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Microorganisms. 2019 Nov 9;7(11). pii: E545. doi: 10.3390/microorganisms7110545.

Integrated Process for Bioenergy Production and Water Recycling in the Dairy Industry: Selection of Kluyveromyces Strains for Direct Conversion of Concentrated Lactose-Rich Streams into Bioethanol.

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Unidade de Bioenergia, Laboratório Nacional de Energia e Geologia, I.P. (LNEG), Estrada do Paço do Lumiar 22, 1649-038 Lisboa, Portugal.
Instituto de Tecnologia Química e Biológica António Xavier, Biology Division, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal.
Department of Chemistry and Bioscience, Section for Sustainable Biotechnology, Aalborg University, A. C. Meyers Vænge 15, 2450 Copenhagen, Denmark.


Dairy industries have a high environmental impact, with very high energy and water consumption and polluting effluents. To increase the sustainability of these industries it is urgent to implement technologies for wastewater treatment allowing water recycling and energy savings. In this study, dairy wastewater was processed by ultrafiltration and nanofiltration or ultrafiltration and reverse osmosis (UF/RO) and retentates from the second membrane separation processes were assessed for bioenergy production. Lactose-fermenting yeasts were tested in direct conversion of the retentates (lactose-rich streams) into bioethanol. Two Kluyveromyces strains efficiently fermented all the lactose, with ethanol yields higher than 90% (>0.47 g/g yield). Under severe oxygen-limiting conditions, the K. marxianus PYCC 3286 strain reached 70 g/L of ethanol, which is compatible with energy-efficient distillation processes. In turn, the RO permeate is suitable for recycling into the cleaning process. The proposed integrated process, using UF/RO membrane technology, could allow water recycling (RO permeate) and bioenergy production (from RO retentate) for a more sustainable dairy industry.


Kluyveromyces; bioethanol; dairy industry; lactose fermentation; water recycling

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