How to treat high-strength organic chemical waste

The Client's Needs

Veolia Water Technologies was selected by Brown & Root to design a biological pretreatment facility for Phenolchemie in Theodore, Alabama. A new facility was required to treat 66 gpm of high-strength organic chemical waste produced in the manufacturing of phenol to meet discharge standards for release to a nearby publicly owned treatment works (POTW). This wastewater contained 5,000 mg/L COD, 4 to 6 percent salt (sodium sulfate), and had a temperature range between 40 and 42°C.

The Solution

Processes and techniques to treat a high-strength organic waste with a high inorganic content were evaluated, and process criteria were established. The treatment system designed by Veolia entails collection of the process wastewater in an equalization tank, followed by cooling and dilution with collected stormwater run-off and cooling tower blowdown prior to treatment in a field-erected package biological treatment plant.

The selected 78-foot-diameter package biological treatment system is comprised of an outer ring anoxic selector chamber, an aeration basin, and an inner clarification chamber. Wastewater collected in the equalization tank is monitored with a RACOD respirometer for toxic materials as a safeguard for the downstream treatment system. The collected wastewater is pumped to the selector chamber of the biological treatment unit where it is mixed with cooled dilution water from a chiller at 22°C and return activated sludge; nutrients (nitrogen and phosphorus) are added to the selector chamber. The wastewater/mixed-liquor mixture flows from the selector chamber to the aeration basin. The aeration basin is fitted with a coarse bubble aeration system to provide oxygen for biological degradation of the constituents (e.g., BOD, phenol, and methanol).

Treated wastewater and biological sludge overflow from the aeration basin to the clarifier where components are separated by gravity settling. The treated process water flows by gravity to the POTW sump. The concentrated biological solids are collected and returned to the selector changer, and a portion of the solids is pumped to sludge dewatering for disposal. Lime and ferric salts are added to the waste sludge in a mix tank, and the conditioned sludge is pumped to a Plate and Frame Filter Press where the sludge slurry is dewatered to form a 30% solids sludge cake that is discharged to a roll-off box. The sludge is hauled to a residual landfill.

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