Enzymatic processes
| Technology | |
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| Technology details | |
| Name: | Enzymatic processes |
| Category: | Biochemical processes and technologies |
| Feedstock: | Garden and park waste |
| Product: | Cellulose, hemicellulose, lignin |
Enzymatic processes utilise enzymes (/ˈɛnzaɪmz/) which are proteins that act as biological catalysts (biocatalysts).[1] In terms of lignocellulosic biomass valorisation, enzymes find two main applications: i) biomass pretreatment, and ii) polysaccharides hydrolysis. Biomass enzymatic pre-treatment falls under the category of "biological pre-treatment". Other pre-treatment methods for lignocellulosic biomass includes, physical (e.g., mechanical), chemical (e.g., acid and alkali), physico-chemical (e.g., steam explosion and AFEX), and a combination thereof[2]. polysaccharides hydrolysis is a concept mostly applied in biorefineries as part of the hydrolysis of plant cell wall constituents like cellulose, hemicellulose, and lignin.
Feedstock
Origin and composition
Lignocellulosic biomass (LCB) can be collected as a waste material from forest residues, agricultural, and industrial activities. LCB is mainly characterized by the presence of two carbohydrate polymers, namely cellulose and hemicellulose, as well as an aromatic polymer called lignin. Other components in LCB, found in smaller amounts, are ash, pectin, and proteins. The percentage content of celluloce, hemicelllulose, and lignin are varied among different lignocellulosic materials. In general, the content of cellulose, hemicellulose, and lignin in LCB is in the range of 30-60%, 20-40%, and 15-25%, respectively.[3] The physical appearance and strenght of the biomass depend on the varying concentration of these polymers and therefore greatly influences the type of pre-treatment strategy applied for its deconstruction.
Structural features LCB:
Cellulose
Cellulose is a polysaccharide polymer of glucose disaccharide units, cellobiose, linked tightly by ß-1,4-glycoside bonds. Cellulose molecules are linked by hdyrogen bonds and have different orientations resulting in different levels of crystallinity. Its crystallinity plays a crucial role in the biodegradation of cellulose and, in general, the higher crystallinity level makes it harder to biodegrade the cellulose.
Hemicellulose
Hemicellulose is a random and branched heterogeneous polymer of different polysaccharides including pentoses (xylose and arabinose), hexoses (glucose, galactose, and mannose) and sugar acids. The branched nature of the hemicellulose allows it to form strong bonds with cellulose (through hydrogen bonds) and lignin (through covalent bonds).
Lignin
Lignin is a complex and large compound made out of phenylpropane units linked in a three-dimensional structure. The main monomers of lignin are p-hydroxyphenyl alcohol, coniferyl alcohol, and sinapyl alcohol. Lignin acts as a cementing material that links celluose and hemicellulose to form the rigid three-dimensional structure of the plant cell wall.
Pre-treatment
The following pre-treatments may be considered prior to enzymatic pre-treatment:
- Sizing (e.g., milling, grinding)
- Steam explosion (hybrid pre-treatment; e.g., combined with laccase pretreatment)[4]
The following pre-treatments may be considered prior to enzymatic hydrolysis[5],[6]:
- Physical (e.g., milling, grinding, ultrasonication, extrusion)
- Chemical (e.g., acid, alkali, ionic liquid, organosolv)
- Physico-chemical (e.g., steam explosion, hot water, AFEX, wet oxidation)
- Biological (e.g., microbial and enzymatic)
Process and technologies
Enzymatic pre-treatment (biological pre-treatment)
Biological pre-treatment systems rely on biological agents (e.g., enzymes) to delignify lignocellulose and make the process of enzymatic hydrolysis more convenient. The effect of enzymes on the lignocellulosic biomass depends on the type of enzymes as well as the composition of the biomass being treated. This is due to enzyme specificity in terms of the type of the reactions that they catalyze. Laccase (Lac), manganese peroxide (MnP) and versatile peroxide (VP) are enzymes that are used extensively to treat the lignocellulosic substrate[7]. Biological pre-treatment of LCB is often knows as a simple, inexpensive, selective, and environmentally-friendly technology. This is mainly due to the fact that biological pre-treatment does not require high energy inputs or chemicals addition. Furthermore, enzymatic treatment has found success in the removal of toxic inhibitory compounds (i.e., complete removal of phenolic compounds). The limitations asociated with enzymatic pretreatment is its production cost, stability, shelf life, and reusability[6].
