Cost effective waste management through composting in Africa

Greenhouse gas (GHG) emissions per person from urban waste management activities are greater in sub-Saharan African countries than in other developing countries, and are increasing as the population becomes more urbanised. Waste from urban areas across Africa is essentially dumped on the ground and there is little control over the resulting gas emissions. The clean development mechanism (CDM), from the 1997 Kyoto Protocol has been the vehicle to initiate projects to control GHG emissions in Africa. However, very few of these projects have been implemented and properly registered. A much more efficient and cost effective way to control GHG emissions from waste is to stabilise the waste via composting and to use the composted material as a soil improver/organic fertiliser or as a component of growing media. Compost can be produced by open windrow or in-vessel composting plants. This paper shows that passively aerated open windrows constitute an appropriate low-cost option for African countries. However, to provide an usable compost material it is recommended that waste is processed through a materials recovery facility (MRF) before being composted. The paper demonstrates that material and biological treatment (MBT) are viable in Africa where they are funded, e.g. CDM. However, they are unlikely to be instigated unless there is a replacement to the Kyoto Protocol, which ceases for Registration in December 2012.     

Carbon--making the right choice for waste management in developing countries

Due to initiatives such as the clean development mechanism (CDM), reducing greenhouse gas emissions for a developing country can offer an important route to attracting investment in a variety of qualifying project areas, including waste management. To date CDM projects have been largely confined to schemes that control emission from landfill, but projects that avoid landfilling are beginning to be submitted. In considering the waste options which might be suitable for developing countries certain ones, such as energy from waste, have been discounted for a range of reasons related primarily to the lack of technical and other support services required for these more sophisticated process trains. The paper focuses on six options: the base case of open dumping; three options for landfill (passive venting, gas capture with flaring, and gas capture with energy production), composting and anaerobic digestion with electricity production and composting of the digestate. A range of assumptions were necessary for making the comparisons based on the effective carbon emissions, and these assumptions will change from project to project. The highest impact in terms of carbon emissions was from using a sanitary landfill without either gas flaring or electricity production; this was worse than the baseline case using open dumpsites. Landfills with either flaring or energy production from the collected gas both produced similar positive carbon emissions, but these were substantially lower than both open dumping and sanitary landfill without flaring or energy production. Composting or anaerobic digestion with energy production and composting of the digestate were the two best options with composting being neutral in terms of carbon emissions and anaerobic digestion being carbon negative. These generic conclusions were tested for sensitivity by modifying the input waste composition and were found to be robust, suggesting that subject to local study to confirm assumptions made, the opportunity for developing CDM projects to attract investment to improved waste management infrastructure is significant. Kyoto credits in excess of 1 tCO2e/t of waste could be realised.     

GHG emission factors developed for the collection,transport and landfilling of municipal waste in South African municipalities

Greenhouse gas (GHG) emission factors are used with increased frequency for the accounting and reporting of GHG from waste management. However, these factors have been calculated for developed countries of the Northern Hemisphere and are lacking for developing countries. This paper shows how such factors have been developed for the collection, transport and landfilling of municipal waste in South Africa. As such it presents a model on how international results and methodology can be adapted and used to calculate country-specific GHG emission factors from waste. For the collection and transport of municipal waste in South Africa, the average diesel consumption is around 5 dm³ (litres) per tonne of wet waste and the associated GHG emissions are about 15 kg CO₂ equivalents (CO₂ e). Depending on the type of landfill, the GHG emissions from the landfilling of waste have been calculated to range from ?145 to 1016 kg CO₂ e per tonne of wet waste, when taking into account carbon storage, and from 441 to 2532 kg CO₂ e per tonne of wet waste, when carbon storage is left out. The highest emission factor per unit of wet waste is for landfill sites without landfill gas collection and these are the dominant waste disposal facilities in South Africa. However, cash strapped municipalities in Africa and the developing world will not be able to significantly upgrade these sites and reduce their GHG burdens if there is no equivalent replacement of the Clean Development Mechanism (CDM) resulting from the Kyoto agreement. Other low cost avenues need to be investigated to suit local conditions, in particular landfill covers which enhance methane oxidation.     

