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Development of a helical coagulation reactor for harvesting microalgae

Zhang, Haiyang, Liu, Chunhua, Ou, Yang, Chen, Ting, Yang, Lan, Hu, Zicheng
Journal of bioscience and bioengineering 2019 v.127 no.4 pp. 447-450
Reynolds number, coagulation, energy, harvesting, hydrodynamics, microalgae, turbulent flow
In this study, an innovative helical coagulation reactor (HCR) was developed for harvesting microalgae by sedimentation with polyaluminium chloride (PAC). The effects of construction and hydrodynamic characteristics on harvesting performance were investigated. Results showed that a higher harvesting efficiency, 96.37%, was achieved for the large and compact flocs generated by the HCR, and the settling rate of flocs was substantially influenced by the velocity gradient (G) and the Reynolds number (Re). When the Reynolds number closed to the transition between laminar and turbulent flow (4000), the flocs settled faster (20.51 m h−1), although settling slowed as the Reynolds number increased further because of ruptured flocs. The settling rate of flocs could be further improved to 23.27 m h−1 by a pulse flow field, mainly due to larger and more compact flocs forming in the plug pipe flow. Furthermore, a comparative investigation of a mechanically agitated vessel and the HCR with the same Camp number (Gt) showed that the HCR achieved higher settling rates and a shorter residence time than those with a mechanical agitator. The HCR provided a uniform dissipation of energy and high velocity gradient while avoiding electrical and mechanical energy consumption, suggesting this reactor is an efficient and economic option for microalgae harvesting.