Brewery spent grain cascade process: protein recovery and improved downstream fermentation for simultaneous volatile fatty acid production and recovery
Castilla-Archilla, Juan
Castilla-Archilla, Juan
Loading...
Publication Date
2022-03-23
Keywords
brewery spent grain, volatile fatty acids, biorefinery, circular economy, anaerobic digestion, chemical building blocks, lignocellulose, carbohydrates, protein, lignin, mixed microbial culture, hydrolysis, pretreatment, thermal diluted acid hydrolysis, severity factor, enzymatic hydrolysis, expanded granular sludge bed, high strength feedstock, electrochemical cell, Science and Engineering, Natural Sciences, Microbiology
Type
Thesis
Downloads
Citation
Abstract
Volatile fatty acids (VFAs) are short chain carboxylic acids currently produced from fossil fuels. Renewable biomass, including organic wastes, could be used as an alternative source of VFAs. Brewery spent grain (BSG) was selected as renewable feedstock for the current work, this is a lignocellulosic feedstock with a large fraction of carbohydrates. VFA can by produced using partially inhibited anaerobic digestion. This is the conversion of organic matter to biogas by four different steps: hydrolysis, acidogenesis, acetogenesis and methanogenesis. VFAs are produced during the acidogenesis and acetogenesis step. Thus, the control of the operational conditions to avoid methanogenesis leads to the accumulation of VFAs. Mainly a low pH (6.0) and high organic content were used to inhibit methanogenesis. Firstly, two different approaches were followed for the production of the VFAs: i) the simultaneous hydrolysis and fermentation, and ii) a two-step process using a pretreatment hydrolysis to obtain a liquid rich in carbohydrates for downstream fermentation as a second step. A second part was developed to recover additional added value compounds from BSG, e.g. proteins and fibre; and optimise the production of VFAs. For this, a cascade process was developed by combining a chemical pretreatment with enzymatic hydrolysis. The best combinations led to a liquid fraction up to 39.9, 52.4 and 44.6 g/L of total carbohydrates. For the last experiment, a high strength synthetic feedstock with glucose (15 to 60 g/L) as sole carbohydrate was used for the simultaneous VFA production and recovery. A novel system was developed by coupling an electrochemical cell to the recycling line of an expanded granular sludge bed reactor. The highest VFA production achieved was above 30 g/L of VFAs. While the electrochemical cell was able to enhance the VFA concentration up to 4 fold, although this was when operating at lower glucose concentration.
Funder
Publisher
NUI Galway