Waste management activities and carbon emissions in Africa

This paper summarizes research into waste management activities and carbon emissions from territories in sub-Saharan Africa with the main objective of quantifying emission reductions (ERs) that can be gained through viable improvements to waste management in Africa. It demonstrates that data on waste and carbon emissions is poor and generally inadequate for prediction models. The paper shows that the amount of waste produced and its composition are linked to national Gross Domestic Product (GDP). Waste production per person is around half that in developed countries with a mean around 230 kg/hd/yr. Sub-Saharan territories produce waste with a biogenic carbon content of around 56% (+/−25%), which is approximately 40% greater than developed countries. This waste is disposed in uncontrolled dumps that produce large amounts of methane gas. Greenhouse gas (GHG) emissions from waste will rise with increasing urbanization and can only be controlled through funding mechanisms from developed countries.     

Composting projects under the Clean Development Mechanism: sustainable contribution to mitigate climate change

The Clean Development Mechanism (CDM) of the Kyoto Protocol aims to reduce greenhouse gas emissions in developing countries and at the same time to assist these countries in sustainable development. While composting as a suitable mitigation option in the waste sector can clearly contribute to the former goal there are indications that high rents can also be achieved regarding the latter. In this article composting is compared with other CDM project types inside and outside the waste sector with regards to both project numbers and contribution to sustainable development. It is found that, despite the high number of waste projects, composting is underrepresented and a major reason for this fact is identified. Based on a multi-criteria analysis it is shown that composting has a higher potential for contribution to sustainable development than most other best in class projects. As these contributions can only be assured if certain requirements are followed, eight key obligations are presented.     

Exploring the clean development mechanism: Malaysian case study.

During 2006 the CDM market in Malaysia became established and by December 2007 a total of 20 Malaysian projects had registered with the CDM Executive Board. The Kyoto Protocol defines the Annex 1 countries, as countries that are obliged to reduce their greenhouse gas (GHG) emissions and the clean development mechanism (CDM) allows Annex 1 countries to develop projects, which contribute to emission reduction, in non-Annex 1 (developing) countries. Currently, two projects have been corrected due to request for review and there is one project for which review is requested. Two projects have been rejected by the Executive Board. The broad knowledge of CDM in Malaysia and the number of successful projects are partly due to the well-functioning CDM institutional framework in Malaysia. As an illustration this article focuses on a Malaysian-Danish project and describes the implementation of CDM in Malaysia and refers to this specific project. The project was registered with the CDM Executive Board in May 2007 and is a methane avoidance project in which methane is captured from a landfill and used to generate electricity.     

Greenhouse gases accounting and reporting for waste management – A South African perspective

This paper investigates how greenhouse gases are accounted and reported in the waste sector in South Africa. Developing countries (including South Africa) do not have binding emission reduction targets, but many of them publish different greenhouse gas emissions data which have been accounted and reported in different ways. Results show that for South Africa, inventories at national and municipal level are the most important tools in the process of accounting and reporting greenhouse gases from waste. For the development of these inventories international initiatives were important catalysts at national and municipal levels, and assisted in developing local expertise, resulting in increased output quality. However, discrepancies in the methodology used to account greenhouse gases from waste between inventories still remain a concern. This is a challenging issue for developing countries, especially African ones, since higher accuracy methods are more data intensive. Analysis of the South African inventories shows that results from the recent inventories can not be compared with older ones due to the use of different accounting methodologies. More recently the use of Clean Development Mechanism (CDM) procedures in Africa, geared towards direct measurements of greenhouse gases from landfill sites, has increased and resulted in an improvement of the quality of greenhouse gas inventories at municipal level.     

