INSTITUTIONEN FÖR GEOVETENSKAPER

Examensarbete i Hållbar Utveckling 17

Selection and Implementation of an Optimal System to Handle Garbage in

Kigali, Rwanda

Innocent Kahigana

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Selection and implementation of an optimal system to handle garbage in Kigali, Rwanda

Master Thesis in Sustainable Development

By

Kahigana Innocent

Supervised by

Associate Prof. Hylander. D. Lars

Examined by

Associate Prof. Kihlberg Tor

Institutionen för Geovetenskaper

Uppsala Universitet

2011

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Content Abstract.......................................................................................................................................iii Keywords.....................................................................................................................................iii

Summary.....................................................................................................................................iv Keywords.....................................................................................................................................iv

1 Introduction..............................................................................................................................1 1.1 Background of the study.....................................................................................................1

1.2 Theoretical framework........................................................................................................2

1.3 Composting.........................................................................................................................3

1.4 Briquetting..........................................................................................................................5

1.5 Incineration.........................................................................................................................7

1.6 Research problem...............................................................................................................9

1.7 Hypotheses of the study.....................................................................................................9

1.8 Purpose of the study...........................................................................................................9

1.9 Specific objectives.............................................................................................................9

1.10 Justification of the study....................................................................................................9

2 Methods and materials……...................................................................................................9

2.1 The preliminary survey....…................................................................................................9

2.2 Sampling frame....................................................................................................................9

2.3 Data gathering....................................................................................................................10

2.4 Data analysis…..................................................................................................................10

3 Study results..........…............................................................................................................11

3.1 Waste flow rate and types…..............................................................................................11

3.2 Control ordinances for waste flow…….............................................................................11

3.3 Effectiveness of optimal system........................................................................................12

3.4 Sensitivity analysis of sub criteria.....................................................................................13

3.5 Leverage of changing systems…......................................................................................14

4 Discussion….….....................................................................................................................14

4.1 Hierarchy of system selection….......................................................................................14

4.2 Accuracy of the system and waste sorting........................................................................16

4.3 Conclusion.…...................................................................................................................17

4.4 Study limitations...............................................................................................................17

4.5 Acknowledgment..............................................................................................................18

5 References….........................................................................................................................18

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Selection and implementation of an optimal system to handle garbage in Kigali, Rwanda

KAHIGANA

Kahigana, N., 201X: Selection and implementation of an optimal system to handle garbage in Kigali, Rwanda. Master thesis in Sustainable Development at Uppsala University, No. XX, YY pp, 30 ECTS/hp

Abstract: Reports from various institutions claim that garbage management in Rwanda has had diverse effects on both the natural environment and human society. Such claims prompted for an exploratory study to find out an optimal system to handle solid waste in Kigali City.

The study considered a literature review and primary data from 400 randomly selected citizens. They were surveyed about their opinions on which system they perceived to be the optimal to handle garbage in Kigali City. The computer software Web-Hipre was used to analyze data on the three systems considered to handle solid waste in Rwanda: briquetting, composting, and incineration.

The results indicate briquetting as the optimal alternative to handle solid waste from homesteads and workplaces of Kigali City. Briquetting considers production of solid fuels that may reduce destruction of forests for fuel. Other major reasons for briquetting, highlighted by respondents, include improved kitchen hygiene and sanitation and replacement of charcoal for a less dusty fuel.

Economic factors governed surveyed participants to prioritise briquetting system to handle solid waste in Kigali. Composting may be considered for transforming organic materials into mulch to support farming activities in rural areas as well as gardening in the towns. However, a centralised incineration system is presently not suitable. The private sector has so far not fully been engaged in the transformation of solid waste into bioenergy in Rwanda.

Keywords: Sustainable Development, Waste, Garbage, Biomass, Composting, Briquetting, Incineration, Combustion, Conversion, Mulch, Biodegradable, Non-biodegradable, Solid fuel, and Bioenergy.

Kahigana, Department of Earth Sciences, Uppsala University, Villavägen 16, SE- 752 36 Uppsala, Sweden

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Selection and implementation of an optimal system to handle garbage in Kigali, Rwanda

KAHIGANA

Kahigana, N., 201X: Selection and implementation of an optimal system to handle garbage in Kigali, Rwanda. Master thesis in Sustainable Development at Uppsala University, No. XX, YY pp, 30 ECTS/hp

Summary: The waste handling system, found in Kigali, Rwanda, is substandard compared to those in countries such as Sweden and United States of America. In general, municipal authorities and other private companies are keen to keep streets and some suburbs clean with the help of open landfill disposal system. They often collect and dump solid waste, mixed of organic and inorganic materials to the only municipal dump site located at Nyanza Hill in the outskirts of Kigali City. The exploratory study – conducted for thesis project – considered briquetting, composting, and incineration systems to handle garbage that have had diverse effects on both the natural environment and human society worldwide. Study revealed that briquetting may be an optimal system to handle garbage in Kigali, Rwanda; perceived by several respondents surveyed to be environmentally friendly. Respondents considered briquetting for production of solid fuels that may reduce destruction of forests for fuel. Other reasons for briquetting, highlighted by respondents, include improved kitchen hygiene and sanitation and replacement of charcoal for a less dusty fuel. Considerations were as well made to the composting system, which respondents preferred to be subsystem. They considered it for transforming organic materials into mulch to support farming activities in rural areas as well as gardening in the towns. However, incineration system is presently not suitable. The private sector has so far not fully been engaged in the transformation of solid waste into bioenergy in Rwanda.

Keywords: Sustainable Development, Waste, Garbage, Biomass, Composting, Briquetting, Incineration, Combustion, Conversion, Mulch, Biodegradable, Non-biodegradable, Solid fuel, and Bioenergy.

Kahigana, Department of Earth Sciences, Uppsala University, Villavägen 16, SE- 752 36 Uppsala, Sweden

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1 Introduction

1.1 Background of the study Homesteads and workplaces are, worldwide, crucial for people in their daily activities to meet their needs. They are thereby producing waste, which includes non-liquid materials thrown away by the people or companies (Ngoc and Schnitzer 2009). These materials can be categorised into two fractions, namely inorganic and organic solid waste (Dimitris and Ham 2006). Both fractions may end up at garbage disposal sites. However, there is a need to respect environmental hygiene at these sites which receive tons of solid waste day after day from various places. There is also need to undertake formal procedures in order to have such hygiene at all garbage dump sites in every country (Serrona and Yu 2009). In the developed countries, such as USA and Sweden, there are legal provisions that regulate the flow of solid waste to various handling sites. These provisions, which local administration authorities undertake, consider apportioning waste handling fee to every producer of solid waste (National Renewable Energy Laboratory 1995). The aim is to reduce flow of solid waste to the landfills, and promote recycling strategy (United States Environmental Protection Agency 1999). However, O’Leary (1999) found it impossible to recycle some solid waste such as soiled papers, light bulbs, window glass, plastic-coated papers, photographic films, and frozen food boxes. Others include blueprints, wrapping papers, disposable diapers, mattresses, and woods treated with pesticides. Additionally, recycling system releases several pollutants to air, land and water. They include carbon dioxide (CO2), methane (CH4), sulphur dioxide (SO2), and nitrogen dioxide (NO2). Others are hydrochloric acid (HC1), hydrocarbons (HC), carbon monoxide (CO), dioxins and furans. CO2 is a gas produced at burning or complete oxidation of the chemical element carbon. CH4 is a gas produced naturally by microbial through degradation of organic matter. CO2 and CH4 are among the greenhouse gases which contribute to climate change. SO2 is a toxic gas with the strong smell. NO2 is a reddish-brown gas produced naturally by bacteria action in soil and by combustion of substance at high temperature. CH1 is a chemical substance produced when molecules of hydrogen chloride are absorbed in water. The two gases, SO2 and NO2 together with CH1, when emitted to the air will result in acid rain as one consequence of this air pollution. HC are chemical substances comprised of hydrogen and carbon. CO is a toxic gas formed when organic matter is combusted with insufficient oxygen access.

