Value-added application of cattle manure bottom ash for phosphorus recovery from water and replenishment in soil

Abstract

This study addresses ways to circulate the flow of phosphorus (P) from water to soil to improve water quality and provide a sustainable supply of P into soil. Here, bottom ash (BA_CCM), the byproduct of the combustion of cattle manure, which is performed for obtaining energy, was used to remove P in wastewater. Next, the P-captured BA_CCM was used as P fertilizer for rice growth. BA_CCM was primarily composed of Ca (49.4%), C (24.0%), and P (9.9%), and the crystalline phases of Ca were calcium carbonate (CaCO₃) and hydroxyapatite (Ca₅(PO₄)₃OH). The mechanism of P removal by BA_CCM involves the formation of hydroxyapatite by reacting Ca²⁺ with PO₄^3-. A reaction time of 3 h was required to achieve P adsorption to BA_CCM, and the maximum P adsorption capacity of BA_CCM was 45.46 mg/g. The increase in solution pH reduced P adsorption. However, at pH > 5, the P adsorption amount was maintained regardless of the pH increase. The presence of 10 mM SO₄^2- and CO₃^2- reduced P adsorption by 28.4% and 21.5%, respectively, and the impact of the presence of Cl^- and NO₃^- was less than 10%. The feasibility of BA_CCM was tested using real wastewater, and 3.33 g/L of BA_CCM dose achieved a P removal ratio of 99.8% and a residual concentration of <0.02 mg/L. The toxicity unit of BA_CCM determined for Daphnia magna (D. magna) was 5.1; however, the BA_CCM after P adsorption (P-BA_CCM) did not show any toxicity to D. magna. BA_CCM after P adsorption was used as an alternative to commercial P fertilizer. Rice fertilized with a medium level of P-BA_CCM showed better agronomic values for most agronomic traits, except root length, than that seen with the commercial P fertilizer. This study suggests that BA_CCM can be used as a value-added product to address environmental issues.

Keywords: Adsorption mechanism; Fertilizer; Phosphorus; Rice growth; Toxicity; Wastewater.