Thermo-gravimetric analysis (TGA) was used to trace the fine dynamics of conversion (mass transfer) of small-size fuel particle (Bi < 0.1) at controlled temperature in thermally inert medium with hindered oxygen access (which prevent particle overheating and its premature burn-out) and mass transfer correlation having the value and sign of thermal effect. Experiments were performed at installation Q1500D (Hungary) according to standard procedure in air medium (ground fuel sample weight was 100 mg, inert medium charge — 400 mg, temperature rise at a speed of 0.3 K/ s, and final temperature 1000оС). The samples were wood particles, seeds and charcoal, products of their fast and slow thermal treatment by above described procedure and soot from ash box of pilot downdraft gas producer. Thermograms are shown in fig. 4.

Since the samples were actually dry, weight loss was mainly determined by coke-ash residue pyrolysis and oxidation effects. Overheating value and the sign of thermal effect were due to oxidizing exothermic processes in volatiles emitted by coke-ash residue (except the initial stage).

Steady heterogeneous burning of carbon of ground charcoal and coke-ash residue of bio fuels started at medium temperature above 350оС. For charcoal and wood particles this process is distinguished by appearance of specific temperature peak at 500оС. On having passed the peak, the burning of charcoal becomes uniform and finishes with some exposure at Т = 1000оС. Overheating curve for wood particles reproduces charcoal curve in shortened variant.

For seeds the pattern differs radically from above cited. In this case there is no overheating in the domain of volatile emission (which is weaker than with wood particles) which means that they behave like chemically inert substances. It is only at Т > 370оС the temperature of seed sample begins to exceed the ambient one. However, it exhibits its specific nature in this range too. Burnout curve for seeds has a low and extended (truncated) peak and a bit greater overheating in steady burning domain. Hence, the pyrolysis may be described as time extended process running in parallel with heterogeneous oxidation of coke-ash residue approximately up to 750оС.

After preliminary thermal treatment according to thermal shock scenario during 15-20 minutes at 400, 600, 800оС the following was found:

Wood after thermal treatment at heating rate of 200 К/20 min retains the peak of volatile emission at 342оС, but the first ("gas") preheating peak disappears, the height of the second peak (coke-ash residue burning) increases but the peak appears with a shift towards higher temperature domain (585оС); conversion process (weight loss) completes earlier (at 706оС instead of 850оС). Hence, the preliminary heating of fossil fuel improves its reactivity. Charcoal after thermal treatment in thermal shock conditions during 15-20 min at 400, 600, 800оС showed that increase of thermal treatment temperature resulted in the shift of coke — ash residue peak occurrence (at 496оС instead of 462оС), heating value and conversion rate were lower, process time and final temperature were rising and the fuel partially seized to burn.

Thus, in case of thermal treatment at 400 К / 20 min the moment of coke-ash residue burn­out coincide with the moment when maximum temperature is achieved in the plant (1000оС), whereas after thermal treatment at 800 К / 15 min the burning process finishes with incomplete burn out (unburned carbon of 9%) and much later after the furnace has been warmed up to maximum.

Charcoal after thermal treatment according to "heating simultaneously with furnace" scenario is characterized by still lower burn out rate and greater unburned carbon (14%) at the same final temperature values. The behavior of solid-phase volatile decomposition products settling in gas generator ash box (soot) is alike. Inert component content in these products (due to specific sampling conditions) reaches 50%, therefore the burn-out process finishes earlier which corresponds to 800оС.

Once that the adsorbent is selected to perform a given CH4-CO2 separation under specific operating conditions (T, P, yCO2), there are only few actions that can be taken to make the adsorption step more efficient (dealing with energy transfer, for example). When designing the upgrading PSA, the most important task is to make desorption efficiently.

The initial work reporting Pressure Swing Adsorption technology was signed by Charles W. Skarstrom in 1960 (Skarstrom, 1960). A similar cycle was developed by Guerin — Domine in

1964 (Guerin and Domine, 1964). The Skarstrom cycle is normally employed as a reference

to establish the feasibility of the PSA application to separate a given mixture.

The Skarstrom cycle is constituted by the following cyclic steps:

1. Feed: the CH4-CO2 mixture is fed to the fixed bed where the adsorbent is placed. Selective adsorption of CO2 takes place obtaining purified CH4 at the column product end at high pressure.

2. Blowdown: immediately before CO2 breaks through, the column should be regenerated. This is done by stopping the feed step and reducing the pressure of the column counter­currently to the feed step. Ideally, this step should be carried out until a new equilibrium state is established as shown in Figure 1. However, the blowdown step is stopped when the flowrate of CO2-rich stream exiting the column is small. With the reduction of pressure, CO2 is partially desorbed from the adsorbent. In this step, the lowest pressure of the system is achieved.

3. Purge: when the low pressure is achieved, the column will have CO2 molecules in the adsorbed phase but also in the gas phase. In order to reduce the amount of CO2 in both phases, a purge step is performed counter-current to feed step. In the purge, some of the purified methane is recycled (light recycle) to displace CO2 from the CH4 product end.

4. Pressurization: Since the purge is also performed at low pressure, in order to restart a new cycle, the pressure should be increased. Pressurization can be carried out co­currently with the feed stream of counter-currently with purified CH4. The selection of the pressurization strategy is not trivial and may lead to very different results (Ahn et al., 1999).

Fig. 6. Schematic representation of the different steps in a Skarstrom cycle. The dotted line represents the external boundary used to calculate performance parameters.

