Effect of L-cysteine on continuous fermentative hydrogen production

Two continuously stirred tank reactors (CSTR) were used to investigate the effect of L-cysteine on continuous dark fermentative hydrogen production system. L-cysteine was added into one of the reactors at 0.1 g/L continuously, the other reactor was without L-cysteine addition. Liquid end products, oxidation-reduction potential (ORP), pH, biomass and hydrogen production rate (HPR) were examined during the operation. The lag time of ethanol generation in the L-cysteine added reactor was shortened to 21 days compared to 25 days in the blank. The HPR increased from 2.73 L/d in the reactor without L-cysteine addition to 2.82 L/d in the added one. The volatile suspended solids (VSS) in the reactor with L-cyateine was 10.1 g/L by the end of the operation compared to 9.2 g/L in the other. Addition of L-cysteine into the hydrogen production system accelerates the formation of ethanol-type fermentation and enhances the hydrogen production by creating an optimal low ORP environment, and by increasing the biomass growth simultaneously.