Bioethanol production from mahula (Madhuca latifolia L.) flowers by solid-state fermentation

There is a growing interest worldwide to find out new and cheap carbohydrate sources for production of bioethanol. In this context, the production of ethanol from mahula (Madhuca latifolia L.) flowers by Saccharomyces cerevisiae in solid-state fermentation was investigated. The moisture level of 70%, pH of 6.0 and temperature of 30 °C were found optimum for maximum ethanol concentration (225.0 ± 4.0 g/kg flower) obtained from mahula flowers after 72 h of fermentation. Concomitant with highest ethanol concentration, the maximum ethanol productivity (3.13 g/kg flower/h), yeast biomass (18.5 × 10⁸ CFU/g flower), the ethanol yield (58.44 g/100 g sugar consumed) and the fermentation efficiency (77.1%) were also obtained at these parametric levels.     

Bioethanol production from thick juice as intermediate of sugar beet processing

The aims of this study were to investigate the bioethanol production of thick juice as intermediate from sugar beet processing in batch culture by free Saccharomyces cerevisiae cells and the effect of sugar concentration on ethanol yield and CO₂ weight loss rate. Thick juice and molasses of sugar beet from a domestic sugar factory were diluted with distilled water to give a total sugar concentration of 5, 10, 15, 20 and 25% (w w^?1). Initial concentration of fermentable sugars of 20% (w w^?1) in culture medium can be taken as optimal, enabling maximal ethanol yield (68%) and maximal CO₂ evolution rate was realized, amounting to more than 90 g L^?1 h^?1. The optimal concentration of fermentable sugar from thick juice for bioethanol production by free S. cerevisiae cells was 20% (w w^?1) at 30 °C, pH 5 and agitation rate 200 rpm gave maximum ethanol concentration of 12% (v v^?1).     

Ethanol fermentation of sugar beet thick juice diluted with crude cheese whey by the flex yeast Kluyveromyces marxianus KD-15

Kluyveromyces marxianus KD-15, called flex yeast, is a strain that is insensitive to catabolite repression and has the capacity to produce ethanol efficiently from a mixture of beet molasses and whey powder. When a fermentation test was conducted in 50 mL of a medium containing 200 mg mL^?1 of sugar as sugar beet thick juice diluted with an arbitrary amount of crude whey, strain KD-15 produced over 99 mg mL^?1 ethanol in all the media tested, and ethanol formation decreased in proportion to the volume of whey by K. marxianus NBRC 1963, the parental strain of KD-15, and Saccharomyces cerevisiae NBRC 0224, the reference strain for conventional ethanol production. Fermentation of thick juice diluted with whey alone by strain KD-15 at 30 °C initially proceeded slower than that at 33 °C–37 °C but finally bore the highest level of ethanol. The maximum ethanol concentration obtained in 1.5 L of a medium using a 2-L fermentor was elevated by aeration of 15–50 mL min^?1and reduced by that in excess of 100 mL min^?1. Under optimized conditions in 72 h, strain KD-15 converted all of the sugars derived from thick juice and whey to ethanol at 102 mg mL^?1, corresponding to 92.9% of the theoretical yield.     

Ethanol production from agroindustrial biomass using a crude enzyme complex produced by Aspergillus niger

This study investigates ethanol production from simultaneous fermentation and saccharification (SFS) and separated hydrolysis and fermentation (SHS) using enzyme complexes produced by Aspergillus niger strains (ATCC 16404, ATCC 1057, ATCC 9029). The enzyme complexes were produced by solid-state fermentation (SSF) on inexpensive and readily available agroindustrial products: rice byproduct (composed of AFEX-treated rice rust and rice bran), whey and sugarcane bagasse. The ethanol was produced by Saccharomyces cerevisiae Y904 using whey and rice byproduct as the substrate and the enzyme complex produced by A. niger. The best result for solid-state fermentation (40 U/g of dry substrate, A. niger ATCC 16404) was obtained in a 0.5 L rotating drum bioreactor at 40 °C filled half filled with solid biomass composed of rice byproduct (86% wt/wt), whey (12% wt/wt) and CaCl₂ (2.0% wt/wt). The best result for ethanol fermentation (11.7 g/L of ethanol) was obtained after 12 h of SFS at pH 4.5 and 35 °C. A comparative study of ethanol production by Trichoderma reesei CCT 2768 and A. niger ATCC 16404 complexes under the same optimised SFS and SSF conditions was also performed, revealing that ethanol production by the A. niger enzyme complex was 2.25 times higher than that by T. reesei. These findings suggest that the ethanol production using crude enzymatic complexes produced by A. niger and agroindustrial biomass described in this paper is very promising in terms of disposal of the whey produced by cheese-making and other dairy food processing.     

