Environmental Engineering Reference
In-Depth Information
eventually by amphibians and fish (Havas 1990).
Artificial buffering of lakes in this way is only a
temporary measure which may be likened to the
use of antacid to reduce acid indigestion. The
neutralizing effects of the lime may last longer
than those of the antacid, but they do wear off
in 3 to 5 years and re-liming is necessary as long
as acid loading continues (Ontario: Ministry of
the Environment 1980). The treatment of the
environment with lime to combat acidity is only
a temporary measure, at best. It can be used to
initiate recovery, or to control the problem until
abatement procedures take effect, but since it
deals only with the consequences of acid rain
rather than the causes, it can never provide a
solution.
Most of the current proposals for dealing with
acid rain tackle the problem at its source. They
attempt to prevent, or at least reduce, emissions
of acid gases into the atmosphere. The only way
to stop acid emissions completely is to stop the
smelting of metallic ores and the burning of fossil
fuels. Modern society could not function without
metals, but advocates of alternative energy
sources—such as the sun, wind, falling water and
the sea—have long supported a reduction in the
use of fossil fuels. These alternative sources can
be important locally, but it is unlikely that they
will ever have the capacity to replace
conventional systems. Nuclear power has also
been touted as a replacement, since it can be used
to produce electricity without adding gases to
the atmosphere. It has problems of its own,
however. Difficulties associated with the disposal
of radioactive wastes remain to be resolved, and
events such as the Chernobyl disaster of 1986
do little to inspire public confidence in nuclear
power. Thus, although the replacement of
fossilfuel-based energy systems with non-
polluting alternatives has the potential to reduce
acid rain, it is unlikely to have much effect in the
near future.
Since SO
2
makes the greatest contribution to
acid rain in North America and Europe, it has
received most attention in the development of
abatement procedures, whereas emissions of
NO
X
—which are both lower in volume and more
difficult to deal with—have been largely
neglected. Similarly the development of control
technology has tended to concentrate on systems
suitable for conventional power stations, since
they are the main sources of acid gases (Kyte
1986a). Sulphur dioxide is formed when coal and
oil are burned to release energy, and the
technology to control it may be applied before,
during or after combustion. The exact timing will
depend upon such factors as the amount of acid
reduction required, the type and age of the system
and the cost-effectiveness of the particular
process (see Figure 4.12).
One of the simplest approaches to the
problem is fuel switching, which involves the
replacement of high sulphur fuels with low
sulphur alternatives. This may mean the use of
oil or natural gas rather than coal. In Britain,
for example, the recently privatized power
industry is actively exploring the increased use
of North Sea gas as a means of reducing SO
2
output, despite concern that this approach is a
waste of a high premium fuel with a relatively
short lifespan (Stevenson 1993). However,
since most power stations use coal and are not
easily converted to handle other fuels, fuel
switching usually involves the replacement of
one type of coal with another or even the
blending of low and high sulphur coal. Much
depends on the availability of the low sulphur
product. In Britain, for example, the supply is
limited (Park 1987), but in western Canada and
the western United States, abundant supplies of
low sulphur coal are available with a sulphur
content only one-fifth of that which is normal
in eastern coal (Cortese 1986). Such a
difference suggests that fuel switching has a
considerable potential for reducing SO
2
production, yet wholesale substitution is
uncommon. The problem is a geographical one.
The main reserves of low-sulphur coal are in
the west, far removed from the large consumers
in the east. Transport costs are therefore high,
and complete switching becomes economically
less attractive than other methods of reducing
SO
2
output. Compromise is possible. Rather
than switching entirely, Ontario Hydro, the
