Hyperthermophilic hydrogen production in a simplified reaction medium containing onion wastes as a source of carbon and sulfur

Abstract

In this study, the hyperthermophilic dark fermentation of onion wastes (OW) for hydrogen production was investigated. OW were used at different proportions in mixed fruit and vegetable wastes (FVW) to evaluate their effect on hydrogen production by Thermotoga maritima. Fermentations were performed in a pH-controlled batch stirred tank reactor (BSTR) using seawater as a simplified reaction medium. Results showed that increasing OW proportions in total fruit and vegetable wastes (tFVW) improved H2 production. Therefore, increasing the OW to tFVW ratio from 0 to 0.8 increased the cumulative H2 production from 109 to 223.6mmol/L. The H2 productivity was also improved from 7.3 to 28.82mmol/h.L. In fact, OW contain carbohydrates, sulfur compounds, and other nutrients, which were used as a carbon source and energetic substrate for H2 production by the halophilic bacterium T. maritima in seawater without additional chemical compounds. Then, a H2 yield of 3.36mol H2/mol hexose was achieved using 200mL of OW, containing 55mmol/L of carbohydrates. A concept of H2 production from FVW at high proportions of OW in a simplified reaction medium was proposed. It allowed a H2 yield of 209LH2/kg volatile solids which could be an interesting future alternative to the current fossil fuel.