Membranes for Biorefineries

Abstract

This thesis tested the hypothesis that whilst membranes may enable biorefineries to meet discharge specifications, such ‘end-of-pipe’ treatment options are sub-optimal. Greater savings can potentially be made by internal and/or upfront use of membranes. Biorefineries are used to make a wide range of products from substrates such as molasses, corn syrup and cellulosic materials, producing biofuels, pharmaceutical products and mass production of various microorganisms. These are generally produced at low concentrations, resulting in large amounts of wastewater. These wastewaters also contain high concentrations of recalcitrant organic compounds, which have high COD and dark colour. Membrane filtration has in the past typically been used as an ‘end-of-pipe’ treatment option, but can be employed to greater effect further upstream in the baker’s yeast production process. Utilising membrane technology to facilitate the recycling of water and salt from molasses wastewater proved to be successful and could also be used to recover water and other components from lignocellulosic wastewater. Melanoidins are recalcitrant organic macromolecules, which are mainly responsible for the dark brown colour in molasses. The presence of these coloured compounds in the fermentation produces a brown coloured yeast, requiring multiple washing stages to meet the market requirements of the yeast product, the majority of which is sold for the large scale production of sliced white bread. Membranes can be used to remove the bulk of this colour with minimal effect on the yeast’s yield and activity. This thesis has successfully demonstrated the potential of using membrane technologies internally and/or upfront in biorefinery processes, rather than in their customary role as ‘end-of-pipe’ treatment options for both the molasses fermentation industry and the cellulosic ethanol industry, suggesting that membrane technologies have the versatility to be applied across a range of biorefinery processes.