Enhancing Microalgal Biomass Productivity in Floating Photobioreactors with Semi-Permeable Membranes Grafted with 4-Hydroxyphenethyl Bromide

Microalgal biomass productivity of semi-permeable membrane photobioreactors (SPM-PBRs) highly depends on diffusion of nutrient ions from surrounding environment through SPMs. The objective of this study was to enhance microalgal biomass productivity in floating photobioreactors (PBRs) with semi-permeable membranes (SPMs) grafted with 4-hydroxyphenethyl bromide (4-HPB) by increasing ion permeabilities and reducing biofouling of SPMs. In this study, we investigated the reduction of biofouling and improvement of biomass productivity by grafting 4-HPB onto SPMs which could decrease hydrophobicity. The degree of alkylation could be increased by up to 4.9%, with water contact angles on alkylated SPM surfaces decreased from 102.5° to 58.2°, indicating decreased surface hydrophobicity. Ion and water permeabilities of SPMs were increased in alkylated SPMs by 148% and 200%, respectively, compared to non-treated SPM control. Moreover, biomass productivity of PBRs with alkylated SPMs was 75% (740 mg m −2 day −1 ) higher than that of the control. Biofouling was also remarkably reduced by up to 40% in 4-HPB grafted SPMs after cultivation of microalgae. These results suggest that decreasing hydrophobicity of SPMs by grafting 4-HPB could enhance biomass productivity in SPM-PBRs through improving ion permeability and reducing biofouling.