Vegetable waste as substrate and source of suitable microflora for bio-hydrogen production

•We studied H2 production by self-fermentation of non-pretreated organic waste, at two mesophilic temperatures (28 and 37 °C).•H2 can be produced with yield of about 23.9 L/kg of the substrate at 28 °C, only by control of pH by a proper buffer.•Screening microbial diversity of the waste is a successful strategy to select new H2-producing bacteria.•In batch experiments an inverse relationship between yield and volumetric hydrogen production occurs.

Self-fermentation of cellulosic substrates to produce biohydrogen without inoculum addition nor pretreatments was investigated. Dark fermentation of two different substrates made of leaf-shaped vegetable refuses (V) and leaf-shaped vegetable refuses plus potato peels (VP), was taken in consideration. Batch experiments were carried out, under two mesophilic anaerobic conditions (28 and 37 °C), in order to isolate and to identify potential H2-producing bacterial strains contained in the vegetable extracts. The effect of initial glucose concentration (at 1, 5 and 10 g/L) on fermentative H2 production by the isolates was also evaluated.H2 production from self-fermentation of both biomasses was found to be feasible, without methane evolution, showing the highest yield for V biomass at 28 °C (24 L/kg VS). The pH control of the culture medium proved to be a critical parameter. The isolates had sequence similarities ≥98% with already known strains, belonging to the family Enterobacteriaceae (γ-proteobacteria) and Streptococcaceae (Firmicutes). Four genera found in the samples, namely Pectobacterium, Raoultella, Rahnella and Lactococcus have not been previously described for H2 production from glucose. The isolates showed higher yield (1.6–2.2 mol H2/mol glucoseadded) at low glucose concentration (1 g/L), while the maximum H2 production ranged from 410 to 1016 mL/L and was obtained at a substrate concentration of 10 g/L. The results suggested that vegetable waste can be effectively used as both, substrate and source of suitable microflora for bio-hydrogen production.