Characteristics of biohydrogen production from simple and complex substrates with different biopolymeric composition

Abstract

The work investigated the characteristics of the dark fermentation (DF) process of a number of simple (starch, sunflower oil, peptone and their mixture) and complex (dog food, pig feed, sewage sludge (SS)) substrates using a mixed culture, pH control (5.5), at 55°C. Peptone and sunflower oil were characterized by the lowest production of H₂, namely 5.0 and 2.3 ml H₂/g COD, respectively. The specific hydrogen yield per decomposed starch was 1.55 mol H₂/mol. The addition of peptone and sunflower oil to starch reduced the specific yield of hydrogen from starch by 23%. A large difference in hydrogen production was observed during DF of complex substrates. The specific hydrogen yield from dog food was 46.5 ml H₂/g COD or 143.4 ml H₂/g carbohydrates, from pig feed – 32.1 ml H₂/g COD or 91.6 ml H₂/g carbohydrates, and from SS – 9.3 ml H₂/g COD or 98.0 ml H₂/g carbohydrates. Possible relationships between the biopolymeric composition of substrates and characteristics of the DF process were analyzed using Spearman's rank correlation coefficients. The concentration of carbohydrates, as well as the ratio of carbohydrates/proteins and carbohydrates/fats, were the main factors influencing the high specific yield of H₂, it's content in biogas, as well as the ratio of H₂/soluble metabolites. The concentration of proteins had a statistically significant positive effect on the accumulation of acetate and succinate, and carbohydrates - on the accumulation of caproate.