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11 Design It is used for applications with high strength waste streams (such as Type 7 applications and any application with a significant volume of restaurant waste, such as Type 5)to condition the waste stream prior to secondary treatment by raising dissolved oxygen levels. An aeration tank,followed by a clarification tank, is situated between the primary treatment system (or pre-anoxic tank if used)and the secondary treatment system. Design Notes and Special Considerations: Pre-aeration units should be sized to provide the appropriate amount of oxygen to reduce organic waste strength or to reduce BODS to less than 400 mg/L. For systems with high BODS influent values from restaurant waste,pre-aeration can be sized to accomplish approximately 50% reduction in BODS values. For systems with extreme BODS influent values from food or wine processing, pre-aeration can be sized to accomplish approximately 75% reduction in BODS values. For recommendations on sizing pre-aeration and clarification tanks,see Appendix A. Pre-aeration is required for all Application Type 7 systems,and highly recommended for systems that have greater than a 50%contribution of flow from restaurants(primarily Application Type 5 systems).Orenco provides a number of standard pre-aeration packages for lower flow rang- es and can assist in sizing and recommendations for higher flow or extreme BODS influent values, Contact Orenco for configurations and sizing. Standard AdvanTex Treatment Stage Purpose and Description: After primary or pre-anoxic treatment,effluent is transported to the recirculation-blend tank or chamber,where it is blended with AdvanTex filtrate.The blended wastewater is distributed over the AdvanTex textile media and percolates down through the media,where it is filtered, cleaned,and nitrified by the naturally occurring microorganisms populating the media.After treatment,a portion of the filtrate is returned to the recirculation-blend chamber while a portion is transported to the next treatment stage or to dispersal. Note that a portion of the recirc-blend (or filtrate) is often returned directly to the pre-anoxic treatment stage. In the secondary treatment process,AdvanTex units filter and clean effluent from the primary treatment system.When loaded at or below the applicable loading rate,they typically achieve treatment levels of< 10 mg/L BODS/cBODS and TSS(30-day average or 30-day arithmetic mean),with total nitrogen (TN) reduction typically>60%and nitrification averages of 95% (range 90-99%). For nitrogen loading rates and sizing requirements,refer to the AdvanTex Unit Sizing section of this document. Post-Anoxic Treatment Stage Purpose and Description: The post-anoxic treatment stage provides additional denitrification after secondary treatment in wastewater systems that require significant reductions in TN,TIN,or NO3-N. Nitrified AdvanTex filtrate from the secondary treatment stage is transported to an anoxic zone inside of the post-anoxic tank. During post-anoxic denitrification, BOD is consumed during the conversion of NO3 to N2 gas by facultative heterotrophic bacteria.The N2 gas is then returned to the atmosphere.There are two options for post-anoxic treatment—standard post-anoxic treatment without media or an anaerobic moving bed bioreactor(MBBRd)with media.A supplemental carbon feed unit is required for both options to provide the post-anoxic stage with the necessary carbon-to-nitrogen ratio for effective denitrification. Design Notes and Special Considerations: Post-anoxic tanks are typically sized at 100%of the Average Day Design Flow. For denitrification to take place,oxygen levels must be depleted to the level that nitrate becomes the primary oxygen source for microorganisms. Requirements for effective denitrification include ... • Dissolved oxygen levels<0.5 mg/L(preferably<0.2 mg/L) • Carbon-to-nitrogen ratio of 4:1 to 8:1 • Sufficient residual alkalinity(100 mg/L±) in the secondary treatment stage to ensure optimum pH in the post-anoxic stage • Temperature of the waste stream shall remain above 50° F(10° C)at all times and should typically be above 59° F(15° C) For standard post-anoxic treatment meeting the above conditions, reduction of nitrate(NO3)through conversion to nitrogen gas(N2)should exceed 70%. For additional nitrogen reduction, Orenco recommends a denitrifying Moving Bed Bioreactor. MBBRd units are built in insulated fiberglass vessels.They can achieve up to 90% reduction of nitrate(NO3)through conversion to nitrogen gas(N2)and are typically configured as follows ... • Fiberglass vessel,sized at 50%Average Day Design Flow,with media retention screens and filters as needed • Media fill is typically 20%of the vessel volume • One pneumatic ejector provided per 4 lineal ft(1.22 m)of vessel to ensure optimal mixing and food delivery to the media • Blowers, housed in a control building,to power ejectors Orenco Systems°•800-348-9843•+1 541-459-4449•www.orenco.com NDA-ATX-1 Rev.8,©10/20 Page 13 of 38