In this book, the focus will be largely on liquid and gaseous transport biofuels that can replace fossil transport fuels. In this section, a brief survey will be given of the ways to produce liquid and gaseous transport biofuels from a variety of feedstocks. These are summarized in Fig. 1.1.

Fig. 1.1 Biofuel production steps

Much agricultural production in Africa, Asia and South America is currently as­sociated with a depletion of nutrients or ‘nutrient mining’ (de Koning et al. 1997; Syers et al. 1997; Sanchez 1999; Tilman et al. 2002). Increasing the use of crop residues for biofuel production may in practice exacerbate the latter problem (Troeh et al. 1999; Sauerbeck 2001). On the other hand, including woody perennials in agricultural strategies may well benefit both biomass-for-energy production and the long-term sustainability of food production, because there is evidence that woody perennials may recycle leached nutrients to near surface layers (Mele et al. 2003) and because several woody perennials are conducive to N-fixation (Sanchez 1999).

Long-term studies on the sustainability of crop production in industrialized coun­tries (Vance 2000) are not easy to interpret as far as nutrients are concerned, because, as pointed out above, there are large unintended inputs of nutrients. However, such unintended inputs are usually well below those necessary for high-productivity crop­ping. Against this background, when harvest residues such as cereal and rape straw are used as biofuel, reuse of ash on arable land has been advocated (Sander and Andren 1997).

Sustainable enhancement of biomass production can be achieved if there are ways to increase nutrient availability indefinitely (Vance 2000; Bhattacharya et al.

2003) . For several nutrients, this is, technically speaking, not a major problem be­cause the elements concerned are relatively abundant. Mg, K and Ca are in this category. However, P especially is geochemically scarce, and N nutrients are often generated by using geochemically scarce fossil fuels. This becomes even more of an issue, because increased biofuel production is expected to be partly based on in­creased yields of crops per hectare, which is linked to intensification of agriculture, including increased N and P inputs (Tilman et al. 2001; Searchinger et al. 2008).

Net natural inputs to farms of P, associated with weathering and deposition (Hedin et al. 2003), allow for very low primary productivity on farms (Newman 1997). Raising the availability of P if compared with pre-industrial times has mainly been achieved by relying on phosphate ore deposits, and there is no known al­ternative to that natural resource for doing so. So, sustainable use necessitates an extremely slow depletion of this stock. Ore deposits deplete rapidly when P used is not retrieved with high efficiency and fed back into biomass production. Non­retrieval associated with agriculture originates in harvesting, erosion (see Sect. 3.2) and leaching. Leaching is increased in agricultural land, if compared with soils un­der native forest (Williams and Melack 1997), and can be very high when soils are saturated with P (Liu et al. 2008). Preventing saturation leads to the need to restrict P additions to agricultural land.

Losses of P may also be linked with activities following harvesting. Much of the phosphate wastes associated with consumption and industrial processing of har­vested biomass currently end up in wastewater. The recycling of such phosphate back into the economy is currently poorly developed (Sims and Riddell-Black 1998; Kvarnstrom and Nilsson 1999). One may also fail to retrieve P when there is burn­ing of biomass. When biomass is burned, P ends up largely in ashes. When there is co-firing with, for instance, coal, such ashes are often considered unfit for agricul­tural use (Woodbury et al. 1999; Nugterenet al. 2001; Adriano et al. 2002; Reijnders 2005), whereas forced extraction of nutrients such as P from such ashes is not prac­ticed. Even in the case of burning pure chicken manure, the composition of ashes may be such that nutrients are not fed back to agriculture (Reijnders and Huijbregts, 2005). Feed additives with high concentrations of trace elements such as Cu and Zn are responsible for this problem. On the other hand, in the case of biomass present in sewage sludge, a process has been developed for the fractionation and recovery of phosphate (Lundin et al. 2004), and this type of approach can, in principle, be applied to all wastes that contain substantial amounts of phosphate.

