Following the worsening energy crisis of unreliable electricity and unaffordable petroleum products coupled with the increase number of poverty-stricken people in Nigeria, the populace is desperately in need of cheap alternative energy supplies that will replace or complement the existing energy sources. Previous efforts by the government in tackling the challenge by citizenship sensitization of the need for introduction of biofuel into the country’s energy mix have not yielded the expected results because of a lack of sustained government effort. In light of the shortcomings, this study assesses the current potential of available biomass feedstock for biogas production in Nigeria, and further proposes appropriate biogas plants, depending on feedstock type and quantity, for the six geopolitical zones in Nigeria. Besides, the study proposes government-driven biogas development systems that could be effectively used to harness, using biogas technology, the estimated 270 TWh of potential electrical energy from 181 million tonnes of available biomass, in the advancement of electricity generation and consequent improvement of welfare in Nigeria.

Following the worsening energy crisis of unreliable electricity and unaffordable petroleum products coupled with the increase number of poverty-stricken people in Nigeria, the populace is desperately in need of cheap alternative energy supplies that will replace or complement the existing energy sources. Previous efforts by the government in tackling the challenge by citizenship sensitization of the need for introduction of biofuel into the country’s energy mix have not yielded the expected results because of a lack of sustained government effort. In light of the shortcomings, this study assesses the current potential of available biomass feedstock for biogas production in Nigeria, and further proposes appropriate biogas plants, depending on feedstock type and quantity, for the six geopolitical zones in Nigeria. Besides, the study proposes government-driven biogas development systems that could be effectively used to harness, using biogas technology, the estimated 270 TWh of potential electrical energy from 181 million tonnes of available biomass, in the advancement of electricity generation and consequent improvement of welfare in Nigeria.

The aim of this study was to convert the spent liquors obtained from acidic sulfite and neutral sulfite semi-chemical (NSSC) pulping processes into protein-rich fungal biomass. Three filamentous fungi, Aspergillus oryzae, Mucor indicus, and Rhizopus oryzae, were cultivated on the diluted spent liquors in an airlift bioreactor with airflow of 0.85 vvm at 35°C and pH 5.5. Maximum values of 10.17 g, 6.14 g, and 5.47 g of biomass per liter of spent liquor were achieved in the cultivation of A. oryzae, M. indicus, and R. oryzae on the spent sulfite liquor (SSL) diluted to 60%, respectively, while A. oryzae cultivation on the spent NSSC liquor (SNL) diluted to 50% resulted in the production of 3.27 g biomass per liter SNL. The fungal biomasses contained 407 g to 477 g of protein, 31 g to 114 g of fat, 56 g to 89 g of ash, and 297 g to 384 g of alkali-insoluble material (AIM) per kg of dry biomass. The amino acids, fatty acids, and mineral elements composition of the fungal biomasses corresponded to the composition of commercial protein sources especially soybean meal. Among the fungi examined, A. oryzae showed better performance to produce protein-rich fungal biomass during cultivation in the spent liquors.

The aim of this study was to convert the spent liquors obtained from acidic sulfite and neutral sulfite semi-chemical (NSSC) pulping processes into protein-rich fungal biomass. Three filamentous fungi, Aspergillus oryzae, Mucor indicus, and Rhizopus oryzae, were cultivated on the diluted spent liquors in an airlift bioreactor with airflow of 0.85 vvm at 35 degrees C and pH 5.5. Maximum values of 10.17 g, 6.14 g, and 5.47 g of biomass per liter of spent liquor were achieved in the cultivation of A. oryzae, M. indicus, and R. oryzae on the spent sulfite liquor (SSL) diluted to 60%, respectively, while A. oryzae cultivation on the spent NSSC liquor (SNL) diluted to 50% resulted in the production of 3.27 g biomass per liter SNL. The fungal biomasses contained 407 g to 477 g of protein, 31 g to 114 g of fat, 56 g to 89 g of ash, and 297 g to 384 g of alkali-insoluble material (AIM) per kg of dry biomass. The amino acids, fatty acids, and mineral elements composition of the fungal biomasses corresponded to the composition of commercial protein sources especially soybean meal. Among the fungi examined, A. oryzae showed better performance to produce protein-rich fungal biomass during cultivation in the spent liquors.