Ethanol production by repeated batch and continuous fermentations of blackstrap molasses using immobilized yeast cells on thin-shell silk cocoons

A thin-shell silk cocoon (TSC), a residual from the silk industry, is used as a support material for the immobilization of Saccharomyces cerevisiae M30 in ethanol fermentation because of its properties such as high mechanical strength, light weight, biocompatibility and high surface area. In batch fermentation with blackstrap molasses as the main fermentation substrate, an optimal ethanol concentration of 98.6 g/L was obtained using a TSC-immobilized cell system at an initial reducing sugar concentration of 240 g/L. The ethanol concentration produced by the immobilized cells was 11.5% higher than that produced by the free cells. Ethanol production in five-cycle repeated batch fermentation demonstrated the enhanced stability of the immobilized yeast cells. Under continuous fermentation in a packed-bed reactor, a maximum ethanol productivity of 19.0 g/(L h) with an ethanol concentration of 52.8 g/L was observed at a 0.36 h⁻¹ dilution rate.     

Energy use and economical analysis of sugar beet production in Tokat province of Turkey

The purposes of this study were to determine energy consumption of input and output used in sugar beet production, and to make a cost analysis in Tokat, Turkey. Data were collected from 146 sugar beet farms in Tokat, Turkey by using a face-to-face questionnaire performed in January and February 2005. Farms were selected based on random sampling method. The results revealed that total energy consumption in sugar beet production was 39 685.51 MJ ha⁻¹, and accounted for 49.33% of fertilizer energy, and 24.16% of diesel energy. The output/input energy ratio was 25.75 and energy productivity was 1.53 kg MJ ha⁻¹. Results further indicated that 82.43% of total energy input was in non-renewable energy form, and only 12.82% was in renewable form. Economic analyses showed that profit–cost ratio of farms was 1.17. The highest energy cost items were labor, land renting, depreciation and fertilizers. Although intensive energy consumption in sugar beet production increased the yield, it also resulted in problems such as global warming, land degradation, nutrient loading and pesticide pollution. Therefore, there is a need to pursue a new policy to force producers to undertake energy-efficient practices to establish sustainable production systems without disrupting the natural resources. In addition, extension activities are needed to improve the efficiency of energy consumption and to sustain the natural resources.     

Optimization of very high gravity fermentation process for ethanol production from industrial sugar beet syrup

In order to reduce production costs and environmental impact of bioethanol from sugar beet low purity syrup 2, an intensification of the industrial alcoholic fermentation carried out by Saccharomyces cerevisiae is necessary. Two fermentation processes were tested: multi-stage batch and fed-batch fermentations with different operating conditions. It was established that the fed-batch process was the most efficient to reach the highest ethanol concentration. This process allowed to minimize both growth and ethanol production inhibitions by high sugar concentrations or ethanol. Thus, a good management of the operating conditions (initial volume and feeding rate) could produce 15.2% (v/v) ethanol in 53 h without residual sucrose and with an ethanol productivity of 2.3 g L h⁻¹.     

Ethanol production from mahula (Madhuca latifolia L.) flowers with immobilized cells of Saccharomyces cerevisiae in Luffa cylindrica L. sponge discs

The dried spongy fruit of luffa (Luffa cylindrica L.), a cucurbitaceous crop available in abundance in tropical and sub-tropical countries has been found to be a promising material for immobilizing microbial cells. The aim of the present study was to examine the ethanol production from mahula flowers in submerged fermentation using whole cells of Saccharomyces cerevisiae immobilized in luffa sponge discs. The cells not only survived but also were physiologically active in three more cycles of fermentation without significant reduction (<5%) in ethanol production. After 96 h, there was 91.1% sugar conversion producing 223.2 g ethanol/kg flowers (1st cycle) which was 0.99%, 2.3% and 3.2% more than 2nd (221 g ethanol/kg flowers), 3rd (218 g ethanol/kg flowers) and 4th (216 g ethanol/kg flowers) cycle of fermentation, respectively. Furthermore, ethanol production by immobilized cells was 8.96% higher than the free cells.     

