Cluster analysis of energy indices and balance energy indices for rice production

In cluster analysis genotypes were classified into four groups based on Ward’s method. Cluster analysis showed that Hybrid and Gohar varieties and Alikazemi, Khazar and Hashemi varieties in group similarities "Figure 9".


Distance Cluster




0 5

10 15 20





-+———— +—-

—- +——


—- +



— + — +



-+ +—

—- +








—- +




Figure 9. Dendrogram of rice genotypes based on different ward method

3.2. Yield function

Relation between amounts of energy efficiency (energy output to input energy ratio) and energy balance efficiency (production energy to consumption energy ratio) and their effect on paddy yield, straw yield, husk yield and biomass yield were showed in figure 10. Paddy yield, straw yield, husk yield and biomass yield were increased with of use energy efficiency and energy balance efficiency "Figure 10". Yield function of paddy yield, straw yield, husk yield and biomass yield obtained by following relationship "Figure 10".

Availability of residual biomass in Ecuador

Ecuador is a biodiverse country with rich and fertile natural regions. In the coastal zone of Ecuador there is the large scale agriculture of a wide variety of crops which have positioned this country as one of the most important producers of bananas, palmito (palm heart), oil palm and other valuable products in South America. Moreover, Ecuador has unique vegetal species that are being exploited in small scale, presenting novel and potential sources of lignocellulose for the future.

In terms of abundance of lignocellulosic residues, the most conspicuous industries producing leftovers—as a consequence of the harvest or the extraction of valuable commodities—are the bananas farms, and the oil palm and sugar cane mills. There are still other important industries located mainly in the highlands such as flowers and cereals that produce lignocellulosic material potentially usable. Nevertheless, the amounts of these residues are not enough for huge biorefining installations, nor even available in an economical and technical way.

As for the availability of residues, studies carried out by researchers from the Neotropical Center for the Biomass Research at the Pontificia Universidad Catolica del Ecuador, reveal that there is a very high potential for lignocellulosic ethanol and biorefineries setting up in Ecuador. Nevertheless, there still exist constraints due to the disperse areas where the agricultural and industrial lignocellulosic materials are disposed; the local roads infrastructure and networks; the lack of development of markets for certain specific residues; the traditional uses and ways of final disposal; the physical and chemical composition of residues; and, the prices per dry ton. There are also social and environmental components to be taken into account when projecting lignocellulosic biorefineries to take the most of the agricultural and industrial byproducts, leftovers or residual material. In our survey we have considered the above-mentioned factors to develop the feasibility study for a biorefinery based on local lignocellulosic residues in the country.

In this survey we have pursued the following general objectives:

1. Evaluate the abundance and the potential of the main crops produced in Ecuador.

2. Determine the utilization, destiny, and availability of the agricultural residues.

3. Estimate the evolution of the agricultural production and residues generation in 5 years (until 2014).

Moreover, we have focused the following specific goals:

1. Determine the main crops in Ecuador, its exact geographical location, and the quantity of biomass residues produced per year.

2. Establish the temporality of crops and harvest.

3. Take current and historical data on volume of waste biomass produced to project future volumes, considering a period of five years. Analyze the succession of crops

4. Determine on the basis of the previous information, the more adequate zones where to install a future biorefinery plant.

In Ecuador there are three crops that worth to be studied with biorefining ends, because of their characteristics in terms of composition, final disposal, abundance and lack of sustainable use. These crops are: bananas, sugar cane and oil palm.

Table 3 shows the complete results of our survey on 13 different crops in Ecuador, the calculation of its dry mass and cellulose average contents as well as the potential for ethanol production. As it is going to be seen, Ecuador potentially could provide at least half of the ethanol needs for replacing gasoline in vehicles if the cellulose contained in agricultural residues were transformed into ethanol.

This suggests that biorefinery plants can be a reasonable and sustainable option for the post oil economy in Ecuador. Moreover, there still exists a huge potential for power generation if biogas from stills and residual lignin are burned in biorefineries.

