. However, the former also contain high levels of impurities, such as cadmium and uranium. Switzerland has very strict limits on the concentration of heavy metals in mineral fertilisers, so it relies mainly on igneous phosphate deposits with low cadmium content and can only source phosphorus for fertiliser production from certain mines. For this reason, Switzerland has until now imported much of its mineral phosphorus fertiliser from Russia. With the war in Ukraine this is no longer possible, which has again highlighted the issue of Switzerland's reliance on imports and the importance of an independent supply of phosphorus.

Overview of global reserves of primary phosphorus

Phosphorus consumption in Switzerland

Switzerland's net phosphorus imports amount to 14,600 tonnes each year as mineral fertiliser (4,200 tonnes), in animal feed (6,200 tonnes), foodstuffs (2,600 tonnes) and chemicals (1,600 tonnes). As there are no primary phosphorus deposits in Switzerland, the country must import phosphorus from abroad in order to cover its current requirements, in particular the demand for phosphorus fertiliser. This overreliance is a cause for concern. The direct application of sludge containing phosphorus onto agricultural land has been banned since 2006. While this prevents pollutants from entering the soil, it also interrupts the cycle of phosphorus back into agriculture.

Switzerland's annual phosphorus imports (based on 2015 figures, Phosphorus flows in Switzerland 2015)
A tractor applying artificial fertiliser to a field
© | fotokostic

Phosphorus recovery – closing an important material cycle

Phosphorus is vital to life on earth. Plants, animals and humans need it to grow and produce energy. We have greatly exceeded the planetary boundary for the phosphorus cycle. Currently, the phosphorus cycle in Switzerland is not closed. In the past, sludge was used as a fertiliser in agriculture. Although this returned the phosphorus to the cycle, there are risks associated with the direct spreading of wastewater sludge as fertiliser. Owing in part to the BSE crisis (mad cow disease), there has been a ban in place since 2006 and the sludge must undergo thermal treatment through incineration. The phosphorus used in agriculture is currently mined from rocks in the form of phosphate, processed into a fertiliser and imported before it is applied to Swiss fields. In the fields, the nutrient is absorbed by plants, which in turn serve as food for humans and animals. The human body absorbs phosphorus as we consume animal and plant-based foods. The nutrient is then excreted and largely ends up in the waste water system. The sludge resulting from waste water treatment is incinerated and the phosphorus it contains ends up either as sludge ash or slag in landfills, or in cement plants, where sewage sludge and animal and bone meal are used as alternative fuels.

The phosphorus cycle

Successfully closing the phosphorus cycle will allow raw materials to be used efficiently and for as long as possible. The recycling and closed-loop management of phosphorus resources makes good environmental and economic sense because it helps conserve natural resources and reduces Switzerland's reliance on imports. That is why in 2016 the Federal Council made phosphorus recovery a requirement under Waste Ordinance.

Cycle of nature
© | ijaper

Legal basis for phosphorus recovery

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 Avoidance 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, sludge from central wastewater treatment plants (WWTPs) and the ash resulting from sludge incineration. 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 the 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). The cantons are responsible for ensuring the requirement is met.

Abwasser / Tierische Nebenprodukte
© | kwanchaichaiudom | Aleximages

Quantitative and qualitative 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. For this goal to be achieved in future, the FOEN's enforcement aid guidelines specify a recovery rate of at least 50%. The enforcement aid module on phosphorus-rich waste provides the cantons and affected business organisations with a framework to ensure that phosphorus recovery processes are as uniform as possible. The guidelines explain the legal requirements and the state of the art in phosphorus recovery. Phosphorus from these waste streams can be used as fertiliser in agriculture if it meets the requirements under the Swiss Fertiliser Ordinance. The use of fertilisers made from recovered phosphorus is currently permitted in conventional agriculture but may not on organic farms.

