Ethanol biosynthesis by fast hydrolysis of cassava bagasse using fungal amylases produced in optimized conditions

Abstract

The search for a renewable platform to produce high-value biochemicals and energy that are environmentally correct has been a current concern. A fast and inexpensive bioprocess for amylase production, able to hydrolyze complex residues in fermentable sugars to be used for ethanol production was developed. High titer amylase from Rhizopus oligosporus in solid state fermentation (SSF) was obtained by optimizing the medium supplementation using agro-industrial waste as substrate. Statistical experimental design and partial least square (PLS) regression were used to establish a relation between added chemical compounds and enzyme production, showing that urea was the most important nutrient. Crude amylase extract had competitive performance features giving higher productivities in starch hydrolysis than a commercial glucoamylase. The amylase produced was applied in the proportion of 15 U/g dry cassava bagasse to obtain cassava bagasse hydrolysate (CBH). More than 42% conversion in reducing sugars was achieved with an efficient 10 h single-step hydrolysis at 55°C in a bioreactor. The concentrated CBH was subsequently used in fed batch process producing 89.2% ethanol yield. Furthermore, comparing just the cost of the raw materials sugarcane and CHB, the latter demonstrated to be a lower-cost feedstock for ethanol fermentation.

Ethanol Production from Waste of Cassava Processing

“…This value inserted in the Brazilian energy matrix could replace about 24% of the first generation ethanol produced from sugarcane sugar. The decision regarding second generation ethanol production should be made considering the opportunity prices for the different biomass derived products (ethanol and other biofuels, bioelectricity and sugar, among others) [3] Therefore, the total use of this biomass received by the industry, including generated residues, is important for the industrial economy balance. In addition, the use of this agro-industrial waste as a carbon source for another process helps to solve the pollution problems.…”

“…This value inserted in the Brazilian energy matrix could replace about 24% of the first generation ethanol produced from sugarcane sugar. The decision regarding second generation ethanol production should be made considering the opportunity prices for the different biomass derived products (ethanol and other biofuels, bioelectricity and sugar, among others) [3].…”

“…For each 250-300 tons of cassava root processed, about 280 tons of bagasse with 85% moisture are produced [2]. Currently, the majority of the cassava bagasse is discarded as waste; however, this residue can be considered as an excellent source of fermentation for higher-value biochemicals [3], as is the case with second generation ethanol.…”

Abscisic acid-enhanced starch accumulation of bioenergy crop duckweed (Spirodela polyrrhiza)

“…Thus, biomass energy production has signicantly increased in the last decade and is expected to grow in the near future. A recent report indicates that the main feedstock for commercial bioenergy production is crops such as cassava, 2 sweet sorghum 3 and rice straw. 4 However, the use of the crops to produce bioenergy leads to a competition against food and feed production, which makes the conversion of the crops for bioenergy production a controversial practice.…”

Evaluation of the acid pretreatment of agroindustrial waste assisted by high-intensity ultrasound for further bioethanol production

“…The abundance of vegetable macromolecules as starch, celulose and hemicelulose makes the cassava bagasse a viable substrate for obtaining products with aggregated value. The cleavage of the glycosidic bonds of such molecules into reducing sugars has been studied with the aim of producing not only bioethanol (Escaramboni et al, 2018;Zhang et al, 2016) but also latic acid (John et al, 2006), whiskers/nanofiber of cellulose and starch nanocrystals Teixeira et al, 2009), fumaric acid (Carta et al, 1999), citric acid (Prado et al, 2005), n-butanol , xanthan gum (Woiciechowski et al, 2004), mushroom cultivation (Beux et al, 1997), volatiles and flavors or even for increasing the fiber content in foodstuff (Fiorda et al, 2013a). Therefore, it is needed to develop an optimized process for the adequate pretreatment and to achive an efficient hydrolysis.…”