Page 162 - Soil Degradation, Conservation and Remediation

6.2 Sources of Soil Pollutants 151

Fig. 6.1 Average
composition of municipal
Food
solid waste ( http://css.snre. scraps, Plastics,
umich.edu/css_doc/ 14.1% 12.3% Metals, 8.6%

CSS04-15.pdf )
Yard
trimmings, Rubber,
13.7% leather, and
textiles, 8.3%

Paper and Glass, 4.8%
Cardboard,
28.2%
Wood, 6.5%
Other, 3.5%

are engineered to protect the environment and prevent pollutants from entering

the soil and possibly polluting groundwater in one of two ways. The first of these is
with the use of a clay liner to block pollutants from leaving the landfi ll. These are
called sanitary landfills, while the second type is called a municipal solid waste

landfill. These types of landfills use synthetic liners like plastic to separate the

landfill’s trash from the land below it.

Municipal solid wastes (MSW) include wastes such as durable goods, for example,
tires and furniture; nondurable goods, for example, newspapers, plastic plates,
containers and packaging, milk cartons, plastic wrap, yard waste, and food. This
category of waste generally refers to common household waste, as well as offi ce and
retail wastes, but excludes industrial, hazardous, and construction wastes.
In 2009, 54.3 % of MSW generated in the USA was disposed of in 1,908 landfi lls
and 11.9 % was disposed of through waste incineration with energy recovery.
Combustion reduces waste to ash by about 75 % by weight for disposal in a landfi ll.
Another 33.8 % of MSW was recovered for recycling or composting, diverting 82 million

tons of material from landfills and incinerators. Recovered composting materials rep-
resent 25 % of all recovered materials (USEPA 2010 ). The average composition of
MSW has been shown in Fig . 6.1 .

6.2.1.1 Composting Municipal Wastes

Composting is a biological process of reducing and stabilizing organic wastes
through microbial digestion and decomposition into a complex of humic substances
containing organic soil conditioners and plant nutrients. A variety of organic
residues including municipal wastes are composted on both small farm scales and
large commercial scales. Municipal wastes are generally composted at a central
composting facility. During the process, part of organic C is released as CO 2 , part

incorporated into microbial cells and part humified. The organic nitrogen primarily