A comparative study of different iron minerals on phosphorus capture from municipal wastewater and subsequent recovery as vivianite through acidogenic fermentation

Exploiting phosphorus resources from waste streams such as municipal wastewater is essential for their recycling and utilization. However, common practice on phosphorus recovery via main-stream biological phosphorus removal and side-stream phosphorus precipitation still faces great challenges such as organic mineralization induced CO2 emission and aeration caused energy consumption. In this work, ferrihydrite and magnetite were respectively dosed into bioflocculation organic carbon capture system to comprehensively evaluate their potential improvements on phosphorus recovery from municipal wastewater. Results showed that ferrihydrite would outcompete magnetite on phosphorus capture, by increasing TP removal efficiency from 17.5% to 91.2% while maintaining a high organic carbon capture efficiency of about 50%. Although both iron minerals were favored for improving sludge settling performance, the potential toxicity of magnetite was higher than that of ferrihydrite. Chemical precipitation and adsorption are the main pathways for phosphorus removal by iron minerals. Subsequent anaerobic fermentation showed that ferrihydrite bounded phosphorus was mainly transformed to vivianite while magnetite captured phosphorus was released into the liquid. Surprisingly, ferrihydrite was favored for the volatile fatty acids rather than biogas production, with an average yield of 523.2 mg/g volatile suspended solids. This work might be valuable for exploring a more sustainable value-added resource recovery paradigm.