Treatment of sanitary landfill leachate: Biological treatment

Abstract

In most cases leachates from sanitary landfills are highly polluted (COD, BOD 5, ammonium) and must be treated before discharge. Treatment experiments with aerated lagoons, activated sludge plants and rotating biological contactors in laboratory and technical scale are described. Treatment with full degradation of organics and oxydation of ammonium (nitrification) are possible with attention to some special problems of leaching treatment such as high ammonium concentrations, the BOD 5 N-ratio , precipitation of inorganics, cooling, foaming etc. From aerated lagoons BOD 5-effluents ⩽ 50 mg l −1 could be obtained at volumetric loadings ⩽ 20 g BOD 5 m −3 day −1. Shorter retention times in activated sludge plants result in lower BOD levels (⩽ 25 mg l −1) at loading rates between 0.02 and 0.05 kg BOD 5 kg MLSS −1 day −1 provided that the BOD 5 N-ratio > 1 . In all other cases the dimension parameter for activated sludge plants is ammonium load ⩽ 0.03 kg N kg MLSS −1 day −1. Similar results are obtained with rotating biological contactors also with ammonium as the critical loading value, here as an area loading ⩽2 g N m −2 day −1. In all cases ammonium is the dominate parameter and careful operation is necessary because nitrification is a very sensitive process. Operation problems could result in serious water pollution problems with discharges of high concentrations of ammonium or nitrite.