PB389
Integrated Solid Waste Management
Numfon Eaktasang, Ph.D.
Thammasat University
Solid Waste Management
Waste
generation
Waste reduction
and separation at the
source
Collection
Separation,
processing &
transformation
Transportation
Disposal
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Disposal Technology
Dumping on land
Burial
Hog feeding
Incineration
Sanitary landfill
Composting
Biogas
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What is composting?
Using the natural process of
decay to change organic
wastes into a valuable
humus-like material called
compost
Compost
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Biological conversion processes

Major objectives of biological conversion processes
= conversion of the organic matter in the waste to
a stable end product

Chemoheterotrophic organisms are of primary importance


use organic compounds both energy and carbon sources
Nutrients


usually rich in MSW
may need to be added in some commercial wastes

Nitrogen
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Types of Microorganisms
Primary importance in biological conversion of
the organic fraction of solid wastes

Procaryotic groups (eubacteria and archaebacteria)


generally referred to simply as bacteria
Eucaryotes group



fungi
yeasts
actinomycetes
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Types of Microorganisms
Bacteria
found in aerobic and anaerobic environments
 wide variety of inorganic and organic compounds
can be used

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Types of Microorganisms
Fungi
ability to grow under lowmoisture conditions
 tolerate relatively low pH


optimum around 5.6, but the
viable range is from 2 to 9
aerobic metabolism
 long filaments
 ability to degrade a wide
variety of organic compounds

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Types of Microorganisms
Yeasts

fungi that can not form
filaments and are
unicellular
Actinomycetes
intermediate properties
between bacteria and
fungi
 similar in form to fungi

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Environmental requirements
 Temperature


one of the important factor for survival and growth of
microorganisms
optimum growth condition occurs within a fairy narrow range
can survive within much broader limits
 growth rates double with approximately every 10 degree-C
increase until the optimum temperature is reached.

Some typical temperature ranges for various bacteria
Temperature, degree-C
Type
Psychrophilic
Mesophilic
Thermophilic
Range
Optimum
-10 – 30
20 – 50
45 – 75
15
35
55
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Types of biological transformations
 Aerobic process
Organic matter + O2 + Nutrients 
new cells + resistant organic matter + CO2 + H2O +
NH3 + SO42- + ... + heat
 Anaerobic process
Organic matter + H2O + Nutrients 
new cells + resistant organic matter + CO2 + CH4 +
NH3 + H2S + heat
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Anaerobic biological transformations
Lipids
Polysaccharaides
Protein
Nucleic acids
Fatty
acids
Monosaccharides
Amino
acids
Purines &
Pyrimidines
Hydrolysis
Simple
aromatics
Acidogenesis
Other fermentation products
(e.g. propionate, butyrate
succinate, lactate ethanol)
Methanogenic substrates
H2, CO2, formate, methanol,
methylamines, acetate
Methanogenesis
Methane + carbon dioxide
Pathways leading to the production of methane and CO2 from the anaerobic digestion
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Biological process selection
Comparison of aerobic composting and anaerobic digestion
processes for processing organic fraction of MSW
Characteristic
Aerobic processes
Anaerobic processes
Energy use
Net energy user
Net energy producer
End products
Humus, CO2, H2O
Sludge, CO2, CH4
Volume reduction
up to 50%
up to 50%
Processing time
20 to 30 days
20 to 40 days
Primary goal
Volume reduction
Energy production
Secondary goal
Compost production
Volume reduction
Waste stabilization
Operation
Relatively simple
Relatively complex
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Aerobic composting
Aerobic composting
most commonly used biological process
 Application to yard waste, separated MSW,
commingled MSW, and co-composting with
wastewater sludge

Process description

3 processes:



preprocessing: removing contaminants, adjusting moisture
content, C/N ratio
aerobic decomposition
product preparation and marketing: may include fine
grinding, screening, air classification, blending with
various additives, granulation, bagging, storage, shipping.
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Aerobic composting
Thermophilic
Mesophilic
Cooling
Maturing
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Aerobic composting
 Important process variables

particle size and its distribution, seeding and mixing
requirements, the required mixing/turning schedule, total
oxygen requirements, moisture content, temperature and its
control, carbon-nitrogen ratio, pH, degree of decomposition,
respiratory quotient (RQ), and control of pathogens
 Composting techniques


Agitated: the material to be composted is agitated periodically
to introduce oxygen, to control the temperature, and to mix
the material to obtain a more uniform product.
Static: the material to be composted remains static and air is
blown through the composting material.
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Types of composting
Windrow composting
Aerated static pile composting
In-vessel composting
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Windrow composting
 Windrow composting


One of the oldest methods
Simplest form
8 to 10 ft high and 20 to 25 ft wide
 turned once per year
 need 3 to 5 years for complete degradation
 may cause odor problem


High-rate form

typically 6 to 7 ft high and 14 to 16 ft wide

depend on type of equipment used to turn
processed by shredding and screening to 1 to 3 inch
 Adjusted to 50 to 60 % of moisture content
 turned twice per week for 3 to 4 weeks



after turning period, 3 or 4 weeks curing period without turning to
allow further reduction of decomposable materials by fungi and
actnomycetes
keep temperature around 55 degree-C
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Windrow composting
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Aerated static pile composting
similar to passively aerated windrows,
force air into pile using pipes with blowers. allows for
large piles and turning in not required.
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Aerated static pile composting
typically 2 to 2.5m height
 Air is introduced to provide the oxygen needed and
to control the temperature within the pile
 Layer of screened compost: for insulation and odor
control
 Material is composed for 3 to 4 weeks, followed by
curing period
 Bulking agent: wood chips




for dewatered wastewater treatment plant sludge
to maintain the porosity of the composting material
to absorb excess moisture
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Aerated static pile composting
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In-vessel composting
 In-vessel
 Confine composting materials within
 building, container, or vessel.
 Forced aeration and mechanical turning
techniques are used to speed the process
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In-vessel composting
 In-vessel composting


accomplished inside an enclosed container or vessel
Two major categories
Plug flow: first-in first-out principle
 dynamic (agitated bed): mixed mechanically


