Abstract
BackgroundNowadays, bioflocculation is considered as a potential technology that could be able to alleviate microalgae dewatering cost regarded as the cornerstone hindrance of their full-scale application. However, most bioflocculation studies reported are laboratory scales. This study examined a pilot-scale and in situ flocculation of freshwater microalgae Desmodesmus brasiliensis by microbial bioflocculant. Biochemical composition of microalgal biomass was analyzed to evaluate the applicability of bioflocculation for microalgae-based biofuel production.ResultsThe flocculation efficiency >98 % was achieved at both pilot-scale and in situ treatment. Bioflocculation is simple, effective, economic, and environmentally friendly. Even though total proteins recovered from biomass harvested by centrifugation and that harvested by bioflocculation were significantly different, there was no significant difference in total carbohydrates and total lipids recovered from either biomass harvested by centrifugation or biomass harvested by bioflocculation.ConclusionThe results herein presented, doubtlessly demonstrated that the γ-PGA bioflocculant produced by Bacillus licheniformis CGMCC 2876 is applicable for commercial-scale microalgae harvesting. In addition, bioflocculation process cost could greatly be reduced by in situ operation as no investment cost is needed for a separate flocculation tank and mixing device. Furthermore, bioflocculation method developed is a worthy microalgae harvesting method for algal-based biofuel production.Graphical abstractThe addition of bioflocculant to microalgae cultures followed by mixing elicits, the formation of heavy flocs which settle out by gravity sedimentation in a relatively short settling time.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0458-5) contains supplementary material, which is available to authorized users.
Highlights
Nowadays, bioflocculation is considered as a potential technology that could be able to alleviate microalgae dewatering cost regarded as the cornerstone hindrance of their full-scale application
The results presented by Lee et al [36, 44] are estimates for designed large-scale microalgae harvesting systems, a full life-cycle assessment (LCA) study based on a pilot-scale or a full-scale data considering all input materials incurred for microalgae harvesting unit would be appropriate to provide more accurate information
This work examined the pilot-scale and in situ flocculation of the freshwater microalgae D. brasiliensis induced by the bioflocculant poly γ-glutamic acid (γ-PGA) produced by B. licheniformis CGMCC 2876
Summary
Bioflocculation is considered as a potential technology that could be able to alleviate microalgae dewatering cost regarded as the cornerstone hindrance of their full-scale application. Biochemical composition of microalgal biomass was analyzed to evaluate the applicability of bioflocculation for microalgae-based biofuel production. Microalgae have appreciable growth rate, high lipids, and carbohydrate yield and other biochemicals such as proteins and vitamins, microalgae cultivation can be incorporated in different environmental bioremediation schemes [3,4,5]. Regardless of these advantages, the major challenge lies in the dewatering of. Flocculation induced by pH increase is ascribable to precipitation of CaCO3, Mg(OH), and calcium phosphate [9], while the flocculation at decreased pH is due to charge neutralization as the Ndikubwimana et al Biotechnol Biofuels (2016) 9:47 carboxylate ions of organic matters attached to microalgal cells accept protons as a result of pH reduction [10].
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