Lecture_note_Solid_Waste_Management_compressed.pdf

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©Rajib Pokhrel, Ph.D
Nepal Engineering College
Lecture note:
Solid Waste Management
Rajib Pokhrel, Ph.D.
Associate Professor
Nepal Engineering College,
Changunarayan, Bhaktapur, Nepal
Email: rajibp@nec.edu.np
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Contents
1. Introduction
-Definition and concept of solid waste
-Waste generation processes
-Characteristics of solid waste
-Classification of solid waste
2. Solid waste management
-Concepts on waste management system
-Generation of waste
-Collection of waste, its system as per location
-Waste transportation system for various types of waste, its practices, methods adopted
in different location
-Waste disposal system – casual dumping sanitary landfilling, composting and incineration
-Design of landfill site
-Health considerations and consequences of unmanaged solid waste
-Environmental management of solid waste

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Contents
3. Resource recovery in solid waste management
-Concepts on resource recovery aspect in SMW reduce, reuse and recycle
-Benefits of resource recovery in SMW
-Various methods of waste recovery as per the characteristics of waste
- Financial management of solid waste
4. Solid waste management in developed and developing countries
-Waste management and retrospect
-Waste management and resource recovery in developed countries of the
world – retrospect and current practices
- practices adopted in developing and South Asian region-management
option and waste recovery aspect in some cities
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Contents
5. Waste management system in urban Nepal
-Historic prospective – concept on traditional waste management system in
Nepal
-Legal and policy setup for waste management system
-Modern waste management practices adopted in rural and urban areas
-Resource recovery practices in Nepal composting, rag pickers, resue, waste
purchase center etc.
6. Modern waste management system in the world
-Zero waste concept
-Waste audit system and its benefits
-Integrated sustainable waste management (ISWM) – public private
partnership (PPP)

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Introduction
Main Reference Source of this note: William A. Worrell, P. Aarne Vesilind (2012) Solid Waste Management.
Cengage Learning (second edition).
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Introduction
• Solid waste is generally dry refuse which includes house refuse, trade
refuse and street refuse.
• (a) House refuse: It consists of vegetable and animal waste matter,
ashes, cinders, rubbish, debris from cleaning and demolitions of
structures.
• (b) Street refuse: Empty packets and bottles, empty matches and
cigarette boxes, fruit peels, tree leaves, street sweepings, etc.
• (c) Trade refuse: Includes solid wastes from factories, commercial and
business centers, slaughter houses, etc.
• Solid waste consists of Garbage, Ashes, Rubbish, Dust, etc.
• It will be organic or combustible matter and inorganic or non-
combustible matter or mineral
• Garbage: It consists of all sorts of putrescible organic waste from
kitchens, hotels, restaurants, in the form of waste food articles,
vegetable and fruit peelings. It is organic in nature.

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Introduction
• Ashes: Ashes are incombustible waste products from houses, industries,
hearths and furnaces.
• Rubbish: It consists of all non-putrescible wastes, excluding ashes.
Common items that fall under this category are rags, paper pieces,
paper packets, glass and plastics bottles, broken pieces of glass, broken
crockery, broken furniture and stationary items, card boards, etc.
• Organic Waste: It includes dry animal and vegetable refuse, cow dung,
excreta of birds, tree leaves, sticks, paper waste, rags. Those products
are subjected to decay with time.
• Inorganic Waste: This consists of non-combustible material such as grit,
dust, mud, metal pieces, metal containers, broken glass and crockery,
tiles, waste building material. It is not subject to decay.
MSW = refuse + (C & D waste) + leaves + bulky items
Where, MSW = Municipal solid waste
C & D waste = Construction and demolition waste
The difference between the collected and the generated refuse is
called diverted refuge
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QN: A community produces the following on an
annual basis:
Fraction Tonnes per year
Mixed household waste 191
Recyclable waste 21
Commercial waste 41
Construction and demolition waste 108
Leaves an miscellaneous 32
The recyclables are collected separately and processed at a materials recovery
facility. The mixed household waste and the commercial waste go to the
landfill. The leaves are composed and the C and D wastes are processed and
used on the next project. Calculate the diversion?

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Solution:
Total waste generated = 393 toones/year
If everything not gong to the landfill is counted as having been diverted,
%
41
100
393
32
108
21





Diversion
This is impressive.
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Composition of solid waste
• Quantity and composition of solid waste varies from place to place and season
to season. Factors such as local climatic condition, culture, food habit, economic
level, awareness, etc. affects solid waste composition and quantity.
• Overall solid waste composition in the municipalities of Nepal are as follows:
organic waste 56%, plastics 16%, paper and paper products 16%, glass 3%,
metals 2%, textiles 2%, rubber and leather 1%, and others 4% (Source:ADB
report 2013)

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Legislation provision of solid waste management in Nepal
Solid Waste Management ACT - 2068 Solid Waste Management Rule - 2070

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Integrated Solid Waste Management
• Integrated SWM is required to
- Manage the solid waste using a holistic approach
- Manage must scientifically, economically and efficiently
Why – the integrated solid waste management?
Various solid waste management techniques are interlocking and
interdependent in response of resource recovery and financing.
US EPA (United States Environment Protection Agency) and European agency
suggested the hierarchy of solid waste management to overcome the above issues.
1. Reducing the quantity of waste generated - > Community need to plan for
reducing the waste at the source
2. Reusing the material - > Reuse the material as much as possible before sending
the recycling.
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Integrated Solid Waste Management
3. Recycling and recovering materials -> this option is undertaken when most of
the waste reduction and reuse options have been implemented
4. Combustion for energy recovery -> The idea is to take the solid waste stream
and to transform into a non polluting product, e.g. Green products
5. Landfilling -> If all the above techniques are implemented, the unused waste (left
waste) is disposed for landfilling

