Improvement of hydrogen production from Chlorella sp. biomass by acid-thermal pretreatment

Abstract

Background Owing to the high growth rate, high protein and carbohydrate contents, and an ability to grow autotrophically, microalgal biomass is regarded as a promising feedstock for fermentative hydrogen production. However, the rigid cell wall of microalgae impedes efficient hydrolysis of the biomass, resulting in low availability of assimilable nutrients and, consequently, low hydrogen production. Therefore, pretreatment of the biomass is necessary in order to achieve higher hydrogen yield (HY). In the present study, acid-thermal pretreatment of Chlorella sp. biomass was investigated. Conditions for the pretreatment, as well as those for hydrogen production from the pretreated biomass, were optimized. Acid pretreatment was also conducted for comparison. Results Under optimum conditions (0.75% (v/v) H2SO4, 160 °C, 30 min, and 40 g-biomass/L), acid-thermal pretreatment yielded 151.8 mg-reducing-sugar/g-biomass. This was around 15 times that obtained from the acid pretreatment under optimum conditions (4% (v/v) H2SO4, 150 min, and 40 g-biomass/L). Fermentation of the acid-thermal pretreated biomass gave 1,079 mL-H2/L, with a HY of 54.0 mL-H2/g-volatile-solids (VS), while only 394 mL/L and 26.3 mL-H2/g-VS were obtained from the acid-pretreated biomass. Conclusions Acid-thermal pretreatment was effective in solubilizing the biomass of Chlorella sp. Heat exerted synergistic effect with acid to release nutrients from the biomass. Satisfactory HY obtained with the acid-thermal pretreated biomass demonstrates that this pretreatment method was effective, and that it should be implemented to achieve high HY.

Bioethanol production from defatted biomass of Nannochloropsis oculata microalgae grown under mixotrophic conditions

“…Effect of acid hydrolysis on total carbohydrates and total reduced sugar content Giang et al (2019) showed that the acid concentration is a limiting factor that can impair microalgal biomass sacchari cation in the autoclave. The total carbohydrate yields were increased with increasing acid concentration during the hydrolysis processes with H 2 SO 4 pre-treatment in the autoclave at 121 °C for 15 min as shown in gure 1.…”

A critical look into different salt removal treatments for the production of high value pigments and fatty acids from marine microalgae Chlorella vulgaris (NIOT-74)

“…Earlier research reports have established the Chlorella c ell wall to be composed of an outer cell wall formed of algaenan and a thinner microfibrillar wall composed of cellulose and chitin-like glycan amino sugars [ 54 ]. Substantial research reports have also evidenced the Chlorella cell wall disruption brought forth by acid wash treatments as a phenomenon caused by the interaction of H + ions of acids with the glycosidic bonds of cell wall components [ 55 ]. This might have caused the severe damage to cell wall apparent herein under the increased acid concentrations.…”

Exogenous Carbon Substrates for Biohydrogen Production and Organics Removal Using Microalgal-Bacterial Co-Culture

“…C. vulgaris has been widely reported as the photolytic and photofermentative H 2 -producing microalgal species. − The purity of the strain was maintained and checked microscopically during the culturing, which was uncontaminated at the time of harvesting. The strains were suspended in the recommended Z -medium at pH 7, which contained all of the supplementary nutrients for microalgae to grow, as shown in the recipe in the Supporting Information (Table S1).…”