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Background, Aim and Scope:
Historically, landfills have been the simplest form of eliminating urban solid waste with the minimum cost. They have been the most usual method for discharding solid waste. However, landfills are considered authentic biochemical reactors that introduce into the environment, large amounts of contaminants in the form of gas and leachates. The dynamics of generation and the movement of gas in landfills depend on input and output parameters, as well as the structure of the landfill and the kind of waste. The input parameters include water introduced through natural or artificial processes, the characteristics of the urban solid waste, and the input of atmospheric air. The main output parameters for these biochemical reactors include the gases and the leachates that are potentially pollutants for the environment. Control systems are designed and installed to minimize the impact on the environment. However, these systems are not perfect and a significant amount of landfill gas could be released to the atmosphere through the surface in a diffuse form, also known as Non-controlled emission. In this paper, the results of the Non-controlled biogenic gas emissions from the Lazareto landfill in Tenerife, Canary Islands, are presented. The purpose of study was to evaluate the concentration and efflux of CH4 and CO2 from the surface of the landfill and to compare these parameters with other similar landfills. In this way, a better understanding of the process that controls biogenic gas emission in landfills is expected.
Materials and Methods:
A Non-controlled biogenic gas emission survey of 281 sampling sites was carried out during February and March, 2002. The sampling sites were selected in order to obtain a well distributed sampling grid. Surface landfill CO2, CH4 efflux measurements were carried out at each sampling site on the surface landfill together with soil gas collection and ground temperatures at a depth of 30-40 cm. Surface landfill gas samples were collected at depth of 30-40 cm using a metallic probe and 20 cc hypodermic syringes, and stored in evacuated 10 cc vacutainers for laboratory analysis of bulk composition. The gas sample was introduced in a vacutainer filled with desionised water and displacing the water until the vacutainer was filled with the gas sample to avoid air contamination entering. Surface landfill temperature of the landfill at 40 cm depth was measured using a digital thermometer type OMEGA 871A. Landfill gases CO2 and CH4 were analyzed within 24 hours using a double channel VARIAN micro-GC QUAD CP-2002P, with a 10 meters PORAPLOT-Q column, a TCD detector, and He as a carrier gas. The temperature was 40ºC and the inject time was 10 msec.
Surface landfill CO2 efflux measurements were performed using a portable NDIR spectrophotometer Licor-800 according to the accumulation chamber method.
Results:
Diffuse CH4 and CO2 efflux values range from negligible values up to 7,148 and 30,573 g m-2 d-1, respectively. Spatial distribution of the concentration and efflux of CO2, CH4 and soil temperature shows three areas of maximum activity in the landfill, suggesting a non-uniform pattern of diffuse degassing. This correlation between high emissions and concentration of CO2, CH4 and soil temperatures suggests that the areas of higher microbial activity and exothermic reactions are releasing movements CO2 and CH4 to the atmosphere from the landfill. Taking into consideration the spatial distribution of the CO2 and CH4 efflux values as well as the extension of the landfill, the Non-controlled emission of CO2 and CH4 to the atmosphere by the Lazareto´s landfill are 185 and 18 t d-1, respectively.
Discussion:
The patterns of gas flow within the landfill seem to be affected by boundary materials at the sides of low permeability basalt layers, and side boundaries the flux emissions at landfill surface are lower. This behavior reflects the possible dissolution of gases into water and deflection of gases towards the surface at the basalt boundary. We observed that the data obtained from this landfill are not concordant with landfills of the same antiquity. The proximity to the sea, the installation of the garden of palms and in consequence the contribution of water coming from the watering of this garden has reactivated the system. Sea water introduction into the landfill and the type of boundary could be defining the superficial gas discharges.
Conclusions:
Results from this study indicate that the spatial distribution of Non-controlled emission of CO2 and CH4 at the Lazareto´s landfill shows a non-uniform pattern of diffuse degassing. The northeast, central and southwest areas Lazareto´s landfill are the three areas of high emissions and concentration of CO2, CH4 and high temperatures.
Correlation between high emissions and concentration of CO2, CH4 and high temperatures that suggest that the areas of higher microbial activity and exothermic reactions are releasing move CO2 and CH4 to the atmosphere from the landfill. High concentration of CO2 is probably due to the presence in the soil atmosphere of the landfill of methanotrofic bacteria.
Role of sea water (animal marine, hotter water) make this landfill behave differently from landfills on land.
Patterns of gas flow within the landfill seem to be affected by boundary materials at the sides of low permeability basalt layers, and side boundaries the flux emissions at the surface are higher. At sides of water and sediment boundaries flux emissions at the landfill surface are lower. This behavior reflects possible dissolution of gases into the water and deflection of gases towards the surface at the basalt boundary.
With this study we can compare the data obtained in this landfill with other landfill and to observe the different levels of emission. We were observed that the data obtained for the Lazareto´s landfill are not concordant with landfill of the same antiquity. The proximity to the sea and the installation of the garden of palms and in consequence the contribution of water coming from the watering of this garden has reactivated the system.
Many landfills worldwide located in similar settings could experience similar gas production processes. Sea water introduction into the landfill and the type of boundary could be defining the superficial gas discharges.
Recommendations and
Perspectives:
The need of investigating and monitoring sea water and sediment quality in these landfills is advisable. Concentrations and fluxes of contaminants and their impact in the area should be assessed.
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