It has been estimated that the resulting net loss of P from the world’s cropland is about 10.5 x 106 Mg per year, nearly one half of the amount of P that is extracted yearly as phosphate ore (Liu et al. 2008). Such large losses of P associated with pro­duction and use of biomass cannot be maintained indefinitely without jeopardizing adequate P levels in soils. If one will no longer be able to add substantial amounts of P to soils, primary productivity will ultimately plummet, negatively affecting both food and biofuel production (Newman 1997). So, indefinitely increased availabil­ity of P in soils is critically dependent on high-efficiency recycling of P involved in biomass production, while keeping soil concentrations of hazardous compounds below critical levels (Kvarnstrom and Nilsson 1999). A major effort is needed to apply this principle to biomass-for-energy.

The increased availability of nitrogen compounds to be used as fertilizer, if compared with the situation before the industrial revolution, is mainly based on the Haber synthesis, which converts fossil methane into ammonia (Galloway et al. 2008). As it stands, there is a large-scale leakage of added nitrogen compounds from biomass production systems such as plantations and annual crops. In well-managed intensive agriculture, the recovery of nitrogen in products is around 50% or less (Tinker 1997; Tilman et al. 2002). Moreover, N compounds present in biomass will largely get lost on burning. Basing the Haber synthesis on fossil fuels cannot be maintained indefinitely, as fossil carbon is virtually non-renewable. In this case, one may circumvent inputs of virtual non-renewables. For instance, hydrogen necessary for converting nitrogen present in air into N fertilizers can also be generated by hydrolysis powered by solar energy, a way of production that may be maintained in­definitely. There may also be scope for improved biogenic nitrogen fixation, which converts N2 into plant nutrients and may partially replace fertilizer amendments.

From the previous sections, it has become clear that in much expanding transport biofuel production, there may often be hard choices to make. Growing crops such as oil palm and corn for transport biofuels may contribute to energy security and mitigate price rises of fossil fuels but may generate for decades more greenhouse gases than fossil transport fuels and have an upward effect on food prices. Growing feedstocks on currently fallow land in the USA and Europe may mitigate the ef­fect of biofuel production on food prices and limit greenhouse gas emissions linked to the transport biofuel life cycle but is probably bad for biodiversity. Intensifying cropping for biofuel feedstocks may be conducive to limiting price increases for food and fuel but may also be unsustainable and have a negative impact on biodiver­sity (Sukhdev 2008). As large-scale production of transport biofuels may come at significant costs, one may well wonder whether preference should be given to other ways of providing for transport services.

So, we return to the alternative option of better energy efficiency in transport and better solar energy conversion in transport energy supply, raised in Sect. 6.3. Improved energy efficiency is not necessarily an easy alternative. Indeed, in many countries, as to cars, fossil fuel input per person-kilometre has remained virtually constant since the 1973 ‘oil crisis’. Potential gains in energy efficiency due to techni­cal progress were ‘eaten away’ by developments such as preferences for improved comfort and safety, lower occupancy of cars and increased congestion (Schipper et al. 1992). However, it is also known that increased fuel prices are conducive to increased energy efficiency in producing transport fuels and increased energy effi­ciency of transport (Schipper et al. 1992; Graham and Glaister 2005), and future prices may well be high (GAO 2007), so that may help in making improvements in energy efficiency more successful than was feasible in the past. To the extent that priority is to be given to renewables, the obvious alternative from the point of view of conversion efficiency (as pointed out in Chap. 2) is the use of physical con­

version technologies producing electricity, which can either be used for storage in batteries or be converted into H2 for use in fuel cells (Armor 2005; Evans 2008; Ros et al. 2009). Again, this is not an easy alternative. The costs thereof are as yet high, though they are expected to be much reduced over the coming decades (Martinot 2006; Braun 2008).