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Characteristics of Municipal Solid Waste (MSW)
• MSW is generally disposed of by landfilling but need to understand the
property and nature of the waste whether it is hazardous or not.
• Moreover, if the waste is going to recycle or use for energy by
combustion, the detail picture of the waste is necessary.
• Characteristics of the solid waste need to understand are
- composition by identifiable items (Steel cans, office paper, etc.)
- moisture content
- particle size
- chemical composition (Carbon, hydrogen, etc.)
- heat value
- density
- mechanical properties
- biodegradability

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Moisture contents
• Moisture contents of the Solid Waste varied with time as the moisture
contents changes during process of collection, transportation, etc.
• It need to understand while the refuse is processed into fuel or when it
is fired directly
100
100






d
d
w
M
w
d
w
M
d
Where,
M = moisture content, wet basis in %
Md = moisture content, dry basis in %
w = initial (wet) weight of sample
d = final (dry) weight of sample
Sometime moisture content exceed 100% therefore geotechnical engineer
prefer to use moisture content on dry basis.
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• Numerical:
A residential waste has the following components
Paper = 50%
Glass = 20%
Food = 20%
Yard waste = 10%
Estimate the moisture concentration using typical value (Paper = 6%, Glass
= 2%, Food = 20% and Yard Waste = 60%)
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Solution:
Assume a wet sample weighing 100 kg.
Then,
Component Percent Moisture Dry Weight (Based
on 100 kg)
Paper 50 6 47
Glass 20 2 19
Food 20 70 6
Yard Waste 10 60 4
Total 76 kg
The moisture content (wet basis) would then be
%
24
100
100
76
100
100 






w
d
w
M

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Particle size: Mixture of particle and the size of particle varied in the solid waste.
Moreover the distribution of particle varied with the types of solid waste, climatic
condition, etc.
The two mixture shown in the curve has very different particle size distributions.
Mixture A has mainly uniformly size particles while Mixture B has a wide variability
in Particle size.
In general, particle size
distribution is analyzed
based on the Uniformity
coefficient and sieve
analysis
10
60
D
D
UC 
Where, UC = Uniformity coefficient
D60 = particle (sieve) size where 60% of the particles are smaller than that size
D10 = particle (sieve) size where 10% of the particles are smaller than that size
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Heat Value:
- It is most important in the resource recovery
- Refused is characterized and made up of organic materials, inorganic materials,
and water. Usually, the heat value is expressed in terms of all three components
(kJ/kg)

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Density: It depends on the type of the refuse and its compaction. Mostly, the
bulk density is measured to understand how much the refuge can be
compacted.

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Principle of Solid Waste Management
Fig: Materials flow through society
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• In general, feasible options for achieving reduced material use and waste generation
are known as R’s principle.
- Reduction
- Reuse
- Recycling
- Recovery
• First three (Reduction, reuse and recycling) are known as 3R principle and Recovery is
also included here as 4R principle
• Method to reducing the waste
- Reducing the amount of material used per product without sacrificing the utility of
the product
- Increasing the lifetime of a product
- Eliminating the need for the product
Waste reduction in the industry is called pollution prevention and reducing the waste in
the household level is called waste reduction or source reduction.

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• Reuse: - How to reuse the material
- Reuse envelops
- Print both side of the paper
- Use rechargeable batteries
- Use refillable printer, fax machine, pens
- Compost organic waste such as leaves, grass
clippings, food waste
- Donate toys, unused clothes
- Re-think the possibility of alternative use
before throwing
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Recycling: -
• Saves limited natural resources
• Prevents greenhouse gas emissions and water pollutants
• Saves energy
• Provides raw materials for industry and creates jobs
• Save landfill space
Example of recycled products:
- Aluminum and steel cans, glass bottles
- Plastic lumber – benches and decks
- EcoSpun fabric – shirts and carpets
- Recycled papers – tissue and copier
- Crumb tires – playground surfaces and soakers houses
- Remanufactured products – toner cartridges and office furniture
- Re-refined motor oil

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Waste Generation Sampling and Characteristics
- Solid waste generation history is less
than a century
- In Nepal, solid waste management
act was only made in 2068 BS
therefore we do have few year
history of solid waste generation
even only in major cities.
- The composition of solid waste is
measured based on the manual
sampling and photography method
- But it is important to decide the
sampling program what is to be
measured and how many categories
of waste are to be used.
- 43 categories (under major 11
categories) were conducted to
estimate the possibility of diverting
waste to the landfill
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Paper - News paper
- Magazines
- Corrugated cardboard
- Telephone books
- Office / computer paper
- Other mixed paper
Glass - Clear
- Green
- Brown
- Other glass
Plastics - PETE (Polyethylene terephthalate)
bottles
- HDPE bottles
- PVC containers
- Polypropylene containers
- Polystyrene
- Other containers
- Films/bags and other rigid plastics
Wood - Lumber
- Pallets
- Other wood
Organics - Food waste
- Textiles/rubber/leather
- Fines (Unidentical small organic
particle)
- Other organics
Inert - Asphalt roofing materials
- Concrete / brick / rock
- Sheet rock
- Ceiling tiles
- Dirt/dust/ash and other inerts
Ferrous materials - ferrous/bimetal cans
- Empty aerosols
- Other ferrous metals
Yard waste - Grass clippings
- Leaves
- trimmings
Non – ferrous
metals
- Aluminum cans
- Other nonferrous metals
Hazardous materials - Lead acid batteries
- Other batteries
- Other hazardous wastes
Electronic
components
- Parts and materials from computers
- Printers
- Copy machines
Categories of sampled waste using manual sampling

