Gas recovery investigation in a Brazilian landfill

Landfill gas (LFG) recovery and utilization have not significantly evaluated in Brazil. A number of reasons might have contributed for this scenario, including: public regulation uncertainties, lack of financial incentives, absence of public and private investments, operational conditions of landfills, and low level of technical support. The only full scale LFG power plant started its operation in the beginning of 2004 with an installed capacity of 20 MW (Bandeirantes Landfill/São Paulo). Nowadays, the international financial incentives for methane emissions abatement, as presented in Kyoto Protocol, seem to be the main way to drastically change the world scenario, especially in the developing countries as Brazil.
Muribeca’s Landfill, located in the metropolitan region of Recife/Brazil, has been monitored since 1994 as part of an environmental recuperation program that aimed to transform an old dumped area in a sanitary landfill. Actually, the LFG recovery potential has been specifically studied in order to evaluate its technical, operational, and environmental feasibility. The purpose of this paper is to present the analysis of LFG composition, pressure, superficial emission, and retention on the cover layer of Muribeca’s Landfill. Experiments were based on static flux chamber tests for measuring CH4 emissions and on a simple device (CPMD) to analyze LFG composition and pressure under the final cover layer. A comparative gas concentration analysis before and after gas percolation through the cover layer allowed to evaluate gas retention in the cover soil. Indirectly, LFG generation and the installed capacity of an eventual LFG power plant were also estimated in this work.
The main parameters observed in this study, which was used in the preliminary analysis of LFG recovery potential, are shown below: • CH4 and CO2 average concentrations: 56% and 42%, respectively; • CH4 emissions, based on six flux-chamber tests: 208 ton/year;
• LFG generation rates: 11.0 to 15.5 m3/ton.year; • CH4 cover soil retention: 4% to 60%, depending on the cover layer thickness and gas
concentration/pressure gradients; • Gas pressure observed at the bottom of the cover layer: (-)100 to 2,500 Pa; • LFG generation potential in 2006: 10.924 m3/h • Installed capacity in 2006: 13 MW • CERs (2006-2012): 2,667,340 tons;
The methodology presented in this paper appears to be well suited to provide useful information for the LFG recovery analysis, although complementary investigations are need to precisely quantify the gas production curve for the particular site conditions found in Muribeca’s Landfill. The results observed in this study allowed to conclude that the final cover layer and the absence of gas drainage system are the major negative aspects for implementing a LFG power plant. Some favorable factors for the LFG recovery project feasibility were also observed in this investigation. The LFG composition, which presented over 55% of CH4 and low H2S concentration, is a positive aspect as the LFG heating value and the maintenance cost of the plant are dependent of these gases. Although the landfill lifetime is very short, the actual and future estimative of LFG production indicate that quantitatively there is enough gas to conduct an emission reduction project. The estimative of CERs and carbon credits for 20 years projection shows that financially this could be an attractive investment.