Diagnosis of the severe clogging of the leach drainage system in Brasília's landfill

Abstract

The landfill leachate drainage system has as its main purpose to minimize the risk of environmental contamination. Once this system is located below layers of heterogeneous waste, its clogging can occur over time, especially when inadequate conceptions are used. In order to determine the causes of the severe clogging observed in the leachate drainage system of Brasília's landfill, in loco inspections were carried out; ample bibliographic survey was made; the executive project and the As Built of the landfill were evaluated; the qualitative and quantitative aspects of the waste, the leachate, the covering soil and of the clogging material itself were analyzed. The results indicated that the formation of large amounts of calcium precipitates was the determining factor for the system clog.  The use of unwashed limestones with a high content of calcium carbonate (around 50%) resulted in the release of significant amounts of calcium cations in the leachate, during the acidogenic phase of the digestion of the waste's organic fraction. Subsequently, in the methanogenic phase, these cations precipitated due to the pH increase of the leachate, caused by the fermentation of volatile fatty acids. This reaction was of such magnitude that it even resulted in incrustations in the leachate's discharge pipes. For this reason, the use of unwashed limestones to fill the leachate drainage system is not recommended by some international regulatory agencies.