Sustainability: Humanity Perspective - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 780

15.3. The planet earth's core is so hot that the middle layer (mantle) is consisting of liquid
ion. The surface of the earth has been cooled down millions of years of ago. Therefore,
geothermal energy or the thermal energy inside the earth can be harvested without
seasonal limitation (thus reliable). Using sustainability concept and briefly describe
(a) Is geothermal energy is renewable?
(b) Is geothermal energy sustainable?
15.4. Evaporation from water body regulates/buffers the temperature nearby. For a water
body covering an area of 10 8 m 2 , howmuch thermal energy is removed by evaporation?
Assume an average water temperature of 290 K and evaporation rate of 1 g/(m 2 $ s).

15.5. Water is the common solvent used by humanity. In chemical processes, there are more
efficient solvents that can improve the economic benefits. For example, ethanol has
been proposed to replace water in pulp production. Using sustainability concept and
briefly describe
(a) Is ethanol use is renewable?
(b) Is ethanol use sustainable?
(c) Is ethanol use more sustainable than water use?
15.6. A hydroelectricity facility was built below a mountainous area. Owing to the
seasonal weather changes from wet to dry, the available water flow changes
significantly. In 1 year, the water flow rate in a low day was just 8% of that in a high
flow “wet” day. Determine the change in the available electricity generation
possible if a reservoir is built to maintain the water level.
15.7. A forested area has been found to have a biomass carrying capacity of 15 kg $ m 2 and
productivity of 0.3 kg $ m 2

$ year 1 . Because of rising demands on energy resources,
the 50-year rotation of the forest is regarded as too long. This area is to be cleared to
plant a perennial crop: switchgrass. It will take a couple of years to establish, but the
annual productivity is expected to be at 1 kg $ m 2

$ year 1 . Discuss the pros and cons

of such a change.
15.8. A large area of farm land has become less productive and farmers starting to move out
of agricultural cropping tendering. Some area has turned into grassland due to
inactivity. A forest product company has started to rent the idle farm land to grow
Aspen trees. Since the land is loaned from farmers, the forest product company is
forced to manage the growth and harvest of the trees at maximum output while
keeping the cost minimum. Discuss the benefit of managing a “forest” land as
comparing to managing a grassland for biomass production.
15.9. Competition of biofuel with food has generated another imbalance among the general
population. Food could be diverted to produce biofuel and thus takes away the food
that is available to certain groups of people. It is decided to switch from corn-based
ethanol to cellulosic ethanol. To ensure this process to be successful, it is decided to
turn the current corn crop land to switchgrass. Switchgrass can produce nearly the
same amount of biomass, but at much lower fertilizer use and less energy input for
cultivation. Briefly describe the sustainability impact and if the conflict was resolved in
a sustainable manner.
15.10. A typical forest growth curve after the seedlings are fully established in the Northeast
USA is shown in Fig. P15.10 . When new seedlings are planted, it takes 5 years to