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Waste management: Appropriate technologies for developing countries (Ethiopia’s case) 1AAiT/AAU
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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 2 AAiT/AAU
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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 3AAiT/AAU
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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 4AAiT/AAU
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Integrated SWM –Deploys four basic management options (strategies) Source reduction Reuse/Recycling Composting Waste-to-energy Landfill/disposal 5AAiT/AAU
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6 Waste generated in the country
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Urban waste 7AAiT/AAU
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Composition AAiT/AAU8 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
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At disposal site 9AAiT/AAU
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Common waste agricultural residues/biomass Coffee residues AAiT/AAU10
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Cotton residues AAiT/AAU11
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Residues from the bio-fuel sector –Jatropha seed production Pulp husk –Caster seed Weed plants & bamboo – Prosopis Juliflora AAiT/AAU12
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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 AAiT/AAU13
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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 W AAiT/AAU14
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Traditional uses of waste biomass For fuel in its low density form For soil nutrient recycling Excess slow biodegradable AAiT/AAU15 burns in the field or agro- processing sites Dumped into the streams
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AAiT/AAU16 Highlight on available waste managements practices
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AAiT/AAU19 Example
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Applied appropriate waste-to-energy technologies Anaerobic digestion to biogas production Briquette c charcoal production AAiT/AAU21
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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) AAiT/AAU22 The status of Biogas technology in Ethiopia
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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 m 3 ) have been built for households, communities and institutions by nine different GOs &NGOs Today, 40% of the constructed biogas plants are non- operational. AAiT/AAU23
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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. AAiT/AAU24
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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 AAiT/AAU25
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Process-Input-Product AAiT/AAU26
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AAiT/AAU30 Use of bio-gas manure Benefits
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AAiT/AAU31 NPK value of FYM and biogas ma nure
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AAiT/AAU32 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, m 3 /hr) –Required biogas amount (Gt) –Hydraulic retention time or sludge age (HRT or )
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AAiT/AAU33 Figure 4.1. General biogas plant drawing for the Sinidu model GGC 2047
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AAiT/AAU34 Gas production rate
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AAiT/AAU36 Empirical relation Volume Geometric
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AAiT/AAU37 Cost of production
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AAiT/AAU38 Installation costs
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AAiT/AAU39 Comparison with conventional fuel
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Briquette charcoal production AAiT/AAU41 Carbonization process has two stages: –Evaporation –Pyrolysis 520 o F (270 o C)
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AAiT/AAU43 Batch carbonization time –Time to drive the water content of the biomass (estimated from graph) –Heating to the pyrolysis starting temperature (270 o C) –Time require to complete pyrolysis process (590 o C)
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AAiT/AAU45 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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AAiT/AAU46 Traditional charcoal making
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Improved carbonizer used AAiT/AAU47
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AAiT/AAU48 Binders The binder materials –Molasses –Starch –Tar –Special mud (Merere cheka) –1.5 kg:30 kg
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AAiT/AAU49 Mixing –carbonized charcoal material is coated with binder. –enhance charcoal adhesion and produce identical briquettes.
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AAiT/AAU50 Briquetting Screw press briquetting
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AAiT/AAU51 –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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AAiT/AAU56 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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AAiT/AAU57 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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AAiT/AAU58 Proximate analysis result of Prosopis charcoal in comparision with other biomass charcoal Type of charcoal Moisture(%) Volatile matter (%) Ash content (%) Fixed carbon (%) Calorific value (cal/gm) Acacia Spp. Charcoal 3.6722.903.6469.797780 Prosopis charcoal 3.9025.903.5066.806959 Bamboo charcoal 9.3115.0314.8060.866256 Cotton stalk charcoal briquette 4.1017.2020.3058.404588 Chat stalk charcoal briquette 8.0428.5816.5446.845100
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AAiT/AAU59 Table 2: Proximate analysis results of agglobriquettes conducted at EREDPC laboratory Type of charcoalMoisture content (%) Volatile matter (%) Ash content (%) Fixed carbon (%) Calorific value (cal/gm) Agglobriquette (cotton stalk) 4.1017.2020.3058.404588 Chat agglobriquette8.0428.5816.5446.845100 Bamboo agglobriquette 6123 Bamboo charcoal9.3115.0314.8060.866959 Prosopis charcoal3.9025.903.5066.806256 Wood charcoal (Girrar) 3.6722.903.6469.797780 Source: EREDPC laboratory
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AAiT/AAU60 Future waste to resource technologies Industrial uses
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AAiT/AAU61 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 AAiT/AAU62
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Improving energy density and Transportation cost AAiT/AAU63 ─ 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; 64AAiT/AAU
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