There still exist other valuable products from biorefining of second generation ethanol such that can be produced from the residual water generated after distillation which, after an anaerobic digestion process, yields biogas, liquid and solid fertilizers (sludge). The non — hydrolyzed fibers as well as yeast biomass obtained after fermentation can be dried and sold as animal feed solid matter. The solid matter that can be recovered from fermenters before distillation is really considerable. Moreover, carbon dioxide from fermentation can be collected and treated to be sold in as much as during the fermentation for ethanol production, almost the same amount of CO2 is released. Theoretically, the production ratio of ethanol to CO2 in fermentation is 92:88. The uses for this gas are very wide including food, drink and chemical industries. CO2 is widely used in soft drinks and beer to carbonation of these beverages. It is also used to fill packs of vegetables and meet to keep it fresh. CO2 can also be used as raw material for the synthesis of methanol, formic acid, and urea. Other applications of CO2 include its use as a medium in supercritical CO2 extraction and in fire extinguishing equipment [4].



Residues by Product

Dry weight (MT/year)

Average cellulose content (IVIT/year)

Theoretical potential ethanol (Gal)




Percent of potentially supplied vehicles per year (Total number of cars: 1.4 MM to 2014)

Soy bean




































Soft corn
























Dry corn












Oil palm












Table 3. The hypothetical potential of lignocellulosic biomass in Ecuador to produce cellulosic ethanol

New algorithm to predict potential biomethane yield

As it was commented above biomethane yield in terms of total slurry mass (BMPTM) significantly correlated with DM concentrations. We tested the possibility of predicting BMPTM using the concentration of DM, VS and the concentration of lignin and VFA, which were a significant variable for BMP. The results of the regression tests are shown in Table 5, where quite high correlations were found for all the models. However, critical relative errors using DM as an independent variable were found, that is, 62.1 %, which seems to be because the wide range of DM improved the correlation level. Hence, when assessing BMPTM, only TS can be used when further characterisation is not possible. Apart from DM, relative errors were much lower when using VS and VS together with lignin and VFA, indicating a good potential of applying the model for prediction.






DM ( g kg -1)




BMPtm = -0.934+0.201*DM

VS (g kg-1)




BMPtm = 0.610+0.229*VS

VS ( g kg -1) Hgnm (% of VS ) and VFA (% of VS)




BMPtm = 4.654+ 0.230*VS +0.009*VFA -0.360*lignin

Table 5. Summary statistics results, algorithm obtained for BMPtm.

5. Conclusion

The study highlights the critical quality of VS in cow manure and the critical quantity of VS in pig slurry which results in low viability of biogas production using animal slurry. The very high concentration of lignin in cattle and dairy cow manure indicates that there is a need of pretreatment either to reduce the influence of lignin by releasing lignocellosic bindings, or by depolymerizing lignin polymer. Whereas low digestibility of cow manure is problematic due to high concentration of lignin, lignin concentration of pig and mink slurry was relatively low. However despite of preferable digestibility of pig and mink slurry, the large amount of water and very low VS concentration in them indicates that there is a need of a qualified control of water content during management. Our study shows that control of DM concentration is more crucial than control of BD of substrate to enhance methane yield. Hence, the study highlights the importance of a qualified control of water content in feedstock by co-digesting solid organic substrates that can enrich VS concentrations prior to improvement of substrate digestibility by pretreatment.

