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)]

Integrated permeate channel (IPC) flat sheet membranes were examined for use as a reverse membrane bioreactor (rMBR) for lignocellulosic ethanol production. The fermenting organism, Saccharomyces cerevisiae (T0936), a genetically-modified strain with the ability to ferment xylose, was used inside the rMBR. The rMBR was evaluated for simultaneous glucose and xylose utilization as well as in situ detoxification of furfural and hydroxylmethyl furfural (HMF). The synthetic medium was investigated, after which the pretreated wheat straw was used as a xylose-rich lignocellulosic substrate. The IPC membrane panels were successfully used as the rMBR during the batch fermentations, which lasted for up to eight days without fouling. With the rMBR, complete glucose and xylose utilization, resulting in 86% of the theoretical ethanol yield, was observed with the synthetic medium. Its application with the pretreated wheat straw resulted in complete glucose consumption and 87% xylose utilization; a final ethanol concentration of 30.3 g/L was obtained, which corresponds to 83% of the theoretical yield. Moreover, complete in situ detoxification of furfural and HMF was obtained within 36 h and 60 h, respectively, with the rMBR. The use of the rMBR is a promising technology for large-scale lignocellulosic ethanol production, since it facilitates the co-utilization of glucose and xylose; moreover, the technology also allows the reuse of the yeast for several batches.

Ethanol production from lignocellulosic biomass is considered more beneficial than its production from starch and sugar based crops, considering the energetics and environmental advantages as well as the readily availability of the feed stock. However, the recalcitrant nature of lignocellulosic materials makes its ethanol production more challenging. Common methods of hydrolysis and fermentation of lignocellulosic materials to ethanol is through the separate hydrolysis and fermentation method (SHF) and the simultaneous saccharification and fermentation method (SSF). During SHF, product inhibition of the enzymes occurs as the sugar concentration increases during the hydrolysis, the process is also associated with increased contamination risk. SSF process makes use of suboptimal conditions for the hydrolysis and the fermentation; also the fermenting organism cannot be reused since it has been mixed with the lignocellulosic biomass. In this study, a new method was developed for hydrolysis and fermentation of lignocellulosic materials to ethanol, called simultaneous saccharification, filtration and fermentation (SSFF). The method allows both the hydrolysis and fermentation at optimum conditions with the use of a membrane bioreactor. It also allows the fermenting organism to be reused for several batches. The method was applied on pretreated spruce using a flocculating yeast strain and also on pretreated wheat straw using encapsulated genetically modified yeast. SSFF was compared with SSF as one of the conventional method, both on 10% suspended solids basis. From pretreated spruce, similar ethanol yield was obtained. Interestingly, from the pretreated wheat straw, 90% ethanol yield of the theoretical value was obtained during the SSFF while just 53% was obtained during the SSF. The study shows that the newly developed method of SSFF has the potential to replace the conventional methods and to improve ethanol production from lignocellulosic biomass.  

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)]

BACKGROUND: Because of its extreme toxicity for microorganisms, the limonene content of citrus wastes (CWs) has been a major obstacle to the conversion of CWs to biofuels. The main objective of this study was to develop a new process for the utilization of CWs that can be economically feasible when the supply of CW is low.

RESULTS: Steam explosion pre-treatment was applied to improve the anaerobic digestibility of CWs, resulting in a decrease of initial limonene concentration by 94.3%. A methane potential of 0.537 ± 0.001 m 3 kg -1 VS (volatile solids) was obtained during the following batch digestion of treated CWs, corresponding to an increase of 426% compared with that of the untreated samples. Long-term effects of the treatment were further investigated by a semi-continuous co-digestion process. A methane production of 0.555 ± 0.0159 m 3 CH 4 kg -1 VS day -1 was achieved when treated CWs (corresponding to 30% of the VS load) were co-digested with municipal solid waste.

