Page 198 - Environmental Control in Petroleum Engineering

184 Environmental Control in Petroleum Engineering

Reverse Osmosis

The most common way to totally remove all dissolved solids from
water is through filtration processes like reverse osmosis. These pro-
cesses, however, are not intended to be used for waste water treatment,
but to provide potable water from nonpotable water. For example,
reverse osmosis is commonly used to provide drinking water from
seawater in desalinization plants. During reverse osmosis, saline water
is pumped through a very small pore filter. The water molecules pass
through the filter, but the larger dissolved solids molecules do not.
Although the water supplied by a reverse osmosis plant is pure enough
to be used for most purposes, the dissolved solids concentration in the
waste stream that does not pass through the filter is higher than before
and must still be disposed. Fouling is the most difficult problem to
overcome when using reverse osmosis on oilfield brines. Pretreatment
of the water prior to entering the reverse osmosis facility is required.
Because of its high cost, reverse osmosis is most commonly used
to provide a supply of pure water in arid areas, rather than as a
treatment method for wastewater. However, in areas where high-quality
water is scarce, reverse osmosis can be used to treat produced water.
(Tao et al, 1993).

Evaporation/Distillation

Another way to obtain potable water from water containing impuri-
ties is to evaporate and condense the water. Like reverse osmosis, this
process is primarily used to provide a stream of pure water, not to
treat a stream of wastewater. Like reverse osmosis, this process
concentrates the wastes, which results in a smaller waste volume that
ultimately must be disposed. This process is also very expensive.

Biological Processes

Although biological processes cannot destroy dissolved solids, they
can alter their chemical form. For example, biological processes can
alter the availability of heavy metals for uptake by plants, as well as
the ability of metals to leach through the soil (Canaratto et al., 1991).
Bacterial remediation has also been successfully used to remove
sulfides from produced water (Sublette et al., 1993).