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Pretreatment of Lignocellulosic Wastes to Improve Ethanol and Biogas Production: A Review  [PDF]
Mohammad J. Taherzadeh,Keikhosro Karimi
International Journal of Molecular Sciences , 2008, DOI: 10.3390/ijms9091621
Abstract: Lignocelluloses are often a major or sometimes the sole components of different waste streams from various industries, forestry, agriculture and municipalities. Hydrolysis of these materials is the first step for either digestion to biogas (methane) or fermentation to ethanol. However, enzymatic hydrolysis of lignocelluloses with no pretreatment is usually not so effective because of high stability of the materials to enzymatic or bacterial attacks. The present work is dedicated to reviewing the methods that have been studied for pretreatment of lignocellulosic wastes for conversion to ethanol or biogas. Effective parameters in pretreatment of lignocelluloses, such as crystallinity, accessible surface area, and protection by lignin and hemicellulose are described first. Then, several pretreatment methods are discussed and their effects on improvement in ethanol and/or biogas production are described. They include milling, irradiation, microwave, steam explosion, ammonia fiber explosion (AFEX), supercritical CO2 and its explosion, alkaline hydrolysis, liquid hot-water pretreatment, organosolv processes, wet oxidation, ozonolysis, dilute- and concentrated-acid hydrolyses, and biological pretreatments.
Effect of chemical pretreatment of some lignocellulosic wastes on the recovery of cellulase from Aspergillus niger AH3 mutant
D Damisa, JB Ameh, VJ Umoh
African Journal of Biotechnology , 2008,
Abstract: Lignocellulosic biomass holds remarkable potential for conversion into commodity products presenting dual advantage of sustainable resource supply and environmental quality. Though their utilization does not compete with food and feed demand, its bioconversion and utilizability is facilitated by pretreatment. The effect of the substrate pre-treatment using acid and alkali at two different concentrations (0.5 and 2 M) for two different residence timings (1 and 3 h) on cellulase production from corncob, corn straw and bagasse was studied using Aspergillus niger AH3. The strain was inoculated into 10 g/L of the processed pre-treated lignocellulosic substrates previously added to batches of the Mandels basal medium. The pH of the medium was adjusted to optimum (4.8) and the flasks with the contents autoclaved, thereafter fermentation begun. Samples of each flask were taken aseptically at regular interval (24 h) throughout the growth phase until the enzyme activity peaked off (between 110 and 170 h), centrifuged and the clear supernatant was used for the enzyme assay. Enzyme expression in all the pretreated biomass increased steadily from day one and peaked off at day four or five for the alkali pretreated residues whereas it was at day six for acid pretreated residues. Generally for the alkali treated residues irrespective of residence time, maximum cellulase yield was at day 5 while for the acid treated residues, maximum cellulase yield was at day 6. Enzyme yield from residues treated for longer period (3 h) using alkali when compared to those using acid under the same condition of fermentation was highly significant. The alkali treated residues showed higher cellulase yield than the acid treated residues. Highest cellulase activity (0.06777 IU/ml/min) was display d by the organism grown on bagasse substrate pretreated with 2M NaOH for one hour. The proximate analysis of the cellulosic residues differed from one substrate to another, with the bagasse being the best. Pulverized substrates syndicated with alkali pretreatment using 2 M NaOH for one hour was optimal for cellulase production from the cellulosic residues.
Vanja Janu?i?,Du?ka ?uri?,Tajana Kri?ka,Neven Vo?a
Poljoprivreda (Osijek) , 2008,
Abstract: Bioethanol is today most commonly produced from corn grain and sugar cane. It is expected that there will be limits to the supply of these raw materials in the near future. Therefore, lignocellulosic biomass, namely agricultural and forest waste, is seen as an attractive feedstock for future supplies of ethanol.Lignocellulosic biomass consists of lignin, hemicellulose and cellulose. Indeed, complexicity of the lignocellulosic biomass structure causes a pretreatment to be applied prior to cellulose and hemicellulose hydrolysis into fermentable sugars. Pretreatment technologies can be physical (mechanical comminution, pyrolysis), physico-chemical (steam explosion, ammonia fiber explosion, CO2 explosion), chemical(ozonolysis, acid hydrolysis, alkaline hydrolysis, oxidative delignification, organosolvent process) and biological ones.
