Innovative separation of reaction and granulation

Various approaches exist for extracting and utilizing phosphorus from the ashes of mono-sewage sludge incinerators. However, these recovery processes are generally not economically viable under the current market conditions, they are very often technically immature and have considerable performance difficulties due to the typical variation in ash composition. What's more, these processes result in products that do not cover the specific nutrient requirements for soil and plants and thus are only of very limited use to farmers.

With PHOS4green, we have developed an innovative, patented process in which a suspension is produced from mineral acid and further nutrient components from the phosphate-containing secondary raw material, e.g. sewage sludge ash. The phosphate in the sewage sludge ash is thereby macerated with the acid.

The suspension that is thereby produced is then spray-granulated in a fluidized-bed apparatus. The production of the suspension and thus the reaction of the phosphate conversion are separated from the process of granulation.

Take advantage of our process innovation for the industrial recovery of phosphate from sewage sludge ash!


Insoluble phosphates are made available to plants using mineral acid

Organic residues, such as sewage sludge, are essentially a cost-effective and sustainable alternative to mineral-based fertilizers. Yet their direct application to fields is becoming increasingly restricted and is cause for concern when it comes to hygiene.

Sewage sludge ashes - compared to unburned sewage sludge - have a much higher phosphate content and are free of organic pollutants. These ashes are therefore a particularly interesting source of phosphate. However, the phosphates inside them are insoluble and thus not able to be absorbed by plants.

Acids can convert these insoluble phosphates into a form that plants can use. On the basis of this little-known approach, we have developed a stable and extremely flexible process, which has been subsequently converted to an industrial scale.
An example reaction of how this largely insoluble phosphate can be utilized by means of acid reaction.

PHOS4green - Beispielreaktion Phosphat durch Säurereaktion nutzbar
Beispielreaktion, wie das weitgehend unlösliche Phosphat durch Säurereaktion nutzbar gemacht werden kann.


Simple, flexible and stable process control thanks to the separation of the process steps

In this modified process, the preparation of the suspension and thus the reaction of phosphate conversion between the phosphate-containing secondary raw material and the mineral acid are separated from the granulation process. This separation brings with it numerous procedural advantages.

  • The spontaneous and vigorous reaction that occurs when the phosphate-containing ashes and the mineral acid are directly mixed becomes manageable and controllable.
  • The free acid is already largely reacted in the suspension, therefore allowing the corrosion of different parts of the plant to be effectively prevented. Lyes, basic salts, etc. can be added to the suspension produced. As a result, the amount of remaining free acid can be reduced further if necessary.
  • In addition, other nutrient components can be added to the suspension, for example nitrogen (N), phosphate (P), potassium (K), magnesium (Mg), sulfur (S) or vital trace elements. This makes it possible to produce standardized mineral fertilizers with exactly the necessary plant and soil specific nutrient composition.
  • By producing a suspension, the raw material components are much better homogenized. This results in a particularly uniform product.
PHOS4green - suspension preparation for phosphate conversion
The production of a suspension for phosphate conversion and flexible adjustment of the product composition.


Fast and safe implementation with easily controllable reaction steps

The development and market launch of new processes and technologies often requires long development times and is a risky undertaking. Many alternatively discussed P-recycling processes are based on completely new developments and are often determined by process steps that are very complex and thus very difficult to control, such as precipitation reactions or extractions. Proof of technical feasibility often has to be provided first, with a correspondingly uncertain outcome.

The PHOS4green process developed by us is based on technology and process steps that have been in use for decades and have been tried and tested and continuously optimized. The production of solutions or suspensions in combination with acids in the chemical industry is state of the art. The process step involving spray granulation in the fluidized bed is also an established process and, at Glatt, forms the core competence in a wide variety of product applications and dimensioning procedures.

PHOS4green combines state-of-the-art and sustainably optimized process steps with standardized technologies. Technical feasibility is thus guaranteed, almost independent in the dimensioning.

PHOS4green - spray granulation system
Glatt has been successfully building spray granulation systems for a wide variety of applications for decades - all over the world.


The fluctuation range of sewage sludge ash is continuously balanced

The fact that sewage sludge ashes undergo a considerable variation in their chemical and mineralogical constitution is problematic for many other phosphorus recovery processes. Not only within the time course of a mono-incinerator, but the ashes of different incinerators also differ massively from each other in some cases.

So essentially the solution, precipitation and extraction processes in wet-chemical P recycling processes can only run ideally within very narrow parameter limits. In operation, the strong fluctuation range of the ash would have to be responded to immediately and accurately, which is difficult to achieve both technically and analytically. Regarding such technical methods it is a known fact that the actual operating conditions will differ considerably from the ideal laboratory conditions. As a result, the P recycling rate and the separation of heavy metals are well below the expectations based on the laboratory studies. That makes these procedures rather unattractive.

In our PHOS4green procedure, the ash is also mixed with the acid. Subsequently, however, there is no separation of the soluble and insoluble fraction, instead the entire mixture is processed by means of granulation into standardized fertilizer. This is technologically much easier, much cheaper and does not produce any waste. Fluctuations in the ash are easily balanced out by adjusting the recipe, ensuring consistently high quality. This makes the procedure extremely flexible and easy to control when it comes to fluctuations in the ash. And even other phosphate carriers (for instance ash from animal meal) can likewise be processed into high quality fertilizers with consistently high quality.

PHOS4green - phosphorus recovery