Phosphorus recycling from sewage sludge ash: New microbiological process

Fritzmeier Umwelttechnik GmbH & Co. KG, together with partners, has developed an environmentally friendly process for phosphorus recycling and made it ready for technical production. This is of great technical and economic importance due to the obligation for operators of large sewage treatment plants to recover phosphorus in the future.

The current Ordinance on the Reorganization of Sewage Sludge Utilization (AbfKlärV) obliges operators of sewage treatment plants to recover phosphorus from sewage sludge. In order to establish a suitable process, there are transition periods until 2032 or 2029. According to this, sewage treatment plants which treat the effluents of more than 50,000 or 100,000 inhabitants must recover phosphorus from sewage sludge or from sewage sludge ash, provided that the sewage sludge has a phosphorus concentration of at least 20 grams per kilogram of dry matter. Wastewater treatment plant operators must be able to present appropriate concepts for recovering phosphorus as early as 2023. However, existing technologies are only partially suitable for this, as they are chemically and cost-intensive.

Fritzmeier Umwelttechnik has developed a patented, environmentally friendly, microbiological process (“p-BAC®”) for recovering phosphorus from sewage sludge ash and, together with partners Münchner Stadtwässerung, Fraunhofer IWKS and ICL Fertilizers, in the project “Phosphorus recycling — from recycled material to intelligent, long-term fertiliser — PriL” transferred to the pilot plant scale. As a result, the process is just about to be ready for the market and offers a variety of advantages over previous technologies:

Phosphorus recycling for use in fertilizers

Fertilizers are usually required to cultivate plants in agriculture and horticulture. These fertilizers contain a significant proportion of phosphorus compounds. The phosphorus required for this currently comes from sedimentary deposits, but around 75% of the world's deposits are located in Morocco and the western Sahara. For example, political uncertainties can lead to supply bottlenecks and speculation on commodity markets can lead to sharp price increases. In addition, crude phosphates mined from sedimentary deposits are increasingly contaminated with toxic heavy metals.

With p-BAC® technology from Fritzmeier Umwelttechnik, up to 90 percent of the original phosphate from the sewage sludge mesh can now be recovered in an environmentally friendly and comparatively economical manner. The phosphorus compounds are very readily available to plants and can therefore be used directly for fertilization. It is also essential for this cost-effective process that p-BAC® technology allows the process water to be circulated so that there are no problematic process flows that are difficult to dispose of.

High environmental friendliness by fixing carbon dioxide from the atmosphere

In chemical processes, for example, sewage sludge ash is treated with large amounts of sulfuric acid in order to dissolve the phosphorus it contains. This is different with the microbiological p-BAC® process. Here, elemental sulfur is added to the microorganisms, which then oxidize it to sulfuric acid by absorbing carbon dioxide from the atmosphere. As a result, heavy metals and phosphorus contained in the sewage sludge ash are converted into water-soluble salts and dissolved. This process is based on microbiological ore leaching (“bio-leaching”). The phosphorus dissolved by the biologically produced sulfuric acid is then selectively converted by microorganisms, which is separated from the leaching solution and can therefore be recovered for further use as fertilizer. This results in a product that meets the requirements of the EU Fertilizer Regulation.

In short: p-BAC® technology is an easily scalable process that is particularly environmentally friendly and offers manifold benefits for operators of sewage treatment plants. Further information is available on the Internet at Fritzmeier-Umwelttechnik.com.

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