Semi-continuous solid substrate anaerobic reactors for H2 production from organic waste: Mesophilic versus thermophilic regime

We evaluated the influence of the operation temperature (mesophilic vs. thermophilic regime) of semicontinuous, acidogenic solid substrate anaerobic digestion (A-SSAD) of the organic fraction of municipal solid waste (OFMSW) at lab scale. The H2 percentage was higher in the thermophilic regime than in the mesophilic operation (58% and 42%, respectively). The H2 yield of thermophilic A-SSAD was significantly higher than in our mesophilic reactors (360 vs. 165 NmL H2/g VSrem) and other studies reported in the literature (range of 62-180 mL/g VS). Mesophilic A-SSAD showed a yield of 37% of the maximum yield based on 4 mol H2/mol hexose, while thermophilic A-SSAD exhibited a yield of 80% of the maximum yield. This result is similar to works with pure cultures of extremophile microorganisms where H2 yields of 83% of the maximum were reported. We found higher concentrations of acetic acid in the digestates of thermophilic A-SSAD, while butyrate was in higher proportion in mesophilic A-SSAD spent solids. The moderate-to-high yields obtained with the semicontinuous process used in this work are in disagreement with previous reports claiming that batch and semicontinuous processes are less efficient than continuous ones.