Environmental Engineering Reference
In-Depth Information
landfilling of biodegradable municipal solid waste in non-hazardous waste landfills. The
priority for control of the gases is to protect the environment and prevent unacceptable
risk to human health, and a landfill gas control system is therefore required. In addition,
control mechanisms are required to minimize the risk of migration of the gases out of the
site.
This chapter will describe the processes that result in gas generation from SWDSs
and the factors which affect the amount of CH
4
produced. It will then describe two
methodologies for estimating CH
4
emissions from SWDSs. One of these methods is a
default base method which all countries can use to estimate CH
4
emissions from different
types of SWDSs. It is recommended that countries which have adequate data also
estimate their emissions using the second method presented. Finally, this section
discusses sources of uncertainty associated with any estimates of CH
4
emissions from
SWDSs, in particular the availability and quality of data required.
I.
I
NTRODUCTION
Throughout Europe and the United States, there is a strong reliance on disposing of waste
in landfills. Furthermore, in many developing countries, conditions for waste disposal are still
rudimentary. In 1997, for instance, 99% (around 90,000 tons per day) of Brazil's collected
waste was being landfilled or simply dumped. Each person in the United Staes generates
about 4.5 pounds of waste per day, which is nearly 1 ton per year. Again, most of this waste is
deposited in municipal solid waste (MSW) landfills. As MSW decomposes, it produces a
blend of several gases, including methane (about 50%).
Landfilling is the oldest and most widely practiced waste disposal option. Modern landfill
sites have developed from uncontrolled dumping sites to be an advanced treatment and
disposal option designed and managed as engineering projects. In addition, modern purpose-
built landfill sites normally incorporate a system for the extraction of landfill gas (arising
from the decomposition of biodegradable wastes), from which energy can be recovered. The
types of wastes suitable for landfilling include biodegradable wastes, aqueous liquids in
limited amounts, inert wastes, and certain special wastes that would not pose toxic threats.
Wastes that are generally considered unsuitable for landfilling include volatile liquids or
solvents, wastes that would introduce unacceptable contamination into the leachate, and
wastes that would interfere with the biological processes in a landfill site.
More recently, increasing attention has focused on the role of CH
4
in global atmospheric
change. Methane from SWDSs contributes a significant proportion of annual global CH
4
emissions, although the estimation is subject to a great deal of uncertainty. Estimates of
global CH
4
emissions from SWDSs range from less than 20 to 70 Tg/yr (Bingemer and
Crutzen 1987; US EPA 1994), or about 5 per cent to 20 per cent of the total estimated
emissions of 375 Tg/yr (IPCC 1996) from anthropogenic sources globally.
There are eight sections in this chapter. Section 2 discusses environmental regulations as
they pertain to landfill gas emissions. Regulations addressed in this section include the
European Landfill Directive [1999/31/EC], Resource Conservation and Recovery Act
(RCRA) solid and hazardous waste management requirements, Clean Air Act (CAA)
requirements, and Clean Water Act (CWA) requirements associated with landfill emissions.
An overview of the different types of bioreactor landfills as a development to sanitary
landfills is provided in Section 3 along with bioreactor features and advantages. Section 4
