11.5 Options for Municipal Solid Wastes Management 301
decomposition. Moisture may also promote chemi-
cal reactions that produce gases.- Temperature
As the landfill’s temperature rises, bacterial activity
increases, resulting in increased gas production.
Increased temperature may also increase rates of
volatilization and chemical reactions.
11.4.2.1 Landfill Methane Capture Technology
The basic process behind capturing the methane that
is emitted by landfills is to place a cap on it (see the
operation of a landfill), using a variety of different
materials based in part on the waste contents of the
landfill, to block the direct emissions of methane into
the atmosphere. A common landfill gas capture sys-
tem is made up of an arrangement of vertical wells
and horizontal collectors, usually placed after the
landfill has been capped, that is used to direct the
flow of the gas This common type of collection is
known as a “passive gas collection system” and the
collection wells can be installed during the initial
construction of the landfill or after the landfill is per-
manently closed.
In the other method, the “active gas collection sys-
tem”, a series of pumps move the gas to collection wells
and through a series of low-pressure chambers to help
direct and control the flow of the gas. The active gas col-
lection method is more expensive than the passive ver-
sion, but the ability to control the flow rate of gas, coupled
with the ability to have multiple collection wells, helps to
make the active gas collection system an economically
viable option for many landfills. There are nearly 500
landfills in the United States that are capturing methane
and either burning it for electricity generation or flaring it,
which converts the methane into carbon dioxide, which
has a lower global warming potential than methane.
11.5 Options for Municipal Solid Wastes Management
Several options exist for the disposal of wastes and
what is adopted in any community, municipal, state or
country, depends much on the economic status of the
unit. As seen in Fig. 11.8, MSW can be sorted into
seven categories: Yard trimmings, food scraps, paper
and paper board, metals, glass, plastics and wood. The
first two, yard trimmings and food scraps, may be
composted, while the other five may recycled and used
for manufacturing. The compost is used as soil
amendment or organic manure in agriculture, while
any materials not decomposable is either sent to the
landfill or incinerated.
The non-decomposable and/or nonrecyclable rem-
nants of the recycled materials among paper, metals,
glass, plastics, and wood are sent to the landfill or for
incineration, depending on their nature.
The breakdown of organic materials in the landfill
leads to methane release which can be used to produce
electricity. The leachate from the landfill must be care-
fully managed to prevent it from getting into ground
water.
All seven categories of MSW may however be
incinerated; sometimes, the heat generated from the
incineration may be used to generate electricity. The
ash generated from the incineration is sent to the land-
fill (Fig. 11.12).
The disposal of wastes (solid or sewage) costs money
and the community must not only have the means to pay
for the service, but must also be willing to pay for it.
When the various options are arranged in descend-
ing order of desirability, the order would be:- Source reduction
- Recycling
- Incineration with energy recovery
- Disposal through:
(a) Incineration
(b) Landfilling
(c) Incineration without energy recovery
The more affluent a society is, the more likely it is
that the options it will select will be nearer to the top
of the list. Many developing countries, for example,
do not have the resources to establish the type of well-
engineered landfills described above, or to invest in
the infrastructure to generate electricity from com-
busted MSW. They end up simply combusting the
wastes, or just dumping them in dumpsites to be col-
lected and buried or incinerated at a latter date (see
Bassey et al. 2006 ).