Chapter 14

Solid Wastes

14.1 INTRODUCTIONN

Slid waste-often called the third pollution after air and water pollution-is that
material which arises from various human activities and which is normally discarded
S useless or unwanted. It consists of the highly heterogeneous mass of discarded
materials from the urban community as well as the more homogeneous accumulation
of agricultural, industrial and mining wastes.

14.2 CLASSIFICATION
Solid wastes may be classified based partly on content and partly on moisture and

heating value. A typical classification is as follows:

) Garbage refers to the putrescible solid waste constituents produced during
etc. These wastes have a
the preparation or storage of meat, vegetables,
moisture content of about 70% and a heating
value of around 6 x 10° Jkg.
either combustible or
() Rubbish is the non-putrescible solid waste constituents,
non-combustible. Combustible wastes
would include paper, wood, scrap,
ceramics etc.
Non-combustible wastes are metals, glass,
rubber, leather, etc. value
wastes contain a moisture content
of about 25% and the heating
These
or the waste is around 15 x 10° J/kg. The moisture
animals and human waste.
Pathological wastes include dead value is
5% non-combustible solids. The heating
COntent is 85% and there are

around 2.5 x 10° J/kg. metal ore

generally include
chemicals, paints, sand,
Industrial wastes

processing, fly ash, sewage

treatment sludge, etc and crop residues.
animal manure
i c u l t u r e wastes contain mainly farm

14.3 COMPOSITION
The solid ref various sizes and types
contains articles of
generated in urban
areas
cone
and consists e waste paper, large
paper-board cartons, glass
bottles, ofO dust, veg
dust, vegetable levels,
animals and night
soil. Table 14.l gives the
c a r c a s s e s of
Out tyres,
189
 AND ENGINERRTATO
IN
ENVIRONMENTAL
SCIENCE
ELEMENTS OF
190
cities of India
and a comparison is
refuse in various withn made with the
composition of from this tabl
1s seen
typical European City. As
withaverage
urban refuse from a about 2% to 3% as comnar
content in the refuse of
Indian cities is
efuse in Indi
Similarly, the density of refuse about about
paper
European city. India is
27% for a typical
refuse generated in the cities of Western countries nuch
higher
of than that of the
the inclusion in it of the street sweepings. The amount of refuse collecte because
urban areas in India is of the order
of 0.3 kg to 0.5 kg per person per day, excl from
night soil.
Table 14.1 Composition of city refuse (percentage by weight)

Kanpur Delhi Kolkata Bangalore Mumbai Typical

City
European
city
Paper,
Vegetable 1.35 5.88 0.14 1.5 3.20 27
Putrescible
matter 53.34 57.71 47.25 75.2 59.37 30
Dust, ash, etc. 25.93 22.95 33.58 12.0 15.90 16
Metals 0.18 0.59 0.66 0.1 0.13 7
Glass .38 0.31 0.24 0.2 0.52 11
Textiles 1.57 .56 0.28 3.1 3.26 3
Plastics,
leather,
rubber 0.66 1.46 1.54 0.9 3
Others
(stones,
wooden
matter, etc.) .59 6.4 16.9 18.9 3
16.4
Density, kg/m$) 500 578 132

Manufacturing industries produce wastes that are solid or semi-solid. Tnese

wastes can be pyrophoric
Most of the industrial(self-igniting), explosive, toxic or radioactive.
wastes generated in cities come from cale
operations and these are usually disposed-off sm o
industries are often located outside along with the city refuse. La
the cities and the
primarily the responsibility of the industries disposal of their waial
wastes are often
recycled (scrap metal and themselves. Some of the n a
energy source for specific paper) while others can be utiise as

from solid wastes by processing plants in some regions. Energy 8y c a n be

recove
numerous thermal rersion.
The toxic and radioactive routes as well as by biochemical
wastes-often classified co
consideration before their
disposal. hazardous wastes-neteu
as

