To sum up, after optimization, the highest BC yield (7.02 g/L) was almost 6 times as that obtained from the untreated WBY (1.21g/L). The cellulose membrane was obviously thicker:
15.4 mm compared to 2.3 mm obtained from the untreated WBY and 5.7 mm from the un-centrifuged WBY (Fig. 4, see Supplementary figure). Moreover, the 100 mL of WBY hydrolysates was almost completely used by G. hansenii CGMCC 3917 to produce BC (Fig. 4C, see Supplementary figure) and its yield doubled that obtained from the conventional chemical media (3.58 g/L) (Ge et al., 2011). Although some researchers have investigated various cellulosic wastes from renewable agro-forestry residues or industrial by-products to produce BC, some extra nutrients are added to media to improve the BC yield. For instance, Hong and Qiu (2008) have obtained an increase of BC production with Ca2+ introduced into the medium of konjac powder hydrolysates, Gomes et al. (2013) have enhanced BC production with supplemented nitrogen and phosphate sources in olive mill residue hydrolysates, Ha et al. (2008) have improved BC yield with adding glucose into waste beer yeast hydrolysates as supplement nutrient. In the pres- ent study no extra nutrient was added. Moreover, BC production using WBY pretreated by ultrasonication displayed a high yield and WBY hydrolysates could totally substitute the conventionally used chemical media. Our findings could not only overcome the high BC production cost, but also reduce the waste of resources and environmental pollution. Therefore, it has been not only demonstrated that waste beer yeast has great potential to produce BC, but also that ultrasonication is an effective pre-treatment tool in biomass pre-treatment technology.
To sum up, after optimization, the highest BC yield (7.02 g/L) was almost 6 times as that obtained from the untreated WBY (1.21g/L). The cellulose membrane was obviously thicker:15.4 mm compared to 2.3 mm obtained from the untreated WBY and 5.7 mm from the un-centrifuged WBY (Fig. 4, see Supplementary figure). Moreover, the 100 mL of WBY hydrolysates was almost completely used by G. hansenii CGMCC 3917 to produce BC (Fig. 4C, see Supplementary figure) and its yield doubled that obtained from the conventional chemical media (3.58 g/L) (Ge et al., 2011). Although some researchers have investigated various cellulosic wastes from renewable agro-forestry residues or industrial by-products to produce BC, some extra nutrients are added to media to improve the BC yield. For instance, Hong and Qiu (2008) have obtained an increase of BC production with Ca2+ introduced into the medium of konjac powder hydrolysates, Gomes et al. (2013) have enhanced BC production with supplemented nitrogen and phosphate sources in olive mill residue hydrolysates, Ha et al. (2008) have improved BC yield with adding glucose into waste beer yeast hydrolysates as supplement nutrient. In the pres- ent study no extra nutrient was added. Moreover, BC production using WBY pretreated by ultrasonication displayed a high yield and WBY hydrolysates could totally substitute the conventionally used chemical media. Our findings could not only overcome the high BC production cost, but also reduce the waste of resources and environmental pollution. Therefore, it has been not only demonstrated that waste beer yeast has great potential to produce BC, but also that ultrasonication is an effective pre-treatment tool in biomass pre-treatment technology.
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