Comparative study of bio-ethanol production from mahula (Madhuca latifolia L.) flowers by Saccharomyces cerevisiae and Zymomonas mobilis

Mahula (Madhuca latifolia L.) flower is a suitable alternative cheaper carbohydrate source for production of bio-ethanol. Recent production of bio-ethanol by microbial fermentation as an alternative energy source has renewed research interest because of the increase in the fuel price. Saccharomyces cerevisiae (yeast) and Zymomonas mobilis (bacteria) are two most widely used microorganisms for ethanol production. In this study, experiments were carried out to compare the potential of the yeast S. cerevisiae (CTCRI strain) with the bacterium Z. mobilis (MTCC 92) for ethanol fermentation from mahula flowers. The ethanol production after 96 h fermentation was 149 and 122.9 g kg⁻¹ flowers using free cells of S. cerevisiae and Z. mobilis, respectively. The S. cerevisiae strain showed 21.2% more final ethanol production in comparison to Z. mobilis. Ethanol yield (Yx/s), volumetric product productivity (Qp), sugar to ethanol conversion rate (%) and microbial biomass concentration (X) obtained by S. cerevisiae were found to be 5.2%, 21.1%, 5.27% and 134% higher than Z. mobilis, respectively after 96 h of fermentation.     

Research on ethanol production and use from sugar beet in Turkey

Emissions of greenhouse gases such as CO₂, CO, CH₄ and NO_X from fossil fuel use are implicated in climate change. The use of bioethanol is one means to reduce fossil fuel use and emissions of greenhouse gases. This study investigated research to produce ethanol from sugar beet and use as fuel in Turkey. The calculated demand for bioethanol amounted to some 220,000 m³ where a 5% ethanol mix in petrol was used. Turkey has the potential to produce 30 million ton of sugar beet, which is sufficient to meet the bioethanol demand.     

Evaluation of an adapted inhibitor-tolerant yeast strain for ethanol production from combined hydrolysate of softwood

In order to evaluate the potential of an adapted inhibitor-tolerant yeast strain developed in our lab to produce ethanol from softwood, the effect of furfural and HMF presented in defined medium and pretreatment hydrolysate on cell growth was investigated. And the efficiency of ethanol production from enzymatic hydrolysate mixed with pretreatment hydrolysate of softwood by bisulfite and sulfuric acid pretreatment process was reported. The results showed that in the combined treatments of the two inhibitors, cell growth was not affected at 1 g/L each of furfural and HMF. When 3 g/L each of furfural and HMF was applied, the adapted strain responded with an extended lag phase of 24 h. Both in batch and fed-batch runs of combined hydrolysate fermentation, the final ethanol concentrations were above 20.0 g/L and the ethanol yields (Y_p/s) on the total amount of fermentable sugar presented in the pretreated materials were above 0.40 g/g. It implies the great promise of the yeast strain for improving ethanol production from softwood due to its high ability of metabolizing inhibitor compounds of furfural and HMF.     

Developing a thermophilic hydrogen-producing co-culture for efficient utilization of mixed sugars

Previous studies on the extreme thermophile Caldicellulosiruptor saccharolyticus revealed that the organism produces high yields of hydrogen on glucose and xylose, the major components of lignocellulosic hydrolysates. Preliminary experiments on mixed sugar substrates, however, indicated that xylose was preferred over glucose. The sugar preference of some other extreme thermophiles, including Caldicellulosiruptor owensensis, Caldicellulosiruptor kristjanssonii and newly enriched, thermophilic compost sludge microflora, was investigated in an attempt to find complementary organisms to C. saccharolyticus for rapid and efficient utilization of lignocellulosic sugars. The behavior of C. owensensis and C. kristjanssonii appeared to be similar to that of C. saccharolyticus, either in pure cultures or in co-cultures with the latter. Co-culturing C. saccharolyticus with the enriched compost microflora resulted in fast, simultaneous consumption of both glucose and xylose in the medium with a relatively high specific hydrogen production rate, 40 mmol (gCDW)⁻¹ h⁻¹, and high volumetric productivity, 22.5 mmol l⁻¹ h⁻¹.     

