A review on flocculation as an efficient method to harvest energy microalgae: Mechanisms, performances, influencing factors and perspectives

Li, Shuangxi; Hu, Tianyi; Xu, Yanzhe; Wang, Jingyi; Chu, Ruoyu; Yin, Zhaoyi; Mo, Fan; Zhu, Linna

doi:10.1016/j.rser.2020.110005

Cited by 175 publications

(81 citation statements)

References 153 publications

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“…The flocculation process and its effectiveness are influenced by many factors, such as the chemical structure and properties (including charge) of both the removed substance and flocculant (in the case of polymers important is also average molecular weight and its distribution), their concentration, environment pH, ionic strength, temperature, rate of mixing, and mechanism of the process [ 5 , 57 , 64 ]. The most important factors discussed in recent studies are presented below.…”

Section: Factors Affecting Flocculationmentioning

confidence: 99%

Recent Achievements in Polymer Bio-Based Flocculants for Water Treatment

2020

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Polymer flocculants are used to promote solid–liquid separation processes in potable water and wastewater treatment. Recently, bio-based flocculants have received a lot of attention due to their superior advantages over conventional synthetic polymers or inorganic agents. Among natural polymers, polysaccharides show many benefits such as biodegradability, non-toxicity, ability to undergo different chemical modifications, and wide accessibility from renewable sources. The following article provides an overview of bio-based flocculants and their potential application in water treatment, which may be an indication to look for safer alternatives compared to synthetic polymers. Based on the recent literature, a new approach in searching for biopolymer flocculants sources, flocculation mechanisms, test methods, and factors affecting this process are presented. Particular attention is paid to flocculants based on starch, cellulose, chitosan, and their derivatives because they are low-cost and ecological materials, accepted in industrial practice. New trends in water treatment technology, including biosynthetic polymers, nanobioflocculants, and stimulant-responsive flocculants are also considered.

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Section: Factors Affecting Flocculationmentioning

confidence: 99%

Recent Achievements in Polymer Bio-Based Flocculants for Water Treatment

2020

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“…The size of the algal flocs during flocculation is crucial in flocculation efficiency since it determines their settling rate, properties of the flocs, and flocculation efficiency [ 22 ]. The floc size can be significantly impacted by several physical and chemical types of interactions between the components, which include charge neutralization, bridging, and sweeping [ 21 ]. Figure 4 shows the size distributions of the C. vulgaris flocs formed by chitosan, WPE, and chitosan + WPE.…”

Section: Resultsmentioning

confidence: 99%

“…Flocculation is based on neutralization or reduction of microalgal surface charges using chemical flocculants (inorganic and organic), biological organisms, or using an electrical impulse [ 14 , 21 , 22 , 23 ]. Flocculation using positively charged ions was tested with a number of chemicals, such as aluminum sulfate, ferric chloride, polyacrylamide, polyethylene oxide, and others [ 3 , 15 , 21 , 24 , 25 ]. However, most of these chemicals covalently bind to the algal surfaces, contaminating the final product, which significantly limits their application.…”

Section: Introductionmentioning

confidence: 99%

Efficient Bioflocculation of Chlorella vulgaris with a Chitosan and Walnut Protein Extract

Zou

Mouradov

et al. 2021

Biology

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Bioflocculation represents an attractive technology for harvesting microalgae with the potential additive effect of flocculants on the production of added-value chemicals. Chitosan, as a cationic polyelectrolyte, is widely used as a non-toxic, biodegradable bioflocculant for many algal species. The high cost of chitosan makes its large-scale application economically challenging, which triggered research on reducing its amount using co-flocculation with other components. In our study, chitosan alone at a concentration 10 mg/L showed up to an 89% flocculation efficiency for Chlorella vulgaris. Walnut protein extract (WPE) alone showed a modest level (up to 40%) of flocculation efficiency. The presence of WPE increased chitosan’s flocculation efficiency up to 98% at a reduced concentration of chitosan (6 mg/L). Assessment of co-flocculation efficiency at a broad region of pH showed the maximum harvesting efficiency at a neutral pH. Fourier transform infrared spectroscopy, floc size analysis, and microscopy suggested that the dual flocculation with chitosan and walnut protein is a result of the chemical interaction between the components that form a web-like structure, enhancing the bridging and sweeping ability of chitosan. Co-flocculation of chitosan with walnut protein extract, a low-value leftover from walnut oil production, represents an efficient and relatively cheap system for microalgal harvesting.

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“…Inorganic salts are [20], in addition to the efficiency in mixing salt with the medium, since aluminum sulfate reacts with water and forms aluminum hydroxides in a time of 1-7 s after the addition, in which phase the aluminum ions (Al 3+ ), aluminum hydroxide ions and aluminum hydroxides adsorb to the surface of the microalgae (negative charge) with an estimated time between 0.2 and 1 s [26]. According to Li et al [27] other free cations, such as Fe 3+ , Mg 2+ , and their hydrolysates are positively charged and can neutralize the negative charges of algae cells, promoting the collision and aggregation of cells to form flakes. Aluminum sulfate required an increase in concentrations to provide an increase in removal efficiency, with 20 mg L −1 stabilizing close to 74%, while 80 and 100 mg L −1 surpassed the efficiency of 95.0%.…”

Section: Discussion Of Preliminary Treatmentsmentioning

confidence: 99%

Evaluation of natural flocculant efficiency in the harvest of microalgae Monoraphidium contortum

et al. 2021

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This study assesses two parameters that can result in high efficiency in the recovery of the microalgae Monoraphidium contortum. The significant contribution of this paper is to test different coagulants in different conditions of concentration in the coagulation and flocculation processes followed by sedimentation to evidence the best coagulant and the best condition for harvesting of Monoraphidium contortum biomass. So the proposed methodology aimed to perform preliminary tests using a tannin-based cationic coagulant (TANFLOC SG®), FeCl2, and Al2 (SO4)3, where they were performed at concentrations of 0, 20, 40, 60, 80, and 100 mg L−1 at a fast mixing speed of 400 RPM. The tests determined 20 mg L−1 of Tanfloc SG® as the most efficient turbidity reduction in the preliminary test. The obtained results were used to construct a non-factorial central composite planning. Therefore, after a design of experiments, the study outcome shows the best turbidity removal range from the main tests came at 35 mg L−1 and 550 RPM of fast mixing speed.

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A review on flocculation as an efficient method to harvest energy microalgae: Mechanisms, performances, influencing factors and perspectives

Cited by 175 publications

References 153 publications

Recent Achievements in Polymer Bio-Based Flocculants for Water Treatment

Recent Achievements in Polymer Bio-Based Flocculants for Water Treatment

Efficient Bioflocculation of Chlorella vulgaris with a Chitosan and Walnut Protein Extract

Evaluation of natural flocculant efficiency in the harvest of microalgae Monoraphidium contortum

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