In-situ synthesis/purification integration strategy for simultaneous capture of ammonium and phosphorus from digested piggery wastewater using magnesium-doped tricalcium aluminate

Simultaneous capture of ammonium (NH₄⁺-N) and phosphate (PO₄³⁻-P) in digested piggery wastewater is of great urgency yet remains a challenge. Recently, the in-situ synthesis/purification integration (ISSPI) strategy, with the essence of converting contaminations to high value-added products, has aroused great enthusiasm in the environmental remediation realm. In the present work, we employed ISSPI method for simultaneous elimination and recovery of NH₄⁺ and PO₄^3- from digested piggery wastewater based on the construction of a novel material system, i.e., Mg-doped tricalcium aluminate (Mg-C₃A), which coupled the features of cement-based material tricalcium aluminate (Ca₃Al₂O₆, C₃A) and Mg dopants. The released metal cations (Ca²⁺, Mg²⁺, and Al(OH)₄⁻) of Mg-C₃A were expected to act as precipitation agents to capture NH₄⁺ and PO₄³⁻ via the formation of Ca(NH₄)₂(HPO₄)_2, MgHPO₄·3H₂O or AlPO₄; OH⁻ established an alkaline environment for the enhancement of NH₄⁺ removal via neutralization; Mg²⁺ played a major role in the recovery of NH₄⁺ and PO₄³⁻, with the formation of valuable struvite as fertilizer. Benefited by these functions, Mg-C₃A exhibited superior removal capacity for NH₄⁺ (43.0 mg·g⁻¹) and PO₄³⁻ (20.2 mg·g⁻¹). More importantly, the ISSPI method using Mg-C₃A was prospective to be applied for authentic effluent treatment as demonstrated by response surface methodology (RSM), with the concentration of both ions down to the discharge standard of livestock and poultry breeding, China (80 mg·L⁻¹ for NH₄⁺; 8 mg·L⁻¹ for PO₄³⁻). This research provided an alternative and promising approach for the simultaneous removal and recovery of NH₄⁺ and PO₄³⁻ from digested piggery effluent, shedding light on environmental remediation.