A schematic representation of the different steps of one column in a single cycle is shown in Figure 6. Note that in this image an external boundary was established. This boundary is used to define the performance parameters of the PSA unit: CH4 purity, CH4 recovery and unit productivity. They are calculated using the following equations:

where CCH4 is the concentration of methane, u is the velocity, tcycle is the total cycle time, Acoi is the column area and wads is the total adsorbent weight. Note that the calculation of CH4 recovery and unit productivity involves the molar flowrates of the different steps where some CH4 is recycled. In the case of changing the cycle configurations, the equations to calculate the process parameters may also be different.

In the cycle developed by Guerin-Domine, a pressure equalization step between different columns take place between feed and blowdown and after the purge and the pressurization. The pressure equalization steps are very advantageous for PSA applications since they help to improve the recovery of the light product, they reduce the amount of gas lost in the blowdown step and as a direct consequence, the purity of the CO2-rich stream obtained in the blowdown (and purge) steps increases and also less power is consumed if blowdown is carried out under vacuum. It should be mentioned that in the PSA process for biogas upgrading, it is important to perform some pressure equalization steps to reduce the amount of methane that is lost in the blowdown step. The amount of CH4 lost in the process is termed as CH4 slip and in PSA processes is around 3-12% (Pettersson and Wellinger, 2009). More advanced cycles for other applications also make extensive use of the equalization steps: up to three pressure equalizations between different columns take place in H2 purification (Schell et al., 2009; Lopes et al., 2011). As an example, in Figure 7, the pressure history over one cycle is shown for the case of a two-column PSA process using a modified Skarstrom cycle with one pressure equalization step (Santos et al., 2011). Continuing with the example of CMS-3K as selective adsorbent for biogas upgrading, the cyclic performance of a Skarstrom cycle is shown in Figure 8. In this example, the feed was a stream of CH4 (55%) — CO2 (45%) resembling a landfill gas (T = 306 K), with a feed pressure of 3.2 bar. The blowdown pressure was established in 0.1 bar and pressurization step was carried out co-current with feed stream (Cavenati et al., 2005). Figure 8(a) shows the pressure history over one entire cycle while Figure 8(b) shows the molar flowrate of each gas exiting the column. It can be seen that in the feed step, a purified stream of CH4 is obtained. In this experiment, the purity of CH4 was 97.1% with a total recovery of 79.4%

(Cavenati et al., 2005). An important feature of the CMS-3K adsorbent is related to the very slow adsorption kinetics of CH4. In Figure 8(c) the simulated amount of CH4 adsorbed is shown. It can be observed that after reaching the cyclic steady state (CSS), the loading of CH4 per cycle is constant: this means that no CH4 is adsorbed in the column. This is very important since no CH4 will be adsorbed in the pressurization step, even with a very strong increase in its partial pressure. Unfortunately, the narrow pores also make CO2 adsorption (and desorption) difficult, reason why only part of the capacity of the bed is employed as shown in Figure 8(d) resulting in small unit productivity.

Fig. 7. Scheduling of a Skarstrom cycle in a two column PSA unit: (a) step arrangement: 1. Pressurization; 2. Feed; 3. Depressurization; 4. Blowdown; 5. Purge; 6. Equalization. (b) Pressure history of both columns during one cycle.

As can be seen, an important amount of CH4 is lost in the blowdown step, since there is no pressure equalization: pressure drops from 3.2 bar to 0.1 bar having at least 55% of CH4 in the gas phase. The main problem of using the Skarstrom cycle for biogas upgrading is that the CH4 slip is quite high. Since the Skarstrom cycle is potentially shorter than more complex cycles, the unit productivity is higher. Keeping this in mind, it may be interesting to employ this cycle in the case of combining the production of fuel (bio-CH4) and heat or electricity where the gas obtained from the blowdown step can be directly burned or blended with raw biogas.

In order to avoid large CH4 slip, at least, one pressure equalization should be employed to reduce the amount of methane in the gas phase that is lost in the blowdown stream. If such step is performed, it is possible to increase the methane recovery from 79.4% to 86.3% obtaining methane with a similar purity (97.1%). It can be concluded that the increase of number of equalization steps will reduce the methane lost in the blowdown step. Furthermore, if less gas is present in the column when the blowdown step starts, the vacuum pump will consume less power. However, to perform multiple pressure equalizations, the number of columns and the complexity of operation of the unit increase. Furthermore, the time required by the multiple pressure equalization steps will reduce the unit productivity resulting in larger units. A trade-off situation is normally achieved in PSA units with four-columns employing up to two pressure equalization steps before blowdown (Wellinger, 2009).

Another source of CH4 slip is the exit stream of the purge step: in the purge, part of the purified CH4 stream is recycled (counter-currently) to clean the remaining CO2 in the column. Since CH4 is not adsorbed, after a short time it will break through the column. However, if the purge step is too short, the performance of the PSA cycle is poor. In order to achieve very small CH4 slip keeping an efficient purge, one possible solution is to recompress and recycle this stream (Dolan and Mitariten, 2003). Furthermore, if this stream is recycled, the flowrate of the purge can be used to control the performance of the PSA cycle when strong variations of the biogas stream take place (CO2 content or total flowrate).

