Physical/Chemical Pretreatment Of Landfill Leachate

For intermediate-old landfill leachate, the high concentration of ammonium and low B/C ratio are major obstacles to direct biological treatment. The pre-treatment capabilities of Magnesium Ammonium Phosphate (MAP) precipitation, also known as struvite precipitation, and Fenton oxidation on this type of landfill leachate were investigated with the aim of determining suitable physical/chemical methods in removing ammonium nitrogen (NH4+-N) and improving leachate biodegradability for subsequent biological treatment.For struvite precipitation, at the optimum operating conditions of pH 9 and MAP stoichiometric ratio of 1:1:1, ammonium nitrogen and COD levels were reduced by as much as over 97.0% and 50.0%, from 2132 mg l-1 and 4113 mg l-1 to 46 mg l-1 and 2057 mg l-1, respectively. COD was lowered by 76% to 987 mg l-1 and NH4+-N by 6.3% to 1997 mg l-1 using Fenton Oxidation at optimized conditions of hydrogen peroxide (H2O2) concentration 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 the above operating conditions, the BOD/COD 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 suitable for biological treatment. It was found that temperature had no significant effect on the treatment efficiency of struvite precipitation, however increasing temperature positively affected the Fenton oxidation treatment process. Struvite precipitation because of its ability to simultaneously treat ammonium and organic matter can be deemed a suitable option for the physical/chemical pre-treatment of intermediate-old landfill leachate, which is characterized by high ammonium-nitrogen levels and low biodegradability, prior to the application of biological treatment processes. Subsequent biological treatment, in the form of aerobic membrane bioreactor, was performed on the struvite precipitated leachate and almost complete removal of ammonium was achieved with the combined operation. Combined TOC and COD removals for the struvite-MBR process was 85% and 80.7% respectively over the entire operating period of almost 60 days.