Simultaneous glucose and xylose uptake was investigated for ethanol prodn. using the simultaneous saccharification, filtration and fermn. (SSFF) process with pretreated wheat straw as a xylose-rich lignocellulosic biomass. A genetically engineered strain of Saccharomyces cerevisiae (T0936) with the ability to ferment xylose was used for the fermns. SSFF was compared with a conventional method of simultaneous saccharification and fermn. (SSF) for glucose and xylose uptake, ethanol prodn., and cell viability on 10% and 12% suspended solids (SS) basis. With 10% SS, an ethanol yield of 90% of the theor. level was obtained during SSFF with 80% xylose uptake while only 53% ethanol yield was obsd. during the SSF process. Increasing the solid load to 12% resulted in an ethanol yield of 77% of the theor. value and 36% xylose uptake during SSFF while only 27% ethanol yield and no xylose uptake was obsd. during the corresponding SSF process. The SSFF process preserved the viability of the genetically engineered yeast throughout the fermn., even when reused for 2 consecutive cultivations. The results show that the SSFF process does not only enhance effective cell performance but also facilitates simultaneous glucose and xylose utilization, which is important for broad range of biomass utilization for lignocellulosic ethanol prodn. [on SciFinder(R)]

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.

A novel method of lignocellulosic ethanol production was developed and evaluated, “Simultaneous Saccharification Filtration and Fermentation (SSFF)”. SSFF is an integrated process which combines the advantages of both Separate hydrolysis and fermentation (SHF) and Simultaneous saccharification and fermentation (SSF). The process involves simultaneous enzymatic hydrolysis of lignocellulosic biomass, filtration and fermentation of the filtrate with yeast Saccharomyces cerevisiae as fermenting organism. Different suspended solid (SS) were evaluated to determine what solid concentration can be pumped through the filtration device and the life span of a cross-flow filter module was assessed. Capacity tests were performed on the fermentation unit to determine the uptake capability of the fermenting organism. It was furthermore investigated how long the cells can be successfully reused. It was observed that up to 14% solids concentration could be pumped through the filtration unit. After enzymatic treatment, a slurry with 14.4% initial SS was filtered continuously for 28 days without clogging or fouling. A flocculating yeast strain (CCUG 53310) was able to consume the glucose from the hydrolysis through the filtration effectively and the yeast culture was reused for 5 batches of SSFF. The SSFF cultivations resulted in an ethanol yield of up to 85.0% of the theoretical yield. Our new process of SSFF could potentially be used in lignocellulosic ethanol production.

Ethanol is the most important renewable fuel in the transportation sector. Its production from lignocellulosic materials, commonly referred to as second generation ethanol, is considered more attractive than production from starch and sugar crops. Bacterial contamination by lactic acid-producing bacteria is still a major problem during ethanol production processes. Bacteria compete with the yeast by consuming the sugars and the nutrients required by the yeast for efficient ethanol production. This often causes substantial economic losses at industrial fermentations. In this study, without any sterilization of the substrate, simultaneous saccharification and fermentation (SSF) was performed using cellulase Cellic® Ctec2 enzyme for hydrolysis and Baker’s yeast, Saccharomyces cerevisiae, was used as the fermenting organism with different loads of suspended solids - 8%, 10% and 12%. With8%and 10% SS, there was a significant contamination, which caused consumption of both hexoses pentose sugars in the fermentation medium, this resulted in lactic acid concentrations of 43 g/L and 36 g/L from 10% SS and 8% SS respectively. In contrast, only 2.9 g/L lactic acid was observed with 12% SS. An ethanol concentration of 47 g/L was produced from high solid loading of 12% SS while just 26 g/L and 23 g/L were produced from 10% and 8% SS respectively. Our results show that SSF with 12% SS has an increased concentration of inhibitors, particularly acetic acid which selectively inhibited the bacterial growth without affecting the metabolic activities of the yeast during the fermentation.

Nigeria is among the World’s 10 most important exporters of petroleum, but has several difficulties in its domestic energy situation. Power outages are frequent in the cities and 49% of the population has no access to electricity at all. The use of fossil fuels and firewood causes many environmental problems and the population increase in combination with a growing economy results in unmanageable amounts of waste in the cities. The use of biofuels has the potential to alleviate some of these problems and this review aims at evaluating the situation regarding biofuel production in Nigeria through literature studies and contacts. It was found that in spite of good geographic conditions and high investment in biofuel production, progress has been slow. The Nigerian sugarcane sector does not yet satisfy the domestic demand for sugar, while large-scale sugarcane-based ethanol production seems distant. Ethanol production from cassava would require input of energy and enzymes and would probably be too expensive. Sweet sorghum, which is relatively easy to process into bioethanol, has some advantages in a Nigerian context, being widely cultivated. Biodiesel production runs the risk of becoming controversial if edible crops currently being imported would be used. Jatropha curcas (non-edible) is an interesting crop for biodiesel production but the complete life cycle of this process should be further analyzed. The biofuel concept, which would bring the most immediate benefits, is probably biogas production from waste. It requires no irrigation or input of land and also provides a cleaner environment. Besides it would reduce the widespread use of firewood and produce fertilizer.

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.

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.

Simultaneous saccharification, filtration and fermentation (SSFF) was developed for lignocellulosic ethanol production. In SSFF, pretreated lignocellulosic material is enzymatically hydrolyzed in a reactor, while the suspension is continuously pumped through a cross-flow membrane. The retentate goes back to the hydrolysis vessel, while a clear sugar-rich filtrate continuously perfuses through the fermentation vessel before it is pumped back to the hydrolysis vessel. The capacity and life span of the cross-flow filter module was examined for 4 weeks using enzymatically hydrolyzed slurry, initially with 14.4% suspended solids, without clogging or fouling. An ethanol yield of 85.0% of the theoretical yield was obtained in SSFF and a flocculating strain of Saccharomyces cerevisiae was successfully reused for five cultivations of SSFF.

A novel method of bioethanol production from lignocellulosic biomass “Simultaneous Saccharification Filtration and Fermentation (SSFF)” was developed and examined. SSFF is an integrated process which combines the advantages of both Separate hydrolysis and fermentation (SHF) and Simultaneous saccharification and fermentation (SSF) together. The process involves simultaneous enzymatic hydrolysis of pretreated lignocellulosic material, cross-flow filtration of the enzymatically treated suspension and fermentation of the sugar-rich filtrate with flocculating strain of yeast Saccharomyces cerevisiae as fermenting organism in a continuous process. The individual units of the SSFF integrated process was examined, and compared with SSF for a slurry of 10% SS (suspended solids) of pretreated lignocelluloses. Capacity tests were performed on the fermentation unit as well. Slurries of up to 14% SS could be pumped through the cross-flow filter membrane module without clogging the module. The yeast strain used was able to efficiently consume the glucose from the hydrolysis passed through the filtration effectively. SSFF cultivations resulted in an ethanol yield of 85% of the theoretical yield, and the flocculating yeast was effectively reused for 5 different batches of SSFF. Our new process of SSFF has the potential to be used in industrial lignocellulosic ethanol production.