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Treatability of Dissolved Organic Nitrogen in Truckee Meadows Water Reclamation Facility Using Coagulation or Ozone Treatment
Civil and Environmental Engineering
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The Truckee Meadows Water Reclamation Facility (TMWRF) has a waste load allocation (WLA) of 500 lbs/day for total nitrogen and a significant portion of the total nitrogen in TMWRF’s effluent is comprised of dissolved organic nitrogen (DON). This research addressed the treatability of DON collected from different process streams at TMWRF using ozone (O3) treatment and chemical treatment with various coagulants. With regard to ozone treatment, the change in bioavailability of DON was assessed following ozone treatment to identify if biological processes downstream of ozonation could remove DON effectively. Ozone oxidation experiments were performed on both filter effluent and final effluent samples. Ozonation alone was able to decrease DON levels; however, the total nitrogen level did not decrease since nitrate (NO3-) accumulation was equal to the DON removal. Following the ozone oxidation experiments, samples of ozonated filter effluent were subject to continuous-flow biodegradation tests to identify whether ozonation increased the biodegradation potential of DON. Separate columns were inoculated with either nitrification or denitrification processes at TMWRF and then fed either filter effluent or ozonated filter effluent. Ozonation and ozonation with hydrogen peroxide (H2O2) addition both appeared to enhance DON removal in biologically-active columns compared to control columns without ozonation. The change in DON, COD, pH, and other nitrogenous species throughout the biological active columns were measured. The best performance was observed in columns subject to O3 and H2O2 addition with DON levels reduced from 1.4 mg N/L to levels as low as 0.8 mg N/L. An economic evaluation on a full-scale ozone treatment system was performed. Chemical coagulation was performed on samples of TMWRF denitrification effluent using various doses and combinations of aluminum sulfate, ferric chloride, and the proprietary polymer Clarifloc®. The maximum observed DON removal when using aluminum sulfate was 59% at a combined dose of 24 mg Al2(SO4)3·14H2O/L and 2 mg/L polymer. When ferric chloride was used, the maximum observed DON removal was 46% at a dose of 100 mg FeCl3/L. Ferric chloride combined with polymer resulted in less DON removal than ferric chloride alone. In all jar test experiments, the total nitrogen decreased commensurately with dissolved organic nitrogen, suggesting adsorption during floc formation and removal during the settling phase. Ozonation, biodegradation, and coagulation were all shown to be viable treatments for partial DON removal from TMWRF’s effluent.