Emissions from mechanically biologically treated waste landfills at field scale

Abstract

Modern waste management tends towards greater sustainability in landfilling, with the implementation of strategies such as the pretreatment of solid waste. This work assesses the behaviour of rejects from a refining stage of mechanically-biologically treated municipal solid waste at the landfill. The main results of 18 months' monitoring of an experimental pilot cell with waste from a full-scale plant are presented. This first stages are expected to be the most problematic period for this type of waste. The evolution of the temperature and the composition of leachate and gas at various points within the cell are included. During the first weeks, pollutant concentrations in the leachate exceeded the reference ranges in the literature, coinciding with a rapid onset of methanogenic conditions. However, there was a quick wash, reducing concentrations to below one third of the initial values before the first year. pH values influenced concentrations of some pollutants such as copper. These results indicate that, right from the beginning of disposal, such facilities should be prepared to treat a high pollution load in the leachate and install the gas emissions control elements due to the rapid onset of methanogenesis.

Release of pollutants in MBT landfills: Laboratory versus field

“…The compost-like material is stored until its commercialization as a soil improver, while the rejects from refining make up the material destined for final deposition in the landfill. The composition of this latter fraction, which represents approximately 40% of the total amount of material deposited in the landfill, can be found in López et al (2018).…”

“…In the pilot cell, other measuring instruments were arranged that allowed the monitoring of other parameters such as the composition of the biogas or the temperature at several points inside it. Details of the cell and its monitoring results are presented in López et al, (2018).…”

“…Figure 2 shows the evolution of the TOC concentration in the pilot cell compared to the evolution observed in the laboratory tests. The initial concentrations registered in the cell, which are higher than in the laboratory, are attributed to the saturated conditions of the columns and to the fact that the waste reaches the field at a high temperature (44ºC) and without having undergone the protocol for sample preservation that is followed in the laboratory (López et al, 2018). It quickly releases the simplest organic compounds, which appear in the first samples.…”

“…The microbiological decomposition, helped by the high temperatures, easily reached the methanogenic phase in the first month. López et al (2018) describe how the gas generated in the cell maintained a methane concentration over 50% after the first three weeks. Under these circumstances part of the organic matter dissolved in the liquid is degraded to gas and therefore disappears from the leachate.…”

“…One important point that stands out is the difference in pH: while in the cell it is basic and increases over time (López et al, 2018), it is below 7 in the columns. The lack of activity of microorganisms in the laboratory prevents the biological processes through which the pH rises in the cell.…”