Estudo das emissões de biogás em aterro de resíduos sólidos urbanos no semiárido brasileiro.

Abstract

The biogas generated by anaerobic biodegradation of Municipal Solid Waste (MSW) is an alternative energy source, however, it has been wasted in many landfills, in the form of emissions of Greenhouse Gases (GHG) to the atmosphere. The generation and emission of gases are influenced by factors associated with the operational characteristics of landfills and waste, as well as those related to local meteorological conditions; which may interfere with the quantity and quality of the generated gases. In this perspective, the study of biogas emissions is an important contribution of landfills management, allowing to evaluate the efficiency of the compacted soil cover layers, besides allowing the optimization of the gas drainage system and the methane energy recovery. Within this context, the objective of this research was to study the biogas emissions in Municipal Solid Waste landfill in the Brazilian semi-arid region, regarding qualitative and quantitative aspects, in order to generate a database to support the sustainable management of these enterprises. This study was conducted in a MSW cell, denominated Cell 2, built in a real-scale landfill and is located in the Campina Grande-PB Landfill. The operation of Cell 2 comprised the period between December 27, 2015 to May 8, 2016, when the final soil cover layer was executed. The total MSW mass of MSW in Cell 2 was approximately 62 thousand tons, with a mean waste disposal rate of around 465 t.day-1. The research methodology encompassed a gas emissions monitoring plan in Cell 2, which consisted of measurements: i) in the vertical biogas drainage system; ii) at the soil-residue interface; iii) in the compacted soil cover layer. Through the results obtained in this research, average concentrations of CH4, in the 9 (nine) Gas Drains (DV), higher than 50% in the monitored period. The total CH4 flow ranged from 59 to 17 Nm³.h-1, in the period from 270 to 570 days after the closure of Cell 2, implying a reduction of this flow by 70% during this time interval. The rate of capture of biogas per tonne of landfill residues varied from 15 to 4 Nm³.t- 1.year-1 (from 270 to 570 days). The surface emissions of methane by the cover layer of Cell 2 totaled a flow lower than 2 Nm³.h-1, during the dry season. However, the CH4 flow through the cover layer was significantly lower than the flow rate for the DVs, corresponding to a percentage lower than 9% in the period under analysis. The main factors that contributed to this performance were the high degree of average compaction obtained for Cell 2, the absence of gas differential pressures at the soil-residue interface, the efficiency of the vertical gas drainage system and the low permeability of the soil to water and air. The CH4 flow accomplished for Cell 2, using the Landfill Gas Emissions Model, are compatible with a maximum power of 80 kW, available until 2047. However, the biogas flow theoretical estimates did not reflect in the behavior of the experimental data, since in these evaluations, the significant decay of the methane flow was not identified after 570 days of monitoring of Cell 2. Therefore, it is necessary to study possible solutions to activate the theoretical energetic potential of the residues in the investigated cell.