Presentation Outline
 Introduction
 Reuse and Recycling Opportunities For Waste Materials
 Materials Recovered At Drop – Off and Buy Back Centers
 Operations For the Separation Of Waste Materials
 Introduction to the Unite Operation Used For the Separation and
Processing of Waste Materials
 Facilities for Handling, Moving, and Storing Waste Materials
 Development and Implementation of MRF
 Waste Transformation Through Combustion
 Impacts of Source Reduction and Waste Recycling on Waste
Transformation Process
Introduction
 Separation, Processing and Transformation make up the fourth of the functional
elements of solid waste management system
 the methods now used to recover source separated wastes materials include curb
side collection and home owner delivery of separated materials to drop off and buy
back centers.
 The further separation and processing of waste that have been source separated
occur at MRF or at large integrated MR-TF.
 Chemical & biological transformation process are used to reduce the volume and
weight of waste requiring disposal and to recover conversion products and energy in
the form of heat.
The most commonly used chemical transformation process is combustion which is
used in conjunction with the recovery of energy in the form of heat.
The most commonly used biological transformation process is aerobic composting.
Reuse & Recycling Opportunities for Waste Materials
 Materials separated from MSW can be used directly as:
 raw material for remanufacturing and reprocessing
 feedstock for production of biological and chemical
conversion products
 fuel source for the production of energy
 land reclamation
 Reuse opportunities for the materials separated from
MSW are reported in Table 9-1.
 In assessing the opportunities for recycling, the
available options for separation and processing of waste
materials, the economics of material recovery and
material specifications are critical
Reuse & Recycling Opportunities for Waste Materials
Reuse & Recycling Opportunities for Waste Materials
Materials Recovered at Drop- off & Buy Back Center
Drop- off Centers
 a drop-off program requires residents or business to separate
recyclable materials at the source & bring them to a specified dropoff or collection center.
 Low participation can be a problem in achieving the diversion rated
desired from these programs.
 Drop-off centers also requires residents and business to store the
materials until sufficient material is collected to warrant a trip to the
drop-off center.
 To encourage participation, most successful programs have made
drop-off centers as convenient to use as possible (e.g., drop off
points at shopping centers are common, in many communities
combination drop –off and buy back centers are located at MRF,
mobile collection centers which can be moved to a new locations
periodically.
Materials Recovered at Drop- off & Buy Back Center
Materials Recovered at Drop- off & Buy Back Center
Materials Recovered at Drop- off & Buy Back Center
Buy – Back Centers
 Buy – Back refers to a drop-off program that provides a monetary
incentive to participate
 In type of this program, the residents are paid for their recyclable
either directly or indirectly through a reduction in monthly
collection and disposal fees. Other incentive systems include
contests t or lotteries
Options for the separation of waste materials
 Separation is a necessary operation in the recovery of reusable
materials from municipal solid waste. Separation can be
accomplished either at the source of the generation or at MRFs.
 Waste separations at the source is usually accomplished by manual
means, the number & types of components separated will depend
on the waste diversion program. Additional separation and
processing will be usually required before these materials can be
reused or recycled.
 MRFs & MR-TFs are used for :
 the further processing of source separated waste
 the separation & recovery of reusable & recyclable materials
from commingled MSW
 improvement inequality ( specification)
 in the simplest term, AMRF can function as centralized
facilities for the separations, cleaning & shipping of large
volume of materials recovered from municipal solid waste
Options for the separation of waste materials
 The separation of waste materials from MSW can be
accomplished manually or mechanically.
 Manual separation is used almost exclusively for the separation of
waste at the source of generation. Many of the early MRFs built in
1970 s were designed to separate the waste components
mechanically. Unfortunately, none of these early facilities is
currently in operation, primarily because of mechanical problem.
 The currant trend is to design MRFs based on the integration of both
manual and mechanical separation functions
Options for the separation of waste materials
Two types of MRF:
MRF for Source – Separated Waste
 MRF for commingled MSW
 The sophistication of the MRF will depend on
 the number and types of the components to be separated
 the waste diversion goals established for the waste recovery
program
 the specifications to which the separated products must conform
Introduction to the Unit Operation Used for the Separation and
Processing of Waste Materials
 Unit operations used for the separation and processing of separated
and commingled wastes are designed to
 Modify the physical characteristics of the wastes so that the
waste components can be removed easily
 Remove specific components and contaminants from the waste
stream
 process and prepare the separated materials for subsequent uses
 Commonly used unit operations for processing of MSW are
summarized in Table 9-3
Introduction to the Unit Operation Used for the Separation and
Processing of Waste Materials
Introduction to the Unit Operation Used for the Separation and
Processing of Waste Materials
Size Reduction
 Size reduction is the unit operation in which as collected waste
material are mechanically reduced in size
 The objective of size reduction is to obtain a final product that is
reasonably uniform and considerably reduced in size in
comparison with its original form.