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Above sampling method is quite cumbersome, time intensive and expensive therefore
the above method is modified as
Paper - Newsprint
- Corrugated
cardboard
- Magazines
- Other papers
Yard wastes - Wood (branches
and lumber)
- Leaves and
clippings
Metal - Aluminum cans
- Steels cans
- Other aluminum
- Other ferrous
- Other nonferrous
Food waste
Glass - Clear (flint)
- Green
- Brown
Others Materials that either
have little recovery
potential or are of low
fractions in refuge
(such as rubber,
ceramics, other glass,
bricks, rocks, etc.
Plastics - HDPE
- PETE
- Other plastics
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Measuring composition by photogrammetry
• In photography method, the photographs should be taken directly of the refuse
(90o angle) with the wide angle lens
• The procure is then projected onto a screen that has been divided into about
10 × 10 grid blocks. The components in each intersection are then identified and
tabulated.
• The photographic techniques has disadvantages
- Its accuracy is dependent on bulk density figures that must be fine tuned.
However some practitioner found the technique is quite accurate
- Time require to analyze is quite long, the manually sampling and weighing may
be less time consuming
The advantage is
- The refuge need not to be touched and smelled, and thus there are no problems
with disease transmission.

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Waste Generation Sampling and
Characteristics
• Refer the Best Practices of solid waste
management in Nepalese cities
https://www.google.com.
np/search?sclient=psy-
ab&site=&source=hp&btn
G=Search&q=Best+Practic
es+of+solid+waste+manag
ement+in+Nepalese+cities
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3. Collection Transfer
and Transport

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Solid waste collection
• Solid waste collection method varies with the
size of the community, development level,
amount of solid waste generation etc.
• Generally, organic and inorganic solid wastes
are separated from individual house and
gathered manually. While refuse is kept
outside the individual house in the small cans
or bags which is removed by sweepers.
• Road side dust is collected by sweeper from
the public dustbin and also collected by
sweeping the road side.
• Collection of refuse form the business area
should be done during off hours.
• Collection chamber / can should be clean after
emptying it. It is due to the fact that the
existing refuse should not decay along with
fresh refuse and control the odor generation.
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Solid waste collection
• Generally, following points need to consider in designing/planning waste collection
system
- Containerization and on-site storage of waste
- Source separation
- Collection mechanism (roadside, collection, door-to-door collection, communal
containers, on-time collection, etc.)
- Cleaning of streets and other public places
- Time of collection
- Type of vehicles used for collection
- frequency of collection
- Route planning
- Number of staff used for collection
- Special collection for bulk waste generators
- Separate collection for special waste such as medical waste and household hazardous
waste
- Transfer of waste from primary collection vehicles to larger vehicles for secondary
transport

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Waste Collection Planning / collection system
Solid waste collection system: -
1. House to Can: The efficiencies and conveniences gained here are personal and not communal
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Numerical: A family of four people generates solid waste at a rate of 1kg/cap/day
and the bulk density of refuse in a typical garbage can is about 120 kg/m3. If
collection is once a week, how many 120 L garbage cans will they need, or the
alternatives, how many compacted 10 kg blocks would the family produce if they
had a home compactor? How many can would they need in that case?
solutions:
Refuge generated in 1 week is
1 kg/cap/day × 4 persons × 7 days/week = 28kg refuse
28 kg /120 kg/m3 = 0.23 m3
0.23 m3 × 1000 L/m3 = 230 L
They require two 120 L cans.
If the refuse is compacted into 10-kg blocks, they would need to produce
three such compacted blocks to take care of the week’s refuge.

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Method of solid waste collection
2. Can to truck (in Nepalese context)
• The solid waste is transported to the disposal site via cart, bicycle, autorickshaws, trailors,
trucks, etc.
Autorickshaws: These having three or four wheels, have covered bodies. Since their
capacities limited to ½ to ¾ tonnes. These are used only for narrow localities where other
heavy vehicles cannot go.
Trailors: Trailors have slightly larger capacity (2 to 3 tonnes). They are also used for localities
where trucks cannot go. Loading of trailors is done manually. However, they are of tilting-
tipping type and hence their unloading is done automatically with the help of hydraulically
operated jacks.
Trucks: Trucks have larger capacity (5 – 10 tonnes). They are generally of tilting – tipping type
so that unloading is automatic. Special types of trucks, capable of bodily lifting covered skip
boxes (in place of ordinary dust bins) are now available. They are used to avoid the nuisance
and flies.
For some developed and ideal city, the central collection system via pipe line has been
operated. While the refuse is separated and put on special bags and those bags are put in
the nearby collection chamber. Those collected refuse transported to the central collection
station thru the pipes
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Source:https://www.google.com.np/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiPiP24sbfQAhXIv4
8KHTn9BqYQjRwIBw&url=http%3A%2F%2Fwww.readorrefer.in%2Farticle%2FSolid-Waste-Management--Vehicle-storage-
method_4034%2F&psig=AFQjCNHD6Rgp5W6w-HlVS4i1gr9xLPEcEw&ust=1479733008754229

