Multistage treatment technology for leachate from mature urban landfill: Full scale operation performance and challenges

Abstract

In the present work, a multistage treatment strategy was applied to a mature urban leachate, at full scale. The treatment system consisted of (i) a sequential batch reactor (SBR), for nitrification/denitrification processes, followed by (ii) a coagulation/sedimentation (C/S) stage, (iii) an advanced oxidation process, in this case the photo-Fenton (PF) reaction, and (iv) a final SBR. Glycerol, a waste-product from biodiesel production, was successfully employed as an external carbon source for denitrification purposes. The C/S and PF stages were conducted in the same tank, which was coupled to 4 FluHelik photoreactors connected in series, thus enabling a compact solution for the multistage facility. The major operational difficulties were found in the: (i) C/S stage, due to the production of dense foam that trapped the sludge; and (ii) PF stage, for iron precipitation. These problems were overcome, respectively, with: (i) sludge removal after nitrite oxidation with hydrogen peroxide (intermediate step prior to PF); and (ii) maintenance of a residual amount of H2O2 before neutralization step. Each treatment sequence was applied to ca. 30 m3 of urban leachate after an aerated lagoon, leading to global removal efficiencies of 98% for COD (from 8.30 to 0.15 g O2/L), 97% for DOC (from 2.32 to 0.08 g C/L) and 85% for TN (from 2.65 to 0.41 g N/L). The sludge produced was also treated in-situ and the compliance with legal disposal standards was verified. The average total operational cost for the complete treatment sequence was 6.7 €/m3, including reagents, energy consumption, sludge treatment and respective disposal.