Agricultural wastes comprise both crop residues and animal wa ner day:s
manure and urine, whereas urban
In India, wastes amount to 0.3-0.5
agricultural wastes amount to kg per petimal and
vegetable wastes contain valuable minerals around 2 kg per person per day. Ani
a g r i c u l t u r a l

wastes contains nitrogen, and nutrients

ts. Humus from re vital to
the fertility of the soil and phosphorus, potash and trace elements wi ich
optimum plant growth.
leads to loss of valuable
nutrients. Burning of wastes fuel furt a
 Chapter 14 SOLID WASTES 191
14.4 SOLID WASTE MANAGEMENT
al of solid
criminate disposal
mu
advers environmental effects. The main
wastes--especially
of hazardous
wastes-causes
objective of solid waste
mise these adverse effects before it
becomes too difficult to management is to
rectify in the future,
14.4.1 Functional Elements

The activities associated with the

management of
solid wastes from the point of
eneration
gene
tofinal disposal have been grouped into the six
functional elements
Figure 14.1). By considering each fundamental element separately, it is possible to:
a identify the fundamental aspects and relationships involved in each element and
) develop, when possible, quantifiable relationships for the purpose of making
engineering comparisons, analyses and evaluations.

Waste
generation

Storage

Collection

Processing/
Transfer
Recovery
Transport

Disposal

Waste Management.
Figure 14.1 Functional Elements of Solid

Waste Generation
Waste generation encompasses those activities in which
materials are identified as
no lor or gathered together for
being of value and are either thrown away
dine
disposal. From th
for
the standpoint of economics, the best place to
sort waste materials

recovery is at the source of generation.

 192 ELEMENTS OF ENVIRONMENTAL SCIENCE AND ENGINEERING -

Onsite Handling, Storage and Processing

This functional element encompasses the activities associated with the .
oint of
storage and processing of solid wastes at or near the point of generation
generation. n , handling
storage is of primary importance because of the aesthetic consideratione nsite
health, public safety and the economics involved. public
Proper onsite storage is of particular importance for municipal refu
contains a significant amount of putrescible garbage. Watertight, rust-Tesi that
containers with suitable covers reduce the incidence of rodent or insect esistant
infestat
and offensive odours and unsightly
conditions may be kept to a minimum if he
containers and storage areas are washed periodically. Larger containers
can be ne
along with mechanical collection trucks. Bulk containers or dumpsters should he uoused
where large volumes of refuse are generated, such as at ed
restaurants, apartment buildings and hotels.
shopping centres
Collection
The functional element of collection includes the
gathering of solid wastes
hauling of wastes after collection to the location where the collection and the
emptied. This location may be a transfer station, a processing station or vehicle is
a landfill
disposal site.
Collection includes all the activities associated with the
wastes and the hauling of the wastes gathering of solid
collected to the location from where the
collection vehicle will ultimately
There
transport it to the site of disposal.
are three basic methods of collection:
G) Community storage point: The
bins and stored till the waste municipal refuse is taken to fixed storage
collection agency collects it daily for disposal in
a vehicle.
(ii) Kerbside collection: In
advance of the collection time, the refuse
brought in containers and placed on the is
by the waste collection agency. footway, from where it is collectea
ii) Block collection: Individuals
over to the collection
bring the waste in containers and hana
staff who empties it into the
returns the container to the waiting vehicle auu
individuals.
The collection truck and crew
make
collection system. Collection trucks most up the most important element
a

compacting type. In other words, compaction commonly used are of the enclos
in a collection vehicle
reduces the refuse volume by as much as
80%.
tempora
Mechanical collection systems are
because of improved aesthetics of curbside becoming popular in many commet communities

container placement as well lor

costs. These systems consist of
standardised as lifting
mechanisms. In fully automatic systems, an containers and truck-mountea the
articulated arm
replaces the container without mechanis
vehicle engages, lifts, empties and nce
Semi-automatic systems require a truck crew manual asS in
position to be automatically hoisted and emptiedmember to place the
contahen
into the collection truck ana
ther
manually returned to its set-out position. All containers ease

of miovement. are wheel-mounted

 Chapter 14 SOLID
WASTES193
collection of garbage and rubbish is
Co
ined generally more economical than
ection of
collection of these
these types of refuse. In many
communities, however, certain
separate a r e ecvcled.
r e c y c l e d . Home owners
aterials
practice source separation; i.e., they
naper plastic
and
and from the remainder of their separate
metal, paper
refuse. The recyclable
lasslsare
glass,
are
then
then picked up
up iin a separate collection truck to prevent the refuse from
materials
contaminatir the recyclable component and lowering its resale value.
noVative collection systems involving pneumatic pipeline transport have
Innovative collecti
been tried. In pneumatic systems, refuse is pulled by suction or vacuum through
nderground pìpes to a central processing plant. Waste collection at the Disney
Worid amusement park in Florida for example, is done by a system of this type. It
inates the
iminates need
the need for noisy and unsightly refuse collection trucks. But complex
tols, valves and high-speed turbines are required for operation of the system
the high-tech appeal of pneumatic waste
snd installation costs are high. Despite
and transport systems, they are feasible only in specialised local situations.
collection