Quantification of greenhouse gas emissions from waste management processes for municipalities--a comparative review focusing on Africa

The amount of greenhouse gases (GHG) emitted due to waste management in the cities of developing countries is predicted to rise considerably in the near future; however, these countries have a series of problems in accounting and reporting these gases. Some of these problems are related to the status quo of waste management in the developing world and some to the lack of a coherent framework for accounting and reporting of greenhouse gases from waste at municipal level. This review summarizes and compares GHG emissions from individual waste management processes which make up a municipal waste management system, with an emphasis on developing countries and, in particular, Africa. It should be seen as a first step towards developing a more holistic GHG accounting model for municipalities. The comparison between these emissions from developed and developing countries at process level, reveals that there is agreement on the magnitude of the emissions expected from each process (generation of waste, collection and transport, disposal and recycling). The highest GHG savings are achieved through recycling, and these savings would be even higher in developing countries which rely on coal for energy production (e.g. South Africa, India and China) and where non-motorized collection and transport is used. The highest emissions are due to the methane released by dumpsites and landfills, and these emissions are predicted to increase significantly, unless more of the methane is captured and either flared or used for energy generation. The clean development mechanism (CDM) projects implemented in the developing world have made some progress in this field; however, African countries lag behind.     

Clean development mechanism: an incentive for waste management projects?

The Clean Development Mechanism (CDM) was introduced by the Kyoto Protocol to provide a financial incentive to establish project activities in developing countries for reducing greenhouse gas emissions while also fostering sustainable development. This article shows that waste management project activities play an important role in achieving the aims of the CDM. It describes how these activities have to prove additionality, how the emission reductions must be calculated and monitored in order to be eligible and in order to lead to Certified Emission Reductions (CERs). The article further provides an analysis about the various challenges that are involved in applying the CDM scheme to waste management project activities, which require a new specific set of technical skills and regulatory standards.     

Strategies for the municipal waste management system to take advantage of carbon trading under competing policies: The role of energy from waste in Sydney

Climate change is a driving force behind some recent environmental legislation around the world. Greenhouse gas emission reduction targets have been set in many industrialised countries. A change in current practices of almost all greenhouse-emitting industrial sectors is unavoidable, if the set targets is to be achieved. Although, waste disposal contributes around 3% of the total greenhouse gas emissions in Australia (mainly due to fugitive methane emissions from landfills), the carbon credit and trading scheme set to start in 2010 presents significant challenges and opportunities to municipal solid waste practitioners. Technological advances in waste management, if adopted properly, allow the municipal solid waste sector to act as carbon sink, hence earning tradable carbon credits. However, due to the complexity of the system and its inherent uncertainties, optimizing it for carbon credits may worsen its performance under other criteria. We use an integrated, stochastic multi-criteria decision-making tool that we developed earlier to analyse the carbon credit potential of Sydney municipal solid waste under eleven possible future strategies. We find that the changing legislative environment is likely to make current practices highly non-optimal and increase pressures for a change of waste management strategy.     

GHG emission factors developed for the recycling and composting of municipal waste in South African municipalities

GHG (greenhouse gas) emission factors for waste management are increasingly used, but such factors are very scarce for developing countries. This paper shows how such factors have been developed for the recycling of glass, metals (Al and Fe), plastics and paper from municipal solid waste, as well as for the composting of garden refuse in South Africa. The emission factors developed for the different recyclables in the country show savings varying from ?290 kg CO₂ e (glass) to ?19 111 kg CO₂ e (metals – Al) per tonne of recyclable. They also show that there is variability, with energy intensive materials like metals having higher GHG savings in South Africa as compared to other countries. This underlines the interrelation of the waste management system of a country/region with other systems, in particular with energy generation, which in South Africa, is heavily reliant on coal. This study also shows that composting of garden waste is a net GHG emitter, releasing 172 and 186 kg CO₂ e per tonne of wet garden waste for aerated dome composting and turned windrow composting, respectively. The paper concludes that these emission factors are facilitating GHG emissions modelling for waste management in South Africa and enabling local municipalities to identify best practice in this regard.     

