Continuous hydrogen production from laminaria japonica via dark fermentation

Abstract

To achieve sustainable development, renewable energy source is required to replace our current fossil fuel based energy system. $H_2$ is such a promising energy carrier to meet our goals. And among various hydrogen-making approaches, biological hydrogen production from biomass can be a relative cost-effective way for sustainable green energy production. However, the complex structure of lignocellulosic biomass and also the generated toxic by-products during pretreatment process baffle its wide application. To overcome those difficulties, marine macro-algae, which is mainly composed of cellulose and hemicelluloses, is considered as potential substrate for hydrogen production. In this study, direct fermentation of Laminaria japonica, one brown algae species, was conducted for biohydrogen production. Firstly, determination of operation parameters was conducted by batch test. As a result, optimal condition was decided as substrate concentration of 20 g Carbo. COD/L, initial pH of 7.5, and cultivation pH of 5.5. Also, under this optimal condition, the obtained $H_2$ yield was around 0.92 mol $H_2$/mol $hexose_{added}$, or 71.4ml $H_2$/ g TS. Secondly, hydrogen producing microflora under different temperature ranges was prepared before continuous operation. ASBR system showed better performance than CSTR system during this experiment. And when temperature increased, microbial community structure was changed, and the diversity of microbes decreased by DGGE result. Thirdly, Continuous hydrogen fermentation was conducted by three ASBR system under mesophilic ($35\degC$), thermophilic ($50\degC$) and hyperthermophilic ($65\degC$) conditions for 55 days. And stable hydrogen production was achieved, with $H_2$ yield of $0.79\plusmm0.03$, $0.56\plusmm0.05$, $0.44\plusmm0.04$ mol $H_2$/mol $hexose_{added}$, respectively. Microbial community analysis was conducted by PCR-DGGE method. As a result, under different temperature condition, microbial species and diversity ch...