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1. Unit IV
Off Site Processing
Syllabus
Processing techniques & Equipments – Resource
Recovery from solid wastes – Composting –
Incineration – Pyrolysis – Options under Indian
conditions.

2. Processing Techniques & Equipments
Purpose of Processing
• The purposes of processing are:
(a) Improving efficiency of SWM system (e.g.)
Shredding
(b) Recovering material for reuse
( c ) Recovering conversion products & energy

3. Various Techniques & Equipments
(a) Mechanical Volume & Size reduction
(b) Component Separation
- Air Separation
- Magnetic Separation
- Screening
( c ) Drying & Dewatering

4. (A) Mechanical Volume & Size Reduction
• Mechanical volume and size reduction is an
important factor in the development and
operation of any SWM system.
• The main purpose is to reduce the volume and
size of waste, as compared to the original form,
and produce waste of uniform size.

5. Volume Reduction (or) Compaction
• Volume reduction (or) compaction refers to
densifying the wastes in order to reduce their
volume.
• The benefits of compaction are:
(a) Reduction in the quantity of materials to be
handled at the disposal site
(b) Improved efficiency of collection and
disposal of wastes
( c ) Increased life of landfills
(d) Economically viable waste management
system

6. Equipments for Volume reduction (or)
Compaction
Stationary Equipments:
• This represents the equipment in which
wastes are brought to, and loaded into, either
manually (or) mechanically.
Movable Equipment:
• This represents the wheeled and tracked
equipment used to place and compact solid
wastes.

7. Low Pressure ( < 7 kg / cm2 ) Compactors
• These compactors are used at apartments,
commercial establishments.
Example:
Baling equipment – For waste papers &
card boards
Stationary compactors – For transfer
station
• In low pressure compaction, wastes are
compacted in large containers.

8. High Pressure ( > 7Kg / cm2 )Compactors
• Compact systems with a capacity up to 351.5
Kg / cm2 came under this category.
• Here, specialized compaction equipment are
used to compress solid wastes in to blocks (or)
bales of various sizes.
• Typically, the reduction ranges from about 3 to
1 through 8 to 1
• Compaction Ratio = V1 / V2
V1 = Volume of waste before compaction
V2 = Volume of waste after compaction

9. Size Reduction (or) Shredding
• This is required to convert the large sized
wastes into smaller pieces.
• Size reduction helps in obtaining the final
product in a reasonable size in comparison to
the original form.

10. Equipments for Size Reduction (or) Shredding
Hammer Mill:
• These are used most often in large commercial
operations for reducing the size of wastes.
• Hammer mill is an impact device consisting of a number
of hammers, fastened flexibly to an inner disk, which
rotates at a very high speed.
• Solid wastes as they enter the mill, are hit by sufficient
force, which crush (or) tear them with a velocity so that
they do not adhere to the hammers.
• Wastes are further reduced in size by being struck
between breaker plates & cutting bars fixed around the
periphery of the inner chamber.

12. Hydro-pulper
• An alternate method of size reduction involves the
use of a hydropulper as shown below:
• Solid wastes and recycled water are added to the
hydro-pulper.
• The high speed cutting blades, mounted on a rotor
in the bottom of the unit, convert palpable and
friable materials in to slurry with a solid content
varying from 25 to 35%
• The rejected material passes down a chute that is
connected to a bucket elevator, while the solid slurry
passes out through the bottom of the pulper tank
and is pumped to the next processing operation.

14. (B) Component Separation
• Component separation is a necessary operation
in which the waste components are identified
and either manually (or) mechanically to aid
further processing.

15. Air Separation
• This technique has been in use for a number of
years in industrial operations for segregating
various components from dry mixtures.
• Air separation is primarily used to separate
lighter materials from the heavier ones.
• The lighter materials may include plastics,
paper products and other organic materials.

17. Equipments used for Air Separation
Conventional Chute Type
• Its one of the simplest type of air classifier.
• In this type, when the processed solid wastes
are dropped into the vertical chute, the lighter
materials are carried by the air flow to the top
while the heavier materials fall to the bottom of
the chute.
• A rotary air lock feed mechanism is required to
introduce the shredded wastes into the
classifier.

18. Zig-Zag Classifier
• It consists of a continuous vertical column
with internal zig-zag deflectors through which
air is drawn at high rate.
• Shredded wastes are introduced at the top of
the column at a controlled rate, and air is
introduced at the bottom of the column.
• As the wastes drop into the air stream, the
lighter friction is fluidized and moves upward
and out of column, while the heavy fraction
falls to the bottom.

20. Magnetic Separation
• The most common method of recovering
ferrous scrap from shredded solid wastes
involves the use of magnetic recovery system.
• Ferrous materials are usually recovered either
after shredding (or) before air separation.

23. Equipments used for Magnetic Separation
Suspended Magnet
• In this type of separator, a permanent magnet
is used to attract the ferrous metal from the
waste stream.
• When the attracted metal reaches the area
where there is no magnetism, it falls away
freely.
• This ferrous metal is then collected in a
separate container.