Enzymatic hydrolysis
Enzymatic hydrolysis processes allow to produce monomeric sugars from (ligno)cellulosic biomass by using specific enzymes (e.g., cellulases and hemicellulases) able to break down the chemical bonds in cellulose and hemicellulose polymers. Several factors can affect the efficiency of this process: accessible surface area and crystallinity of the biomass, as well as pH, time and temperatures of the process[8]. Enzymatic hydrolysis is gaining increased attention with respect to acid hydrolysis due to equipment corrosion, energy consumption, non-recyclability of reagents, and fermentation inhibitors production during acid hydrolysis [9]. Different enzymes play different roles in the hydrolysis of lignocellulosic biomass:
Cellulases
Cellulases are one of the key enzymes in biomass hydrolysis. Cellulases are a family of enzymes that synergistically act on cellulose to hydrolyze it to its monomers. Cellulases acts on the ß-1,4-glycosidic linkages in cellulose. The complete hydrolysis of cellulose is mediated by combination of three main cellulases, namely endoglucanases (EC 3.2.14), exoglucanases (EC 3.2.1.91), and glycosidase (EC 3.2.1.21). T. reesei-based cellulases have been the focus of research for the past several years and are widely used in laboratory- as well as pilot-scale studies for bioethanol application. Most commercially accessible enzymes for biomass hydrolysis are actually cocktails of cellulases from Trichoderma or Aspergillus supplemented with ß-glucosidases from other sources.
Hemicellulases
Hemicellulose consists of a mixture of glucose and sugar monomers. Xylan is the most abundant hemicellulose-containing pentose sugars, such as xylose. The enzyme xylanase helps to catalyze the hydrolysis of xylan. Hydrolysis of xylan is mediated by the action of multiple xylanases (i.e., endoxylanases and exoxylanases). Commercially, xylanases are produced from T. reesei, A. niger, humicola insolens, and Bacillus sp.
Pectinases
Pectinase is a complex enzyme that degrades the pectin present in lignocellulosic biomass. Pectin is a polymer of α-1,4-linked D-galacturonic acid. This enzyme breaks down polygalacturonic acid (GalA) into a monomeric unit by opening glycosidic linkages. It helps the softening of biomass and therefore aids in the hydrolysis of biomass.
Other accessory enzymes
The accessory enzymes are also a crucial part in the hydrolysis of LCB and enhance the hydrolysis yield and reduce the enzyme cost and dosages. The breakdown of hemicelluloses is further accompanied by the addition of ß-xylosidases which produces a final product of oligomer with different length as intermediates. Another important accessory enzyme is α-arabinofuranidase for breaking down arabinose into monomers of furanose and pyranose.
Product
Products enzymatic pre-treatment:
- Cellulose
- Hemicellulose
- Lignin
Potential products after fermentation:
- Bioethanol
- Biodiesel
- Biobutanol
- Methane
- Spcialty chemicals
Technology providers
NovelYeast bv
| General information | |||
| Company: | NovelYeast bv |
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| Country: | Belgium | ||
| Contact: | johan.thevelein@novelyeast.com | ||
| Webpage: | https://www.linkedin.com/in/johan-thevelein-aab60a10/ | ||
| Technology and process details | |||
| Technology name: | Enzymatic saccharification, In-situ enzyme production | Technology category: | Conversion (Biochemical processes and technologies) |
| TRL: | 3-5 | Capacity: | Lab scale kg·h-1 |
| Agitator: | Controlled parameters: | Standard parameters | |
| Processable volume: | 5 L | Reactor: | Shake flasks, static tubes with magnetic stirring |
| Reactor material: | Glass | Safety restrictions: | Standard microbiological practice |
| Temperature: | 25-60 °C | Other: | Application of commercial enzyme cocktails, development of in situ enzyme production |
| Feedstock and product details | |||
| Feedstock: | 1G and 2G feedstocks | Product: | Fermentable sugars |
NovelYeast bv was founded in 2019 by Prof. Johan Thevelein (KU Leuven and VIB) to continue his R&D activities after his retirement in 2020 as emeritus. The company focusses on the development and industrial implementation of yeast cell factories for the production of biofuels, bio-based chemicals as well as specialty sugars and ingredients with first- and second-generation feedstocks. It also develops cell factories for the production of specific proteins for food applications and enzymes for saccharification of lignocellulosic biomass. In addition, it uses yeast as a tool for biomedical and agroindustrial applications, including yeast probiotics and anti-cancer drugs selected by screening in yeast. NovelYeast has several R&D service collaborations with companies world-wide.
