Anaerobic-Aerobic Treatment of Municipal Solid Waste Leachate

Abstract

This paper describes the organic matter removal from sanitary landfill leachate using an anaerobic reactor and an aerobic one as post-treatment. Average characteristics of the leachate from Montevideo's sanitary landfill are: COD, 18500 mg l⁻¹; BOD₅, 10500 mg l⁻¹; NH₄-N, 1500 mg l⁻¹; P, 17 mg l⁻¹; pH, 8.0; Cr, 2.6 mg l⁻¹; Fe, 41 mg l⁻¹; Ca, 408mg l⁻¹. A system composed of an anaerobic reactor (UASB) and an aerobic rotating biological contactor (RBC) was tested. The maximum load for the anaerobic step was 20 kgCOD m⁻³ d⁻¹ (1.8 kgCOD kgVSS⁻¹ d⁻¹) for an HRT of 2 days, with COD removal efficiencies higher than 80%. RBC efficiency was 72% at the maximum loading rate of 15 gCOD m⁻² d⁻¹. During the experiences, changes occurred in the landfill leading to a leachate pH increase. Due to the high free ammonia concentrations of leachate, inhibition threshold values reported in the literature were reached in the UASB reactor. However, this inhibition could be reverted by adjusting the inlet pH. In order to investigate metal accumulation inside the UASB reactor, additional experiments were carried out. As a result, the reactor operated with phosphorus addition presented lower solids accumulation and improved performance, probably due to metal precipitation at the inlet or metal complexation in the reactor. No inhibition problems caused by metal accumulation were detected under the working conditions. The system (UASB+RBC) operated with an overall COD removal efficiency of 94%.

Keywords:

• MSW leachate
• UASB reactor
• RBC
• metal accumulation
• sanitary landfill