The European and Asian strategy to improve climate change and fossil fuel depletion problems is based mainly on the chemically catalyzed biodiesel obtained from vegetable oils. There is a variety of feedstocks for the production of this biofuel, from inedible oils, (mainly rapeseed oil in Europe or jatropha oil in Asia), to edible oils (principally sunflower oil in Europe and palm oil or soybean oil in Asia, although corn, peanut, cotton seed or canola oil can also be cited) (Ranganathan et al., 2008; Abdullah et al., 2009). As the elected method for industrial biodiesel production is chemical catalysis, these vegetable oils are preferred to other heterogeneous lipids sources. These other lipids need pretreatment prior to their use (Peterson, 1986; Fortman et al., 2008), and include waste frying oils, waste — activated bleaching earth from the oil refinery industry, and even animal origin lipids such as beef tallow, lard, yellow grease and poultry grease or fat from fat traps, septic tanks, or waste water sludges. The need for economically viable vegetable oils for biodiesel production implies the cultivation of greater areas with oil-producing crops such as sunflowers or palm oil trees. Thus, the previously mentioned rising corn prices, owing to the derivation of huge amounts of grain for the industrial production of bioethanol, is neither an isolated case in developing biofuel industries nor the only aspect of the biofuel industry issue. Like the bioethanol industry, the European and Asian biodiesel industries have the energy and chemical problems associated with the current biofuels model. These limitations can be summarized according to nearly obsolete technology, being strongly dependent on chemical catalysis, non-renewable materials and promotion of non­sustainable market and farming practices (Guerrero-Compean, 2008; Demirba§, 2009; UNCTAD, 2010).

Considering the above discussion on the properties, it is obvious that the fuel quality of bio­oils is inferior to that of petroleum-based fuels. There have been intensive studies on bio-oil upgrading research and various technologies have been developed for bio-oil upgrading. Table 4 summarizes current techniques in bio-oil upgrading. The characteristics, as well as recent progress, advantages, and disadvantages of each technique are also described as follows:

Biodiesel has the advantage that it can be used in any diesel engine without modification. It is produced by the transformation of renewable oils, such as those synthetized by plants, algae, bacteria and fungi. First-generation biodiesel is considered to be the result of a two- stage process that involves (i) the crushing of raw material (typically oilseeds) in specialized mills to expel the oils and (ii) the transformation of oil into biodiesel. Free fatty acids (FFA) or triglycerides are converted into alkyl-esters by reaction with short-chain alcohols (such as methanol or ethanol) in the presence of a catalyst. The reaction involved in the conversion of FFA to alkyl-esters is called esterification, whereas that involved in the conversion of triglycerides is called transesterification. Fatty acid methyl-esters are only partly biological, as the methanol involved is generally produced from fossil methane (natural gas). However, biodiesel can also be produced by replacing methanol with ethanol, resulting in fatty acid ethyl-esters. If the ethanol is of biological origin, the product is fully biological. The purpose of the transesterification process is to lower the viscosity of the oil with transesterification being less expensive than the pyrolysis that is used in bio-oil processing. According to the EU standards for alternative diesel fuels, alkyl-esters in biodiesel must be >96.5 wt%.

The previous sections show the rapeseed production, the rapeseed processing to obtain oil and the use of the cake meal obtained from the seed processing. This information can be
used to develop a cropping model that comprises the introduction of rapeseed to the current agricultural rotation based on wheat and barley (WBBB, where W stands for wheat and B for barley). The proposed rotation would preserve the 3 years of barley after one year of wheat in each field portion adding on year rapeseed prior to wheat (RWBBB). The introduction of rapeseed increases the two next following crop yields by 10% (wheat) and 3% (barley) for normal weather conditions. Additionally to the introduction of rapeseed to the rotation, the processing of the seed into oil and cake meal would allow its use as straight vegetable oil to fuel the exploitation tractor.

The proposed model for small-scale biofuel self consumption exploitations is graphically represented in Fig. 4, where the basis model, the rapeseed processing and the fate of the different products obtained are shown.

In order to design this model some hypotheses have to be made. First of all, small-scale producers are considered. The mean farmer is supposed to work an arable land of about 100 ha. The proposal involves using approximately 10% of the arable land for self-supply. In the studied area, as a dry Mediterranean zone, irrigated lands are nearly inexistent, being the traditional sowed crops wheat and barley. It is proposed to cultivate rapeseed as a dry crop in order to avoid putting pressure on water resources. Secondly, the system of crop-rotation jointly with direct seeding is going to be applied. Thus, rapeseed can be seeded in the same land one out of five years. Only the seeds are extracted whereas the rest of the plant is crushed while gathering the seed and left on the fields to be rot. Doing so, the soil recovers part of the nutrients contained in the straw from the plant, thus avoiding the use of some amount of fertilizer. Finally, the farmers bring the harvest to the farmer’s cooperative, which is located near their lands and where there is an industrial press for extracting the oil of the rapeseed harvest.

Important institutions such as the Food and Agriculture Organization (FAO) of the United Nations support good agricultural practices to mitigate negative impacts, in particular on carbon, soil and water resources. Among such practices we find no tillage and direct seeding, retention of soil cover, multiple cropping, appropriate crop choice and crop rotations. There are mainly three systems of harvest namely traditional seeding, minimum cultivation and direct seeding that nowadays coexist in the studied area, being direct
seeding the chosen one for its lower impact, better carbon retention in soil and reduced fuel consumption.

General assumptions are made in this model. For example, the press is assumed to extract in average 80-85% of the total oil content from the seeds. This means that after pressing, seeds are converted in a 35% of oil and a 65% of meal cake. Additionally, according to a survey answered by farmers in the Anoia area (EUETII-UPC, 2010), the average yield of the rapeseed harvest in this area is a minimum of about 2300 kg of rapeseed/ha.

