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MAR-30-'93 TUE 08:3:. :SHELL SOCK-ON 9694 PO4 ENVMEX LTD. After leaving the nozzles, the water rises through the fluid bed with a uniform velocity profile, separating the particles from one another, and providing gentle particle mobility. Microbial growth occurs as organic material, and nutrients are converted to new cell mass. Simultaneously, respiration of the microbes converts dissolved oxygen to carbon dioxide. A portion of the clean effluent water is recycled to the inlet of the fluidization pumps, thereby assuring that the fluidization flow remains constant. The remaining effluent is discharged. Microbial growth results in a continuous addition of solid mass to the fluidized bed, causing the bed to expand and rise. When the bed reaches the bottom of the growth control mixer, excess bed (or cell matter) breaks away from the GAC particles, The separated cell mass leaves the reactor with the effluent, and the "cleaned" GAC is now heavy enough to fall back through the active bed. 2.2 Chemisay and Theory The GAC Fluid Bed is an attached growth biological treatment system; that is, the microorganisms used to treat the wastewater are grown on a solid media which holds the biomass and the contaminated water. The key to making attached growth systems more efficient is to maximize the contact between the contaminated water and the active biomass. Only the outer skin of biomass is actually in direct contact with the wastewater. The GAC Fluid Bed provides extremely large areas of microbial growth in direct contact with wastewater. The flow of water gently separates the particles from each other, exposing more surface area while maintaining narrow interparticle spacing and high interparticle fluid velocities needed for maximizing contact between microbes and contaminants. 2.2.1 Fluid Bed Mechanics The GAC Fluid Bed uses granular activated carbon (GAC) as the solid media. GAC consists of very porous solid particles of carbon, with up to 900 square meters of internal surface area per gram, The porosity of GAC gives it the ability to adsorb and hold a large amount of organic contaminants from a dilute solution in water. The larger internal passages also serve as additional surface on which to anchor and grow biomass. As water pushes upward through the bed of GAC, it gently lifts and separates the particles, causing the bed to "fluidize' and increase in height, so that each particle of GAC is essentially free floating within the bed, completely surrounded by water and not resting on any other particles. Page 2-6