P-binding mineral materials to enhance phosphate removal using nature-based solutions in urban areas

The increase in urbanization has caused a deterioration of the quality of water bodies and ecosystems such as rivers, streams and lakes. Urban hydrology, which reflects the anthropogenic impact on water balance, results in an excess of phosphorus (P) and their eutrophication in urban water bodies. Nature-based solutions (NBS) are a measure for the restorations of green areas and the mitigation of urban stormwater problems. Despite many advantages, in some specific cases (e.g., green roofs), NBS may be a source of water pollution. The way to decrease P release from NBS construction is by using P-binding mineral materials (P-BMM). The aim of the study is: (1) to assess the sorption abilities of five different P-BMMs: autoclaved aerated concrete (AAC), Filtralite (R) Nature P (FNP) (Norway), limestone, Opoka and zeolite, (2) to determinate of the equilibrium contact time with P solution, and (3) to dimension the P-BMM filter mass needed to enhance P-removal from green roof run-off before it reaches the receiver. Based on the Langmuir isotherm equation, P-BMM maximum sorption capacity (S-max) and equilibrium sorption capacity (S-max_(Eq)) follow the sequence: FNP > Opoka > AAC > zeolite > limestone. The most suitable P-BMM for filling up the filter for green roof runoff seems to be AAC. This is because it took the shortest time to achieve equilibrium (300 min) and had high S-max_(Eq) value (66.28 mg g(-1)). The mass of AAC P-BMM needed to provide the P retention from 100 m(2) of a green roof ranges from 2.4 to 11.2 kg. The P-BMM filter, with a discharge to rain garden, was proposed as a P-removal enhancing system for green roof runoff.