Dioxins and furans are poisonous chemical substances, which produce carcinogenic gas that cause cancer to human beings (Wehmeier et al. 2006, Hosetti 2006, Ahrens 2007). In the developing countries, such as Rwanda, flow of solid waste to landfills occurs in a less restricted manner. This is because of lack of effective solid waste handling system at local or national level to control environmental pollution, mainly from garbage heaps (Zurbrugg, 2003). However, the environmental law enacted by the Government of Rwanda in 2005 prohibit free flow of solid waste to dump sites which pollute the environment. Rwanda Utility Regulatory Agency in 2009 regulated that the flow of solid waste to landfills has to match with environmental management standards. The aim is to prevent future threats to the ecosystem. The agency prohibits disposal of, hazardous, solid waste to dump sites; also prescribed control measures for erosion incidences at landfills in Rwanda. It recommended covering decomposed waste with soil for a clean environment. However, the agency set strict standards for landfill without considering possible loopholes; hesitation of waste collectors to follow standards as a result of the urgent need for open landfill to handle volumes of waste from Kigali City. Schiopu et al (2009) explained how leachate, emerging from stacks of garbage rotting at an open landfill, may pollute soil and groundwater. Dumping of organic solid waste at open landfills releases CO2 and CH4 gases, of which especially CH4 largely contributes to global warming (Velinni 2007). The open landfills, such as one at Nyanza hill located in the outskirts of Kigali City, are the source of rotting garbage threatening residents around with toxic fumes and polluted rainfall runoff (Beeman 2009). The threats, mainly from Nyanza dump site, which Beeman considers being multiplying each year is a complex issue in the expansion of Kigali City. The 2009 Rwanda Environment Management Authority (REMA) report linked garbage threats to lack of integrated waste management system in the Kigali City development plan. Report explain how some parts of Kigali, residential and commercial areas, evolve in a way that causes irregular municipal waste collection and disposal system. This is due to lack of a centralised system for waste collection. Lack of such system prompts some institutions to practise inefficient handling of some solid waste from their premises. If not, municipal authorities and few private companies collect and dump large volumes of solid waste at Nyanza dump site. In addition, the everyday dumping of loads of solid waste at Nyanza site appear in a less restricted

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manner. This enables volume of prohibited waste to enter this dump site (Bishumba 2010). REMA report together with Ngoc and Schnitzer study warn that lack of strict restricted manner could lead to allocation of large land to serve as dump sites. It could also lead to the failure of concerned authorities to control environmental costs caused by waste disposal. Moreover, Rwanda is a small country which covers an area of 22336 sq km (DeRouen and Bellamy 2008); and experience a high population density (408 people per km2 in 2008) as well as rapid urbanisation. The challenge is that, the need for large land to serve as the waste dump sites occur with the distribution of chunks of land to annexes of Kigali City (United Nations-Habitat 2004). The REMA report warns that the garbage flow to Nyanza dump site, if not prevented could contribute to environmental health threats. These threats, mainly to urban residents, include air, water, and soil pollution; cause diseases such as cholera, conjunctivitis, pneumonia, scabies, oral infections, and acute respiratory infections. Residents exposed to these health threats are those, in Kagarama suburb, near Nyanza dump site (Ministry of Health 2008). These health threats, according to the REMA report, could hinder the role of a nationwide campaign against unsanitary conditions. The Ministry of Health (2008) explained that this campaign aims at improving environmental health conditions at community and household levels by getting rid of polluted soil, water and air around. However, bringing such hygienic conditions in the areas around Nyanza dump site is still an arduous task to undertake. The cause of health threats, as a result of accumulation of solid waste, according to Ngoc and Schnitzer is due to several challenges. They include institutional weakness, financial and technical constraints, regulatory, knowledge, and public participation limitations. These challenges cause improper garbage disposal due to lack of facilities for treating solid waste (National Institute of Statistics of Rwanda 2007). The rapid population growth also increases solid waste predicament. As population increases in Kigali City with activities which produce more solid waste, residents still think too little about possibilities for developing a useful waste management system (Drakenberg 2008). 1.2 Theoretical framework Undervaluing the developing of waste management system hinders possible control measures for garbage threats to the residents around waste disposal sites. However, waste management system, which is a comprehensive and

multifunctional method, helps to handle waste. The system thereby prevents possible methane gas explosions and formation of leachate from garbage stack to soil and groundwater (United Nations Development Programme 2010). In addition, waste management theory helps to channel environmental management into engineering design. This theory is a cohesive body of knowledge about waste management system. It mainly considers the framework of industrial ecology, built with interdisciplinary method that favours composting, briquetting and incineration systems for handling garbage, especially, in the urban areas (Pongracz et al. 2003). The method would generate revenue and curb garbage threats. The challenge that economists face is to discover solid waste handling system with less cost to achieve the general objective with public impulses. The set of assumption of cost effectiveness is that total benefits have to be high for such objective to dominate decisions, and even win political support to enable the pursued objective to have a general framework. This ensures that recognition and assessment of benefits and costs are from society’s perspective. Thereby enabling decision-making approaches to provide the basis for the required framework (Mishan and Quah 2007). In order to give support to the characterisation of decision-making approaches, there is a need to consider; cost-benefit theory, decision theory, and social choice theory. The cost-benefit theory, which emerged from application of economic theory, identifies the most favourable alternative in terms of an efficiency criterion. It states that favourable alternative should measure probable advantages and disadvantages. This theory explains how advantages and disadvantages join to obtain total measure of social capital or societal gain (Merkhofer 1987). Decision theory describes how to formulate decisions from individuals considering uncertainty. The theory, which is fundamental to different scientific disciplines, explains about the probabilities of consequences of a certain decision and the value of those consequences to the decision-maker (Parmigiani et al. 2009). The social choice theory is all about the investigation of procedures that attempt to merge the preferences of individuals within a social ranking of alternative. The theory considers the viewpoint that the appropriate criterion is a preference of majority to be affected by the decision taken (Kelly 1988, Johnson 1998). For example, optimality for one of the three (composting, briquetting, and incineration) systems integrates preferences of individuals. It also

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anticipates possible consequences of the selected alternative (Nas 1996). 1.3 Composting Scientific literatures define composting as the natural break down of organic solid materials into a component of soil comparable substance called compost. This break down supports the postulations of individual scholars that nature composting process provides fertilizers for healthy plants (Bertoldi and European Commission 1996). Humans thereby replicated the process by placing pile of organic solid waste on the topsoil or in a silo for microbes to degrade while synthesising their own food (McNelly 2009, Pommier et al. 2008). Composting process for organic solid materials occurs under the influence of micro and macro organisms such as actinomycetes, fungi, bacteria, mites and snails (College of Agriculture Consumer and Environmental Science 2010). Some of the organic solid materials to compost include cardboard rolls, news papers, fruits, vegetables, yard trims, sawdust, and coffee husks, and straws (United States Environmental Protection Agency 2000). In traditional composting systems, organic material is just piled together and then left for a year, while more elaborated composting systems take 2 to 3 weeks for complete decomposition. This system necessitates that the materials to compost be chopped up, into small pieces, and carbon (C) to nitrogen (N) ratio not exceeding 30:1. It also requires moisture content in the compost between 40 to 60%, achieved by adding in water during construction and turning of the compost pile. Effective composting needs to take place at the temperature range of 30-70o C, and regular turning of the compost pile to prevent overheat that would kill microbes (Raabe 2001). Another important factor to achieve rapid composting, which Raabe warned for, is to avoid adding more organic materials into the bin once the composting process is in progress. The reason is that the effective breakdown of materials takes place within a fixed period. He also discouraged the adding of materials, for instance soil and ashes from the fireplace or cooking stoves, into the bin. These materials add weight to the compost pile, thus making the turning of the solid waste pile more strenuous. Ashes may also influence the power of hydrogen (pH). The effective composting system requires effective environmental conditions to help microbes break down organic materials (figure 1). The three significant factors, which determine these conditions, include; (a) quality and quantity of carbon (food) as an energy source and a source of minerals (b) shape and physical dimensions of the

organic ingredients; (c) the appropriate population of organisms engaged in the decomposition of organic solid materials into substantial manure (Cooperband 2000).