Transfer and Transport

involves two steps: (i) the transfer
The functional element of transfer and transport
the larger transport equipment; and
of wastes from the smaller collection vehicle to
the
the subsequent transport of the wastes, usually over long distances, to
()
disposal site.
collection trucks
Transfer Stations: It is not always feasible for individual
especially if the
naul refuse to a waste processing plant or final disposal site, the
in which
timate destination is not in the immediate vicinity of the community
one or more
15 collected. To solve this waste transport problem etiiciently,
ase
transfer stations may be used. collection
which solid wastes from individual
a facility at
A ranster station isinto vehicles, such as tractor-trailer
units. It is more
are consolidated larger the consolidated solid
waste
vehicles to transport
C a l for a few of these larger location, rather than having
distance to the processing or disposal
e 1Dng-haul Individual transfer
station capacities may vary
ecton truck make the trip. waste per day, depending
fr than 500 tons of
ueWhat less than 100 tons to
more direct
modes of operation:
On
on the size of the two basic
har and the community. There are
transfer station, the
refuse is
discharge
first storage discharge. In a storage discharge
pit or onto a large platform
emptied from the collection trucks into a storageempties direetly into larger
the
In a direct refuse truck
discharge station, each and hold
about 75 m' the
transport
solid
vehi ne
trailers typically have a capacity
of
compacted
and from up to eight
waste from four ion vehicles if it
is not
collection vehicles if itcollectio
is pacted.

Processi
The
ng and Recovery recovery
includes all the
techniques,
functional
and other
eaupment and
nd
nent oprocessing
both to improve
the efficieney of the
trom solid
elwastes. facilities
ements andtoto recover
es usused
conversion
products
energy
or

Over usable materials,

 194 ELEMENTS OF ENVIRONMENTAL SCIENCE AND ENGINEERING
Municipal solid waste may be treated or processed prior to final diano
waste processing provides several advantages.
osal. Solid
First, it can serve to reduce the total volume and weight of waste materi.
requires final disposal. terial that
Volume reduction helps to conserve land resources, since the land
ultimate sink or repository for most waste material. It als0 redue 1s the
duces the total
transporting the waste to its final disposal site. In addition to vol
olume and weighcost of
duction, waste processing changes its form and improves its handling charactere
Processing can also serve to recover natural resources and energy in the eristics
material for reuse or recycling. waste
Shredding and Pulverising
Size reduction of
municipal solid waste is accomplished by the physical processee
shredding pulverising. Shredding refers to the actions of cutting and tearingof
or
whereas pulverising refers to the actions of crushing and grinding. ing,
Shredding and
pulverising reduce the overall volume of the original or raw waste materio
sometimes by as much as 40%. ,
There are many reasons for size reduction of municipal solid
waste, Tha
production of refuse-derived fuel, or RDF, requires processing of the raw solid waste:
this typically includes shredding and pulverising.

Hammer Mills
One of the most types of equipment used for processing MSW into a uniform or
common
homogeneous mass is the hammer mill. A hammer mill is a mechanical impact device in
which the raw solid waste material is cramped with a force sufficient to crush or
tear
individual pie of the waste. Impact is provided by several hammers that rotate at
speeds (up to 1500 rev/min.) around a centre horizontal or vertical shaft.
high
A hammer mill is a very versatile size reduction device because it will
accept
almost any type of waste material (except of course, very bulky or dense ones such as
tree stumps or engine blocks). It is possible to reduce the size of solid waste material
components to uniform fragments between 25 and 50 mm with proper operation.

