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. 2019 Nov 9;7(11):545.
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

Maria José Leandro  1   2 , Susana Marques  1 , Belina Ribeiro  1 , Helena Santos  2 , César Fonseca  1   3
Affiliations

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

Maria José Leandro et al. Microorganisms. .

Abstract

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.

Keywords: Kluyveromyces; bioethanol; dairy industry; lactose fermentation; water recycling.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study, in the collection, analyses, or interpretation of data in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Lactose consumed (gray bars) and ethanol produced (black bars) at 16 h fermentation in the NF and RO media. Km, K. marxianus PYCC strain; Kl, K. lactis PYCC strain; Kll, K. lactis var. lactis PYCC strain; dash line, average initial lactose concentration in the assays in NF retentate; and dot line, average initial lactose concentration in the assays in RO retentate. Error bars represent standard deviation from the average value of three independent experiments.
Figure 2
Figure 2
Fermentation profiles of the K. marxianus PYCC 3286 strain (a,b), the K. lactis PYCC 4356 strain (c,d), and the K. marxianus CBS 397 strain (e,f), in NF media, in mild oxygen-limiting conditions (left panels) and severe oxygen-limiting conditions (right panels). Lactose (♦), ethanol (◯), glycerol (□), and acetic acid (△). Error bars represent standard deviation from the average value of three independent experiments.
Figure 3
Figure 3
Fermentation profiles of the K. marxianus PYCC 3286 strain (a,b), the K. lactis PYCC 4356 strain (c,d) and the K. marxianus CBS 397 strain (e,f), in the RO media, in mild oxygen-limiting conditions (left panels) and severe oxygen-limiting conditions (right panels). Lactose (♦), ethanol (◯), glycerol (□), and acetic acid (△). Error bars represent standard deviation from the average value of three independent experiments.
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