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The TetraPhos® process – a lighthouse project promoting sustainability and environmental protection

There can be no life on our planet without phosphorus! This raw material is needed to produce food, fertiliser and corrosion inhibitors but supplies are limited. It not only makes sense, therefore, to recover this substance so it can be reused – it is also necessary. With this in mind, a team of chemists and engineers from REMONDIS Aqua set about developing a process to recover phosphorus. In a recent interview, REMONDIS Aqua managing director, Dr Martin Lebek, talked about this future-proof project and its results.

REMONDIS Aqua collaborates with Hamburg Wasser to recover phosphorus from sewage sludge. What prompted this cooperation work?

REMONDIS and Hamburg Wasser have run the Vera sewage sludge incineration plant as a joint venture for many years now. Talks about implementing the TetraPhos® process there began early on when the project was just being developed. A two-year pilot phase was then set up at the sewage treatment plant in Hamburg so that the ash there could be used to test the process and technology and get it ready for the market.

This project focuses on recovering phosphorus, which is still a very new area of research within the recycling industry. What specialist areas of expertise were needed to actually implement your plan?

Both chemists and engineers were involved in developing the actual TetraPhos® process at the beginning of the project. Specialist in-house divisions (such as the analytics department) and the company’s many years’ experience of recovering recyclable materials were instrumental in the TetraPhos® process being developed and becoming such as success. The expertise of REMONDIS Aqua’s wastewater and material flow (sewage sludge recycling) divisions was also essential. Thanks to its wide range of skills and experience, REMONDIS Aqua was able to develop the process itself and have it patented.

REMONDIS Aqua is responsible for the project’s recycling technology. The TetraPhos® process was developed specifically as a means to recycle sewage sludge. Could you give us some details about how it works?

The TetraPhos® process mineralises sewage sludge and treats it using a wet chemical procedure. Phosphoric acid is used to dissolve and absorb the phosphates in the sewage sludge. Having been enriched with these phosphates from the sewage sludge, this phosphoric acid solution is then cleaned several times. This process, therefore, produces high quality phosphoric acid – a very pure product – that can be supplied to the market as a raw material.

The phosphoric acid, which is used to dissolve the phosphates, can be returned to the TetraPhos® cycle and re-used, thus reducing the need for chemicals and cutting costs. The quality of the phosphoric acid produced by this process is considerably higher than that of the raw material from natural deposits. Marketed under the brand name RePacid®, it is used to manufacture a variety of products, such as corrosion inhibitors, animal feed and phosphate fertiliser. Besides producing phosphoric acid, this process also generates gypsum for the building supplies industry as well as iron and aluminium salts. These salts can then be used by the sewage treatment plant to eliminate phosphate.

The TetraPhos® process is, therefore, like a puzzle piece that fits perfectly into the process chain enabling the phosphorus cycle to be fully and sustainably closed for the very first time.

What challenges did the team have to face as they set about developing the TetraPhos® process?

Having worked in the field of recycling for so many years, we follow a specific maxim when it comes to developing processes that must prove their worth on the market. Put simply, a recycling system must meet the requirements of industrial businesses if it is to be cost effective. In other words, there must be a constant supply of the secondary raw materials and these must be of a consistent quality, be able to be used flexibly and be sold at usual market prices. The TetraPhos® process meets all these points.

Why is it actually worth making the effort to recover phosphorus from sewage sludge?

There are a number of reasons why it’s worth recovering phosphorus from sewage sludge. On the one hand, phosphorus is a vital raw material – it is impossible to have life on earth without it. On the other, natural deposits of this substance are found in just a few countries around the world. Europe is almost entirely dependent on imports and the quality of the raw material is deteriorating as it contains more and more pollutants. Moreover, phosphorus is a central chemical element for producing food, which means that its importance will continue to grow as the world’s population increases. This is also the reason why the legislator has made it mandatory to recover phosphorus from sewage sludge from 2029 onwards.

The TetraPhos® process offers a number of other important advantages:

Improved carbon footprint:

Several product life cycles are closed and high quality secondary raw materials produced. Moreover, the RePacid® production process cuts carbon emissions by 60% compared to imported phosphoric acid – giving it an excellent environmental footprint.

Nutrients and pollutants safely separated:

The phosphoric acid is a standard and fully marketable secondary raw material – there are no restrictions.

Legally compliant:

Way over 80% of the phosphorus is recovered from the sewage sludge which more than satisfies the targets set out in the amendment of the Federal Sewage Sludge Ordinance [AbfKlärV] – making it a future-proof system for sewage treatment plants.

Excellent quality:

The recovered phosphoric acid, RePacid®, is of a higher quality than the raw material from natural resources.

The foundation stone for the world’s first phosphorus recovery plant was laid in Hamburg on 01 March 2019; it will be commissioned in 2020. What volumes can the facility process?

The facility in Hamburg processes all sewage sludge generated by the City of Hamburg as well as external volumes treated by the Vera (Köhlbrandhöft) sewage sludge mono-combustion plant. Approx. 7,000t of high purity phosphoric acid, 35,000t of iron and aluminium salts and 12,000t of gypsum can be generated from this volume of material.

The Federal government in Berlin has said that phosphorus must be recovered from wastewater and recycled from 2029 onwards at the latest. How can your facility help to ensure this regulation is met?

The TetraPhos® phosphorus recovery process already fulfils the regulations that will be coming into force, making it a sound and future-proof investment. What’s more, the phosphorus recovery facility in Hamburg is the first plant in the world able to recover phosphorus from sewage sludge. It is, therefore, not only a lighthouse project showing how the government’s plans can be implemented, it is also a milestone on the path to protecting natural resources and recovering essential raw materials – working for the future.

The project at the Köhlbrandhöft plant in Hamburg is being supported by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU).

Many thanks for taking the time to speak to us!


REMONDIS Industrie Service GmbH & Co. KG