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– 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 transport4AAiT/AAU

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

Urban waste

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Composition

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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 wastes

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– 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– 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 WAAiT/AAU 14

Traditional uses of waste biomass

For fuel in its low density form For soil nutrient recycling Excess slow biodegradable

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• burns in the field or agro- processing sites• 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 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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The status of Biogas technology in Ethiopia

– 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 non-operational.

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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

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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

– 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

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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.KT = temperature difference between the head air and

the temperature of the wood, Kw = latent heat of water, kJ/kg

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Traditional charcoal making

Improved carbonizer used

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Binders

The binder materials

– 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 Proximate analysis result of Prosopis charcoal in comparision with other biomass charcoalcomparision with other biomass charcoal

Type of Type of charcoalcharcoal

MoistureMoisture

(%)(%)

Volatile Volatile mattermatter

(%)(%)

Ash Ash contentcontent

(%)(%)

Fixed Fixed carbon (%)carbon (%)

Calorific Calorific valuevalue

(cal/gm)(cal/gm)

Acacia Acacia Spp. Spp. CharcoalCharcoal

3.673.67 22.9022.90 3.643.64 69.7969.79 77807780

Prosopis Prosopis charcoalcharcoal

3.903.90 25.9025.90 3.503.50 66.8066.80 69596959

Bamboo Bamboo charcoalcharcoal

9.319.31 15.0315.03 14.8014.80 60.8660.86 62566256

Cotton Cotton stalk stalk charcoal charcoal briquettebriquette

4.104.10 17.2017.20 20.3020.30 58.4058.40 45884588

Chat stalk Chat stalk charcoal charcoal briquettebriquette

8.048.04 28.5828.58 16.5416.54 46.8446.84 51005100

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Table 2: Proximate analysis results of agglobriquettes conducted at EREDPC laboratory

Type of charcoal Moisture content(%)

Volatile matter(%)

Ash content(%)

Fixed 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

– 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

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─ 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

Summary Biogas and carbonization/briquetting organic waste

reduce the volume of waste generatedGenerate clean energyProduce 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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