Dark fermentative hydrogen production from food waste: Effect of biomass ash supplementation

This work aimed to investigate the effects of supplementing two distinct types of ash, namely fly ash (FA) and bottom ash (BA) on the dark fermentation (DF) process of food waste (FW) for H2 production. Both types of biomass combustion ash (BCA) were collected in an industrial bubbling fluidized bed combustor, using residual forest biomass as fuel. Results indicated that adding BCA at different doses of 1, 2 and 4 g/L could effectively enhance H2 generation when compared to the control test without BCA addition. This stimulatory effect was attributed to the crucial role of metal elements released from BCA such as sodium, potassium, calcium, magnesium, and iron in the provision of buffering capacity and inorganic nutrients for the functioning of hydrogen-forming bacteria. The highest H2 yield of 169 mL per g of volatile solids (VS) were obtained by adding only a small amount of BA (1 g/L) to the reactive system, representing a significant increment of 1070% compared to the control reactor. Furthermore, a significant decrease in the bacterial lag phase time from 26 h to 2.7 h, as well as about a 12-fold increase in the energy recovery as H2 gas was observed at BA dosage of 1 g/L in comparison with the control reactor. Overall, this study suggested that a proper addition of BCA could promote the DF process of FW and enhance biohydrogen production.