Water hyacinth (Eichhornia crassipes), as one of the important invasive aquatic species, commonly covers the surfaces of rivers and lakes and has caused a series of environmental problems due to its rapid growth and high reproducibility in both clear water and wastewater. These characteristics also make it useful for water treatment and bioethanol production based on its excellent ability to utilize nitrogen in wastewater and abundant lignocellulosic biomass that is suitable for the production of fermentable sugars ( Abdel-Fattah and Abdel-Naby, 2012 and Bayrakci and Kocar, 2014). Currently, large-scale cultivation and collection of water hyacinth using artificial plant floating islands represents a promising strategy for water treatment in the Dianchi Lake basin of Yunnan Province. This government measure is expected to produce a large amount of lignocellulosic water hyacinth biomass. Therefore, an environmentally friendly strategy for the economical utilization of lignocellulosic biomass is urgently needed.วันที่ หลายการศึกษาได้สำรวจวิธี การใช้ชีวมวล lignocellulosic ได้แสดงให้เห็นว่าตบชวาที่สามารถใช้ในการผลิต bioethanol (Guragain et al., 2011 และ Bayrakci และ Kocar, 2014), ก๊าซชีวภาพ (Cheng et al., 2010 เฉิง et al., 2015a และ al. et เกา 2013), l-lactate (Akao et al., 2012), และกรด levulinic (Girisuta et al., 2008) ได้อย่างง่าย ๆ ด้วยการหมัก โปรแกรมประยุกต์เหล่านี้ bioethanol ผลิตจากชีวมวลตบชวาได้ดึงดูดความสนใจ (Ma et al., 2010 และ Bayrakci และ Kocar, 2014) มากที่สุดจำนวน โครงสร้างผลึกและองค์ประกอบทางเคมีของวัสดุ lignocellulosic มีสองปัจจัยหลักที่ส่งผลต่อผลผลิตของ bioethanol และวิธีการ pretreatment มีประสิทธิภาพปรับปรุง (Bayrakci และ Kocar, 2014)Alkaline-oxidative pretreatment through adding NaOH–H2O2 or CaO2 is considered to be potential pretreatment strategy of dry or wet water hyacinth biomass for fermentable sugar production at mild conditions (Mishima et al., 2008 and Cheng et al., 2015b). A comparative study of several chemical pretreatments (including NaOH, HCl, H2SO4, peracetic acid, H2O2, NaOH/H2O2, and alkaline–oxidative) used for water hyacinth demonstrated that the alkaline-oxidative pretreatment (H2O2 added consecutively) is the most effective and economical pretreatment strategy at mild conditions (room temperature for 24 h) (Mishima et al., 2008). However, the yield of reducing sugars achieved with NaOH/H2O2 pretreatment (H2O2 added simultaneously) was only half that achieved with alkaline–oxidative pretreatment and even lower than that achieved with NaOH pretreatment and H2O2 pretreatment separately at equal concentrations. In fact, previous studies confirmed that co-treatment with NaOH/H2O2 solution is a green and effective pretreatment for many types of lignocellulosic biomass, including wheat straw (Barakat et al., 2014), empty palm fruit bunch (Misson et al., 2009), furfural residues (Ma et al., 2014), and sugarcane bagasse (Cheng et al., 2008).The pretreated lignocellulosic biomass can be enzymatically hydrolyzed and fermented in different process configurations, two of which are separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) (Mukhopadhyay and Chatterjee, 2010). The SSF strategy is an interesting option for lignocellulosic ethanol production that offers the advantages of minimizing inhibition by cellobiose and glucose accumulation and allowing higher substrate loadings (Kim et al., 2008). However, the difference between the optimum temperature of the cellulolytic enzymes (around 50 °C) and the fermentation (generally <37 °C for most yeast strains) is the major obstacle in successful application of the SSF process (Bayrakci and Kocar, 2014). The use of thermotolerant microorganisms has the potential to overcome this obstacle by offering advantages such as the shorter time required of SSF, reduced cooling costs, and better saccharification and ethanol yields (Abdel-Banat et al., 2010 and Moreno et al., 2013). However, until now, the microorganisms used in the bioethanol fermentation with lignocellulosic water hyacinth were Saccharomyces cerevisiae strains with an optimum fermentation temperature below 37 °C ( Abraham and Kurup, 1996, Mishima et al., 2008 and Mukhopadhyay and Chatterjee, 2010). A thermal-tolerant S. cerevisiae strain from Angel Yeast Co. Ltd, was tested by Ma et al. (2010) for bioethanol fermentation with water hyacinth, but using SHF, rather than SSF.The main objectives of this study were (i) to pretreat water hyacinth with NaOH/H2O2 at mild conditions and to (ii) select the thermotolerant yeast strains capable of fermenting the pretreated water hyacinth to produce bioethanol at 42 °C via the SSF process.
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