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This study evaluated the performance of sequencing batch reactors (SBR) in the fate and transport of dissolved organic nitrogen (DON) using a blend of wastewater and landfill leachate. Most nitrogen removal methods concentrate on inorganic nitrogen, whereas some biological processes add DON to the effluent. Two reactors were introduced with wastewater and landfill leachate of high and low organic carbon and compared them to a reactor without leachate. DON transformation, characterization, and microbial community dispersion were examined to understand the effects of leachate-induced effluent DON on the biological nitrogen removal process. The ammonium removal efficiencies were found 96, 97, and 98%; COD removal efficiencies were 75, 59, and 63%; and total nitrogen (TN) removal efficiencies were 83, 86, and 88%, for R1, R2, and R3, respectively. The effluent nitrate concentrations were found 1.67 ± 0.89 (R1), 3.05 ± 2.08 (R2), and 1.31 ± 1.30 (R3) mg/L and DON went down from 9.67 ± 2.5 to 6.02 ± 2.8 mg/L (R1), 9.29 ± 3.4 to 7.49 ± 3.6 mg/L (R2), and 3.59 ± 1.6 to 2.08 ± 1.1 mg/L (R3). Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and excitation-emission matrices (EEMs) with parallel factor (PARAFAC) analysis were used to characterize DON. Microbial community analysis was also conducted. Leachate-induced DON discharge's environmental effects were assessed using in-situ aquatic ecosystem algal bioassay. SBR system removed most inorganic nitrogen species and a small amount of leachate-induced DON. The study emphasizes the need for independent investigations to assess their effects on receiving water bodies. 

Landfill leachate contains high levels of dissolved organic nitrogen (DON) that can be detrimental to aquatic life and water quality because it promotes the growth of harmful algal blooms (HABs). This study used physicochemical treatment technologies such as Fenton treatment and Granular Activated Carbon (GAC) adsorption to assess the breakdown and removal of landfill leachate-induced DON. The physicochemical treatments were applied to effluents of two bioreactors treating blended wastewater and landfill leachate. Bioreactor-1 (R1) was fed with high organic landfill leachate, and bioreactor-2 (R2) was fed with low organic landfill leachate. For R1 effluent, the Fenton treatment removed 66±9.2% COD and 52.4±8.7% DON at an optimum dosage of 200mg/L H2O2 and 1000mg/L FeSO4.7H2O. On the other hand, GAC removed 94.4±4.9% COD and 85.9±4.6% DON at an optimum dosage of 10g/L GAC. For R2 effluent, the Fenton treatment removed 75.8±6.6% COD and 60.3±3.2% DON at an optimum dosage of 200mg/L H2O2 and 1000mg/L FeSO4.7H2O. On the contrary, GAC treatment removed 92.2±4.3% COD and 92.3±3.7% DON at an optimum dosage of 10g/L GAC. Moreover, fluorescence spectrophotometry combined with parallel factor analysis (PARAFAC) was employed to provide insight into the DON degradation mechanisms. The study found that Fenton treatment and GAC adsorption both can effectively reduce DON in landfill leachate. However, GAC treatment was superior to Fenton treatment in eliminating DON from landfill leachate, while Fenton treatment may convert DON into inorganic nitrogen. The study emphasizes properly handling landfill leachate to avoid nitrogen contamination and harmful algal blooms in aquatic ecosystems.