 Note that size reduction does not necessarily imply volume
reduction. In some situations, the total volume of the material
after the size reduction may be greater than that of the original
volume.
 Size reduction equipment used for the processing of wastes
includes
 Shredders
 Glass crushers
 Wood grinders
Introduction to the Unit Operation Used for the Separation and
Processing of Waste Materials
 Shredders
 the three most common types of shredding devices used to
reduce the size of MSW are
• Hammer mill
• Flail mill
• Shear shredder
Introduction to the Unit Operation Used for the Separation and
Processing of Waste Materials
 Glass Crushers
o glass crushers are used to crush glass container and other
glass products found in MSW
o glass is often crushed after it has been separated to reduce
storage and shipping costs
o crushed glass can also be separated optically by color.
However, because the equipment of the optical sorting of
glass is expensive and on-line reliability of such equipment
has not been good, optical sorting is not used commonly at
present
 Wood Grinders
o Typically, most wood grinders are wood chippers, used to
shred large pieces of wood into chips, which can be used
as a fuel and finer material which can be composted
Introduction to the Unit Operation Used for the Separation and
Processing of Waste Materials
Screening
 Screening is used to separate mixtures of materials of different
sizes
 The principal applications of screening devices in the
processing of MSW include:
o removal of oversized materials
o removal of undersized materials
o separation of waste into light combustible and heavy
combustible
o recovery of paper, plastic and other light materials from
glass and metal
o Separation of glass, girt and sand from combustible
materials
o Separation of rocks and oversized debris from soil
excavated at construction sites
o removal of oversized materials from combustion ash
Introduction to the Unit Operation Used for the Separation and
Processing of Waste Materials
Screening
 The types of screen used most commonly for the separation
of solid waste materials are
o Vibrating screens
o Rotary screens
o Disc screens
• self cleaning
• adjustability with respect to the spacing of the discs
on the drive shafts
Insert Figure 9-8
Introduction to the Unit Operation Used for the Separation and
Processing of Waste Materials
Introduction to the Unit Operation Used for the Separation and
Processing of Waste Materials
Density Separation (Air Classification)
 Air classification is used to separate light materials from
heavier material, based on the weight difference of the
material in an air stream.
Introduction to the Unit Operation Used for the Separation and
Processing of Waste Materials
Magnetic Separation
 Magnetic separation is a unit whereby ferrous metals are
separated from waste materials (Source – separated,
commingled and shredded MSW) by utilizing their magnetic
properties
 The specific location (s) where ferrous materials are recovered
will depend on
o The objectives to be achieved such as the reduction of
wear and tear on processing and separation equipment
o The degree of product purity to be achieved
o The required recovery efficiency
Densification (compaction)
 Densification is a unit operation that increases the density of
waste materials so that can be stored and transported more
efficiently
 Several technologies are available for the densification of solid
wastes and recovered materials including baling, cubing and
pelleting.
Introduction to the Unit Operation Used for the Separation and
Processing of Waste Materials
Balers
 balers reduces the volume of waste for storage , prepare the
waste for marketing and increase the density of the waste
thereby reducing the shipping costs
 the materials most commonly baled include paper, cardboard,
plastics, aluminum and tin cans and large metal component
Introduction to the Unit Operation Used for the Separation and
Processing of Waste Materials
Can Crushers
 Can Crushers are used to crush aluminum and tin cans, thus
increasing their density and reducing handling and shipping
costs.
 Typically, aluminum cans are crushed and blown into large
transport trailers for shipping.
Facilities for Handling, Moving and Storing Waste Material
To handle, move and store at MRFs, the following are used:
 Conveyors
 Conveyor facilities (picking belts) in conjunction with the manual
separation of waste
 Pneumatic conveyor
 Movable and fixed waste-handling equipment
 Scales
 Storage facilities
Facilities for Handling, Moving and Storing Waste Material
Conveyors
 Conveyors transfer wastes from one location to another
 The principal types may be classified as hinge, bucket, belt drag,
vibrating and pneumatic
 The conveyance of unprocessed commingled wastes with conveyors
has not been trouble free
 conveyors have been damaged by solid wastes dropped onto them,
especially those containing some of the heavier components often
found in the waste. Problems have also developed at transfer points
(e.g., where the waste are discharged from one conveyor to
another)
 waste spillage and overflows are common
Facilities for Handling, Moving and Storing Waste Material
Conveyor Facilities Used in Conjunction with the Manual Sorting of
Waste
 The manual separation of wastes at a MRF is usually accomplished
by removing the individual waste components from the waste
stream
 To improve the separation of waste components from commingled
MSW, plastic bags used for on-site storage must be open and the
contents spread out on the belt.