The consequences of the increased use of transport biofuels for food prices and food security (access to affordable, adequate food supplies) have been other major topics in the debate on biofuels. In 2007, the rapid expansion of biofuels production con­tributed to increased prices for cereals and oilseeds (OECD-FAO 2007; Renewable Fuels Agency 2008). This effect of the growth in transport biofuel production on food prices has not gone unnoticed in society. Late in 2006, the Chinese govern­ment halted the expansion of corn-based ethanol production (Koizumi and Ohga

2007) . At the beginning of 2007, Mexico was confronted by a tortilla crisis, includ­ing protests of poor people against rising prices for tortillas, which are made from corn. The Mexican government was forced to change its fiscal policy. Argentina, which has substantial soybean-based biodiesel production, raised its export taxes on soybeans by 4% to provide subsidies to lower the cost of soybean flour to live­stock producers (OECD-FAO 2007), which in turn sparked angry farmer protests. In December 2007, the government of South Africa banned growing corn for bio­fuel to counteract price rises. 2008 saw widespread food rioting in Asia, Africa and South America. Several predictions suggest that a further rapid expansion of trans­port biofuel production will lead to (further) rises in food prices (Naylor et al. 2007; Eickhout et al. 2008) and that these rises may lead to an increased insufficiency of food for the world’s poorest people that currently spend 50-80% of their total household income on food (Naylor et al. 2007; Runge and Senauer 2007; Daschle et al. 2007; Renewable Fuels Agency 2008). This has led to a coining of the slogan ‘transport biofuels for the rich and hunger for the poor’.

When it is assumed that straw should be returned to a large extent to soils, the in­put of fossil fuels in the life cycle of bioethanol from European wheat is such that, whatever the allocation between ethanol and co-products [DDG(S) and glycerol], there is a rather small margin between the fossil-fuel-based energetic input and en­ergetic output of the life cycle (vonBlottnitz and Curran 2007; Reijnders and Huij­bregts 2007). This limited advantage regarding the emission of greenhouse gases for bioethanol is, however, well exceeded by the average emissions N2O and CO2 from conventionally tilled soils on which wheat is grown, whatever the allocation cho­sen (Crutzen et al. 20007; Reijnders and Huijbregts 2007). When indirect effects on land use are also factored in, ethanol from European wheat does worse than fossil gasoline, whatever the choices regarding allocation (Fritsche 2007; Reijnders and Huijbregts 2007).

Example 3: Palm Oil

Palm oil has been proposed for use as a heavy-duty transport fuel in warm climates (Prateepchaikul and Apichato 2003). It may also be used in electricity production and after transesterification as biodiesel in cars (Reijnders and Huijbregts 2008a). In the case of palm oil, there is, both in monetary and physical terms, one major mar­ketable output of production (palm oil) and one minor one: palm kernel cake (which may be used as animal feed). For the establishment of oil palm plantations, a variety of land use changes is possible, and the effects thereof canbe distributed overtime in different ways (Reijnders and Huijbregts 2008a; Wicke et al. 2009). It turns out that when the plantation is on mineral soil and native forest is cleared, palm oil will do worse than diesel based on mineral oil unless the changes in C content of the ecosys­tem are distributed over a long time span (Reijnders and Huijbregts 2008a; Wicke et al. 2009). When the plantation is on peaty soil, palm oil does much worse regard­ing the emission of carbonaceous greenhouse gases and N2O than diesel based on mineral oil (Danielsen et al. 2008; Fargione et al. 2008; Reijnders and Huijbregts 2008a; Wicke et al. 2009). On the other hand, when a palm oil plantation is estab­lished on abandoned mineral soils, palm oil will do much better than fossil diesel (Germer and Sauerborn 2007; Wicke et al. 2009).

