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Design • 0 Nitrification and Denitrification Once primary treated effluent is introduced into the secondary treatment process,nitrogen removal occurs first by nitrification and then by denitrification.In the first step of nitrification,an ammonium-oxidizing autotrophic bacteria,(Nitrosomonas),converts ammonium to nitrite.In the second step of nitrification,a nitrite-oxidizing bacteria,(Nitrobacter),converts nitrite to nitrate.Both of these processes occur under aerobic condi- tions.Lastly,denitrification occurs when nitrate is converted to nitrogen gas by heterotrophic bacteria under anoxic conditions(DO<0.5 mg/L). Therefore,treatment for NH3-N and TKN occurs through an aerobic process while treatment for NO3-N,TIN,and TN occurs through a combination of aerobic and anoxic processes. For more information about the nitrogen process in wastewater,see Metcalf&Eddy's"Small and Decentralized Wastewater Management Sys- tems,"4th Edition (1999).For information on pH and temperature effects on Nitrification and Denitrification,see pH Effect on Nitrification and Temperature Effect on Nitrification and Denitrification in the Design Considerations section on page 19. Discharge Treatment Levels and Sampling Requirements Discharge treatment levels and sampling requirements play a significant role in treatment facility design.Secondary treatment(effluent concentra- tions of BODS and TSS of s 30 mg/L based on a 30-day average) is a simple process typically requiring only a single-stage AdvanTex Treatment System.Additionally,advanced secondary treatment(BODS and TSS of s 10 mg/L based on a 30-day average)can typically be accomplished in the same manner. However many permits are now requiring some higher level of nitrogen treatment as well as providing values of"not to exceed" in place of"30-day average"or"30-day arithmetic mean." In these instances a safety factor of some kind is typically applied (or additional pro- cesses added)so that the discharge parameters are not exceeded even under maximum day flow conditions or maximum day primary-treated effluent concentrations. Likelihood of System Expansion and Potential Permit Changes Permits are typically limited in duration,and over the past two decades treated effluent discharge requirements have become stricter. In fact, many permit renewals are now asking for measurement of various constituents that were not part of the original treatment facility design.When designers are planning for future expansion,or for future modifications to permits,Orenco recommends using incremental engineering to plan for and provide space for potential future treatment upgrades.By understanding the various stages used in AdvanTex Treatment Systems,designers can lay out the treatment facility in a manner that allows for additional stages in the event that a planned build-out or future permit modification requires it.Please see sections titled Treatment System Configurations and Process Stages for more information. Highly Variable or Seasonal Flow Considerations Hundreds of AdvanTex systems are installed in parks, campgrounds, resorts,and lodges that experience highly variable flows (or complete shutdowns for long periods) due to seasonal use and they are ideally suited for these applications.Shortly after the system is placed in ser- vice, a thin bacterial film develops in the upper portion of the textile media; removal of BOD5/TSS occurs the first day after being in service. Independent tests show AdvanTex systems are capable of removing > 85% cBOD5 and > 97%TSS within the first few days of operation. Many other technologies (especially suspended growth technologies) require weeks to treat to this level and struggle during periods of low loading, The Operations&Maintenance (0&M) manual provided with each AdvanTex system can help guide the operator on appropriate 0&M for systems with highly variable or seasonal flows, including the use of trending to automatically adjust recirculation ratios. For more informa- tion on determining which 0&M method is best for a particular highly variable or seasonal flow application,contact Orenco. Water Softener Backwash Water softener regenerate (backwash) must not be plumbed into any Orenco AdvanTex treatment system.The concentration of sodium and chlorides in water softener backwash alters the settling and general solids segregating characteristics through the system and chlorides are elevated above the 180 mg/L toxicity or inhibitory threshold established by EPA for nitrogen removal. This backwash is bacteria-free and not an organic-based wastewater. Essentially it is a "salt/mineral-laden water,free of contaminates," suitable for ground discharge as recognized by many states. In fact, many jurisdictions prohibit salt water regenerate from being dis- charged to septic systems, advanced treatment systems, and/or sanitary sewer. Instead, there is a provision for constructing a separate small dispersal area for backwash. 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