SWM L15-L28_drhasan (Part 2).pdf

Solid and Hazardous Waste
Management
Lecture prepared by
‘Dr. Hasanliketo beliefthat solidwasteisa valuableraw
materialslocatedat a wrongplace’
Md. Mahmudul HASAN, Engr., PhD
Associate Professor and Head
Dept. of Civil Engg.
BAUST, Saidpur
(Former: Assistant Prof., Dept. of Civil Engg., UAP
Head & Assistant Prof., Dept. of Civil Engg., UITS)

Chapter 05:
Recycling and Reuse
2
Dr. Engr. Md. Mahmudul HASAN

Recycling and Reuse
Recycling and reuse involve recovery of resources from the waste stream in the form of
both materials and energy. Recycling can be practised at household level and at material
recovery facilities (MRF) or full stream processing plants.
Depending on the reuse of recycled materials this process may be broadly categorised
into:
primary recycling:
This is the part of a material recovery system where recycled materials are reused in
their same form; for example, paper for packaging in retailers’ shops; textiles for
machinery wiping; textiles, shoes, etc. for reuse by the poor; demolition waste for land
reclamation; beverage bottles for refilling; containers such as bottles for use as domestic
containers. This is the most efficient form of recycling and involves a few processes;
sometimes only cleaning.
secondary recycling:
This includes both materials and energy recovery where recycled materials are used for
re-manufacturing or to produce energy. For example, paper for repulping; textiles for
paper making; metals and glass for remoulding; rubber for low-grade rubber
production; plastic for inferior grade production; waste recovered as feedstock for
biological processes; refuse-derived fuel; etc. These processes are more energy
intensive than primary recycling. 3

Recycling and Reuse: Environmental Justification
There are numerous environmental justifications for recycling and reuse:
i. It minimises the use of virgin raw materials directly (when recycled materials are
used as raw materials) or indirectly (reuse minimises the demand for new
products).
ii. It saves energy both directly (when recycled materials are used as feed to produce
energy) and indirectly (saves energy required to manufacture products or for their
disposal).
iii. It reduces the amount of waste that must be disposed of, which reduces the energy
required for transportation and disposal and minimises overall environmental
pollution.
iv. It limits emissions of greenhouse gases such as methane through the removal of
organic waste from open dumping (the most common method in most low- and
middle-income countries) and at landfill disposal sites.
v. It generates income through recycling (often informal in low-income countries),
trade which improves the quality of life of a section of the poor.
vi. It reduces overall waste management costs.
4

Recycling and Reuse: Risks
There are numerous environmental justifications but having some risks:
i. It involves health hazards to the people working in this sector, particularly when
recycling hazardous materials and sharps.
ii. The production costs of reusable products may be high. For example, reusable
containers should be more durable and therefore may consume more materials
and energy compared to a product for one use. It may also involve energy to
clean and sterilise them to safeguard public health.
iii. The collection of recycled materials may involve additional collection vehicles
which may increase the volume of traffic.
iv. In some cases more energy may be required in the recycling processes
themselves than would be used in the manufacture of new materials.
v. It is apparent from Virtanen and Nilsson (1993) that the maximum level of
paper recycling in Austria leads to greater emissions of sulphur dioxide, nitrous
oxide and carbon dioxide in comparison with the component of energy
recovery by incineration allowing a reduction in the overall use of fossil fuels
5

Recycling and Reuse: Bangladesh Pattern in Urban area
Figure: Recycling
pattern for urban solid
waste in Bangladesh
6

Recycling and Reuse: Effectiveness factors
The development of an effective recycling programme and selection of materials that can
be recycled should be based on the following:
i. Legislation may demand diversion of certain materials from waste streams (for
example, present legislation in many industrialised country bans disposal of certain
materials on the landfill, and the final disposal option may involve a higher tipping fee
for selected materials).
ii. Recycling opportunities provide a market for recycling materials; however, to design
centralised recycling plants, particularly in developing countries, if a small percentage
of targeted materials are available in the waste stream because of their very high
market value (so that they are recycled at household level), then a centralised
recycling system may not be cost effective.
iii. Commitment of organisations involved in solid waste management and protection of
environment is essential – depending on the level of commitment, there may be
subsidies, loans, incentives, etc. for recycling selected materials.
iv. Labour and equipment infrastructures must be available.
v. Finance is required for the programme – including the cost of planning awareness
programmes; capital costs (for recycling plant); programme operation and
maintenance costs; and marketing costs (of recycled products).
7

Recycling and Reuse: Processes
The activities involved in material recycling processes may be broadly categorised
into:
1. Separation of materials:
Separation (sorting) of materials from the waste stream is the first essential elements
in any recycling operation. The possibility of contamination of source separated
materials is minimised if they can be separated at household level. Commonly
practised separation mechanisms involve:
o manual sorting
o mechanised sorting
o both manual and mechanised sorting.
2. Conversion of materials:
Waste materials can be converted into usable materials and energy. The main
conversion processes are:
o thermal conversion – incineration to recover energy or heat, pyrolysis
o biochemical conversion – anaerobic digestion, composting, hydrolysis.
8

Recycling and Reuse: Processes
manual sorting
9

Recycling and Reuse: Mechanised sorting
Mechanized material separation techniques:
1. conveyors (pan, belt, bucket or pneumatic) – to pick and/or convey waste in the
recycling plant (manual sorting of selected materials from conveyor can also be
done),
2. shredding (flair or hammer mills, shear shredders, glass crushers, wood grinders)
equipment – used to break various constituents of waste to extract them more
easily,
3. screens (rotary drum or disk type) – process of separation by size, but it is
generally plugged by a number of things,
4. cyclone/density separators – occasionally used to separate light materials from air
stream or prepared waste,
5. magnetic and electromechanical separators – often used for the purification of
feed streams containing unwanted magnetic impurities or concentration of
magnetic materials,
10

