Anaerobic membrane gas extraction facilitates thermophilic hydrogen production from Clostridium thermocellum

Abstract

Clostridium thermocellum is among the most efficient bacteria to convert cellulosic biomass into H₂ during dark fermentation. However, despite great progress the H₂ yield and rate are still not satisfactory for large scale applications. The purpose of this study was to evaluate whether in situ gas extraction using membrane bioreactors would increase H₂ production from Clostridium thermocellum when compared to a conventional anaerobic fermentation setup in thermophilic conditions. C. thermocellum DSM 1313, a cellulotyic, thermophilic bacterium was grown on cellobiose and Avicel in an anaerobic-fermenter (AF) and an anaerobic-membrane-bioreactor (AnMBR). Compared to the AF, the AnMBR increased cumulative H₂ production by 63%, from 25.8 to 42.1 mmols, increased the max H₂ production rate by 24%, from 3.4 to 4.2 mmol h⁻¹, and increased yield by 58%, from 0.43 to 0.68 mmol H₂ per mmol hexose, on cellobiose. Likewise, on Avicel, the AnMBR increased cumulative H₂ production by 59%, from 46.8 to 74.6 mmols, increased the max H₂ rate by 87%, from 3.1 to 5.8 mmol h⁻¹, and increased the yield by 59%, from 0.76 to 1.21 mmol H₂ per mmol hexose. These results show that anaerobic membrane gas extraction can be an effective approach to increasing both rate and yield of fermentative H₂ production.