Continuous co-production of ethanol and xylitol from rice straw hydrolysate in a membrane bioreactor

Abstract

The present study was set to develop a robust and economic biorefinery process for continuous co-production of ethanol and xylitol from rice straw in a membrane bioreactor. Acid pretreatment, enzymatic hydrolysis, detoxification, yeast strains selection, single and co-culture batch fermentation, and finally continuous co-fermentation were optimized. The combination of diluted acid pretreatment (3.5 %) and enzymatic conversion (1:10 enzyme (63 floating-point unit (FPU)/mL)/biomass ratio) resulted in the maximum sugar yield (81 % conversion). By concentrating the hydrolysates, sugars level increased by threefold while that of furfural reduced by 50 % (0.56 to 0.28 g/L). Combined application of active carbon and resin led to complete removal of furfural, hydroxyl methyl furfural, and acetic acid. The strains Saccharomyces cerevisiae NCIM 3090 with 66.4 g/L ethanol production and Candida tropicalis NCIM 3119 with 9.9 g/L xylitol production were selected. The maximum concentrations of ethanol and xylitol in the single cultures were recorded at 31.5 g/L (0.42 g/g yield) and 26.5 g/L (0.58 g/g yield), respectively. In the batch co-culture system, the ethanol and xylitol productions were 33.4 g/L (0.44 g/g yield) and 25.1 g/L (0.55 g/g yield), respectively. The maximum ethanol and xylitol volumetric productivity values in the batch co-culture system were 65 and 58 % after 25 and 60 h, but were improved in the continuous co-culture mode and reached 80 % (55 g/L) and 68 % (31 g/L) at the dilution rate of 0.03 L per hour, respectively. Hence, the continuous co-production strategy developed in this study could be recommended for producing value-added products from this hugely generated lignocellulosic waste.

Production of 2,3‐butanediol byKlebsiella pneumoniaeBLh‐1 andPantoea agglomeransBL1 cultivated in acid and enzymatic hydrolysates of soybean hull

“…These results are comparable to data reported in previous researches, in which soybean hulls hydrolysates did not present any apparent cell toxicity, using other hydrolyses treatments such as with CO 2 − H 2 O or with dilute alkaline pretreatment . In contrast, nondetoxified biomass hydrolysates from rice hulls, sugarcane bagasse, and corncob hydrolysates have shown varying degrees of microbial cell toxicity.…”

A Bibliometric Study of Scientific Publications regarding Hemicellulose Valorization during the 2000–2016 Period: Identification of Alternatives and Hot Topics

“…Moreover, the combination of typical ethanol producers from hexoses with other organisms that consume xylose to produce alternative products has been proposed [192,193]. In these cases, the sugar mixture can be diversified to obtain different products from hexoses and pentoses.…”

Lignocellulosic bioethanol production: prospects of emerging membrane technologies to improve the process – a critical review

“…Time-consuming and expensive pretreatment processes are the main prerequisites to avoid membrane fouling while working with waste materials. Specific agricultural lignocellulosic waste substances such as rice straw and wheat straw (Ishola et al 2013, 2015a,b, Ylitervo et al 2014, Zahed et al 2016 have been mainly exploited in experimental studies of membrane reactor facilitated lignocellulosic bioethanol production process. In some experimental studies (Lee et al 2000, Ylitervo et al 2014, general lignocellulosic hydrolyzate materials were investigated in MBR-based bioethanol production process.…”

“…Concentration polarization is another common problem that can influence membrane performance during high solid loading saccharification process and comes up with enzyme activity loss, although such difficulty can be controlled by adopting optimized hydrolysis reaction rate by selecting a suitable dilution rate of substrate (Andrić et al 2010). Existing experimental studies of membrane reactor systems for lignocellulosic bioethanol production mainly focused on the utilization of abundant agricultural lignocellulosic waste substances such as rice straw and wheat straw (Ishola et al 2013, 2015a,b, Ylitervo et al 2014, Zahed et al 2016, but still now many more promising lignocellulosic substrates such as kans grass and coconut mesocarp are overlooked by researchers in the field of membrane-based lignocellulosic bioethanol production.…”