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ADVANTEX° O&M ,MANUAL Dissolved Oxygen — Dissolved oxygen also alkalinity can be restored in the recirc or process provides critical information with which to diag tank,wherever denitrification occurs(and adjust- nose haw well a system is performing.Measures ing the recirc ratios may also bring the pH back of Dissolved Oxygen should be in the range of to preferred-operating levels). But wastewater 2.5 to 6 mg/L.If the DO level drops,the degree streams that are alkalinity-starved c&t provide of nitrification will normally drop as well,which for 100%nitrification. could be a sign of blinding or saturated flow con- The use of low flush fixtures requires special con- ditions—anything that might inhibit free air sideration.Low flush fixtures tend to reduce from flowing into the system.(Though it's quite hydraulic loads,which causes elevation of waste- possible to have low filtrate DOs and still have water constituents (i.e.,higher concentrations of high effluent quality,as measured by BOD and BOD,TSS,TKN,etc.). In this case, the available TSS levels.) alkalinity in the water supply may not be ade- Biologital Growth on Filter —.With"fired quate to accomplish rhe full level of nitrification film"treatment systems,biological growth on the desired. filter media is natural.The biotnat should appear These constraints exist for all wastewater treat- light-brown to dark-brown in color and gelati- ment operations,regardless of whether the opera- nous peranous in texture. tion involves a suspended growth contact stabi- Influent Cheracteristica -- Influent character- lization process or an attached growth packed istics (see p.7)will greatly affect the amount of bed filter. Packed bed systems will perform better, nitrogen reduction that is possible from any especially if they have a large attached growth wastewater treatment system.High solids and/or surface area per unit volume ratio,because of the fats and cooking oils increase the oxygen micro-sites near the attached side of the biomar, demand and accumulation of material on and where denitrification typically occurs,returning within the media,affecting the available oxygen some of the alkalinity.Textile packed bed filters, for nitrification. because of their large surface area per unit vol- pH— For normal residential nitrogen loads,pH ume ratio,tend to perform even better. is typically maintained between 6-8. Nevertheless,additional buffering may be neces- sary to accomplish the level of nitrification Aftfl fy—The nitrification process releases desired.In low alkalinity conditions,pH adjust- hydrogen ions into solution,which tends to ment can be made with the addition of Quick or lower the pH level.Alkalinity is essential for Hydrated lime,soda ash,or caustic. (Mote. at nitrification.For each part ammonia that is nitn- process points preceding sedimentation zones, fled,7.14 parts alkalinity are consumed(buffer- lime adjustment—buffering—would be pre- ing the acidity caused by the release of hydrogen ferred.Soda ash and caustic both contain sodi- ions).Consequently,if the degree of nitrification tart,which is a dispersant.) is less than expected,it could simply be a lack of sufficient alkalinity to support more.Typical resi- dential nitrification requires alkalinity above 250t mg/L for recirculating processes and double that for single pass processes.Many wastewater streams do not have sufficient alkalinity to support complete nitrification. Wastewater streams without sufficient alkalinity to support complete nitrification may,depending on the type of process,cause a depletion in the alkalinity to the point where its ability to buffer stops.The pH correspondingly drops to a level that retards the microbial activity(<6t). Recirculating the effluent helps,since half the