Hydrothermal Pretreatment of Lignocellulosic Biomass and Kinetics  [PDF]
Hanwu Lei, Iwona Cybulska, James Julson
Journal of Sustainable Bioenergy Systems (JSBS) , 2013, DOI: 10.4236/jsbs.2013.34034

The study focus was an examination of the hydrothermal pretreatment method applied to the lignocellulosic substrate, represented by the prairie cord grass, and comparison between different conditions based on the yield of glucose after enzymatic hydrolysis. The treatment did not involve any chemicals usage. Enzymatic hydrolysis was performed in order to examine the amount of glucose which was released from pretreated materials. The most efficient pretreatment conditions were at high temperature and relatively short reaction time (210°C and 10 min), after which the lignocellulose structure was the most available for enzymes actions which resulted in a pretreatment conversion rate of 97%. Temperature had a significant influence on glucose release during the hydrolysis, which was confirmed by the Michaelis-Menten and kinetic models. Kinetic models were used to fit the inhibitors and their conversion rates were related to temperature.

Chemical Pretreatment Methods for the Production of Cellulosic Ethanol: Technologies and Innovations  [PDF]
Edem Cudjoe Bensah,Moses Mensah
International Journal of Chemical Engineering , 2013, DOI: 10.1155/2013/719607
Abstract: Pretreatment of lignocellulose has received considerable research globally due to its influence on the technical, economic and environmental sustainability of cellulosic ethanol production. Some of the most promising pretreatment methods require the application of chemicals such as acids, alkali, salts, oxidants, and solvents. Thus, advances in research have enabled the development and integration of chemical-based pretreatment into proprietary ethanol production technologies in several pilot and demonstration plants globally, with potential to scale-up to commercial levels. This paper reviews known and emerging chemical pretreatment methods, highlighting recent findings and process innovations developed to offset inherent challenges via a range of interventions, notably, the combination of chemical pretreatment with other methods to improve carbohydrate preservation, reduce formation of degradation products, achieve high sugar yields at mild reaction conditions, reduce solvent loads and enzyme dose, reduce waste generation, and improve recovery of biomass components in pure forms. The use of chemicals such as ionic liquids, NMMO, and sulphite are promising once challenges in solvent recovery are overcome. For developing countries, alkali-based methods are relatively easy to deploy in decentralized, low-tech systems owing to advantages such as the requirement of simple reactors and the ease of operation. 1. Introduction Cellulosic or second generation (2G) bioethanol is produced from lignocellulosic biomass (LB) in three main steps: pretreatment, hydrolysis, and fermentation. Pretreatment involves the use of physical processes (e.g., size reduction, steaming/boiling, ultrasonication, and popping), chemical methods (e.g., acids, bases, salts, and solvents), physicochemical processes (e.g., liquid hot water and ammonium fibre explosion or AFEX), biological methods (e.g., white-rot/brown-rot fungi and bacteria), and several combinations thereof to fractionate the lignocellulose into its components. It results in the disruption of the lignin seal to increase enzyme access to holocellulose [1, 2], reduction of cellulose crystallinity [3, 4], and increase in the surface area [5, 6] and porosity [7, 8] of pretreated substrates, resulting in increased hydrolysis rate. In hydrolysis, cellulose and hemicelluloses are broken down into monomeric sugars via addition of acids or enzymes such as cellulase. Enzymatic hydrolysis offers advantages over acids such as low energy consumption due to the mild process requirements, high sugar yields, and no unwanted wastes.
