Application of dead-end ultrafiltration and hollow fibre transverse vibration systems as pre-treatment for the valorisation of bioethanol dunder

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Journal Article
Journal of Membrane Science, 2020, 597
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© 2019 Elsevier B.V. Valorisation of high-strength molasses spentwash (biodunder) was investigated using two-stage membrane processing for the recovery of moderate-to-high value organic acids. Conventional techniques relying on precipitation are often problematic, consuming large volumes of chemicals and have poor selectivity within complex sample matrices. Both stirred-cell and hollow fibre transverse vibration systems were compared and assessed in terms of transmembrane pressure stability, dissolved organic matter (DOM) fractionation, organic acid separation and fouling reversibility during long-term operation. For the same membrane material and effluent dilution (10 fold), stirred cell filtration with a UF 30 kDa membrane revealed a critical flux (Jcritical) value of about 6.2 L/m2h, markedly lower than that obtained with a larger MWCO (UF 100 kDa) counterpart wherein Jcritical was situated around 12.7 L/m2h. On the contrary, transverse vibration of submerged hollow fibres demonstrated a greater tenacity to withstand more aggressive feed solutions (i.e. 5 and 2 fold dilution) even at fluxes above Jcritical, coupled with almost 60% restoration of membrane resistance by simple deionised water rinsing following 6.5 h of constant flux filtration. Size exclusion chromatography (LC-OCD) findings highlight considerable rejection of biopolymers (proteins and polysaccharides) in addition to humic, building block and LMW neutrals content of the effluent DOM. Importantly, HPLC analyses indicated the transmission of selected moderate-to-high value organic acids was greatest during submerged hollow fibre vibration with minimal (5 fold) effluent dilution. Further concentration via nanofiltration suggested almost 80% transmission of succinic acid during the polishing of UF permeate. Recovery of such constituents may contribute to substantially improve the economic viability of bioethanol production.
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