Modeling of continuous dark fermentative hydrogen production in an anaerobic up-flow column bioreactor.

Dark fermentation (DF) of several types of wastes is a promising process to alleviate environmental pollution as it leads to the production of valuable hydrogen (H) gas and high added value products, such as volatile fatty acids (VFAs). In this study a kinetic model for fermentative H production in an Up-flow column reactor (UFCR) is presented. Τhe model structure includes seven biochemical reactions taking place in a two-phase biofilm-liquid system. The observed difference in the overall stoichiometry of the bioconversion process for different hydraulic retention times (HRTs) is predicted by this model as it is attributed to the difference in the extent of individual bioconversion steps, each of which has a constant stoichiometry but a different rate depending on the HRT. The respective kinetic parameters were estimated through model fitting to the experimental results of the UFCR, which operated at different HRTs (12-2 h) and fed with the soluble fraction of a food industry waste (FIW). A good agreement of the experimental and predicted values of soluble metabolic products and H production was obtained, rendering this model as a useful tool for further investigation and prediction of the characteristics of the DF process in attached-biomass growth systems.