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 μS cm−1; alkalinity=21 470 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-or-equal, slanted 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 pre-treatment, 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.