Figure 1, schematic of the composting process for raw organic materials into finished compost. Source: Rynk R. 1992. 0n-farm composting handbook. Retrieved on 30/09/2010 from www.region18.com. The effective composting system, often performed by microbes, occurs within the recommendable carbon to nitrogen ratio in waste materials. The recommendable mass ratio of carbon to nitrogen is: 30:1. This ratio enables microbes to speed up the decomposition process. The carbon to nitrogen ratio below (table 1) helps to avoid the lengthy decay in case of excess carbon. The ratio also prevents foul smell from the compost pile, which occurs when nitrogen content is too high (Ebeling 2003). Table. 1, estimated carbon and nitrogen content of some organic materials Materials with high nitrogen values Materials C:N ratio

Vegetable wastes 12-20:1

Coffee grounds 20:1 Grass clippings 12-25:1 Cow manure 20:1 Horse manure 25:1 Horse manure w/ Litter 30-60:1 Poultry manure (Fresh) 10:1 Poultry manure (w/ Litter) 13-18:1 Pig manure 5-7:1 Materials with high carbon values

Materials C:N ratio Foliage (Leaves) 30-80:1 Corn stalks 60:1 Straw 40-100:1 Bark 100-130:1 Papers 150-200:1 Wood chips and sawdust 100-500:1

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Source: modified from Department of Natural Resources and Environmental Control, 2007. Balancing carbon-to-nitrogen ratio requires proper identification of common organic materials, with high concentration of carbon, are brown in colour. Those with high concentration of nitrogen contain green colour. The moisture content of organic materials is also critical. Leaves and sawdust have 40%, fruits and vegetables 80 to 90%, grass clippings 80%, and shrub trims 15% (Trautmann and Krasny 1997). Cornell Waste Management Institute (CWMI) in 2001 used the following methods to determine the percent of moisture content and carbon to nitrogen ratio for suitable organic solid materials to compost. Procedures for determining moisture content: Measure the mass of a container to be used, Measure 10g of each organic material inside the container, Use 24 hours to dry the sample in an oven with 105 to 110oC, Weigh the sample again, deduct the weight of a container used, and calculate the moisture content with the help of the following formula: Mn = (Ww-Wd) x 100 Ww Whereby the equations: Mn= total weight of moisture content in organic materials used, Ww = weight of the wet sample, Wd= weight of the dry sample. To calculate the carbon to nitrogen ratio CWMI applied the following formula;

Where the: R = carbon to nitrogen ratio of compost mixture, Qn = weight of all organic materials used (“as is wet”, or “dry weight”), Cn = percent of carbon of all organic materials used, Nn = percent of nitrogen of all organic materials used, Mn = percent of moisture content of all organic materials used. In addition, most of the organic solid materials with excess nitrogen have moderate, low, C:N ratio. They need to be varied or covered with other organic materials that have high brown colour for healthy composting. The advantage of using organic solid materials with high carbon values in aerobic composting system is to increase air penetration into a compost pile (American Planning Association 2006).

The aerobic composting system requires oxygen to produce carbon dioxide, nitrogen, water and heat needed by microbes (United States Environmental Protection Agency 1995, Bruce 2000). The process is a significant factor of the natural reduction of pollutants at various dump sites of organic solid waste. It enables the rapid break down of oxygen demanding organic solid materials by microbes to produce odour and leachate, and compost at the final stage (Sarika 2007). Besides, Dimitris and Ham identified ammonia (NH3), a gas with a strong odour, and CO2 as the two leading pollutants from composting. Suitable aerobic composting of the mixed green and brown coloured organic solid waste occurs in stages namely: the pre-processing stage in which incoming organic solid waste qualifies for successful composting. At this stage, material recovery involves crushing of solid waste. The final stage is the separation in which break down of complex organic solid materials generates carbon dioxide, water and compost. The ultimate product is mulch, used to improve soil fertility for agriculture purpose and urban green edges (Hester and Harrison 2002). The aerobic composting of organic solid materials uses different technologies, which United States Environmental Protection Agency considered being aerated static pile, in-vessel, and windrow methods. Other essential technology is the one that protects persons, from health threats, mainly engaged in the sorting of inorganic from organic solid waste. Besides, composting organic toxins follow similar principles that govern composting process which involves the frequent turning of pile. Differences are the frequent inoculation of microbes within toxins and imposing technique to enrich conditions that support the proliferation of microbes. These microbes are capable to use elements of nutrient in the molecules of a substance that is acted upon in a biochemical reaction (Diaz et al. 2007). An aerated static pile This method uses positive pressure aeration based on what Asesay et al. (1998) described as temperature feedback control. It mixes organic solid materials together in one large pile. This method is suitable for a relatively homogenous organic solid waste mixed together and covered under a shelter. Aerated static pile is suitable especially in the arid climate, to avoid possible evaporation. It requires careful monitoring to make sure that the heat inside the compost pile is more than heat outside layer of the pile. More internal heat reduces odours with the support of applied thick layer, with about 15cm, of finished compost over the stack. This maintains high temperatures all

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over the pile, with 40-55% of moisture content (Diaz et al. 2007). In-vessel This is a composting method where the decomposition of organic solid materials happens within an enclosed drum, silo, or vessel. This enables the operator to maintain a closer control of the process (United States Environmental Protection Agency 2000). It has the advantage of operating at most favourable temperature conditions and moisture content. In-vessel facilitates composting of a wider range of organic materials; it captures and treats odours from the composting process. The treatment occurs within 21 days at the temperature level of up to 65oC (Insam et al. 2002).

Figure.2, flow diagram showing an in-vessel composting facility Source: USEPA, 2000: retrieved on 15/04/2010 from. www.htmlimg4.scribdassets.com. Windrow This composting method places the mixed organic solid waste in long, tapered piles turned on a regular basis. The turning process mixes the composting materials and increases passive aeration. The efficiency turning of organic solid materials within windrow depends on the equipment used, which also determines the shape, size and its spacing. The windrow’s size that can be effectively aerated depends on quality of many small holes on it. The holes allow water to pass through slowly (Misra et al. 2003). In Kigali City, companies such as Amizero, Cooped, Agruni and Cosen are composting. They are aware that composting enables production of manure needed for croplands. However, lack of proper solid waste handling systems and designed garbage trucks to transport solid waste cause production of poor composts. The current waste collection and transportation systems mix inorganic

and organic solid materials. This makes the whole composting process difficult (Paulin Buregeya, unpublished observations). 1.4 Briquetting It is the conversion of organic solid materials, through different processes including hydraulic pressing, piston and screw pressing, into solid fuel. Several scientific descriptions about briquetting system stretch from resource exploitation, to the invention of technologies to cut back further human depletion of natural resources (Demirbas 2010). The Shree Khodiyar Engineering Works (unpublished observations) warned that the reliance of human beings, for survival, to natural resources is irreversible. Several scientific studies have also invented technologies to overcome depletion of natural resources for energy generation. These technologies transform organic solid waste into raw materials for heat production. The invention of such technologies led to the development of briquetting theory (Filho and Butorina 2002). Briquetting is used in emerging economies in the solid waste management. It may incorporate both raw material recovery and environmentally sound handling of organic solid waste (Koufodimos and Samaras 2002). Since 1990, organic solid waste became the leading source of solid fuel worldwide. Countries such as Germany and Netherlands have realised contribution of briquetting organic solid waste for heat production (Bautista and Pereira 2006). These countries transform different organic solid waste including cardboard, sawdust, shavings, waste papers, yard trims, and other assorted municipal solid waste into pellets or briquettes for heat production (Plistil et al. 2005). Transforming organic solid materials into solid fuel requires starch or a binder for sticking flaked materials together to produce a pellet or briquette. The next step is to dry it to increase its physical strength. The drying of a pellet or briquette is at about 80oC in a furnace or the sun (Food and Agriculture Organisation 1987). It is usually prepared by passing on hot air to reduce moisture content from 25% to 10% (Environmental Information System 2006).

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Figure. 3, schematic design showing the process of producing briquettes from organic solid waste. Source: Hood. 2010. Adopted from United States Agency for International Development. However, pollution can be generated out of inappropriate briquetting method. This happens, especially, when putting a variety of organic solid waste together to produce briquettes conducted in an uncontrolled environment (Niaounakis and Halvadakis 2006). The pollutant mainly consists of sulphur contents that are soluble in water (Sakamoto and Murano 1996). There are three different methods (roll, extrusion, and palletising) suitable for briquetting organic solid waste. The roll briquetting is mainly for dry granular materials, such as food waste, sludge, and minerals. It uses a screw feeder to direct materials between two opposing rotating presses, which include pockets (Li and Liu 2000). Picutre.1, shows a depiction of roll briquetting machine for producing solid fuels

Source: retrieved on 18/05/2011 from http//: www.image.made-in-china.com Extrusion briquetting uses a ram/piston press that move backwards and forwards to push the base materials through a tapered die. The success of extrusion briquetting depends on actual measurements of temperature, and moisture content of 6 to 15%. This ensures the production of quality briquettes (Zachry Engineering Corporation 2009). Picture. 2, shows a depiction of extruder briquetting machine for producing solid fuels.

Source: retrieved on 18/05/2011 from http://img.tootoo.com.

