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Waste Treatment Methods 195

vapors. These casing gases can be collected in a separate gathering
system and treated by adsorption (Peavy and Braun, 1991).
Another source of hydrocarbon emissions are the fugitive emissions
arising from leaking valves and fittings. Because these emissions are
generally too spread out to be collected, their release must be pre-
vented by replacing and repairing the leaking equipment.
Emissions from remediation projects of hydrocarbon-contaminated
sites can contain volatile hydrocarbons. These hydrocarbons can be
collected by passing the emissions through a bed of activated carbon
or adsorptive polymer. Alternatively, the vapors can be bubbled through
water, where the hydrocarbons become dissolved. Although the dis-
solution process can be effective in lowering hydrocarbon air emis-
sions, the subsequently contaminated water must then be treated and
disposed. For some projects, catalytic oxidation may be used as a low-
temperature alternative to incineration of volatile hydrocarbons.

6.3.2 Sulfur Oxides

Sulfur oxides are generated from the combustion of fuels containing
sulfur. Although these emissions can be treated to remove the sulfur,
the emission of sulfur can also be reduced or eliminated by the use
of low-sulfur fuel. A variety of scrubber systems are available to
remove sulfur from air emissions (Goodley, 1979).

6.3.3 Nitrogen Oxides

Nitrogen oxides are generated from high-temperature combustion
and from the combustion of fuels containing nitrogen (crude oil).
Unfortunately, these emissions are difficult to treat and may require
specially designed equipment.
Equipment to minimize the emission of nitrogen oxide in combus-
tion gases includes low NO x burners, flue gas recirculators, selective
catalytic reduction devices, and selective noncatalytic systems. The
amount of nitrogen oxides emitted can also be lowered by reducing
the amount of oxygen in the combustion process. Unfortunately,
lowering oxygen in the combustion process increases the amount of
partially burned hydrocarbons created.
The impact of nitrogen oxides from fixed installations, such as
natural gas compressor stations, can be minimized by the stack height,