Screening:
Factors that must be considered in the selection of screening equipment include:
1. specification of materials for the components to be screened
2. characteristics of the waste materials to be screened, including particle size
shape, density, etc.
3. screen design characteristics including materials of construction, opening size,
surface area of the screen, speed of the rotor, etc.
4. separation efficiency and overall effectiveness
5. site, access, noise and environmental limitations.
The efficiency of a screen can be evaluated in terms of the percentage recovery of the
material in the feed stream by using the following expression:
11

Screening: The efficiency of a screen can be evaluated in terms of the percentage
recovery of the material in the feed stream by using the following expression:
Hence, the effectiveness of screen can be deduced by the following
expression:
12

Recycling and Reuse: Determination of screen recovery efficiency
and effectiveness
Example:
Given that 2500kg/h of
municipal solid waste with
10% glass is applied to a
rotary screen for the
removal of glass prior to
shredding. Weight of
underflow is 500kg/h and
weight of glass in screen
underflow = 200kg/h,
determine the recovery
efficiency and
effectiveness of the screen.
13

Recycling and Reuse: Promotion and planning
Following Activities may help with promotion and planning for recycling and reuse:
i. Involvement of all stakeholders
The recycling programme should aim to involve all waste generators, governments,
NGOs, etc. to operate the system efficiently.
ii. Public education campaign
As their participation is important for well-planned recycling, it is necessary to
encourage greater participation of waste generators (for example, separation of
materials at source) and to support them by providing information and education.
iii. Commitment of local government
Local as well as national government has a major responsibility to develop a recycling
plan with some targets, and local government should play an advocacy role to
motivate and encourage generators.
iv. Assessment and augmentation of existing system
It is vital to identify the successes, problems and limitations of any existing system so
that appropriate measures can be planned, such as modifying or formulating waste
management legislation.
14

Recycling and Reuse: Promotion and planning
v. Building local expertise
If a new technological solution is being adopted, operation and maintenance of pilot-
scale plants may help develop local expertise and will also minimize planning errors.
vi. Possibility of integration with other waste management elements
Waste management can be integrated with transfer stations and disposal sites as this
has a positive impact on other waste management elements and may help to sustain
the programme.
vii. Assessment of local waste stream
Both quantity and composition of different constituents should be assessed, to
identify materials with potential to be recycled.
viii. Market specification of recovered materials
The market needs to be investigated, to assess the costs associated with meeting the
required specification for recovered materials.
ix. Recycling opportunities
The ultimate success of many recycling plants depends on marketing of recovered
materials. It should take into account market uncertainties. 15

Chapter 06:
Anaerobic Digestion
16

Anaerobic Digestion
The following terms are frequently used as synonyms for anaerobic digestion:
o biogasification
o biogas generation
o fermentation
o methane fermentation
o methane production.
The main advantages of anaerobic digestion are:
i. produces renewable energy
ii. energy recovery rate is much higher than the energy recovery inform landfill (all gas produced
can be collected and utilised, but landfill gas collection efficiency never exceeds 50 per cent and
in many situations landfill gas collection efficiency is very low)
iii. cured sludge can be used as a soil conditioner
iv. produces less saline product than compost
v. minimises odour and aesthetic problems compared with composting systems
vi. low or no energy consumption in operation
vii. occupies very little land
viii. reduces volume for final disposal for solid waste and avoids landfill gas generation
ix. minimises greenhouse gases
x. provides low environmental impact - reducing water, soil and air pollution.
17

Anaerobic Digestion: Unit operations and steps
Figure: Typical unit operations and steps
in the anaerobic digestion
of solid waste
18

Anaerobic Digestion: Mechanism
The anaerobic digestion of solid waste involves the microbial decomposition of the
organic fraction of solid waste, in the absence of molecular oxygen, by a group of
micro-organisms, which convert waste organic materials to produce: mostly methane
(CH4) and carbon dioxide (CO2) and very small amounts of other gases such as
hydrogen sulphide (H2S), ammonia (NH3), depending on the composition of the feed
materials.
The mechanism of this anaerobic process is very complex and it follows several
pathways to decomposition by several groups of anaerobic micro-organisms. This
includes the following stages:
Stage1: hydrolysis: the polymer breakdown of organics of higher molecular weight
into smaller, soluble molecules/monomers, carried out by extracellular enzymes.
Proteins, carbohydrates and lipids are transformed to amino acids, sugars and fatty
acids (and glycerine) respectively. However lipids are hydrolysed very slowly,
particularly at temperatures below 200 C, and therefore hydrolysis might be (including
methane production) a rate-limiting step for waste containing a higher percentage of
lipids and other slow-hydrolysing compounds, such as piggery waste.
19

Stage 2: fermentation (acidogenesis and acetogenesis) soluble monomers are
fermented to simple organic compounds, volatile fatty (acetic, butyric, propionic, and
also lactic and formic) acids and in some situations, CO2 and/or hydrogen by acid-
forming bacteria, depending on the composition of waste materials.
Stage 3: methanogenesis methane is produced from methogenic substrates or from
the reduction of carbon dioxide by hydrogen using acetotrophic and
hydrogenotrophic bacteria respectively. The hydrogen consumption also improves
the environment of the conversion processes of butyrate and propionate to acetone.
Methanogenic substrates generally include acetate, methanol, formate,
methylamines, methyl mercaptants and reduced metals. Micro-organisms may also
directly produce methane from carbon monoxide, carbon dioxide and hydrogen.
20

Figure: Different stages of anaerobic digestion
All the above processes are successive, but in a continuous-feed digester they may take
place at any time. The better the different fermentation processes merge, the shorter
the digestion period.
21

Anaerobic Digestion: Overall Reactions
The general anaerobic transformation of solid waste can be described by means of the
following equation:
If it is assumed that the organic wastes are stabilised completely, the
corresponding expression is:
22

Anaerobic Digestion: Reactions at different stages
The typical reaction that may take place in 1st stage i.e. hydrolysis process is:
The typical reactions that may take place in the 2nd stage i.e. fermentation
process caused by acid-forming bacteria are:
23

