Mineral pollutants removal through immobilized microalgae-bacterial flocs in a multitrophic microreactor

Microalgae-bacterial flocs (MaB-flocs) immobilization technique using polyvinyl alcohol (PVA) crosslinked with sodium alginate represent a novel approach for sustainable pollutants removal. The present work was performed to evaluate the performance of a multitrophic batch reactor at microscale for treating two synthetic wastewater solutions prepared with two different initial Chemical Oxygen Demand (COD): 200 mg.L^-1 and 450 mg.L^-1, respectively. Three MaB-flocs concentrations were entrapped into PVA-alginate beads: C₁ (2%, v/v), C₂ (5%, v/v) and C₃ (10%, v/v), without O₂ supply, during three periods 2, 4 and 6 days of batch incubation. PVA-alginate beads containing the highest concentration C₃ of MaB-flocs improved the performance of the microreactor to remove significantly NH₄⁺ and PO₄^3- of about 61% and 82%, respectively, from wastewater more than two other concentrations used. This result confirms that C₃ of MaB-flocs displays not only a good potential for nutrients removals but also the highest MaB-flocs morphological progression after 6 days of treatment with the highest COD of 450 mg.L^-1. The feasibility of the PVA-alginate for cells immobilization, investigated through microscopy analysis, reveals that the evolution of multicellularity in MaB-flocs, for all experiments.