As also pointed out in Chap. 1, estimates have been made of the maximum efficiency for the conversion of incident sunlight into biomass by algae. These vary between

5.5 and 11.6% (Heaton et al. 2008b; Vasudevan and Briggs 2008). Several authors have suggested that algal transport biofuels can beat terrestrial transport biofuels in the conversion of solar energy to transport biofuel by at least one order of magnitude (e. g. Chisti 2007; Chisti 2008a; Groom et al. 2008; Nowak 2008; Li et al. 2008). Here we will survey the suggestions that have been made for producing transport biofuels from algae and aquatic macrophytes and what is known about the solar energy conversion efficiency of such biofuels.

Harvesting biomass has an impact on living nature present in the location where harvesting takes place. If all net primary production were harvested, the extinction of most heterotrophic organisms would be expected. At lower levels of harvesting, food chains may still be significantly impacted (Haberl and Geissler 2000). In the case of more limited harvesting of forests, the amount of dead wood in forests is reduced, and this in turn has an impact on the many species that are dependent on dead wood (Norden et al. 2004; Rudolphi and Gustafsson 2005). Also, long­term effects of harvesting trees have been noted on soil arthropods and the quantity of ectomycorrhizal roots in the organic horizon of forests (Mahmood et al. 1999). On the other hand, limitation of harvesting may allow for species conservation. In Swedish temperate-oak-dominated hardwood stands, a 25% harvest of understory was compatible with conservation of vascular plants, fungi, saprophytic and herbiv­orous beetles and mycetophilid insects (0kland et al. 2008). Management of stands on much longer than current rotations to maintain understory species, which require long periods to recover from disturbance, has been suggested as a way to limit the negative impact of harvesting on biodiversity (Halpern and Spies 1995; Kerr 1999; Ramovs and Roberts 2003). Other suggestions for forests (including ‘production forests’ or plantations) which are (to be) harvested have been: increasing the extent of mixed stands and improvement in vertical structure of forests through variations in stand treatments (Kerr 1999; Eriksson and Berg 2007).

All in all, harvesting of forests has been found to affect vegetation cover, animal biomass and biodiversity (Milton and Moll 1988; Halpern and Spies 1995; Carey and Johnson 1995; Chen et al. 1998). This, in turn, can entail loss of non-monetary ecosystem services that are useful to mankind (Symstad et al. 2003). For instance, in Oregon, harvesting forests increased peak flow into surface water by, on aver­age, 30% due to the combined effect of changes in flow routing and water balance (Brauman et al. 2007). Damage to vegetation due to harvesting trees may also im­pact water quality. After harvesting in temperate forests, there is a transient peak in nitrate losses to surface water that may last up to 5 years (Gundersen et al. 2006). More in general, harvesting is associated with increased loss of minerals and nutri­ents to ground and surface water (Pare et al. 2002; Lawrence et al. 2007). Repeated harvesting in dry tropical forests may lead to depletion of nutrients to the extent that primary productivity may be negatively affected (Lawrence et al. 2007). Low­ered primary productivity associated with repeated harvesting has also been noted elsewhere (Nord-Larsen 2002). Soil erosion due to harvesting trees may also be substantial (Pimentel et al. 1981). In arid environments dominated by shrubs, over­harvesting may lead to loss of vegetation cover and biodiversity that may lead to desertification, including an increase in Aeolian processes such as erosion and the transportation and deposition of sand (Brown 2003; McNeely 2003).

Sucrose — or Starch-Based Biofuels

Sucrose (from sugar cane, sugar beet and sweet sorghum) and starch (from starch crops such as corn, grain sorghum, potato, Jerusalem artichoke, cassava, rye, barley, sago palm and wheat) can be converted into ethanol by hydrolysis and fermentation. There is also the possibility of converting sugar in whey and starch and sugar in wastes (potato peel, spoiled fruit) into ethanol by fermentation (Acharya and Young 2008). The fermentation used to produce ethanol is usually yeast based. The reaction starts with a C6 sugar and is:

C6H12O6 ^ 2CO2 + 2C2H5OH (ethanol) .

