Dark Fermentation of Sweet Sorghum Stalks, Cheese Whey and Cow Manure Mixture: Effect of pH, Pretreatment and Organic Load

Margarita Andreas Dareioti,Aikaterini Ioannis Vavouraki,Constantina Zafiri,Michael Kornaros,Konstantina Tsigkou

doi:10.3390/pr9061017

Margarita Andreas Dareioti, Aikaterini Ioannis Vavouraki + Show 3 more

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https://doi.org/10.3390/pr9061017

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Abstract

The aim of this study was to determine the optimal conditions for dark fermentation using agro-industrial liquid wastewaters mixed with sweet sorghum stalks (i.e., 55% sorghum, 40% cheese whey, and 5% liquid cow manure). Batch experiments were performed to investigate the effect of controlled pH (5.0, 5.5, 6.0, 6.5) on the production of bio-hydrogen and volatile fatty acids. According to the obtained results, the maximum hydrogen yield of 0.52 mol H2/mol eq. glucose was measured at pH 5.5 accompanied by the highest volatile fatty acids production, whereas similar hydrogen productivity was also observed at pH 6.0 and 6.5. The use of heat-treated anaerobic sludge as inoculum had a positive impact on bio-hydrogen production, exhibiting an increased yield of 1.09 mol H2/mol eq. glucose. On the other hand, the pretreated (ensiled) sorghum, instead of a fresh one, led to a lower hydrogen production, while the organic load decrease did not affect the process performance. In all experiments, the main fermentation end-products were volatile fatty acids (i.e., acetic, propionic, butyric), ethanol and lactic acid.

Highlights

Renewable energy production has attracted great interest from the international community during the last decades, with biomass being one of the oldest and most promising energy sources
The aim of this study was to investigate the effect of pH during dark fermentation of an agro-waste mixture consisting of Cheese whey (CW) and liquid cow manure (LCM) with sweet sorghum stalks on hydrogen production and end-products (i.e., volatile fatty acids (VFAs), lactic acid, ethanol) distribution
CW can be described as a high organic load waste stream, mainly due to its carbohydrates content, whereas LCM was characterized by a high concentration of VFAs and nitrogen

Summary

Introduction

Renewable energy production has attracted great interest from the international community during the last decades, with biomass being one of the oldest and most promising energy sources. Organic wastes and by-products such as animal manures, wastewaters, energy crops, agricultural and agro-industrial residues have been extensively investigated as potential feedstocks for efficient production of biofuels. The valorization of agro-industrial wastes, livestock wastes and by-products, and the generation of renewable energy from wastes among others, are in line with sustainable development. Anaerobic digestion (AD) is considered as an alternative waste management process that complies with the European circular economy concept [1]. Due to its high organic content (up to 70 g Chemical Oxygen Demand (COD)/L), CW disposal contributes to environmental pollution with lactose being mainly responsible for its high COD. Among hydrogen- and biogas-producing agro-industrial wastes, CW appears to be one of the most promising feedstocks [3]. Cow manure is one of the most polluting agro-industrial by-products.

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