Pelletizing method squeezes solid waste through several holes of a furnace giving high pressure from rollers to the materials. The process produces a pellet with 8-15% moisture content, and energy value of 16.3 - 18.6 MJ/kg (Klass 1998). Environmental Information System suggested the size of this pellet with a diameter ranging from 10-12 mm as optimal because of density for transportation and storage purpose. This is smaller than a briquette with about 25 mm. In addition, pelletizing briquetting method requires electricity ranging from 15- 40 Kwh per ton of dry materials (Hood 2010) as compared to extrusion requiring 13 – 60 Kwh per ton of the same materials (Grover and Mishra 1996). Picture.3, shows a depiction of pelletizing machine for producing pellets Source: retrieved on 18/05/2011 from http://www.pelletmill.net/pelelt-mill-szlh250.html. Additionally, Zachry Engineering Corporation identified the need for organic solid materials with moisture content ranging from 6 to 15% to produce a briquette with density of 9.1- 15.9 kg/m3. The briquette, produced, is about 0.08 metre diameter and 0.04 metre thick. However, production of a quality briquette depends more on the residues and briquetting method used. Compressive strength or bonding, density, ash content, and calorific value are also variable parameters for determining production of quality briquette (Eh-Haggar 2007). The private companies, for instance Cosen, Cooped, and Amizero, practise small scale briquetting of organic solid waste from Kigali suburbs. However, they use poorly equipped workforce in the collection and separation of waste (Levine 1995). Regardless of the ill-equipped workforce and undeveloped briquetting system in Kigali, turning organic solid waste into briquettes may be financially viable. It also saves natural environment and minimises odour of garbage from the dump sites (Poverty Environmental Initiative 2006).

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The control of the natural environment destruction and garbage odour Koufodimos and Samaras study described it as an integrated waste management strategy. The co-authored study considered solid waste as valuable materials with energy potential that maximises economic benefits. In addition, Food and Agriculture Organisation “forestry paper 41” explained that the successful producing of briquettes from the organic solid waste could be minimising air pollution and solid waste disposal problems in the southern part of USA. 1.5 Incineration Surprenant et al. (1988) developed incineration theory, which describes the destruction of solid waste by combusting them as a means to use bioenergy to light and heat. Bioenergy is the power or heat generated from renewable and biological materials. Incineration theory explains how this thermal treatment of solid waste in the presence of oxygen facilitates the energy recovery process. This treatment is a chemical process in which solid waste is, however, converted into residues which require landfill for final disposal (Mishra 2008). Incineration involves conversion of solid waste into steam, gas and finally residues to release heat and light (Salvato et al. 2003). The level of energy recovery from incineration of solid waste depends on which use the heat energy may have (McDougall et al. 2001). Surprenant with other scholars noted pyrolysis, a thermal chemical decomposition of organic material at high temperature in the absence of oxygen, oxidation reactions, and free radical as the reaction sequences that take place in the incineration of solid waste. Free radical is a system with the unpaired electron (Herzberg 2003). Besides, Surprenant team recommended that temperature, which affects the rate of reaction, adequate contact of waste with air, and residence time are the key parameters for mass burn incineration process of solid waste. Aubrey and Woods Hole Oceanographic Institution (1997) described residence time as the length of time a liquid substance will stay in a sub-system until other substance replace it from outside such sub-system. Whereas mass burn incineration is the transformation of huge solid waste into potential energy supplies for commercial purpose (McDougall and White 2001). Mass burn incineration uses excess oxygen within five distinctive stages. These stages are incineration process, energy recovery, emission control, and treatment of solid residues. Some European countries practise mass burn incineration, which destroys at least 100 to 1000 tons of solid waste per day (Young 2010). For example, Netherlands has the average mass burn incinerator plants which

burn over 480,000 tons per year. Italy and Norway incinerator plants destroy less than 100,000 tons of municipal solid waste annually (Williams 2005). Several scientific studies on the role of incineration identify types of incinerators for solid waste. These types include rotary kiln incinerator that handle solid and liquid waste, grate incinerator that handle large irregular-shaped waste, which allow air into the waste, and fluidised-bed incinerator for sludge or liquid and uniformly sized solid waste (Nemerow et al. 2008). The rotary kiln incinerator burns wide range of solid waste at a temperature from 760 to 1370˚C. It controls very easily the residence time for thermal incineration and enables uniform contact of air with waste (Bagchi 2004). Surprenant with other scholars concluded that incineration gas flow rate, turbulence and waste processing rate, and incineration size determine residence time. In addition, the effective incineration depends up on the boiler, which is a pressure container used in burning of flue in the form of liquid or gas and generates energy. Excess air is required for complete incineration of flue gases; amount of air needed depends on the fuel used (Jayamaha 2006). Countries such as Germany, Sweden, Italy, Switzerland, Luxembourg, Netherlands, and Japan incinerate more than 50% of their municipal solid waste. These countries build their incineration plants with treatment facility for the flue gases. These plants have two main components; rotary kiln combustion chamber for solid and liquid waste, and afterburners chambers that destroy materials not burnt in the initial process. Besides, ash residues collected in a large container, from the rotary kiln, can be tested to identify harmful material concentration levels prior to landfill disposal, or before being used in construction (Baskar and Baskar 2007). In Denmark, construction process for roads, bicycle ways and car parks use ash residues from incineration process. In Netherlands, construction companies use fly ash residues to construct embankment and base of roads. In Germany, they use fly ash to build sound barrier and road base (Hester and Harrison 2008). However, the use of fly ash residues to construct embankments, road bases and bicycle ways is a horrible threat to phosphorous, a non-metallic chemical element which is essential for every biological process (Beatty 2001). Fly ash residues have concentration of toxic elements such as mercury, which pollute soils, air and freshwater bodies (Mika et al. 1985).

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Incineration is often associated with production and emissions of by-products – such as dust particles, sulphur oxides, nitrogen oxides, carbon monoxide, and volatile chlorinated organic compounds. Others are furans, dioxins, leads and mercury, polycyclic aromatic compounds, and acid gases. These compounds and chemical elements pollute the air and subsequently soil and water. Therefore, air pollution control devices or systems are necessary to curb emissions from incinerator plants. Devices such as electrostatic precipitator help to remove dust, and wet scrubbers remove gases dissolved in water to control airborne particles. Wet scrubbers, dry-sorbent injection, or spray-dryer absorbers and fabric filters can control heavy metals, hydrochloric acid, dioxins, and sulphur dioxide emission to air. Incineration process modification and urea injection or ammonia through selective catalytic or non-catalytic reduction can control, in part, nitrogen oxides. The injecting of activated carbon into the flue gas or passing cold flue gas through a carbon sorbent bed helps to reduce dioxins and mercury concentrations (Hylander et al. 2003, National Research Council 2000).

Figure. 4, schematic diagram of an incineration plant at Vattenfall Varme Uppsala AB, with pollution control devices for water and flue gases. Source: Hylander et al. 2003. Retrieved from the journal of The Science of the Total Environment, 304:137–144. The air pollution control devices/systems enable the detoxification of toxic organic waste that would cause environmental health threats. They thereby reduce impact of CO2, though it will come out in any case, and CH4 from the landfills, which are more than that of other greenhouse gases generated from incinerator plants (Niessen 2002). Therefore, incineration process causes less global warming than open landfill disposal; landfill generates CH4 with global warming potential of 21 tons in the

timeframe of 100 years (Bracmort et al. 2011). Landfill also generates CO2 with global warming potential of 1300kg in the time horizon of 100 years (Ananthanarayanan 2005). However, incinerator plants with pollution control systems limit the CO2 emission to the atmosphere (Porter 2002). The success of incineration depends on the amount of solid waste available, which requires in-depth knowledge of industrial/commercial and demographic structure of solid waste generation and collection areas. Calculating domestic solid waste generation volume is crucial to have at least economically feasible lifespan of the solid waste incineration plant of at least 15 to 20 years. Lifespan helps in forecasting solid waste quantity for given incineration plant. In addition, sorting solid waste to a rational degree of accuracy requires staff with advance training; especially the pickers must be knowledgeable enough, to identify different categories of waste. Staff should be able to empty bags, cans, and jars before placing them into waste collection containers. Institutional framework also ensures that the success of waste incineration plants correspond with what the quantity of solid waste and technology are able to do. This framework include the authorities to control and enforce operating standards, the energy sector, the organisation and management of incineration plant itself, and solid waste sector (Rand et al. 2000). As part of safer treatment of organic waste, the government of Rwanda through its Health Ministry devised 2002-2009 incineration strategy for medical solid waste. The concern by the government is that the strategy will substantially treat all special healthcare solid waste. However, lack of appropriate technology and skilled workers remains a challenge to the needed incineration system. Regardless of such challenge in Rwanda, treatment of some pharmaceutical and municipal solid waste considers incineration as the best option (United States Agency for International Development 2004). It is, therefore, necessary to develop proper composting, briquetting, and incineration as solid waste handling systems in Kigali City. The three systems are ineffectively undertaken around Rwanda (Young and Khennas 2003). However, they are the best systems to handle solid waste. Composting converts them into manure for croplands and other green edges in towns. Briquetting turns organic solid waste into solid fuel such as pellets or briquettes for heating purpose. Incineration helps in combustion of solid waste into energy (Kellam 2004).

