Enzymatic-based hydrolysis processes for ethanol from lignocellulosic materials : A review.

This article reviews developments in the technology for ethanol production from lignocellulosic materials by “enzymatic” processes. Several methods of pretreatment of lignocelluloses are discussed, where the crystalline structure of lignocelluloses is opened up, making them more accessible to the cellulase enzymes. The characteristics of these enzymes and important factors in enzymatic hydrolysis of the cellulose and hemicellulose to cellobiose, glucose, and other sugars are discussed. Different strategies are then described for enzymatic hydrolysis and fermentation, including separate enzymatic hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), non-isothermal simultaneous saccharification and fermentation (NSSF), simultaneous saccharification and co-fermentation (SSCF), and consolidated bioprocessing (CBP). Furthermore, the by-products in ethanol from lignocellulosic materials, wastewater treatment, commercial status, and energy production and integration are reviewed

Acid-based hydrolysis processes for ethanol from lignocellulosic materials : A review.

Bioethanol is nowadays one of the main actors in the fuel market. It is currently produced from sugars and starchy materials, but lignocelluloses expect to be major feedstocks for ethanol production in the future. Two processes are developed in parallel for utilization of lignocelluloses to ethanol, “acid-based” and “enzyme-based” processes. The current article is dedicated to review the progress of “acid-based-hydrolysis” process. This process was industrially used in 1940s, during wartime, but was not economically competitive afterward. However, intensive research and development on its technology in the last three decades and expanding ethanol market may revive the process in large scale once again. In this paper, ethanol market, composition of lignocellulosic materials, concentrated- and dilute-acid pretreatment and hydrolysis, plug-flow, percolation, counter-current and shrinking-bed hydrolysis reactors, fermentation of hexoses and pentoses, effects of fermentation inhibitors, downstream processing, wastewater treatment, analytical methods used, and the current commercial status of the acid-based ethanol processes is reviewed

Enzymatic-based hydrolysis processes for ethanol from lignocellulosic materials : A review.

This article reviews developments in the technology for ethanol production from lignocellulosic materials by “enzymatic” processes. Several methods of pretreatment of lignocelluloses are discussed, where the crystalline structure of lignocelluloses is opened up, making them more accessible to the cellulase enzymes. The characteristics of these enzymes and important factors in enzymatic hydrolysis of the cellulose and hemicellulose to cellobiose, glucose, and other sugars are discussed. Different strategies are then described for enzymatic hydrolysis and fermentation, including separate enzymatic hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), non-isothermal simultaneous saccharification and fermentation (NSSF), simultaneous saccharification and co-fermentation (SSCF), and consolidated bioprocessing (CBP). Furthermore, the by-products in ethanol from lignocellulosic materials, wastewater treatment, commercial status, and energy production and integration are reviewed

Antimicrobial properties of fungal chitosan

Cell wall of zygomycetes fungus is an alternative source for chitosan production. In this study chitosan was extracted from cell wall of filamentous fungus Rhizopus oryzae and its antimicrobial properties was studied against three typical human pathogenic microorganisms, Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus. The viability of these bacteria reduced by more than 60%, when 200 ppm of the fungal chitosan was present in the solution. However, the Minimum Bactericidal Concentration (MBC) of the fungal chitosan was 300, 500 and 700 ppm for S. aureus, E. coli and K. pneumoniae, respectively. The antimicrobial activity of fungal chitosan was lower than that of crustacean shells chitosan, which had MBC of less than 100 ppm for the above mentioned bacteria. Furthermore, fungal chitosan similar to crustacean shells chitosan exhibited better inhibitory effects against gram-positive compared to gram-negative bacteria. The possible mechanism for antimicrobial activity of fungal chitosan could be the disruption of the outer membrane of cells but not preventing the nutrients from entering into the cell

Borås, a Zero Waste City in Sweden

Waste is a wealthy resource in the city of Borås in Sweden. The city has developed a sustainable waste management mechanism by reducing landfill, recovering fuel from the waste and recycling in collaboration with University of Borås, local municipality and other private partners. The system was designed back in 1986 to convert waste into value- added products such as biogas, electricity and heat. Hardly less than 1% of waste ends in landfills, thus Borås has given a new model of utilizing waste in a useful and economical way for a better environment. In most of the countries the waste is thrown away in the landfills which leads to health hazards, safety issues and loss of valuable resources. The Borås model emphasizes on ''reduce, recycle and recover energy'' before dumping. Before 1996 more than 40% of waste was landfilled in Sweden and today it has approached to zero landfill. The household waste is sorted in 30 fractions and then used. In a city of 100,000 population through using waste more than 3 million m3 biogas is produced every year which runs the buses, garbage trucks and around 300 CNG vehicles in the city. 960 MWh heat and electricity is also generated everyday. More than 90% recycling of PET and aluminum bottles is done in Sweden. The University of Borås actively conducts research and workshops in the sector. This public, private partnership model has made Borås a zero waste city

