18.4.Recycling and Domestic Waste 383 TABLE 18.6.Average annual yield of certain materials produced on 1 hectare(104 m2 or 2.47 acres)of land 30 kg of woola 105 kg of juteb 500 kg of natural rubber 700 kg of linen (flax)fiber 1,000 kg of cotton 7,000 kg of wheat 10,000 kg of rice 70,000 kg of sugar beets aSheep may eventually end up as meat. Of which maximal 7.5%is fiber. disadvantage of biodiesel is,however,that it is uneconomic.At present,the price of RME before taxes is about twice that of conventional diesel.Expressed differently,the energy price given in dollars per gigajoule is 10.2 for rapeseed oil,13.8 for RME, and 5.2 for diesel oil.2 However,one should not forget in this context that crops for energy production may eventually compete for prime land on which food is grown for a steadily increasing world population. Mankind may eventually have to make a choice and decide how much of the available farm land is utilized for food and clothing, and how much is used for renewable energy,including solar en- ergy.It is therefore instructive to know the quantity of various goods that can be harvested from a given piece of land.Table 18.6 provides this information.It is,of course,realized that not all land is equally suited for each of the listed raw materials,and that the availability of water is also a major factor for some crops,par- ticularly for rice. 18.4.Recycling and Domestic Waste As already discussed,Table 18.2 contains the projected number of years at the end of which the currently known world reserves may be exhausted.These data strongly suggest the necessity for recycling if we want to preserve essential resources for future generations.This is particularly true for copper (pipes,wires), lead (batteries),zinc (galvanized steel,brass plumbing fixtures), 2 Source: Bundesministerium fur Umwelt,Naturschutz und Reaktor- sicherheit,Berlin,Germany,(2000).disadvantage of biodiesel is, however, that it is uneconomic. At present, the price of RME before taxes is about twice that of conventional diesel. Expressed differently, the energy price given in dollars per gigajoule is 10.2 for rapeseed oil, 13.8 for RME, and 5.2 for diesel oil.2 However, one should not forget in this context that crops for energy production may eventually compete for prime land on which food is grown for a steadily increasing world population. Mankind may eventually have to make a choice and decide how much of the available farm land is utilized for food and clothing, and how much is used for renewable energy, including solar en￾ergy. It is therefore instructive to know the quantity of various goods that can be harvested from a given piece of land. Table 18.6 provides this information. It is, of course, realized that not all land is equally suited for each of the listed raw materials, and that the availability of water is also a major factor for some crops, par￾ticularly for rice. As already discussed, Table 18.2 contains the projected number of years at the end of which the currently known world reserves may be exhausted. These data strongly suggest the necessity for recycling if we want to preserve essential resources for future generations. This is particularly true for copper (pipes, wires), lead (batteries), zinc (galvanized steel, brass plumbing fixtures), 18.4 • Recycling and Domestic Waste 383 2 Source: Bundesministerium für Umwelt, Naturschutz und Reaktor￾sicherheit, Berlin, Germany, (2000). TABLE 18.6. Average annual yield of certain materials produced on 1 hectare (104 m2 or 2.47 acres) of land 30 kg of woola 105 kg of juteb 500 kg of natural rubber 700 kg of linen (flax) fiber 1,000 kg of cotton 7,000 kg of wheat 10,000 kg of rice 70,000 kg of sugar beets aSheep may eventually end up as meat. bOf which maximal 7.5% is fiber. 18.4 • Recycling and Domestic Waste