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Efficient membrane microalgal harvesting: Pilot-scale performance and techno-economic analysis

Wang, Lan, Pan, Bo, Gao, Yunxiao, Li, Cheng, Ye, Jing, Yang, Li, Chen, Yongsheng, Hu, Qiang, Zhang, Xuezhi
Journal of cleaner production 2019 v.218 pp. 83-95
Scenedesmus, biomass, harvesting, industrialization, microalgae, ultrafiltration, zooplankton
In this study, a pilot-scale ultrafiltration membrane system was developed for harvesting of oleaginous Scenedesmus acuminatus by adjusting transmembrane pressure-TMP (cross flow velocity-CFV changed accordingly) and applying air-assisted backwashing technology to increase membrane flux, reduce flux declining rate and enhance flux recovery rate. A two-stage harvesting strategy (normal filtration–strengthening concentration) was performed for harvesting of 53 m3 of S. acuminatus suspension to achieve both high flux and concentration factor. The results showed that TMP (CFV) had positive impact on average flux, and the increase could effectively overcome the decrease in average flux when harvesting microzooplankton contaminated S. acuminatus culture. Shortening the interval of air-assisted backwashing to 15 min enhanced the average flux up to 12%. The average flux decreased with the increased loading volume, and volumetric reduction factor had a negative effect on average flux. For the harvesting of 53 m3 of S. acuminatus suspension, an average membrane flux reached up to 53.6 L/(m2·h), with a concentration factor of 145, a final dry weight of 136 g/L, and a biomass recovery of 93% after backwashing. Techno-economic analysis for annual harvesting capacity of 10000 t dry biomass showed that the total harvesting cost was $0.30/kg dry microalgal biomass with a volumetric reduction factor of 50, and membrane harvesting under CFV of 0.5–0.6 m/s may lead to a moderate flux of 60–66.6 L/(m2·h) and minimal total cost of $0.27/kg dry biomass based on the sensitivity analysis. The results of this study suggest that this clean and efficient ultrafiltration membrane approach has high industrialization potential.