ULiège has developed a demonstrator for recovering phosphorus from our wastewater

In Europe, we have no phosphorus... but we have projects to recover it!

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The University of Liège has presented the PULSE (Phosphorus ULiège Sludge Extraction) demonstrator, a pre-industrial pilot device that enables phosphorus to be recovered from dried sludge directly from wastewater treatment. This equipment, based on a unique chemical extraction process, is currently operational at the AIDE wastewater treatment plant in Oupeye, in the area of Liège.

Phosphorus is an essential element for agriculture and life on Earth. But the resource is limited and the European Union classifies it as a critical mineral raw material, both from an economic and availability point of view. Rather than wasting phosphorus, the recommended approach is to recover it and recycle it in a circular economy.

From 400 kg of dewatered and dried sludge, the PULSE demonstrator ultimately recovers about 12 kg of phosphorus-enriched product, free of heavy metals and safe for recycling as fertiliser in agriculture.

The equipment was developed by ULiège as part of the European Phos4You project, which brings together several European universities and regions to pursue various phosphorus recycling and recovery projects.

The development of PULSE represents an investment of 1.5 million euros, made by Interreg North-West Europe (60%), Wallonia (30%) and ULiège (10%). One third of the amount is devoted to the construction of the pilot, and two thirds to the salaries of two research engineers for 4 years.

Professor Angélique Léonard, President of the Chemical Engineering Research Unit, School of Engineering  of ULiège, academic co-leader of the project with Professor Andreas Pfennig: "Life cycle analysis is used in the framework of Phos4You to verify the environmental interest of phosphorus recovery processes. Various indicators, such as global warming, resource depletion, eutrophication... are evaluated in order to avoid transferring impacts and to develop processes with the lowest possible environmental footprint."

"The participation in the project of various regions in the north-western European zone (Scotland, Ireland, The Netherlands, Wallonia, Flanders, France, Germany) has made it possible to highlight, in a concerted manner, the obstacles to the use of secondary materials from recycling. At the end of the project, the consortium will submit a list of recommendations aimed at facilitating the marketing and use of fertilisers based on recycled phosphorus."

Jean-Luc-Martin, Chairman of the Management Committee of the Société Publique de Gestion de l'Eau (SPGE), commented on the project: "Sustainability is always present in the background of our activities. It is part of our DNA! Our core business is based on three words: environment, sustainability and innovation. Water resources and the fabulous tool that is the sewage system can meet a crucial challenge for our future: the circular economy. Phosphorus, an essential element for agriculture, is present in wastewater and sewage sludge in an almost inexhaustible way."

PULSE: a unique process

In the PULSE process, acid leaching (a solvent extraction technique) is used to dissolve phosphorus from dried sludge. By using dried sludge, the acid consumption for leaching is reduced and the separation of solid and liquid fractions is easier compared to the use of dewatered sludge.

The metals and heavy metals that are extracted with the phosphorus in the leaching stage are then removed in the reactive extraction stage. The phosphorus is then recovered by precipitation (a reaction in which the mixture of aqueous solutions yields a solid compound) as calcium phosphate.

The mobile PULSE equipment has a treatment capacity of approximately 100 kg of dewatered sludge per batch and was built to demonstrate in a real environment the effectiveness of the process developed by ULiège chemical engineers.

After being designed and tested in the laboratories of the ULiège Chemical Engineering Research Unit, the demonstrator was dismantled and installed in April at the AIDE wastewater treatment plant in Oupeye, from where the researchers have direct access to the sewage sludge.

In a next step, expected in May, the demonstrator will be transferred to a wastewater treatment plant in Scotland, where other project partners are working.

About Phos4You

Phos4You addresses the challenge of phosphorus. Phosphorus (P) is an essential nutrient for all living organisms. Although it is a limited resource on Earth, phosphorus is widely wasted today. The EU recognised this by adding phosphate rock to its list of critical raw materials in 2014. There is a need to increase the recovery of phosphorus and to use this so-called "secondary" material.

Phos4You specifically targets the recovery of phosphorus from wastewater and accelerates the exploitation of this potential. Estimated at 113,000 tonnes of P per year, this potential could cover 26% of the demand for mineral phosphorus in the North-Western Europe region. The region imports almost 100% of its mineral phosphorus needs. At the end of the project, it should exploit 3.5% of this potential, 35% after 5 years, 90% after 10 years.

The project should help decide which technology is best suited to different territorial situations. To ensure the phosphorus cycle and the effective link between P recovery and recycling, Phos4You must show to what extent fertilisers containing secondary phosphorus are beneficial to plants, with low levels of contaminants and in compliance with current legislation.

The steps to achieve this:

  • Construction and operation of demonstrators using innovative technologies for P recovery under real conditions from municipal wastewater;
  • Incorporation of recovered phosphate materials into the fertilisation chain;
  • Proposal of a European standard for the quality assessment of fertiliser products containing recycled materials;
  • Development of business plans for P recycling in urban and rural areas.

The Phos4You project is supported by the European Interreg North-West Europe funds. It involves several universities, research centres and companies (INRAE, Cork Institute of Technology, Fachhochschule Nordwestschweiz, Emschergenossenschaft, Glagow Caledonian University, University of the Highlands and Islands, Veolia Environnement, NV HVC, Scottish Water, UGent and ULiège). It is financially supported by the European regions. Its overall budget is €11 million, of which €6.5 million comes from the European Interreg North-West Europe funds.

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About the Chemical Engineering Research Unit (ULiège)

The Chemical Engineering Research Unit (RU) is one of the 4 RUs of the School of Engineering of ULiège. 70 people are affiliated to the RU, including about 30 PhD researchers. The annual budget is between 4 and 5 million euros, with a majority of external funding coming from the European Union (Interreg, H2020...), Wallonia (Greenwin, Win2wall projects...), the Fund for Scientific Research – FNRS and consultancy activities for industry. The members of the UR develop research activities in 5 main application areas (energy, environment, health, resources and recycling, space), materials being a transversal theme.

Some current research projects:

  • power to fuel or the transformation of CO2 and hydrogen into energy carriers;
  • the synthesis of innovative materials for the production of batteries and other electrochemical systems;
  • the elimination of micropollutants (drugs, etc.) from water by photochemical means;
  • the design of bioreactors for the culture of stem cells.

One of the Chemical Engineering Research Unit strengths is its strong experimental component, with the presence of numerous pilot-scale installations and characterisation tools. A platform for characterisation techniques of porous materials has recently been created in order to offer internal and external services (CARPOR).

Chemical Engineering


About SPGE

The Société Publique de Gestion de l'Eau (SPGE) coordinates and finances the water sector in Wallonia in order to preserve public health and to protect and restore water resources and aquatic systems from pollution of all origins. In consultation with its partners, it deals primarily with wastewater treatment and the protection of water catchments.

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