Supposing a direct harvesting system of cultivation, the fuel consumption would be about 7000 l per 100 ha. As explained, the production of rapeseed SVO is supposed to be 875 l per ha. Therefore, dedicating 10% of the arable land to cultivating rapeseed is enough for self fuel supply. Also there is a small excess of SVO that could be sold for other needs. Vegetable oils can be also used in the production of additives that are useful for various industrial purposes as pointed out by (Hancsok et al., 2008). The 15000 kg of rapeseed cake per 10 ha would be used to feed the animals in this area as calculated in section 5.

Vegetable oils are expensive and require large areas of farmland for their production, so the direct usage of these oils for biodiesel production is expensive and unsustainable. However, there are multiple and as yet unexploited alternative fatty acid sources. Similarly, bioethanol production for its direct use as a biofuel or as a biodiesel precursor requires huge amounts of corn grain or sugar cane. Nevertheless, industrial residues such as the vegetable oil refinery waste, as well as farming, forestry, livestock and domestic solid and liquid waste (Chen et al., 2009; Dizge et al., 2009) are widespread and huge sources of lipids and carbon. Wang et al. proposed the soybean oil deodorizer distillate (SODD), a by-product from the soybean oil refineries that represents 0.3-0.5% of the soybean oil processed, to produce biodiesel. With 45-55% of triglycerides and 25-35% of free fatty acids, these authors estimated that around 80% of the SODD can be transformed into biodiesel in a transesterification with methanol by the Thermomyces lanuginosa and Candida antarctica lipases in the presence of tertbutanol and 3A molecular sieve (Wang et al., 2006). Park et al.

used waste-activated bleaching earth (ABE), a residue of the rapeseed or palm oil refinery industry that stores 35-40% of oil and can be used to synthesize multiple bulk chemicals, including biodiesel. As in the Wang example, these authors chose methanol as alcohol, but their solvent choice was fuel oil and kerosene, the catalyst was Candida cylindracea lipase and the obtained FAME was extracted with a filter press (Park et al., 2008). Al-Zuhair and colleagues studied the production of biodiesel from simulated waste cooking oil (SWCO) with free — and immobilized — on ceramic beads Candida antarctica and Burkholderia cepacia lipases, with or without organic solvent. They obtained the best yield when they used B. cepacia without organic solvent, and observed that the system worked better when the enzymes were immobilized, probably because the clay structural microenvironments offered the lipases protection against the methanol derived denaturation (Al-Zuhair et al., 2009). Recently, Steen et al., among others, have proposed the direct fermentation of cellulosic biomass to produce biodiesel, fatty alcohols, waxes and other valuable chemicals (Steen et al., 2010). Their approach combines the waste management and the guidelines defined by Steinbuchel et al. with the new trends in synthetic biology and consolidated bioprocesses. This multidisciplinary approach brings a new flexible, easy-to-modify toolbox, composed of genetically modified FAEE synthetic strains, harbouring the enzymatic apparatus needed to produce ethanol from raw (hemi)cellulosic materials, to transesterificate it with fatty acids, or to synthesize both the fatty acids and the ethanol directly from the cellulose (Steen et al., 2010).

The digestate, the waste from digesters during biogas production, is composed of solid phase and liquid phase (fugate). We have demonstrated that the solid phase of the digestate is not an organic fertilizer because its organic matter is very stable and so it cannot be a relatively expeditious source of energy for the soil microedaphon (Kolar et al. 2008). Neither is it a mineral fertilizer because available nutrients of the original raw material and also nutrients released from it during anaerobic digestion passed to the liquid phase — fugate. The digestate, and naturally the fugate, have a low content of dry matter (fugate 0.8 — 3% by weight) and this is the reason why analytical data on the ones to tens of weight % of available nutrients given in dry matter foster an erroneous opinion in practice that these wastes are excellent fertilizers. In fact, fugates are mostly highly diluted solutions in which the content of the nutrients that are represented at the highest amount, mineral nitrogen, is only 0.04 — 0.4% by weight.

The surplus of water during fertilization with this waste increases the elution of this nutrient in pervious soils while in less pervious soils the balance between water and air in the soil is impaired, which will have negative consequences.

The quality of the digestate as an organic fertiliser (labile, not organic material that is hard to decompose) substantially influences not only the microbial decomposability of the input material but also the level of anaerobic digestion in the digester. In the past when the sludge digestion was carried out in municipal waste treatment plants in digesters at temperatures of 18°C-22°C (psychrophilic regime), the decomposability of the substrate after fermentation was still good, therefore the digested sludge was a good organic fertiliser. These days we work with less decomposable substrates in mesophilic ranges (around 40°C) or even in thermophilic conditions. The degree of decomposition of organic matter during fermentation is consequently high and the digestate as organic fertiliser is practically worthless.

Electricity is the foundation of modern societies, yet more than 1.6 billion people remain without access to the electrical grid. A majority of this population lives in South Asia and sub-Saharan Africa. Despite global economic expansion and advances in energy technologies, roughly 1.4 billion people (or 18% of the world’s population) will still be without power by 2030 unless major governmental incentives are put into place (Dorian et al., 2006).