CONCLUSION: The process developed can easily be applied to an existing biogas plant. The equipment cost for this process is estimated to be one million USD when utilizing 10 000 tons CWs year -1. 8.4 L limonene and 107.4 m 3 methane can be produced per ton of fresh citrus wastes in this manner. 

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.

Oil palm empty fruit bunches (OPEFB), a lignocellulosic residue of palm oil industries was examined for ethanol production. Milled OPEFB exposed to simultaneous saccharification and fermentation (SSF) with enzymes and Saccharomyces cerevisiae resulted just in 14.5% ethanol yield compared to the theoretical yield. Therefore, chemical pretreatment with phosphoric acid, a biological pretreatment with white-rot fungus Pleurotus floridanus, and their combination were carried out on OPEFB prior to the SSF. Pretreatment with phosphoric acid, combination of both methods and just fungal pretreatment improved the digestibility of OPEFB by 24.0, 16.5 and 4.5 times, respectively. During the SSF, phosphoric acid pretreatment, combination of fungal and phosphoric acid pretreatment and just fungal pretreatment resulted in the highest 89.4%, 62.8% and 27.9% of the theoretical ethanol yield, respectively. However, the recovery of the OPEFB after the fungal pretreatment was 98.7%, which was higher than after phosphoric acid pretreatment (36.5%) and combined pretreatment (45.2%).

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.

Biofuels production and utilisation can reduce the emission of greenhouse gases, dependence on fossil fuels and also improve energy security. Ethanol is the most important biofuel in the transportation sector; however, its production from lignocelluloses faces some challenges. Conventionally, lignocellulosic hydrolysis and fermentation has mostly been performed by separate hydrolysis and fermentation (SHF) or simultaneous saccharification and fermentation (SSF). SHF results in product inhibition during enzymatic hydrolysis and increased contamination risk. During SSF, suboptimal conditions are used and the fermenting organism cannot be reused. Bacterial contamination is another major concern in ethanol production, which usually results in low ethanol yield. In these studies, the above-mentioned challenges have been addressed. A novel method for lignocellulosic ethanol production ‘Simultaneous saccharification filtration and fermentation (SSFF)’ was developed. It circumvents the disadvantages of SSF and SHF; specifically, it uses a membrane for filtration and allows both the hydrolysis and fermentation to be carried out at different optimum conditions. SSFF also offers the possibility of cell reuse for several cultivations. The method was initially applied to pretreated spruce, with a flocculating strain of yeast Saccharomyces cerevisiae. SSFF was further developed and applied to pretreated wheat straw, a xylose rich lignocellulosic material, using encapsulated xylose fermenting strain of S. cerevisiae. High solids loading of 12% suspended solids (SS) was used to combat bacterial contamination and improve ethanol yield. Oil palm empty fruit bunch (OPEFB) was pretreated with fungal and phosphoric acid in order to improve its ethanol yield. An evaluation of biofuel production in Nigeria was also carried out. SSFF resulted in ethanol yield of 85% of the theoretical yield from pretreated spruce with the flocculating strain. Combination of SSFF with encapsulated xylose fermenting strain facilitated simultaneous glucose and xylose utilisation when applied to pretreated wheat straw; this resulted in complete glucose consumption and 80% xylose utilisation and consequently, 90% ethanol yield of the theoretical level. High solids loading of 12% SS of pretreated birch resulted in 47.2 g/L ethanol concentration and kept bacterial infection under control; only 2.9 g/L of lactic acid was produced at the end of fermentation, which lasted for 160 h while high lactic acid concentrations of 42.6 g/L and 35.5 g/L were produced from 10% SS and 8% SS, respectively. Phosphoric acid pretreatment as well as combination of fungal and phosphoric pretreatment improved the ethanol yield of raw OPEFB from 15% to 89% and 63% of the theoretical value, respectively. In conclusion, these studies show that SSFF can potentially replace the conventional methods of lignocellulosic ethanol production and that high solids loading can be used to suppress bacterial infections during ethanol productions, as well as that phosphoric acid pretreatment can improve ethanol yield from lignocellulosic biomass.

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.