Anaerobic Digestion: Reactions at different stages
The typical reactions that may take place in the 3rd stage i.e. methanogenesis
phase are:
24

Anaerobic Digestion: Gas estimation
Problem:
Estimate the total theoretical amount of gas that could be produced under
anaerobic conditions in a sanitary landfill per unit weight of solid waste. Given that
the chemical formulas of the typical waste are as follows:
Without water: C60.0 H94.3 O37.8 N
With water : C60.0 H156.3 O69.1 N
Given that the total weight of organic material in 1001b of solid wastes is equal to
58.5 lb including moisture.
Solution:
1. Determine the total amount of dry decomposable organic waste, assuming
that 5% of the decomposable material will remain as an ash:
Decomposable organic wastes (dry basis), lb = 58.5 * 0.95 = 56.0 lb
2. Using the chemical formula C60.0H94.3O37.8N estimate the amount of methane
and carbon dioxide that can be produced, using Equation
25

Problem:
For the given chemical formula, here,
a = 60.0 b = 94.3 c = 37.8 d = 1
26

27

6. Determine the total theoretical amount of gas generated per unit weight of
solid waste:
28

Anaerobic Digestion: Factors affect
The important factors affecting anaerobic digestion are:
pH: The anaerobic digestion process requires an environment with a neutral pH,
where methanogenesis progresses at a relatively higher rate. The desirable pH range
is from 6.5 to 8, but microbial activity may take place between pH 5 and pH 9. Beyond
this pH limit the rate of methanogenesis decreases. The stability of pH is also
important.
Environmental factors: o pH
o alkalinity
o temperature
o Toxicity
Other factors: o Loading rate
o Retention time
o Nutrients
o Solid content
o Pre-treatment
o Mixing
29

Alkalinity: Alkalinity indicates the capability of fermentative fluid in neutralising excess
acidic or basic substance. It is evident that biogas fermentation can occur in fermentative
fluid if the alkalinity range is between 1,000 to 10,000 mg/l (when expressed as CaCO3).
Temperature: In anaerobic digestion, there exists a direct relationship between the extent
and intensity of microbial activity and temperature. Biogas production efficiency increases
with increasing temperature. According to the temperature of the digester content, the
following types of digestion are distinguished:
o psychrophilic digestion (0 C– 20 C)
o mesophilic digestion (20 C– 40 C)
o thermophilic digestion (40 C–70 C).
The retention time for psychrophilic, mesophilic and thermophilic digestion may be more
than 100 days, 20 days and 8 days respectively.
Many micro-organisms, especially methaneproducing bacteria, are sensitive to sudden
changes of temperature. The generation of biogas will be slowed down noticeably if there
is an abrupt change of temperature of 5 C or more.
Toxins: Many compounds such as heavy metals, antibiotics, disinfectants, detergents,
pesticides, chlorinated hydrocarbons and other organic solvents at inhibitory
concentrations affect the rate of anaerobic digestion. Therefore, care must be taken so that
the feed materials or the water used are not polluted by such materials.
30

Loading rate : The loading rate is generally expressed as weight of organic matter [volatile
solids (VS) or chemical oxygen demand (COD)] per unit of digester capacity per unit of time.
The loading rate is significantly influenced by the nature of the waste. It is apparent from
different investigations that the lower loading rate is more desirable for easily
biodegradable feed materials (like animal manure, sewage, meat, green leaves), as these
foods are readily available for bacterial consumption, Higher loading rates can be applied to
refractory organic materials (like paper and dry organic materials).
The loading rates can range from 1 to 5 kg/m3/d depending on the type of feed materials,
the size of digester and the climatic conditions.
Retention time : The term retention time or residence time indicate the length of time spent
by the feed materials in an anaerobic digester. The retention time depends on digestion
temperature and, in some situations, on the nature of feed materials.
Nutrients: Nitrogen, phosphorus and potassium are required for anaerobic digestion. An
appropriate carbon-nitrogen ratio (C/N) is essential in the nutrient balance of most of the
micro-organisms. A high C/N ratio favours acid formation and thus may slow down
digestion, particularly the methanogenesis process. Similarly, the presence of insufficient
carbon to convert nutrients into protoplasm, eliminates excess nitrogen, often as ammonia.
Therefore, proper attention has to be paid in selecting feed materials to minimise these
effects, and it is very important to mix the raw materials in accordance with the C/N ratio to
ensure better performance of anaerobic digestion. 31

Solid content: Generally 6-12% of solid concentration of the feed material is
considered to be optimal for the production of biogas. This also depends on the
fermentation temperature and the type of materials used.
Pre-treatment: Pre-treatment may include separation of contaminants, size
reduction of feed materials and partial decomposition of refractory materials.
Separation of contaminants (non-biodegradable waste or recyclables) from the
organic fraction of solid waste improves the efficiency of biological processes and
enhances the quality of the digested residue – generally used as compost.
Reduction of particle size increases the exposed surface areas for bacterial action
and thus enhances the digestion process.
Mixing: Mixing enhances the efficiency of the anaerobic digestion processes.
Mixing also minimises the problems associated with the formation of scum. This
can be carried out by mechanical stirring devices or through digester design
modification, by liquid and/or gas recycling, or by a combination of both
mechanical and re-circulation arrangements together.
32

