Fate and Transformation of Landfill Leachate Dissolved Organic Nitrogen and Its Implications for Estuarine Algal Growth

We investigated the fate and transformation of dissolved organic nitrogen (DON) during biological nitrogen removal (BNR) cotreatment of landfill leachate and municipal sewage. Three sequencing batch reactors (SBRs) were operated with high-, medium-, and no-leachate inputs. Systems were maintained at a solids retention time of 15 days and hydraulic retention time of 1 day, with methanol addition to support denitrification. Analytical methods included Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), Fourier transform infrared spectroscopy (FTIR), carbon-13 nuclear magnetic resonance (13C NMR), 16S rRNA gene sequencing, and algal bioassays. All reactors achieved ∼99% ammonium removal and 87–92% total nitrogen removal, with effluent nitrate < 1.1 mg N/L. DON remained the dominant nitrogen form (73–80% of total nitrogen), with concentrations of 5.5, 6.5, and 2.2 mg N/L. FTICR-MS showed more bioavailable protein-like DON in high-leachate conditions (20%) and more refractory lignin-like DON in medium-leachate conditions (60%). Algal bioassays indicated limited short-term bioavailability. Results demonstrate that while BNR effectively removes dissolved inorganic nitrogen, it produces DON-rich effluent with composition-dependent ecological implications.