Biological Hydrogen Production by Dark Fermentation in a Stirred Tank Reactor and Its Correlation with the pH Time Evolution

Abstract

Dark fermentation is a hydrogen generating process carried out by anaerobic spore-forming bacteria that metabolize carbon sources producing gas and short-chain acids. The process can be controlled, and the hydrogen harvested if bacteria are grown in a reactor with favorable conditions. In this work, bacteria selected from natural sources were grown with a defined culture media, while pH was monitored, with the aim of relating the amount of generated hydrogen to the increase in hydron ion concentration. Therefore, a model based on the acid-base species mass balance is proposed and solved to estimate the lag phase time and measure the hydrogen production efficiency and kinetics. Hydrogen production in a stirred batch reactor was performed for 150–200 h, at given operating conditions using a previously defined growth media, to validate the model. Using the proposed model, the cumulated moles of produced hydrogen correlate well with those predicted from the pH curve. Hence, the modified Gompertz model parameters, largely used for describing the hydrogen generation kinetics by dark fermentation, were estimated from the pH curve and from the experimentally measured generated hydrogen. Satisfactory agreement was found, thus, validating the method.