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^-1_hexose to 0.90molH₂mol^-1_hexose. 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.

Keywords: Biohydrogen; Electrodialysis; End product inhibition; Homoacetogenesis; Hydraulic retention time; Increased hydrolysis.