24. Magnetic Pulley
• This consists of a drum type device containing
magnets (or) electromagnets over which a
conveyor (or) a similar transfer mechanism
carries the waste stream.
• The conveyor belt conforms to the rounded
shape of the magnetic drum and the magnetic
force pulls the ferrous material away from the
falling stream of solid waste.

25. Screening
• Screening is the most common form of
separating solid wastes, depending on their size
by the use of one (or) more screening surfaces.
• Screening has a number of applications in solid
waste resource & energy recovery systems.
• Screens can be used before (or) after shredding
and after air separation of wastes in various
applications dealing with both light & heavy
fraction materials.

27. (C) Drying & Dewatering
• Drying and dewatering operations are used
primarily for incineration systems with (or)
without energy recovery systems.
• These are also used for drying of sludges in
wastewater treatment plants, prior to their
incineration (or) transport to land disposal.

28. Drying
• The following methods are used to apply the
heat required for drying the wastes.
• Convection Drying: In this method, hot air is in
direct contact with the wet solid waste stream.
• Conduction Drying: In this method, the wet
solid waste stream is in contact with a heated
surface.
• Radiation Drying: In this method, heat is
transmitted directly to the wet solid waste
stream by radiation from the heated body.

30. Dewatering
• When drying beds, lagoons (or) spreading on land are
not feasible,
• Other mechanical means of dewatering are used.
• The objective is to reduce the liquid volume in the solid
waste stream.
• Once dewatered, the sludge can be mixed with other
solid waste, and the resulting mixture can be:
(i) incinerated to reduce volume
(ii) used for the production of recoverable by-products
(iii) used for production of compost
(iv) buried in a landfill

31. Resource Recovery from solid
wastes – MRF
• A Materials Recovery Facility (or) Materials
Reclamation Facility (or) Materials Recycling
Facility (MRF) is a specialized plant that receives,
separates and prepares recyclable materials for
marketing to end-user manufacturers.
• Generally, there are two different types of MRF
are there:
Clean MRF & Dirty MRF

32. Clean MRF
• A clean MRF accepts recyclable commingled
materials that have already been separated at
the source from municipal solid waste
generated either by residential (or)
commercial sources.
• There are varieties of clean MRFs.
• The most common are “Single Stream Type”
where all recyclable material is mixed (or)
“Dual Stream Type”

33. Dirty MRF
• A dirty MRF accepts a mixed solid waste
stream and then proceeds to separate out
recyclable materials through a combination of
manual and mechanical sorting.
• The sorted recyclable materials undergo
further processing to meet technical
specifications established by end-markets

35. Composting
• Composting is one of the important technologies
for solid waste management.
• Any organic material that can be biologically
decomposed is compostable.
• Composting is depending upon type of organic
materials being composted and the designed
properties of final product.
• The overall composting process can be explained
as follows:
Organic matter + O2 + Aerobic bacteria → Co2 +
NH3 + H2O + other end products + Energy

36. Principles of Composting
• Decomposition and stabilization of organic
waste matter is a natural phenomenon.
• Composting is an organized method of
producing compost manure by adopting this
natural phenomenon.
• Composting can be carried out in two ways,
aerobically & anaerobically.

37. Aerobic Composting
• During composting, aerobic micro-organisms
oxidize organic compounds to CO2, Nitrite and
Nitrate.
• Carbon from organic compounds is used as a
source of energy.
• Due to exothermic reaction, temperature of
the mass rises.

38. Anaerobic Composting
• The anaerobic micro-organisms, while
metabolizing the nutrients, breakdown the
organic compounds through a process of
reduction.
• A very small amount of energy is released during
the process and the temperature of composting
mass does not rise much.
• The gases evolved are mainly Methane & Carbon
dioxide.
• An anaerobic process is a reduction process and
the final product is subjected to some minor
oxidation when applied to land.

41. Methods of Composting
• Manual composting was systemized by
Howard and his associates.
• It was further developed by Acharya &
Subramanyam and the methods are
conventionally referred as Indore and
Bangalore methods of Composting.

42. Bangalore Method
• This is an anaerobic method conventionally
carried out in pits.
• Formerly the waste was anaerobically stabilizes
in pits where alternate layers of MSW and night
soil were laid.
• The pit is completely filled and a final soil layer is
laid to prevent fly breeding, entry of rain water
into the pit and for conservation of the released
energy.
• The material is allowed to decompose for 4 to 6
months after which the stabilized material is
taken out and used as compost.

43. Indore Method
• This method of composting in pits involves
filling of alternate layers of similar thickness as
in Bangalore method.
• However, to ensure aerobic condition, the
material is turned at specific intervals for
which a 60 cm strip on the longitudinal side of
the pit is kept vacant.

44. • For starting the turning operation, the first
turn is manually given using long handled
rakes 4 to 7 days after filling.
• The second turn is given after 5 to 10 days.
Further turning is normally not required and
the compost is ready in 2 to 4 weeks.