Author details

Jin M. Triolo[2], Lene Pedersen and Sven G. Sommer

University of Southern Denmark, Faculty of Engineering, Institute of Chemical Engineering,

Biotechnology and Environmental Technology, Odense M, Denmark

Alastair J. Ward

Aarhus University, Dept. of Biosystems Engineering, AU Foulum, Tjele, Denmark

Fractionation of lignocellulosic feedstock

2.2. Definition

Conversion of lignocellulosic materials to higher value products requires fractionation of the material into its components: lignin, cellulose, and hemicellulose, which convert to fuels, and chemicals for the production of most of our synthetic plastics, fibres, and rubbers is technically feasible. Liquefaction of LCF might serve as feedstocks for cracking to chemicals in the similar way that crude oil is presently used. Currently commercial products of LCF fractionation include levulinic acid, xylitol, and alcohols [104]. The ultimate goal of LCF fractionation is the efficient conversion of lignocellulose materials into multiple streams that contain value-added compounds in concentrations that make purification, utilization, and/or recovery economically feasible [15].

Fractionation of LCF is being developed as a means to improve the overall biomass utilization. Hemicellulose when separated from the LCF may find broader use for chemicals, fuel, and food application. The lignin separated in the process can be used as a fuel [105]. Unlike the lignin generated from pulping process, lignin fractionated from biomass by our approach is relatively clean, free of sulphur or sodium.

Fractionation of lignocellulosic materials is very difficult to accomplish efficiently, because of their complex composition and structure [106, 107]. However, fractionation of lignocellulosic materials is essential for some important applications, for example, paper­making, and in their conversion into basic chemical feedstocks or liquid fuels.

> iottch./ch*m (cal’

high value-added products [108]. Achieving high fractionation yields and maintaining the integrity of the macromolecular fractionation products are of major importance regarding the effectiveness of the whole refining process [109].

Figure 8. Lignocellulosic Feedstock Biorefinery [110]

Further research on the distilled fractions

Based on the molecular distillation results, a scheme of the process combining molecular distillation separation with bio-oil upgrading is proposed. The light fraction rich in carboxylic acids and other light components could be used for esterification, catalytic cracking, and steam reforming, to produce ester fuel, hydrocarbons, and hydrogen, respectively. For the middle fraction, steam reforming at high temperature or hydrodeoxygenation at high pressure could efficiently convert this fraction into hydrogen or hydrocarbons. The heavy fraction, which consisted mainly of pyrolytic lignin and sugar oligomers, could be emulsified with diesel to obtain emulsion fuel with a relatively high heating value. On the other hand, the extraction of some valuable chemicals can benefit the overall economy of this process.

Recently, some further research has been performed, aiming at investigating some characteristics of the distilled fractions and devising more promising upgrading methods. Thermal decomposition processes and the pyrolysis products of crude bio-oil and distilled fractions were investigated by means of TG-FTIR by Guo (Guo et al., 2010a). The light

fraction (LF) was completely evaporated at 30-150 °C, with the maximum weight loss rate at about 100 °C due to the volatilization of water and compounds of lower boiling point. The middle fraction (MF) and heavy fraction (HF) contained more lignin-derived compounds, and these decomposed continuously over a wide temperature range of 30-600 °C, leaving a final residue yield of 25-30%. Upgrading of the distilled fraction rich in carboxylic acids and ketones was carried out by Guo (Guo et al., 2011). Carboxylic acids accounted for 18.39% of the initial fraction, with acetic acid being the most abundant. After upgrading, the carboxylic acid content decreased to 2.70%, with a conversion yield of 85.3%. The content of esters in the upgraded fraction increased dramatically from 0.72% to 31.1%. The conversion of corrosive carboxylic acids into neutral esters reduced the corrosivity of the bio-oil fraction.

Figure 6. A scheme of the process combining molecular distillation separation with bio-oil upgrading.

Author details

Shurong Wang Zhejiang University, China


The author acknowledges the financial support from the Program for New Century Excellent Talents in University, the International Science & Technology Cooperation Program of China (2009DFA61050), Zhejiang Provincial Natural Science Foundation of China (R1110089), the Research Fund for the Doctoral Program of Higher Education of

China (20090101110034), the National Natural Science Foundation of China (50676085) and

the National High Technology Research and Development Program of China

(2009AA05Z407). The author also highly appreciates the kind support from Mr. Zuogang

Guo, Mr. Qinjie Cai, Mr. Long Guo and Miss Yurong Wang, who have been involved in the

experimental research and the preparation of this chapter.