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3. Truck from House to House:
- If the refuse is in the truck, it is compacted as the truck moves from house to house.
Higher the compaction ratio, higher the solid waste to be loaded to make to trip to
the landfill
- The organized way of eliminating the amount of time the crew actually works in
collecting refuse is to enumerate all of the various ways they spend time. The total
time in a workday can be calculated as
Y = a + c(b) +c(d) +e + f +g
Where,
Y = the total time in a workday in minutes
a = time from the garage to the route, including the marshaling time or that time
needed to get ready to get moving
b = actual time collecting a load of refuse
c = number of loads collected during the working day
d = time to derive the fully loaded truck to the disposal facility, deposit the refuse and
return to the collection route
e = time to take the final (not always full) load to the disposal facility and return to the
garage
f = official breaks including time to go to the toilet
g = other lost time such as traffic jams, breakdowns, etc.
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4. Truck routing:
When planning the truck routing network, time and efficiency of collection need
to be considered. Some are useful guidelines for determining overall strategy
when planning a network.
- The route should not overlap, should be compact and should not be fragmented
- The starting point should be as close to the truck garage as possible
- Heavily traveled streets should be avoided during rush hours
- One-way streets that cannot be traversed in one line should be looed from the
upper end of the street
- Dead-end streets should be collected when on the right side (left side in Nepal)
of the street
- On hills, collection should proceed downhill so that the truck can move freely
- Clockwise turns (it depends on the traffic guide line, in case of Nepal, it should
be anti-clock wise) around blocks should be used whenever possible
- Long straight paths should be routed before looping Anti-clockwise
- U turn can be avoided by never leaving one two-way street as the only access
and exit to the node.

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Fig: routing for collection truck movement (The movement should be anti-
clockwise if the vehicle drive in the left side as in Nepal)
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Fig: routing for collection truck movement (The movement should be anti-
clockwise if the vehicle drive in the left side as in Nepal)

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5. Truck to disposal
- For smaller isolated communities, the macro routing problem reduces to one of
finding the most direct road from the end of the route to the disposal site.
- For regional system or large metropolitan areas, developing the optimum disposal
and transport scheme can be used to great advantage.
- Less travel time, maximum collections are the basic concept
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Transfer stations
• Waste transferring at the station varied with the type of truck which collect the
waste
• Generally, automatic tilting trucks are used for collecting the waste at the end
Dumpster (truck) emptied at the station
where waste travel on the separation
channel
Dumpster collection truck being
emptied at the landfill

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Fig: Processing and management of solid waste
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Fig: Management of solid waste

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Disposal of the solid waste
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Disposal of solid waste by dumping
• Landfills are created by land dumping. It
involves the mass dumping of waste into a
designated area, usually a hole or side-hill
or low land. After the waste is dumped, it
is then compacted by large machines.
When the dumping cell is full, it is then
"sealed" with a plastic sheet and covered
in several feet of dirt.
• It is economic as compared with other
method but it has several drawbacks such
as it takes large spaces, waste spread to
the surrounding area, nuisance odor in the
surrounding area, leachate cause water
pollution, etc.

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Disposal of solid waste by sanitary landfill
- Land filling involves the controlled disposal of solid waste on or in the upper
layer of the earth’s mantle
- The garbage is dumped into low lying areas or depressions available nearby
- Dumping is done by layers of 1 – 2 m, and each layer is covered by 0.2 m
thickness or good earth. A rest of 2 to 3 weeks is given before filling the rest
layer of solid waste.
Landfilling methods and operations
- The principal methods used for landfilling dry area may be classified as (1) Area,
(2) Trench (3) Depression
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Disposal of solid waste by sanitary landfill
• Advantages:
- It is simple and economical
- No plant/equipment is required
- Separation of various material of the refuse is not required
- There are no by-products and hence there is not problem of the disposal of the by-
product
- The low laying area can be reclaimed and put to better served by this method
• Disadvantages:
- The proper site may not be available nearby
- Wind direction may not be favorable
- Large land areas are required
- It may be difficult to get large quantities of covering material
- Dumped garbage containing carcinogenic, non-biodegradable matter such as plastics,
unused medicine, paints, insecticides, sanitary napkins etc. may cause trouble later
- Leachate from the dumped garbage may pollute surface water as well as ground water

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Landfill Design
• The landfill design and construction must include elements that permit control
of leachate and gas
• Major design components of a landfill include the liner, the leachate-collection
and management system, gas management facilities, storm water management
and final caps.
Liners: The liner system is required to prevent migration of leachate form the
landfill and to facilitate removal of leachate.
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- Soil liner usually are constructed of
natural clays or clayey soils.
- Commercial clay (Bentonite) can be
mixed with sands to produce suitable
liner material.
- High density polythene (HDPE) tends
to be used in MSW landfill liners most
commonly because I is resistant to
most chemical found in landfill
leachates

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Incineration process
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Incineration methods
Advantages:
- This method is most hygienic method, since it ensures complete
destruction of pathogens
- There is no odor trouble or dust nuisance
- The heat generated can be used for raising steam power
- Clinker produced can be used for road purposes
- The disposal site can be located at a convenient distance
- Lesser space is required for the disposal of the residues
- Modern incinerators can burn a great variety of refuse materials which
are otherwise not biodegradable
- Adverse weather condition have no effect on the incinerators operation
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Incineration methods
Disadvantages:
- Large initial expenditure
- Improper operation results in air pollution problems and incomplete
reduction of the waste materials
- Disposal of the remaining residue is required
- High stacks need for natural draft chimneys present safety problems
- Air pollution control system is required to control the fly ash and other
toxic chemicals emission
In general, municipal incineration of solid waste or refuse is a volume
reduction process and it is not for complete or ultimate disposal purpose