Pretreatment of sweet sorghum bagasse for hydrogen production by Caldicellulosiruptor saccharolyticus

Pretreatment of sweet sorghum bagasse, an energy crop residue, with NaOH for the production of fermentable substrates, was investigated. Optimal conditions for the alkaline pretreatment of sweet sorghum bagasse were realized at 10% NaOH (w/w dry matter). A delignification of 46% was then observed, and improved significantly the efficiency of enzymatic hydrolysis. Under hydrolysis conditions without pH control, up to 50% and 41% of the cellulose and hemicellulose contained in NaOH-pretreated sweet sorghum bagasse were converted by 24 h enzymatic hydrolysis to soluble monomeric sugars. The extreme thermophilic bacterium Caldicellulosiruptor saccharolyticus showed normal growth on hydrolysates of NaOH-pretreated biomass up to a sugar concentration of 20 g/L. Besides hydrogen, the main metabolic products detected in the fermentations were acetic and lactic acid. The maximal hydrogen yield observed in batch experiments under controlled conditions was 2.6 mol/mol C6 sugar. The maximal volumetric hydrogen production rate ranged from 10.2 to 10.6 mmol/(L h). At higher substrate concentrations the production of lactic acid increased at the expense of hydrogen production.     

Enzymatic saccharification and fermentation of paper and pulp industry effluent for biohydrogen production

Paper and pulp industry effluent was enzymatically hydrolysed using crude cellulase enzyme (0.8–2.2FPU/ml) obtained from Trichoderma reesei and from the hydrolysate biohydrogen was produced using Enterobacter aerogenes. The influence of temperature and incubation time on enzyme production was studied. The optimum temperature for the growth of T. reesei was found to be around 29 °C. The enzyme activity of 2.5 FPU/ml was found to produce about 22 g/l of total sugars consisting mainly of glucose, xylose and arabinose. Relevant kinetic parameters with respect to sugars production were estimated using two fraction model. The enzymatic hydrolysate was used for the biohydrogen production using E. aerogenes. The growth data obtained for E. aerogenes were fitted well with Monod and Logistic equations. The maximum hydrogen yield of 2.03 mol H₂/mol sugar and specific hydrogen production rate of 225 mmol of H₂/g cell/h were obtained with an initial concentration of 22 g/l of total sugars. The colour and COD of effluent was also decreased significantly during the production of hydrogen. The results showed that the paper and pulp industry effluent can be used as a substrate for biohydrogen production.     

Hydrogen gas production from acid hydrolyzed wheat starch by combined dark and photo-fermentation with periodic feeding

Hydrogen gas production from acid hydrolyzed waste wheat starch by combined dark and photo-fermentation was investigated in continuous mode with periodic feeding and effluent removal. A mixture of heat treated anaerobic sludge and Rhodobacter sphaeroides (NRRL-B 1727) were used as the seed culture for dark and light fermentations, respectively with biomass ratio of Rhodobacter/sludge = 3. Hydraulic residence time (HRT) was changed between 1 and 8 days by adjusting the feeding periods. Ground waste wheat was acid hydrolyzed at pH = 3 and 121 °C for 30 min using an autoclave and the resulting sugar solution was used as the substrate for combined fermentation after pH adjustment and nutrient addition. The highest daily hydrogen gas production (41 ml d⁻¹), hydrogen yield (470 ml g⁻¹ total sugar = 3.4 mol H₂ mol⁻¹glucose), volumetric and specific hydrogen production rates were obtained at the HRT of 8 days. The highest biomass and the lowest total volatile fatty acids (TVFA) concentrations were also realized at HRT = 8 days indicating VFA fermentation by Rhodobacter sp. at high HRTs. The lowest total sugar loading rate of 0.625 g L⁻¹ d⁻¹ resulted in the highest hydrogen yield and formation rate. Hydrogen gas production by combined fermentation with periodic feeding was proven to be an effective method resulting in high hydrogen yields at long HRTs.     