Introducing mechanical biological waste treatment in South Africa: a comparative study

This paper presents the results of the first pilot project on mechanical biological waste treatment (MBWT) in South Africa. The study has shown that biological waste treatment in windrows using a passive aeration system that utilises thermal convection to drive the aeration process within a windrow of waste is appropriate for South Africa, in relation to low capital costs, low energy inputs, limited plant requirements and potential for labour-intensive operations. The influence of climate, waste composition and operational facilities was evaluated to optimise the treatment technique to local conditions. The maximum temperatures reached during the intensive thermophilic stage were effectively equivalent to the German experience. The lower CO2 production experienced in the South African trials was attributed to a different waste stream (high presence of plastics) due to the absence of a proper source separated waste collection system. An accurate adjustment of the input material (structural matter in particular) to the specific ambient conditions and irrigation during composting should result in higher organic carbon degradation efficiency in equivalent timeframes. This preliminary experience suggests that the applicability of MBWT in emerging countries, such as South Africa, is directly dependant on the mechanical treatment steps, available operational facilities and nature of the input material.     

Evaluation of landfill gas production and emissions in a MSW large-scale Experimental Cell in Brazil

Landfill gas (LFG) emissions from municipal solid waste (MSW) landfills are an important environmental concern in Brazil due to the existence of several uncontrolled disposal sites. A program of laboratory and field tests was conducted to investigate gas generation in and emission from an Experimental Cell with a 36,659-ton capacity in Recife/PE - Brazil. This investigation involved waste characterisation, gas production and emission monitoring, and geotechnical and biological evaluations and was performed using three types of final cover layers. The results obtained in this study showed that waste decomposes 4-5 times faster in a tropical wet climate than predicted by traditional first-order models using default parameters. This fact must be included when considering the techniques and economics of projects developed in tropical climate countries. The design of the final cover layer and its geotechnical and biological behaviour proved to have an important role in minimising gas emissions to the atmosphere. Capillary and methanotrophic final cover layers presented lower CH₄ flux rates than the conventional layer.     

Emission assessment at the Burj Hammoud inactive municipal landfill: Viability of landfill gas recovery under the clean development mechanism

This paper examines landfill gas (LFG) emissions at a large inactive waste disposal site to evaluate the viability of investment in LFG recovery through the clean development mechanism (CDM) initiative. For this purpose, field measurements of LFG emissions were conducted and the data were processed by geospatial interpolation to estimate an equivalent site emission rate which was used to calibrate and apply two LFG prediction models to forecast LFG emissions at the site. The mean CH(4) flux values calculated through tessellation, inverse distance weighing and kriging were 0.188±0.014, 0.224±0.012 and 0.237±0.008lCH(4)/m(2)hr, respectively, compared to an arithmetic mean of 0.24l/m(2)hr. The flux values are within the reported range for closed landfills (0.06-0.89l/m(2)hr), and lower than the reported range for active landfills (0.42-2.46l/m(2)hr). Simulation results matched field measurements for low methane generation potential (L(0)) values in the range of 19.8-102.6m(3)/ton of waste. LFG generation dropped rapidly to half its peak level only 4yrs after landfill closure limiting the sustainability of LFG recovery systems in similar contexts and raising into doubt promoted CDM initiatives for similar waste.     

Carbon emissions reduction strategies in Africa from improved waste management: A review

The paper summarises a literature review into waste management practices across Africa as part of a study to assess methods to reduce carbon emissions. Research shows that the average organic content for urban Municipal Solid Waste in Africa is around 56% and its degradation is a major contributor to greenhouse gas emissions. The paper concludes that the most practical and economic way to manage waste in the majority of urban communities in Africa and therefore reduce carbon emissions is to separate waste at collection points to remove dry recyclables by door to door collection, compost the remaining biogenic carbon waste in windrows, using the maturated compost as a substitute fertilizer and dispose the remaining fossil carbon waste in controlled landfills.     

