Transcript MANAGEMENT OF SOLID WASTES

Waste management: Appropriate
technologies for developing countries
(Ethiopia’s case)
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 Objective of the lecture
– Introduction to the nature of the waste in cities and
rural areas in the developing countries;
– Highlight on available waste managements
practices;
– Two appropriate technologies practiced for waste
valorization in Ethiopia
– Future waste to resource technologies
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Introduction
Solid wastes
– all the wastes arising from human and animal activities that
are normally solid
– discarded as useless or unwanted
– encompasses the heterogeneous mass of throwaways
Socio-economic problem
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Aesthetic
Land-use
Health, water pollution, air pollution
Economic considerations
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Solid Waste Management
 Selection and application of suitable techniques, technologies,
and management programs to achieve specific waste
management objectives and goals
 Respond to the regulations developed to implement the various
regulatory laws
 The elements of solid waste management
– Sources
– Characteristics
– Quantities and composition of solid waste
– Storage and handling
– Solid waste collection
– Transfer and transport
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Integrated SWM
– Deploys four basic management options
(strategies)
• Source reduction
• Reuse/Recycling
• Composting
• Waste-to-energy
• Landfill/disposal
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Waste generated in the country
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Urban waste
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Composition
 Estimated bio-organic waste generated in cities
and towns
─ About 4600 tons/day = 1.7 M tons/year
─ Does not night soil
─ Does not include industrial, commercial and institutional
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wastes
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At disposal site
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Common waste agricultural residues/biomass
 Coffee residues
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 Cotton residues
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 Residues from the bio-fuel sector
– Jatropha seed production
• Pulp
• husk
– Caster seed
 Weed plants & bamboo
– Prosopis Juliflora
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Assessment of Energy Recovery Potential of SW
 Thermo-chemical conversion
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Total waste quantity : W tonnes
Net Calorific Value : NCV k-cal/kg.
Energy recovery potential (kWh) = NCV x W x 1000/860 = 1.16 x NCV x W
Power generation potential (kW) = 1.16 x NCV x W/ 24 = 0.048 x NCV x W
Conversion Efficiency = 25%
Net power generation potential (kW) = 0.012 x NCV x W
If NCV = 1200 k-cal/kg., then
Net power generation potential (kW) = 14.4 x W
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 Bio-chemical conversion
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Total waste quantity: W (tonnes)
Total Organic / Volatile Solids: VS = 50 %, say
Organic bio-degradable fraction : approx. 66% of VS = 0.33 x W
Typical digestion efficiency = 60 %
Typical bio-gas yield: B (m3 ) = 0.80 m3 / kg. of VS destroyed
= 0.80 x 0.60 x 0.33 x W x1000 = 158.4 x W
Calorific Value of bio-gas = 5000 kcal/m3 (typical)
Energy recovery potential (kWh) = B x 5000 / 860 = 921 x W
Power generation potential (kW) = 921 x W/ 24 = 38.4 x W
Typical Conversion Efficiency = 30%
Net power generation potential (kW) = 11.5 x W
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Traditional uses of waste biomass
 For fuel in its low density form
 For soil nutrient recycling
• burns in the field or agroprocessing sites
 Excess slow biodegradable
•
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Dumped into the streams
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Highlight on available waste
managements practices
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Example
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Applied appropriate waste-to-energy
technologies
 Anaerobic digestion to biogas
production
 Briquette c charcoal production
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Anaerobic digestion to biogas production
 The status of Biogas technology in Ethiopia
 The Ministry of Energy and Water has two departments work
on biogas and energy related activities:
– the Alternative Energy Technical Dissemination and
Promotion Directorate covering the household energy
efficiency;
– the Alternative Energy Design and Development
Directorate (AEDDD)
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– In 1957/58, the first was introduced into Ambo
Agricultural College Ethiopia
– In 1970s, two pilot biogas units as a project with FAO
promote biogas
• one with a farmer near Debre Zeit that is still
functioning,
• another with a school near Kobo in Wollo were build
– In the past two and half decades
• around 1000 plants (size ranging 2.5 – 200 m3) have
been built for households, communities and institutions
by nine different GOs &NGOs
• Today, 40% of the constructed biogas plants are nonoperational.
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 The National Biogas Program for Ethiopia
– a standardized design, participatory planning to
produce a commercially viable system
– aims to create local jobs,
– uses proven technology
– build capacity in technical ability.
– 14,000 plants are planned to be installed over five
years (2009 – 2013)
– 50% of the plants are expected to include a toilet
attachment.
