Abstract
This study focuses on the treatment of a mature landfill leachate by coagulation and photo-Fenton at different conditions. Optimal coagulation is carried out with ferric chloride in acid conditions; and with alum in near-neutral conditions, to minimize the use of sulphuric acid for pH adjustment (1 g/L vs. 7.2 g/L), the generation of sludge and the increase of conductivity in the final effluent. In both cases, a similar chemical oxygen demand (COD) removal is obtained, higher than 65%, which is high enough for a subsequent photo-Fenton treatment. However, the removal of absorbance at 254 nm (UV-254) was significantly higher with ferric chloride (83% vs. 55%), due to the important removal of humic acids at acid pH. The best results for coagulation are 2 g/L ferric chloride at initial pH = 5 and 5 g/L alum at initial pH = 7. After coagulation with ferric chloride, the final pH (2.8) is adequate for a homogeneous photo-Fenton using the remaining dissolved iron (250 mg/L). At these conditions, using a ratio H2O2/COD = 2.125 and 30 min contact time, the biodegradability increased from 0.03 to 0.51. On the other hand, the neutral pH after alum coagulation (6.7) allows the use of zero valent iron (ZVI) heterogeneous photo-Fenton. In this case, a final biodegradability of 0.32 was obtained, after 150 min, using the same H2O2/COD ratio. Both treatments achieved similar results, with a final COD, UV-254 and color removal greater than 90%. However, the economic assessment shows that the approach of ferric chloride + homogeneous photo-Fenton is much cheaper (6.4 €/m3 vs. 28.4 €/m3). Although the discharge limits are not achieved with the proposed combination of treatments, the significant increase of the pre-treated leachate biodegradability allows achieving the discharge limits after a conventional biological treatment such as sequencing batch reactor, which would slightly increase the total treatment cost.
Highlights
Municipal solid waste (MSW) generation is increasing due to population growth, the modification of lifestyles and increased industrialization all around the world
The results show that similar chemical oxygen demand (COD) removal (>65%) and color removal (>90%) can be obtained with alum and ferric chloride coagulation at optimal conditions, contrary to the results from previous publications treating Landfill Leachate (LL)
7.2 g/L for ferric chloride), a 25% lower sludge production, the lower conductivity of the treated LL (17.1 vs. 22.5 mS/cm) as well as a slightly lower cost. This justifies its combination with zero valent iron (ZVI) in heterogeneous photo-Fenton treatment to increase biodegradability at neutral pH
Summary
Municipal solid waste (MSW) generation is increasing due to population growth, the modification of lifestyles and increased industrialization all around the world. Even landfilling is the last waste-management option; this option is still necessary for the disposal of non-recyclable materials; it has been extensively used extensively in the past due to its simplicity and lower management cost [1,2,3]. Other management options such as energy valorization are more expensive and still produce 10–20%. LL is produced during landfill operation and decades after its complete closure, representing a high risk for the environment [5,6].
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