Prospects of utilizing seawater as a reaction medium for pretreatment and saccharification of rice straw

Functional characterisation of a new halotolerant seawater active glycoside hydrolase family 6 cellobiohydrolase from a salt marsh

Realising a fully circular bioeconomy requires the valorisation of lignocellulosic biomass. Cellulose is the most attractive component of lignocellulose but depolymerisation is inefficient, expensive and resource intensive requiring substantial volumes of potable water. Seawater is an attractive prospective replacement, however seawater tolerant enzymes are required for the development of seawater-based biorefineries. Here, we report a halophilic cellobiohydrolase SMECel6A, identified and isolated from a salt marsh meta-exo-proteome dataset with high sequence divergence to previously characterised cellobiohydrolases. SMECel6A contains a glycoside hydrolase family 6 (GH6) domain and a carbohydrate binding module family 2 (CBM2) domain. Characterisation of recombinant SMECel6A revealed SMECel6A to be active upon crystalline and amorphous cellulose. Mono- and oligosaccharide product profiles revealed cellobiose as the major hydrolysis product confirming SMECel6A as a cellobiohydrolase. We show SMECel6A to be halophilic with optimal activity achieved in 0.5X seawater displaying 80.6 ± 6.93% activity in 1 × seawater. Structural predictions revealed similarity to a characterised halophilic cellobiohydrolase despite sharing only 57% sequence identity. Sequential thermocycling revealed SMECel6A had the ability to partially reversibly denature exclusively in seawater retaining significant activity. Our study confirms that salt marsh ecosystems harbour enzymes with attractive traits with biotechnological potential for implementation in ionic solution based bioprocessing systems.

Sustainable process for fractionation of lignin by the microwave-assisted chemical additive approach: Towards sugarcane leaf biorefinery and characterization

The microwave assisted pretreatment on sugarcane leaf (SCL) biomass for delignification was studied to enhance cellulose digestibility. In this work, microwave assisted with additives were used to delignification SCL for maximize sugar yield recovery. Single factorial and Central composite design (CCD) were employed to optimize the microwave assisted pretreatment conditions for improve delignification efficiency and the sugar yield recovery. The optimized pretreatment conditions were determined to be 4 min pre-treatment time, 500 W microwave power, 1.0 M Na2CO3 and 10 % biomass loading condition produce maximum reducing sugar yield (601 mg g-1) and glucose sugar yield (231 mg g-1) were achieved during saccharification. Pretreated biomass produced reducing sugar and glucose yields that were 4.5 and 4.1 times higher than those of untreated (native) SCL-N biomass, respectively. Additionally, the recyclability study of black liquor, obtained from optimized conditioned treatment of SCL-MSC (Microwave-assisted sodium carbonate pretreated SCL) resulted in considerable saccharification yield up to three pretreatment cycles. The 1H NMR and 13C NMR spectra studies illustrate that aromatic units present in SCL fractionated lignin samples. The variations of structure features and chemical compositions of the raw and pretreated SCL biomass were analyzed by SEM, XRD and XPS analysis. Overall, SCL-MSC pretreatment condition significantly delignification of SCL and led to the maximum sugar production optimized strategies pretreatment conditions was produced maximum amount of sugar, which is great potential for bio-refinery product development.

Microwave-assisted alkali pre-treatment medium for fractionation of rice straw and catalytic conversion to value-added 5-hydroxymethyl furfural and lignin production

In the current study, the use of microwave-assisted sodium hydroxide medium (MWSH) for pre-treatment and saccharification of rice straw to obtain sugar syrup for the production of 5-hydroxymethyl furfural (5-HMF) was investigated. The optimization of the MWSH pre-treatment was carried out using central composite methodology, resulting in a maximum reducing sugar yield of 350 mg/g of treated rice straw (TRS) and a glucose yield of 255 mg/g of TRS under the conditions of a microwave power of 681 W, a NaOH concentration of 0.54 M, and a pre-treatment time of 3 min. Additionally, the microwave assisted transformation of sugar syrup with titanium magnetic silica nanoparticle as catalyst, producing 41.1 % yield of 5-HMF from the sugar syrup after 30 min microwave irradiation at 120 °C with catalyst loading of 2.0:200 (w/v)). The structural characterization of the lignin was analysed using ¹H NMR techniques, and the surface carbon (C1s spectra) and oxygen (O1s spectra) composition changes of the rice straw during pre-treatment were analysed using X-ray photoelectron spectroscopy. The rice straw based bio-refinery process which contains MWSH pretreatment followed by dehydration of sugars achieved high efficiency of 5-HMF production.

Rice straw structure changes following green pretreatment with petha wastewater for economically viable bioethanol production

Energy efficient and environment friendly pretreatment processes for the production of biofuel have remained elusive and the research is further compounded by the high cost of processing lignocellulosic biomass-an essential factor for producing sustainable biofuels. In the last few decades, a number of pretreatment methods have been proposed, specifically chemical pretreatments but are either expensive or harmful to the environment. To address this urgent need, we propose a green pretreatment method that utilises the highly alkaline by-product, petha wastewater to pretreat the lignocellulosic waste rice straw (RS). The effectiveness of the pretreatment was analysed by monitoring both enhanced cellulose content and reducing sugar yield along with removal of hemicellulose and lignin. We found that PWW pretreatment yielded five times more reducing sugar than native RS with 10.12% increment in cellulose content. SEM and EDX studies further revealed that our process enhanced surface roughness and carbon content (from 32.19% increased to 41.59% and 41.66% for A and D, respectively) along with reduction in silica content (from 8.68% in RS to 4.30% and 7.72% for A and D, respectively). XRD and FTIR analyses indicate crystallinity index (CI) and alteration in lignocellulosic structure of RS, respectively. Decrease in CI was about 43.4% in A whereas only 4.5% in D as compared to native RS (CI 54.55%). Thereby we found PWW to be better substitute of an alkali for pretreatment of RS with negligible environmental impacts.