Abstract
This study developed a coagulation–flotation process for microalgae Chlorella sp. XJ-445 harvesting, which was composed of algal surface modification by combined use of Al3+ and cetyltrimethylammonium bromide (CTAB) and followed dispersed bubble flotation. Dissolved organic matter (DOM) in the medium was firstly characterized and mainly consisted of hydrophilic low molecular weight molecules. The dosage of collector (CTAB) and coagulant (Al3+) were optimized, and with the pretreatment of 40 mg Al3+ and 60 mg CTAB per 1 g dry biomass without pH adjustment, a maximum flotation recovery efficiency of 98.73% can be achieved with the presence of DOM. Algal cells characterization results showed that the combined use of CTAB and Al3+ largely enhanced the algal floc size, and exhibited higher degree of hydrophobicity, which favoured the flotation, and can be interpreted by DLVO (Derjaguin, Landau, Verwey and Overbeek) modelling. A benefit in fatty acid conversion was further found with the optimized coagulation–flotation process. It was suggested that this coagulation based flotation is a promising strategy for high-efficiency harvesting of microalgae.
Highlights
Microalgae as an alternative feedstock for biodiesel production has attracted much attention due to their high lipid content, high photosynthetic efficiency, CO2 reduction in the environment, and producing different value-added products compared to conventional crops
After 7 days cultivation, when the algal cells reached a biomass concentration of about 1.0 g l−1, they were centrifugally harvested at 6000g, and the supernatant was collected for Dissolved organic matter (DOM) analysis
In terms of dissolved organic carbon (DOC), HPI fractions dominated the DOM, constituting above 90% of DOM, whereas HPO and transphilic (TPI) only accounted for 3.3% and 3.5% of DOM, respectively. This observation on high proportion of hydrophilic property of DOM was consistent with the results reported previously by other researchers [26,27]
Summary
Microalgae as an alternative feedstock for biodiesel production has attracted much attention due to their high lipid content, high photosynthetic efficiency, CO2 reduction in the environment, and producing different value-added products compared to conventional crops. Commercial microalgae-based biofuel production is not economically viable yet. Discounting the not inconsiderable costs and difficulties associated with biomass production, the process of harvesting and dewatering has often been cited as one of the major factors preventing a scalable industry [1]. This is because the algal cells are small
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