Life-cycle-assessment of the historical development of air pollution control and energy recovery in waste incineration

Incineration of municipal solid waste is a debated waste management technology. In some countries it is the main waste management option whereas in other countries it has been disregarded. The main discussion point on waste incineration is the release of air emissions from the combustion of the waste, but also the energy recovery efficiency has a large importance.The historical development of air pollution control in waste incineration was studied through life-cycle-assessment modelling of eight different air pollution control technologies. The results showed a drastic reduction in the release of air emissions and consequently a significant reduction in the potential environmental impacts of waste incineration. Improvements of a factor 0.85–174 were obtained in the different impact potentials as technology developed from no emission control at all, to the best available emission control technologies of today (2010).The importance of efficient energy recovery was studied through seven different combinations of heat and electricity recovery, which were modelled to substitute energy produced from either coal or natural gas. The best air pollution control technology was used at the incinerator. It was found that when substituting coal based energy production total net savings were obtained in both the standard and toxic impact categories. However, if the substituted energy production was based on natural gas, only the most efficient recovery options yielded net savings with respect to the standard impacts. With regards to the toxic impact categories, emissions from the waste incineration process were always larger than those from the avoided energy production based on natural gas. The results shows that the potential environmental impacts from air emissions have decreased drastically during the last 35 years and that these impacts can be partly or fully offset by recovering energy which otherwise should have been produced from fossil fuels like coal or natural gas.     

Gas production, composition and emission at a modern disposal site receiving waste with a low-organic content

AV Miljø is a modern waste disposal site receiving non-combustible waste with a low-organic content. The objective of the current project was to determine the gas generation, composition, emission, and oxidation in top covers on selected waste cells as well as the total methane (CH₄) emission from the disposal site. The investigations focused particularly on three waste disposal cells containing shredder waste (cell 1.5.1), mixed industrial waste (cell 2.2.2), and mixed combustible waste (cell 1.3). Laboratory waste incubation experiments as well as gas modeling showed that significant gas generation was occurring in all three cells. Field analysis showed that the gas generated in the cell with mixed combustible waste consisted of mainly CH₄ (70%) and carbon dioxide (CO₂) (29%) whereas the gas generated within the shredder waste, primarily consisted of CH₄ (27%) and nitrogen (N₂) (71%), containing no CO₂. The results indicated that the gas composition in the shredder waste was governed by chemical reactions as well as microbial reactions. CH₄ mass balances from three individual waste cells showed that a significant part (between 15% and 67%) of the CH₄ generated in cell 1.3 and 2.2.2 was emitted through leachate collection wells, as a result of the relatively impermeable covers in place at these two cells preventing vertical migration of the gas. At cell 1.5.1, which is un-covered, the CH₄ emission through the leachate system was low due to the high gas permeability of the shredder waste. Instead the gas was emitted through the waste resulting in some hotspot observations on the shredder surface with higher emission rates. The remaining gas that was not emitted through surfaces or the leachate collection system could potentially be oxidized as the measured oxidation capacity exceeded the potential emission rate. The whole CH₄ emission from the disposal site was found to be 820 ± 202 kg CH₄ d⁻¹. The total emission rate through the leachate collection system at AV Miljø was found to be 211 kg CH₄ d⁻¹. This showed that approximately ¼ of the emitted gas was emitted through the leachate collections system making the leachate collection system an important source controlling the overall gas migration from the site. The emission pathway for the remaining part of the gas was more uncertain, but emission from open cells where waste is being disposed of or being excavated for incineration, or from horizontal leachate drainage pipes placed in permeable gravel layers in the bottom of empty cells was likely.     