Anaerobic Digestion: Types of digester
Different anaerobic treatment processes and a wide variety of digester models (including a few large-scale
installations) are currently available to carry out anaerobic digestion:
i. batch- and dry-fermentation or batch digester: It is simple and requires no control if the start-up
is successful. But the main disadvantage of this system is that biogas production varies with time,
limiting its usage
ii. fixed dome (Chinese model): This is the most common digester type in developing countries, and
the basic design originated in China. The reactor consists of a gastight chamber constructed from
bricks, stone, or poured concrete. Both the top and bottom of the reactor are hemispherical, and
are joined together by straight sides.
iii. floating cover (Indian or KVIC design): most popular in India. It is also used extensively throughout
the world, being the most common type of digester used for treating sewage sludge in many
industrialised countries.
iv. flexible bag: The bag digester is essentially a long cylinder (generally with length /diameter ratios
ranging from 3 to 14) made of either PVC, a Neoprene-coated fabric (Nylon), or red mud plastic
v. septic tank: A number of purpose-made anaerobic reactors are currently used in the USA, Europe,
Japan and some other countries, mostly to digest sewage.
vi. plug flow: A typical plug-flow reactor consists of a trench cut into the ground and lined with either
concrete or an impermeable membrane (Figure 6.7). To ensure true plug-flow conditions, the
length has to be considerably greater than the width and depth.
vii. anaerobic baffler reactor: The reactor is a simple rectangular tank, with physical dimensions
similar to a septic tank, and is divided into 5 or 6 equal volume compartments by means of walls
from the roof and the bottom of the tank. The liquid flow is alternative upwards and downwards
between the walls
viii. anaerobic filter: Both upflow and downflow anaerobic filters are used on a limited scale, mainly to
treat industrial wastewater, and the system is very costly.
ix. large-scale installation. 33

Anaerobic Digestion: Batch digester
34

Anaerobic Digestion: Batch digester
35

Anaerobic Digestion: Economic and Environmental aspects
Economic aspects:
The cost of waste treatment largely depends on local conditions such as the cost of
labour, the availability and cost of materials, land prices, taxes and subsidies and so
on. It is apparent that the investment costs for anaerobic digestion appear to be a
factor of 1.2-1.5 higher than for composting.
The capital costs of a modern anaerobic digestion plant are lower than those for
energy from waste plants, but similar to those of MRF.
Environmental aspects:
During the digestion process, a significant reduction of BOD occurs. It is evident
that about 70 per cent of BOD removal occurs within five days of the retention
period. Thus, the digestion process improves the quality of digester effluent and
minimises environmental damage, particularly ground water pollution.
36

“Composting (also called ordinary composting) is the biological decomposition of the
biodegradable organic fraction of MSW under controlled conditions to a state of sufficiently
stable for nuisance-free storage and handling and for safe use in land applications.”
The specification “biological decomposition” confines composting to the treatment and disposal
of the biologically originated organic fraction of MSW. The term “controlled conditions”
“differentiates the composting process from the simple organic waste decomposition that
happens in open dumps and landfills (in composting, it is a way of harnessing the natural
processes of decomposition to speed up the decay of waste). The specification, “sufficiently
stable,” is a prerequisite for nuisance-free storage and handling and for safe use in land
applications.
During the composting process, heat, various gases and water vapors are released, greatly
reducing the volume and mass of the pile.
Decomposition of solid waste may be accomplished aerobically or anaerobically. Anaerobic
process however involves offensive odors and is extremely slow. Most composting operations
are therefore aerobic.
Composting provides a means of accomplishing all three of the Rs: the amount of rubbish sent
to the landfill is reduced, organic matter is reused rather than being damped, and it is recycled
into a useful soil amendment.
The composting process is explained in the Fig 1.
Composting: Explanation
38

Figure: Organic solid waste
Figure 01: Composting process
Composting: Process
39

Composting: Compost or Humas
Figure 3: Compost or Humas: End product of the composting
The end product remaining after bacterial activity is called “humus” or “compost”
(as shown in the Fig. 3). The Characteristics of the compost are given in the
following table:
40

Figure: process flow diagram for MSW composting facilities
Composting: process flow diagram for MSW composting facilities
Composting process consists of
four basic steps:
(1) preparation;
(2) digestion,
(3) curing, and
(4) finishing.
Preparation
Digestion
Curing
Finishing
41

Preparation
o The non-compostable materials such as plastics, textile, leather, bones, glass,
metals etc. are removed from the feed stock.
o This will prevent any damage to the machines during the subsequent
operations.
o Also improves the compost quality.
o Sorting, Shredding, Grinding, Screening are the common steps to separate
non-compostable materials during preparation.
Digestion
o Main process of the composting.
o In modern composting plants/facilities, digestion takes place within windrows
(area method) or in mechanical digesters (High rate digestion method).
42

Curing
o In this step, carbon is further converted to carbon dioxide and humus; and nitrogen
into nitrates.
o the population of the microorganisms decreases and the type of the organisms is
changed too.
o This lowers the temperature of the compost pile.
o Curing is needed to ensure complete stabilization.
Finishing
o In this step, the compost is passed through a 1 to 1.25cm fine screen to remove
oversized and non-compostable materials.
o Further improves the quality of the compost.
o In developed countries, there are established standards for the compost quality
which are met before sending it to the market for sale. Therefore proper quality
testing is required.
o Also includes the operations of making pellets, granulation, regrinding,
rescreening, blending with various additives and adjustment of moisture content
and bagging etc.
43

Composting: technologies currently used
1. Passive windrow 2. Turned windrow 3. Aerated static pile 4. In-vessel channel
44

Composting: essential factors of effective composting
45

Composting: essential factors of effective composting
Following conditions are essential for effective composting:
i. For optimum results, the size of the waste should lie between 2 and 8 cm.
ii. The minimum size of the compost heap should be such that it does not dissipate moisture
and heat from the pile. The minimum recommended volume is about 3 cubic metres.
iii. Sufficient number of microorganisms to be present to perform digestion. Sewage sludge is
added for this purpose.
iv. The presence of nitrogen, phosphorous, potassium and some other trace elements helps the
composting process. Due to the high microbial activity in the composting process, a large
supply of nutrients is required by bacteria. The essential range of C/N ratio should be 30 to 50
and C/P ratio should be 100 or less.
v. Moisture content should be 50 to 60%. Addition of water is done to raise moisture contents,
if required. Excess MC (>65%) generally replaces air from the inter-spaces within the particles
that minimizes the level of available oxygen and thus may lead to anaerobic conditions. Again
if a certain amount of moisture is absent (<12%), the metabolic activity of the
microorganisms may cease. The optimum MC for the composting process depends on the
physical characteristics of the materials also.
vi. pH should vary between 5.5 to 8.5 throughout the process although organic materials with a
wide range of pH values (from 3 to 11) can be composted.
vii. Air should be thoroughly dispersed throughout the organic waste. This is done by frequently
turning and mixing the wastes.
viii. Temperature should be maintained between 50 to 60oC for active composting period i.e. this
range ensures more suitable environment for thermophilic micro-organisms and results in a
significant reduction in pathogens and parasites.
46

