Environmental Engineering Reference
In-Depth Information
Table 5. Methane Yield Based on the Stoichiometric Method
Sources
Methane (L/kg dry waste)
373 carbohydrate
274 protein
Barlaz et al. (1989)
Ham et al. (1989)
270
El-Fadel et al. (1996)
220-270
Peer et al. (1993)
230-270
(Source: El-Fadel et al. 1997)
Using this method, the estimated yield of the landfill gas is 440 L/kg wet waste with a
composition of 53% methane and 46% CO
2
(Ham 1979). El-Fadel et al. (1997) reported,
based on the stoichiometric method that the estimated methane yield is in the range of 220-
270 L/kg dry waste after complete decomposition. Table 5 summarizes the estimated methane
yield based on this method.
In the
experimental approach
, the landfill gas yield can be obtained from laboratory scale
studies. The amount of biogas produced by biodegradation of MSW can be measured in the
laboratory. The biodegradation of MSW can be controlled and enhanced by manipulating
environmental factors such as pH, temperature, moisture, nutrients, etc. The range of methane
yield from lab scale studies varies from no generation to 107 L CH
4
/kg dry waste.
D. LFG Emission
LFG emissions are governed by gas-generation mechanisms and gas-transport
mechanisms. The following paragraphs describe these mechanisms and the major factors
influencing gas generation and transport.
1. LFG Generation
1.1. LFG generation mechanisms
The three primary causes of LFG generation are volatilization, biological decomposition,
and chemical reactions.
Volatilization
Volatilization is due to the change of chemical phase equilibrium that exists within the
landfill. Organic compounds in the landfill volatilize until the equilibrium vapor
concentration is reached. This process is accelerated when biological activity increases the
temperature of the waste mass. The rate at which compounds volatilize depends on their
physical and chemical properties.
Biological decomposition
The rate and composition of landfill gas vary according to the stabilization stages of
MSW. Five main stages of degradation of biodegradable wastes have been identified
(Kjeldsen et al 2002; Waste Management Paper 26B, 1995; McBean et al 1995). Figure 4
