Enhanced photo-fermentative H2 production using Rhodobacter sphaeroides by ethanol addition and analysis of soluble microbial products

Biotechnology for Biofuels

Dong-Hoon Kim³  Ji-Hye Lee³  Seoktae Kang⁴  Patrick C Hallenbeck²  Eui-Jin Kim⁵  Jeong K Lee⁵  Mi-Sun Kim¹ 

[1] Division of Renewable Energy Engineering, University of Science and Technology, 217 Gajeong-ro, Daejeon, Yuseong-gu 305-350, Republic of Korea

[2] Departement of Microbiology and Immunology, University of Montreal, CP 6128, Succursale Centre-Ville, Montreal, QC H3C 3J7, Canada

[3] Biomass and Waste Energy Laboratory, Korea Institute of Energy Research, 152 Gajeong-ro, Daejeon, Yuseong-gu 305-343, Republic of Korea

[4] Department of Civil Engineering, Kyung Hee University, 1732 Deokyoungdaero, Yongin, Giheung, Gyeonggi-do 446-701, Republic of Korea

[5] Department of Life Science and Basic Science Institute for Cell Damage Control, Sogang University, Mapo, Shinsu 1, Seoul 121-742, Republic of Korea

关键词: Size exclusion chromatography;    Lactate;    Ethanol;    Soluble microbial products;    Electron balance;    Photo-fermentative hydrogen production;   

Others  :  792382
DOI  :  10.1186/1754-6834-7-79

 received in 2014-01-09, accepted in 2014-05-09,  发布年份 2014

【 摘 要 】

Background

Biological fermentation routes can provide an environmentally friendly way of producing H₂ since they use renewable biomass as feedstock and proceed under ambient temperature and pressure. In particular, photo-fermentation has superior properties in terms of achieving high H₂ yield through complete degradation of substrates. However, long-term H₂ production data with stable performance is limited, and this data is essential for practical applications. In the present work, continuous photo-fermentative H₂ production from lactate was attempted using the purple non-sulfur bacterium, Rhodobacter sphaeroides KD131. As a gradual drop in H₂ production was observed, we attempted to add ethanol (0.2% v/v) to the medium.

Results

As continuous operation went on, H₂ production was not sustained and showed a negligible H₂ yield (< 0.5 mol H₂/mol lactate_added) within two weeks. Electron balance analysis showed that the reason for the gradual drop in H₂ production was ascribed to the increase in production of soluble microbial products (SMP_s). To see the possible effect of ethanol addition, a batch test was first conducted. The presence of ethanol significantly increased the H₂ yield from 1.15 to 2.20 mol H₂/mol lactate_added, by suppressing the production of SMPs. The analysis of SMPs by size exclusion chromatography showed that, in the later period of fermentation, more than half of the low molecular weight SMPs (< 1 kDa) were consumed and used for H₂ production when ethanol had been added, while the concentration of SMPs continuously increased in the absence of ethanol. It was found that the addition of ethanol facilitated the utilization of reducing power, resulting in an increase in the cellular levels of NAD⁺ and NADP⁺. In continuous operation, ethanol addition was effective, such that stable H₂ production was attained with an H₂ yield of 2.5 mol H₂/mol lactate_added. Less than 15% of substrate electrons were used for SMP production, whereas 35% were used in the control.

Conclusions

We have found that SMPs are the key factor in photo-fermentative H₂ production, and their production can be suppressed by ethanol addition. However, since external addition of ethanol to the medium represents an extra economic burden, ethanol should be prepared in a cost-effective way.

【 授权许可】

   
2014 Kim et al.; licensee BioMed Central Ltd.

【 图 表 】

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