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1.6 Research problem Huge volumes of solid waste generated from homesteads and workplaces in Kigali City flow continuously to Nyanza dump site in the outskirts of the city. In addition, a nationwide campaign for promoting proper waste handling has enabled Kigali streets, some urban homesteads and workplaces to be clean; but causes environmental health threats, especially to the residents, of Kagarama suburb, near the Nyanza dump site. Collection and dumping of waste at Nyanza dump site is the focus of the current waste handling strategy for the needed hygiene conditions in Kigali. 1.7 Study hypotheses If the solid waste from workplaces and homesteads of Kigali City, Rwanda, could be transformed into heat energy and manure, tons of garbage flowing daily to the Nyanza dump site could be reduced. The recovery of potential resources from solid waste could possibly be done by the use of cost-effective systems such as, composting, briquetting, or incineration systems. 1.8 Purpose of the study The aim of the study was to identify the optimal system for handling garbage in Kigali, Rwanda. How it could be implemented, was another main goal of this study. The study compared three possible systems (composting, incineration, and briquetting for use as fuel) for waste management. The analysis of public opinions, field notes and literatures from the library and internet materials helped to determine economic, environmental and social effectiveness of each system. It also used Web-Hipre computer software to determine the optimal, suboptimal, and least alternative system. 1.9 Specific objectives To identify types of solid waste generated from homesteads and workplaces in Kigali City and their flow rates to the designated dump site. To survey the control ordinances for solid waste flow to the dump site and assess the probable effectiveness of the three garbage handling systems. To find out the expected costs associated with the selection and implementation of an optimal system to handle garbage, from environmental, social and economic perspectives. 1.10 Justification of the study

The need for relevant information on the potential systems to handle garbage worldwide is most useful, as well as how solid waste can become raw material. Besides, possible value of solid waste, the study conducted in Kigali, Rwanda unveiled the potentiality of three (briquetting, composting, and incineration) systems to handle garbage. It also propounded the linkage between solid waste handling, energy recovery, and manure production. It enabled participants surveyed to bring forward the need for converting the organic solid waste into briquettes, which is a positive step to promote the use of such solid fuel in Rwanda.

2 Methods and materials

2.1 The preliminary survey A pilot study conducted in the five local administrative sectors of Kigali City surveyed 15 participants. These participants include local residents from high and low standard suburbs, and key experts and officials from few institutions handling solid waste. The preliminary survey of the reachable population depended on the purposive sampling method. This method draws study conclusion, randomly, based on the purpose and prior knowledge of a sample unit (Burns and Grove 2005). The study, which lasted for two months, tested the three preliminary objectives. The first objective was to identify the generating rate of solid waste. The second objective was to determine among the three (composting, briquetting, and incineration) systems, the most favourable to handle garbage. Third objective was to find out individuals or companies engaged in solid waste handling. As the results of the pilot study, the generating rate of solid waste is high. The few private companies collect and dump waste at the Nyanza dump site. Briquetting considered being optimal, composting considered suboptimal, and incineration least considered, were the three systems considered for handling garbage in Kigali City. 2.2 Sampling frame The purpose of the sampling frame for this study was to have a metropolis representation of solid waste issue and establish possible systems to handle garbage in Kigali, Rwanda. Kothari (2004) described sampling as a theory of studying interrelations existing between a group of individuals of the same type and samples drawn from the finite population. The theory helps in obtaining accurate estimates to make full use of available information (Leather and Watt 2004,

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Yanagawa and Shirahata 2008). In sampling theory, the data collection process depends on randomness technique; a probability sample has to be observed in the entire population (Renssen 1998). The Rwandan capital Kigali was a case study for selection and implementation of optimal system to handle garbage in urban areas. Literature review and public opinions gathered information about composting, briquetting and incineration systems. Data, which include field observations, enabled the study to identify optimal system to handle garbage in Kigali. A sample size was 385 local residents out of total 912,573 target population of Kigali City. The study considered precision level (e) of about (±0.05) for ±5%, sample size needed (p) of at least (0.5) for 50%, and confidence level (Z) of about (1.96) for 95% respectively. The following formula used propounded by Glenn (2009) to determine the sample size; Sample Size= (Z)² *(p)2 (e)2 Which is: (1.96)² * (0.5)2 = 385 local residents. (0.05)² Besides, the sample size for accessible respondents was from all 35 administrative sectors of Kigali City. Two-stage random sampling method ensured equal distribution of sample size of 385 local residents among 35 administrative sectors of Kigali City. This method combines cluster and simple random sampling techniques. Simple random sampling considered each administrative sector as a sample unit. Cluster random sampling considered a group of 11 local residents from each administrative sector as a sample unit (Fraenkel and Wallen 2006). The purposive sampling method enabled the survey of 15 participants consisted of experts and officials from the municipal authorities, companies handling solid waste, organisations or institutions and workplaces producing different kinds of waste. Others were waste management experts from government parastatals responsible to set ordinances to handle waste in Rwanda. 2.3 Data gathering Literature review was the first step in this study, to have a broad perspective on the solid waste management worldwide. Literature highlighted how solid waste can become valuable raw material. Study considered composting, briquetting and incineration systems for conversion of solid waste into a valuable resource. This self-administered survey started with the pilot study of Kigali City

and later proceeded with the final survey. The aim was to obtain first-hand information on optimal system to handle garbage especially in Kigali City. The tools used to collect data from the field were interviews, and survey questionnaires of closed and open-ended questions. These tools helped to obtain public opinions from 385 participants consisted of local residents, and 15 key experts and officials. Questions focused mainly on environmental, social and economic aspects associated with the implementation of optimal system to handle garbage in Kigali City. The three systems considered in the survey include composting, briquetting, and incineration. Field trips depended on observation, another tool used, to identify the availability of systems to handle solid waste at generation and collection points. These trips enabled the survey to reveal the in-depth information about the state of solid waste handling techniques in Kigali involving different institutions or organisations. Gathering of primary data was in Kigali City, Rwanda a small country located in the east central of Africa. The city, covering an area of 730 km2 in the central part of Rwanda, serves about a million people. Kigali City, built on interlocking hills, has an annual average temperature of about 20oC and green vegetation. Kigali has both the surface and underground water sources managed by the government authority called Energy Water and Sewage Authority (EWASA). 2.4. Data analysis The study depended on two research techniques (qualitative and quantitative) for coherent analysis of secondary and primary data. These techniques helped to minimise errors and test hypotheses of the study. Computer software Web-Hipre helped to analyse a most favourable, among composting, briquetting and incineration, system to handle garbage. Qualitative analysis enabled the interpretation of the raw textual and observation data to describe the rationale of systems for solid waste handling. Quantitative analysis interpreted the descriptive and inferential statistics of study findings. Descriptive statistics in this report consist of tables, figures and numerical displays, which summarise findings by mean and standard deviation measurements. Inferential statistics include categorical results from testing hypotheses, by relating study findings to sample size. Making inferences about sample size and study results established range of values about the limit of population of study. It as well showed the reliability of a sample estimates. These estimates, measured by the standard error of the sample mean, were from the sample mean and standard deviation

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of reachable population. The data analysis techniques aligned study results with the opinions of 385 local residents, and 15 key informants. This alignment supports the assumption that study results represent true fraction of 912,573 target population of Kigali City in Rwanda.

