Investigation of potassium magnesium phosphate for wastewater recovering towards sustainable cities

•Recovering nutrients from wastewater contributes to sustainable city development.•MPP precipitation can simultaneously recover P and K from wastewater.•A relatively low MPP dosage is beneficial for ryegrass growth in laterite.•MPP can advance the germination time and chlorophyll contents of ryegrass.•Soil nutrient loss using MPP is clearly lower than those using MKP. Phosphorus (P) and potassium (K) are the two main nutrients of plants. It is of great significance to recover P and K from wastewater, which can reduce phosphate and potash ore mining and ensure secure fertilizer supply for the sustainable development of cities. The potassium magnesium phosphate (MgKPO4·6H2O; MPP) is recovered from wastewater. The current work systematically assessed the fertilizer efficiency of MPP by investigating its effect on seed germination, root development and growth of ryegrass. The experimental results showed that MPP promoted the growth of ryegrass at a relatively lower dosage (0.3 g MPP/pot). Compared with the commercial fertilizer of KH2PO4 (MKP), MPP shortened the germination time of ryegrass and increased the content of chlorophyll because it also contained magnesium. The loss rate of P in MPP was 12.66% lower than that in the MKP. When MPP was used, the soil's acidity was improved with the pH value of 6.75. Indeed, MPP was an effective fertilizer that could promote the growth of ryegrass, reduce the loss of nutrients and slightly improve the soil acidity. Therefore, it is of great significance to develop the crystallization of MPP for recycling P and K from wastewater, which favors the sustainable development of cities.