The effect of calcium and magnesium on the aggregation of a purple phototrophic bacteria mixed consortium

Abstract BACKGROUND An essential aspect of applying Purple Phototrophic Bacteria (PPB) technology for wastewater treatment is the biomass separation from the aqueous phase. Ca 2+ and Mg 2+ have been used to enhance the aggregation of different biological matrices. In this paper, the effect of Ca 2+ and Mg 2+ on the aggregation of a mixed culture of PPB was evaluated. Key physical and chemical parameters, including extracellular polymeric substance segregation and characterization, zeta potential, and particle size, were evaluated to elucidate the mechanism of PPB aggregation. RESULTS Using Ca 2+ alone and a combination of Ca and Mg enhances the separation of the biomass. The presence of Ca 2+ effectively increases the hydrophobicity and particle size of PPB. The combination of Ca 2+ and Mg 2+ improves the hydrophobicity of cells up to 75%. The SVI and settling velocity of the obtained PPB aggregates were 26 ± 4 mL g −1 and 3.5 ± 0.2 m h −1 , respectively. Evidence suggests that Ca 2+ interaction with polysaccharides enables agglomeration and reduced exposure of hydrophilic structural rearrangement, making it the main aggregation mechanism rather than double‐layer compression. CONCLUSIONS Our results demonstrate that a combination of CaMg enhances the aggregation ability of the mixed culture of PPB due to a high hydrophobicity and potential EPS binding phenomena. Our strategy allows the formation of floccular PPB aggregates with good settling properties. © 2026 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).