Abstract. Three-dimensional field monitoring of a gasoline plume showed rapid decay of toluene and ethylbenzene during downgradient transport with slower decay of xylenes, benzene, and MTBE under mixed aerobic-denitrifying conditions. Decay was most rapid near the source but slower farther downgradient. Effective first-order decay coefficients

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There is a continuing need to expand and upgrade the treatment capability of existing wastewater treatment facilities. Membrane bioreactor (MBR) technology is proven to provide reuse quality water and offers a unique capability to do this upgrading while minimizing the need to build additional tanks or use more space on site. A new MBR technology using external, tubular membranes arranged into membrane "skids" greatly simplifies plant upgrading and retrofitting by placing the membranes outside of the bioreactor, rather than immersing them in the mixed liquor. The flexibility offered by this external membrane design now makes an MBR upgrade practical for any suspended growth treatment plant, regardless of its bioreactor configuration or tank dimensions. In addition, the operating cost of the innovative, external membrane system is less than an immersed system due to the inclusion of a unique airlift that internally air scours and cleans the tubular membranes as they operate. As a result, significantly less scour air is required than with immersed systems, and the overall operating cost of the MBR system is reduced. KEYWORDSMembrane bioreactors; external membrane systems; water reuse; wastewater plant upgrade; retrofit 374 Membrane Technology 20083. Minimize onsite construction -additional biological tanks and membrane tanks are not needed. 4. Minimize disruptions of ongoing treatment operations during retrofitting 5. Provide proven, long-life of rugged tubular membranes; 6. Provide sustainable high flux and permeability with low operating costs; 7. Offer simple and safe membrane access 8. Provide automatic and in-place cleaning to minimize operator attention.

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