The world average annual electricity consumption is between 2 and 4 TW. The cost of fossil- derived electricity is now in the range of US$ 0.02-0.05/kW/hr, including storage and distribution costs (Lewis & Nocera, 2006). For comparison, the options of non-biological electricity generation are as follows. (i) The light-water reactors that make up most of the world’s nuclear capacity produce electricity at costs of US$ 0.025-0.07/kW/; however, there is no consensus as to the solution to the problem of how to deal with the nuclear wastes that have been generated in nuclear power plants over the past 50 years (Schiermeier et al., 2008). (ii) Hydroelectric energy sources have a generating capacity of 800 GW (i. e., 10 times more power than geothermal, solar and wind power sources combined) and currently supply approximately one-fifth of the electricity consumed worldwide. Annual operating costs are US$ 0.03-0.10/kW/h, which makes such sources competitive with coal and gas. Because only approximately 30% of worldwide hydroelectric capacity is currently used, energy from these sources can still be tripled (Schiermeier et al., 2008). (iii) Wind turbines can produce 1,500 kW at US$ 0.05-0.09/kW/h making wind competitive with coal; wind power could provide up to 20% of the electricity in the grid. The EU should be able to meet 25% of its current electricity needs by developing wind power in less than 5% of the North Sea and is heavily investing in that option. (iv) Exploitation and resulting use of the best geothermal sites is estimated to cost approximately US$ 0.05/kW/h. Thus, 70 GW of the global heat flux is seen as exploitable. However, because of the great deal of investment required, exploitation of geothermal power lies outside of current priorities except in regions with significant volcanic activity (Schiermeier et al., 2008). (iv) Commercial photo­voltaic (PV) electricity costs US$ 0.25-0.30/kW/h, which is still 10 times more than the current price of electricity on the grid.

The possibility for use of current PV technology is limited to 31% by theoretical considerations. A conversion efficiency of >31% is possible if photons with high energies are converted to electricity rather than to heat. With use of such technology, the conversion efficiency could be >60% (Lewis, 2007). The absence of a cost-effective storage method for solar electricity is also a major problem. Currently, the cheapest method of solar-energy capture, conversion, and storage is solar thermal technology, which can cost as little as US$ 0.10-0.15/kW/h for electricity production. This requires the focusing of the energy in sunlight for syngas or synfuel synthesis (Lewis & Nocera, 2006) or its thermal capture by heat-transfer fluids that are able to sustain high temperatures (>427 °С) and resulting electricity generation through steam production (see in Shinnar & Citro, 2006). Solar power is among the most promising carbon-free technologies available today (Schiermeier et al., 2008). The earth receives approximately 100,000 TW of solar energy each year. There are areas in the Sahara Desert, the Gobi Desert in central Asia, the Atacama in Peru and the Great Basin in the US that are suitable for the conversion of solar energy to electricity. The total world energy needs could be fed using solar energy captured in less than a tenth of the area of the Sahara. Residential and commercial roof surfaces are already being used in several countries to allow the people to sell their own PV electricity to the grid (and in this way saving substantial annual costs). This elegant strategy could be extended to other systems of energy production.

The capital costs of biomass are similar to those of fossil fuel plants. Power costs can be as little as US$ 0.02/kW/h when biomass is burned with coal in a conventional power plant. Costs increase to US$ 0.04-0.09/kW/h for a co-generation plant, but the recovery and use of the waste heat makes the process much more efficient. The biggest problem for new biomass power plants is finding a reliable and concentrated feedstock that is available locally. Biomass production is limited by land-surface availability, the efficiency of photosynthesis, and the water supply. Biomass potential is estimated at ~5 TW (Schiermeier et al., 2008). Photosynthesis is relatively inefficient if one considers that in switchgrass (one of the fastest — growing crops), energy is stored in biomass at an average rate of <1 W/m2/ yr. Given that the average insolation produces 200-300 W/ m2, the average annual energy conversion and storage efficiency of the fastest growing crops is only <0.5% (Lewis 2007; Lewis & Nocera,

2006) . However, photosynthetic efficiency can be improved by genetic engineering (Ragauskas et al., 2006). Another potential problem with biomass production is that it could result in an increase of water consumption of two to three orders of magnitude. This is an important consideration because basic human necessities and power generation are increasingly competing for water resources (King et al., 2008).

The potential availability of wind (Pryor & Barthelmie, 2010), solar and biomass energy varies over time and location. This variation is not only caused by the individual characteristics of each resource (e. g., wind and solar regimes, soils), but also by geographic (land use and land cover), techno-economic (scale and labor costs) and institutional (policy regimes and legislation) factors (de Vries et al., 2007). The regional potential in energy units/year must be integrated over the geographical units that belong to a particular region. The model from de Vries et al. (2007) showed the following: (i) electricity from solar energy is typically available from Northern Africa, South Africa, the Middle East, India, and Australia; (ii) wind is concentrated in temperate zones such as Chile, Scandinavia, Canada, and the USA; (iii) biomass can be produced on vast tracts of abandoned agricultural land typically found in the USA, Europe, the Former Soviet Union (FSU), Brazil, China and on grasslands and savannas in other locations. In many areas of India, China, Central America, South Africa and equatorial Africa, these energy sources are available at costs of below US$ 0.1/kW/h and are found in areas where there is already a large demand for electricity (or there will be such demand in the near future). A combination of electricity from wind, biomass and/or solar sources (Eugenia Corria et al., 2006) may yield economies-of-scale in transport and storage systems. Regions with high ratios of solar-wind-biomass potential to current demand for electricity include Canada (mainly wind), African regions (solar-PV and wind), the FSU (wind and biomass), the Middle East (solar-PV) and Oceania (all sources). In other region (such as Southeast Asia and Japan), the solar-wind-biomass supply is significantly lower than the demand for electricity. Ratios of around one are found in Europe and South Asia. The potentials just described depend on many parameters, and their achievement will depend on future land-use policies (de Vries et al., 2007; Miles & Kapos, 2008).

