Microwave Assisted Alkali Pretreatment of Rice Straw for Enhancing Enzymatic Digestibility

Abstract

Rapid industrialization, increasing energy demand, and climate change are the conditions that forced the researchers to develop a clean, efficient, renewable, and sustainable source of energy which has a potential to replace fossil fuels. Ethanol is one of the attractive and suitable renewable energy resources. In present study, effectiveness of microwave pretreatment in combination with sodium hydroxide (NaOH) for increasing enzymatic hydrolysis of rice straw has been investigated and under optimum conditions obtained a maximum reducing sugar (1334.79 g/mL) through microwave assisted NaOH pretreatment. Chemical composition analysis and scanning electron microscope (SEM) images showed that the removal of lignin, hemicellulose, and silicon content is more in microwave assisted NaOH pretreatment than the blank sample. X-ray diffraction (XRD) analysis revealed that the crystallinity index of rice straw treated with microwave assisted alkali (54.55%) is significantly high as compared to the blank (49.07%). Hence, the present study proves that microwave assisted alkali pretreatment can effectively enhance enzymatic digestibility of rice straw and it is feasible to convert rice straw for bioethanol production.

Optimization of microwave‐assisted alkali pretreatment of cassava rhizome for enhanced enzymatic hydrolysis glucose yield

“…The results suggested that microwave power played a major role in variations of glucose yield. Specifically, high microwave power, given low NaOH concentration, effectively degraded lignin and increased enzymatic accessibility, consistent with Kamalini, Muthusamy, Ramapriya, Muthusamy, and Pugazhendhi () and Singh, Tiwari, Srivastava, and Shukla ().…”

“…Aqueous NaOH also increased the cleavage of intermolecular ester bonds crosslinking lignin and other components such as hemicelluloses. Similar increases in CrI were reported for MAP‐treated cassava stems (Table ) and other lignocelluloses (Boonsombuti et al, ; Singh et al, ; Velmurugan & Muthukumar, ; Wanitwattanarumlug, Luengnaruemitchai, & Wongkasemjit, ). It could be concluded that increased CrI led to enhanced enzyme digestibility.…”

Fast Microwave-assisted Pretreatment for Bioconversion of Sawdust Lignocellulose to Glucose

“…A pretreatment with a microwave oven at a frequency of 2.45 GHz and with a wattage of 950 Watt with varied times and rice straw powder sizes showed a highly significant increase in cellulose content and a highly significant reduction in lignin and hemicelluloses content [2]. Combining microwave pretreatment with NaOH can increase the glucose content and reduce the lignin and hemicellulose content [21]. A pretreatment with a microwave oven combined with NaOH increased the cellulose content of banana stems compared to other treatments.…”

“…Microwave pretreatment with an acid has advantages at the reaction conditions such as corrosion, high temperatures, and economically cheaper. If the concentration of acid/alkali is increased, the glucose content also increases [21][22] reported that pretreatment with microwave combined with distilled water, NaOH and H 2 SO 4 at a temperature ranging from 130 to 200 o C on miscanthus showed H 2 SO 4 resulted in maximum glucose content at a temperature of 180 o C. At 200 o C, however, the glucose content significantly decreased. The mechanism of how a microwave increases the chemical reaction has yet to elucidate.…”

“…Those effects were compared to the effects of the conventional heating. The degradation was expected to be able to break down the hemicellulosic bonds, reduce the lignin content, and convert crystal structures of the celluloses to simple sugars [20][21]. In addition, it was expected to find a broader explanation of the microwave effects on the chemical processes, especially on the pretreatment for cellulose hydrolysis.…”