Anaerobic-aerobic treatment of municipal solid waste leachate

This paper describes the organic matter removal from sanitary landfill leac hate using an anaerobic reactor and an aerobic one as post-treatment. Avera ge characteristics of the leachate from Montevideo's sanitary landfill are: GOD, 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 C OD removal efficiencies higher than 80%. RBC efficiency was 72% at the maxi mum loading rate of 15 gCOD m(-2) d(-1). During the experiences, changes oc curred in the landfill leading to a leachate pH increase. Due to the high f ree ammonia concentrations of leachate, inhibition threshold values reporte d in the literature were reached in the UASB reactor. However, this inhibit ion could be reverted by adjusting the inlet pH. In order to investigate me tal accumulation inside the UASB reactor, additional experiments were carri ed out. As a result, the reactor operated with phosphorus addition presente d lower solids accumulation and improved performance, probably due to metal precipitation at the inlet or metal complexation in the reactor. No inhibi tion problems caused by metal accumulation were detected under the working conditions. The system (UASB+RBC) operated with an overall COD removal effi ciency of 94%.