Composting: Micro-Organisms and Functions
Following function are performed by the composting process:
a) Stabilizes the putrescible organic matter.
b) Kills pathogens and weed seeds.
c) Conserves N, P, K, and resistant organic matter found in the raw material.
d) Produces uniform, relatively dry end product free from objectionable and
harmful objects.
e) Conducts the process in a sanitary manner. If conditions are controlled well
then it is free from insects, rodents and odors.
Types of Micro-Organisms in composting:
The principal classes of microorganisms involved in the aerobic decomposition of solid
wastes are; (1) bacteria, (2) fungi , (3) actinomycetes, (4) algae, (5) protozoa and (6)
some larva.
The general class of microorganisms which play active role in the conversion of solid
wastes to either cell mass or some by-product of cell metabolism are called “protists”.
Bacteria, fungi, yeasts and actinomycetes are of major concern. Protozoa and algae are
also protists but are not of primary importance.
47

Composting: Advantages
1. Composting is the only presently operational technology which provides for the
recycling of organic residuals.
2. Composting can be used to dispose of many organic industries' wastes which because
of their non-fluid nature are not amendable to treatment by activated sludge or trickling
filter process.
3. The process is used in many parts of the world to convert human and often animal
excrement with plant trimmings and other organic refuse to soil conditioner.
4. Composting plants offer favorable conditions for reclaim of paper, cans, metals, rags
and glass.
5. A well located refuse composting plant may reduce the cost of hauling refuse to the
points of disposal.
6. Flexibility of operation permits a 100-200% overload design capacity for several days by
increasing the time, receiving bins and grinders' operation.
7. Weather does not affect an enclosed system.
8. There is no leachate control problems involved.
9. There are no air pollution control problems as involved in incineration.
10. Composting produces potentially useful end product, which is utilized as soil
conditioner, helps soil conservation in sloppy area, replaces the organic content
exhausted by the excessive use of lands, improves porosity of soil and thus water
retaining property for nourishment of the crops.
11. Sludge addition saves disposal cost.
48

Composting: Disadvantages
1. Capital and operating costs apparently are relatively high. Cost/ton of refuse is about
400-500% that of sanitary landfill if the end product is not sold.
2. Uncertainty of the market for compost as a fertilizer or soil conditioner undermines the
desirability of the system especially in large population centers.
3. Seasonal use of the end product may require special marketing procedure or outdoor
storage.
4. Refuse that damages the grinders must be removed and disposed of separately e.g.
pipes, heavy stones.
5. Trained personnel to operate composting plants are not readily available.
6. Site procurement is a problem as every kind of refuse disposal facility is considered a
nuisance in most neighborhoods.
7. A secondary disposal is always required, working also as alternate outlet in case of
breakdown and for inorganic and non-recyclable materials.
49

Composting: Reasons of failure
Most of mechanized compost plants have failed for economic or technical reasons:
Economic reasons
i. Cost of raw materials – often this involves the cost of transportation of feed
materials,
ii. Quality of the compost – this is governed by the quality of raw materials and
maintenance of the composting process,
iii. Location of composting plants – this influences the costs of transportation for both
raw materials and the end product,
iv. Government policies and legislation – for example, the import policy for chemical
fertilizers, source separation initiatives, incentives to encourage recycling and
resource recovery etc.,
v. Public awareness – public education and information,
vi. The availability and cost of other soil conditioners and fertilizers.
Technical reasons
i. In many situations, the mechanised pre-processing of mixed waste cannot
accommodate the diverse nature of solid waste, and it therefore does not produce
good compostable materials.
ii. In other cases, inadequate attention is paid to ensuring the proper environment
and nutrients to improve the performance of composting (biological) processes. 50

Composting: O2 requirements
The process is performed under aerobic conditions. The products of aerobic
digestion and the amount of oxygen required for the job are expressed by the
following equation:
Where,
51

Composting: O2 requirements
Determine the amount of oxygen required to compost 1000 kg of solid wastes.
Assume that the initial composition of the material to be composted is given by
[C6H7O2(OH)3]5 , that the final composition is estimated to be [C6H7O2(OH)3]2, and
that 400 kg of material remains after the composting process.
52

Composting: Vermicomposting
o Also called 'vermiculture', 'composting with worms’ or 'worm composting’
o Uses worms and micro-organisms to break down organic materials under
aerobic conditions, but at a relatively low temperature, to give nutrient-rich end
product (compost).
o Specific species of earthworms (for example, eisenia foetida – commonly
known as redworms, brandlingworms or tigerworms, and lumbricus rubellus,
are suitable for vermicomposting.
o The worms (a worm is made of about 70-95% water and 5-30% protein)
consume both partially decomposed organic materials and micro-organisms
which are also constantly involved in composting
o The average weight of 2,000 adult worms is about 1kg, and these worms can be
accommodated in an area of 1m2.
o Produce better quality rich in nitrates, potassium, phosphorus, calcium and
magnesium) and finer (enhance particle size reduction) of compost.
o Since this type of compost is rich in nutrients, so can mix this compost with
ordinary compost before using as manure.
o The composting in this process takes place in a relatively cool environment (0o C
to 30o C) so, the end product may contain pathogens.
o Compared to ordinary composting, this process requires more manpower and
careful control of the environment (mainly temperature and moisture levels). 53

