Two-step hybrid system of microbiological hydrogen production with the diluted solid wastes from chewing gum production as a substrate was studied. As the first step, dark fermentation with the digested sludge at different concentrations of waste was performed. The effluent originating from the dark process was subsequently applied in photofermentation with Rhodobacter sphaeroides bacteria. In the first step, the degradation of sweetening substances as well as Talha gum remaining in waste was observed. Hydrogen, carbon dioxide and liquid metabolites (Volatile Fatty Acids - VFAs) were the main products. The maximum hydrogen production in dark fermentation (0.36 L/L-medium) was observed at concentration of 67 g waste/L. Effluents from the first step, containing mainly xylitol, butyric, acetic, lactic and propionic acids, served as the source of organic carbon for photofermentation. The maximum amount of hydrogen at this step reached 0.80 L H-2/L of diluted (1:8) effluent. The presence of significant concentration of ammonium ions (similar to 480 mg/L) in non-diluted effluent completely ceased the hydrogen formation by nitrogenase, therefore reduction in the amount of NH4+ ions in the medium was necessary. This was realized by the dilution of effluent from dark fermentation. The total amount of hydrogen produced in sequential dark and photo-fermentation process under the optimized reaction conditions reached the volume of similar to 6.7 L H-2/L of non-diluted waste. (C) 2018 Elsevier Ltd. All rights reserved.