Degradation and selective ligninolysis of wheat straw and banana stem for an efficient bioethanol production using fungal and chemical pretreatment
Shilpi Thakur,Bhuvnesh Shrivastava,Snehal Ingale,Ramesh C. Kuhad,Akshaya Gupte
3 Biotech , 2013, DOI: 10.1007/s13205-012-0102-4
Abstract: Lignocelluloses from agricultural, industrial, and forest residues constitute a majority of the total biomass present in the world. Environmental concerns of disposal, costly pretreatment options prior to disposal, and increased need to save valuable resources have led to the development of value-added alternate technologies such as bioethanol production from lignocellulosic wastes. In the present study, biologically pretreated (with the fungus, Pleurotus ostreatus HP-1) and chemically pretreated (with mild acid or dilute alkali) wheat straw (WS) and banana stem (BS) were subsequently subjected to enzymatic saccharification (with mixture of 6.0 U/g of filter paper cellulase and 17 U/g of β-glucosidase) and were evaluated for bioethanol production using Saccharomyces cerevisiae NCIM 3570. Biological and chemical pretreatments removed up to 4.0–49.2 % lignin from the WS and BS which was comparatively higher than that for cellulose (0.3–12.4 %) and for hemicellulose (0.7–21.8 %) removal with an average 5.6–49.5 % dry matter loss. Enzymatic hydrolysis yielded 64–306.6 mg/g (1.5–15 g/L) reducing sugars from which 0.15–0.54 g/g ethanol was produced from Saccharomyces cerevisiae NCIM 3570.
Chemical and Physicochemical Pretreatment of Lignocellulosic Biomass: A Review  [PDF]
Gary Brodeur,Elizabeth Yau,Kimberly Badal,John Collier,K. B. Ramachandran,Subramanian Ramakrishnan
Enzyme Research , 2011, DOI: 10.4061/2011/787532
Abstract: Overcoming the recalcitrance (resistance of plant cell walls to deconstruction) of lignocellulosic biomass is a key step in the production of fuels and chemicals. The recalcitrance is due to the highly crystalline structure of cellulose which is embedded in a matrix of polymers-lignin and hemicellulose. The main goal of pretreatment is to overcome this recalcitrance, to separate the cellulose from the matrix polymers, and to make it more accessible for enzymatic hydrolysis. Reports have shown that pretreatment can improve sugar yields to higher than 90% theoretical yield for biomass such as wood, grasses, and corn. This paper reviews different leading pretreatment technologies along with their latest developments and highlights their advantages and disadvantages with respect to subsequent hydrolysis and fermentation. The effects of different technologies on the components of biomass (cellulose, hemicellulose, and lignin) are also reviewed with a focus on how the treatment greatly enhances enzymatic cellulose digestibility. 1. Introduction The goals stated in the recent roadmap published by the United States Department of Energy (US DOE) [1] is to accelerate biomass to energy conversion research, helping make biofuels practical and cost competitive by 2012 and offering the potential to displace up to 30% of the nation’s current gasoline use by 2030. A major source of biomass which will form the focus of energy research is the lignocellulosic biomass which is particularly well suited for energy applications because of its large-scale availability, low cost, and environmentally benign production. In particular, many energy production and utilization cycles based on cellulosic biomass have near-zero greenhouse gas emissions on a life-cycle basis [2–4]. One of the key steps in the biochemical platform of the biomass to fuels or chemicals process being developed by the US DOE is depolymerization of cellulose to glucose by fungal cellulases before fermentation to ethanol or other products by microbial biocatalysts (Biomass Multiyear Program Plan, March 2008, Office of Biomass Program, EERE, DOE). Novozymes, an enzyme production company, estimated (2007 values) that the cost of enzymes to depolymerize cellulose and hemicellulose to sugars for fermentation would be about 40–100 times higher than the cost of enzymes for starch hydrolysis to glucose on a per gallon ethanol basis [5]. Major cellulase producers estimate (2010) the cost of fungal cellulases to be about $0.50 per gallon [6] of cellulosic ethanol produced. Since this price of enzymes is about 25% of
Canonical correlations between chemical and energetic characteristics of lignocellulosic wastes  [PDF]
Thiago de Paula Protásio,Gustavo Henrique Denzin Tonoli,Mário Guimar?es Júnior,Lina Bufalino
CERNE , 2012,
Abstract: Canonical correlation analysis is a statistical multivariate procedure that allows analyzing linear correlation that may exist between two groups or sets of variables (X and Y). This paper aimed to provide canonical correlation analysis between a group comprised of lignin and total extractives contents and higher heating value (HHV) with a group of elemental components (carbon, hydrogen, nitrogen and sulfur) for lignocellulosic wastes. The following wastes were used: eucalyptus shavings; pine shavings; red cedar shavings; sugar cane bagasse; residual bamboo cellulose pulp; coffee husk and parchment; maize harvesting wastes; and rice husk. Only the first canonical function was significant, but it presented a low canonical R2. High carbon, hydrogen and sulfur contents and low nitrogen contents seem to be related to high total extractives contents of the lignocellulosic wastes. The preliminary results found in this paper indicate that the canonical correlations were not efficient to explain the correlations between the chemical elemental components and lignin contents and higher heating values.
