Increased biohydrogen yields, volatile fatty acid production and substrate utilisation rates via the electrodialysis of a continually fed sucrose fermenter.

ABSTRACT

Electrodialysis (ED) removed volatile fatty acids (VFAs) from a continually-fed, hydrogen-producing fermenter. Simultaneously, electrochemical removal and adsorption removed gaseous H2 and CO2, respectively. Removing VFAs via ED in this novel process increased H2 yields by a factor of 3.75 from 0.24molH2mol-1hexose to 0.90molH2mol-1hexose. VFA production and substrate utilisation rates were consistent with the hypothesis that end product inhibition arrests H2 production. The methodology facilitated the recovery of 37g of VFAs, and 30L H2 that was more than 99% pure, both of which are valuable, energy dense chemicals. Typically, short hydraulic and solid retention times, and depressed pH levels are used to suppress methanogenesis, but this limits H2 production. To produce H2 from real world, low grade biomass containing complex carbohydrates, longer hydraulic retention times (HRTs) are required. The proposed system increased H2 yields via increased substrate utilisation over longer HRTs.