Studies of biosorption of heavy metals with aerobic bacteria using biomass support in batch system

For studies of biosorption of heavy metals using aerobic bacteria and a support for the biomass, using 500 mL Erlenmeyer flasks, which are placed 5 g of the support for the immobilization of selected biomass, 90 mL of a solution containing the metal study established at an initial concentration, 10 ml of biomass with a density of 1 g/L and as target, 100 mL of metal with 5 g of support material. The flasks were plugged with a cotton swab having aeration, then is placed in an incubator with shaking at 100 rpm and temperature established for mesophilic bacteria to 45 °C. Samples are taken at set times to analyze the concentration of metals by atomic absorption. The conditions are the same for the studies using only bacteria without carrier material. All experiments were performed in duplicate and the efficiency of biosorption (E) is calculated using the equation:

E = ( C° — Cf ) *100 (23)


Where: Co y Cf initial and final amounts of the metal (mg/L).

The logistic curve approach

According to Graham (1939), the maximum yield that can be extracted from a wild stock is found at the half of the virgin size of that population, as seen in Fig. 1A, B. A similar view is commented by Zabel et al. (2003). After this premise, a simplistic approach can be adopted by assuming that when the catch trend shows a maximum, followed by a decline, then that

Figure 1. Principles of the logistic growth of a population (A) and the surplus yield of an exploited stock (B). Horizontal scale of Fig. A is time and in Fig. B indicates population size.

maximum yield corresponds to the half of the population size at the virgin stock. Stock assessment based upon this approach is very limited and despite that its ecological principles as background are valid, there are many factors constraining the validity of this procedure and therefore other approaches more accurate and based upon age structure have been adopted over time.

By following the former statements, a simple approach to roughly estimate the stock biomass is by just fitting a parabola to the catch records of some fisheries or regions, even deliberately ignoring a relationship of the stock density of populations, just by usually using the catch per unit of effort as an indicator of stock density. In this case, time was used as an indirect indicator of fishing effort, because the information on this variable is not easily available and because it is beyond the scope of this paper. Therefore, second degree regressions were used to several fisheries and regions just to have an idea on when the maximum yields, presumably equivalent to the Maximum Sustainable Yields (MSY), were attained. It is assumed that the stock biomass is at least twice bigger than the maximum yield attained in a certain time, and in that point is supposed that the exploitation rate E, is 50 per cent. This approach is conservative, because the intrinsic growth rate is not provided, given that many populations are involved. In the stock assessment process, the E value is usually lower than 0.5; however, by considering that many species are involved in the procedure is analysis, is likely to expect that in this collection there may be species which are overexploited, as well as others which may be underexploited. For this reason, it is reasonable to adopt a conservative criterion instead of being too optimistic assuming that the biomass could reach higher values. It is pertinent to mention that most of the regressions applied and described in the following paragraphs excepting three, provided high and significant R2 coefficients.

On being consistent with this idea, estimations of the MSY by applying a parabola were fitted to catch data of the world fisheries exploited and recorded for different regions as shown in Fig. 2 (A — F) and in Table 1. The time scale of catch extracted from FAO (2010), data goes from 1950 to 2010. It is evident that in most cases the catch has attained a maximum yield, which for practical purposes; it can be considered as equivalent to the MSY level.

Continuous fermentation process

Bioethanol production from agave juice continuous fermentation process is shown below. In continuous fermentation process, the effects of dilution rate, nitrogen and phosphorus source addition and micro-aeration on growth, and synthesis of ethanol of two native Saccharomyces cerevisiae S1 and S2 strains were studied.