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Leachate collection and removal system
• Leachate is directed to low points at the bottom of the landfill through the use
of an efficient drainage layer composed of sand, gravel, or geosynthetic
material.
• The percolated pipes are placed at low points to collect leachate and are sloped
to allow the moisture to move out the landfill
Leachate collection and storage
- The primary purpose of lining the landfill cell is to minimize the potential for
groundwater contamination
- The liner serves as a barrier between the buried waste and the groundwater
and forms a catch basin for leachate produced by the landfill
- The leachate should remove from the liner cell as quickly as possible, generally
the restricted maximum restricted maximum depth is 30 cm
- The leachate is typically removed using gravity flow or by pumping
- The storage of leachate is important for equalization of flow quantities and
constituent quality to protect the downstream treatment facilities.
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Various components of a leachate collection system for an MSW landfill typically
includes
- Protective and drainage layers
- Perforated collection lateral and header pipes
- Pump station
- Leachate pumps
- Pump controls
- Pump station appurtenances
- Force main or gravity sewer lines

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Leachate collection system design equations and
techniques
• As it is restrict the leachate head to 30 cm on top of the liner, the drainage
length, slope, permeability of the drainage materials and the leachate
impingement rate control depth on the liner
• Darcy’s law in conjunction with the law of continuity can be used to develop an
equation to predict the leachate depth on the liner based on anticipated
infiltration rates, drainage material permeability, distance from the drain pipe,
and slope of the collection system.
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The more convenient equation is

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Numerical:
Determine the spacing between pipes in a leachate collection system using granular
drainage material and the following properties. Assume that in the most conservative
design all storm water from a 25 year, 24 hours storm enters the leachate collection
system.
Design storm (25 years, 24 hours) (q) = 0.00024cm/s
hydraulic conductivity (K)= 10-2 cm/s
Drainage slope (α) = 2%
Maximum drainage depth on liner (Ymax) = 15.2 cm
Moreover, the geosynthetic drainage material have been introduced to increase
the efficiency of the leachate collection systems over such natural materials as
sand or gravel. A geonet consists of a layer of ribs superimposed over each other,
providing highly efficient transmissivity. If a geonet is used between the liner and
drainage gravel, the spacing between the collection pipes can be estimated from


PSin
Y
qP
2
4 max
2


Where θ = transmissivity of the geonet, m2/day
80/124

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Leachate treatment and disposal:
- In wet area, leachate treatment, use, and disposal represents one of the major
expenses of landfill operation
- Leachate treatment is often difficult because of high organic strength, irregular
production rates and composition, variation in biodegradability, and low
phosphorous content (if biological treatment is considered)
- The most economical alternative for leachate treatment is often to transport the
wastewater off-site to a publicly owned treatment works or commercial waste
water treatment facility
Homework:
Generation of leachate from the landfill site is common and it has
environmental impact. Explain the leachate and the efficient way to manage
leachate based on your understanding. Explore the possible pioneer
technologies for the treatment of the leachate.
82/124

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Gas generation and management
• There are two basic systems for gas emissions control (1) passive collection and
(2) active extraction
• Passive collection system: It collects landfill gas using vent collectors and
release the gas to the atmosphere without treatment or conveyance to a
common point
- Passive vents reach only a few feet below the cap or may reach up to 75% of the
landfill depth.
- Typical spacing for a passive vent is one per 7500 m3
• Active collection system: It links collection wells with piping and extract the gas
under vacuum created by a central blower. The active extraction well may be
horizontal or vertical. Generally, it is vertical.
- The central blower that creates the negative pressure in the pipe network. The
blowers are sized according to the volume of gas they move
- The collection system must be designed to minimize the head loss by providing
sufficiently large pipes and by minimizing the number of valves and bends in the
pipes.
84/124

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• The velocity of the flow through the piping system can be estimated using the
continuity equation if compressibility is neglected
Av
Q 
gD
fLv
P
2
2



Where,
Q = landfill gas flow rate, m3/s
v = landfill gas velocity, m/s
A = cross-sectional interior area of the pipe, m2
Head loss through the pipe can be estimated using the Darcy-Weisbach equation
Where,
∆P = pressure drop, m
f = Darcy-Weisbach friction factor, function of pipe
roughness and diameter
v = velocity, m/s
g = gravitational constant, m/s2
D = diameter, m
ρ = gas density, kg/m3
86/124
gD
fLv
P
2
0096
.
0 


The above equation can be modified as below if the length units are in feet
∆P = pressure drop when a gas is flowing in the pipe, m
ρ = density of the gas, kg/m3
RT
MP


Where,
ρ = density of the gas, kg/m3
M = molecular weight of the gas, g/mole
P = pressure, Pa (N/m2)
R = universal gas constant, N.m/mole.K
T = Absolute temperature, K
Typically, the pressure inside the collection pipe is close to atmospheric,
about 7470 N/m2 of water. The molecular weight of the gas can be
estimated as 14 g/mole, with the universal gas constant even having unit of
N.m/mole.K

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Numerical: Calculate the pressure drop in 240 m of 10 – cm diameter PVC pipe
carrying 15 m3/min of landfill gas at 49oC. Assume the pressure in the pipeline is
close to atmospheric (about 93,772 N/m2) and molecular weight of the landfill gas is
14 g/mole. Assume the gas is incompressible. The area of a 10 cm diameter PVC
schedule 40 pipe is 0.008m2
. Assume all other necessary data.
88/124
Landfill Cap or final covering of MSW landfill
• Landfill cap is provided to prevent the production of leachate that can contaminate
groundwater. Effect of keeping water out of landfill is to maintain dry condition and
hinder the process of biodegradation of the waste.
• Once the landfill reaches design height, a final cap is placed to minimize infiltration of
rainwater, minimize dispersal of wastes, accommodate settling and facilitate long-
term maintenance of the landfill.
• The cap may consists of vegetation and supporting soil, a filter and drainage layer, a
hydraulic barrier, foundation for the hydraulic barrier and a gas control layer.
• Slope stability and soil erosion are critical concerns for landfill caps. Typical side slope
are 1:3 to 1:4.
• A geomembrane placed directly on top of low permeability soil are not
recommended
• Alternative cap: the evapotranspiration cover or capillary barrier places a thin (15
cm) layer of silt over a 76 cm thick layer of uncompacted soil. The silt layer supports
vegetation for transpiration while the soil layer provides moisture storage.

