The sewage sludge ordinance forces wastewater treatment plants to ensure the recovery of phosphate from the produced sewage sludge. In most cases, this obligation is transferred to the company in charge of the sludge disposal. For the recovery process, technology-specific but not product-specific specifications are made. The present article gives an overview of the products of different processes and their possible marketing in two routes: direct marketing and integration into the fertilizer industry. Possibilities, limits, requirements and potential product revenues for selected products are discussed against the background of current world market prices. Finally, the chemical expenditure of certain processes and logistical considerations are addressed. The considerations suggest that wet chemical ash processes should best be integrated in chemical parks.

With the new sewage sludge ordinance from 2017, phosphorus recovery becomes obligatory for large sewage treatment plant operators. Within the last year, the interpretation of this ordinance due to the exact wording has changed. As an example, a process aiming to recover phosphorus within the sewage treatment plant from waste water or sludge before the sludge is legally understood as waste. Therefore, a benchmark of 20 g Phosphorus (P)/kg dry matter (DM) is foreseen. However, this benchmark is an obstacle to increasing energy efficiency and sludge reduction, since carbon and dry matter is transferred into biogas in anaerobic digestion. Normally, raw sludge has a phosphorus content around 20 g P/kg DM, while digested sludge has a phosphorus content of about 35 g P/kg DM. The paper shows estimations of different full-scale combinations targeting phosphorus and advanced energy recovery and the resulting phosphorus content in sewage sludge per kg DM. Furthermore, this paper discusses the legal framework regarding phosphorus recovery from ash based on the sewage sludge ordinance, the national fertilizer regulation, the European Union fertilizing product regulation and the European Union feed/fodder regulation. The author concludes, that the legal framework is not explained properly to sewage treatment plant operators, which leads to confusions. Several questionable paragraphs and their wording should be addressed in future regulation amendments. Finally, there should be a regulatory need to establish phosphorus recovery from demand side (fertilizer industry, farmers) and not only from supplier side (sewage treatment plants). Because otherwise products must be produced, whereby no actual market for these products is established.