Investigating flocculation performance of cationic guar gum and combined with foam flotation for enhanced microalgae harvesting

Despite the substantial potential of microalgae as biomass feedstocks, their commercial development hindered by the lack of economically viable and technically efficient harvesting methods. In the current study, an environmentally friendly bioflocculant cationic guar gum (CGG) was successfully developed. The harvesting efficiency and resultant floc morphology of CGG were evaluated experimentally and compared with those of common flocculants (alum, CPAM, and CS). CGG presented a promising alternative to traditional flocculants, offering distinct advantages in harvesting efficiency, dispersibility, and biocompatibility. Subsequently, a combined flocculation-flotation harvesting method was developed using CGG and the collector cetyltrimethylammonium bromide (CTAB). The incorporation of CGG as a pre-flocculation step significantly enhanced the microalgae recovery rate achieved by CTAB. Independently, CTAB at 20 mg L −1 achieved a recovery rate of only 28.4%. In contrast, adding CGG at concentrations ranging from 10 to 30 mg L −1 increased the recovery rate to 86.9–96.0%. Furthermore, characterization of floc particle size and fractal dimension across different harvesting stages confirmed that the role of that CTAB enhanced the utilization efficiency of CGG. The introduction of 20 mg L −1 CTAB increased the median floc diameter from 7.9–16.2 μm to 10.3–22.8 μm, while simultaneously improving floc compactness as evidenced by structural analyses. These findings provided a combined flocculation-flotation process for efficient microalgae harvesting and deeper insights into the synergistic effect of flocculant-collector on microalgae.