Potential for phosphorus recovery in Switzerland

Each year, some 6,900 tonnes of phosphorus could potentially be recovered from Swiss waste streams. Sludge is the most important source of phosphorus-rich waste. About 5,700 tonnes of phosphorus ends up in sewage sludge each year. Today, phosphorus can be recovered most effectively from wastewater, sewage sludge and sewage sludge ash. Sewage sludge must always be thermally treated in accordance with the ban on direct spreading of sludge in agriculture. Animal by-products are the second major phosphorus-rich waste stream (animal and bone meal). 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 easy to recycle from a technical perspective. By achieving a recovery rate of 80%, Switzerland could produce enough recycled phosphorus to cover just under 40% of its annual consumption.

Switzerland's phosphorus potential with annual consumption vs. waste stream recovery potential, at a recovery rate of 80%

Phosphorus recovery options

Phosphorus recovery from sewage sludge, the ash resulting from the thermal treatment of sewage sludge, and animal and bone meal is a new branch of technology. In recent years, various technologies have been developed, tested and optimised in pilot projects and technical trials. The processes are based on different principles and have different starting points. In decentralised processes, phosphorus is extracted directly at wastewater treatment plants (WWTPs) from the wastewater and from sewage sludge streams. Centralised processes currently treat the sewage sludge ash after incineration and can take place at other locations independently of the wastewater treatment plants.

Phosphorus recovery options (abbreviations: sewage sludge (SS), animal and bone meal (ABM))

Current state of progress in recovery technologies

In recent years, the spectrum of sufficiently well-developed and feasible recovery processes has narrowed considerably to focus mainly on sludge ash-based processes. Wet chemical extraction or digestion using sewage sludge ash has become the preferred method. The advantages are a high recovery rate and compliance with the limits for heavy metals in phosphorus fertilisers. In Switzerland, there are currently projects in the pipeline for three processes: Phos4Life, REALphos and ZAB. Decentralised approaches are not expected to play a significant role in phosphorus recovery, partly due to low recovery rates. Wastewater treatment plants with well-functioning biological phosphorus recovery can achieve recovery rates of 50% at best.

Planned phosphorus recovery plants

Phos4Life (Emmenspitz, SO)

A large-scale plant based on the Phos4Life (P4L) process is planned on the waste management site operated by KEBAG/Solothurn-Emme wastewater association (ZASE) in Zuchwil (SO). Project partners are ZAR, ACR (TI), ERZ (ZH), Epura (VD), ERZO (AG), REAL (LU), Saidef (FR), SIG (GE) and ZASE (SO). The plant will use a wet-chemical process to extract high-quality technical-grade phosphoric acid from sewage sludge ash. This can then be marketed directly to the chemical/technical industry in Switzerland and throughout Europe. The technical-grade phosphoric acid can also be used to produce low-pollutant fertilisers such as TSP46 in Switzerland. At the current stage of the project, it is estimated that the P4L plant will be able to recover around 2,200 tonnes of phosphorus per year. Construction is scheduled to start in mid-2027 and the plant will be operational in 2030.

P4L Emmenspitz – Overview of the planned quantities, product and simplified process diagram, as at October 2023

Phosphor26 (Oftringen, AG)

As part of the Phosphor26 project, a sewage sludge drying plant and a large-scale plant based on the REALphos process are planned in partnership with Holcim at the site of the Zofingen waste disposal facility (erzo; Entsorgung Region Zofingen) in Oftringen (AG). The partners on this project are erzo (AG), REAL (LU), and Holcim. The REALphos or leaching process employs wet chemical extraction to produce phosphoric acid for fertiliser using sewage sludge ash. The resulting phosphoric acid will then be sent to ZAB Bazenheid for further processing into fertiliser. Projections at this stage of the project suggest that the plant will be able to recover 1,300 tonnes of phosphorus per year. Once investment is secured, construction will start and the plant should be operational in about 3.5 years.

