E. I. du Pont de Nemours & Co., Inc.
The primary objective of this project was to reduce the benzene concentration in the ethylene wastewater going to the bioponds from 350 ppm to less than 72 ppb. Failure to make this reduction will result in this water stream being classified as a RCRA hazardous waste.When the project began in December of 1988, the proposed EPA Toxicity Characteristics (TC) List contained a benzene level of 72 ppb. When this list was promulgated in March of 1990, the benzene level had been raised to 500 ppb. If a listed component is contained in a waste stream at a level greater than the level defined in the TC list, then the waste stream is defined as a RCRA hazardous waste. The TC list became effective in September, 1990.
The project team selected steam stripping as the appropriate process for removing the benzene from the wastewater. Carbon adsorption, activated sludge and Ultrox were also considered. Steam stripping was the preferred method of recovering organics from the wastewater stream. This method was chosen because the steam stripping process recovers a saleable organic product, has a significantly lower operating cost and does not generate a new solid waste.The project's intent was for the unit to have 100 percent utility; therefore, two steam strippers, a surge tank, two decanters, and two Trane refrigeration units were installed as the major pieces of equipment.
When the project started operation in April, 1990, the benzene concentration in the stream going to the biopond was reduced to below 50 ppb. In addition, the benzene emissions from the bioponds have been reduced about 70 tons per year.
Details of Reductions
Additional Information :
The benzene and other hydrocarbons are being recovered and sold as heavy aromatic distillate (HAD). The successful completion of this project allows the Company to avoid the cleanup and closing costs that would have been associated with contaminating the bioponds with a RCRA waste. These costs have been estimated to be in excess of $100 million.