Treatment of Petrochemical Wastewater

This report does not deal with particular chemicals, as most Process Economics Program reports do, but with the wastes from the industry. It is therefore organized around processes of broad applicability. These include processes for removing entrained liquids and solids; biological, adsorption, and oxidation processes for removing a broad spectrum of pollutants; and the processes for treating cooling tower blowdown.

Clearly it is impractical to evaluate the disposal of specific pollutants from so broad a field as the petrochemical industry, However, the types of pollutants, reported methods of treatment, and references are tabulated for many specific products. Also, the significance of pollutional parameters is discussed as background information for use in setting objectives and in working with control authorities.

Although this report deals with treatment of aqueous wastes, the problem is often more effectively solved by in-plant design and operational changes before the waste is formed. There are reports of 90% reduction in wastewater flow by such methods. Examples of such changes include elimination of once-through cooling water, provision of separate sewers for clean storm water, substitution of surface condensers for barometric condensers, and use of oil rather than water as a quenching medium. Such effective changes are possible because many plants were built before waste treatment was a legal requirement. The economic effect of such reductions may be judged from estimates that a 50% reduction of flow reduces waste treatment capital 2070, a 50% reduction of biochemical oxygen demand reduces capital 15%, and a 50% reduction of both simultaneously reduces capital 32%. Treatment requirements are being set in terms of a given amount of pollution per unit of plant output, rather than in terms of quality of the wastewater. This approach favors minimizing water usage and its pollutional load by inplant processing.

A corollary of the less crowded conditions that led to the former casual attitude toward pollution was the greater availability of land area for treating facilities, Thus solutions to tightening restrictions have often included biological treatments developed for domestic sewage. Besides requiring large areas, these methods suffer from the inability to remove contaminants completely. Current efforts at reducing these defects include the use of oxygen in place of air to speed up the biological processes and the substitution of physical and chemical processes for biological ones, Similar efforts are being made to reduce the size of facilities for separating entrained oil and solids. This report will evaluate conventional methods used by the petroleum and petrochemical industries as well as some of the newer methods.