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An activated sludge system was implemented for removal of BTEX from a recovered groundwater stream at a U.S. refinery containing between 5 and 10 ppm benzene and lesser amounts of toluene, ethylbenzene, and xylene. Activated sludge would normally not be feasible for treatment of this type of stream because of the difficulty of maintaining a sufficient mixed liquor population.with such a low organic content of the water (TOC between 5 and 10 ppm; BOD5 between 10 and 20 ppm). Because of the relatively high flow rate of this stream (3000 to 5000 gpm), however, more typical BTEX removal technologies such as granular activated carbon (GAC) and air stripping were quite expensive. During bench-scale testing with another technology (fluidized bed bioreactor), it was discovered that upon oxidation and subsequent precipitation, the iron in the water helped form a good settling floc in which the iron precipitate was intimately bound with the biomass. This finding was the basis for testing, and ultimately implementing a very cost-effective activated sludge system for treatment of this stream with a relatively low hydraulic detention time (4 –6 hours) and high clarifier surface overflow rate (800 gal/d/ft2). A year of operation demonstrated that the system is performing quite well, with greater than 99.5% of the influent benzene biodegraded and excellent effluent quality.

This presentation describes the pilot study leading to the final design, the design and operating data of the full scale system, and the results of a mass balance study in evaluating the destruction efficiencies for volatile organics of this unique groundwater treatment system.

Document Type: Research Article


Publication date: January 1, 2003

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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