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90/124
Modes of Landfill Cap failure

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Operation of landfill
• Landfill equipment: It is used for the placement, and compaction of waste and
cover in a landfill require a variety of large machines, including tractors, loaders,
and compactors.
• Support equipment including motor graders, hydraulic excavators, water trucks,
and service vehicles
• Track-type bulldozers are used in landfills which spread and compact he refuse. It
is also used for placing and spreading covering material as well as preparing the
site, building roads, hauling trees, and removing stumps.
• Filling sequences: Waste placed in layers on top of the liner and leachate
collection system to depths of 20m or greater.
• Area or mound type of landfill construction is commonly used in areas with a high
groundwater table or subsurface conditions that prevent excavation
• Trench technique provides waste placement in cells or trenches dug into the
subsurface. The remove soil can often used for daily cover, intermediate or final
cover
• Canyon or gorges are also be alternative if it is available
92/124
Fig: Commonly used
landfill methods (a)
Excavation trench/cell,
(b) area and (c)
canyon/depression.

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• Daily cover: Waste is cover at the end of each working day with soil (15 cm) or
alternative daily cover such as textiles, geomembrane, carpet, foam, or other
proprietary materials.
- It is required to control disease vectors and rodents; to minimize odor, air
emissions; to reduce the risk of fire; and to minimize leachate production.
- The landfill sides are sloped to facilitate maintenance and to increase slope
stability; generally, a maximum slope of 1:3 is maintained.
• Monitoring: Landfill monitoring is critical to the operation of a landfill.
Generally, the landfill operators monitors the leachate head on the liner, leakage
through the landfill liner, ground water quality, ambient air quality (to ensure
compliance with the clean air act), gas dispersion in the surrounding soil,
leachate quality and quantity, landfill gas quality and quantity, and stability of
the final cover.
- Ground water monitoring is generally accomplished through the construction
and sampling of monitoring wells in the vicinity of the landfill.
- Monitored at multiple depths
- Monitoring should be done in different cluster
Operation of landfill
94/124
Fig: Porous cup suction lysimeter for the collection of liquid samples form the landfill. Source:
Integrated solid waste management issued by tchobanoglous, G.H. Theisen, and S. Vigil.

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Resource Recovery
96/124
Material separation and processing
• Binary separators: Individual material is separated from the mixed waste by
multiple iteration as the efficiency of the system is not perfect.
- Assume the x and y mixture fed to the separator is x0 and y0, respectively. The
mass per unit time of x and y exiting in the first output stream is x1 and y1, and
the second output stream is x2 and y2.

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Recovery of the component x in the first output stream is Rx1, and the recovery of y
in the second output stream is Ry2 defined as
100
100
0
2
2
0
1
1




















y
y
R
x
x
R
y
x
Mass balance holds
Then,
2
1
0 x
x
x 

100
2
1
2
0
1 











x
x
x
x
Rx
The effectiveness of a
separator cannot be judged
only on the basis of recovery.
A second operational
parameter is required and
this is usually an expression
of purity.
Where, Px1 is the purity of the
first output stream in terms
of x, which is expressed as a
percentage. Similarly, the
purity of the second output
stream in terms of y is Py2
100
100
2
2
2
2
1
1
1
1






















y
x
y
P
y
x
x
P
y
x
98/124
The input and output streams are more conveniently expressed in terms of
concentrations instead of mass/time. The equations for calculating the
effectiveness of the separation is as follows
    
 
    
 
100
2
1
0
2
0
1
1 











x
x
x
x
x
x
Rx
 
   
100
1
1
1
1 










y
y
x
x
x
x
Px



Purity of x would be
Where, ρx and ρy are the densities of x and y, respectively.

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Polynary separators: Two types of polynary systems are possible. In the first case,
x0 and y0 are the two components in the feed, and the separator has more than
two output streams with x and y appearing in all of them.
Recovery of x in the first output stream and purity are
100
0
1
1 









x
x
Rx
100
1
1
1
1 










y
x
x
Px
Recovery of x in mth output stream is
100
0










x
x
R m
xm
100/124
Effectiveness of separation: it gives the single value of separation effectiveness in
place of recovery and purity. This value is useful for process design or sizing
conveyor belts.
- This term is not a measure of separation effectiveness, it should not be used in
describing the operation of materials separation.
- Measure of separation effectiveness (by Rietema) for a binary separation with
input of x0 and y0 is defined the effectiveness as
100
0
0
1
1
, 










y
x
y
x
OR y
x
0
2
0
2
0
1
0
1
, 100
100
y
y
x
x
y
y
x
x
E y
x 



Another means of obtaining a single value of binary separator performance,
developed by Worrell and modified by Stessel as
100
2
/
1
0
2
0
1
, 










y
y
x
x
E y
x
Numerical: A binary separator has a feed rate of 1 ton/h. It is operated so that during any 1
hour, 600 kg reports as output 1 and 400 kg as output 2. Of the 600 kg, the x constituent is
550 kg, while 70 kg of x ends up in output 2. Calculate the recoveries and the effectiveness of
the separation.

