At the same time, the recovery of phosphorus,in turn, contributes to environmental pollution. Common practices such as the direct use of sewage sludge or sewage sludge products such as fertilizer also have the risk of pollution. AIK Technik AG is familiar with different processes and can provide you with active support. As a process specialist with over 13 years of in-house experience, we will find the right solution for you.
In the following process are shown in more detail, in which we are very well versed of.. Unfortunately, phosphorus cannot be produced synthetically and there are no comparable substitutes. Therefore, it is important to actively recover phosphorus and bring it back into the cycle.
Why do we need phosphorus?
Phosphorus is an important nutrient for humans, animals and plants. We need phosphorus for the development, structure and function of body parts such as bones, muscles, DNA and teeth.
Currently, a lot of phosphorus is lost because it is disposed of in landfills after sewage sludge incineration and has not yet been recycled.
A very proven process is Leachphos which was developed and patented by AIK Technik AG. In a demonstration plant (EWB Bern), the wet chemical phosphorus recovery (in an urban mining process) from sewage sludge ash following the FLUWA process (acid fly ash washing) was verified in cooperation with ZAR and AWEL.
The Leachphos process consists of:
A wet chemical phosphorus recycling process of municipal sewage sludge ash from mono- incineration.
- Wet chemical extraction of ash with diluted mineral acid
- Targeted precipitation of the phosphorus product at ideal pH values
- Possible utilization of the washed-out sewage sludge ash filter cake.
In the demonstration plant in which 45 tons of sewage sludge ash were purified, about 6 tons of phosphorus fertilizer could be produced, the fertilizer effectiveness of which was confirmed with field tests.
The end product is thus a finished product. A fine, whitish fertilizer powder which can be distributed directly on the fields. This product can be produced in the sewage treatment plants and does not require any further export or import of phosphorus semisolids.
In 2006, Switzerland already legally banned the direct fertilization of fields with sewage sludge from wastewater treatment plants. Because in addition to phosphate, heavy metals and other pollutants such as pharmaceuticals, pathogens, flame retardants and nanomaterials are contained in the sewage sludge, which would accumulate in the fields.
Since 2016, the largest waste incineration plants in Switzerland have therefore been required to incinerate sewage sludge as a mono-combustion process. What remains is a reddish ash from which phosphorus can be dissolved. In 2018, a total of 46,000 tons of sewage sludge were thermally utilized in Switzerland and the remaining ash was absorbed into cement. As a result, the phosphorus is bound in the structure and can no longer be used as a nutrient.
The Ordinance on the Prevention and Disposal of Waste in Switzerland (Waste Ordinance, VVEA) stipulates that phosphorus must be recovered from phosphorus-rich waste such as sewage sludge by 2026 at the latest.
The aim is to evaluate the most promising processes that allow the use of the existing wastewater disposal infrastructure in Switzerland.
Currently, 100 percent of phosphorus fertilizer in Switzerland is imported. Whereas with the phosphorus volume which should be recycled, the entire demand could be met.
Another problem is that the imported phosphorus fertilizer often does not comply with the legal limits. The heavy metals contained remain in the soil and thus have possible consequences for the environment and health.
Phosphorus recycling is thus worthwhile from an ecological and economic point of view.
It is a big step towards the sustainable use of raw materials.
Phosphorus recycling from sewage sludge has three advantages:
- The phosphorus reserves are conserved
- Since imports will no longer be necessary, no harmful heavy metals such as uranium and cadmium will continue to be used in Switzerland
- Swiss farmers are no longer exposed to an uncertain price development of the phosphorus raw material
This is also an important issue throughout Europe, which is why phosphorus will probably have to be recycled by law by 2030.