Ethanol has its disadvantages vis-a-vis fossil-based gasoline. Its lower heating value is considerably lower (see Table 1.2), and it is hygroscopic and more corrosive (cf. Table 1.3). Against this background there have been proposals to convert ethanol to hydrocarbons (‘biogasoline’) (Tsuchida et al. 2008) or H2 (Ni et al. 2007; Kon — darides et al. 2008). However, in practice, ethanol may do well as transport fuel in Otto motors, both as such and as a mixture with fossil hydrocarbons (Szklo et al. 2007). Ethanol may also be applied in a mixture with fossil diesel fuel in diesel motors — with an additive to prevent phase separation (Fernando and Hanna 2004; Antoni et al. 2007; Wang et al. 2007; Song et al. 2007). In Otto motors, ethanol is used as a gasoline extender, octane booster and oxygenate suitable for driving during winter in temperate climates (MacLean and Lave 2003). Claims have been made that admixture of ethanol improves the fuel efficiency of Otto motors, but available evidence (Roberts 2008; Kamimura and Sauer 2008) suggests that differ­ences in average fuel efficiency are not statistically different from the differences in heating value. Ethanol can also be used to produce ETBE (ethylester of t-butanol) or ethylesters of fatty acids, which can be applied in Otto and diesel motors respec­tively. Currently the production thereof is in chemical reactors. For the combined production of ethanol from sugars and ethylesters of fatty acids, a synthesis em­ploying genetically modified Escherichia coli has been demonstrated (Kalscheuer et al. 2006).

Starch and sucrose may also serve as a basis for fermentation into butanol, or to be more precise, a mixture of acetone, butanol and ethanol (ABE). After World War II, bacterial fermentation generating ABE from starch and sucrose was applied on an industrial scale in a wide variety of countries. This production process ul­timately succumbed to the price competition of petrochemical butanol (Ng et al. 1983; Reinharz 1985; Jones and Woods 1986; Gutierrez et al. 1998; Zverlov et al. 2006; Chiao and Sun 2007; Ezeji et al. 2007; Qureshi et al. 2008a). There currently is pilot-scale industrial production of butanol by bacterial fermentation processes starting with starch or sucrose and a substantial amount of research and development aimed at ‘engineering out’ the production of acetone and ethanol (Wackett 2008). Up to about 18% ABE may be mixed with fossil diesel fuel, which is then suitable for powering diesel motors (Willke and Vorlop 2004). Butanol can be mixed into gasoline for use in Otto motors, as such or after esterification with t-butanol (Scott and Bryner 2006; Antoni et al. 2007; Ezeji et al. 2007). Butanol is a biofuel that can also be used in high thrust-to-weight applications such as aircraft engines. Butanol has the added advantages that, unlike ethanol, it will not solidify at the low tem­peratures of high altitudes at which airplanes operate and that it is not hygroscopic. Disadvantages are that the concentration of butanol achievable by fermentation is currently low and that the boiling point is high, which necessitates relatively high energy inputs for butanol distillation (Fortmanet al. 2008; Hayes 2008).

It has also been shown that the production of branched chain butanols (isobu­tanol, 2-methyl-1-butanol, 3 — methyl-1-butanol) from glucose is possible using meta­bolic engineering of micro-organisms (Atsumi et al. 2008). Such branched chain butanols can also be mixed into gasoline.

A last important non-energy natural resource for biomass production is water. The potential for biomass production on suitable soils is strongly influenced by fresh­water availability (Tuskan 1998; Rabbinge and van Diepen 2000; Ryan et al. 2002; Kahle et al. 2002; Deckmyn et al. 2004), and in semi-arid areas, it may well be the main limiting factor (Ong and Leakey 1999). Of the yearly renewable stock of fresh­water, approximately 30-50% is currently used in the economy (Postel et al. 1996; Raskin et al. 1997; Rockstrom 2003). Worldwide, growing crops is the main con­sumer of freshwater (Pimentel et al. 1997a). Even if growing of rain-fed crops is not considered to be use of water, growing crops accounts for at least 66% of current wa­ter use (Gleick 2000; Wallace 2002; van Dijk and Keenan 2007; Gordon et al. 2008; Zimmerman et al. 2008). Water consumption is projected to go up considerably, grossly paralleling growth of the world population and economic growth, much of the increase being associated with the expected increase in food and feed production (Gleick 2000; Berndes 2002; Swedish Environmental Advisory Council 2007).