3 Study results

The half a year study results collected from all 35 administrative sectors of Kigali City in Rwanda were later put together to have a coherent presentation. Results composed of field observations from the solid waste handling sites and public opinions of 400 participants responded to the survey questionnaires. The 400 participants consisted of 385 local residents and 15 key experts and officials. Opinions of the two groups of participants were equally gathered on nine attributes and three systems (figure 5) considered for handling solid waste. The raw data gathered were about the types of solid waste, control ordinances for solid waste flow rate to dump site, and the optimal system to handle garbage. The data included descending rankings of the three systems for handling garbage. The study aligned rankings of alternative with environmental, economic, and social effectiveness of the optimal system to handle garbage in Kigali City. Every one of 400 participants surveyed responded to the survey questionnaires. Besides, regarding the functionality of nine attributes for an optimal system to handle garbage, 373 (93%) respondents weighed pollution control. At least 348 (87%) valued landfill reduction; 379 (95%) well thought-out of reserving of natural resources. Those who valued potential business were 372 (93%), income generation were 381 (95%), and 386 (97%) considered resource recovery. At least 393 (98%) weighed diversion of waste flow from the dump site; 379 (95%) agreed on the need for the provision of sanitation to the surrounding. About 379 (95%) respondents valued the employment opportunity for people engaged in waste handling. Out of 385 (100%) local residents surveyed on possible means they used to send waste to dump site, 368 (96%) respondents said they contact private companies, 362 (94%) take them individually. Moreover, in a week, 350 (91%) respondents said that they send solid waste once, and 355 (92%) send them twice to a dump site. The daily generation rate of solid waste, on average, is 7 kg per homestead in Kigali City. However, some solid wastes from a number of workplaces end up in pits of respective institutions where they are burnt to ash. This open burning, with its environmental threats, some institutions still perceive it as a cheap method to handle solid waste. Solid waste, burnt in the respective pits of these

institutions, include office papers, cardboards, yard trims, and plastic package wrappers. 3.1 Waste flow rate and types Solid waste dumped at Nyanza site, with estimation flow rate of over 100 tons per day; include non biodegradable and biodegradable solid waste. Non biodegradable consist of plastics, fabrics, glasses, metals and electronic materials. Although some plastics such polythene papers, used as carrier bags banned in Rwanda, they still make up substantial portion of solid waste. They appear as package wrapper trashes from different commercial centres of Kigali City. The fabrics such as mosquito nets observed at this dump site used as package wrappers for other torn textiles. Other inorganic solid wastes include glasses mainly composed of intact and broken liquor bottles; electronics consisted of broken parts of radios, TV sets, and computer devices. Solid waste also include little steel metal scraps consist of small containers for biscuits, tinned foodstuff, and powdered milk. Biodegradable solid wastes at this site were cardboards, charcoal residues, hedge trimmings, wooden furniture, and all agro trashes. The two main types of solid waste flow, when they are mixed, at a high rate to the sole municipal dump site at Nyanza hill. These solid waste arrive in tipper-trucks, with a group of people (waste-pickers) seated on top. Most of them are workers of companies that collect waste from homesteads, workplaces, and streets of Kigali. 3.2 Control ordinances for waste flow The flow of solid waste, from Kigali homes and workplaces, to Nyanza dump site is partially regulated. The aim of city authority, regardless of techniques which waste collectors use, is to keep Kigali streets and all suburbs clean. Such aim enables certain companies or individuals to collect waste using substandard techniques. They often use vehicles not specifically designed to be transporting waste, and ill-equipped staff vulnerable to waste threats. In some suburbs, solid wastes from few homes are manually collected and transported by a group of people to neighbourhood dump site. The group, badly equipped, do some composting of organic solid waste. They sort out inorganic solid waste and deposit them to nearby pits; leaving organic solid waste to decompose at the neighbourhood dump site. They supply composted mulch to small-scale urban agriculture farmers in and around Kigali City. Besides, private companies as well do composting of organic solid waste from different parts of Kigali. However, their production scale still limited, because of what they described as lack of land. Obtaining private owned land in

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Kigali for large scale composting, most of the participants surveyed claimed that, is still expensive. Contrary to composting, the briquetting of organic solid waste by only some private companies is declining. These companies professed shortage of market for briquettes they produce. However, several respondents expressed concern about substandard briquettes, on the local market, which flare and release smoke. Respondents claimed that, these briquettes have low calorific value. Experts surveyed, on bioenergy efficiency, attributed low calorific value to the use of hydraulic press to mix and press flakes of solid waste together. As a result, wood charcoal remains the highly demanded solid fuel in Kigali City. In addition, incineration system, the one with a single combustion chamber, is partially practiced at some major hospitals. The system is especially used, instead of open pit burning, to destroy with fire the medical waste. It helps to ignite to ash a small amount of solid waste, mainly, generated from laboratory operations. Remaining amount of such waste can be sent to the Nyanza dump site. Few private companies collect and dump solid waste at one and only municipal dump site at Nyanza hill. These companies depose mixture of solid waste at this site in a nonrestrictive manner. Authorities concerned to monitor waste that flow to this dump site use apathetic approach to check. Their officials, always stationed, at this site just perform unfocused checking of waste in each arriving tipper-truck and allow them to be offloaded. Participants surveyed said that lack of rationale values, to quantify environmental hygiene or threats, is an obstacle to revamp solid waste handling system in Kigali City. The study for needed optimal system opened up general gathering of quantifiable values. At least 381(99%) of total 386 (100%), local residents were willing to pay on average Rwandan Francs (Frw) 5,329 per month, while 5 (1.3%) were ready for Frw10,000 monthly contribution to the solid waste control measures in Kigali City. Residents in high standard suburbs are already paying monthly charges of Frw 6,000, and those in low standard suburbs pay Frw 1,500 to private companies collecting solid waste. However, lack of proper transport system, road network, especially in the slummy suburbs reported to be a challenge to the waste collectors. Some homes cannot be easily accessed, making it difficult to waste collecting vehicles to pick waste at doorsteps or collection points of the respective suburbs. Lack of a comprehensive system or

national authority responsible for solid waste handling is another obstacle. Local administrations are responsible to make sure that their respective suburbs are clean. However, limited financial support from central government seems to hinder efforts to handle solid waste. Because of financial constraints, local administrations depend on goodwill of private companies collecting waste. In contrast, these companies were as well concerned about the failure by some home owners to pay them monthly waste collection charges. Companies surveyed claimed that such defaulting slow down their attempt to initiate effective control measures for solid waste in Kigali City. Interesting to point out is that, all 385 (100%) local residents surveyed on effective waste control measures agreed that some of the measures do exist in their suburbs. These residents expressed their willingness to pay amount of money to support such measures in their respective suburbs. They attributed their willingness to pay to some environmental, economic, and social factors. Environmental factors, which participants agreed upon involve reduction of unhygienic conditions in the kitchen especially from firewood, and limit charcoal burning from forests. The one and only economic factor participants considered was the need for low-cost system to recover energy from organic solid waste. With social factors, respondents committed to own waste treatment facilities, and form partnership with stakeholders to engage in solid waste handling. All factors meant to identify relevant cost-benefits associated with optimality of the one of three systems considered for handling garbage in Kigali City. 3.3 Effectiveness of optimal system The effectiveness in the selection and implementation of an optimal system considered three alternatives (composting, briquetting, and incineration) to handle garbage in Kigali. The utility function, in the social, economic, and environmental perspectives, determined the effectiveness of each alternative. The study results below (Table 2) summarise utility function for each of the nine attributes across the three alternatives. Table. 2, the effectiveness of each alternative and attribute in environmental, social and economic perspective Ranking Systems Aspects Utilities

1 Briquetting Social 0.71

2 Composting Economic 0.63

3 Incineration Environmental 0.6

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Source: survey results, 2011. Utility, which is the measurement of relative satisfaction among the 400 participants, was determined using the relation between mean value and standard deviation. This helped to weigh participants’ views to rank the optimal and suboptimal alternatives, including the least preferred alternative (Table 2). Every one of the 400 participants of the survey responded to all survey questions administered to them. The participants included 385 local residents and 15 key informants, and were randomly chosen with the help of cluster and purposive methods. The study used computer software Web-Hipre (figure 5) for decision analysis in the evaluation and prioritization of the optimal system, out of three alternatives considered, to handle garbage in Kigali, Rwanda.

Figure.5, the hierarchical principle of Web-Hipre model used to select the optimal system to handle garbage Source: survey results, 2011. The rankings presented in numerical forms of 1= most considered, 2=considered, and 3=least considered (table 2), were assigned to the three alternative systems. This was matched with the sample size of 4000 participants, using weights of (1.0= most important, 0.5= important, and 0.1= least important) every sub criteria in relation to each alternative. Such numerical ratings, (table 2), represent the relative satisfaction of respondents in regard to the optimal system to handle garbage in Kigali. The model run after cross-checking the clarity of the information analyzed in relation to the main goal of the study; there were differences in terms of weights and utility functions among the three alternative systems. With the weights interval, most of the respondents considered briquetting being the optimal system, followed by composting being suboptimal, and

incineration being the least preferable system to handle garbage in Kigali. Most of the respondents pointed out lack of direct and quick benefit from incineration to private companies engaged in garbage handling. Reason was that incineration is expensive and brings meagre long term gains which many respondents did not value as such. This is illustrated in Figure 6, below from the computer software Web-Hipre simulations.

