Sustainable processing of algal biomass for a comprehensive biorefinery

Digestion of lignocellulosic biomass under an innovative pneu-mechanical system and optimization of process

In this study, an anaerobic pneumatic mechanical digester (PMD) was designed for the first time to investigate the impact of pneumatic agitator on increasing the bioethanol production and compared with a mechanical digester (MD). Fermentation was performed during an optimized pretreatment and hydrolysis process by RSM (Response Surface Method). Ultrasound optimized points (the time values, the acid concentration, and the biomass load) were 30 min, 1.95% v/v, and 6%, and hydrolysis was done within 45 min at the acid concentration of 2.04% v/v and temperature of 148.4 °C. The hydrolysis solutions were poured and the fermentation process took place within 20 days in the PMD and MD. The sampling sequence was every 5 days. According to the results, the PMD could produce bioethanol more than the MD by 27.94%. Besides, CO, H2S and O2 were measured through fermentation. In PMD, the amount of H2S and O2 was lower than the MD, but then the production of CO in the PMD was meaningfully higher. Finally, by the application of the PMD, the amount of harmful mixtures produced throughout the process can be controlled. It can be said that with the new method designed in this study, it is possible to take an important step in the biorefinery and use the biomass produced in nature in an economical and environmentally friendly way.

Efficient production of hydroxymethyl-2-furfurylamine by chemoenzymatic cascade catalysis of bread waste in a sustainable approach

In this study, efficient and sustainable conversion of waste bread (WB) to 5-hydroxymethyl-2-furoamine (HMFA) was achieved in a cascade reaction in betaine:malonic acid (B:MA) - water. 5-HMF (30.3 wt% yield) was synthesized from WB (40.0 g/L) in B:MA - water (B:MA, 18 wt%) in 45 min at 190 °C. By using the newly created recombinant E. coli HNILGD-AlaDH cells expressing L-alanine dehydrogenase (AlaDH) and ω-transaminase mutant HNILGD as biocatalyst, the WB-valorized 5-HMF was biologically aminated into HMFA in a high yield (92.1%) at 35 °C for 12 h through in situ removal of the amino transfer by-products of the amine donor, greatly reducing amine donor dosage (from D-Ala/5-HMF = 16/1 to D-Ala/5-HMF = 2/1, mol/mol) and improving the productivity of HMFA (0.282 g HMFA per g WB). This two-step chemical-enzymatic cascade reaction strategy with B:MA and HNILGD-AlaDH whole-cell provides a new idea for the chemoenzymatic synthesis of valuable furan chemicals from waste biomass.

Concurrent production of ferulic acid and glucose from wheat bran by catalysis of a putative bifunctional enzyme

The aim of this work is to study a bifunctional endoglucanase/carboxylesterase in Sphingobacterium soilsilvae Em02 and express it in soluble form in engineered Escherichia coli. The molecular weight of the recombinant protein of the bifunctional enzyme was 41 KDa. This research also determined the enzymatic activities of the bifunctional enzymes using microcrystalline cellulose and p-nitrophenyl butyrate as substrates and found 40 °C as the optimum temperature for their enzymatic activities. The optimal pH in dual function was 6.0 for endoglucanase and 7.0 for carboxylesterase. The bifunctional enzyme also exhibited enzymatic activities on the natural biomass by generating up to 3.94 mg of glucose and 49.4 μg of ferulic acid from 20 mg of destarched wheat bran. This indicates the broad application prospects of the bifunctional enzyme in agriculture and industry.

Recent advances in lignocellulosic and algal biomass pretreatment and its biorefinery approaches for biochemicals and bioenergy conversion

As the global demand for sustainable energy increases, lignocellulosic (such as agricultural residues, forest biomass, municipal waste, and dedicated energy crops) and algal (including macroalgae and microalgae) biomass have attracted considerable attention, because of their high availability of carbohydrates. This is a potential feedstock to produce biochemical and bioenergy. Pretreatment of biomass can disrupt their complex structure, increasing conversion efficiency and product yield. Therefore, this review comprehensively discusses recent advances in different pretreatments (physical, chemical, physicochemical, and biological pretreatments) for lignocellulosic and algal biomass and their biorefining methods. Life cycle assessment (LCA) which enables the quantification of the environmental impact assessment of a biorefinery also be introduced. Biorefinery processes such as raw material acquisition, extraction, production, waste accumulation, and waste conversion are all monitored under this concept. Nevertheless, there still exist some techno-economic barriers during biorefinery and extensive research is still needed to develop cost-effective processes.

Microalgae and Cyanobacteria Biomass Pretreatment Methods: A Comparative Analysis of Chemical and Thermochemical Pretreatment Methods Aimed at Methane Production

Anaerobic digestion of microalgae and cyanobacteria was first proposed as a destination for algal biomass accumulated on stabilization ponds since it could not be disposed of directly in the environment. Now, the versatility of algal biomass makes them a suitable candidate to produce biofuels and other biomolecules in biorefineries. Anaerobic digestion of biomass is advantageous because it does not require the extraction of specific cellular constituents or drying of the biomass. Nevertheless, challenges remain regarding biomass concentration and their resistant cell walls, which are factors that could hamper methane yield. Many pretreatment methods, including chemical and thermochemical, have been proposed to break down the complex polymers present on the cell wall into smaller molecules. Unfortunately, the relationship between biomass solubilization and methane yield is not well defined. This article intends to review the anaerobic digestion of algal biomass and the role of chemical and thermochemical pretreatments in enhancing methane production. Several pretreatment conditions selected from the scientific literature were compared to verify which conditions actually improve methane yield. The severity of the selected pretreatments was also assessed using the combined severity factor. Results suggest that thermochemical pretreatment in less severe conditions is the most efficient, leading to a greater increase in methane yield. Only enzymatic pretreatments and some thermal pretreatments result in a positive energy balance. The large-scale implementation of pretreatment methods requires technological innovations to reduce energy consumption and its integration with other processes in wastewater treatment plants.