Implementing separate waste collection and mechanical biological waste treatment in South Africa: A comparison with Austria and England

The degradation of organic compounds found in municipal solid waste (MSW) under the anaerobic landfill conditions produces gas and liquid emissions that can protract well into the landfill after-care period. The European Landfill Directives regulate the amount and nature of the organic compounds disposed into landfills. In South Africa and other developing countries, MSW is still landfilled without any kind of pre-treatment. This paper presents a pilot project of mechanical biological waste treatment (MBWT) in South Africa implemented at municipal level in the city of Durban using passively aerated open windrows. Based on case studies from Austria, England and South Africa, a waste minimisation model which can facilitate full-scale implementation of MBWT in developing countries is presented. MSW was treated in open windrows for 8 weeks. Composting temperature reached a maximum of 65 °C in less than 10 days. The results of eluate tests on waste samples from the windrows at the end of composting show a reduction of BOD₅ and BOD₅/COD ratios equal to 35.7% and 16.7%, respectively. The percent waste composition of the treated MSW was 28.3% putrescibles, 17.4% garden refuse, 13.3% plastic, 12.4% fabrics, 12% paper and other elements. The waste composition shows that more than 40% of un-treated organic material and also more than 40% non-biodegradable and recyclable materials are still landfilled without any form of biological treatment or resource recovery. A simple wet and dry waste collection model can promote recycling, treatment of biological waste before landfilling, resource recovery, labour intensive jobs and hence sustainable landfilling in the South African scenario as well as in similar developing countries.     

Measured gas emissions from four landfills in south africa and some implications for landfill design and methane recovery in semi-arid climates.

The magnitude of annual global emissions of methane from municipal solid waste landfills without landfill gas control systems implies that these landfills are significant contributors to the atmospheric load of greenhouse gases. There have been a number of field studies undertaken internationally to measure actual fluxes of methane and carbon dioxide from landfills, with a view to corroborating modelled predictions of the contribution of landfills to the global greenhouse gas budget. The vast majority of these studies have been undertaken in more temperate climates and in developed countries. This paper reports a study of landfill gas emissions from four large landfills located in the semi-arid interior of South Africa. A static accumulation chamber was used and measurements were made at each site over a period of two to three days. The results were analysed by three different methods, all of them leading to the same general conclusion that landfill gas emission rates were lower than expected. A common conclusion based on results from all four sites was that capping of landfills in semi-arid climates with low permeability covers would probably significantly retard the already low rate of waste degradation and thus gas generation. While this may be regarded as advantageous in the short term, it cannot be relied upon in perpetuity as clayey landfill covers will inevitably desiccate and crack in a semiarid environment. In addition, reasonable after-care periods for such landfills are likely to extend well beyond the currently stipulated 30-year period, and efforts to encourage energy recovery from landfills may be hampered because gas generation rates decrease as the waste dries out under conditions of minimal recharge from precipitation. A landfill cover that allows small amounts of percolation of rainfall into the waste may therefore in fact be beneficial in semiarid climates, although care would need to be taken to carefully regulate this infiltration.     

Life-cycle greenhouse gas emissions and economic analysis of alternative treatments of solid waste from city markets in Vietnam

We utilize life cycle assessment to trace conversion of degradable organic carbon (DOC) contained in organic waste from city markets in Da Nang, Vietnam. Our methodology makes explicit the process of conversion of DOC under aerobic and anaerobic conditions, as well as the balance of nutrients. Greenhouse gas emissions were calculated for six alternative scenarios: (i) anaerobic landfilling (current situation); (ii) semi-aerobic landfilling; (iii) landfill gas capture; (iv) composting; (v) pre-composting before landfill; and (vi) biogas production. We calculate that 1 t of waste in anaerobic landfilling emits 1.70 t CO₂-eq. with life-cycle perspective. Lowest emission occurs in biogas scenario with 0.26 t CO₂-eq./t. Composting occupies an intermediate position with 0.39 t CO₂-eq./t. Likewise, we estimate that cost of emission reduction in solid waste sector of Vietnam is 15.13 US$/t CO₂-eq., given by alternative of composting and taking anaerobic landfilling as reference. On the other hand, if social cost of carbon (SCC) is incorporated lowest cost to treat 1 t of waste is given by composting and semi-aerobic landfilling at discount rate of 5 %. However, using lower discount rates, and consequently higher values of SCC, composting and biogas production become the alternatives with lowest treatment costs.