Composting: Vermicomposting
54

Composting: Barrel composting
o Barrel composting has been developed especially for developing countries as an
alternative low-cost and sustainable waste management system.
o Municipal domestic waste is kept within the barrel for aerobic digestion for
about one month. After digestion is complete, the waste is taken out and
processed to maturation stage.
o The barrel may be perforated on its surface and a perforated pipe may be
inserted and attached to the base of the barrel to sustain the aerobic
conditions. The top cover of the barrel prevents rainwater from entering the
barrel.
55

56

A barrel of 55 gal (US) litres has been used to install a barrel composting plant at Gazipur
(population 500) in Bangladesh. The plant will operate throughout the year. The average
temperature measured within the waste is 43 oC. The composition of solid waste in a 100
kg as shown in table. The targeted loss of volume is 54% and the average density of the
waste is 450kg/m . The waste generation rate of Gazipur is 0.4kg/capita/day. Calculate the
number of barrels required in barrel composting plant.
57

Solution:
Step 1: Find out the total composition
In the composting process, the non-compostable materials must be screened out for
digestion of the waste. So, in this 100kg sample, cardboard (8kg), plastics (5kg) and wood
(5kg) must be screened out.
58

59

60

Chapter 08:
Ultimate Disposal
61

Final disposal of solid waste
Final disposal of the municipal solid waste can be accomplished in following ways:
1. Into water bodies
2. Onto land
(1) open dumping (Controlled and uncontrolled)
(2) sanitary landfilling.
62

(1) Open dumping (Controlled and Uncontrolled):
o Open dumping refers to placing the solid waste, at a designated place,
without any cover.
o A cheap disposal method
o Highly undesirable as it poses serious threats to the air, soil, ground water
and human health (Fig. 8.1). Although some measures are taken to minimise
the risk to public health and the environment in controlled open dumping
method.
o Open dumping results in littering of waste with wind. Rain water may result
in dissolving organics and toxic matters, which may either infiltrate and join
groundwater or may join surface water due to run off.
o Poor implementation of environmental regulations, lack of awareness,
technical expertise and resources are the major factors for the use of this
method.
o It is mostly practiced in developing countries.
63

64

(2) Sanitary landfill:
o Sanitary landfill is a scientific and an engineered method of final disposal of solid waste, in a
manner that protects the public health and the environment.
o The process by which wastes are placed in the landfill is called landfilling.
o Historically, the most economical and environmentally acceptable method for the disposal of
solid waste in the developed countries and in some of the developing countries too. Even
with implementation of waste reduction, recycling and transformation technologies, disposal
of residual solid wastes in landfills still remains an important component of integrated solid
waste management.
o It includes the following activities:
i. Monitoring of the incoming waste stream,
ii. Placement and volume reduction of the waste through mobile compactors such as
bulldozers etc., and
iii. Installation of the landfill and environment control facilities.
o In a sanitary landfill, waste is spread in thin layers, compacted to the smallest practical
volume, and covered with the soil or other suitable material at the end of each day. When the
disposal site reaches its ultimate capacity i.e., after all disposal operations are completed, a
final layer of 0.6 meter thick or more of cover material is applied.
o A typical sustainable sanitary landfill site is show in Fig. 8.2.
65

66

Open dump Controlled dump Sanitary landfill
o Poorly sited
o Unknown capacity, No
cell planning
o Little or no site
preparation
o No leachate management
o No gas management
o Only occasional cover
o No compaction of waste
o No fence, no record
keeping
o Waste picking and
trading
o Planned capacity
o No cell planning
o Grading, drainage in site
preparation
o Partial leachate
management
o Partial or no gas
management
o Regular cover
o Fence
o Basic record keeping
o Controlled waste
picking and trading
o Site based on EnRA
o Planned capacity,
o Designed cell development
o Extensive site preparation
o Full leachate and gas
management
o Daily and final cover,
compaction
o Fence and gate
o Record volume, type,
source
o No waste picking
Characteristics
67

o Easy access
o Extended lifetime
o Low initial cost
o Aerobic decomposition
o Low cost, access to
waste pickers
o Materials recovery,
income
o Less risk of
environmental
contamination
o Permits long term
planning
o Low initial cost
o Easier rainfall runoff
o Moderate cost
o Extended lifetime
o Controlled access and
use
o Materials recovery,
Income, lower risk to
o pickers
o The most economical method
of disposal where land s
available.
o Initial investment is low.
o Can receive all types of solid
wastes, eliminating the
necessity of separate
collections.
o Minimised environmental risk
o Permits long term planning
o Reduced risk
o Vector control, aesthetics
o Extended lifetime and flexible
o Secure access, gate records
o Eliminate risk to pickers
Advantages
68

o Environmental
contamination
o Overuse, many
noxious sites
o Unsightly, needs
remediation
o Water contamination
o Risk of explosions
o Vectors/disease,
Shorter lifetime
o Indiscriminate use,
Vermin
o No record of landfill
content,
o Least efficient for
material record
o Perhaps less accessible
o Perhaps environmental
contamination
o Slower decomposition,
so total cost is high
o Maintenance required
o Harassment, Possible
displacement of
o pickers and buyers,
Fewer recyclable
o resources
o In highly populated areas,
suitable land may not be
available within an economical
hauling distance.
o Located in residential area can
provoke extreme public
opposition.
o Access, longer siting process
o Cost, preparation time
o Slower decomposition
o Regular maintenance
o Equipment use
o Displacement of pickers and
buyers
o Loss of recyclable resources
o Methane, an explosive gas, and
other gases produced may
become a hazard or nuisance.
Disadvantages
69

