Ludwig Hermann
Senior Advisor
Proman Consulting
Austria
l.hermann@proman.pro
The predominant method of nutrient recycling in the Baltic Sea Region (BSR) involves the use of animal by-products (livestock manure), digestate and sewage sludge on arable land, typically following sanitation or other moderate treatment processes, such as composting. Some BSR countries have certification schemes, such as the Revaq scheme (https://www.ri.se/en/expertise-areas/services/certification-of-wastewater-treatment-plants-revaq) in Sweden. Germany is an exception in that it requires phosphorus (P) to be technically recycled if wastewater treatment plants exceed a population equivalent of 100,000 from 2029 and 50,000 from 2032. The preferred recycling route in Germany will be mono-incineration of sewage sludge and recovery of P from the ash, in compliance with the German Sewage Sludge Ordinance (AbfKlärV, https://www.gesetze-im-internet.de/abfkl_rv_2017/), and a minimum P recovery rate of 80%.
Germany is the only BSR country pursuing technical nutrient recycling, but the Nordic countries have advanced technical recycling companies and promising recycling initiatives.
EasyMining AB (www.easymining.com), part of the Ragn-Sells Group in Sweden, specialises in nutrient and material recycling. The company has developed several innovative processes for recovering valuable resources: The Ash2Salt process for salt recovery from municipal solid waste incineration fly ash with a capacity of 130,000 t/a is already in operation in Upplands-Bro, near Stockholm. Two Ash2Phos plants with a combined capacity of 60,000 t/a of sewage sludge ash (SSA) have got operating permits and construction will start in 2025 in Schkopau (Germany) and 2026 in Helsingborg (Sweden).
The Ash2Phos process is characterised by an acid attack of the SSA, followed by a series of precipitation steps to separate the different material streams. Phosphate is recovered in the form of calcium phosphate, iron and aluminium are returned to the wastewater treatment plant as coagulants, the silicate residue is suitable for cement replacement and the metals are potentially delivered to smelters for copper and zinc recovery.
The most important characteristic of the Ash2Phos products is their high purity - the material streams are separated to such an extent that the recycled product contains no relevant impurities or pollutants. The return of materials to their original function also reduces the environmental footprint - each stream replaces a primary raw material stream with sometimes relevant carbon emissions. Furthermore, calcium phosphates from the Ash2Phos process have been recommended for use in certified organic farming by the EGTOP expert group, and the European Commission has already proposed a corresponding amendment to Regulation (EU) 848/2018 and the implementing Regulation (EU) 1165/2021. Aqua2N is characterised by the removal of ammonia from the liquid phase and the reaction of the gas with sulphuric, phosphoric or nitric acid to form an ammonium sulphate, phosphate or nitrate solution that can be crystallised into a solid fertilising product.
LKAB, the Swedish state-owned mining and minerals group, has launched a highly relevant mining and recycling initiative (https://lkab.com/en/what-we-do/our-transformation/critical-minerals/). At its Per Geijer mine north of Kiruna, where apatite is the main valuable mineral apart from iron ore, phosphate and rare earth metals - the latter needed for wind turbines, electric cars and mobile phones - can be extracted as by-products. For many years, apatite was separated from iron ore and stored in mine tailings because it was not profitable to produce phosphate fertilisers. Recently, a new technology has been developed that makes phosphate processing economically viable. The initiative is supported by recent geopolitical developments and the European Commission's Critical Raw Materials Act, which aims to increase supply chain resilience and reduce dependence on supplies from less reliable countries. Some European fertiliser manufacturers and distributors rely on supplies of phosphate rock with negligible cadmium concentrations, partly due to the use of a processing by-product such as phosphogypsum in construction applications, and partly due to low cadmium limits in fertilisers in Nordic countries. Currently, the only low-cadmium source in the EU is the Siilinjärvi phosphate rock mine in eastern Finland. Beyond the EU's borders, Russia has similar low-cadmium magmatic phosphates, but the EU should avoid co-financing the war in Ukraine by importing phosphate rock and fertilisers from Russia. The Per Geijer mine could supply seven times Sweden's P fertiliser needs and become a significant source of clean phosphate in the EU.
LKAB is gradually implementing these plans. The apatite will be concentrated at the mine sites and transported to a new industrial park in Luleå, where the phosphorus and rare earth elements will be processed. LKAB's resources and reserves are estimated at four billion tonnes of iron ore, about twice the amount mined since 1980. “LKAB has applied for the iron ore mine in Gällivare, the planned industrial park in Luleå and the Per Geijer iron ore deposit in Kiruna, which is rich in rare earth elements and phosphorus, to be designated as strategic projects under the EU's Critical Raw Materials Act” (https://lkab.com/en/press/lkab-constructs-facility-for-critical-minerals-the-first-of-its-kind-in-europe/, accessed 24/03/2025).
HSY Helsinki's RAVITA Process (https://www.hsy.fi/en/ravita/process/) is a cutting-edge technique for the direct recovery of phosphorus and nitrogen from wastewater at the final stage of treatment. For P recovery, phosphorus is removed from treated wastewater through a chemical precipitation process. The resulting precipitate is then dissolved using phosphoric acid. Following dissolution, the phosphorus and the precipitating chemical are separated. The precipitating chemical is then recycled back into the post-precipitation process. A portion of the recovered phosphoric acid is reused in the process, while the excess becomes a product for the fertiliser industry and potential other industrial applications. Nitrogen recovery is applied to the reject water (condensate) from sludge drying with high ammoniacal nitrogen content. This nitrogen is recovered using a stripping process that utilises the recovered phosphoric acid. The end product is ammonium phosphate, which can be used as a fertiliser straight away. The process offers a sustainable way to purify wastewater while recovering essential nutrients for agricultural and industrial use.
The RAVITA DEMO pilot plant, situated at the Viikinmäki wastewater treatment plant, is engineered to evaluate the phosphorus recovery process on a reduced scale. It serves a population equivalent of 1,000 and is divided into three key areas:
A. Chemical sludge production with three steps: 1) Precipitation – phosphorus is removed from wastewater. 2) Disc filtration – removes nearly 95% of phosphorus in the first stage. 3) Sludge drying – preparing sludge for further processing.
At full-scale operation, two precipitation and separation stages will be needed to ensure very low phosphorus levels in the effluent. The resulting chemical sludge has a low heavy metal content, making it cleaner than sludge from traditional co-precipitation.
B. Sludge dissolution and phosphoric acid treatment: the process of breaking down sludge and refining phosphoric acid is being optimised. The objective is to transform the recovered phosphorus into a marketable product for industrial application.
The RAVITA DEMO plant is instrumental in refining this technology before its large-scale implementation in wastewater treatment plants.
The examples of cutting-edge technologies for nutrient recycling in the Baltic Sea Region have been selected by the author for their sustained development and backing by powerful institutions. The selection is based on the author's experience and is non-exhaustive. The author is aware of ongoing research projects that will complement the list with alternative approaches and some of these are partly presented in the same BRE Review issue.