Morphological and structural changes in paddy straw influenced by alkali and microbial pretreatment

Abstract

Paddy straw is a lignocellulosic waste rich in holocellulose (cellulose+hemicellulose) content. It can be used as a good substrate for biogas, bioethanol and biodiesel production. However, the recalcitrant cell wall components i.e. lignin and silica are the main deterrent to efficient utilization of paddy straw. This stringent sheath of lignin and silica does not allow fermenting microbes to access holocellulose. Pretreatment of paddy straw is, therefore, crucial to get rid of lignin and silica. In this context, paddy straw was pretreated with various alkalis viz. NH3, Na2SO3, Na2CO3 and NaOH in the current study. All the alkali pretreatments were supplemented with microwave irradiations (720 W, 18°C) for 30 minutes. Paddy straw was also pretreated microbially with Pleurotus florida for 15 days via spawning. Morphological and structural changes in the pretreated paddy straw were visualized via Scanning Electron Microscopy (SEM). The straw turned remarkably fragile with enhanced bulk density and surface wettability after 4% NaOH-30 min microwave pretreatment. The pretreated straw was also found to lack silicified cuticle layer and lignin sheath which exposes straw sugars (cellulose and hemicellulose) to fermenting microbes.