Bioremediation of Brewery Sludge and Hydrogen Production Using Combined Approaches

Abstract

Hydrogen is re-emerging as a serious alternative to fossil fuels. It is a clean gas with high energy density and its combustion only generates water vapour. Nevertheless, the hydrogen industry has a significant carbon footprint since this gas is mostly derived from fossil fuels reforming processes. This project focusses on the development of sustainable alternatives to conventional hydrogen production, in which approaches based on dark fermentation (DF) using an inexpensive residue from the brewery industry as primary feedstock are presented. Firstly, a fungal pre-treatment (FT) was proposed to degrade a high-strength brewery waste slurry (BWS) to obtain an effluent with a lower concentration of chemical oxygen demand (COD) but rich in readily fermentable sugars for the ensuing DF, thus improving hydrogen yields (HY). Secondly, microbial electrolysis and fuel cells (MECs and MFCs) were proposed to assist DF, generating electricity in MFCs while improving HY by MECs. Coupling both microbial electrochemical technologies sequentially after DF did not show any advantage. However, promising results were obtained for electricity and hydrogen production when taking a single-staged approach. Treating BWS directly by MFCs produced 2.0 watts/g COD consumed, while the DF process assisted simultaneously by MECs (DF/MEC) produced 1.6 times more hydrogen than DF alone. An average HY of 2.32 ± 0.06 mol H₂/mol glucose was attained between both DF/MEC and DF after FT, hence approaching the theoretical value of 2.4 mol H₂/mol glucose, representing roughly a 50% improvement compared to DF alone. With an overall COD reduction above 76%, the DF after FT exhibited the highest energy conversion rate per substrate consumed (6.3 kJ/g COD). As valuable by-products obtained, up to 31 g/L of fungal biomass, which is appreciated in many state-of-the-art biomaterials applications, was produced by using BWS. While in the DF/MEC process, 18 g/L of butyric acid were generated, which is three times more than with DF alone. Butyric acid being the precursor to butanol and building block of biodegradable thermoplastics, this result is not without significance. The proposed approaches not only valorize BWS but also validate their economic and environmental attractiveness as promising alternative hydrogen production methods.