Geographically speaking, water stocks are unevenly distributed. Currently, struc­tural water shortages affect about 300-400 million people mainly in Africa and Asia in a band from China to North Africa (Gleick 2000; Wallace 2002). As much growth of the world population is expected in the same area, this does not bode well (Gleick 2000). But elsewhere there are problems, too. For instance, in the USA, roughly 20% of the irrigated area is supplied by groundwater pumped in excess of recharge (Tilman et al. 2002). Also, there are areas where climate change may lead to a struc­tural decrease in rainfall, such as the south and east of Africa (Funk et al. 2008).

Large additional water requirements follow from expected population growth and changes in dietary habits, especially the increased consumption of animal pro­duce (Rockstrom 2003; Falkenmark and Lannerstad 2005; Liu and Savenije 2008). The estimated size of the additional water requirement depends on the assumptions made. Assuming an intake of 3,000kcal person-1 day-1 and using available pre­dictions about world population growth, Rockstrom (2003) estimated an additional water requirement of 3,800km3year-1 in 2025 and of 5,800km3year-1 in 2050. Assuming business as usual, which does not include a substantial production of modern biomass-for-energy, it has been suggested that shortages of freshwater may well become a fact of life for up to 2.5-6.5 billion people by 2050 (World Water Council 2000; Wallace 2002). Expanding modern biomass-for-energy production may substantially exacerbate this trend.

The National Research Council of the USA has warned about more local water shortages due to the expanded production of corn for supplying ethanol (NRC 2007). This problem is especially pressing in the Western USA, where climate change threatens to exacerbate water shortages anyway (Barnett et al. 2008) and where there is already a substantial groundwater overdraft (Falkenmark and Lannerstad 2005). Excess water withdrawals may also be a problem in Brazilian sugar cane expansions (Dias de Oliveira et al. 2005), where hydrological flows are already much impacted by sugar cane cultivation (Gordon et al. 2008). India and China are expected to have increasing shortfalls in meeting national food demand due to water scarcity, necessitating increasing food imports (Falkenmark and Lannerstad 2005; Liu and Savenije 2008), and this leaves little scope for cropping feedstocks for transport biofuels.

In Hungary, there has been evidence that the use of cornstalks as biofuel wors­ened a drought by removing cover and reducing soil organic matter (Engelhaupt

2007) . Berndes (2002) has pointed out that in the case of large-scale bioenergy pro­duction, a European country such as Poland may face absolute water scarcity. Com­petition between fast-growing Eucalyptus and food for water resources in Ethiopia has led to government restrictions on the former (Jagger and Pender 2003). Else­where, competition between short rotation trees and food crops for scarce water re­sources has also been noted (Ong and Leakey 1999; Sanchez 1999; Berndes 2002; Ong et al. 2002; van Dijk and Keenan 2007). On the other hand, when growing feed­stocks are rain fed, there are some places subject to waterlogging and/or secondary salinization, where large uptakes of water by energy crops may be considered a ben­efit (Morris and Collopy 1999; Mahmood et al. 2001; Ryan et al. 2002; Palm et al.

2007) , though it should be noted that the use of Eucalyptus globulus for this pur­pose in Western Australia has turned out to be disappointing (Sudmeyer and Simons

2008) .

Data about seed-to-wheel water use are very patchy (Royal Society 2008). Data about water inputs into feedstock processing, especially, are largely lacking. Never­theless, it is clear that biomass processing can lead to substantial water consumption. A case in point is the factories that produce ethanol from sugar cane in the relatively dry winter period in Brazil (Smeets et al. 2008). Also, in generating electricity from biomass in power plants, there is often water cooling that consumes large amounts of water (King and Webber 2008). However, it would seem likely that most of the seed-to-wheel water inputs concern the growing of feedstocks, in line with agricul­ture being the dominant consumer of water in the economy.