The goal of this study was to develop an operational steam explosion pretreatment for effective modification of rice straw chemical structure in order to improve its biodegradability and methane yield. The parameters of pressure (5 bar to 15 bar), moisture (0% to 70%), and time (1 min to 15 min) were studied in steam explosion pretreatment. The steam explosion efficiency was investigated according to the changes in crystallinity structure and chemical composition on rice straw, as well as the methane yield from straw. Steam explosion changed the structure linkages between the lignin and carbohydrate, which was indicated by a reduction in the peak intensities in the bonds from 1648 cm(-1) to 1516 cm(-1). After pretreatment, the crystallinity index of the rice straw in the 10 bar-10 min cycle with no moisture and 15 bar-10 min cycle with 70% moisture increased from 22.9% to 28.3% and 28.6%, respectively. Steam explosion efficiently decreased the lignin. The highest reduction in the amount of lignin was observed with the 10 bar-10 min cycle, which reached from 18.6% to 13.0%. The methane yield increased with the cycles 10 bar-10 min and 15 bar-15 min with 35% moisture, and 15 bar-10 min with 70% moisture by 113%, 104%, and 147% compared to that of the untreated straw, respectively. Moreover, the highest biodegradation percent of the rice straw was obtained in these cycles.

Pretreatment of straw separated from cattle and horse manure using N-methylmorpholine oxide (NMMO) was investigated. The pretreatment conditions were for 5 h and 15 h at 120 °C, and the effects were evaluated by batch digestion assays. Untreated cattle and horse manure, both mixed with straw, resulted in 0.250 and 0.279 Nm3 CH4/kgVS (volatile solids), respectively. Pretreatment with NMMO improved both the methane yield and the degradation rate of these substrates, and the effects were further amplified with more pretreatment time. Pretreatment for 15 h resulted in an increase of methane yield by 53% and 51% for cattle and horse manure, respectively. The specific rate constant, k0, was increased from 0.041 to 0.072 (d-1) for the cattle and from 0.071 to 0.086 (d-1) for the horse manure. Analysis of the pretreated straw shows that the structural lignin content decreased by approximately 10% for both samples and the carbohydrate content increased by 13% for the straw separated from the cattle and by 9% for that separated from the horse manure. The crystallinity of straw samples analyzed by FTIR show a decrease with increased time of NMMO pretreatment.

The effects of three heavy metals on hydrogen production via syngas fermentation were investigated within a metal concentration range of 0-1.5 mg Cu/L, 0-9 mg Zn/L, 0-42 mg Mn/L, in media with initial pH of 5, 6 and 7, at 55 °C. The results showed that at lower metal concentration, pH 6 was optimum while at higher metal concentrations, pH 5 stimulated the process. More specifically, the highest hydrogen production activity recorded was 155.28% ± 12.02% at a metal concentration of 0.04 mg Cu/L, 0.25 mg Zn/L, and 1.06 mg Mn/L and an initial medium pH of 6. At higher metal concentration (0.625 mg Cu/L, 3.75 mg Zn/L, and 17.5 mg Mn/L), only pH 5 was stimulating for the cells. The results show that the addition of heavy metals, contained in gasification-derived ash, can improve the production rate and yield of fermentative hydrogen. This could lead in lower costs in gasification process and fermentative hydrogen production and less demand for syngas cleaning before syngas fermentation.