Figure. 6, the composite priorities of optimal system to handle garbage. Source: survey results, 2011

3.4 Sensitivity analysis of sub criteria When environment aspects were considered, (figure 7) the optimal system to handle garbage in Kigali is briquetting for either pellets or briquettes. When economic aspects are considered, (figure 8), briquetting is still the optimal system. In both aspects, utility is decreasing at a stable rate. With the social aspect, (figure 9), briquetting remains optimal at an increasing rate. Besides, sensitivity analysis is as follows in the figures below.

Figure.7, weight of briquetting system in relation to the environmental aspects.

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Source: survey results, 2011

Figure. 8, the weight of briquetting in relation to the economic aspects. Source: survey results, 2011

Figure.9, weight of briquetting with regard to the social aspects. Source: survey results, 2011 3.5 Leverage of changing systems The change among the three systems considered for handling solid waste creates differences in the behaviour of the Web-Hipre simulations. Therefore, it is essential to notice how opting for briquetting by several respondents surveyed changed human perception against wood charcoal. It is as well logic to consider how respondents perceived solid fuel materials as potential resources. Besides, change of systems to handle solid waste for environmental, economic or social aspects occurs above average elicitations. The fact that sensitivity analysis designates briquetting being an optimal system for handling garbage in Kigali, respondents longed solid fuels to replace charcoal from wood. Participants agreed that charcoal production, with unhygienic conditions in kitchen, destroys forests of Rwanda. The Web-Hipre simulations (figures 7, 8, and 9) show how

change of alternative systems to handle solid waste reacted differently.

4 Discussion

4.1 Hierarchy of system selection The optimality of briquetting system to handle solid waste in Kigali, Rwanda, spells-out the transformation of solid waste into raw material. The transformation of organic solid waste into a valuable resource could provide hygiene in Kigali City. It may as well save natural resource exploited to serve heating purposes. Additionally, the interests of all stakeholders engaged in conversion of solid waste to raw material have to be respected. This enables effective contrast of benefits and costs of briquetting biological solid waste in Kigali. Briquetting, considered being an optimal system to handle solid waste, can be an easy task to practise if biological solid materials are available and local communities are willing to support. Some of the materials available in Kigali for briquetting are dry leaves, sawdust, coffee husks, shavings, twigs or branches of the tree, and papers. Others are rice straws, groundnut shells, tea residues, cardboard, water hyacinth, and sugarcane trashes. As well as vegetable and food residues, bean stalks/stubble, bean pods, peelings (sweet potatoes, and cassava), maize corn cobs, and potato stalks for starch to bind briquette (Bharat 2010). The rational leaning of local residents and potential markets would as well support contrast of benefits and costs of converting organic solid waste into briquettes or pellets. As expected, solid waste conversion system considers three categories of aspects. First category is about environmental aspects, which include pollution control, landfill reduction, and conservation of natural resources. Second category is about economic aspects including potential business, income generation, and resource recovery. Third category is for social aspects consisting of diversion rate of solid waste flow from the dump site, providing sanitation to the surrounding, and employment opportunity. Bharat urged that the principle of optimality is realistic if conversion of solid waste is technically feasible, cost-effective, and publicly acceptable. Suitable recovery of raw materials from solid waste would be a result of enhanced trade and reserving capacity of complementary items in Rwanda. For instance, the existence of solid fuel stoves would enable successful conversion of waste into briquettes or pellets. In addition, political will would encourage new ventures in to solid waste conversion sector. This sector has economic

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potential still unexploited. Given that briquetting is crucial in solid waste handling, there is the need to consider accountability, accessibility and transparency. This ensures that substantial benefits be tapped from conversion of solid waste. It is substantial benefits that would persuade for private investments into briquetting system. Private investors thereby recognize briquetting not only as solid waste handling system, but also as a system to enable them turn solid waste into solid fuels for commercial transaction. Transformation of solid waste into solid fuels to replace charcoal would promote conservation of few surviving forests in Rwanda. Formulation and implementation of briquetting system necessitates for estimation of monetary value of briquettes at the end user. Supply-side and demand-side approaches are necessary. Supply-side approach looks at collection, conversion, transportation, and storage cost of both waste and briquettes. However, supply approach does not consider the quality or calorific value of briquette for heating purpose. Demand-side approach determines the quantity and cost of briquettes. This approach considers the amount, in monetary value, of fossil fuel to be replaced by use of solid fuel (Banwari and Reddy 2005). Production of high quality briquette requires the use of what Chaiklangmuang et al (2008) described as a binder which is sensitive to water and materials with porous filter to make briquette resistant to weathering conditions. Though several factors such as briquetting pressure and bulk density of biomass affect density of biomass briquettes, the most notable aspect to consider in briquetting system is intact thickness. This experiment conducted by Patomsok (2009) identified stability of briquette, for weathering resistance, to be effective after one week of briquetting. Effective briquetting process increases calorific value (energy content) of organic solid waste from 800-1000 kcal/kg to 3500-3800 kcal/kg by decreasing water content. The calorific value of different kinds of solid waste varies from 4 to 15 MJ/kg (596-3585 kcal/kg) or higher. Releasing heat energy from solid waste involves chemical and physical methods. Chemical method focuses on properties of mass of organic materials (biomass) determined from ultimate analysis and proximate analysis. Ultimate analysis looks at elements such as hydrogen, carbon, oxygen, and nitrogen. This analysis of these elements is represented by the ratio of oxygen to carbon, hydrogen to carbon, and carbon to nitrogen. Besides, most organic materials have 45-50% of carbon, 5-10% of hydrogen, and 40-45% of oxygen. Proximate analysis involves the

measurements of parameters such as volatile matter, fixed carbon, moisture content, and ash content. Physical method looks at the measurements of heat weight (thermo-gravimetric) analysis, calorific value, and specific gravity. The heat weight analysis aims at knowing temperature, and at which combustion level can be initiated and when the ignition rate is maximum. Calorific value is the unit quantity of heat produced, under the specified conditions, by burning solid waste in the presence of oxygen (Goel 2005, Speight 2005). Goel propound that calorific value also known as gross calorific value or high heating value (HHV) is equivalent to 0.475C - 2.38 MJ/kg for dry materials. He described C as a representation of percentage of fixed carbon. Specific gravity, which is relative weight of each unit volume of biomass, is used to show the density of organic material, ranging from 0.4-1.4 kg/m3. The materials used for briquetting, as well as compressive strength based on the technology used, also determine the specific gravity (Calle 2007). The study by El-Haggar explored a number of appropriate technologies, classified into high pressure and low pressure, for briquetting organic solid waste. Calle urged that high pressure briquetting technology uses mechanically or hydraulically driven piston to press raw materials through a narrow press cone. This technology as well uses a rotating screw to compress organic solid waste against heated die. The low pressure briquetting technology uses hydraulic press, which compress materials to lower pressure. High pressure technology applies more than 500 pressure units (bars) to compress a briquette with a central hole and 1.1 to 1.2 g/cm3 density using a binder. The low pressure technology employs less than 50 pressure units to produce a briquette with about 0.5 to 0.7g/cm3 density, achieved after drying the produced briquette. Hydraulic press is used to produce such briquette with low calorific value for heating purpose. However, the produced briquette is of no use; because hydraulic press technology is suitable to handle waste with 30% minimal content of moisture. Its only piston and screw press technologies suitable for effective briquetting of such solid fuel with high heating value (Mashra et al. 2007). The fact that study also considered composting system to handle waste in Kigali, a number of participants weighted it as a suboptimal; these residents have to know waste materials that do not go into the compost pile, and why composting is beneficial to practitioners (Koontz 2007). Understanding the materials not allowed into the compost pile ensures the successful composting system. Some materials identified by Elibing as inadmissible for composting include bones that are