Continuous cultures were carried out in a 3 L bioreactor (Applikon, The Netherlands) with a 2 L working volume. Cultures were started in a batch mode, by inoculating fermentation medium with 3.5 x 106 cells/mL (97±2 %. initial viability) and incubating at 30 °C and 250 rpm for 12 h. Afterwards, the culture was fed with fermentation medium (12 °Brix = 95 ± 5 g/L reducing sugar and 1 g/L of ammonium sulfate). Culture media were sterilized at 121 °C for 15 min.

To reach the steady state in each studied condition, the culture was maintained during five residence times and samples were taken every 6 h. A steady state was reached, when the variation in the concentrations of biomass, residual sugars and ethanol were less than 5%. Data presented on tables and figures are the mean ± standard deviation of three assays at the steady state.

Effect of the dilution rate on S. cerevisiae strains fermentative capability in continuous cultures

Both yeast strains (S1 and S2) were used and fermentation medium was fed at different D (0.04, 0.08, 0.12 and 0.16 h-1) for studying the effect of dilution rate (D) on the kinetic parameters and concentrations of biomass, residual reducing sugar and ethanol at a steady state of agave juice continuous fermentation process (Table 5 and Figure 5).

Concentrations of biomass and ethanol decreased as D increased for both strains cultures while residual reducing sugars increased parallel with the increase of D (Figure 5).

Figure 5. Concentration of Residual reducing sugar (Sr), Ethanol (Pf) and Biomass (Xf) at the steady state of continuous culture of two strains of S. cerevisiae (S1 and S2) fed with agave juice at different dilution rate (D). Data are presented as mean ± standard deviation of four assays at the steady state.

Although, S. cerevisiae S2 consumed more reducing sugars than S1 for each D, ethanol yields reached by S1 were higher than those obtained by S2, which were near the theoretical value (0.51) with no significant differences among the different D tested (p>0.05) (Table 5).

At D = 0.04 h-1, S1 and S2 strains reached the highest ethanol productions (43.92 and 38.71 g/L, respectively) and sugar consumptions (96.06 and 94.07 g/L, respectively) which were similar to those obtained using batch fermentations (see Batch fermentation process section). The low fermentative capacities displayed by both strains at higher D than 0.04 h-1 could be due to a low content of nutrients and/or toxic compounds in agave juice cooked [15].

Both strain cultures reached maximal ethanol production rates at 0.12 h-1 (2.37 and 2.53 g/L-h, respectively for S1 and S2), maximal growth rates were achieved at 0.16 h-1 (0.44 and 0.38 g/L-h, respectively for S1 and S2) and maximal sugar consumption rates were obtained at 0.08 h-1 (5.08 g/L-h) for S1 and at 0.12 h-1 (9.96 g/L-h) for S2 (Table 5 and Figure 6).

Effect of the pH value on the fermentative capacity of S1 and S2 strains — The effect of pH was observed, switching from a controlled pH (at 4) to an uncontrolled pH (naturally set at 2.5±0.3). Figure 7 shows biomass and ethanol productions for strain S1, in non-aerated or aerated (0.01 vvm) systems fed with sterilized medium. Results did not show significant differences on the biomass or ethanol productions (P > 0.05) between the fermentations with control (4) and with no control (2.5) of pH. Conversely, biomass and ethanol productions increased on aerated culture compared to that non aerated, for both pH levels studied. These results agreed with those reported by Diaz-Montano et al. [20]. These results are important, since the operation of a continuous culture naturally adjusted to a low pH would limit the growth of other yeasts [21, 22] or bacteria [23, 24], indicating the feasibility of working with non-sterilized media on an industrial scale. Another advantage of not controlling the pH is that instrumentation for this operation is not required, thus removing it from the initial investment [25].



