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Waste Treatment Methods 181

effective, however, oxidation normally must be conducted at high
temperatures or with ultraviolet irradiation. Oxidation is not practical
for most oilfield applications.

6.1.3 Removal of Suspended Solids

During many drilling and production activities, solids will be
suspended in water that must be removed prior to water disposal.
These solids include cuttings generated during drilling and sand and
clay particles produced during oil production. Several methods are
available for removing these suspended solids from the water.

Gravity Separation

The simplest way to separate the larger solid particles is to use
gravitational settling. Fluids can be discharged into pits or tanks, where
the solids settle to the bottom. Gravitational settling, however, is not
effective for very small particles. The use of settling pits may also be
limited by environmental regulations and the potential for future
liability. Centrifuges can be used for enhanced gravitational separation.

Filtration

Another way to remove suspended solids is to filter the water. The
water passes through the filter, while the solids are retained. The
resulting filter cakes may be nonhazardous and could be disposed of
like pit bottom sludge. Filtration has considerable promise for separat-
ing oil field wastes (Townley et al., 1989).

Coagulation

An effective way to enhance the separation of suspended particles
is to coagulate (flocculate) the particles into larger agglomerations. The
larger agglomerations can then be separated more easily by gravita-
tional settling, centrifugation, or filtration.
One successful way to coagulate suspended solids is to add chemi-
cals that overcome the electrostatic repulsive charges on the solids to
allow them to flocculate. Chemicals that can be used include calcium
chloride, ferric chloride, or aluminum potassium sulfate (Hinds et al.,