Phosphorus Recycling

Phosphorus Recycling

Phosphorus is a finite resource. In 2014 it was put on the List of critical Raw Materials (EU). Since 2017 it is mandatory in Germany (transition periods apply) to recover phosphorus from sewage sludge. We at P.C.S. have long been doing that. As early as 2006 we started to plan and design/build the first large-scale sludge treatment and phosphate recovery plant. Over the years, we have designed the process-engineering concept in numerous projects and often realised the projects on a large-scale basis.

We are looking forward to employing our experience and skills for your benefit.

The problem

Pursuant to the new German Sewage Sludge Regulation of 2017 municipal sewage plant operators (population equivalent: > 50,000) must recover at least 50% phosphorus from sludge. At the same time, it is prohibited to use sewage sludge as fertiliser.

Though there is a transition period during which the regulations must be implemented, the above is a large-scale project that cannot be realised within a short period of time. Though sludge can be incinerated in mono-incineration plants first and phosphate recovered later, such procedures have never been tested, let alone implemented, on a large scale. Instead of solving the problem, it is simply deferred. It’s time to act, but how do you meet the legal requirements, operate with a profit and protect the environment?

Our solution

P.C.S. will develop a bespoke, sustainable phosphate strategy for your sewage plant - on request in co-operation with your trusted engineering office.

Drawing on our many years of experience in the development, design and construction of phosphate recovery plants we are now working on solutions that meet the high requirements of recent legislation.

We combine several procedures in a clever way to ensure that the limit values defined in the new Sewage Sludge Regulation are complied with. We do away with ash generation through mono-incineration. Our various techniques, which have been specifically developed for sewage plants and include the generation of plant-available magnesium ammonium phosphate (MAP), enable us to prepare a bespoke solution for you. Our Struvex® plant concept meets the requirements of the various process and expansion levels - from MAP precipitation downstream of digestion to improve further sludge treatment all the way to maximum MAP recovery rates in a precipitation step upstream of digestion.

Benefit from a thorough pre-analysis at the laboratory or on a semi-industrial scale, which we will perform in co-operation with our partner, Ewert Consult GmbH. We will be delighted to demonstrate to you in practice the functionality and operational safety of the process based on a pilot plant concept.

Your benefits

These are your benefits if you use the procedures we developed:

  • You recover phosphate as reusable material
  • You improve sludge dewatering rates
  • You prevent crystallisation and thus operational disruptions
  • You save transport and processing costs as you do not need to dispose of your sludge in mono-incineration plants
  • You save incineration ash storage costs that you would incur if the sludge was disposed of in mono-incineration plants
  • You tackle the challenge now, in a lasting way and in compliance with legal requirements.

There is an alternative - make use of it!

Target industries

Our skills in this area are particularly sought after by municipal sewage plant operators.

Our references

Berliner Wasserbetriebe

engineering consulting

Berliner Wasserbetriebe asked us to redesign the original reactor in Berlin with the aim to fully automate the discharge of MAP generated from the process.

Project Details

Sewage plant in Mönchen-Gladbach

phosphorus recycling

Due to massive crystallisation in the about 400m-long sludge pipe section between digestion and dewatering as well as constant problems in the dewatering centrifuges at the Neuwerk sewage plant in Mönchen-Gladbach, processes had to be adjusted to reduce disruptions. A test phase was followed by the installation of a large-scale turnkey plant.

Project Details

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Challenges sewage plants face

Today’s sewage plants do a lot more that just cleaning wastewater. The requirements in sludge treatment in particular have increased tremendously in the past years. Operators also face new legal requirements. The key topics in the industry are now energy optimisation and nutrient recovery, eco-friendly sludge dewatering processes, and optimised disposal concepts.

Together with our customers we develop and implement process-engineering concepts that are innovative and sustainable - an exciting task! Our process-engineering concepts are as individual as the requirements of a sewage plant. The size and infrastructure of the plant as well as the efficiency potential of optimisation measures play a pivotal role - together we will take on the challenge.

Phosphorus Recovery from Sewage Sludge in the Form of plant-available Magnesium Ammonium Phosphate (MAP) with the Struvex® process technologies

The Struvex® process technologies to recover phosphorus have been developed based on our many years of experience in process development and the construction of MAP plants. The technologies use magnesium salts downstream of the digestion process.

Due to additional requirements set forth in the new German Sewage Sludge Regulation and a phosphate discharge rate target of > 50% the conventional Struvex® B(asic) process has been further developed.

The Struvex® A(dvanced) process combines the advantages of sludge hydrolysis and the possibility to substantially increase phosphorus discharge rates by disintegrating sludge upstream of digestion.


Struvex B(asic) is the original process downstream of digestion:

By adding magnesium salt and increasing the ph value, MAP is recovered and separated from the sewage sludge.

The process has a positive impact on sludge dewatering rates (increased DS discharge and simultaneous reduction of polymer additives in sludge dewatering) and disrupts the sewage plant’s internal phosphate recycling by producing almost 100%-phosphate-free centrate downstream of sludge dewatering. On top, undesired incrustations are prevented.

However this process requires the use of bio P in wastewater treatment. Also, the MAP discharge rate is limited as the viscosity and structure of digested sludge limit phosphorus discharge rates to between 20% and 30%.

Several industrial-scale reference processes, for instance at the sewage plants of Salzgitter, Amsterdam, Mönchengladbach and Berlin, were established in the past years based on this process.

The process is still useful for plants that do not require increased phosphorus recycling and where sludge will in future be disposed of in mono-incineration plants.


The advanced process - known as Struvex A(dvanced) - is complemented by a hydrolysis process, which substantially increases phosphate concentrations in the initial substrate. Moreover, phosphates are separated upstream of digestion. Combined these measures achieve considerably higher MAP discharge rates as required in the new German Sewage Sludge Regulation (phosphorus discharge rate > 50% or final values of < 20 g P/kg DS).

In addition to the benefits the hydrolysis process offers (increased gas yield during digestion, increased digestion capacity and significantly improved sludge dewatering rates) the requirements of the new German Sewage Sludge Regulation are met and operators can continue to dispose of sludge with lower P concentrations in sewage sludge co-incineration.