 The design of facilities for sorting waste components depends to a
large extent on the
o characteristics of the waste
o number of commingled recyclable items that are to be
separated
o throughput capacity of the facility
o width of the belt
o speed of the belt
o the average thickness of the waste materials on the belt
Facilities for Handling, Moving and Storing Waste Material
Conveyor Facilities Used in Conjunction with the Manual Sorting of
Waste
 The manual separation of wastes at a MRF is usually accomplished
by removing the individual waste components from the waste
stream
 To improve the separation of waste components from commingled
MSW, plastic bags used for on-site storage must be open and the
contents spread out on the belt.
 The design of facilities for sorting waste components depends to a
large extent on the
o characteristics of the waste
o number of commingled recyclable items that are to be
separated
o throughput capacity of the facility
o width of the belt
o speed of the belt
o the average thickness of the waste materials on the belt
Facilities for Handling, Moving and Storing Waste Material
Facilities for Handling, Moving and Storing Waste Material
Pneumatic Conveyors
 pneumatic conveying can be defined as materials transport using air
as the transport medium.
 Two types of pneumatic transport system (positive pressure and
vacuum)
 Velocities needed for the pneumatic transport of unprocessed solid
waste are in the range of 4800 to 6000 ft/min.
Facilities for Weighing
 weighing facilities are an important and necessary part of any MRF
 the types of weighing facilities used at MRFs vary from the small
scales used to weigh the amounts of wastes brought in by
individuals to the platform scales used for weighing collection
vehicles
Facilities for Handling, Moving and Storing Waste Material
Storage facilities
 Materials that have been separated and processed must be stored
until a buyer picks them up.
 In some facilities, space is provided for materials to be displayed for
viewing by purchasers
 Key considerations are these:
 will the buyer provide storage containers for recovered
materials
 with what frequency will the buyer pick up and remove
prepared materials from MRF
 is it possible to rent temporary storage facilities for the
processed materials away from the MRF
Development and Implementation of MRFs
Development and Implementation of MRFs
Development and Implementation of MRFs
Development of Separation Process Flow Diagrams
 A process flow diagram is defined as the assemblage of unit
operations, facilities and manual operations to achieve a specified
waste separation goal or goals.
 The following factors must be considered in the development of
the process flow diagrams:
o identification of the characteristics of the waste materials to
be processed
o consideration of the specifications for the recovered
materials now and in the future
o the available types of equipment and facilites
o For example, specific waste materials cannot be separated
effectively from commingled MSW unless bulky items are
first removed.
o A typical process flow diagram for the separation of source –
separated paper and cardboard is shown in Fig. 9-20a
Development and Implementation of MRFs
Development and Implementation of MRFs
Material Balances and Loading Rates
 Once the process flow diagram has been developed, the next step
in the design of MRF is to estimate the quantities of materials that
can be recovered and the appropriate design loading rates.
 the expected process loading rates must be known in order to
select and size equipment properly. Loading rate for a given process
are based on a mass balance
 Loading rates for most processes are expressed in tons per hour. In
determining the design loading rates, one should make careful
analysis to determine the number of hours per day and the year
equipment will be operated.
 Based on 1820 operating hours per year, the base hourly loading
rate is given by the following expression:
Loading rate, ton/h = (Number of ton/year / 1820 processing
h/yr)
Development and Implementation of MRFs
System Layout and Design
 the layout and design of the physical facilities that make up the
processing facilities will depend on the types and amounts of
materials to be processed.
