Treatment train for mature landfill leachates: Optimization studies

In the current study, a treatment train strategy for urban mature leachates, comprising biological and physicochemical processes, was tested for full legal compliance. The leachate presents a high organic and nitrogen content (1.1 g C/L; 3.6 g O-2/L; 2.0 g N/L) and low biodegradability (BOD5/COD 0.05). In the first stage, a sequential batch reactor (SBR), operated in a 24 h-cycle mode (15 h aeration +8.5 h anoxic, with methanol as external carbon source +0.5 h settling), was tested for total nitrogen (TN) removal. The maximum daily TN load that could be treated, reaching the legal limit (< 15 mg N/14, increased by 50% with the rise in temperature from 20 to 30 degrees C. For the following coagulation stage, the highest dissolved organic carbon (DOC) removal (64%) and lower final turbidity (33 NTU) were obtained with 240 mg Fe3+/L, at pH 3.0. The jar-tests, comparing nitrified (L-NIT) and nitrified/denitrified (L-N/D) leachate, stressed the effect of the leachate alkalinity, generated during the denitrification reaction, on process efficiency. For the coagulated LN,D., with alkalinity of 1.1 g CaCO3 L, the final concentration of sulfate was only slightly below the legal limit (< 2 g/L). A photo-Fenton (PF) oxidation process (pH range of 2.8-3.0, 60 mg Fe2+/L), as third treatment step, promoted a significant enhancement on leachate biodegradability, consuming 75 mM of H2O2 and 8.9 kl 1 of accumulated UV energy, to achieve an effluent that can be further biologically treated in compliance with the COD discharge limit (150 mg O-2, L) into water bodies. Biological continuous mode tests using a conventional activated sludge process, with an hydraulic retention time (HRT) of 12 h, allowed to obtain COD and TSS values (107 +/- 3 and 50 +/- 2 mg/L, respectively) below the legal limit. (C) 2019 Elsevier B.V. All rights reserved.