Page 194 - Environmental Control in Petroleum Engineering

180 Environmental Control in Petroleum Engineering

enhancing any biological degradation of dissolved hydrocarbons remaining
in solution.

Biological Processes

Biological treatment can be used to remove low levels of dissolved
hydrocarbons from wastewater streams. Biological treatment consists
of mixing oxygen and nutrients with the water in a tank. The bacteria
then degrade the organic compounds. This process is widely used in
municipal water treatment plants, but may be too slow for oilfield
applications. Because the high salinity of produced water inhibits
biological growth, biological treatment will not be effective in most
cases. Another limiting factor is the lack of dissolved oxygen for
bacteria. Although oxygen could be added, it would significantly
increase the corrosion rate of the equipment.

Precipitation

The solubility of many organic molecules decreases as the pH
decreases. By lowering the pH, some organic materials can be precipi-
tated. Precipitation, however, will not remove all dissolved hydro-
carbons and will acidify the water.

Ultraviolet Irradiation

The use of ultraviolet radiation (including solar radiation) to break
down hydrocarbons has also been studied (Green and Kumar, 1990).
In this process, high-energy, short-wavelength photons are used to
break the chemical bonds of dissolved hydrocarbons. When combined
with heating to high temperatures, e.g., by solar collection panels,
virtually complete destruction of hazardous hydrocarbon molecules in
water has been observed. This method may have potential for treating
some hazardous chemicals, but is probably too expensive for treating
oilfield waters.

Oxidation

Dissolved hydrocarbons can also be destroyed through oxidation.
Ozone, peroxide, chlorine, or permangenate have been tested. To be