Enhanced phosphorus recovery via chemical precipitation coupled with microbially induced recrystallization into vivianite from sludge digestion liquor

Phosphorus (P) recovery is critical for sustainable resource management, given its non-renewable nature and geopolitical supply risks. This study addresses the limitations of conventional approaches for inducing vivianite crystallization in wastewater, including low yield per unit volume, limited phosphorus recovery efficiency, and low vivianite purity. To overcome these challenges, we propose a two-stage hybrid strategy that combines chemical precipitation with microbially induced recrystallization under semi-solid conditions. In the first stage, iron-based coagulation captures the majority of phosphate as amorphous Fe–P complexes. In the subsequent stage, dissimilatory iron-reducing bacteria (DIRB) facilitate the reduction of Fe(Ⅲ) and drive its recrystallization into vivianite. Compared with liquid-phase crystallization, this approach supports higher P loading, thereby improving spatial efficiency and enhancing vivianite purity. Batch experiments demonstrated that increasing the solid content consistently enhanced the vivianite fraction in the product, achieving a maximum P recovery efficiency of 97.7 % and a vivianite purity of 92.6 %, which is markedly superior to other reported crystallization methods. Microbial community analysis revealed Trichlorobacter and Geobacter are key dissimilatory Fe-reducing genera driving the recrystallization of precipitates to vivianite. Successful application to real sludge digestion liquor confirmed the method's robustness.