Nutrient recovery through struvite precipitation from anaerobically digested poultry wastewater in an air-lift electrolytic reactor: Process modeling and cost analysis

Anaerobic digested poultry wastewater (ADPW) is characterized by high levels of nutrients (nitrogen and phosphorus), which need to be removed and recovered before the wastewater is discharged into water bodies with advanced nutrient recovery technologies that are cheap and eco-friendly. In this study, an innovative air-lift electrolytic reactor (ALER) with a magnesium anode was developed for phosphate (PO43−) and ammonia–nitrogen (NH3–N) recovery from anaerobically digested poultry wastewater through electrochemical struvite (MgNH4PO4‧ 6H2O) precipitation. Under constant current density (12.4 A/m2) and superficial velocity (107.42 m/h), the maximum removal efficiencies of PO43− and NH3–N were 99.9% and 97.3%, respectively. Kinetic modeling revealed that PO43− and NH3–N removal from the liquid phase by the ALER followed a pseudo-first-order reaction model, with rate constants (k) of 0.0188 min−1 and 0.0143 min−1, respectively. The recovered precipitate was characterized with FTIR, XRD, and SEM-EDS which also identified that precipitates as high-purity (88.5%) struvite with a mean particle size of 142.95 μm. Mean particle size and size distribution were found to be linearly increased with superficial upflow velocity. The electrical energy consumption per order (EEO) of the ALER was 0.824 kWh/m3, and the space–time yield is achieved at 0.988 kg/m3h with a corresponding operating cost of 3.87 $/m3. The ALER process has proven to be energy efficient in nutrient recovery from ADPW with struvite products suitable to be used in agricultural practices.