Production and characterization of alginate beads for growth of immobilized Desmodesmus subspicatus and its potential to remove potassium, carbon and nitrogen from sugarcane vinasse

Abstract Among the main industrial wastewaters, sugarcane vinasse figures as an actual environmental concern, due to its polluting potential and large volumes available, about 10–15 L per liter of ethanol. Microalgae immobilization in biopolymeric matrices, such as alginate, represents a promising strategy for wastewater treatment aiming the removal of nutrients. Alginate beads for immobilization of Chlorophyceae microalgae D. subspicatus were prepared with different biopolymer and crosslinking agent concentrations. Alginate beads showed good stability in vinasse probably owned to wastewater high calcium content. The growth of immobilized and free microalgae in sugarcane vinasse (bulk phase) and its potential to remove potassium, carbon and nitrogen from this wastewater were evaluated. Immobilized D. subspicatus showed maximum specific growth rate (μmax) of 0.009 h-1 for alginate beads (2%) crosslinked with 5% CaCl2, with 38, 27 and 28% of carbon, nitrogen and potassium removal. Free microalgae cultivation exhibit two μmax of approximately 0.01 h-1 (between 0-24 h and 48–72 h) and maximum carbon, nitrogen and potassium removals of 45, 49 and 8%, respectively. Potassium adsorption by the biopolymer matrix was significant, with maximum removals (37 and 35%) obtained by blank and immobilized microalgae alginate beads (2%) crosslinked with 10% CaCl2. Results indicate interesting perspectives for the use of D. subspicatus immobilized in alginate for removal of nutrients from sugarcane vinasse.