The load limits have been exceeded: namely, the global limit values specified by the concept of Planetary Boundaries for biochemical material flows, i.e. nitrogen and phosphorus. "The planetary 'crash barriers' are like crash barriers in traffic: We would do better to comply with them," explained Dr. Holger Hoff of the Stockholm Environment Institute at the opening of the 24th DBU-Sommerakademie "Das richtige Maß: Zukunftsstrategien für Phosphor und Stickstoff" ("The Right Amount: Future Strategies for Phosphorus and Nitrogen") at the Evangelisches Zentrum Kloster Drübeck. At the invitation of the DBU, around 90 representatives from science, water management, agriculture, government, specialist authorities, local authorities and business discussed - in plenary sessions and three workshops from 4 to 6 June - how the input of the nutrients nitrogen and phosphorus into the environment can be reduced, and with which communication concepts this can be supported.
"Do more with less," as Prof. Dr. ir. Wim de Vries from Wageningen University & Research summed up his solution proposal. This refers to increasing the efficiency of nitrogen and phosphorus use and thus reducing the discharge of these plant nutrients into air and water. To this end, de Vries formulated four approaches: 1) eating less meat, 2) recycling animal and human excrements, 3) recycling harvest waste and 4) avoiding food losses and food waste. Prof. Dr. Friedhelm Taube of the Christian-Albrechts-Universität zu Kiel specified with regard to nitrogen that "more with less" should not necessarily mean more yield, but rather more eco-efficiency. The aim is to achieve the lowest possible emissions level per product unit with the highest possible production. He added: “For more than 20 years, the implementation of political goals in the agri-environmental sector in Germany has been a major political failure - that is the real problem.”
With regard to phosphorus, the amended Sewage Sludge Ordinance (Klärschlammverordnung, AbfKlärV) stipulates that phosphate must be recovered from sewage sludge and sewage sludge ash beginning in 2029. As of 2023, all sewage treatment plants, regardless of their size, must submit concepts on how they will handle their sewage sludge in the future under the stipulations of the recycling law. "Phosphorus recycling must not be an end in itself, but must be economical," emphasized Dr. Rainer Schnee, Chairman of the Deutsche Phosphor-Plattform (DPP e. V.). Using the recovered phosphates as fertilizers in organic farming was described as a "very sensible way of recycling".
The final panel discussion, in particular, showed that among the many measures taken and concepts for phosphorus recovery from sewage sludge, there is currently a trend towards mono-combustion. It is therefore essential to develop procedures to process the ash from mono-combustion into usable fertilizer. But regardless of this, all technologies that have reached a certain level of maturity should be brought to market readiness with accompanying research.
A look across the national border at our German neighbors is also revealing: material flow analyses for nitrogen and phosphorus, such as those carried out in Austria, were highlighted as useful and the Danish fertilizer ordinance, which prescribes absolute upper limits for nitrogen and phosphorus fertilization, was regarded as exemplary.
"Nitrogen and phosphorus emissions can be reduced, there are examples of this," said DBU Deputy Secretary General Prof. Dr. Werner Wahmhoff in his closing remarks. "The DBU will continue to ask where it can help with support." For many years now, the DBU has supported methods of fertilization, animal husbandry and -feeding through which significantly fewer nitrogen compounds are released into the environment, and projects that contribute to closing the phosphorus cycle, as well as proposals to impart new knowledge and educational concepts for specific target groups.