Baling
Compactingsolid waste into the form of rectangular blocks or bales is
called baling
MSW bales are typically about 1.5 ms in size and weigh roughly 1 kN. Solid waste
can be compacted under high pressures (about 700 kPa) in either vertical or
horizontal presses; the bales are frequently wrapped with steel wire to help retan
their rectangular shape during handling. They also may be enclosed in hot asphalt
plastic or Portland cement, or tied with metal bands, depending on the intended use
or disposal method. If moisture content and
compaction
pressures are high
eno
they may retain their shape without being wire-wrapped or encased. Semi-automa
horizontal presses can bale up to 36 kN per hour of MSW. Volume reduction can
as much as 90% of the original waste volume.
ease
The basic advantages of an MSW baling process include the significant decre
in waste volume, the ease of handling the compacted refuse and the reducuL of
litter and nuisance potential.
 Chapter 14 SOLID WASTES 195

Compostig

process in which the organic portion of MSW is allowed to

is a
decompose
Compos
ting under refully controlled conditions. It is a biological rather than a
carefullv

chemical or me
nical process; decomposition and transformation of the waste
accomplished by the action of bacteria, fungi and other micro-organisms
s t e r i a l a r e a c c o m p l i s h e

ntrol of moisture and temperature, a composting plant can reduce

Withfproper
raw organic material by as much as 50%. In aeration, a composting
for
the stabilise the waste and produce an end product that may be recycled soil
1Se. The
p l a n t

end product is called compost or humus. It resembles potting

benetio odour and it can be used as a soil conditioner or mulch. A
in texture a n d . earthy
olid
waste composting operation includes sorting and separating,
lete municipal soli
product upgrading and finally, marketing.
coding and pulverising, digestion,
nioestion may istake place in open windrows or in an enclosed mechanical
a long, low pile of the prepared organic waste, usually about
facility. A windrow

base.
and about 2 m high. Most windrows are conical in cross-section
at the
wide
3 in length. The composting waste is aerated by periodically turning
m
dahout 50 m done manually with a pitch-fork, but at most large
ch windrow. This can be of
mechanically by specially designed machinery. Some
frilities it is accomplishedrebuild
turn and the windrow directly behind the machine; others
these machines
to its original position. Turning frequency
rebuild the turned windrow adjacent maintained
content and other factors. When moisture content is
varies with moisture
windrows are turned two or three times a
week and in some cases daily.
at about 50%,
humus can be sold for use as a mulch or
Before the stabilised compost or its quality
be processed further to upgrade or improve
soil conditioner, it must pelletising.
includes drying, screening and granulating or
and appearance. This efficient
in bags, although bulk sale is more
Sometimes, the compost is placed
market for compost is agriculture. Land
and economical. The largest potential
fields.
reclamation and landscaping are the other application

Salvage or Manual Component Separation

waste components is
Before ultimate disposal, the manual separation of solid
to achieve the recovery and reuse of materials. Cardboard, newsprint,
accomplished manually sorted
aluminium cans, etc. are
nigh-quality paper, glass, metals, wood and
Out or salvaged, either for recycling or for resale.

neineration or Thermal Volume Reduction

and combustible
gnly combustible like plastics, cardboard, paper, rubber
wastes
food wastes, etc. are subjected to
e s like cartons, wood scrap, floor sweepings, Incineration results in air
nell on i.., burning at very high temperatures. installed to avoid contamination
o n and so proper control equipment need to be heat generated during
Vronment. In order to make this method economical, the a waste heat
ho:atlon is usefully utilised by generating steam or by ofputting waste collection and
dinathe incinerator, thereby partly recovering the
cost

sal. The in the incineration of solid waste is shown

operations involved
in Figure 14.2.basic
 SCIENCE AND
ENGINEERING
ENVIRONMENTAL

OF
196 ELEMENTS
Treated
Emissions
Vapour Afterburner Quench Stacks
Control
Emissions

Air
Waste Waste Incinerator Pollution
Waste Feed
Preparation Control
Storage

Residue Residue
Handling Handling
Water
Solids
Treated
Solids
Figure 14.2 Flow Diagram of Incineration Process.

