The high energy input required for harvesting microalgae means that commercial production of microalgal biodiesel is economically unfeasible. In this study, we investigated the flocculation efficiency and synergistic mechanisms of novel coupled flocculants, AlCl3 and compound bioflocculants (CBF), to overcome this difficulty. AlCl3 flocculation was found to be very sensitive to pH, and flocculation efficiency increased from 55 to 95 % when pH increased from 4 to 10. CBF was environmental friendly, less reliant on pH, but had a relatively low flocculation of 75 % in optimum conditions. The harvesting efficiency of Chlorella regularis can achieve a satisfactory level of 96.77 % even in neutral conditions, with a CBF dosage of 0.26 g/L, AlCl3 dosage of 0.18 g/L, and coagulant aid (CaCl2) dosage of 0.12 g/L. Interestingly, compared with the use of single flocculant, the dosage of CBF, AlCl3, and coagulant aid (CaCl2) were reduced by about 52, 49, and 66 %, respectively. Besides, the aluminum (Al) ion content of the supernatant decreased significantly to a residue of only 0.03 mg/L, therefore meeting the downstream process needs easily. Patching and bridging played key roles in coupled flocculant flocculation, in which AlCl3 mainly carried out the electrical neutralization. This work provides new insight into an efficient, economical, and environmentally friendly protocol for microalgae harvesting.
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The authors are grateful for the financial support from the National Natural Science Foundation of China (NSFC NO. 51578117), the Development Plan Project of Science and Technology of Jilin Province (20140101006JC) and the Fundamental Research Funds for the Central Universities (2412016KJ011). Moreover, we appreciate the Rhizobium radiobacter (F2) and Bacillus sphaeicus (F6) strain supplied by the Heilongjiang Environmental Biotechnology Key Laboratory of China.
Compliance with ethical standards
This study was funded by the National Natural Science Foundation of China (No. 51,578,117), the Development Plan Project of Science and Technology of Jilin Province (20140101006JC) and the Fundamental Research Funds for the Central Universities (2412016KJ011).
Conflict of interest
The authors declare that they have no competing interests.
This article does not contain any studies with human participants or animals performed by any of the authors.
Informed consent was obtained from all individual participants included in the study.
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