2. Management and sustainability

Adam Smith’s notion that by pursuing his own interest a man "frequently promotes that of society more effectively than when he really intends to promote it" and Karl Marx’s picture of a society in which "the free development of each is the condition for the free development of all" are both limited by one obvious constraint. The world is finite. This means that when one group of people pursues its own interests, it damages the interests of others (Vertes et al., 2006). The model of Western economies was established using this logic. The theoretical framework of this philosophy is a mathematical model that is based on energy-conservation equations formulated by von Helmholtz in 1847, in which physical variables were arbitrarily substituted by economic ones. The consequences of this model are as follows: (i) the market is a closed circular flux between production and consumption, without inflows or outflows; (ii) natural resources are located in a domain that is separate from that of the closed market system; (iii) the costs of environmental destruction because of economic activities must be considered as unrelated to the closed market system (or at least they cannot be included in the price-formation processes of that system); (iv) the natural resources that are used by the market system are endless and those that are limited in quantity can be substituted by others that are endless; and (v) biophysical limits to the increase of the market system simply do not exist (Nadeau, 2006). This model is obsolete and is based on hypotheses that have no grounding in scientific bases. Sustainable economic solutions to global warming and environmental destruction are impossible to establish under the logic of this model.

As a consequence, the US alone has reached a level of oil consumption in the transportation sector that approaches 14 Mbl/ day and corresponds to a release of 0.53 gigatons of carbon per year (Gt C/yr). The current global release of carbon from all fossil fuel usage is estimated to be at 7 Gt C/ yr and is expected to rise to ~14 Gt C/yr by 2050 (Agrawal et al.,

2007) . It has been estimated that global energy consumption could reach 30-60 TW by 2050. With world population expected to reach 8 billion by 2030, the scale-up in energy use that is needed to maintain economic growth is critical. China, with 1.3 billion people and a fast­growing economy, has overtaken Japan to become the second-largest oil consumer behind the US. The Asian giant is currently the largest producer and consumer of coal (Tollefson,

2008) and has announced the construction of 24-32 new nuclear reactors by 2020 (Dorian et al., 2006). If current trends continue, the world will need to spend an estimated $16 trillion over the next three decades to maintain and expand its energy supply. Generation, transmission, and distribution of electricity will absorb almost two-thirds of this investment, whereas capital expenditures in the oil and gas sectors will amount to almost 20% of global energy investment.

Experts believe that peak of world oil production should not occur before at least 30-40 years from now. To put global oil needs into perspective, demand for oil is projected to rise from nearly 80 Mbl/day today to over 120 Mbl/day by 2030. The OPEC nations are currently operating at near full capacity, which caused oil prices to reach US$ 120/bl in August 2008. Clearly, the world must find more efficient ways to manage energy. Some argue that the supplies of oil needed to satisfy the growing world demand will become available because of a combination of price and technology incentives (Rafaj & Kypreos, 2007). As oil prices continue to rise because of increasing difficulties in reaching remaining oil resources, other energy forms will appear (Herrera, 2006). A transition from oil to renewable energy should occur at some point before the world runs out of oil resources (Dorian et al., 2006). Renewable energy sources, including solar, wind, and geothermal, but excluding biofuels, currently provide only 3% of world energy demand (Dorian et al., 2006). Solutions that use these energy sources should be increased worldwide and should be connected to the electricity grid.

Renewable biodiesel from palm oil and bioethanol from sugarcane are currently the two leaders of plant bioenergy production per hectare. They are being grown in increasing amounts; however, continuous increases in their production are not sustainable and will not resolve the enormously increasing demands for energy. Palm oil yields ~5,000 l/ha. In Brazil, the best bioethanol yields from sugarcane are 7,500 l/ha. Most of the energy needed for growing the sugarcane and converting it to ethanol is gained from burning its wastes (e. g., bagasse). For every unit of fossil energy that is consumed by producing sugarcane ethanol, ~8 units of energy are recovered (Bourne, 2007). The rates of energy recovery from other biofuel crops are usually less than 5. Biofuel crops from the EU are much less productive than palm oil and sugarcane; therefore, B5 enforcement would require that ~13% of the EU25 arable land be dedicated to biofuel production. This is hardly sustainable (the present situation is ~5 times less).

Regarding environmental impact, ethanol from corn (for example) contains costs that stem from the copious amounts of nitrogen fertilizer used and the extensive topsoil erosion associated with cultivation. Every year, pesticides, herbicides and fertilizers run off the corn fields and bleed into groundwater. River contamination promotes eutrophication, algal blooms and ‘dead zones’. In addition, ethanol importation by industrialized nations could lead to increased ecological destruction in developing countries as indigenous natural habitats are cleared for energy crops (Gui et al., 2008; Marris, 2006; Thomas 2007).

The general feeling is that first-generation biofuels are already reaching saturation because of the limited availability of arable lands. Brazil has additional lands available for sugarcane and physic nut production, whereas India is promoting physic nut cultivation on its extensive wastelands. However, the development of these fuels has already been a success because they have demonstrated that motor technology running on ethanol or biodiesel is feasible and can (at least) be used to power public transport.

Fortunately, second-generation biofuels from biomass offer additional opportunities. The cost of feedstock is lower for lignocellulose as compared to the agricultural crops that now contribute up to 70% of the total production costs for first-generation bioethanol. Even if they are more expensive now, synfuel from biomass sources (such as poplar, willow, and reed grass) could have higher cost effectiveness in the near future than does fuel from sugar beets, wheat and rapeseed sources (Wesseler, 2007; Styles & Jones, 2008).

