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  • 1.
    Purwadi, R.
    et al.
    University of Borås, School of Engineering.
    Brandberg, T.
    Taherzadeh, M.J.
    University of Borås, School of Engineering.
    A Possible Industrial Solution to Ferment Lignocellulosic Hydrolyzate to Ethanol: Continuous Cultivation with Flocculating Yeast2007In: International Journal of Molecular Sciences, ISSN 1422-0067, E-ISSN 1422-0067, Vol. 8, no 9, p. 920-932Article in journal (Refereed)
    Abstract [en]

    Cultivation of toxic lignocellulosic hydrolyzates has been a research topic in recent decades. Although several methods have been proposed, there has been doubt about their industrial applications. The current work deals with a solution to this problem which has a good potential application in industrial scale. A toxic dilute-acid hydrolyzate was continuously cultivated using a high-cell-density flocculating yeast in a single and serial bioreactor which was equipped with a settler to recycle the cells back to the bioreactors. No prior detoxification was necessary to cultivate the hydrolyzates, as the flocks were able to detoxify it in situ. The experiments were successfully carried out at dilution rates up to 0.52 h-1. The cell concentration inside the bioreactors was between 23 and 35 g-DW/L, while this concentration in the effluent of the settlers was 0.320.05 g-DW/L. The ethanol yield of 0.42-0.46 g/g-consumed sugar was achieved, and the residual sugar concentration was less than 6% of the initial fermentable sugar (glucose, galactose and mannose) of 35.2 g/L.

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  • 2.
    Purwadi, Ronny
    University of Borås, School of Engineering.
    Continuous ethanol production from dilute-acid hydrolyzates: detoxification and fermentation strategy2006Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The production of fuel ethanol from cellulosic biomass is of growing interest around the world. Lignocellulosic residuals can be used to produce transportation fuel, with the overall process having little net production of greenhouse gases. Lignocellulosic materials are available as a by-product of many industrial processes and agricultural materials, or can potentially be produced from dedicated energy crops. The production of ethanol from lignocellulosic materials includes hydrolysis which breaks the cellulose and hemicellulose polymers to fermentable sugars, followed by cultivation which converts the sugars into ethanol, and finally a separation process where ethanol purification is carried out to produce fuel ethanol. However, some byproducts such as furan compounds are released during chemical hydrolysis and inhibit the yeast during cultivation. This work contributes a solution to overcome these problems especially for a continuous process which is economically superior. Hydrolyzate detoxification using lime (â overlimingâ ) in concert with the capability of yeast to carry out in-situ detoxification is focused upon in the work. The kinetics of the overliming process were studied, where both sugars and furan compounds are degraded through a formation of complex ion. The sudden addition of lime in a batch process shows severe degradation of sugars together with furan compounds. This knowledge leads to development of a continuous detoxification process where gradual addition of lime can save 25% of the initial sugar with similar detoxification effects under certain conditions. Cell immobilization and cell flocculation have been studied to develop a high cell density system. High cell density is effective in carrying out in-situ detoxification. This study shows a good combination of continuous detoxification and cell immobilization where continuous ethanol production of 5.14 g/L·h can be carried out at a high feeding rate of 0.648 h-1. In addition, the application of a serial bioreactor has been found to increase the utilization of substrates. A gain in substrate assimilation of 11.6% has been achieved when using a serial bioreactor at residence time of 2.32 h. Furthermore, a cell flocculating system has been studied and developed. In a steady-state condition, the cell flocculation system could cultivate fresh hydrolyzates at a high feeding rate of 0.52 h-1 without any additional chemical detoxification, while sugar assimilation and ethanol productivity were 96% and 7.4 g/L·h respectively. In conclusion, this study proposes a concept of rapid continuous production of ethanol where inhibitory obstacles can be overcome by chemical detoxification and/or in-situ detoxification by yeast.

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  • 3.
    Purwadi, Ronny
    et al.
    University of Borås, School of Engineering.
    Taherzadeh, Mohammad J.
    University of Borås, School of Engineering.
    The performance of serial bioreactors in rapid continuous production of ethanol from dilute-acid hydrolyzates using immobilized cells2008In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 99, no 7, p. 2226-2233Article in journal (Refereed)
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