Enzymes for Biomass Pretreatment: A Comprehensive Review.

Energy assessment and enhancement of the lipid yield of indigenous Chlorella sp. KA-24NITD using Taguchi approach

Enzymatic pretreatment of lignocellulosic biomass for enhanced biomethane production-A review

Enzymatic and alkali pretreatments were employed to improve nickel biosorption capacity of Rhizomucor pusillus biomass. Pretreatment with 0.002–80 g l−1 NaOH and 0.0001–0.1 Anson Unit (AU) g−1 protease enhanced the biosorption capacity of fungal biomass. Increasing the concentration of NaOH from 0.002 to 5 g l−1 improved nickel removal from 93.2 to 100.0 % while untreated biomass showed 64.6 % Ni(II) removal. Pretreatment with higher concentrations of NaOH, 5–80 g l−1 resulted in nearly complete removal of nickel ions. Pretreatment of the biomass with 0.0001 AU g−1 protease improved the nickel removal to over 91 %, while increasing the enzyme loading to 0.1 AU g−1 improved the removal to 93 %. Untreated biomass removed 78.4, 63.0, and 96.3 % of chromium, copper, and lead ions, respectively, from a mixture solution of the ions. Respective metal removals were increased to 100, 98.9, and 100 % after pretreatment with 0.2 g l−1 NaOH solution and to 87.8, 86.7, and 100 % after the enzymatic pretreatment with 0.1 AU g−1 protease. Scanning electron microscopy analysis indicated that alkali and enzymatic pretreatments enhanced the porosity of the biomass. Furthermore, compositional analysis showed that both of the pretreatments removed a major part of fungal proteins (2.1–95.8 % removal). Glucosamine, N-acetyl glucosamine, and phosphates were the major ingredients of the pretreated biomass.

Microalgal biomass is a sustainable source of bioactive lipids with omega-3 fatty acids. The efficient extraction of neutral and polar lipids from microalgae requires alternative extraction methods, frequently combined with biomass pretreatment. In this work, a combined ultrasound and enzymatic process using commercial enzymes Viscozyme, Celluclast, and Alcalase was optimized as a pretreatment method for Nannochloropsis gaditana, where the Folch method was used for lipid extraction. Significant differences were observed among the used enzymatic pretreatments, combined with ultrasound bath or probe-type sonication. To further optimize this method, ranges of temperatures (35, 45, and 55 °C) and pH (4, 5, and 8) were tested, and enzymes were combined at the best conditions. Subsequently, simultaneous use of three hydrolytic enzymes rendered oil yields of nearly 29%, showing a synergic effect. To compare enzymatic pretreatments, neutral and polar lipids distribution of Nannochloropsis was determined by HPLC–ELSD. The highest polar lipids content was achieved employing ultrasound-assisted enzymatic pretreatment (55 °C and 6 h), whereas the highest glycolipid (44.54%) and PE (2.91%) contents were achieved using Viscozyme versus other enzymes. The method was applied to other microalgae showing the potential of the optimized process as a practical alternative to produce valuable lipids for nutraceutical applications.

Green chemical and hybrid enzymatic pretreatments for lignocellulosic biorefineries: Mechanism and challenges

Bioethanol production and its demand in India will be an increasing trend in the future. There are huge quantities of lignocellulosic feedstocks available for bioethanol production to fulfil the growing bioethanol demand. For lignocellulose-based bioethanol production, biomass pretreatment is an inevitable process for even the best lignocellulosic feedstock produce bioethanol. Paddy straw is a lignocellulosic agricultural residue obtained after the threshing process and it has challenges in safe disposal due to its low bulk density, inefficient burning methods and associated environmental pollution. To overcome these issues, paddy straw can be effectively used for bioethanol production after biomass pretreatment. Several pretreatment methods like chemical, irradiation, hot water, fungal, popping, and enzymatic pretreatment are available to pretreat the straw for bioethanol production. The pretreatment processing cost is almost 33% of the total cost of bioethanol production, which is the main barrier for bioethanol industry to run economically. The selection of an appropriate pretreatment method still remains one of the significant hurdles in economic bioethanol production from paddy straw. The use of paddy straw has a dual advantage as it is not only used as feedstock for bioethanol production, but will also help in controlling environmental pollution related to the burning of waste in the field. This chapter discusses the different pretreatment technologies used for paddy straw to remove the lignin content and how it is further used to produce bioethanol.