Biomass fuels will be another opportunity for the EU to meet its target of energy production from renewable sources. However, this goal has not been met by 2010 as was initially expected (Fischer et al., 2010; Havlik et al., 2010). The European CO2 emissions-trading system of carbon credits seems to be much more cost effective than its biodiesel program because it allows for the purchase of units of CO2 sequestration in tropical climates that have much higher rates of fixation than do temperate ones (Frondel & Peters, 2007). Third-generation biofuels have also entered the race for fuel renewability. In terms of total dry matter, sugarcane typically yields ~75 t biomass per hectare, whereas microalgae are able to produce two times more biomass per hectare (Brennan & Owende, 2010; Chisti, 2007, 2008). Considering a productivity of 150 t/ha and an average dry-weight oil content of 30%, the oil yield per hectare would be ~123 m3 over 90% of the year (i. e., 98.4 m3/ha). If 0.53 Gm3 of biodiesel are needed in the US to power transport vehicles, microalgae should be grown over an area of ~5.4 Mha (3% of the US). Producing algal biomass in a 100 t/yr facility has been estimated to cost approximately US$ 3,000/ton. The feasibility of oil extraction for microalgal biomass has been demonstrated (Belarbi et al., 2000; Sanchez Miron et al., 2003) and the majority of algal biomass residues from oil extraction can be recycled by anaerobic digestion to produce biogas.

Impediments to large-scale culture of microalgae are mainly economic and are tied to the investment requirements for the algae cultivation. One solution would be to increase the oil productivity by genetic and metabolic engineering (Leon-Banares et al., 2004; Mathews & Wang, 2009). One may expect the expansion of algal technology via CO2 filtration because power plants can incorporate this technology immediately into their management systems. This technology is expected to spread slowly with the accumulation of experience.

Nearly half of the world’s oil consumption is dedicated to the transportation sector, which also accounts for 32% of GHG emissions. The overall efficiency of energy conversion to work in the transportation segment is lower than it is in large-scale power plants and the goal is to increase it from the current level of 15-35 to 60-80% (Song, 2006).

Unfortunately, advanced transportation technologies (such as hydrogen fuel cell vehicles and alternative fuels including gas-to-liquids, coal-to-liquids, and biodiesels) are not likely to significantly penetrate the conventional transportation fuel market before 2030 (except on a regional basis). The growth in oil consumption for transportation use in the coming decades may be slowed by the adoption of fourth-generation technologies such as hybrids and fuel cell cars. However, the necessary technological breakthroughs will not occur without unprecedented policy actions worldwide to promote the use and inclusion of these technologies in everyday life (Doniger et al., 2006; Haug et al., 2011; Michel 2009). Currently, there are approximately half a million hybrids and 30 million advanced clean-diesel engines globally. The use of hybrid cars is growing in the US and Japan, whereas advanced clean — diesel motors are mostly concentrated in Europe (Dorian et al., 2006).

Actually, auto-mobility is a self-organizing and non-linear system that presupposes and calls into existence an assemblage of cars, drivers, roads, fuel supplies, and other objects and technologies. Modern social life has become interconnected with auto-mobility. However, this mode of mobility is neither socially necessary nor inevitable (Urry, 2008). One billion cars were produced during the last century. World automobile travel is predicted to triple between 1990 and 2050 (Hawken et al., 2002). Today, world citizens move 23 Gkm annually. Auto-mobility forces people to contend with the temporal and spatial constraints that it itself generates (Mills et al., 2010). Fortunately, some 35-year-old projects have begun to be finally implemented (i. e., the integration of car and bicycle rentals into public transportation systems, such as occurs in some European cities). A post-car future will involve changes in lifestyles, city architecture, thinking and social practices. Increased active transport (e. g., walking and bicycling) will help to achieve substantial reductions in emissions while improving public health. Cities require safe and pleasant environments for active transport as well as easy accessibility of public transport. Adverse health effects because of transportation include traffic injuries, physical inactivity (the cost of obesity in the USA is estimated to be around US$ 139 bn/yr), urban air pollution, energy-related conflicts, and environmental degradation. For instance, urban air pollution accounts for 750,000 deaths each year, of which 530,000 are in Asia (Woodcock et al., 2007). Because of limited energy resources, it has been argued that the world will be required to move toward virtual travel (such as internet surfing, virtual sensorial traveling, and video conferences) to replace physical travel as much as possible (Moriarty & Honnery, 2007).

In reality, the situation outlined above is the result of consideration of humanity only within social contexts and without the necessary environmental perspective (Thomas, 2007). The concept of environmental crime barely operational; if it exists at all, it is very recent and is not generally applied. Logical human societies should take into account the amount of land that human beings and wildlife actually need to reasonably sustain themselves. Not doing this will lead to increasing worldwide destruction (Urry, 2008) and will threaten the future of humanity. These considerations led to the formulation of the Gaia principle (Lovelock & Margulis, 1974). This principle states that one should consider the planet Earth as a whole, with the consequence that the destruction of one ecosystem can affect all of the others. Concern for the value of ecosystems is recent (Costanza et al., 1997). Society has only begun to address human integration with the environment because of the threat of global warming and its potentially disastrous effects (Stern, 2006). A discussion of the economic accounting for ecosystem services from the perspective of sustainable development has also been proposed (Maler et al., 2008).