Typical operation of a municipal solid waste incinerator

.Optimal multi-fuels composed of different portions of wood, paper, plastic,
rganic and other waste are fed into the silo.
.The fuel is transported from silo to fuel magazine.
.The fuel is fed into the oven on a regular basis according to need.
.The fuel is mechanically pushed over the grating in the oven's primary
chamber and is incinerated at the end of the grating.
Combustible gases are incinerated in the secondary chamber. The residual
ashes are fed into the ash container.
The heated fue gas goes from the oven into a boiler. The flue gas is cooled and
hot water vapour is produced.
.Energy in the form of vapour goes to the energy receptacle.
After the boiler, the cooled flue gas goes to a reactor, where calcium and
active carbons are added.
.In the filter, the gas is purified of dust particles, calcium and active cardo
.Purified flue gas is sent via a stack to the
atmosphere.
High temperatures-870°C to 1,200°C (1,400°F to
tilise and combust (in the presence of 2,200°F)-are used to vo
oxygen) halogenated and other refractor
organics in hazardous wastes. Often auxiliary fuels are
sustain combustion. The destruction and employed to initiate a
removal (DRE) for prope
operated incinerators exceeds the 99.99% requirementefficiency
for hazardous waste ana d
be operated to meet the 99.9999%
requirement for PCBs and dioxins. Off-gases a
combustion residuals generally require treatment.
Incinerator off-gas requires treatment to
by an air pollution control sys
remove
particulates and neutralise and remove acid
gases (HCI, NO, ana
0,).
Baghouses, venturi scrubbers and wet electrostatic
packed-bed scrubbers and spray driers precipitators remove parteue
remove acid gases.
 Chapter 14 SOLID WASTES 197
Pyrolysis or Destructive Distillation

his
In th disposal method,the solid wastes are heated under anaerobic conditions
hurning without
e., burning witho oxygen). The organic components of the solid wastes
s liquid and gaseous fractions (CO0, CO2, CH4, tar and split up into
gaseou
charred carbon). Unlike
highly
the exothermic process of combustion, pyrolysis is highly endothermic
highly exothermic
a
not is why it is also called destructive distillation (Figure 14.3). process

Clean Offgas

Condensed
volatiles
Gas Spent Carbon
Treatment
System Water

Excavate Material Desorption Treated

and g Optional Pyrolysis Medium

Oversized
Rejects
Figure 14.3 Pyrolysis.

Pyrolysis is formally defined as chemical decomposition induced in organic

to achieve a
materials by heat in the absence of oxygen. In practice, it is not possible with less
oxygen-free atmosphere; actual pyrolytic systems are operated
COmpletely
than stoichiometric quantities of oxygen. Because some oxygen will be present in any

If volatile or semi-volatile materials

pyrolytic system, nominal oxidation will occur.
are present in the waste, thermal desorption will also occur.
into gaseous components,
Pyrolysistransforms hazardous organic materials
and a solid residue (coke)
containing fixed carbon and ash.
5tnall quantities of liquid
including carbon mono-
of organic materials produces combustible gases,
toysis the off-gases are cooled,
and methane, and other hydrocarbons. If
1 ydrogen and contaminated water. Pyrolysis
producing an oil/tar residue
condense, temperatures above
430°C (800°F).
and att operating
y occurs under pressure The off-gases may be
treated in a
further treatment.
S rOysIs gases require condensed. Particulate
removal
flared and partially
a r y combustion chamber, are als0 required
or wet scrubbers
pment such as fabric filters such as rotary kiln, rotary
hearth
methods,
furnoventional thermal
treatment Kilns or furnaces used
pyrolysis.
furnace or idised bed furnace, are used for waste
and with less air supply
than
temperature
Would be operating at lower may also
be used tor waste
Would 1 s
equired for combustion.Molten salt process

pyrolysis.
Landfarming
In thi biodegradable
industrial wastes
are treated
soil.
by the
the of the
biologicald1sposal method, the surface
biological,
Pysical and chemical
p r o c e s s e s
occurring in
 ELEMENTS OF
ENVIRONMENTAL SCIENCE AND ENGINEERINC
198
either applied on top of the land o r
inict. ,

The organic wastes are

where they undergo bacterial nd
oelow the
the
suitable equipment,
soil surface with
intervals, the landfarming sites can be reused
chemica
cal
decomposition. At frequent without
the landfarming site is properly managed,
any adverse effects provided