In this study, benefits of the enzymatic pretreatment of mixed biomass wastes to a thermochemically favourable precursor for production of ecological biofuels are demonstrated. Biochar briquettes derived from the enzymatic- hydrolysis assisted, mild-temperature pyrolysis of biomass wastes are rich in carbon, exhibit higher calorific values and emit less toxic gases during combustion. Specifically, HHV value of the pretreated briquette increases one half of that of untreated briquette. Levels of CO and CO2 emission during the production and consumption of the treated briquette are lower than those of the untreated one. The results indicate a superior performance of biochar produced from the mixtures of various biomass wastes via the combined enzymatic pretreatment and mild-temperature pyrolysis processes in sustainable applications including biofuels.

Improving biogas production from microalgae by enzymatic pretreatment

Enzymatic pretreatment of algal biomass has different optimal conditions for biogas and bioethanol routes

"This paper presents a method for the enzymatic pretreatment of algal biomass used as a fermentation substrate in anaerobic bioreactors for biogas production, in order to improve the energy efficiency of the biogas systems. The pretreatment method aims at breaking compact carbohydrates (cellulose and hemicelluloses) macromolecular structures from algal biomass under the action of a hydrolytic enzymes mixture secreted by the fungal species Trichoderma reesei, Trichoderma versicolor, Penicillinum chrysosporium, Fusarium solani, Chaetomium thermophile and Myrothecium verrucaria, thus facilitating access of anaerobic fermentation bacteria to heavily biodegradable cellulosic fibres, reducing fermentation time length and implicitly increasing the biomethane yield of anaerobic reactors. The laboratory experiments involving the marine macroalgae Ulva sp. have proven a significant increase in the concentration and total volume of biomethane in the fermentation gas produced by the enzymatically pretreated sample with the selective fungal mixture, compared to the untreated sample. It is expected that such a non-corrosive pretreatment method can bring higher biomethane production with minimal conditioning costs and fewer process residues, thus increasing the biogas systems profitability."

Chemical and enzymatic sequential pretreatment of oat straw for methane production

Enzymatic cell disruption of the microalgae Chlamydomonas reinhardtii for lipid and protein extraction

The plant biomass has evolved with different mechanisms for enhancing the robustness of its structure. It naturally resists the chemical or enzymatic attack on its structural components by microbes and other organisms in nature. Several factors such as the degree of polymerization, fiber strength, higher order structures, lignin content, presence of lignin cover, an intricate matrix of lignocellulosic components and their coherence, cellulose crystallinity, and the porosity of biomass are known to contribute to the toughness of the biomass structure. It reduces the accessibility of sugar polymers through a physical barrier, which is formed due to the formation of lignin-carbohydrate complexes. The main objective of the pretreatment process is to minimize the recalcitrance of biomass to increase the accessibility of sugar polymers for their enzymatic hydrolysis in the subsequent step of saccharification. The biomass pretreatment can be done using different methods, viz., physical, physicochemical, and biological pretreatment. Each method has its advantages and limitations. The efforts are underway to reduce the time of pretreatment by various means. Some studies have suggested combining biological pretreatment with mild physical or chemical methods. Also, enzymatic pretreatment may give faster results as it does not depend on the growth of microbes on biomass directly.

Sustainability assessment of lignocellulosic biorefineries under uncertainty

Microalgal biomass is a sustainable and valuable source of lipids with omega-3 fatty acids. The efficient extraction of lipids from microalgae requires fast and alternative extraction methods, frequently combined with biomass pre-treatment by different procedures. In this work, Pressurized liquid extraction (PLE) was optimized and compared with traditional lipid extraction methods, Folch and Bligh and Dyer, and with a new Ultrasound Assisted Extraction (UAE) method for lipids from microalgae Isochrysis galbana. To further optimize PLE and UAE, enzymatic pre-treatment of microalga Isochrysis galbana was studied with commercial enzymes Viscozyme and Celluclast. No significant differences were found for lipid yields among different extraction techniques used. However, advanced extraction techniques with or without pre-treatment are a green, fast, and toxic solvent free alternative to traditional techniques. Lipid composition of Isochrysis was determined by HPLC-ELSD and included neutral and polar lipids, showing that each fraction comprised different contents in omega-3 polyunsaturated fatty acids (PUFA). The highest polar lipids content was achieved with UAE (50 °C and 15 min) and PLE (100 °C) techniques. Moreover, the highest omega-3 PUFA (33.2%), eicosapentaenoic acid (EPA) (3.3%) and docosahexaenoic acid (DHA) (12.0%) contents were achieved with the advanced technique UAE, showing the optimized method as a practical alternative to produce valuable lipids for food and nutraceutical applications.