D (h-i)





Biomass (g/L)


5.83 ± 0.21

3.38 ± 0.03

3.04 ± 0.04

2.75 ± 0.07


4.89 ± 0.12

3.18 ± 0.08

2.86 ± 0.08

2.39 ± 0.06

Ethanol (g/L)


43.92 ± 0.81

29.63 ± 0.79

19.76 ± 0.32

9.95 ± 0.39


38.71 ± 0.74

27.33 ± 1.60

21.10 ± 0.48

15.20 ± 0.51

RS (g/L)


3.94 ± 0.53

35.34 ± 0.94

59.75 ± 0.81

79.08 ± 1.08


5.93 ± 1.16

13.69 ± 1.70

16.96 ± 0.43

70.70 ± 2.17

Glucose (g/L)



1.41 ± 0.06

2.32 ± 0.06

3.07 ± 0.16



0.43 ± 0.03

0.65 ± 0.04

3.46 ± 0.48

Fructose (g/L)


2.79 ± 0.57

32.12 ± 0.85

51.48 ± 0.28

65.94 ± 1.39


2.14 ± 0.05

10.54 ± 0.37

15.74 ± 0.50

63.10 ± 2.82

Glycerol (g/L)


2.44 ± 0.28

1.94 ± 0.04

1.70 ± 0.03

1.86 ± 0.26


2.09 ± 0.09

2.34 ± 0.07

2.54 ± 0.08

1.32 ± 0.05

Yx/s (g/g)


0.06 ± 0.00

0.05 ± 0.00

0.08 ± 0.00

0.17 ± 0.01


0.05 ± 0.00

0.03 ± 0.00

0.03 ± 0.00

0.07 ± 0.01

Yp/S (g/g)


0.46 ± 0.01

0.47 ± 0.02

0.49 ± 0.01

0.47 ± 0.01


0.39 ± 0.01

0.30 ± 0.02

0.24 ± 0.00

0.44 ± 0.04

rx (g/Lh)


0.23 ± 0.01

0.27 ± 0.00

0.36 ± 0.01

0.44 ± 0.01


0.19 ± 0.01

0.25 ± 0.01

0.34 ± 0.01

0.38 ± 0.01

rs (g/Lh)


3.80 ± 0.02

5.08 ± 0.08

4.69 ± 0.10

2.52 ± 0.17


3.96 ± 0.05

6.91 ± 0.14

9.96 ± 0.05

4.69 ± 0.35

rp (g/Lh)


1.76 ± 0.03

2.37 ± 0.06

2.37 ± 0.04

1.59 ± 0.06


1.55 ± 0.03

2.19 ± 0.13

2.53 ± 0.06

2.43 ± 0.08

RS: Residual reducing sugar concentration, Yx/s: yield of biomass, Yp/s: yield of ethanol, rx: growth rate, rs: reducing sugars consumption rate, rp: ethanol production rate, nd: not detected at the assayed conditions. Data are presented as mean ± standard deviation of four assays at the steady state.

Table 5. Kinetic parameters at the steady state of continuous cultures of two strains of S. cerevisiae (S1 and S2) fed with agave juice at different dilution rates (D).

phosphorus supplementation on S. cerevisiae S1 sugar consumption

Since both S. cerevisiae strains were unable to consume sugars efficiently in cultures fed at D higher than 0.04 h-1, a nutritional limitation and/or some inhibitory substances formed in the agave cooking step (Maillard compounds), which can act on S. cerevisiae strain activity. In fact, Agave tequilana juice is deficient in nitrogen sources (Table 3). Amino acids are the most important nitrogen source in agave juice; however, their natural concentrations (0.02 mg N/L) are not enough to support balanced yeast growth and the complete fermentation of sugars [26]. Therefore, agave juice supplemented with ammonium sulfate at 1 g/L could be insufficient. Several authors point out the importance of nitrogen sources (type and
concentration) for achieving a complete fermentation, since they improve cell viability, yeast growth rate, sugar consumption and ethanol production (11; 20). It is worth noting that ammonium phosphate (AP) was chosen as a nitrogen source, since the two macronutrientes frequently implied in the causes of stuck fermentation when present in small quantities are nitrogen and phosphate (see the reviews by Bisson [11]).

