Physical Characteristics of Solid Waste
By: Haseeb Jamal
There are many different physical
characteristics of solid waste.
In order to identify the exact
characteristics of municipal wastes, it is necessary that we analyze those
using physical, chemical and biological parameters which are discussed below:
Physical
Characteristics of Solid Waste
Information and data on the physical
characteristics of solid wastes are important for the selection and operation
of equipment and for the analysis and design of disposal facilities.
The required information and data include
the following:
1.Density
2.Moisture Content
3.Particle size &
distribution
4.Field Capacity
5.Permeability of
compacted wastes
Density
Density of solid waste, i.e., its mass per
unit volume (kg/m3), is a critical factor in the design of a SWM system, e.g.,
the design of sanitary landfills, storage, types of collection and transport
vehicles, etc.
Usually it refers to un-compacted waste.
To explain, an efficient operation of a
landfill demands compaction of wastes to optimum density.
Any normal compaction equipment can achieve
reduction in volume of wastes by 75%, which increases an initial density of 100
kg/m3 to 400 kg/m3.
In other words, a waste collection vehicle
can haul four times the weight of waste in its compacted state than when it is
un-compacted.
A high initial density of waste precludes
the achievement of a high compaction ratio and the compaction ratio achieved is
no greater than 1.5:1.
Significant changes in density occur
spontaneously as the waste moves from source to disposal, due to scavenging,
handling, wetting and drying by the weather, vibration in the collection
vehicle and decomposition.
Note that:
o the effect of
increasing the moisture content of the waste is detrimental in the sense that
dry density decreases at higher moisture levels;
o soil-cover plays an
important role in containing the waste and is one of the important Physical
Characteristics of Solid Waste;
o there is an upper
limit to the density, and the conservative estimate of in-place density for
waste in a sanitary landfill is about 600 to 1200 kg/m3.
It varies with geographic location, season
of the year, and length of time in storage.
Range and typical values of density for
various components of solid waste are presented in table 1 below.
Components |
Density Range (kg/m3) |
Typical (kg/m3) |
Food wastes |
130-480 |
290 |
Paper |
40-130 |
89 |
Plastics |
40-130 |
64 |
Yard waste |
65-225 |
100 |
Glass |
160-480 |
194 |
Tin cans |
50-160 |
89 |
Aluminum |
65-240 |
160 |
Typical density values during different stages of municipal solid waste (MSW) i.e. at the point of generation or storage of solid waste, into collection vehicle, transformed into bales for their final disposal to land fill site are presented in Table 2.
Condition |
Density (kg/m3) |
Loose MSW, no processing or compaction |
90-150 |
In compaction truck |
355-530 |
Baled MSW |
710-825 |
MSW in a compacted landfill (without cover) |
440-740 |
Moisture
Content of Solid Waste
Moisture content is defined as the ratio of
the weight of water (wet weight - dry weight) to the total weight of the wet
waste.
It is one of the important physical
characteristics of solid waste.
Analysis
Procedure:
o Weigh the aluminum
dish
o Fill the dish with
SW sample and re-weigh
o Dry SW + dish in an
oven for at least 24 hrs at 105°C.
o Remove the dish
from the oven, allow to cool in a desiccator, and weigh.
o Record the weight
of the dry SW + dish.
o Calculate the
moisture content (M) of the SW sample using the equation given (Eq. 1)
Where;
M= Moisture Content in %
w=Wet Weight of the sample, grams
d=Dry weight of the sample, grams
Typical moisture content of different types of wastes is presented in the Table 3 as shown below:'
|
Types of waste |
Moisture Content % |
|
|
|
Range |
Typical |
Residential |
Food wastes (mixed) Paper Plastics Yard Wastes Glass |
50 - 80 4 - 10 1 - 4 30 - 80 1 - 4 |
70 6 2 60 2 |
Commercial |
Food wastes Rubbish (mixed) |
50 - 80 10 - 25 |
70 15 |
Construction & demolition |
Mixed demolition combustibles Mixed construction combustibles |
4 - 1 4 - 15 |
8 8 |
Industrial |
Chemical sludge (wet) Sawdust Wood (mixed) |
75 - 99 10 - 40 30 - 60 |
80 20 35 |
Agriculture |
Mixed Agricultural waste Manure (wet) |
40 - 80 75 - 96 |
35 50 |
Moisture increases the weight of solid
wastes, and thereby, the cost of collection and transport.
In addition, moisture content is a critical
determinant in the economic feasibility of waste treatment by incineration,
because wet waste consumes energy for evaporation of water and in raising the
temperature of water vapor.
Generally, wastes should be insulated from
rainfall or other extraneous water.
A typical range of moisture content is 20
to 40%, representing the extremes of wastes in an arid climate and in the wet
season of a region of high precipitation. However, values greater than 40% are
not uncommon.
Particle
Size of Solid Waste
Measurement of size distribution of
particles in waste stream is important characteristic of solid waste because of
its significance in the design of mechanical separators and shredders.
Generally, the results of size distribution
analysis are expressed in the manner used for soil particle analysis.
That is to say, they are expressed as a
plot of particle size (mm) against percentage, less than a given value.
The size and distribution of the components
of wastes are also important for the recovery of materials, especially when
mechanical means are used, such as trammel screens and magnetic separators.
For example, ferrous items which are of a
large size may be too heavy to be separated by a magnetic belt or drum system.
The size of waste components can be
determined using the following equations:
Sc = LSc = (L+w)/2Sc = (L+w+h)/3
Where; Sc : size of component, mm
L : length, mm
W : width, mmh : height, mm
Field
Capacity of Solid Waste
The field capacity of MSW is the total
amount of moisture which can be retained in a waste sample subject to
gravitational pull.
It is a critical physical characteristics
of solid waste because water in excess of field capacity will form leachate,
and leachate can be a major problem in landfills.
Field capacity varies with the degree of
applied pressure and the state of decomposition of the wastes.
The concept of Field capacity is shown in the Figure 12.
I
am a Civil Engineer, graduated from University of Engineering and Technology,
Peshawar, Pakistan in 2010. I also have a PG-Diploma in Disaster Management and
MS in Urban Infrastructure Engineering (In Progress). My expertise include
civil related softwares like AutoCAD, SAP2000, MS Project, Primavera, MS Office
and GIS. My technical skills include project management, monitoring and
evaluation, structural assessment, disaster risk management, Quantity survey,
land survey, material testing, site management and technical writing. I am
trained in writing project progress reports as well as proposals and concept
papers. I have also received advanced training on surveying, proposal writing,
Monitoring and Evaluation of projects as well as organizations.
I
have worked as Project Engineer at National Research and Development
Foundation, Peshawar and CENCON Associates. I also worked with Spectra
Engineering Solutions as Senior Civil Engineer in monitoring of World Bank and
UNDP funded projects all over Khyber Pakhtunkhwa and FATA. Currently, I am
working as Deputy Manager Development at NayaTel, Peshawar.
https://www.aboutcivil.org/physical-characteristics-of-solid-waste
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