 Important factors in the layout and design of such system include
o the methods and means by which the waste will be delivered
to the facility
o estimates of material delivery rates
o definition of the materials loading rates
o development of materials flows and handling patterns within
MRF
o Development of performance criteria for the selection of
equipment
Development and Implementation of MRFs
Typical Materials Recovery Facilities for Source – Separated Wastes
 in this text book, there are two types of MRFS
o MRF designed to process source – separated wastes
o MRF designed to process garden trimmings and wood
wastes
Development and Implementation of MRFs
Development and Implementation of MRFs
Development and Implementation of MRFs
Development and Implementation of MRFs
Development and Implementation of MRFs
Planning and Design Process for MRFs
 The planning and design of MRFs involve three basic steps
o Feasibility analysis
 the purpose of the feasibility analysis is to decide whether the
MRF should be built
 the feasibility study should provide the decision makers with
clear recommendations on the technical and economic merits
 A typical feasibility analysis may contain sections dealing with
integrated waste management plan, conceptual design,
economics, ownership and operation, and procurement
o Preliminary design
 the preliminary design includes development of the process
flow diagram
 development of material mass balances and loading rates for
the unit operations that make up the MRF and the layout of
the physical facilities
 the cost estimate developed in the feasibility study is refined
in the preliminary design report using actual price quotations
from venders
Development and Implementation of MRFs
Planning and Design Process for MRFs
o Final design
 final design includes preparation of final plans and
specifications that will be used for construction
 A detailed engineers cost estimate is made based on
materials take offs and vender quotes
 the cost estimate will be used for the evaluation of
contractor bids if the traditional procurement process is
used
Development and Implementation of MRFs
Issues in the Implementation and Operation of MRFs
 the principal non-engineering issues associated with the
implementation of the MRFs are related to
o Siting
o Environmental emissions
• traffic, noise, odor, dust, airborne debris, liquid
discharge, visual unsightliness and vector control
o Public health and safety
o Economics
Development and Implementation of MRFs
Waste Transformation Trough Combustion
 Transformation processes are used to reduce the volume and
weight of waste requiring disposal and to recover and to recover
conversion products and energy
 The organic fraction of MSW can be transformed by a variety of
chemical and biological processes.
 The most commonly used chemical transformation process is
combustion, which can be used to reduce the original volume of
the combustible fraction of MSW by 85 to 95 percent. In
addition, the recovery of energy in the form of heat is another
attractive feature of the combustion process
 Although combustion technology has advanced in the past two
decades, air pollution control remains a major concern in the
implementation
Waste Transformation Trough Combustion
Waste Transformation Trough Combustion
 The principal elements of solid wastes are carbon, hydrogen,
oxygen, nitrogen and sulfur.
 Under ideal conditions, the gaseous products derived from the
combustion of MSW with stoichiometric amount of air would
include CO2, H2O, N2, SO2.
 the basic reactions for the oxidation of the carbon, hydrogen
and sulfur contained in the organic fraction of MSW are as
follows
For carbon,
C + O2
For Hydrogen,
2H2+O2
For Sulfur,
S+O2
CO2
2H2O
SO2
Waste Transformation Trough Combustion
Waste Transformation Trough Combustion
Types of Combustors
Solid waste combustors can be designed to operate with two types
of solid waste fuel
 Mass-Fired Combustor
 Refuse – Derived Fuel – Fired Combustors
Energy Recovery
 Energy can be recovered from the hot flue gases generated by
combusting processed MSW or from unprocessed MSW
 Either hot water or steam can be generated.
 Hot water can be used for low-temperature industrial or space
heating applications
 Steam is more versatile, as it can be used for both heating and
generating electricity.
Waste Transformation Trough Combustion
Volume Reduction
 Among the factors that must be considered in assessing the
combustion process for MSW are the amount of residue
remaining after combustion and whether auxiliary fuel will be
required when heat recovery is not of primary concern
 The amounts of residue depends on the nature of the wastes to
be combusted
Waste Transformation Trough Combustion
Waste Transformation Trough Combustion
Waste Transformation Trough Combustion
Issues in the Implementation of Combustion Facilities
 Siting
o in many communities, combustion facilities are located in
remote locations within the city limits or at the landfill sites
 Air Emissions
o the operation of combustion facilities results in the
production of a variety of gaseous and particulate
emissions, many of which are thought to have a serious
health impacts
o In some cases, the cost and complexity of the
environmental control systems are equal or even greater
than the cost of the combustion facilities
 Disposal of Residue
o Bottom ash
o fly ash
o scrubber product
o Management of these soild residuals is an integral part of
the design and operation of a combustion facility ( ash is
now disposed of in lined MSW landfill or in double lined
monofills devoted solely to the disposal of ash
Waste Transformation Trough Combustion
Liquid Emissions
 liquid emissions from combustion facilities can arise
from one or more of the following sources
o wastewater from the ash removal facilitis
o effluent from wet scrubbers
o Wastewater from pump seals, cleaning, flushing,
and general housekeeping activities
o Wastewater from treatment systems used to
produce high quality boiler water
o Cooling tower blowdown
o The proper handling and disposal of these liquid
emissions is also an important part of the design
of combustion facilities
 Economics
o the best way to compare alternatives is by the
use of life cycle coasting, which accounts for
operating and maintenance costs over the
lifetime of the system
Waste Transformation Trough Aerobic Composting
 With the exception of plastic, rubber components, the organic
fraction of most MSW can be considered to be composed of proteins,
amino acids, lipids, carbohydrates, cellulose and ash
Waste Transformation Trough Aerobic Composting
 The general objectives of composting are
o to transform the biodegradable organic materials into a
biologically stable material and in the process reduce the
original volume of waste
o to destroy pathogens, insect eggs and other unwanted
organisms and weed seeds that may present in MSW
o to retain the maximum nutrients ( nitrogen, phosphorus and
potassium content)
o To produce a product that can be used to support plant growth
and as soil amendment
 In general, the chemical and physical characteristics of compost vary
according to the nature of starting material , the condition under
which the composting operation was carried out and the extent of
the decomposition.