The effects of three heavy metals on hydrogen production via syngas fermentation were investigated within a metal concentration range of 0 to 1.5 mg Cu/L, 0 to 9 mg Zn/L, 0 to 42 mg Mn/L, in media with initial pH of 5, 6, and 7, at 55 degrees C. The results showed that at lower metal concentration, pH 6 was optimum while at higher metal concentrations, pH 5 stimulated the process. More specifically, the highest hydrogen production activity recorded was 155% +/- 12% at a metal concentration of 0.04 mg Cu/L, 0.25 mg Zn/L, and 1.06 mg Mn/L and an initial medium pH of 6. At higher metal concentration (0.625 mg Cu/L, 3.75 mg Zn/L, and 17.5 mg Mn/L), only pH 5 was stimulating for the cells. The results showed that the addition of heavy metals, contained in gasification-derived ash, can improve the production rate and yield of fermentative hydrogen. This could lead to lower costs in gasification process and fermentative hydrogen production and less demand for syngas cleaning before syngas fermentation.

Comparison of vacuum and high pressure evaporated wood hydrolyzate for ethanol production by repeated fed-batch using flocculating Saccharomyces cerevisiae

Zygomycetes fungi are able to produce ethanol, and their biomass may hold a high market value, making them interesting microorganisms from a biorefinery perspective. In the present study, the inhibitor tolerance of the Zygomycetes fungus Rhizopus sp. was evaluated and compared with a flocculating strain of Saccharomyces cerevisiae. The inhibitors furfural, 5-hydroxymethylfurfural [HMF], acetic acid, and levulinic acid and the phenolic compounds catechol, guaiacol, and vanillin were applied in different combinations in a semi-synthetic medium. Glucose uptake and conversion of HMF in the presence of inhibitors were analyzed for the two organisms, and it appeared that the inhibitor resistances of Rhizopus sp. and S. cerevisiae were comparable. However, in the presence of catechol (0.165 g L-1), guaiacol (0.186 g L-1), and vanillin (0.30 g L-1), the glucose uptake by S. cerevisiae was only 3.5% of its uptake in a medium without inhibitors, while under equal conditions, Rhizopus sp. maintained 43% of its uninhibited glucose uptake.

Spent sulphite liquor, the major byproduct from the sulphite pulp production process, was diluted to 50% and used for production of an edible zygomycete Rhizopus sp. The focus was on production, yield, and composition of the fungal biomass composition. The fungus grew well at 20 to 40°C, but 32°C was found to be preferable compared to 20 and 40°C in terms of biomass production and yield (maximum of 0.16 g/g sugars), protein content (0.50-0.60 g/g), alkali-insoluble material (AIM) (ca 0.15 g/g), and glucosamine content (up to 0.30 g/g of AIM). During cultivation in a pilot airlift bioreactor, the yield increased as aeration was raised from 0.15 to 1.0 vvm, indicating a high demand for oxygen. After cultivation at 1.0 vvm for 84 h, high yield and production of biomass (up to 0.34 g/g sugars), protein (0.30-0.50 g/g), lipids (0.02-0.07 g/g), AIM (0.16-0.28 g/g), and glucosamine (0.22-0.32 g/g AIM) were obtained. The fungal biomass produced from spent sulphite liquor is presently being tested as a replacement for fishmeal in feed for fish aquaculture and seems to be a potential source of nutrients and for production of glucosamine.

Mixtures of starch and lignocelluloses are available in many industrial, agricultural, and municipal wastes and residuals. In this work, dilute sulfuric acid was used for simultaneous pretreatment of lignocellulose and hydrolysis of starch, to obtain a maximum amount of fermentable sugar after enzymatic hydrolysis with cellulase and β-glucosidase. The acid treatment was carried out at 70-150°C with 0-1% (v/v) acid concentration and 5-15% (w/v) solids concentration for 0-40 minutes. Under the optimum conditions, obtained at 130°C, 1% acid, and 7.5% solids loading for 30 min, the starch was almost completely converted to glucose. However, the acid treatment was not successful for efficient hydrolysis of pure cellulose. A mixture of pine softwood and potato as representatives of lignocellulosic and starch components, respectively, were treated at the optimum conditions for acid hydrolysis of starch. The dilute-acid treatment resulted in 1.2, 60.5, and 23.6% hydrolysis of glucan, xylan, and mannan of pine wood and 67% of potato starch to fermentable sugars. After the acid treatment, the solid residue of the mixture was subjected to enzymatic hydrolysis. The enzymatic hydrolysis under the optimum conditions resulted in conversion of 76% of the glucan in the treated softwood. Therefore, using acid treatment of the mixture is a promising process for pretreatment of wood in addition to the hydrolysis of starch.