Landfill Classification
Depending on the principles of a particular landfill waste management strategy,
landfills may be classified as:
i. dilute and attenuate landfills
ii. containment landfills
The present design and operation practices of landfill are mostly focused on the
containment principle.
i. Dilute and attenuate landfills
o These landfills allow leachate to be absorbed within the waste or to migrate
into the surrounding environment for attenuation by physico-chemical or
biological processes.
o This involves processes of dilution and dispersion if attenuation of leachate is
not achieved within the landfill environment. Therefore, the landfill designer
should clearly visualise the hydrogeological and geochemical characteristics of
the site and surrounding environment.
o These landfills involve the risk of contamination of water and soils.
70

Landfill Classification
ii. Containment landfills
o In these landfills, leachate is contained within the landfill site
boundary by the use of liner materials.
o Containment involves the degradation of waste within the landfill. It
also involves controlled migration of gas within the landfill.
o This requires a much greater degree of site design, engineering and
management, and thus ensures a larger degree of protection to public
health and the environment.
o The main components of a containment-type sanitary landfill are
illustrated in Figure 9.1.
o In a contemporary context this is the most acceptable means of
disposal of waste to land.
71

Major stages of waste degradation in landfills
The process of degradation of
the organic fraction of solid
waste within a landfill may be
broadly divided into five
stages.
Organic materials degrade in
presence of oxygen (aerobic
conditions) in the first and
fifth stages, but they degrade
essentially in the absence of
oxygen (anaerobic conditions)
in the second, third and fourth
stages.
All these processes are
successive, but because of
heterogeneous characteristics
of waste they may take place
at any time until all of them
have advanced to stage five.
72

Sanitary Landfill: Planning, Design and Operation
Planning, Design and Operation of Sanitary Landfills
The planning and design of sanitary landfills involves careful consideration at all stages from
site selection to final closure and post-closure care. The stages involved in well-engineered
sanitary landfills are:
i. siting
ii. design
iii. construction and operation
iv. closure and post-closure care
v. environmental monitoring and corrective action.
o Siting
A site investigation is the important element in identifying a possible landfill site.
The site selection process should accommodate the preliminary investigation/surveying of a
number of sites with a checklist of important points to consider along with the assessment
of environmental impacts.
The various merits and demerits should be addressed at a public meeting to minimise
public concern at the beginning of the process.
The evaluation process may consider a wide range of site selection factors including:
73

1. Location restriction –In many industrialised countries, a number of location restrictions
are imposed by the state. For example, the EPA Regulations on Criteria for Classification
of Solid Waste Disposal Facilities and Practices (40 CFR 258) (USEPA, 1993) presents the
location restrictions as shown in Table 9.3 to address both the potential effects that a
MSW landfill unit may have on the surrounding environment and the effects that
natural- and manmade conditions may have on the performance of the landfill unit.
2. Type of waste –The characteristics of the waste to be landfilled indicate the risks
associated with particular landfill operation practices.
3. Size –This depends on the expected life of the landfill site (i.e. the number of years for
which it can operate) and the quantities of waste generated. One should take into
account projected future populations and waste generation rates for the entire design
life. The density of landfilled waste depends on the degree of compaction, depth of
waste filled, depth of cover materials, properties of the cover materials and the stage of
decomposition. UKDOE 3 3 (1995) reports a range of density from 0.4 tonnes/m to 1.23
tonnes/m . For 3 3 planning purposes, a density of between 0.65 tonnes/m to 1.0
tonnes/ m may be used.
74

4. Transport to site –The site should be easily accessible and should be close enough to
the major waste generation areas. The method of transport should be considered. If
transport is to be by road, the present quality of road must be considered and the
potential impact of heavy waste vehicle traffic on road surfaces. Proper attention should
be paid to the present use of the road, congestion, areas through which the waste
transportation vehicles will have to travel and so on.
5. Soil type –Clay and silty soil is a more desirable landfill base material than sand, gravel
or organic clay deposits.
6. Topography –Equipment operation and movement of vehicles becomes difficult on
steep slopes (severe in >15%, moderate in 3-15% and minimal in <3%).
7. Hydrological, geotechnical and hydrogeological characteristics of the site –The
hydrological characteristics will help to identify the expected quantities of leachate and
hence the form of leachate management system. Knowledge of the geotechnical and
hydrogeological characteristics (the geological factors relating to water) is necessary to
determine what natural protection of the groundwater etc. is available against pollution
by the leachate and landfill gas, and to identify potential flow path of leachate and
gases. For example, a proposed site which is underlain naturally by clay may need little
in the way of extra leachate protection. However, a site which is underlined by fissured
rock will pose greater problems, as leachate may be able to percolate into groundwater.
The degree of limitation of landfill design associated with groundwater occurrence
appears to be severe, moderate or minimal if groundwater depths are less than 3m, 3-
7.5m and more than 7.5m respectively. 75

8. Climatic conditions –Extreme climatic conditions may disrupt landfill operation. For
example, heavy rainfall during the rainy season in a particular area may demand the use
of a separate landfill.
9. Drainage –The resent drainage conditions of a site need to be assessed, including the
existence of a watercourse within or adjacent to the site and the cost of surface water
diversion (if required). The desirable location of a landfill site from a stream/ lake is
more than 300m.
10. Availability of land –A reasonable size of landfill site with an adequate buffer zone
should be selected to maximise its cost-effectiveness. Availability of land for cover
materials is also an important consideration. The cost of auxiliary facilities do not
increase much with an increase in landfill area.
11. Land use –This is a very important consideration because the presence of places of
historic or cultural significance may restrict the use of the site for landfill. Other factors
such as the location of groundwater abstraction points for drinking or irrigation
purposes, overhead or underground electrical cables and so on must all influence the
location of the site. The extent of limitation of landfill location associated with wells
appears to be severe, moderate or minimal if they are at a distance of less than 90m,
90-300m and more than 300m respectively.
76

12. Impact on the locality – It is important to consider how the development of a landfill
site at a location will impact the local area in terms of noise, odour, traffic, possible
leachate and gas pollution, the spreading of disease vectors, hazards to health and the
value of property and so on. There should be an adequate buffer zone from the nearest
housing.
13. Local opposition –The opposition of local people to the site selection may be reduced
by including them in the decision making process.
14. Ultimate use for completed landfill –This will affect landfill design and operation, and
the remediation cost is always much higher if the ultimate use is not planned at the
earliest stage.
15. Cost of land –This will always be a key consideration in the decision-making process.
77