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 Commonly used in rural areas with livestock manure as major
feedstock;
 There is national level project to erect 14000 biogas plants in
rural Ethiopia
 In urban areas, there are some biogas plant
– human waste – institutions
– Cow dung and vegetable wastes
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Process-Input-Product
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Use of bio-gas manure
 Benefits
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NPK value of FYM and biogas
manure
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Designing the bio-digester
 Design parameters:
– Selection/characterization feed materials
• Biodegradability
• C/N ratio
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Biomass (availability) feed rate (Q, kg/day)
Gas production rate (G, m3/hr)
Required biogas amount (Gt)
Hydraulic retention time or sludge age (HRT or )
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Figure 4.1. General biogas plant drawing for the Sinidu model GGC 2047
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Gas production rate
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Empirical relation
 Volume
 Geometric
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 Cost of
production
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Installation costs
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Comparison with conventional fuel
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Briquette charcoal production
 Carbonization process
• has two stages:
– Evaporation
– Pyrolysis
• 520oF (270oC)
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Batch carbonization time
– Time to drive the water content of the biomass
(estimated from graph)
– Heating to the pyrolysis starting temperature
(270oC)
– Time require to complete pyrolysis process
(590oC)
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 Rate of drying the biomass
• h is the heat transfer coefficient kJ/s/m2.K
• T = temperature difference between the head air and
the temperature of the wood, K
• w = latent heat of water, kJ/kg
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 Traditional charcoal making
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 Improved carbonizer used
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Binders
 The binder materials
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Molasses
Starch
Tar
Special mud (Merere cheka)
1.5 kg:30 kg
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Mixing
– carbonized charcoal
material is
coated with binder.
– enhance charcoal
adhesion and produce
identical briquettes.
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Briquetting
 Screw press briquetting
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– Designed to make a small size of 20mm diameter
and produce six briquette charcoal at a time.
– made from sheet metals and angle iron
– the extruder fly wheel is made of concrete
– a screw type press made of a sheet metal which is
welded on a solid steel shaft, designed to produce
high density briquette
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 Beehive Briquette
1. Lever operated hand press
(produces 8 briquettes at a time)
2. Single unit
(Produces 1 briquette at a time)
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 Agglomerator
• A rotating drum glueing
powder particles together
using binder
• Agglomerated charcoal
briquettes are spherical
and have a diameters of
20 to 30 mm
• Production capacity
30-50 kg/hr
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Proximate analysis result of Prosopis charcoal in
comparision with other biomass charcoal
Type of
charcoal
Moisture
(%)
Volatile
matter
(%)
Ash
content
(%)
Fixed
Calorific
carbon (%) value
(cal/gm)
Acacia
Spp.
Charcoal
3.67
22.90
3.64
69.79
7780
Prosopis
charcoal
3.90
25.90
3.50
66.80
6959
Bamboo
charcoal
9.31
15.03
14.80
60.86
6256
Cotton
stalk
charcoal
briquette
4.10
17.20
20.30
58.40
4588
Chat stalk
charcoal
briquette
8.04
28.58
16.54
46.84
5100
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Table 2: Proximate analysis results of agglobriquettes
conducted at EREDPC laboratory
Type of charcoal
Moisture
content
(%)
Volatile
matter
(%)
Ash
Fixed
content carbon
(%)
(%)
Calorific
value
(cal/gm)
Agglobriquette
(cotton stalk)
4.10
17.20
20.30
58.40
4588
Chat agglobriquette
8.04
28.58
16.54
46.84
5100
Bamboo
agglobriquette
6123
Bamboo charcoal
9.31
15.03
14.80
60.86
6959
Prosopis charcoal
3.90
25.90
3.50
66.80
6256
Wood charcoal
(Girrar)
3.67
22.90
3.64
69.79
7780
Source: EREDPC laboratory
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Future waste to resource
technologies
Industrial uses
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Fuel energy consumption
Example cement industry
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Substituting finance oil or heavy fuel
Planned up to 20 % substitute
Target industry – cement industry
Reduced imported fuel
Reduce greenhouse gas emissions
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Improving energy density and Transportation
cost
─ Density
• 50 to 80 kg/m3
─Moisture
• Up 20 %
– Densifying
• > 600 kg/m3
– Pelletizing
• Increasing surface are
for combustion
– Torrifying or roasting
• Further increasing the
energy density
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Summary
 Biogas and carbonization/briquetting organic waste
 reduce the volume of waste generated
 Generate clean energy
 Produce very good bio-fertilizer
 Appropriate waste management technologies
 convert waste into resources for different economic
activities;
 help the generators to add value to their waste and generate
income;
 Reduce dependence on fossil fuel and greenhouse gas
emission;
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