Contamination by lactic acid-producing bacteria is frequently a major challenge in ethanol processes. In this work, high solids loading was used both to keep bacterial infection under control in simultaneous saccharification and fermentation (SSF) of lignocellulosic biomass and to increase the ethanol productivity of the process. With no sterilization of the substrates, lactic acid bacteria contaminated the fermentation process with 8 and 10% suspended solids (SS) substrates, consumed both pentoses and hexoses, and produced lactic acid. However, a high solids loading of 12% SS prevented lactic acid formation, which resulted in higher ethanol yield during the SSF process. This high SS resulted in an ethanol concentration of 47.2 g/L, which satisfies the requirement for industrial lignocellulosic ethanol production.

Pretreatment of forest residues using N - methylmorpholine - N - oxide (NMMO or NMO) prior to anaer obic digestion was investigated , where the effects of particle size, NMMO concentration , and pretreatment time were the primary focus. The pretreatments were carried out on forest residues; with different particle size s of 2, 4 and 8 mm , at 120 °C for 3, 7 , and 15 h in two different modes of NMMO - treatment : dissolution by 85% NMMO and swelling without dissolution using 75% NMMO solution in water . The pretreatment process led to minor changes in the composition of the forest residues . The best improvement in methane yield of the forest residues was achieved by pretreatment using 85% NMMO for 15 h at 120 °C. This treatment resulted in 0.1 7 Nm 3 /kg VS methane yield , which corresponds to 83 % of the expected theoretical yield of carbohydrates present in the material. Additionally, the accumulated methane yield and the rate of the methane production were highly affected by the amounts of remaining NMMO when it was not well separated during the washing and filtration step s after the treatment. The p resence o f concentrations even as low as 0.008 % NMMO resulted in a decrease in the final methan e yield by 45% , while the presence of 1% of this solvent in the digester completely terminated the anaerobic digestion process.

The chemical composition of rice hulls produced in an artisan mill and its conversion to fermentable sugars was investigated. The carbohydrate fraction represented 59.2% (w/w) of the dry hulls. Cellulose, with 36.6%, was the main component, followed by xylan with 13.9%. An important contribution of starch (8.7%) was also detected. The content of ash (19.6%) and lignin (15.5%) was comparable with that of rice hulls obtained in industrial mills. Dilute-sulphuric acid hydrolysis at different temperatures, from 160 to 210°C, was evaluated for production of fermentable sugars. Due to starch hydrolysis, the concentration of glucose in the hydrolysates produced at 160°C was higher than the values that have previously been reported for industrial sorts of rice hulls under comparable conditions. The xylan-to-xylose conversion increased steadily with increase of the temperature and reached a maximum (67.7%) at 190°C. Further increases of the hydrolysis temperature decreased the yield of sugars due to their dehydration to furfural and HMF.

The fungus Mucor indicus is able to produce ethanol from xylose as well as dilute-acid lignocellulosic hydrolyzates. The fungus completely assimilated 10 g/L xylose as the sole carbon and energy source within 32 to 65 h at an aeration rate of 0.1 to 1.0 vvm. The highest ethanol yield was 0.16 g/g at 0.1 vvm. Xylitol was formed intermediately with a maximum yield of 0.22 g/g at 0.5 vvm., but disappeared towards the end of experiments. During cultivation in a mixture of xylose and glucose, the fungus did not assimilate xylose as long as glucose was present in the medium. The anaerobic cultivation of the fungus in the hydrolyzate containing 20% xylose and 80% hexoses resulted in no assimilation of xylose but complete consumption of the hexoses in less than 15 h. The ethanol yield was 0.44 g/g. However, the xylose in the hydrolyzate was consumed when the media were aerated at 0.067 to 0.333 vvm. The best ethanol yield was 0.44 g/g at 0.067 vvm. The results of this study suggest that M. indicus hydrolyzate can be first fermented anaerobically for hexose assimilation and subsequently continued under oxygen-limited conditions for xylose fermentation.

