Valuable phosphorus from sewage sludge

DBU supports AVA cleanphos technology in Karlsruhe

To further develop a new process to extract phosphorus from HTC-coal produced from municipal sewage sludge, the German Federal Environmental Foundation (DBU) is supporting an AVA cleanphos pilot plant in Karlsruhe.

The AVA cleanphos process, based on hydrothermal carbonisation (HTC), has already been successfully tested in AVA-CO2’s laboratories. It will now be tested at pilot scale for the next 12 months, in cooperation with the project partners – the University of Hohenheim and the project group for material cycles and resource strategy at the Fraunhofer Institute for Silicate Research. The project will demonstrate that with AVA cleanphos technology, recycling fertiliser with a high, plant-available nutrient content can be produced efficiently and cost-effectively from sewage sludge.

For the industry, AVA cleanphos could be a breakthrough in phosphorus recovery, a requirement from an amendment to the Sewage Sludge Ordinance.  The AVA cleanphos process has the potential to be more efficient and cost-effective than existing methods, as municipal sewage sludge is converted first into HTC-coal before the phosphate is isolated.  This creates two products of commercial interest – a valuable fertiliser and phosphorus-free HTC-coal, which could be used as a substitute for brown or black coal in the future and lead to substantial CO2 emissions savings.  “The HTC process, in combination with the AVA cleanphos solution, paves the way for a useful, long-term application for sewage sludge”, says Thomas Kläusli, Chief Marketing Officer at AVA-CO2.

For the agricultural sector, the method also offers new possibilities. “Although sewage sludge contains a lot of valuable phosphate, there is a lot to be said against its use in agriculture.  Sewage sludge can carry pathogenic substances and contains many heavy metals,” says Prof. Dr. Andrea Kruse, agricultural technologist at the University of Hohenheim. “Many existing phosphorus recovery technologies incinerate sewage sludge to extract the phosphorous from the ash and make fertiliser. However, these methods are more expensive and complicated than HTC.”

Phosphate is being mined in China, the US and Morocco, says Prof. Dr. Andrea Kruse: “These mines are being so exploited that they have to keep expanding deeper.  The deeper the mining, the more heavy metals like uranium contaminate the phosphate and ending up with fertiliser, on the fields.  Therefore, we need new phosphate sources. With the HTC-based AVA cleanphos technology, phosphorous can be made from sewage sludge.”

The project group at the Fraunhofer Institute for Silicate Research is also providing scientific support to the project and will provide detailed analysis in line with fertiliser regulations.

About AVA-CO2

Leading biotechnology company AVA-CO2 uses hydrothermal processes to produce materials and energy from biomass.

AVA-CO2 provides a range of services, including a patented process for the large-scale production of bio-based platform chemical 5-Hydroxymethylfurfural (5-HMF).  5-HMF is a renewable alternative to petro-based materials and is used in the chemical and pharmaceutical industries.  AVA-CO2’s subsidiary, AVA Biochem, already produces high-purity 5-HMF for the speciality chemicals markets.  AVA-CO2 is a leader in using hydrothermal carbonisation (HTC) to efficiently dispose of sewage sludge and other organic residues and for producing high-performance carbons such as powdered activated carbon or carbon black.  As a leader in hydrothermal carbonisation, the company has enabled the development of a proprietary process, ‘AVA cleanphos’, to recover phosphorous from carbonised biomass efficiently.

A Swiss company, AVA-CO2 is based in Zug, Switzerland and has subsidiaries in Switzerland and Germany.  In October 2010, the world‘s first industrial-scale demonstration HTC plant opened in Karlsruhe, Germany.  In February 2014, the world’s first commercial plant for 5-HMF production, Biochem-1, was commissioned.

About University of Hohenheim

Established in 1818 after a devastating famine, the University of Hohenheim conducts research to provide innovative solutions to pressing social issues. The University of Hohenheim teaches a range of subjects and it is the top German University for agricultural research and food sciences.  The University has a strong profile in economics and communications as well as natural and social sciences.


Deutsche Bundesstiftung Umwelt (DBU)
Fraunhofer-Institut für Silicatforschung (ISC)
Universität Hohenheim


Renewable Carbon News – Daily Newsletter

Subscribe to our daily email newsletter – the world's leading newsletter on renewable materials and chemicals