In view of increasing water scarcity, the water efficiency of transport biofuels requires considerable attention. As to water use in biomass processing, there is, for instance, scope for improving the water efficiency of Brazilian factories for the con­version of sugar cane into ethanol by increasing the water recycling rate and by replacing cane washing with dry cleaning of cane (Smeets et al. 2008). Similarly, consumption of cooling water by power plants processing biomass can be much reduced by, for example, switching to closed loop and air cooling systems (King and Webber 2008). The water efficiency in the growth of feedstocks is especially important (Hanegraaf et al. 1998; Rytter 2005; Almeida et al. 2007; Rockstrom et al. 2007). On average, the water efficiency of C4 crop plants appears to be bet­ter than the water efficiency of C3 crop plants (Cernusak et al. 2007; Heaton et al.

2008) . Growing 1 kg of aboveground (dry) biomass of the C3 crop wheat on aver­age requires about 0.55 m3 of water (calculated from data in Zwart and Bastiaanssen

2004) , whereas 1 kg of dry biomass for the C4 crops sugar cane or Miscanthus prob­ably needs less than 0.2 m3 (Rockstrom et al. 1999; Beale et al. 1999).

The water efficiency of soybeans and other annual oil crops is much poorer than the water efficiency of wheat (Liu and Savenije 2008). The microalga Tetraselmis suecica, which is considered for biofuel production, has been estimated to require 0.31-0.57 m3 water kg-1 dry weight biomass (Dismukes et al. 2008). As transport biofuels are the product of biomass processing, such biofuels will need a larger amount of water per kilogram of biofuel than per kilogram of biomass. In the case of ethanol based on cornstarch, while assuming an average water productivity of corn (Zwart and Bastiaanssen 2004) and a 0.294 kg ethanol yield from 1 kg of corn kernels (Kheshgi et al. 2000), for each kilogram of bioethanol, 1.9 m3 of water is needed in cultivation, when all water use is allocated to ethanol production. In the case of wheat, the estimated water input in cultivation is about 3.1m3 water per kilogram of wheat-starch-based ethanol, when all water use is allocated to ethanol production. Water efficiency may change due to climate change linked to increas­ing greenhouse gas concentrations in the atmosphere. There is only very limited study thereof. A study on water use efficiency by a plantation producing willow as a feedstock for biofuels suggests that climate change may lead to a decrease in water efficiency (Tricker et al. 2009).

The difference in water efficiency between C3 and C4 crop plants is not the only noteworthy difference relevant to feedstock production. When the aim is to produce ethanol from carbohydrates, sugar crops tend, on average, to do so more efficiently than starch crops, whereas starchy root crops tend to be more water efficient than cereals (Rockstrom et al. 2007). In dry areas, the water efficiency of producing sugar by sugar beet may be better than that of sugar cane (Rytter 2005). Also, there may be ‘drought-resistant’ varieties of crops that would do better under such circumstances than other varieties (Rytter 2005). There is large variability in water efficiency be­tween woody plants that may be used for biofuel production (Cernusak et al. 2007). Growing 1 kg of aboveground dry oil palm biomass requires approximately 1.5 m3 of water (Rockstrom et al. 1999), and growing 1 kg of willow biomass (dry weight) requires 0.2-0.3 m3 of water (Linderson et al. 2007). The olive tree is well adapted to drought stress (Sofo et al. 2008), whereas current varieties of Eucalyptus are less so (Dale and Dieters 2007). Eucalyptus biomass on rain-fed soil would require about 0.46 m3 of water kg-1 dry biomass (calculated from data in Stape et al. 2008 and Kheshgi et al. 2000). So, choice of feedstock may have a large impact on water consumption.

