Integration of struvite precipitation and membrane stripping in a single reactor for dual nutrient recovery: A feasibility assessment with synthetic wastewater

Abstract

Integrating complementary nitrogen (N)- and phosphorus (P)-oriented recovery processes is crucial for advancing wastewater treatment plants toward water resource recovery facilities. This study proposes an innovative one-reactor system for dual nutrient recovery, combining P chemical precipitation and ammonia (NH3) absorption into acid via gas-to-liquid membrane stripping (GLMS), using elevated temperature (T) and alkaline pH to promote both struvite formation and NH₃ volatilization. Laboratory-scale batch tests were performed using synthetic wastewater to evaluate the integrated technology feasibility and understand the effects of pH (7.3–10.0), T (20–50°C), and feed concentration (1.0–3.0 gNdm⁻³; 0.4–1.2 gPdm⁻³) on recovery performance and product purity. The system achieved up to 99.3 %P and 93.1 %N recovery, with GLMS increasing N recovery by 37.0 ± 24.6 % compared to struvite precipitation alone, though the dominant N recovery pathway (crystallization vs. absorption) depended on the applied operational conditions. Struvite was the dominant P phase at pH ≤ 9.0, whereas highly alkaline and thermal conditions, together with a higher feed concentration, affected product purity and homogeneity. Conversely, elevated pH and T were the main drivers of NH₃ volatilization, showcasing the mutual effect of NH3 stripping and struvite precipitation. Operation under moderate conditions (pH 8.0–9.0, 38–41°C) yielded high-purity struvite (∼100.0 %), > 93.0 %P and > 40.0 %N recovery effectiveness. This study demonstrates the feasibility of integrating struvite precipitation with NH3-oriented GLMS in a compact system for enhanced nutrient recovery from wastewater, enabling the production of two wastewater-derived fertilizers while reducing spatial footprint, energy consumption, and chemical demand compared to conventional two-stage N and P recovery systems.