Page 164 - Soil Degradation, Conservation and Remediation

6.2 Sources of Soil Pollutants 153

and a complex form of organic matter – compost. Process management can be
optimized for a number of criteria, including the rate of decomposition (to reduce
residence time in reactors and thus minimize facility size requirements), pathogen
control, and odor management. The key parameters are the available carbon to
nitrogen (C:N) ratio, moisture, oxygen, and temperature.

6.2.1.2 Benefits of Municipal Waste Compost
The bioconversion process is gradually emerging as a natural, promising,
environment- friendly and potential microbial process to degrade environmental
contaminants (Colwell 1994 ). At present, the municipal solid waste composting is
being encouraged in many countries of the world and researchers have experienced

the benefits of using MSW compost in the field (Paul and Howard 1997 ; Abigail
1998 ; Pokhrel and Viraraghavan 2005 ). However, the influence of C-rich materials,

like municipal organic wastes compost, on soil physical, chemical, and biological
properties depends upon several factors: amount and components of added organic
materials, soil type, and weather conditions (Unsal and Ok 2001 ; Drozd 2003 ).
As pointed out by Giusquiani et al. ( 1995 ), the use of composts from MSW improves
the restoration of degraded soils and allows an appropriate final disposition of such

materials, solving a major environmental and economical problem generated in the
cities. Municipal waste composts have been used successfully for conditioning soil
and supplying plant nutrients. Compost has the potential of being a fertilizer
(Montemurro et al. 2005 ) and can thus be environmentally beneficial by substituting

artificial fertilizers. To what degree the compost will enhance the nutrient status of

the soil depends on both the waste that the compost is made from and the treatment
technology (Guster et al. 2005 ). Even if the compost is low in nutrients, it can be
valuable since application of compost, or any other form of humic material, effectively
enhances soil structure, improves the water holding capacity, and reduces the sensi-
tivity to erosion (Manser and Keeling 1996 ). Several tests also show that application

of compost represses plant diseases in the field (Ros et al. 2005 ).

6.2.1.3 Municipal Waste Incineration

The role of waste incineration differs in the countries of the world. While in the indus-
trialized countries in Europe as well as in Japan, the USA, and Canada the proportion
of waste burned in waste incineration plants can be very high (up to 100 %), in most

developing countries landfilling is the more common waste management practice.
The thermal treatment of solid municipal waste mostly takes place in plants
equipped with grate firing systems; in individual cases, in pyrolysis, gasifi cation, or

fluidized bed plants; or in plants using a combination of these process stages.

Residual municipal waste is delivered to grate furnaces as a heterogeneous mixture
of wastes. Combustible components account for a content of about 40–60 %.
Since the municipal waste incinerated is a heterogeneous mixture of wastes, in terms