Waste Transformation Trough Aerobic Composting
 When added to soil, compost has been found to lighten heavy soils,
to improve the texture of light sandy soil, and to increase the water
retention capacity of most soil.
Process Description
 Most modern composting operations consists of three basic steps
o preprocessing of the MSW
o decomposition of the organic fraction of the MSW
o preparation and marketing of the final compost product
Waste Transformation Trough Aerobic Composting
Waste Transformation Trough Aerobic Composting
Process Design and Control
 Although the composting process is easy to grasp conceptually,
the actual design and control of the process are quite complex
 Important process variables that must be considered in the
design and operation of composting facilities include
o Particle size
o particle size distribution of the materials to be composted
o Seeding and mixing requirements
o The required mixing/turning schedules
o Total oxygen requirements
o moisture contents
o temperature and temperature control
o carbon – nitrogen ratio of the waste to be composted
o pH
o degree of decomposition
o respiratory quotient
o control of pathogens
Waste Transformation Trough Aerobic Composting
Composting Techniques
 Windrow Composting
 Aerated Static Pile Composting
 In-Vessel Composting Systems
Waste Transformation Trough Aerobic Composting
Waste Transformation Trough Aerobic Composting
Waste Transformation Trough Aerobic Composting
Waste Transformation Trough Aerobic Composting
Process Application
 Composting is an increasingly popular waste management
option as communities look for ways to divert portions of the
local waste stream from landfills.
 The principal applications of composting are for
o Yard wastes
o Organic fraction of MSW
o partially processes commingled MSW
o co-composting of the organic fraction of MSW with
wastewater sludge
Waste Transformation Trough Aerobic Composting
Issues in the Implementation of Composting Facilities
 the principal issues associated with the use of compost process
are
o the production of odors
o the presence of pathogens
o the presence of heavy metals
o the definition of what constitutes and acceptable compost
o unless the questions related to these issues are resolved,
composting may never be a viable technology
Waste Transformation Trough Aerobic Composting
Production of Odors
 it is fair to say that every existing composting facility has had an
odor event and in some numerous events. As a consequence,
facility siting, process design and biological odor management
are of critical importance
Facility Siting
 important issues in siting as related to the production and
movement of odors include proper attention to local
microclimates as they affect the dispersion of odors, distance to
odor receptors, the use of adequate buffer zones and the use of
split facilities ( use of different locations for composting and
maturation operations)
Waste Transformation Trough Aerobic Composting
Proper Process Design and Operation
 if composting operations are to be successful, special attention
must be devoted to the following items
o preprocessing
o aeration requirements
o temperature control
o turning and mixing requirements
Biological Odor Management
 Cause of odors in composting operations include
o law carbon to nitrogen ratio
o poor temperature control
o excessive moisture
o poor mixing
o in enclosed facilities, odor control facilities such as packed
towers, spray towers, activated carbon contactors , biological
filters have been used for odor management
Waste Transformation Trough Aerobic Composting
Public Health Issues:
 the absence of pathogenic organisms is critical if the product is
to be marketed for use in application where the public health
may be exposed to the compost
 In general, most of pathogenic organisms found in MSW and
other organic materials to be composted will be destroyed at
the temperature and exposure times used in controlled
composting operations ( typically 55C for 15-22 days
Product Quality
 Product quality can be defined in terms of
o nutrient content
o organic content
o pH
o texture
o particle size distribution, moisture content, the presence
of foreign material , the presence of pathogenic organisms
and the concentration of heavy metals
Impact of Source Reduction And Waste Recycling on Waste Transformation
Processes
 As more state adopt legislation mandating the development of
waste diversion and recycling progrms, the quantities and
composition of the wastes collected will change.
 The impact of change in composition will vary depending on
the other types of waste management programs that are in
place.
Impact of Source Reduction And Waste Recycling on Waste Transformation
Processes