14.4.2 Disposal of Solid Wastes

The final functional element in the solid waste management system depicted in
Figure 14.1 is disposal. Disposal is the ultimate fate of all solid wastes, whether tho
are wastes collected and transported directly to a landfill site, semi-solid waste
(sludge) from industrial treatment plants, incinerator residue, compost or other
substances from various solid-waste-processing plants that are of no further use.
Due to heterogeneity of the city refuse, it is important t0 select the
most
appropriate solid waste disposal method keeping in view the following objectives:
. I t should be economically viable, i.e., the operation and maintenance costs
must be carefully assessed.
I t should not create a
health hazard.
. I t should not cause adverse environmental
effects.
. I t should not be aesthetically unpleasant, i.e., it should not result in offending
sights, odours and noises.
I t should
preferably provide opportunities for recycling of
The
materials.
methods of disposal commonly used are:

Open Dumping
Open dumping of solid wastes is done in
and cities. Being low-lying areas and outskirts of the tow
in India. However,
comparatively cheaper, this method of disposal is extensively useu
major disadvantages are:
Public health hazards are caused by the breeding
and other pests. of flies, mosquitoes, tats
Obnoxious gaseous and
thecombustible particulate matter
solid are produced by burins
wastes, resulting in air
Open dumping requires large pollution.
land areas, which further the
problem of land shortage for human habitation. aggravates
Sanitary Landfilling or Controlled
Sanitary landfilling involves the Tipping
layers of the earth's mantle, disposal of municipal wastes on or in per
especially in the
In
landfilling, the solid wastes are degraded areas in need of restora ach
layer being uniformly covered by a compacted and spread in thin
cover of about one
layer of soil. The final layer is
and
metre of earth to
prevent
scattering. This is a biological method rodents from
covereu refuse
digestion results in of waste burrowing
in l refuse
decomposition treatment and bacter which
can be harnessed as products like CO, CH, NH3, HS and wh
renewable sources of lg
energy.
 Chapter 14 SOLID WASTES 199
This method loes not ause environmental damages by creating nuisances or
health h a z a r d s a s refuse is covered and prevents
vectors. Besides, there is no danger of air
breeding
pests and disease of
pollution resulting
from burning and no
provided is taken to avoid leachates of refuse from conta-
mina
Phe Surface or underground water sources. This prevention can be taken by
nlastic membrane or waterlight membrane on the base. Nevertheless, most
using
a pl
is stil1 disposed off on land. But the waste is now buried in a sanitaryy
icipal waste
mu not. simply deposited in a pile on the ground. A sanitary landfill is not a dump.
land
carefully planned and engineered facility for solid waste disposal. This means
Itiis a
t is designed, constructed and operated in an environmentally sound manner that
tha
n o t threaten public health or safety, and that also minimises public nuisances
ch s windblown litter and unpleasant odours). Three key characteristics of a
nicipal sanitary landfill distinguish it from an open dump. They are

Solid waste is placed in a suitably selected and prepared (for example, lined)
landfill site in a carefully manner. prescribed
.The waste material is spread out and compacted with appropriate heavy
machinery.
.The waste is covered each day with a layer of compacted soil.
of modern sanitary landfill design is the
Perhaps the most salient feature In the recent past, it w a s believed
technology used to prevent groundwater pollution. soil between the bottom of
that a suitable depth or thickness of naturally occurring
table or bedrock would suffice to prevent
the landfill site and the groundwater of a MSW
seeping out from the bottom
pollution. It was thought that pollutants
be filtered and absorbed (in a process
landfill in a liquid called leachate) would
down into the groundwater aquifer.
called natural attenuation) as they percolated
landfill' m e a n s an operation in which
Sanitary Landfills: The term 'sanitary and covered with a layer of soil at the
off a r e compacted
ne wastes to be disposed When the disposal site has reached its ultimate capacity,
end of each day's operation. a final layer of 2
ft or m o r e of
a r t e r all disposal operations
have been completed, from
14.4). Open dumping, as distinguished
(Figure
COver material is applied used in parts of the country but is no longer an acceptable
sanitary landfilling, is still environmental or sanitary
standpoint.
ueans of land disposal from a n aesthetic,