The concept of "willingness-to-pay" (WTP) has also been recently introduced. This concept allows for the monetary measurement of individual preference to avoid a negative impact. It aims to estimate the need for improved environmental quality. WTP measures how much individuals are ready to pay to improve their quality of life or that of other people. The sum of the WTP of all individuals gives the value that a group of individuals are ready to pay to maintain their environment in an unaffected state. For example, the pathways of polluting substances are followed from their release sources to the points of damage occurrence with associated "external" costs of reparation. Taking external costs into account in the full cost of energy production leads to the estimation of the "real" cost of an activity and supplies an efficient policy instrument for reducing the negative impacts of energy use (Nast et al., 2007). The approach of merging production costs with external costs into a total specific cost serves as a comparative indicator for the evaluation of the economic-environmental performance of energy options and technologies (Rafaj & Kypreos, 2007). The scenarios proposed under this new cost-accounting strategy reveal the possibilities for the diffusion of advanced technologies and fuel switching into the electricity production system. Following this model, renewable energies increase their competitiveness and the dependency of the electricity sector on fossil fuels is decreased considerably. Additionally, emissions of SO2 and NOx decrease by 70-85% by 2030. Although the analysis indicates that advanced technologies with emission controls and carbon sequestration will undergo significant cost reduction and will become competitive in the long run, policies supporting these technologies are a prerequisite to their establishment in electricity markets (especially during their initial period of market penetration). This model refers to policy measures for the stimulation of technological progress via investments in research and development that assist carbon-free technologies to progress along their necessary learning curves (Haug et al., 2011; Rafaj & Kypreos, 2007).

3. Conclusions

The time has come for the integration of the technological and social sciences to find a route to environmental and economic sustainability on earth. If such a solution is not reached, economic growth will occur at the cost of the human population size (Urry, 2008). Fortunately, because of the continuous increase in the price of fossil fuel, investigations into sources of renewable energy have become economically viable. It is now clear that technologies for renewable energies have reached a pivotal stage such that there is no turning back. There are at least 5 regional blocks (the USA, the EU, China, Brazil, and India) that are interested in decreasing their dependence on fossil fuels. It does not appear to be in anyone’s interest to shut this process down by mean of aggressive oil price cutting and market dumping. In fact, biotechnology is intimately bound to agricultural processes that are also supported by governments because of geostrategic issues. In addition, climate change is becoming obvious and will soon overcome particular interests to become a general concern of humanity.

Biofuels and sources of bioenergy will pass through a rapid succession of technological improvements and developments before they arrive in their final forms. It is expected that bioethanol from sweet crops will be surpassed by bioethanol from biomass. Synfuel from biomass and solar energy should also progressively replace plant biodiesel. Biotechnology is expected to increase its participation in microdiesel fuel production, in genetic engineering of plants and microorganisms and in the contribution of enzymes to nanotechnology.

The integration of renewable energies into the electricity grid is just beginning, but is already progressing rapidly. It is expected to make a significant contribution; however, it should be accompanied by policies of energy management and urbanization to avoid unnecessary energy waste that could negate the benefits of technological breakthroughs and developments. New concepts (such as willingness-to-pay, carbon credits and external costs) are now being taken into account in the calculation of energy life cycles. This toolbox will expand with increasing government regulations and should include fundamental concepts such as "biodiversity credits" and the definition of a "minimal territorial unit" for living entities to warrant sustainability of wildlife and humanity. Biodiversity is a source of nanostructures and nanomachines. It should not be destroyed without consideration when we are aware that it required three billions years to develop and that humanity is just beginning to investigate it.

As a result of energy saving requirements, the cars of the near future will run on combinations of fuel combustion and electricity. Such options can reduce fossil fuel consumption and greenhouse gas emissions by 30 to 50%, with no gross vehicle modifications required. In addition, they will allow for connection to the electricity grid for additional cost saving on electricity consumption. These so-called plug-in hybrids will likely travel three to four times farther per kW/h than other vehicles. Ideally, these advanced hybrids will also be flexible and capable of running on bio/fossil blends and gas (Romm,

2006) .

At some point during the first half of this century, a transition from fossil fuels to a non­carbon-based world economy will begin and will seriously affect the type of society experienced by future generations (Dorian et al., 2006).

Rafael Picazo-Espinosa, Jesds Gonzalez-Lopez and Maximino Manzanera

University of Granada Spain

1. Introduction

Modern societies’ welfare relies greatly on fossil fuels. The current energy model, based on the extensive utilization of fossil fuels, is affected by economic and environmental problems. The United States Department of Energy 2009 report estimates that, within the next two decades, global energy consumption will double (Conti, 2009). On the other hand, the European Commission 2009 report indicates that the management of climate change problems in Europe, since 2000, has been globally unfavourable. Nevertheless, there are some positive signs, such as the 1.4% reduction in 2007 of CO2 emissions with respect to the figures obtained from 2000 to 2004 in the European Union of Fifteen (E-15). However, considering the 27 European states (E-27), and paying attention to the consumption and production of renewable energy and biofuels, the reduction in emissions has not fulfilled the European Union objectives. Among the motives of this negative evaluation, the fall in the companies’ productivity, increased transport and industry emissions and the reduction in research and development areas can be cited (Radermacher, 2009). First- and second — generation biofuels could ameliorate or solve the associated fossil fuel depletion problems, although their recent implantation has raised some doubts. The main problems associated with biofuels are the food vs. fuel controversy; the agricultural and forestry land usage and the actual sustainability of biofuels’ production. Third-generation biofuels, based on the microbiological processing of agricultural, urban and industrial residues, could be a possible solution. However, several technical problems must be solved to make them economically viable and easily affordable for the industry (Robles-Medina et al., 2009).