Environmental Engineering Reference
In-Depth Information
negative. Although energy crops grown conventionally with pesticides and fertilizers
threaten water supplies through chemical run-off and eutrophication (organic pollution of
aquatic ecosystems), perennial woody crops such as palm oil consume far less water than
All in all it is very difficult to calculate whether a practice, commodity, or product is
sustainable. To do so, we must conduct what is called a life cycle assessment, taking into
account its environmental and social impact from production through manufacturing to
disposal.
6.9 The Impacts of Geothermal Energy
The hot water tapped from the Earth at geothermal plants is not pure. It contains minerals
that leached from the reservoir rock, variable quantities of GHGs (mainly carbon dioxide),
andsomehydrogensulphide,whichisresponsiblefortherotten-eggsmellthatoftenoccurs
near vents and geysers. The chemicals present in geothermal fluids, if released at the
surface, can have adverse effects on the ecology of rivers, lakes, or marine environments.
In the past, before the dangers were sufficiently understood, geothermal fluids were often
released at the surface. Nowadays, it is usually injected back into the reservoir after passing
through a steam turbine. The twin advantage of this approach is that it helps to maintain
high pressure in the reservoir and avoids contamination of watercourses.
There is no combustion involved in geothermal energy. In closed-loop power plants,
where the geothermal fluid passes through a heat exchanger before being reinjected into
the ground, carbon dioxide emissions are close to zero. In direct heating applications,
Piercing the Earth's crust to depths of hundreds or thousands of metres affects its
geological structure. As with other deep drilling projects, pressure or temperature changes
induced by stimulation, production, or injection of fluids can lead to geo-mechanical
stress changes. The rock interstices, there for millions of years, are quickly emptied of
hot liquid and filled with colder liquid coming from the power plant. Some claim that
geothermal energy production may cause micro-earthquakes, steam eruptions, and ground
subsidence. Yet, no buildings have been significantly damaged by shallow earthquakes
resulting from the extraction and reinjection of geothermal fluid. Ground vibrations or
noise from EGS demonstration projects have not been large enough to lead to human
injury or significant property damage. At a few high-temperature geothermal fields, the
reduction in underground pressure because of extraction of geothermal fluid has led to