Simultaneous saccharification and fermentation (SSF) of non-starch polysaccharides and starch from fresh tuber of Canna edulis ker at a high solid content for ethanol production

Canna edulis ker is a potential feedstock for ethanol production because of its low nutrition requirements and the high starch content of its tubers. The processing of C. edulis is limited by the high viscosity of the biomass. In this study, cell wall degrading enzymes (CWDEs) containing acid xylanase and β-glucanase were successful in reducing the viscosity (from 167.30 Pa s to 8.66 Pa s) at 50 °C for 120 min. The effect of CWDEs on simultaneous saccharification and fermentation (SSF) was investigated. Addition of CWDEs before SSF, resulted in an increase in total sugar and fermentable sugar. Meanwhile, the viscosity decreased sharply from approximately 200.00 Pa s to 2.98 Pa s, thereby improving the fermentation parameters and the mass fraction of the theoretical ethanol yield was 94.5%. Only special demand of nutritional ingredients was nitrogen, urea at 750 mg kg⁻¹ was found to be suitable for this purpose. In the verification experiments, the mass fraction of the theoretical ethanol yield in a 5 L fermentor was 98.3%. In conclusion, the pretreatment with CWDEs has significant effect on high level ethanol production using roots and tubers on an industrial scale from the biomass utilization efficiency and economic standpoint.     

Ethanol production from food residues

Food residues were converted to ethanol by simultaneous saccharification with an amylolytic enzyme complex (a mixture of amyloglucosidase, ??-amylase, and protease), and fermentation (SSF) with the yeast, Saccharomyces cerevisiae. About 36 g dm⁻³ of ethanol was obtained from 100 g dm⁻³ food residue in 48 h of fermentation. In the SSF with no nitrogen supplements, 25 g dm⁻³ of ethanol was produced from 100 g dm⁻³ food residues. In addition, none of the nutrient components except yeast extract from the SSF medium were found to affect ethanol production from food residues. This result indicates that food residues could be a good economic bioresource for ethanol production.     

A pilot-scale study of biohydrogen production from distillery effluent using defined bacterial co-culture

We evaluated the feasibility of improving the scale of hydrogen (H₂) production from sugar cane distillery effluent using co-cultures of Citrobacter freundii 01, Enterobacter aerogenes E10 and Rhodopseudomonas palustris P2 at 100 m³ scale. The culture conditions at 100 ml and 2 L scales were optimized in minimal medium and we observed that the co-culture of the above three strains enhanced H₂ productivity significantly. Results at the 100 m³ scale revealed a maximum of 21.38 kg of H₂, corresponding to 10692.6 mol, which was obtained through batch method at 40 h from reducing sugar (3862.3 mol) as glucose. The average yield of H₂ was 2.76 mol mol⁻¹ glucose, and the rate of H₂ production was estimated as 0.53 kg/100 m³/h. Our results demonstrate the utility of distillery effluent as a source of clean alternative energy and provide insights into treatment for industrial exploitation.     

Estimating hydrogen production potential in biorefineries using microbial electrolysis cell technology

Future biofuel and bioproducts industries are expected to generate significant volumes of waste streams containing easily degradable organic matter. The emerging MEC technology has potential to derive added-value from these waste streams via production of hydrogen. A methodology to determine hydrogen production potential from wastewaters is reported. Biorefinery process streams, particularly the stillage or distillation bottoms contain underutilized sugars as well as fermentation and pretreatment byproducts, in the case of lignocellulosic biorefineries. Estimates of hydrogen production from existing starch-based biorefineries indicate potential to generate 750-8900 m³/hr of hydrogen. In a lignocellulosic biorefinery designed to produce 265,000 m³ of ethanol per year, it is estimated that 1260-7200 m³/hr of hydrogen can be generated. Removal of fermentation and pretreatment byproducts from stillage streams has the added potential to enable water recycle.