Alkaline pretreatment with NaOH under mild operating conditions was used to improve ethanol and biogas production from softwood spruce and hardwood birch. The pretreatments were carried out at different temperatures between minus 15 and 100ºC with 7.0% w/w NaOH solution for 2 h. The pretreated materials were then enzymatically hydrolyzed and subsequently fermented to ethanol or anaerobically digested to biogas. In general, the pretreatment was more successful for both ethanol and biogas production from the hardwood birch than the softwood spruce. The pretreatment resulted in significant reduction of hemicellulose and the crystallinity of cellulose, which might be responsible for improved enzymatic hydrolyses of birch from 6.9% to 82.3% and spruce from 14.1% to 35.7%. These results were obtained with pretreatment at 100°C for birch and 5°C for spruce. Subsequently, the best ethanol yield obtained was 0.08 g/g of the spruce while pretreated at 100°C, and 0.17 g/g of the birch treated at 100°C. On the other hand, digestion of untreated birch and spruce resulted in methane yields of 250 and 30 l/kg VS of the wood species, respectively. The pretreatment of the wood species at the best conditions for enzymatic hydrolysis resulted in 83% and 74% improvement in methane production from birch and spruce.

Cellulose Solvent-And organic Solvent-Based lignocellulose fractionation (COSLIF) has been repeatedly shown to be a Cost-Effective and promising process to modify the structure of different lignocelluloses. It has been repeatedly reported to improve enzymatic hydrolysis and ethanol production from different lignocelluloses. In this study, COSLIF was used to improve biomethane production from pine (softwood), poplar (soft hardwood), and berry (hard hardwood) via solid state anaerobic digestion (SSAD). Feed to inoculum (F/I) ratio, which plays a major role in SSAD, was set to 3, 4, and 5. After the pretreatment, 39, 33, and 24% higher methane yield from pine was achieved for F/I ratios of 3, 4, and 5, respectively. However, the methane yield from the hardwoods was not improved by the pretreatment, which was related to overloading of the digester. Compositional analysis showed considerable reduction in hemicellulose and lignin content by the pretreatment. Structural changes in the woods, before and after the pretreatment, were examined by X-Ray diffractometer and scanning electron microscopy. The results showed that the crystallinity of cellulose was decreased and accessible surface area was drastically increased by the pretreatment.

A mixed substrate (MS) comprising oil palm empty fruit bunch (EFB), oil palm frond (OPF), and rice husk (RH) was evaluated for endoglucanase prodn. by Bacillus aerius S5.2. Effects of sulfuric acid, sodium hydroxide, N-methylmorpholine-N-oxide (NMMO), and hydrothermal pretreatments on endoglucanase prodn. were investigated. Endoglucanase prodn. by B. aerius on the untreated (0.677 U/mL) and pretreated MS (0.305 - 0.630 U/mL) was generally similar, except that the acid (0.305 U/mL) and hydrothermal (0.549 U/mL) pretreatments that were more severe consequently produced significantly lower titers. Alkali pretreatment supported the highest enzyme prodn. (0.630 U/mL) among all pretreatments that were studied. When endoglucanase prodn. on the alkali-pretreated MS and single substrates (SS) was compared, alkali-pretreated EFB produced a titer (0.655 U/mL) similar to the MS, and this was significantly higher than titers recorded on OPF (0.504 U/mL) and RH (0.525 U/mL). Lower enzyme prodn. was found to be consistent with higher pretreatment severity and greater removal of amorphous regions in all the pretreatments. Furthermore, combining the SS showed no adverse effects on endoglucanase prodn. [on SciFinder(R)]

