The Zero‑P project was carried out from 2019 to 2022 with funding from the German Federal Ministry of Education and Research (BMBF, grant 02WPL1445A). The consortium was coordinated by Emscher Wassertechnik GmbH and included Nordic Water GmbH, the Technical University of Berlin, and the associate partner BRAWAG GmbH. The aim of the research was to demonstrate that very low phosphorus effluent limits, as required by the EU Water Framework Directive and the Surface Water Ordinance, can be achieved at a full‑scale wastewater treatment plant by combining a downstream phosphorus precipitation step with a continuous sand filter.
A semi‑technical pilot plant was installed at the Briest wastewater treatment plant in Brandenburg an der Havel. The plant was operated in a flow‑proportional mode to replicate real operating conditions. Phosphorus was precipitated by automated dosing of iron(III) chloride, the most effective coagulant identified in preliminary jar tests. The precipitate was formed in a reaction tank and then passed through a DynaSand filter supplied by Nordic Water GmbH. The filter featured continuous bed monitoring using sand‑cycle technology, allowing real‑time assessment of filter performance. Online monitoring of phosphorus concentrations was performed with a Hach Lange RTC module, although the accuracy of online analysers for the very low target concentrations proved challenging.
The technical results show that the combined precipitation and filtration system was able to keep orthophosphate (PO4‑P) concentrations below the target of 0.03 mg L⁻¹ in the effluent. However, the annual mean total phosphorus (Pges) target of 0.1 mg L⁻¹ could not be fully met because of a non‑precipitable phosphorus fraction (snrP) that remained in the stream. When the snrP contribution was excluded from the calculation, the system achieved the 0.1 mg L⁻¹ target. Across all experimental phases, the snrP fraction was reduced by an average of 48 %. The DynaSand filter also contributed to further reduction of orthophosphate by promoting flocculation within the filter bed. The plant’s performance was evaluated against laboratory 24‑hour composite samples and online measurements, confirming that the filter could sustain the required low PO4‑P levels under realistic operating conditions.
In addition to effluent quality, the project assessed the plantability of the phosphorus‑rich sludge. Tests indicated that the phosphorus bound in the tertiary sludge remained available to plants, suggesting a potential for agricultural reuse of the recovered material. This finding aligns with the project’s goal of not only protecting water bodies but also recovering phosphorus for resource recovery.
The project faced constraints during the COVID‑19 pandemic and due to reagent supply shortages, which limited the duration of some experimental runs and prevented the testing of alternative precipitants, sand grain sizes, and multi‑stage configurations. These limitations highlight the need for further research to refine the design and operation of the system for even stricter phosphorus limits.
Overall, the Zero‑P study demonstrates that a near‑complete phosphorus precipitation coupled with a continuously operated DynaSand filter can achieve very low orthophosphate effluent concentrations and significantly reduce total phosphorus, while also enabling phosphorus recovery from sludge. The collaboration among industry partners, academia, and a municipal water company, supported by BMBF funding, provided a comprehensive platform for translating laboratory findings into a semi‑industrial demonstration that informs future full‑scale implementations.