Wang et al. (2013) reported 90% removal efficiency for Microcystis aeruginosa from water by utilizing a tannin dosage of 20 mg/L. Mezzari et al. (2014) utilized tannin for C. vulgaris harvesting, which grew within a PBR of wastewater digestate. In this study, the performance of natural organic and modified tannin with polyacrylamide to harvest C. vulgaris biomass was evaluated and reported with 95% using 165 mg/L of tannin at pH 5. Several applications of tannin used for microalgae harvesting are summarized in Table 3. Tannin reported significant efficiencies (90–99%) for microalgae harvesting in different types of cultivation with different pH levels. Because of the neutral electric charge, the particles’ adsorption capabilities will be strong at pH levels ranging from 7 to 9 (Xia et al. 2008). The variation in the removal efficiencies may be attributed to several factors such as the type and concentration of microalgae, tannin dosage, the volume of the cultivation reactor, the physiochemical characteristics, and the element contents in the cultivation medium. However, the effect of these factors on microalgae harvesting using tannin was not well explained in the literature. By interacting with tannin particles, cations in a cultured medium may promote coagulation by neutralizing and destabilizing the negative charges of the coagulant functional group residue (Zhang et al. 2013). Monovalent and multivalent cation concentrations, such as Mg2+, Ca2+, Na+, and Fe2+, stimulated and promoted flocculation activities (Wang et al. 2010; Okaiyeto et al. 2013).

Table 3

Tannin applications for microalgae harvesting

Type of cultivationTannin dosageExperimental conditionsMicroalgae removal (%)References
Microalgae cultivated at the wastewater treatment plant 100 mg/L Sedimentation time 5 min; pH 7.2 90 Teixeira et al. (2022)  
Cultivated microalgae used for wastewater treatment 20–50 mg/L Sedimentation time 10–20 min >90 Xia et al. (2008)  
Lab-scale cultivation tank 35 mg/L Fast mixing rate (550rpm) 99 Ruggeri et al. (2021)  
Cultivated microalgae in anaerobic domestic experimental sewage treatment plant 100 mg/L Sedimentation time 5 min; pH 9 95.6 Cassini et al. (2017)  
Cultivated microalgae in PBR of wastewater digestate 165 mg/L pH 5–7 95 Mezzari et al. (2014)  
Cultivated microalgae used for wastewater treatment 20 mg/L pH 9 90 Wang et al. (2013)  
Type of cultivationTannin dosageExperimental conditionsMicroalgae removal (%)References
Microalgae cultivated at the wastewater treatment plant 100 mg/L Sedimentation time 5 min; pH 7.2 90 Teixeira et al. (2022)  
Cultivated microalgae used for wastewater treatment 20–50 mg/L Sedimentation time 10–20 min >90 Xia et al. (2008)  
Lab-scale cultivation tank 35 mg/L Fast mixing rate (550rpm) 99 Ruggeri et al. (2021)  
Cultivated microalgae in anaerobic domestic experimental sewage treatment plant 100 mg/L Sedimentation time 5 min; pH 9 95.6 Cassini et al. (2017)  
Cultivated microalgae in PBR of wastewater digestate 165 mg/L pH 5–7 95 Mezzari et al. (2014)  
Cultivated microalgae used for wastewater treatment 20 mg/L pH 9 90 Wang et al. (2013)  

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