45. Comparison of the methods:
• The Bangalore method requires longer time
for stabilization of the material & hence needs
larger load space.
• The gases generated in this anaerobic process
also pose smell & odour problems.
• The Indore method on the other hand
stabilizes the material in shorter time & needs
lesser land space.
• As no odourous gases are generated in this
process, it is environment friendly & hence
commonly preferred.

46. Windrow Composting
• The organic material present in Municipal
Waste can be converted into a stable mass by
aerobic decomposition.
• Aerobic micro-organisms oxidize organic
compounds to carbon di oxide and oxides of
Nitrogen and carbon from organic compounds
is used as a source of energy, while Nitrogen is
recycled.

47. • In areas / regions were higher ambient
temperatures are available, composting in open
windrows is to be preferred.
• In this method, refuse is delivered on a paved /
unpaved open space but leveled and well
drained land in about 20 windrows with each
windrow 3m long x 2m width x 1.5m high with a
total volume not exceeding 9 m3
• Each windrow would be turned on 6th & 11th
days outside to the centre to destroy insects
larvae and to provide aeration.

48. • On 16th day, windrow would be broken down
and passed through manually operated rotary
screens of about 25mm square mesh to
remove the oversize contrary material.
• The screened compost is stored about 30 days
in helps about 2m x 1.5m high and up to 20m
long to ensure stabilization before sales

56. Mechanical Composting
• Mechanical composting preferred where
higher labour costs and limitations of space
exist.
• Mechanical composting plant is a combination
of various units which perform specific
functions.

61. Factors affecting Composting
(i) Organisms
(ii) Use of cultures
(iii) Moisture
(iv) Temperature
(v) C/N Ratio
(vi) Aeration
(vii) Addition of sewage & sewage sludge

62. Incineration
Definition
• Incineration process can be defined as an
engineered process using controlled flame
combustion to thermally degrade waste
materials in presence of oxygen.

63. Necessity of Incineration
• Waste volume reduced to less than 5%
• At sufficiently high temperature, and
residence time, any hydrocarbon vapour can
be oxidized to carbon di oxide and water.
• Relatively simple devices capable of achieving
very high removal efficiencies.
• Heat can be recovered
• Most gases are burnt – well designed systems
• Easy to maintain
• Only solution for certain waste types.

64. Incineration system components
• Waste pre-treatment ( pre-heating (or) shredding
)
• Waste loading systems ( conveyors, hoppers,
sprayers )
• Burner management system
• Combustion chambers
• Heat recovery
• Air pollution control device
• Ash disposal
• Emission monitoring systems

65. Process Description
• The System concept consists of the following
three (3) essential main components:
1. Rotary kiln with subsequent afterburner
chamber
2. Heat exchanger or steam boiler for energy
utilization
3. Multi-layer flue gas purification, including
catalyst

67. Pyrolysis
Definition
• Pyrolysis is a thermochemical decomposition
of organic material at elevated temperatures
without the participation of oxygen.
• It involves the simultaneous change of
chemical composition and physical phase, and
is irreversible.
• Pyro = fire; lysis = separating

68. Advantages of Pyrolysis
• Conversion up to 100%
• No Green house and other harmful gas emission
into the atmosphere
• No toxic waste to dispose of
• Reduced public health risk
• Simultaneous treatment of various types of waste
materials
• Reliable energy source, high energy output
• Low capital and operation cost
• Low energy consumption

69. System Components
• Pre-processing & feeding system
• Pyrolysis reactor
• Thermal oxidizer
• Energy generator
• Off gas depuration system

70. Process Description
Step 1: Waste pre-processing and feeding
system
• Pre-processing- filtering materials that are not
suitable for pyrolysis (metals, glass and inerts)
• The remaining waste stream is chipped into
small pieces up to 50mm in diameter.
• In the dryer its moisture content is reduced
down to 20% in order to provide higher
conversion results.

71. Step 2: Pyrolysis of waste
• The high-temperature pyrolysis process takes
place in an indirectly heated pyrolytic chamber
at 700-7500C in an oxygen-free environment
• Allowing conversion of the waste into synthesis
gas (90-98%) and a solid cocking residue, or
carbon char (2-10%), without any liquid tar
fractions being formed
• The specific temperature maintained eliminates
any dioxins or furans in the carbon char residue
thereby allowing further use of this byproduct.
• Dioxins are contained in syngas only.

72. Step 3: Thermal Oxidizer
• Syngas is mixed with air in the main burner
and directed to the oxidizer for combustion at
1200ο C.
• The oxidized gasses have high thermal
capacity and are partly utilized by the system
to maintain the temperature in the pyrolytic
chamber

76. Step 4: Energy Generation
• As oxidized gas leaves the thermal oxidizer, its
high temperature is heat exchanged to a
waste heat boiler.
• Thermal energy captured from the oxidized
gas is converted into high temperature steam
supplying energy to turbine generators which
in turn produce clean electric power

77. Step 5: Pollution Control System
• The cooled (flue gasses) are passed through a
multi-stage pollution control system to be
cleaned of harmful impurities and safely
released into the environment.
• Waste off gasses utilized for pyrolysis reactor
heating are also directed to the waste heat
boiler, and, after being cooled, pass through a
similar depuration system.