An in situ method for synthesis of magnetic nanomaterials and efficient harvesting for oleaginous microalgae in algal culture

Abstract

An in situ approach for magnetic nanomaterial synthesis and harvesting of oleaginous Chlorella sp. HQ in an algal culture was explored. Fe-based nanomaterials were synthesized by an in situ reduction reaction using NaBH4 and FeCl3∙6H2O in an algal culture. The various reactant molar ratios and the reaction system of a water solution or an algal culture determined the different formation pathways of magnetic nanomaterials. With the optimal reactant molar ratio of 2:1, this in situ magnetic harvesting method obtained a high harvesting efficiency in a broad pH and temperature range and different algal concentration levels with cost of $505 US per ton of algal biomass harvested. During this in situ process, the algal antioxidant defense system efficiently eliminated the cellular reactive oxygen species caused by nanomaterials via catalase and superoxide dismutase. Fatty acid methyl ester composition analysis indicated that the Fe-based nanomaterials affected the relative contents of several components, but the predominant types were still palmitic acid (C16:0), linoleic acid (C18:2) and γ-linoleic acid (C18:3), which were suitable for biofuel production. Additionally, the recycled cultivation medium maintained normal algal cell growth within 18 days after the biomass had reached the harvesting level. This novel in situ method has promising potential for the harvest of oleaginous microalgae with good biocompatibility.