Novozymes (Bagsvaerd, Denmark)
DSM (Delft, Netherland)
Dupont (Wilmington, United States)
Open access pilot and demo facility providers
Patents
Currently no patents have been identified.
References
- ↑ , 2021: Enzyme , Last access 24-09-21. https://en.wikipedia.org/wiki/Enzyme
- ↑ E. Hosseini Koupaie, S. Dahadha, A.A. Bazyar Lakeh, A. Azizi, E. Elbeshbishy, 2018: Enzymatic pretreatment of lignocellulosic biomass for enhanced biomethane production - A review. Journal of Environmental Management, Vol. 233, 774-784. doi: https://doi.org/10.1016/j.jenvman.2018.09.106
- ↑ Sawatdeenarunat, C., Surendra, K., Takara, D., Oechsner, H., Khanal, S.K., 2015: Anaerobic digestion of lignocellulosic biomass: challenges and opportunities. Bioresour. Technol., Vol. 178, 178-186. doi: https://doi.org/10.1016/j.biortech.2014.09.103
- ↑ Weihua Qiu, Hongzhang Chen, 2012: Enhanced the ezymatic hydrolysis efficiency of wheat straw after combined steam explosion and laccase pretreatment. Bioresource Technology, Vol. 118, 8-12. doi: https://doi.org/10.1016/j.biortech.2012.05.033
- ↑ Rajeev Ravindran, Amit Kumar Jaiswal, 2016: A comprehensive review on pre-treatment strategy for lignocellulosic food industry waste: Challenges and opportunities. Bioresource Technology, Vol. 199, 92-102. doi: https://doi.org/10.1016/j.biortech.2015.07.106
- ↑ a b Bikash Kumar, Nisha Bhardwaj, Komal Agrawal, Venkatesh Chaturvedi, Pradeep Verma, 2019: Current perspective on pretreatment technologies using lignocellulosic biomass: An emerging biorefinery concept. Fuel Processing Technology, Vol. 199, . doi: https://doi.org/10.1016/j.fuproc.2019.106244
- ↑ Baruah J., Nath B.K., Sharma R., Kumar S., Deka R.C., Kalita E., 2018: Recent Trends in the Pretreatment of Lignocellulosic Biomass for Value-Added Products. Front. Energy Res., Vol. 141, . doi: https://doi.org/10.3389/fenrg.2018.00141
- ↑ Saverio Niglio, Alessandra Procentese, Maria Elena Russo, Giovanni Sannia, Antonio Marzocchella, 2019-06-01: Investigation of Enzymatic Hydrolysis of Coffee Silverskin Aimed at the Production of Butanol and Succinic Acid by Fermentative Processes. BioEnergy Research, Vol. 12, (2), 312–324. doi: https://doi.org/10.1007/s12155-019-09969-6
- ↑ Gabriela Piccolo Maitan-Alfenas, Evan Michael Visser, Valéria Monteze Guimarães, 2015-02-01: Enzymatic hydrolysis of lignocellulosic biomass: converting food waste in valuable products. Current Opinion in Food Science, Vol. 1, 44–49. doi: https://doi.org/10.1016/j.cofs.2014.10.001