Soil water conservation is also dependent on tillage (and soil organic carbon lev­els) with conservation tillage conducive to water conservation (Wallace 2002; Rock­strom 2003). Mulching and intercropping to maximize canopy cover also help in in­creasing water productivity or crop yield for a specified input of water (Rockstrom 2003). So, for instance, on the Loess Plateau in China, no tillage with mulching does better in soil water conservation than conventional tillage, leading to substantially improved water use efficiency of winter wheat (Su et al. 2007). It has furthermore been shown that there are irrigation techniques that lead to higher water efficiencies than traditional furrow irrigation. These include variable application (Al-Kufaishi et al. 2006), subsoil irrigation and drip irrigation. Improvements in water efficiency may be considerable. Subsoil irrigation, with controlled diffusion of irrigation wa­ter from a clay pipe, has been shown to increase grain yield of Iranian winter wheat per kilogram of water by at least a factor of 2.5 (Banedjschafie et al. 2008). And

in Uzbek cotton growing, which might supply cotton oil for biodiesel production, the improvement in yield by switching from furrow irrigation to drip irrigation was 35% to somewhat more than 100% (Ibragimov et al. 2007).

Apart from the quantitative impact on the availability of water, water quality may also be influenced by growing biofuels (NRC 2007). The expansion of corn production for the supply of ethanol is a case in point, as it leads to an increased nutrient and pesticide load of water resources (NRC 2007). And water discharges for algal biofuel production in open ponds may also be problematic in view of high pH, nutrient and/or salt levels present in pond water (Dismukes et al. 2008).

When biomass is used for powering transport, there are benefits to burning this in power plants for electric traction. Upward impact on food prices and negative im­pacts on biodiversity thereof will be lower per unit of energy output than in the case of the conversion of biomass to transport biofuels for internal combustion en­gines. Also, net greenhouse gas emissions may be relatively low. As pointed out in Sect. 1.6, use of this option depends on a much-increased social acceptability of electric traction in car transport. As pointed out in the same section, opinions on the ease with which such increased acceptability may be achieved vary greatly. If the moderate pessimists are right in this respect, government intervention to create incentives for electric cars may be useful.

Problems with the impacts of biofuel production on food prices may further­more be considerably reduced when biofuel production can be restricted to currently abandoned and fallow agricultural lands and land that currently sequesters little C. As pointed out in Sect. 6.4, this probably cannot be achieved without major govern­ment intervention. In the case of drylands, which currently sequester little C, large government investments may be needed in improved water management and con­servation practices (Thomas 2008). Such investments are also conducive to an in­creased resilience against climate change (Thomas 2008). In the case of abandoned agricultural land, incentives should be given that compensate for the financial dis­advantages if compared with the cultivation of good agricultural land. Government intervention may focus on limiting the cultivation of biofuel crops to marginal and abandoned agricultural lands or go one step further and establish government-owned companies that grow such crops. Such intervention is not a mission impossible. For instance, the government of Taiwan has focused its support for biodiesel on feed­stocks from polluted and fallow agricultural land (Huang and Wu 2008).

Limited use of organic wastes may also be useful in limiting negative side effects of transport biofuel use. In view of current prices for such biofuels (see Chap. 1), government intervention will often be needed to stimulate the production thereof. An evident priority is the improvement of technologies for the conversion of wastes into transport biofuels. As pointed out in Chap. 1, such technologies seem to offer much scope for lowering costs and improving conversion efficiencies. A mandate such as in the Energy Independence and Security Act 2007 of the USA for phase-in of lignocellulosic ethanol may also be helpful. Furthermore, to establish an environ­mental benefit, criteria have to be established which restrict marketing to biofuels that at least have a predefined benefit. Both the EU and the USA have restrictions in place for the life cycle greenhouse gas emissions of transport biofuels. It would seem useful to extend such criteria, for instance to safeguard soil organic matter and nutrient stocks and to limit negative effects on biodiversity.