Sewage sludge as a raw material and heat supplier

18.07.2025

Source: E & M powernews

Future requirements for sewage sludge recycling are leading to new projects for mono-incineration and phosphorus recycling. The first plants are already in operation.

From 2029, sewage treatment plants that treat wastewater from more than 100,000 people will no longer be allowed to dispose of the sewage sludge produced on fields, but will have to recycle it thermally and the phosphorus it contains must also be recovered. Smaller plants have a transitional period until 2032, which means that the practice of spreading sludge on fields, which has often been practiced up to now, will no longer apply - the cheaper alternative for many local authorities and sewage treatment plant operators.

Projects such as those from waste disposal service provider EEW Energy from Waste show how disposal obligations, heat generation and raw material recovery can be combined economically. EEW recently commissioned a new mono-incineration plant (MWIP) in Stavenhagen (Mecklenburg-Western Pomerania). The investment sum is around 70 million euros. The plant is designed to treat 160,000 tons of original substance per year. It is therefore dimensioned in such a way that it could incinerate all municipal sewage sludge in Mecklenburg-Vorpommern.

EEW is also planning to use the waste heat generated in Stavenhagen for local supply. The company's calculations show that around 80 percent of the town's heating requirements could be covered. Work is underway to connect the waste incineration plant to the district heating network and to expand the network in the town. Heat is to be provided from 2026.

EEW's third major project - phosphorus as a secondary raw material

With Stavenhagen, EEW has now commissioned the third of five approved sewage sludge mono-incineration plants. The other two are located in Helmstedt (Lower Saxony) and in Delfzijl in the Netherlands, while a further plant is currently being commissioned in Magdeburg.
"We have also been affected by the rise in energy and raw material prices. We are therefore carefully considering when it is worth completing which plant," says Timo Poppe, CEO of the EEW Group, in an interview with the editorial team. "Our plants are not currently running at full capacity." Thermal treatment is more climate-friendly, but involves higher costs for local authorities - up to three times more expensive than the previous method, according to Poppe.

The plants also create the conditions for a second legal requirement: from 2029, the recovery of phosphorus from the ash produced will be mandatory. One argument for the use of mono-incineration plants is the high purity of the ash. As only sewage sludge is incinerated, a homogeneous residue is produced, which improves the conditions for economical phosphorus recycling.

Regional differences in thermal utilization

According to figures from the Federal Statistical Office, sewage treatment plants in Germany thermally recycled around 1.32 million tons of sewage sludge in 2023. This corresponds to 81% of the total quantity of 1.63 million tons disposed of. The proportion of processes with technical phosphorus recovery capability increased by 12% to 656,000 tons compared to the previous year.

However, there are regional differences: In Baden-Württemberg, North Rhine-Westphalia and Bavaria, the proportion of thermal recovery in 2022 was between 89 and 99 percent. In Lower Saxony, Mecklenburg-Western Pomerania and Thuringia, only 44 to 58 percent of sewage sludge was incinerated. According to Poppe, the agricultural structure plays a role. In northern federal states, spreading on large arable areas is more economical.

The company relies on cooperation to recover phosphorus. EEW and Phosphorgewinnung Schkopau GmbH (PGS), a joint venture between the Swedish company "EasyMining" and Gelsenwasser AG, signed a contract in June: EEW will supply the ash so that it can be processed there in future.

EEW has previously entered into further partnerships with Remondis and Veolia. Veolia has been working on testing a process chain for sewage sludge recycling with phosphorus recycling since 2020. The waste recycler has entered into a partnership with Stickstoffwerke Piesteritz for this purpose. Remondis has built a recovery plant at the Hamburg sewage treatment plant in cooperation with Hamburg Wasser. According to Timo Poppe, the process is not yet running smoothly in Germany. However, he assumes that stable processes will be available by 2029.

An additional reason for the obligation to recover phosphorus is geopolitical dependency: around 80 percent of global phosphate production is accounted for by five countries - including China, Morocco and Russia. Germany is almost entirely dependent on imports. The new recycling obligation is intended to help secure raw materials.

Author: Heidi Roider