Therefore, the effect of the ammonium phosphate (AP) addition on S. cerevisiae S1 sugar consumption was studied in a continuous culture (Figure 8). To study the effect of nitrogen and phosphorus source addition on the agave juice fermentation by S. cerevisiae, S1 strain was used and fermentation medium was fed at D of 0.08 h-1, while after the steady state was reached, the ammonium phosphate (AP) concentration was gradually increased, as follows: 1g/L (first addition), 2 g/L (second addition), 3 g/L (third addition) and 4 g/L (fourth addition).

The fermentation was started in batch mode using the fermentation medium. After 12 h, the culture was fed using medium supplemented with 1 g/L of AP (first addition). At the steady state, residual concentrations of sugars and ammonium nitrogen were 29.42 and 0.08 g/L, respectively. These results were not significantly different (p>0.05) from the condition previously tested for the same strain (at D = 0.08 h-1), feeding an unsupplemented fermentation medium (Figure 5).

Figure 8. Effect of the addition of ammonium phosphate to the agave juice fed to S. cerevisiae S1 chemostat culture (at D=0.08 h-1), on the consumptions of reducing sugars (□) and ammonium-nitrogen (0). First addition: 1 g/L; Second addition: 2 g/L; Third addition: 3 g/L; Fourth addition: 4 g/L.

Those residual concentrations of reducing sugars (high) and ammonium nitrogen (low) indicate the necessity of adding more AP. At the steady states of the second (2 g/L), third (3 g/L) and fourth (4 g/L) additions of AP, the residual sugars concentrations were 25.96, 21.25 and 17.60 g/L, respectively. This indicates that the residual ammonium nitrogen concentrations were 0.31, 0.36 and 1.29 g/L, respectively; indicating that the AP addition improved S. cerevisiae S1 fermentative capability, but other nutritional deficiencies still existed [27].

Effect of the micro-aeration rate on S. cerevisiae S1 fermentative capability — Lack of oxygen has proved to be a main limiting factor to fermentation [11], since yeasts require low amounts of oxygen for synthesizing some essential lipids to assure cell membrane integrity [28]. Because S. cerevisiae is Crabtree-positive, alcoholic fermentation is privileged in culture media containing high sugars concentrations, even in the presence of oxygen [29]. The effect of the micro-aeration rate (0, 0.01 and 0.02 vvm) on the fermentative capacity of S. cerevisiae S1 (at D = 0.08 h-1) was studied for investigating the yeast oxygen requirement during the continuous fermentation, using the last fermentation medium supplemented with 4 g/L of AP for feeding at D of 0.08 h-1. Biomass and ethanol concentrations increased as air flow increased, reaching at the steady state, 5.66, 7.18 and 8.04 g/L, and 40.08, 44.00 and 45.91 g/L, respectively for 0, 0.01 and 0.02 vvm (Figure 9).

Figure 9. Concentration of Residual reducing sugar, Ethanol and Biomass at the steady state of continuous culture of two strains of S. cerevisiae S1 fed with agave juice (D = 0.08 h-1) at different micro-aeration rates. Data are presented as mean ± standard deviation of four assays at the steady state.

Meanwhile, residual sugars decreased as micro-aeration increased, reaching 17.67, 10.71 and 4.48 g/L, respectively for 0, 0.01 and 0.02 vvm; showing an improvement in the fermentation process due the dissolved oxygen in the must. However, statistical differences were not found in biomass and ethanol yields at the different tested aeration rates (p>.05) (Table 6). In addition, sugars consumption rates and ethanol and biomass productions increased as micro-aeration increased, achieving a faster fermentation (Table 6). These results were in accordance to those reported by Diaz-Montano [20]. Viability of the S1 strain was 100% in aeration experiments.

Glycerol is a metabolite providing yeast metabolic activity information. In fact, yeasts produce glycerol mainly for reoxidating the NADH generated by glycolysis. Since the citric acid cycle and the respiratory chain are slightly activated by micro-aeration, NAD might be partially regenerated, and consequently, glycerol concentration decreases [30]. However, in this work, glycerol concentration increased as aeration increased (Table 6). Given that
biomass concentration and fermentation efficiency also increase as aeration increases, glycerol production could contribute to faster NAD regeneration.