1 to 2 weeks for detention time


total system needs 4 to 12 weeks for whole process
Popularity increase recently
Easiness of process and odor control
 faster throughput and smaller area requirements
 lower labor costs

 Other composting systems

Developed many composting systems and used in commercial
basis
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In-vessel composting
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 In-vessel
composting
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Aerobic composting
 Design and operational considerations











Particle size
Carbon to Nitrogen ratio (C/N ratio)
Blending and seeding
moisture content
Mixing/turning
Temperature
Control of pathogens
Air requirements
pH control
Degree of decomposition
Land requirement
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Aerobic composting
Particle size
influences the bulk density, internal frictions and
flow characteristics
 Reduction of particle size increase the biochemical
reaction rate
 should be between 25 and 75 mm

C/N ratio

Initial carbon to nitrogen ratios between 25 and 50.


lower ratio: Release or inhibition of ammonia
higher ratio: lack of nitrogen as a nutrient
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Aerobic composting
Nitrogen content and nominal
C/N ratios of selected
compostable materials
(dry basis)
Material
Food processing wastes
Fruit wastes
Mixed slaughterhouse waste
Manures
Cow manure
Pig manure
Sludge
Digested activated sludge
Raw activated sludge
Wood and straw
Sawdust
Wheat straw
Wood (pine)
Paper
Mixed paper
Newsprint
Yard wastes
Grass clippings
Leaves
Biomass
Water hyacinth
Percent N
C/N ratio
1.52
7.0-10.0
34.8
2.0
1.7
3.75
18.0
20.0
1.88
5.6
15.7
6.3
0.10
0.3
0.07
200-500
128
723
0.25
0.05
173
983
2.15
0.5-1.0
20.1
40-80
1.96
20.9
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Aerobic composting
Blending and seeding
Blending based on C/N ratio and moisture content
 Seeding involves the addition of a volume of
microbial culture sufficiently large to effect the
decomposition of the receiving material at a faster
rate

Moisture content

should be between 50 and 60
Mixing/turning
to prevent drying, caking and air channeling
 to achieve more uniform distribution of nutrients
and microorganisms

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Aerobic composting
 Temperature


50 to 55 degree C for first few days, 55 to 60 degree C in the
remainder of the active composting period
controlled by
airflow
 turning frequency

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Aerobic composting
 Control of pathogens

Between 60 and 70 degree C for 24 hours are required to kill
all the pathogens

Required temperature and time is different in each pathogen
 Air requirements


can estimate the theoretical quantity of oxygen required
Air with at least 50 % of the initial oxygen concentration
remaining should reach all parts of the composting material
 pH control


should remain at 7 to 7.5 range
should not rise above about 8.5 to avoid ammonia gas release.
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Aerobic composting
 Degree of decomposition

can be estimated by measuring the final drop in temperature,
degree of self heating capacity, amount of decomposable and
resistant organic matter in the composted material, rise in the
redox potential, oxygen uptake, growth of the fungus
Chaetomium gracilis, starch-iodine test
 Control of odor


mainly caused by organic acids, generated in a partially
anaerobic condition
enough oxygen supply, reduction of particle size, remove
nonbiodegradable materials
 Land requirements

1.5 to 2.0 acres for 50 ton/d capacity
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Aerobic composting
Comparison of aerobic composting processes
Item
Windrow
Aerated static pile
In-vessel, forced aeration
With agitation
(dynamic)
No agitation
(plug flow)
Capital costs
Generally low
Generally low in
small systems, can
become high in
large systems
Generally high
Operating
costs
Generally low
High (in sludge
digestion)
Generally low
High
Low, but can increase if windrow
drying or cutting required
Complete
Complete
Land
requirements
High
Control of air
Limited unless
forced aeration is
used
Operational
control
Turning frequency, Airflow rate
amendment, or
compost recycle
addition
Airflow rate,
agitation,
amendment, or
compost recycle
addition
Airflow rate,
amendment, or
compost recycle
addition
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Aerobic composting
Comparison of aerobic composting processes, contd.
Item
Windrow
Aerated static pile
In-vessel, forced aeration
With agitation
(dynamic)
No agitation
(plug flow)
Sensitivity to
cold or wet
weather
Sensitivity unless
in housing
Demonstrated in
cold and wet
climates
Demonstrated in cold and wet
climates
Control of
odors
Depends on
feedstock,
potential largearea source
May be large-area
source but can be
controlled
Potentially good
Potential
operating
problems
Susceptible to
adverse weather
Control of airflow
rate is critical,
potential for
channeling or
short-circuiting air
supply
High operational
flexibility, system
may be
mechanically
complex
Potential for
channeling or
short circuiting
of air supply,
system may be
mechanically
complex
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Aerobic composting
Issues in the implementation of composting
facilities

Odor

every existing facility has had an odor event

facility siting, process design and biological odor
management are of critical importance.
Presence of pathogens
 Presence of heavy metals



Contamination in shredding process
Definition of what constitutes an acceptable
compost
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Composting of cow manure in Japan
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Composting area in TU
THANK YOU
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