Phosphor26 – Overview of the planned quantities, product and simplified process diagram, as at October 2023

ZAB (Bazenheid, SG)

The Bazenheid (ZAB) waste management association is developing a large plant to implement its phosphorus recovery process at its site in Bazenheid (SG). The project partners are the wastewater interest group Klärschlamm-Interessengemeinschaft Ost (KIGO), wastewater association Altenrhein (AVA), Landi Aachtal (fruit growers' agricultural association Oberaach TG, OGO), ZAB and the TMF Extraktionswerk Ltd. The enterprise will take the form of a public limited company, 'P-AG Bazenheid'. The plant is designed to produce P30, P38 or TSP46 fertiliser through wet-chemical digestion of sewage sludge, animal and bone meal ash using phosphoric acid. The TSP46 (triple superphosphate fertiliser containing 46% phosphate) will be sold in Switzerland as a fertiliser or for processing into a mixed fertiliser. P4L's technical-grade phosphoric acid is suitable for the production of TSP46. Fertilisers containing 30% or 38% phosphate (P30, P38) are intended for export. However, they can also be used in Swiss agriculture. REALphos phosphoric acid for fertiliser can be used for the production of P30 and P38 fertiliser. According to the project information, the plant should produce 14,000 tonnes of TSP46 fertiliser containing 3,000 tonnes of phosphorus and 15,000 tonnes of P30/38 fertiliser containing 2,300 tonnes of phosphorus annually. Construction will start in spring 2025 with a view to launching operations in summer 2026.

ZAB – Overview of the planned quantities, product and simplified process diagram, as at October 2023

Products and market

Various grades of phosphoric acid and P30, P38 or TSP46 fertilisers are the main products that can be made from recovered phosphorus. Technical-grade phosphoric acid can be used in the chemical/technical industry or for the production of TSP46 fertiliser. Fertiliser-grade phosphoric acid is intended for the production of P30 or P38 fertiliser. All the fertilisers mentioned (P30, P38, TSP46) meet the legal requirements and may be used in Swiss agriculture. P30 and P38 fertilisers do not meet current Swiss fertiliser industry requirements, which is why these fertilisers are currently intended for export. TSP46 fertiliser meets the Swiss fertiliser industry requirements and will be sold on the Swiss market. The three planned projects Phos4Life, Phosphor26 and ZAB have the capacity to recover phosphorus from large quantities of sewage sludge ash. However, these three projects will not allow Switzerland to exploit the full potential of sewage sludge as a source of phosphorus. There is an overlap of stakeholder interests and in many cantons, it is not yet clear how and where phosphorus recovery will take place.

Overview of source materials and possible products – Status of implementation as at October 2023
Mineral fertiliser
© istockphoto | Srinuan Hirunwat


The cost of the development, construction and operation of phosphorus recovery plants are expected to exceed the market revenue from the sale of the recycled phosphorus products. Depending on the process, the additional costs are likely to be in the range of CHF 5 per resident per year. The additional costs will be covered by wastewater charges.

A legal basis for financing these additional costs through the wastewater charge already exists in the form of the Water Protection Ordinance (WPO, SR 814.201). This ensures a sharing of the costs by those who generate wastewater, and because enforcement can rely on established procedures it can be implemented immediately. As it stands, the percentage increase in wastewater charges required to cover the additional costs would be in the single-digits. This would therefore be significantly lower than differences in current charges among treatment plants and municipalities.

Current developments in other countries

In Germany, the Sewage Sludge Ordinance (AbfKlärV), which came into force in 2017, requires sewage treatment plants with a capacity of at least 100,000 population equivalents to recover phosphorus from sewage sludge from 2029 and smaller plants from 2032. The use of sludge from the wastewater treatment plants is prohibited in agriculture or horticulture, however. With the entry into force of the EU Fertiliser Products Regulation in 2022, the provisions are now in place to allow phosphorus fertilisers from sewage sludge ash and digested sludge to be sold on the European market.

Last modification 09.11.2023

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