Effect of temperature on fermentative hydrogen production by mixed cultures

Abstract

Effect of temperatures ranging from 20 °C to 55 °C on fermentative hydrogen production by mixed cultures was investigated in batch tests. The experimental results showed that, at initial pH 7.0, during the fermentative hydrogen production using glucose as substrate, the substrate degradation efficiency and hydrogen production potential increased with increasing temperatures from 20 °C to 40 °C. The maximal substrate degradation efficiency was 98.1%, the maximal hydrogen production potential was 269.9 mL, the maximal hydrogen yield was 275.1 mL/g glucose and the shortest lag time was 7.0 h. The temperature for fermentative hydrogen production by mixed cultures was optimized to be 40 °C. The expanded Ratkowsky models could be used to describe the effect of temperatures on the hydrogen production potential, maximum hydrogen production rate and the lag time during fermentative hydrogen production.

Introduction

Environmental pollution due to the use of fossil fuels as well as their shortfall makes it necessary to find alternative energy sources that are environmentally friendly and renewable. Hydrogen satisfies the above requirements because it produces only water, when it is combusted as a fuel or converted to electricity. Among various hydrogen production processes, biological method is known to be less energy intensive, for it can be carried out at ambient temperature and pressure. In addition, it is of great significance to produce hydrogen from organic wastes by fermentative hydrogen production, because it plays the dual role of waste reduction and energy production. Therefore fermentative hydrogen production has been received increasing attention in recent years [1], [2], [3].

Many factors, such as the substrates, their concentration, pH and temperature can influence the fermentative hydrogen production [4], [5], [6]. Among them, temperature is a very important factor, because it can affect the activity of hydrogen-producing bacteria by influencing the activity of some essential enzymes such as hydrogenases for fermentative hydrogen production. It has been demonstrated that in an appropriate range, increasing temperature could increase the ability of hydrogen-producing bacteria to produce hydrogen during fermentative hydrogen production, but temperature at much higher levels could decrease it with increasing levels [7], [8], [9], [10], [11]. For instance, Lee et al. investigated the effects of temperature on hydrogen production using sucrose as substrate, and concluded that, in general, hydrogen production rate and yield trended to increase with increase in temperature from 30 °C to 40 °C, while they trended to decrease with further increase temperature from 40 °C to 45 °C [7].

Although, there have been several studies reporting the effects of temperature on fermentative hydrogen production by mixed cultures, their results differed considerably in terms of the optimal temperature for fermentative hydrogen production. For example, the optimal temperature reported by Lee et al. was 40 °C [7], while the optimal temperature reported by Valdez-Vazquez et al. [10] was 55 °C. The possible reasons why their results were different greatly may be the differences among their studies in terms of the substrates, their concentrations, reactor type, ranges of the temperature studied and the seed sludge.

Since temperature is essential for fermentative hydrogen production by mixed cultures and the optimal temperature reported for it differed a great deal, the objective of this study was to investigate the effect of temperature ranging from 20 °C to 55 °C on fermentative hydrogen production by mixed cultures from glucose in batch tests at initial pH 7.0, with the purpose of obtaining the optimal temperature for fermentative hydrogen production by mixed cultures.