Advances in lignocellulosic biotechnology: A brief review on lignocellulosic biomass and cellulases  [PDF]
Tanzila Shahzadi, Sajid Mehmood, Muhammad Irshad, Zahid Anwar, Amber Afroz, Nadia Zeeshan, Umer Rashid, Kalsoom Sughra
Advances in Bioscience and Biotechnology (ABB) , 2014, DOI: 10.4236/abb.2014.53031

From the last few decades, there has been an increasing research interest in the value of lignocellulosic biomass. Lignoellulosic biomass is an inexpensive, renewable abundant and provides a unique natural resource for large-scale and cost-effective bio-energy collection. In addition, using lignocellulosic materials and other low-cost biomass can significantly reduce the cost of materials used for ethanol production. Therefore, in this background, the rapidly evolving tools of biotechnology can lower the conversion costs and also enhance a yield of target products. In this context, a biological processing presents a promising approach to converting lignocellulosic materials into energy-fuels. The present summarized review work begins with an overview on the physio-chemical features and composition of major agricultural biomass. The information is also given on the processing of agricultural biomass to produce industrially important enzymes, e.g., ligninases or cellulases. Cellulases provide a key opportunity for achieving tremendous benefits of biomass utilization.

The impacts of pretreatment on the fermentability of pretreated lignocellulosic biomass: a comparative evaluation between ammonia fiber expansion and dilute acid pretreatment
Ming W Lau, Christa Gunawan, Bruce E Dale
Biotechnology for Biofuels , 2009, DOI: 10.1186/1754-6834-2-30
Abstract: Comparative evaluation on these two pretreatments reveal that (i) AFEX-pretreated corn stover is significantly more fermentable with respect to cell growth and sugar consumption, (ii) both pretreatments can achieve more than 80% of total sugar yield in the enzymatic hydrolysis of washed pretreated solids, and (iii) while AFEX completely preserves plant carbohydrates, dilute acid pretreatment at 5% solids loading degrades 13% of xylose to byproducts.The selection of pretreatment will determine the biomass-processing configuration, requirements for hydrolysate conditioning (if any) and fermentation strategy. Through dilute acid pretreatment, the need for hemicellulase in biomass processing is negligible. AFEX-centered cellulosic technology can alleviate fermentation costs through reducing inoculum size and practically eliminating nutrient costs during bioconversion. However, AFEX requires supplemental xylanases as well as cellulase activity. As for long-term sustainability, AFEX has greater potential to diversify products from a cellulosic biorefinery due to lower levels of inhibitor generation and lignin loss.Cellulosic ethanol, in comparison with first generation biofuels, is substantially more advantageous with regard to feedstock abundance and greenhouse gas reduction [1,2]. However, unlike the corn ethanol industry, lignocellulosic biomass processing requires higher severity pretreatments due to the inherent recalcitrance of plant material [3]. The selection of pretreatment method has a far-reaching impact on the overall process, including feedstock handling, biological conversions, and downstream processing [4]. The ability to generate steam and electricity from residual lignin is also crucial to maximize the economic profitability and environmental benefits of this industry [2].Among potential pretreatment processes, dilute acid pretreatment and ammonia fiber expansion (AFEX) are regarded as promising candidates for large-scale cellulosic biofuel production. Di
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