The astronomical increase in global energy demand makes locating energy sources other than fossil fuels worthwhile. The use of tropical biomass wood waste as a renewable energy source was investigated in this study. The thermal conversion analysis of Albizia gummifera (ayinre) was carried out in a thermobalance reactor via steam gasification under varying temperature (700 to 1000 °C) and steam partial pressure (0.020 to 0.050 MPa). The experimental data was evaluated using three gas-solid reaction models. The modified volume reaction model (mVRM) gave the overall highest coefficient of determination (0.9993) and thereby the best conversion prediction. The observed char activation constant rates (from paired reaction conditions) indicated, on average, an increase in reactivity as the parameters increased. The results showed that the activation energy of the mVRM gave the lowest value (32.54 kJ/mol) compared with those of the shrinking core model (SCM) and the volume reaction model (VRM) (49.29 and 49.89 kJ/mol, respectively).

Brewer’s spent grain (BSG) is the main solid by-product of the brewing sector. High moisture and nutrient-rich content render BSG easily perishable, leading to waste generation and environmental impacts. BSG has narrow applications in both feed and food sectors due to its composition including high fiber and low protein. Therefore, a processing strategy leading to the nutritional valorization of BSG could widen its applications. In this study, submerged cultivation of edible filamentous fungi (Aspergillus oryzae, Neurospora intermedia, and Rhizopus delemar) was introduced as a strategy to enhance the protein content of BSG. The growth of all strains in BSG increased the protein content of the fermented BSG. The highest increase of protein content (from 22.6% to 34.6%), was obtained by cultivation using A. oryzae and medium supplementation. The protein content increase was followed by a decrease in the content of polysaccharides (up to ca. 50%), namely starch, glucan, xylan, and arabinan. The addition of cellulase resulted in enhanced ethanol production from BSG but led to lower concentration of recovered solids. In conclusion, simple processing of BSG using edible filamentous fungi can lead to quality improvement of BSG, providing potential economic and environmental benefits to the brewing sector.

Enzyme cocktails can alter the lignin and hemicellulose content in wood cell walls, improving the bleaching process during pulp production and offsetting the need for toxic chemicals. In this study, brown pulp was biobleached with a mixture of crude fungal extracts rich in xylanase and laccase, respectively produced from Aspergillus tamarii Kita and Trametes versicolor on waste materials. The optimal conditions for biobleaching were a mixture of xylanase and laccase crude extracts (1 to 2 v/v), at a temperature of 36 degrees C and a pH of 5.5. The treated brown cellulose pulp showed a reduction in the Kappa number by 1.83 points, representing an efficiency of 20.3%. In addition, the brightness increased by 4.65 points in comparison to the control. Hence, studies involving the application of the standardized cocktail during the hydrolysis of lignocellulosic residues, e.g., barley residue and sugarcane bagasse, led to the formation of 85 g/L and 25 g/L of reducing sugars, respectively. Moreover, the standardized cocktail caused greater deinking of the recycled paper pulp.

In a novel valorization approach for simultaneous pectin extn. and pretreatment (SPEP) of citrus waste (CW) by dil. nitric acid and ethanol, almost all of the CW was converted to bio-derived chems. in a singlestep process at a low/moderate temp. The SPEP was performed at different temps. (70 °C and 80 °C), pH (1.8, 3.0, and 4.3), and extn. times (2 h and 3 h) with a full factorial design. The max. pectin yield of 45.5% was obtained at pH 1.8, 80 °C, and 2 h. The pectin yields at pH 1.8 were much higher than at pH 4.3 and 3. Also, the degree of methyl-esterification at pH 1.8 was higher than 50%, whereas at the higher pH, low methoxyl pectins were extd. The treated CW obtained after the SPEP, free from limonene, was subjected to sep. cellulolytic enzymic hydrolysis and ethanolic fermn. The glucose yields in the enzymic hydrolyzates were higher for the CW treated at pH 1.8. The fermn. of the enzymic hydrolyzates by Mucor indicus resulted in fungal biomass yields in the range of 355 to 687 mg per g of consumed sugars. The optimum conditions for obtaining the max. SPEP yield (glucose + pectin (g) / raw material (g)*100) were pH 1.8, 80 °C, and 2 h, which resulted in a yield of 58.7% (g/g CW). [on SciFinder(R)]

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.