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102/124
1. Picking (Hand Sorting): It is the manual picking method and it is the most
primitive method for the separation of materials from waste picking. When the
civilization began, scavengers have been an integral part of society. Selectively
accepting others people’s waste, collecting and processing it, and selling it at a
profit is a time-honored profession and recently it become a quite profitable
business.
2. Screens: Screening is a process of separation of solid waste by size. A series of
uniform-sized aperture allows smaller particles to pass while rejecting the larger
fraction. A particle can pass a screen if it is smaller than the opening in at least two
dimensions. The material that pass through the hole is called extract and the
material that does not pass is called reject.
- Screens, like other separation devices, cannot be expected to attain 100%
recovery. In other words, some undersized material (smaller that the screen
apertures) will report as reject and not be removed as extract.

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2.1 Trommel Screens: The trammel screen works by allowing the refuse in the
screen to tumble around until the smaller pieces find themselves next to the
apertures and fall through. They are of two kinds
- Cascading: The charge (solid waste) is lifted up by the circular motion of the
scree and then tumbles down on top of the layer heading upward.
- Cataracting: The speed of the screen is sufficiently great to actually fling the
material into the air, where it will drop along a parabolic trajectory back to the
bottom of the screen.
Cataracting produces the greatest turbulence, and the trammel should achieve
the greatest efficiency. As the drum speed is increased further, a third type of
motion is eventually attained.
104/124
Fig: Trommel screen Fig: Two types of particle paths in a
trammel screen

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2.2 Reciprocating and disc screens: This consists of rotating discs that move solid
waste across the screen. The screens are very rugged and can process large
quantities of solid waste. The second type of screen is an inclined or horizontal
shaking screen. It readily plugged by rags, paper and other objects and is limited in
its application to cleaner feeds.
Fig: Disc Screen
106/124
3. Float/Sink Separators: The process for all float/sink separator is the settling
(or rising) velocity of a solid particle within a fluid. One of the earliest float/sink
separators was the process of winnowing, in which the farmer threw the
mixture of grain seed and chaff into the wind and the wind was able to carry off
the chaff without suspending the grain. More accurately, the settling velocity of
the grain was much higher that the settling velocity of chaff, and the grain thus
fell quickly to the earth. In solid waste, the number of operation use the
float/sink principle.
4. Magnetic and electromagnetic separators:
Magnets are used to separate ferrous metals from the rest refuse. The code is
the magnetic property of ferrous material.
Eddy current separators respond to the problem of separating nonferrous
metals from the remainder of refuse and depend on the ability of metals to
conduct electrical current. The feed to an eddy current separator might be the
reject component from air classifiers from which the ferromagnetic components
(mostly steel cans) has been removed.
5. Electrostatic separation process: Charged particles under the influence of
electrostatic forces obey laws of attraction and repulsion as magnets.

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Biological Transformation:
Disposal of solid waste by composting
• Composting is a method in which putrescible organic matter in the solid
waste/refuse is digested anaerobically and converted into humus and stable
mineral compounds.
• Compost is widely used as a manure which is rich in nitrogen content. Due to
composting, volume of refuse is very much reduced and the resulting matter
becomes free from pathogenic organisms.
• There are three methods of composting
- Composting by trenching
- Open window composting
- Mechanical composting
108/124
Fig: Composting by trenching
Composting by trenching: Trenches of 4 – 10 m long, 2 -3 m wide and 0.7 – 1 m
deep are excavated with a clear spacing of 2 m. Trenches are then filled with
refuse/garbage in layers of 15 cm. On the top of each layer, 5 cm thick
sandwiching layer of night soil/animal dung is spread in semi-liquid form. On the
top layer, protruding 0.3 ma above the original ground surface, a 10 cm layer of
good earth is spread so that flies do not get access to the refuse and also the
refuse does not get blown by the wind. The refuse get stabilized in 4 – 5 months.

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Open window composting: Large
proportion of mineral mater like dust,
stone, broken glass pieces etc. are first
removed from the refuse. The refuse is
then dumped on the ground in the form
of 0.6 to 1 m high, 6 m long and 1 to 2 m
wide piles at about 60% moisture
contents. The pile is then covered with
night soil, cowdung, cattle urine etc.
through which the organisms or germs
that are necessary for fermentation are
added. Biological activities takes place
which raise the temperature up to 75oC
and the process repeats. The complete
process my take 4 – 6 weeks.
Fig: Open window composting
110/124
Mechanical composting:
The composting by trenching and open
window composting methods require very
large area. The process are laborious and
time consuming. In large cities the large
area may not be available and therefore
mechanical composting is adopted which is
very fast mechanical devices are employed
in turning the solid waste undergoing
composing. The stabilization of the wastes
takes only about 3 to 6 days.
The operation involves (1) reception and
refuse, (2) segregation, (3) shredding, (4)
stabilization and (5) marketing the humus
Fig: Mechanical composting

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111/124
Vermicompost is the product of the composting process using various species of
worms, usually red wigglers, white worms, and other earthworms, to create a
heterogeneous mixture of decomposing vegetable or food waste, bedding materials,
and vermicast, also called worm castings, worm humus or worm manure, is the
end-product of the breakdown of organic matter by an earthworm. These castings
have been shown to contain reduced levels of contaminants and a higher saturation
of nutrients than do organic materials before vermicomposting
112/124
Emerging Waste Conversion Technologies
• Provides overview of pyrolysis, gasification, and
anaerobic digestion technology use in the United
States for MSW (specific components)
• Includes database of planned and operational
facilities
• Compares emerging technologies to conventional
technology using MSW-DST to conduct life-cycle
analysis
• EPA/600/R-12/684; October 2012
http://nepis.epa.gov/Adobe/PDF/P100FBUS.pdf
Homework: Review the resource recovery technologies practiced and suggest
the better options for developing country like Nepal.