- 2 ft final earth
cover

Terrace as

required
cover
Final CellN 2 ft final earth
on slope face

.2:1 or 3:1 typical slope

Cell 6 in intermediate earth
Cell cover

Compacted solid
Cell
Daily c o v e r Wastes

Cell width
variable
6 in intermediate
earth cover
Landfill.
of a Sanitary
Sectional View
Figure 14.4
 ELEMENTS OF ENVIRONMENTAL SCIENCE AND ENGINEERING
200

Reactions Occurring in Completed Landfills: To plan

and design
landfills effectively, it is important to understand what takes place within sanitary
ry
after filling operations have been completed. Solid wastes placed in a sanitary lander
undergo a number of simultaneous biological, physical and chemical changes, Amona
the more important of these changes are the following: nong
G) The biological decay of organic, putrescible material, either
aerobically or
anaerobically, with the evolution of gases and liquids;
i) The chemical oxidation of materials;
(ii) The escape of gases from the fill and lateral diffusion of
the fill
gases through
iv) The movement of liquids caused by differential
heads;
(v) The and
dissolving leaching organic and inorganic materials
of
by water and
leachate moving through the fill;
(vi) The movement of dissolved material by concentration gradient and osmosis
and
(vii) The unevensettlement caused by consolidation of material into voids. The
decomposition and stabilisation in a landfill depend on many factors, such
as the
composition of the wastes, the degree of compaction, the amount of
moisture present, the
presence of inhibiting materials, the rate of water
movement and temperature.
Gases in Landfills: Gases
found in landfills include air, ammonia,
dioxide, carbon monoxide, hydrogen, carbon
oxygen. Carbon hydrogen
dioxide and methane are the sulphide, methane, nitrogen an
anaerobic decomposition of the principal gases produced from tae
organic solid
percentage of carbon dioxide is the result waste components. The high inid
of aerobic
decomposition continues to occur until the oxygen in the decomposition. Aerooe
compacted wastes is depicted. Thereafter, air initially present n tne
decomposition will
composition of the gas remains proceed
After about 18 months, the anaerobica
reasonable.
Aduantages
.Where land is available, a
sanitary landfill is usually the most economica
method of solid waste disposal
.The initial investment is low when
.A compared
sanitary landfill is a complete or final
with
other disposal methods
incineration and composting, which disposal method as compareu to
require additional treatment or dispe
operations for residue, quenching water,
A sanitary landfill can receive unusable materials, ete.
all types
necessity of separate collections. of solid wastes, eliminatin8 the
.A sanitary landfill is tlexible; inereased
of solid cat be
disposed off with little additional personnelquantities
and
wastes
Submarginal land may be reclaimed for use as equipment. golf
courses, airports, etc. parking lots, playgrou
 Chapter 14 SOLID WASTES 201
Disadvantages

Inhighly populated areas, suitable land

may not be
economical hauling distance. available within
Proper sanitary landfill standards must be adhered to
may result in an open dump. daily or the operation
Sanitary landfills located in residential areas can
provoke extreme
opposition. publie
A complete landfill will settle and require periodic maintenance.
Special design and construction must be adopted for buildings on
landfills because of settlement. completed
Methane-an explosive gas-and other gases produced from the decom
pOsition of the waste may become a hazard or nuisance and interfere with the
use of the completed landfill.

14.5 WASTE MINIMISATION

Waste minimisation is an approach to prevent pollution in the environment. This is
the concept of taking preventive measures at the source of waste generation. These
measures include efficient use of energy, water, raw materials, housekeeping. ete.
The cleaner production can bring opportunities to entrepreneurs to reap benefits
These include:
Quality improvement
Development of new products
New avenues for marketing
.Creation of conducive working environment
Better acceptability of products
Easy access to consumers
Assured quality products.
minimisation and cleaner production.
are three principles of waste
Dere
They are
Reduction at source
Recycling and
Reuse.
14.5.1 Reduction at Source
t covers undertaken at the shopfloor.
different pects of process a quality output.
produce
PrOpriate selection and uses of input to

Training of personnel.
Maintenance of machine on schedule
appropriateiy.
process parameters
Cessity to follow the
waste for producing
new produets

.elope new ideas to utilise the other

manufacturers tor reuse.

materials to
Option to supply waste
p
 ELEMENTS OF ENVIRONMENTAL SCIENCE AND ENGINEERINC
202
14.5.2 Recycling
Recycling primarily involves evaluation of the process for an easy recover
from the disposed-off items.
ery of waste

Evaluate to reprocess disposed-off items recovered from the waste.

