a b s t r a c t The start-up of continuous biohydrogen fermentations is a complex procedure and a key to acceptable hydrogen production performance and successful long-term operation. In this review article, the experiences gained and lessons learned from relevant literature studies dealing with various aspects of H 2 producing bioreactor start-up are comprehensively surveyed. Firstly, the importance of H 2 -forming biosystem start-up including its main steps is outlined. Afterwards, the role of main influencing factors and methods (e.g. strain selection, seed pretreatment and inocula stimulation, switch-over time, bioreactor design, operating conditions) in avoiding the deterioration of starting a reactor is analyzed and presented in detail. Finally, the so far suggested applicable start-up strategies and the corresponding findings are critically discussed pointing out the advantages and disadvantages of each strategy