Micro-aeration rates




Yx/S (g/g)

0.06 ± 0.00

0.07 ± 0.00

0.08 ± 0.00

Yp/S (g/g)

0.48 ± 0.01

0.49 ± 0.00

0.48 ± 0.01

rx (g/Lh)

0.45 ± 0.01

0.57 ± 0.00

0.64 ± 0.01

rS (g/Lh)

6.55 ± 0.08

7.14± 0.02

7.64 ± 0.05

rP (g/Lh)

3.21 ± 0.03

3.52 ± 0.02

3.67 ± 0.04

Yx/s: yield of biomass, Yp/s: yield of ethanol, rx: growth rate, rs: reducing sugars consumption rate, rp: ethanol production rate. Data are presented as the mean ± standard deviation of four assays at each steady state.

Table 6. Kinetic parameters of S. cerevisiae S1 continuous cultures at steady state fed with agave juice (D = 0.08 h-1) at different micro-aeration rates.

Catalytic brown coal gasification

It is very important to increase the thermal efficiency of coal conversion for not only protecting the limited coal resources but also reducing CO2 and air pollutant emission. Steam gasification of coal is one of the most promising energy conversion technologies for producing hydrogen.

Current development in cellulosic bioethanol

At present, much focus is on the development of methods to produce higher recovery yield bioethanol from lignocellulosic biomass. This can be done through two methods; (1) use of pre-treatment to increase the readiness of lignocellulosic biomass for hydrolysis. (2) increase the conversion yield of lignocellulosic biomass into bioethanol through simultaneous fermentation of glucose and xylose into bioethanol.

As mentioned, one barrier to the production of bioethanol from biomass is that the sugars necessary for fermentation are trapped inside the lignocellulosic biomass. Lignocellulosic biomass has evolved to resist degradation and to confer hydrolytic stability and structural robustness to the cell walls of the plants. This robustness is attributable to the crosslinking between the polysaccharides (cellulose and hemicellulose) and the lignin via ester and ether linkages. Ester linkages arise between oxidized sugars, the uronic acids, and the phenols and phenylpropanols functionalities of the lignin. The cellulose fraction can be only hydrolysed to glucose after a pre-treatment aiming at hydrolytic cleavage of its partially crystalline structure. A number of pre-treatment methods are now available — steam explosion, dilute acid pre-treatment [31] and hydrothermal treatment [32]. Hydrothermal treatment prevent the degradation of cellulose content inside the lignocellulosic biomass during pre-treatment because hydrothermal can be performed without addition of chemicals and oxygen to the lignocellulosic biomass. Hydrothermal treatment involves two process where during the first process, lignocelluosic biomass was soaked in water at 80 °C to soften it before being treated in the second process with higher temperature at 190-200°C.

Another way to increase the recovery yield of bioethanol from lignocellulosic biomass is to convert every bit of biomass into bioethanol. This means using all the available sugars from cellulose and hemicelluose and fermented into bioethanol. Lignocellulosic biomass have high percentage of pentoses in the hemicellulose, such as xylose, or wood sugar, arabinose, mannose, glucose and galactose with majority sugar in hemicelluloses is xylose which account more than 90% present. Unlike glucose, xylose is difficult to ferment. This meant that as much as 25% of the sugars in biomass were out of bounds as far as ethanol production was concerned. At the moment, research shows that steam explosion or mild acid treatment performed under adequate temperature and time of incubation, render soluble the biomass hemicellulose part with the formation of oligomers and C5 sugars that are easily extracted from the biomass. The C5 sugar stream can be individually fermented to ethanol by microorganisms such as E. coli, Pichia stipitis and Pachysolen, that are able to metabolise xylose, or be used as carbon source in a variety of other fermentative processes [33].