Phosphorus recovery via vivianite precipitation in anaerobic digestion and fermentation processes: A comprehensive review

Abstract

Phosphorus recovery is gaining importance due to its supply risk. Wastewater treatment plants (WWTPs) are sinks of phosphorus from municipal and industrial discharges, making them ideal sites for recovery. In WWTPs, the dosage of FeCl3 favours spontaneous formation of vivianite (Fe3(PO4)2⋅8H2O). The optimal Fe:P molar ratio and pH are 2.5:1 and 7–9, respectively. These conditions can achieve phosphate recoveries as vivianite of 70–90 % after the anaerobic digestion (AD) stage. Nonetheless, excessive addition of iron ions and/or vivianite formation in AD can hinder organic matter degradation and lower biogas yields. Anaerobic fermentation (AF) and seeding have enhanced phosphorus recovery yields. The former mobilises more phosphorus and iron into the soluble fraction, while the latter promotes larger crystal sizes by reducing the supersaturation demand. Vivianite precipitation is a promising technology for phosphorus recovery due to its potential applications in industry and agriculture, all while supporting the circular economy. This literature review provides a comprehensive overview of current knowledge on vivianite precipitation in WWTPs, including detection and quantification methods. It also identifies key disadvantages of vivianite formation in WWTPs and provides valuable recommendations for future research.