Abstracts:
13th Biosolids Conference Paper: [click here to view]
The suitability and effectiveness of a waste treatment process or strategy depends upon a waste stream’s physical and chemical composition. Chemical properties of UK waste streams, particularly MSW, are limited while physical properties are better documented. Consequently this presents a degree of uncertainty with the waste’s properties, manifesting itself as financial risk in the investment of new treatment or disposal plant. To mitigate this uncertainty, a number of UK waste surveys have been reviewed to determine if there is significant difference in the calorific value between waste streams. Ultimate and proximate analysis data from a number of sources have been collected and used to approximate the chemical composition of each waste fraction. To facilitate the comparison of each waste stream, a hypothetical compound of the form C6HaOb has been determined for each. Based on this analysis, all UK waste streams share the hypothetical formula C6H10O3, indicating that on a dry basis, the composition of waste in the UK is fairly consistent. Monte Carlo analysis of the hypothetical compound structure revealed that for both household and civic amenity waste streams, the hydrogen and oxygen content only deviate slightly from the mean values. Since MSW is predominantly comprised of household and civic amenity waste, the hypothetical compound C6H10O3 can be used to approximate UK MSW.
14th Biosolids Conference Paper: [click here to view]
Legislative reform of the Renewable Energy Obligation has resulted in a new statutory instrument, the Renewables Obligation Order (ROO), in which electricity generating technologies are “banded” to encourage emerging processes into the market. Many of the the technologies identified in the ROO feature in integrated waste management systems throughout the EU and other developed nations. Therefore, the waste management sector offers opportunities to reduce the size of its own carbon footprint whilst simultaneously mitigating the environmental burden from generating electricity in the UK. However, renewable electricity can only be attributed to energy generated from the biogenic carbon compounds that comprise the fuel used. Different waste management technologies produce energy in a variety of ways using a diverse range of fuels that vary in biogenic carbon content. Furthermore, each type of technology will generate different levels of revenue depending upon the outputs utilised from the process (e.g. heat, electricity, stabilite, oils, char, etc.). With the electricity revenue linked to biogenic carbon content, the choice of technology to invest in is not an obvious one. This paper discusses the ROO with specific relevance to waste management technologies to identify potential opportunities and difficulties arising from generating electricity in the waste management sector. As with achieving Landfill Directive compliance, a counterintuitive ramification of technology “banding” may indeed jeopardise renewable energy targets, despite being introduced to support this aim.
ISWA 2009 Paper: [click here to view]
The calorific value (CV) of waste is a function of its chemical composition which is altered as various waste fractions are recycled. However, not all households recycle effectively, and not all fractions of waste can be recycled. Different waste management strategies employed across the UK further alters the composition of the residual waste streams requiring disposal. Uncertainties in waste composition represent a risk to the business case and perhaps even inhibit investment in EfW plant. By approximating the waste stream as a hypothetical compound of the form CaHbOcNdSe, its CV can be determined using a modified Dulong equation. Performing a parametric analysis using Monte Carlo techniques on various properties of the waste stream (e.g. carbon content, moisture content, etc.) and recycling participation rates and limits, enables the upper and lower bounds of the CV to be quantified.
The objective of this study was to examine how potential changes in the recycling behaviour of householders could affect the CV of residual waste. Four scenarios were developed and analysed to explore the effect that recycling has on the chemical content of residual waste streams and, therefore, on its calorific value: a business as usual (BAU) case using the current recycling rates of each category; a behaviour shift scenario explored the effect on recycling rate if each household ‘moved up’ a recycling category; a worst case scenario in which each household is a non-recycler; and a best case scenario in which each household becomes a super-committed recycler.
Plastics tend to dominate the variance of CV in all scenarios. They have one of the lowest recycling limits yet one of the highest relative CVs in the waste stream. Hence as plastic begins to dominate the residual stream it will have a greater influence on the CV. As recycling potential improves, results from this analysis indicate that the mean CV could increases from 10 to 15 MJ/kg because the relative proportion of plastics increases. However, there is a trade-off: as the CV increases the quantity of residuals decreases at a much greater rate such that a much larger ‘catchment area’ would be required to meet a facility’s operational capacity. Furthermore higher proportions of plastic in the residual stream means that more of the energy comes from a fossilised source so the ROC-able content of the waste will diminish.
Therefore new build EfW plant will need combustion technologies that can cope with a variation in CV should recycling rates improves in the future. Removal of recyclables reduces the mass of residuals considerably, which suggests that EfW plant might be better suited in locations close to large urban areas to ensure adequate throughput of feedstock. And since biowaste content is a dominant parameter, regions of the UK that employ a separate organics collection strategy may be more suitable for the location of EfW plant.
Regardless of the recycling potential of the public, householders can only generate waste from the products that they purchase. therefore, rather than the existing 'end of pipe' approach to waste recovery, the onus should be on the manufacturer to change their ethos and supply products that can be managed sustainably.
The objective of this study was to examine how potential changes in the recycling behaviour of householders could affect the CV of residual waste. Four scenarios were developed and analysed to explore the effect that recycling has on the chemical content of residual waste streams and, therefore, on its calorific value: a business as usual (BAU) case using the current recycling rates of each category; a behaviour shift scenario explored the effect on recycling rate if each household ‘moved up’ a recycling category; a worst case scenario in which each household is a non-recycler; and a best case scenario in which each household becomes a super-committed recycler.
Plastics tend to dominate the variance of CV in all scenarios. They have one of the lowest recycling limits yet one of the highest relative CVs in the waste stream. Hence as plastic begins to dominate the residual stream it will have a greater influence on the CV. As recycling potential improves, results from this analysis indicate that the mean CV could increases from 10 to 15 MJ/kg because the relative proportion of plastics increases. However, there is a trade-off: as the CV increases the quantity of residuals decreases at a much greater rate such that a much larger ‘catchment area’ would be required to meet a facility’s operational capacity. Furthermore higher proportions of plastic in the residual stream means that more of the energy comes from a fossilised source so the ROC-able content of the waste will diminish.
Therefore new build EfW plant will need combustion technologies that can cope with a variation in CV should recycling rates improves in the future. Removal of recyclables reduces the mass of residuals considerably, which suggests that EfW plant might be better suited in locations close to large urban areas to ensure adequate throughput of feedstock. And since biowaste content is a dominant parameter, regions of the UK that employ a separate organics collection strategy may be more suitable for the location of EfW plant.
Regardless of the recycling potential of the public, householders can only generate waste from the products that they purchase. therefore, rather than the existing 'end of pipe' approach to waste recovery, the onus should be on the manufacturer to change their ethos and supply products that can be managed sustainably.
14th biosolids paper.pdf | |
File Size: | 121 kb |
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13th biosolids paper.pdf | |
File Size: | 133 kb |
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ISWA 2009 paper.pdf | |
File Size: | 127 kb |
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