Fenton's pre-treatment of mature landfill leachate

The aim of this study was to check the effectiveness of the Fenton's reagent (Fe2+ + H2O2 + H+) for the pre-treatment of a municipal landfill leachate with the objective of improving its overall biodegradability, evaluated in terms of BOD5/COD ratio, up to a value compatible with biological treatment. The leachate came from a municipal sanitary landfill located in southern Italy and the average values of its main parameters were: pH = 8.2; COD = 10 540 mg l(-1); BOD5=2300 mg l(-1); TOC=3900 mg l(-1); NH4-N=5210 mg l(-1); conductivity = 45350 muS cm(-1); alkalinity= 21470 mg l(-1) CaCO3. The effect of initial pH value on the pre-treatment effectiveness was evaluated by titrating the amount of acidic by-products formed. The extent of leachate oxidation was monitored and controlled by both pH and redox potential measurements. The best operational conditions for achieving the desired goal (i.e., BOD5/COD greater than or equal to 0.5) resulted: Fe2+ = 275 mg l(-1); H2O2 = 3300 mg l(-1); initial pH = 3; reaction time = 2 h. At the end of the Fenton's pretreatment, in order to permit a subsequent biological treatment, residual ferric ions were removed increasing the pH up to 8.5 by adding 3 g l(-1) of Ca(OH)(2) and 3 mg l(-1) of a cationic polyelectrolyte, the latter as an aid to coagulation. This final step also resulted in a further modest removal of residual COD due to co-precipitation phenomena. (C) 2003 Elsevier Ltd. All rights reserved.