Anaerobic biofilm reactors for dark fermentative hydrogen production from wastewater: A review

•A review on anaerobic biofilm reactors for bio-H2 production from wastewater.•Effect of substrate type, substrate concentration, and hydraulic retention time.•Effect of carrier material, inoculum type and pretreatment, temperature, and pH.•Investigation of microbial dynamics, fermentation pathways, and metabolites.

Dark fermentation is a bioprocess driven by anaerobic bacteria that can produce hydrogen (H2) from organic waste and wastewater. This review analyses a relevant number of recent studies that have investigated dark fermentative H2 production from wastewater using two different types of anaerobic biofilm reactors: anaerobic packed bed reactor (APBR) and anaerobic fluidized bed reactor (AFBR). The effect of various parameters, including temperature, pH, carrier material, inoculum pretreatment, hydraulic retention time, substrate type and concentration, on reactor performances was investigated by a critical discussion of the results published in the literature. Also, this review presents an in-depth study on the influence of the main operating parameters on the metabolic pathways. The aim of this review is to provide to researchers and practitioners in the field of H2 production key elements for the best operation of the reactors. Finally, some perspectives and technical challenges to improve H2 production were proposed.