Select and adopt appropriate technology to process it economically.
B e sure to produce a quality product from waste after recycling

The benefits of recycling are given in Figure 14.5.

Reduces Reduces acid Reduces urban

warming deposition air pollution
L
Reduces air
Saves energy
pollution
Makes fuel
supplies last
longer

Reduces Reduces solid

energy waste disposal

Recycling

Reduces water Reduces mineral

pollution demand

Reduces habitat
Protects
destruction
species

Figure 14.5 Benefits of Recycling.

14.5.3 Product Reuse

the
find
to
materials and also
also
to.,
. To assess the utility of different raw nd
effective utlsa
ation.

to use raw materials in any other form for be

opportunity whether 1
of an end product and evaluate
To assess product reuse

to minimise waste
without degrading quality.
reused
 Chapter 14 SOLID
TYPICAL MRF OPERATION
WASTES 203
14.6

Incoming
ucks are weighed and the waste is then
loor. Any
unsuitab, materials seen
the floor on dumped on a concrete tipping
ontainers for haul to the landfill (Figure 14.6). are removed by hand and placed in
Outside uses

Energy recovery Incinerator (paper.

Steam & electricity) plastics, rubber, food.
yard waste)

Shredder
Separator Food. grass.
eaves

Pipeline

Metals
RubberGlass Plastic
Pape Residue Compost

Recycled to primary manufacturers or Landfill &

reformulated for new products reclaiming
disturbed
land

Fertiliser

Consumer (user)

Figure 14.6 Material Recovery Facility MRF).

A large inelined rubber-belt
front-end loader then pushes the material onto
Conveyoy
CDveyors
one or more workers who remove deleterious
materials

Such pass by
largeametal
y then passes under
as an

pots, garbage. The conveyor

electroma
he parator
ots, bricks
that
or

removesthe tin cans and other ferrous

metals from

andCommingled
baling prior
waste
to
stu to steel mills.
shipment
se stream. This metal is then conveyed
to a baler for
compression

The on a shaker table to

then screened
remaining commingled
e the dirt commingled material is
or no
has little
resale value and

rOken
hroken
glass. This broken glass
glass terial
material such glassphalt. as

The will be used in the of paving sueve

lowers tobottles.
manufacture
blowers remove the plast
and alumin:e
aluminium material
con with large These glass
nd is then classified unbroken glass
bottles are aners from the remaining

room,
where
workers separate
the bottles by

Veyed into a sorting

 SCIENCE AND ENG
204 ELEMENTS OF
ENVIRONMENTAL
NEERIN
not separated by colour, it has no r e s a l a .
colour; if the glass is value. In most MR
the glass bottles
are further processed by crushing them
particles and then removing bottle caps and other such materiol roughly 12
a rotating drum
is marketable as furnace-ready cullet
The resultant glass product
containers are also conveyed to aa..
The plastic and aluminium sortin area
separation of plastic is typically
accomplished by hand with skille area. "The
can identify the plastic types
through experience. Recently,
its chemical properties and
equipmentsorter
ha
has
who
been
developed that can identify plastic by can allow
complete automation of plastic sorting.
The equipment is
expensive W but it the
can
eliminate three or four sorters who normally have to separate the thalt a
manually.
material
After the plastic is separated, it is either baled or chipped for shiome
market. Other types of plastics such as polystyrene and styrofoam are not
recovered because of low tonnages and high processing costs. rally
The aluminium is usually separated from the plastics and other remaining
non
recyclable materials on the conveyor belt through the use of a device called an edi
current separator. This device repels aluminium up into the air and off the belt
allowing it to be captured and baled or densified for shipment to market.
Paper is processed in a MRF on a separate conveyor line. Old newspaper (ONP
is generally bundled at the curb and not allowed to mix with the other papers in the
collection truck. At the MRF, the ONP is dumped in a separate area prior to being
conveyed past quality control workers, who remove materials that are considered to
be contaminants. It is baled and loose-loaded into tractor-trailers and shipped to
paper mills for use in making newspaper. Much of the remaining paper is sutable
for sale to tissue mills.