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not grinded, meats, fish, and any food containing eggs, milk and oils. Other materials are plants treated with some pesticides, magazines (inks and dyes), lime, and dog/cat/bird faeces. Elibing urged that these inadmissible materials create bad odour or attract pests with the compost pile. The major benefit of composting system is that; good compost is the source of organic matter and food for microbial. Such compost brings nutrients back into the soil. In addition, compost increases the ability of soil to hold nutrients and water, and bind soil together to prevent possible erosion (Macaskill 2011). Composting system provides potential humus to improve soil quality and healthy crop products. Humus, when applied to the soil, helps to hold accessible water and nutrients’ requirements of crops (Amal Karam Sayed Abou El-Goud unpublished work). As long as there is air and water support, composting becomes an appropriate, beneficial, and economical way to handle organic solid waste. It helps the environment by reducing garbage disposals (Binggeli 2003). Composting is beneficial in reducing organic solid waste initial weight of about 25 to 30% (Zhu et al. 2008). It as well turns organic solid materials into compost with the high quality nutrients needed by plants (Piet et al. 2001). These organic solid materials should be suitable for peak performance of microorganisms. Peak performance of microbes relies on stable maintenance of physical, biological, and chemical processes. Physical process considers mixing of organic feedstock with water, particle size of organic materials, optimum temperature range of 30-60oC, and pile size. Chemical process considers hydrogen ion or power of hydrogen (pH) between 6 and 8 mol/L for complete mineralised compost. PH is the measurement of degree of hydrogen ion concentration in aqueous/watery solution (Kohlmann 2003). Chemical process also considers nitrogen ratio within materials to compost as reported earlier (Table. 1). Biological process considers aeration of compost with concentration of CO2 and O2 contents inside the pile. The study by McFarland (2001) found optimal concentration of O2 to be ranging from 5-15% while CO2 range from 0.5-5%. However, concentration of O2 level drops in the compost pile when the CO2 content increases (Diaz et al. 2007). Final opinion surveys indicate incineration system as the least alternative for handling solid waste in Kigali. Yet the US Nation Research Council described it as the widely used system for solid waste disposal. This system destroys kinds of household, medical, and hazardous waste. It depends on proper sorting and homogeneity of the solid waste to be incinerated. This proper sorting is one of the measures the National Research Council

urged to consider to address public concerns over the health threats from incinerator residues. Mishra urged that incineration system, as thermal treatment of solid waste in the presence of oxygen for energy recovery; itself requires a fuel to burn solid waste. Salvato et al explained that needed fuel should be equal to the quantity of energy to be recovered from incinerating solid waste. This equitation enables incineration to become one of the optimal systems to handle garbage. Incineration, used in some countries, helps to transform huge solid waste into energy for household use and even commercial purpose. Private sector has an advantage out of incineration system when used to generate revenue out of solid waste handling. In terms of environmental protection, incineration becomes an obstacle. It releases air pollutants. These by-products are threats to the environment and human health. In that case, there is a need for air pollution control devices to limit emissions from incinerator plants. US National Research Council identified some of these devices as electrostatic precipitator, wet scrubbers or fabric filters to trap airborne particles. Financial resource and technical know-how are essential factors for effective briquetting and incineration systems. This makes briquetting or incinerating in homes more difficult. There is also lack of air pollution control devices and lower temperature of the combustion at home level that will result in release of more dioxins. 4.2 Accuracy of the system and waste sorting While briquetting considered being an optimal, composting considered suboptimal, and incineration considered least, system to covert garbage into potential resources, it is not easy for unsorted solid waste. There is a need to sort organic materials from inorganic to easy, especially, briquetting and composting systems; as well as the need for technology to destroy heavy metal waste effectively; mainly mercury, lead and cadmium residues which affect environment (Vattenfall 2009). Success of solid waste sorting and recovery of energy or mulch depends on the managerial structure at solid waste generation and collection areas. Sorting solid waste to a reasonable degree of accuracy requires workforce with advanced training. The workforce should be able to identify different categories of solid waste. Staff should be able to separate solid waste before placing them into waste collection containers. The separation of solid waste is a lengthy process practiced in number of steps. Goel’s study unveiled how metal and iron waste can be separated from other organic solid waste by magnetic separation; grit and sand

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(very small pieces of stones) be removed by segmented screening. Also, separation of leather, glasses, and other inert materials made of clay from organic solid waste make use of air conveyer belts. Besides, institutional framework is necessary for successful solid waste separation and conversion into bioenergy or compost. This framework include the authorities to administer and enforce operating standards, the bioenergy and composting sectors, organisation and management of bioenergy plants, and solid waste collection sector. There is also a need for public private partnership to deal with environmental challenges from municipal solid waste (Coad et al. 2005). 4.3 Conclusion The optimal system to handle garbage in Kigali in Rwanda depends on the importance paid to environmental, economic, and social factors in an interdisciplinary approach. The success of briquetting, considered as optimal system, would as well depend on the four aspects; waste materials available, institutional structure, profitable activities, and technology to use. Types of solid waste materials available for quality briquette are dry leaves, sawdust, coffee husks, shavings, twigs or branches of the trees, and papers. Others are rice straws, groundnut shells, tea residues, cardboard, water hyacinth, and sugarcane trashes. There is also vegetable and food residues, bean stalks/stubble, bean pods, peelings (sweet potatoes, and cassava), maize corn cobs, and potato stalks for starch to bind briquette. The institutional structure for solid waste handling – at community, district, and national levels – is necessary to involve both private and public sectors. Public-private partnership needs to be emphasised to attain equal responsibility to handle garbage at each level. Profitable activities would include recovery of bioenergy for heating or mulch for soil fertility. When recovery of such materials from solid waste becomes profit making, it will attract more private investors. Briquetting process, by the use of piston and screw press technologies, would be at community level. At this level, private investors together with members of local communities would merge their efforts for effective and extensive conversion of solid waste into solid fuel. With composting as subsystem, a range of organic solid materials available for that include leaves, grass clippings, household solid waste such as vegetable residues. Others are coffee grounds, yard trimmings, papers and sawdust. Converting these materials into mulch, by either aerated static pile, in-vessel, or windrow methods, would be practiced at home level. It requires limited financial and human resources; several compostable organic

materials are available at each homestead. However, these materials are more available in rural areas than urban centres. Thereby enable rural communities to play a big role in the implementation of composting system to handle organic solid waste in Rwanda. Effective recovery of energy or mulch would rely on prior sorting of solid waste by workforce with effective training for suitable briquetting or composting. Besides, there is a need for the technology capable to handle inorganic solid waste including glasses, synthetic leather and synthetic fabrics. Specifically designed trucks or other vehicles such as bicycle carts are needed to transport solid waste to either briquetting plants or sites where composting takes place. Toxic waste should be separated at the source or preferably, not be generated in order to reduce health threats to waste pickers as well as to the environment and public health. Slummy suburbs and road networks within should be upgraded to facilitate collecting solid waste at the homes. The recovery of energy and mulch from garbage would reduce flow of organic solid waste to Nyanza dump site. The flow rate of non-organic solid waste, especially steel metal scraps, would remain minimal. Reason is that, a group of individuals in the business of collecting and selling metal scraps provide substantial help. They send these scraps to steel rolling mill plants in Uganda to transform them into iron-bars and other building hardware. Briquetting system would reduce the flow of organic solid waste to the dump site, because it converts the waste into solid fuel, which could replace charcoal for heating and cooking purposes. Composting organic solid materials into mulch would do well to support farming activities in rural areas and gardening in the towns. However, a centralised incineration system is presently not suitable. Solid waste available to incinerate is hitherto not enough, and effective technology for that is still lacking. The private sector has so far not fully engaged in the transformation of biological solid waste into bioenergy in Rwanda. 4.4 Study limitations Constraints of this survey were cross-sectional as findings were from several domains. The data collected from a number of respondents, considered mainly environmental and economic aspects. They prefer briquetting system for solid fuel recovery in order to replace charcoal. It was difficult, because of short study time, to find out if briquetting would

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be cheaper to run than composting in Rwanda. It was not easy to establish the cost of technology to convert organic solid waste either into briquette or mulch. This necessitates deeper study for complete results. It also requires study about the private sector interest to invest in incineration infrastructure for energy generation in Rwanda. 4.5 Acknowledgement The successful finishing of this research would not have been possible without substantial assistance of different groups of people. I wish to thank all local residents whose cooperation in proving the necessary information was so crucial to the study. I also thank the key informants from various organisations, who provided valuable assistance that helped me to complete this study. Thanks are as well due to Mr. Ahimibisbwe Reuben, from the Department of Infrastructure, Kigali City Council whose advice during my field study was of great important. In addition, I highly thank my chief supervisor Associate Prof. Hylander D. Lars, from the Department of Earth Sciences, Uppsala University for having supervised my research project. His efforts, suggestions, and guidance helped me so much to compile my work in a good way. This research report is an output of Swedish Institute, which financed my postgraduate studies at Uppsala University in Sweden for a period of two years. Its funding enabled me to collect and compile data without any financial challenge. However, views expressed in this work are not necessarily those of Swedish Institute. I retain full responsibility of this work.

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