Challenge

Chemical processor Repsol Quimica, a division of Repsol YPF, Tarragona, Spain, looked at several wastewater treatment alternatives for its new 678,000 tons per year polypropylene oxide/styrene monomer (PO/SM) and chemical production facility, which came online in 1999.

The process had to:

• meet local environmental regulations,
• produce effluent that could be discharged to the Mediterranean Sea,
• withstand contaminants that were difficult to treat with biological processes.

Test work with solvent extraction, incineration, and other systems did not produce satisfactory results.

Solution

The company turned to Siemens Water Technologies to test the Zimpro® wet air oxidation process and the PACT system on the wastewater. The testing was conducted at the Siemens Water Technologies pilot testing plant in Rothschild, Wisconsin, USA.

The results demonstrated successful treatment of the diverse waste streams, and a full-scale system incorporating wet air oxidation, PACT, and Hydro-Clear® sand filters was designed, installed, and started up in 2000. The plant capacity is 90 cubic meters per hour of liquid wastes and rainwater collected at the facility.

The wet air oxidation process treats the PO/SM wastewater and polyol ether streams. Then the wet air oxidation effluent, and other waste streams, pass through the PACT system where powdered activated carbon adsorption and biological treatment combine to produce a high quality effluent and withstand shock loadings. Finally, the treated water is filtered and discharged. The spent carbon and waste sludge are sent to a second wet air oxidation system where the carbon is regenerated and the sludge is oxidized.

Results

Once commissioned, the system has operated in compliance with the environmental standards. The average COD in the effluent is well below minimum requirements. Plant personnel also report significant savings in sludge disposal and powdered carbon costs.

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