Determination of suitable pretreatment method for old-intermediate landfill leachate

For old-intermediate landfill leachate, the high concentrations of ammonium and low BOD/COD (B/C) ratios are the main obstacles to biological treatment. Magnesium ammonium phosphate (MAP) precipitation (struvite precipitation) and Fenton oxidation were employed as pretreatment options on this type of leachate. Results revealed that at optimum operating conditions of pH 9 and MAP ratio of 1:1:1, ammonium and COD were reduced by 97.8% from 2132 mg l(-1) to 46 mg l(-1) and by 50.0% from 4113 mg l(-1) to 2057 mg l(-1), respectively using struvite precipitation. COD was lowered by 76% and ammonium by 6.3% using Fenton oxidation at optimized conditions of H2O2 dosage of 3500 mg l(-1), Fe2+ dosage of 437.5 mg l(-1), pH 4, a mass ratio of 8 for H2O2: Fe2+ dosage and reaction time of 30 minutes. At their respective operating conditions, the B/C ratios for both pre-treatment methods were increased from 0.35 in the raw leachate to 0.66 and 0.71, for MAP precipitation and Fenton oxidation respectively, values that are suitable for biological treatment. This study shows that struvite precipitation is a suitable pretreatment option resulting in the simultaneous removal of ammonium and organic matter in old-intermediate landfill leachate.