Movement and Control of Leachate in Landfill
Leachate may be defined as liquid that has percolated through solid waste and is
comprised of dissolved and suspended materials and/or microbial contaminants.
In most landfills the leachate is composed of the liquid produced from the
decomposition of the wastes and liquid that has entered the landfill from external
sources (such as surface drainage, rainfall etc.).
In general, it has been found that the quantity of leachate is a direct function of
the amount of external water-entering the landfill. In fact, if a landfill is
constructed properly, the production of measurable quantities of leachate can be
eliminated. When sewage sludge is to be added to the solid wastes to increase the
amount of methane produced, leachate control facilities must be provided.
A leachate management system includes an efficient leachate collection system for
its proper collection and treatment.
Representative data on the chemical characteristics of leachate, reported in Table
8.2, indicates that the range of concentration values for the various constituents is
rather extreme. For this reason; no average value can be given for leachate. The
typical values reported are intended to be used only as a guide. 78

Leachate Treatment
79

Leachate Treatment
Treatment processes
for leachate
80

After-use of Landfill Sites
After-use of Landfill Sites
Once a landfill site is closed and the capping completed, the area is then
available for further use.
In high-income countries, landfill sites often become recreational areas such as
parks, golf courses or nature reserves. However, in some situations, where land is
in higher demand, there may be strong competition for the use of the land.
When deciding on the after-use of the site the properties of the land must be
fully considered and the following potential should be addressed:
o Fill settlement (total as well as differential settlement)
o Load-bearing capacity
o Hazards associated with combustible and potentially explosive gases
o Degree of stabilisation and the corrosive nature of decomposition
products.
81

Chapter 09:
Special Waste management
(H-Waste and E-Waste)
82

Special wastes
In addition to residential and commercial areas, solid waste is also generated
from other sources like healthcare facilities, industries, electronic shops,
packaging services and slaughterhouses. These are termed as special wastes.
Handling, collection and disposal of these wastes is sometimes quite different
from municipal solid waste. Hence these are discussed separately.
Healthcare Waste and its Source
The waste generated from the healthcare facilities is called “healthcare waste” or
“medical waste”.
Healthcare waste in generated as a result of the following activities:
a) Diagnosis and treatment of diseases at healthcare facilities
b) Research activities in biomedical research centers
c) Production and testing of the pharmaceuticals.
Broadly, the main sources of healthcare waste are: hospitals, clinics, laboratories,
dispensaries, pharmacies, nursing homes, maternity centers, blood banks,
research institutes and veterinary hospitals. Such a waste is also generated when
healthcare is being provided to the patient at home and is usually mixed with
municipal waste.
83

Special wastes
Healthcare Waste Management:
The healthcare waste management is a sensitive issue and comprises of knowledge of
quantity and quality of waste, its storage, handling, transportation and disposal in a
manner that helps in
(1) containment of infections; and (2) reduces public health risks both within and
outside the healthcare facility.
Generation rates, for hospitals, are normally
expressed as kg/bed of the hospital/day.
After generation, waste is segregated, stored
on site, transported within and outside the
hospital, treated and finally disposed.
Hospitals generate large quantities of solid
waste which can be categorized into two
distinct types i.e. (1) Non- hazardous waste:
which is not infected, does not entail more
risk and hence comparable to normal
domestic solid waste. Usually it constitutes
75 – 90% of the total quantity of waste
generated in a hospital. 84

Special wastes
(2) Hazardous waste:
consists of materials that
are susceptible to contain
pathogens (or other toxins)
to cause diseases to a
potential host. This waste
may be contaminated by
one or more types of
bacteria, viruses, parasites
or fungi. Usually, it is 10 –
25% of the total hospital
waste. More categorized as
this Fig:
85

Special wastes
86

Special wastes
87

Special wastes
88

Special wastes
89

Special wastes
Electronic Waste (E-Waste) Management:
E-waste is term used for electronic products nearing the end of their useful life. It
includes old, outlived or discarded electrical and electronic equipment and appliances
such as computers, televisions, VCRs, stereos, copiers, fax machines, electric lamps,
cell phones, audio equipment, refrigerators, and batteries which have been discarded
by their original users. Broadly, e-waste is loosely discarded, surplus, obsolete,
broken, electrical or electronic devices.
The processing of electronic waste
in developing countries causes
serious health and pollution
problems due to the fact that
electronic equipment contains
toxic contaminants such as lead,
cadmium, beryllium and
brominates flame retardants. Even
in developed countries recycling
and disposal of e-waste involves
significant risk.
90

Special wastes
E-Waste Management Challenges:
a) Lack of Awareness regarding E-waste management.
b) Inadequate regulatory measures, inadequate strategies and poor implementation of
law.
c) Lack of technical expertise in this area.
d) Non availability of technology for recycling of E-waste.
e) Lack of coordination among different stakeholders and ministries / departments.
f) Lack of system to regulate the import of refurbished e-waste.
g) Low attention from government on ewaste.
h) Inadequate funding available for the implementation of various provisions of Basel
Convention.
i) Non availability of proper inventories of hazardous waste, particularly in Ewaste.
j) No research and development work in this area so far.
k) Non availability of guidelines for recycling and disposal of E-waste.
l) Inadequate public awareness about the toxicity of chemicals in E-waste and their health
impacts.
m) Unskilled workers/technicians for handling of E-waste.
n) Lack of proper system for inventory of imported and local E-waste.
o) No mechanism for developing centralized E-waste recycling facility.
91

Special wastes
92

93
Thanks
“STUDY HARD,
no matter if it seems impossible,
no matter if it takes time,
no matter if you have to stay up all night
just remember that the feeling of success is
the best thing in the entire world”

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