Phosphorus removal from municipal wastewater using calcium/iron oxide composites: Adsorption efficiency and impact on plant growth.

Phosphate minerals are crucial for the production of fertilizers, but limited availability does not meet the growing agricultural demand. At the same time, the discharge of phosphorus by municipal wastewater treatment plants leads to eutrophication. Removal and recovery of phosphorus from wastewater can both provide nutrients to agriculture and decrease eutrophication. This research aims to evaluate phosphorus removal from municipal wastewater in Latvia by mineral-based calcium/iron composites and examine spent oxides' phytotoxic effect on plant growth. Two CaFeOxides from Latvian earth pigments (iron oxide pigments) deposits were synthesized and characterised by X-ray powder diffraction, differential scanning calorimetry/thermogravimetry, scanning electron microscopy-energy dispersive X-ray analysis and specific surface area analysis. Adsorption properties of obtained oxides were evaluated with a standard phosphate solution, and real municipal wastewater. The phytotoxic effect of P-loaded composites was evaluated in a hydroponic system with common wheat (Triticum aestivum). The results indicated that calcium/iron oxide composites have higher P adsorption efficiency than the commercial Polonite material. The maximum sorption capacity of CaFeOxides was 63.29 and 83.33 mg P/g, and 53.19 mg/g for Polonite. Furthermore, the P-loaded CaFeOxides demonstrated no phytotoxic effect on the growth of Triticum aestivum, and at higher CaFeOxides concentrations, morphological and physiological parameters of wheat increased, showing great potential for reuse in agriculture.