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.

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.

Optimization study of citrus wastes Saccharification by dilute acid hydrolysis

Different substrate characteristic analyses have been studied on rice and triticale straw pretreated with NMMO (N-methylmorpholine-N-oxide) prior to biogas production. Simons’ stain, water retention value (WRV), and enzymatic adsorption were used to measure the change in the accessible surface area of the lignocellulosic substrates. FTIR was used to measure the change in cellulosic crystallinity and Time-of-Flight-Secondary-Ion-Spectroscopy (ToF-SIMS) to measure the ratio of cellulose to lignin on the sample surface. All methods showed increased accessible surface area and a decrease in crystallinity after the pretreatments. These qualities were linked to improved biogas production. In the future, the tested methods could replace the time-consuming methane potential analysis to predict the methane production of lignocellulosic materials. Simons’ stain, enzymatic adsorption, and crystallinity measurement by FTIR can be regarded as the recommended methods for the prediction of the improved biogas production as a result of the pretreatment.

Encapsulation of methane-producing bacteria was carried out with the objective of enhancing the rate of biogas production. Encapsulation with a one-step liquid-droplet-forming technique was employed for the natural membrane, resulting in spherical capsules with an average diameter and a membrane thickness of 4.3 and 0.2 mm, respectively. The capsules were made from alginate, using chitosan or Ca 2+ as counter-ions, together with the addition of carboxymethylcellulose (CMC). A Durapore® membrane (hydrophilic PVDF) with a pore size of 0.1 μm was used for synthetic encapsulating sachets having width and length dimensions 3×3 and 3×6 cm 2 for holding the bacteria. During the digesting process, the dissolved substrates penetrated through the capsule membrane, and biogas inside the capsules was able to escape by diffusion. The results indicate encapsulation to be a promising method of digestion, with a high density of anaerobic bacteria. The method holds considerable potential for further development of membranes and their applications.

Encapsulation of methane producing bacteria was performed to enhance the rate of biogas production, using natural as well as synthetic membranes. A one-step liquid-droplet-forming method was employed for the natural membrane, resulting in spherical capsules with an average diameter and a membrane thickness of 4.3 and 0.2 mm, respectively. The capsules were made from alginate, with chitosan or Ca2+ as counter-ions, with addition of carboxymethylcellulose (CMC). For synthetic capsules, the Durapore® membrane (hydrophilic PVDF), with a pore size of 0.1 µm, was used for capsules of the sizes 3×3 and 3×6 cm, holding the bacteria. During the digesting process the dissolved substrates penetrated through the capsule membranes, and biogas developed inside the capsules, escaping by diffusion. The results indicate that encapsulation is a promising method of digestion, with a high density of anaerobic bacteria. The method holds a considerable potential for further development of membranes and their applications.

A new method was developed for production of low molecular weight chitosan, in which high molecular weight chitosan was treated with dilute sulfuric acid at 120°C. Chitosan was dissolved in the acid solution in a few minutes, and as depolymerized to low molecular weight chitosan by longer times. Low molecular weight chitosan was recovered from the acid by cooling down the solution and increasing the pH to 8-10. A low molecular weight chitosan with Mv (viscosity average molecular weight) of 174×103 was prepared from a high molecular weight chitosan (Mv = 1,388×103) with 82% recovery by using 72 mM sulfuric acid solution for 30 min. Increasing the time to 240 min reduced the Mv to 24×103, though the recovery of chitosan was reduced to 54%. Higher concentrations of acid (216 and 360 mM) resulted in higher depolymerization degrees and lower recoveries of chitosan in identical treatment times. Analysis of glucosamine and N-acetyl glucosamine showed that the prepared low molecular weight chitosan had more than 80% purity.