A novel microalgal biofilm reactor using walnut shell as substratum for microalgae biofilm cultivation and lipid accumulation

Microalgae are a potential candidate for biofuels, but the high cost and low biomass yield hinder the scale-up application of microalgae. In this study, a novel walnut shell based self-permeating biofilm reactor (WSPBR) was proposed for cultivation of Chlorella vulgaris (C. vulgaris) and Scenedesmus obliquus (S. obliquus). Major influencing factors such as walnut shell size, light intensity and CO2 concentration were studied in detail. The results showed that CO2 can enhance the storage of metabolic products in microalgal cells. Thermodynamics analysis indicated that C. vulgaris and S. obliquus were likely to adhere on the surface of walnut shells. S. obliquus and C. vulgaris biomass reached the maximum values of 97.43 and 70.49 g m(-2), respectively, corresponding to the walnut shell size of 0.8-1.2 mm, light intensity of 150 mmol m(-2) s(-1) and CO2 concentration of 2%. The lipid contents of these microalgal cells were 34.32% and 28.94%, respectively. These results indicated that WSPBR was an efficient system for microalgae cultivation as feedstock for biofuels. (C) 2021 Elsevier Ltd. All rights reserved.