Effect of carbon/nitrogen ratio, temperature, and inoculum source on hydrogen production from dark codigestion of fruit peels and sewage sludge

Abstract

This paper studies the use of fruit peel biomass and waste sludge from municipal wastewater treatment plants in the metropolitan area of Monterrey, Mexico as an alternative way of generating renewable energy. Using a Plackett-Burman experimental design, we investigated the effects of temperature, inoculum source, and the C/N (Carbon/Nitrogen) ratio on dark fermentation (DF). The results indicate that it is possible to produce hydrogen using fruit peels codigested with sewage sludge. By adjusting the C/N ratio in response to the physicochemical characterization of the substrates, it was revealed that the quantities of carbohydrates and nitrogen were sufficient for the occurrence of the fermentation process with biogas production greater than 2221 ± 5.8 mL L-1 Reactor and hydrogen selectivity of 23% (366 ± 1 mL H2·L-1 Reactor) at the central point. The kinetic parameters (Hmax= 86.6 mL· L-1, Rm = 2.6mL L-1 h-1, and λ = 1.95 h)were calculated using themodified Gompertz model. The quantification of soluble metabolites, such as acetic acid (3600 mg L-1) and ethyl alcohol (3.4 ± 0.25% v/v), confirmed the presence of acetogenesis in the generation of hydrogen.