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Combustion and energy recovery
• Unit of energy is joule, calorie and kilowatt-hour (kWh)
• In general amount of energy or heat value of unknown fuel can be estimated by
ultimate analysis
1. Ultimate analysis: Analysis uses the chemical makeup of the fuel to
approximate its heat value. The most popular method using ultimate analysis is
the DuLong equation, which was developed for estimating the heat value of coal.
kJ/kg = 336.4C + 1438.4(H-O/8)+ 92.8
Where, C, H, O are the weight percentage (dry basis) of carbon, hydrogen, and
oxygen. This formula does not give the heat value other than coal
The alternative equation for estimating the heat value of refuse using ultimate
analysis is
kK/kg = 334.1C + 1559 H +14.4 O +96 S – 25.1N
Where, C, H, O, S and N are the weight percentage (dry basis) of carbon, hydrogen,
oxygen, sulfur and nitrogen, respectively. The total fraction of the percentage
should be 100%.
114/124
2. Compositional Analysis: Formulas based on compositional analysis are an
improvement over the formula based on ultimate analysis
kJ/kg = 113.7 R + 52.2 (G+P) – 7.66 W
The compositional model has also been improved as
kJ/kg = 2872 + 36.2 R + 10.2 P + 6.3 G – 48 W
Where,
R = plastics, percent by weight of total MSW, on dry basis
G = food waste, percent by weight of total MSW, on dry basis
P = paper, percent by weight of total MSW, on dry basis
W = water, percent by weight of total MSW, on dry basis
Moreover, the heat value of the complex fuel can be calculated by using typical
heat values of its components if the heat value of such components is known.

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116/124
Numerical: 1 (Example 7-1)
Numerical: 2

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3. Proximate analysis: Fuel is composed of two types of materials: volatiles and
fixed carbon. The amount of volatiles can be estimated by loss of weight when the
fuel sample is burned at some elevated temperature such as 600 or 800oC and
fixed carbon is estimated by the weight loss when the sample is combusted at
950oC. Commonly used proximate analysis equation is
kJ/kg = 18,560 A + 33,640 B
Where,
A = volatiles, fraction of all dry matter lost at 600oC
B = fixed carbon, fraction of all dry matter lost between 600oC and 950oC
Another method is
kJ/kg = 5800 D – 765.6 W
Where, D = fraction volatile material, dry basis, defined as weight loss at 800oC
W = fraction water, dry basis
Depending on whether the moisture is included or not, the results are presented
as kJ/kg as received or in a dry basis
118/124
4. Calorimetry: Calorimetry is the most reliable
method for determine the heat value of mixed
fuel. The Bomb is the stainless-steel ball that
screws apart. The ball has empty space inside
into which the sample to be combusted is
placed.
Homework: Review the working principle of
Bomb calorimeter in detail.

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Materials and thermal balances
1. Combustion Air: Combustion of organic fraction of refuse is simply a very rapid
decomposition process. The end products form the combustion of the
hydrocarbons are essentially the same as I slower biochemical decomposition that
reaches the final low-energy products.
- Heat value of pure materials can be estimated form thermodynamics;
combustion of pure carbon is a two-stage reaction
C + O -> CO + 10,100 J/g
And CO + O -> CO2 + 22,700 J/g
-------------------------------------------------
C+ O2 -> CO2 +32,800 J/g
The amount of oxygen necessary to oxidize some hydrocarbon is known as
stoichiometric oxygen. While, consider the simple combustion of carbon
C + O2 -> CO2 + heat
One mole of carbon combines with one mole of molecular oxygen. The molecular
weight of carbon is 12 and oxygen 16, so it takes two oxygens or 32 grams of
oxygen to react with 12 grams of carbon. The stoichiometric oxygen is then (2.67 g
O2 / g C)
120/124
2. Efficiency: Water is heated to steam in a boiler, and the steam is used to turn a
turbine, which drives a generator. According to conservation of energy, the input
energy should be equal to output energy.
Rate of energy accumulated = (rate of energy IN – rate of energy OUT + rate of
energy produced – rate of energy consumed)
Materials and thermal balances

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According to the steady state condition, defined as no change occurring over
time, energy systems also can be in steady state.
[rate of energy IN] = [rare of energy OUT]
If some of the energy out is useful and the rest is wasted
[rate of energy IN] = [rate of energy USED] + [rate of energy WASTED]
IF the input and useful output from a black box are known, the efficiency of the
process can be calculated as
(%)
100
efficiency
E
where
IN
energy
USED
energy
E



Using he energy balance equation
0 = Q0 – QU – Qw
Where, Q0 = energy flow in
QU = useful energy out
Qw = wasted energy out
122/124
Numerical

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Thermal balance on a waste to energy combustor
• Thermal balance on a large combustion unit is difficult because much of the
heat cannot be accurately measured. A black box can be used to describe the
thermal balance.
• The heat input to the black box is from heat value in the fuel and the heat in the
water entering the water-wall pipes. The output is the sensible heat in the stack
gases, the latent heat of water, the heat in the ashes, the heat in the steam, and
the heat lost due to radiation.
Fig: Black box showing energy flow in a combustor
124/124
Combustion hardware used for MSW
Waste to energy combustors: Modern combustors combine solid waste
combustion with energy recovery such combustors have storage pit for storing and
sorting the incoming refuse, a crane for charging the combustion chamber, a
combustion chamber consisting of bottom grates on which the combustion occurs,
the heat recovery system of pipes in which water is turned to steam, the ash-
handling system, and the air pollution control system

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Fig: Waste storage pit with crane
126/124

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