Rapid Biodegradation of Methyl tert-Butyl Ether (MBTE) by Pure Bacterial cultures

Two pure bacterial strains capable of rapid degrading methyl tert–butyl ether (MTBE) were isolated from an industrial wastewater treatment plant, identified and characterized. These strains are able to grow on MTBE as the sole carbon and energy sources and completely mineralize it to the biomass and carbon dioxide. The strains were identified as Bacillus cereus and Klebsiella terrigena. Both strains are able to grow in the presence of 48 g/l MTBE in water, which is almost the maximum concentration of MTBE in the water. They were able to completely degrade 10 g/l MTBE in less than a day. The specific degradation rate of MTBE at optimum conditions were 5.89 and 5.78 g(MTBE)/g(cells). h for B. cereus and K. terrigena, respectively. The biomass yield was 0.085 and 0.076 g/g, respectively. The cultivations were carried out successfully at 25, 30 and 37 °C, while they showed the best performance at 37 °C. Neither of the strains was able to grow and degrade MTBE anaerobically

A Possible Industrial Solution to Ferment Lignocellulosic Hydrolyzate to Ethanol : Continuous Cultivation with Flocculating Yeast

Cultivation of toxic lignocellulosic hydrolyzates has been a research topic in recent decades. Although several methods have been proposed, there has been doubt about their industrial applications. The current work deals with a solution to this problem which has a good potential application in industrial scale. A toxic dilute-acid hydrolyzate was continuously cultivated using a high-cell-density flocculating yeast in a single and serial bioreactor which was equipped with a settler to recycle the cells back to the bioreactors. No prior detoxification was necessary to cultivate the hydrolyzates, as the flocks were able to detoxify it in situ. The experiments were successfully carried out at dilution rates up to 0.52 h-1. The cell concentration inside the bioreactors was between 23 and 35 g-DW/L, while this concentration in the effluent of the settlers was 0.320.05 g-DW/L. The ethanol yield of 0.42-0.46 g/g-consumed sugar was achieved, and the residual sugar concentration was less than 6% of the initial fermentable sugar (glucose, galactose and mannose) of 35.2 g/L

Antimicrobial properties of fungal chitosan

Cell wall of zygomycetes fungus is an alternative source for chitosan production. In this study chitosan was extracted from cell wall of filamentous fungus Rhizopus oryzae and its antimicrobial properties was studied against three typical human pathogenic microorganisms, Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus. The viability of these bacteria reduced by more than 60%, when 200 ppm of the fungal chitosan was present in the solution. However, the Minimum Bactericidal Concentration (MBC) of the fungal chitosan was 300, 500 and 700 ppm for S. aureus, E. coli and K. pneumoniae, respectively. The antimicrobial activity of fungal chitosan was lower than that of crustacean shells chitosan, which had MBC of less than 100 ppm for the above mentioned bacteria. Furthermore, fungal chitosan similar to crustacean shells chitosan exhibited better inhibitory effects against gram-positive compared to gram-negative bacteria. The possible mechanism for antimicrobial activity of fungal chitosan could be the disruption of the outer membrane of cells but not preventing the nutrients from entering into the cell

Protective Effect of Encapsulation in Fermentation of Limonene-contained Media and Orange Peel Hydrolyzate

This work deals with application of encapsulation technology to eliminate inhibition of D-limonene in fermentation of orange wastes to ethanol. Orange peel was enzymatically hydrolyzed with cellulase and pectinase. However fermentation of the released sugars in this hydrolyzate by freely suspended S. cerevisiae failed due to inhibition of limonene. On the other hand, encapsulation of S. cerevisiae in alginate membranes was a powerful tool to eliminate inhibition of limonene. The encapsulated cells were able to ferment the orange peel hydrolyzate in 7 h, and produce ethanol with yield 0.44 g/g fermentable sugars. Cultivation of the encapsulated yeast in defined medium was successful, even in the presence of 1.5% (v/v) limonene. The capsules’ membranes were selectively permeable to the sugars and the other nutrients, but not limonene. While 1% (v/v) limonene was present in the culture, its concentration inside the capsules was not more than 0.054% (v/v)