(9e) Life Cycle Analysis for Urban Waste Treatment Optimization

Global consumption has rapidly increased and the amount of waste generated by mankind has raised significant concerns over the associated burden on human and environmental health. However, the conventional notion of waste is an ill-defined concept. In a sustainable society waste should be thought of as raw materials, which can be utilized for use in other economic sectors. For a sustainable future, waste disposal methods should be transformed to ensure an ecological balance with the intention that this vital resource does not harm the environment or humans’ health. If all waste streams could have multiple options at the end of their life then this would be a giant step towards zero waste. Therefore effectively managing solid waste is a huge challenge for environmental decision-makers. 

Greece currently deals with a number of changes regarding environmental management. The most significant one is management of municipal solid waste (MSW). Here, the country has not kept at pace with its European or other Western world counterparts. In contrast to what happens in the rest of Europe and much of the Western world, landfilling remains the dominant waste management option in the country. The main factors contributing to these changes are European and national waste legislation, continuous public pressure and the increasing awareness of adverse health and environmental problems. The above lead to the need for more advanced treatment processes and technologies reinforcing recycling, pre-selection of waste, energy and material recovery. MSW consists of household and commercial waste discarded in urban areas such as fractions of paper, food waste, plastics, glass, ferrous metals and other materials. In the present study four alternative scenarios aimed at minimizing the material fraction disposed of in landfills are analyzed. 

The methodological framework followed is life cycle impact assessment (LCIA). LCIA is a tool commonly used by decision makers regarding various applications concerning environmental interactions during the life of a product from raw material acquisition to production, use and, finally, disposal. The approach was applied to assess municipal solid waste management options in the two largest cities of Greece, Athens and Thessaloniki, paying special attention to energy and material balances including potential global and local scale airborne emissions, groundwater and soil releases. Moreover, material flow accounting, gross energy requirement, emergy intensity, airborne emission and release intensity and morbidity or mortality indicators have been used to support the comparative assessment. 

To date, landfilling remains the most common waste management practice in Greece in spite of enforced regulations aimed at increasing recycling, pre-selection of waste and energy and material recovery. In this paper selected alternative scenarios aimed at minimizing the unused material fraction to be disposed of in landfills are analyzed. The life cycle impact of collection and different waste disposal strategies in eastern Attica and Thessaloniki such as landfilling with and without landfill biogas exploitation, biogas and compost via anaerobic digestion and composting, and waste incineration, was performed by means of a multi-method multi-scale approach.

Results are given in the form of indices of efficiency, effectiveness, environmental and public health impacts. Material flow accounting, gross energy requirement, emergy intensity, emission and release intensity and morbidity or mortality indicators have been used to support the comparative assessment. The results of the assessment based on selected impact indicators lead to the following conclusions:

Material flow accounting. The disposal of 1 g of waste requires the production of ca. 0.14 g of further waste as abiotic matter (the four scenarios analyzed range from 0.1 for anaerobic digestion to 0.2 g for incineration). This underlines the need for waste prevention and reduction systems before waste streams reach the processing plants or the landfill in order to minimize the generation of additional waste. It should be noted that none of the scenarios considered avoid the use of landfilling of the residues, even though anaerobic digestion seems to reduce the need for landfilling significantly.

Gross energy requirement. Anaerobic digestion (primarily) and incineration have the highest gross energy requirement. In general, technological scenarios succeeding in minimizing the amount of residual waste directed to the landfill require more energy when compared to baseline landfilling. However, these systems can provide a consistent energy output that can be used for power or heat generation, offsetting partially the increased energy demand.

Emergy synthesis. Comparative assessment of emergy synthesis for the four scenarios shows that anaerobic digestion is the least emergy demanding, whereas landfilling requires the highest emergy investment per g of waste. Incineration also demands higher emergy investment per g of waste than composting. The overall emergy demand for all options is some 20% higher in Thessaloniki than in eastern Attica. This is due to differences in waste composition, which make some technological options more prone to the need for enhanced environmental support.

Global and local emissions into the air. Incineration is the most polluting waste management option (concerning GWP, AP and TOPP) at the global scale, followed closely by landfilling without recovery and use of the biogas produced. Anaerobic digestion is the best option in terms of GWP and AP. However, when it comes to TOPP, it is landfilling with biogas and energy recovery that comes out at the top. With regard to local air emissions, landfilling with no biogas recovery is by far the worst waste management option. It is particularly bad when considering pollutants such as particulate matter and PAHs, which have been associated with adverse health impacts.

Health impacts. The main adverse health effects considered herein were pre-mature mortality (estimated in terms of years of life lost in the population of the two urban areas), decreased birth rate and increased incidence of congenital anomalies in neonates. Incineration was primarily linked with pre-mature mortality, resulting in ca. 4-5 years of life lost in the populations of eastern Attica and Thessaloniki. Landfilling without biogas recovery did not show a very high incidence of reproductive health problems, mostly due to the relatively low population density in the vicinity of the landfill sites in both urban areas considered. This finding underlines the need for well-studied land use planning when considering the siting of new landfills or waste incineration plants.

Coupling all the indicators above, this multi-method and multi-scale analysis showed that landfilling with no biogas recovery (the most common option in waste management currently in Greece) is the worst management option. Results also show that a sorting plant coupled with power and biogas production using anaerobic digestion could well be the best option for waste management, despite the non-negligible local emissions, especially considering tropospheric ozone precursors. Furthermore, both in the case of anaerobic digestion and in the case of incineration, a non-negligible amount of energy becomes available, in spite of a slight increase in the fossil fuel energy input, while waste residues sent to landfills are minimized and rendered inert. 

Finally, it should be noted that none of the scenarios succeeds in doing away with landfills. Thus, waste prevention policies and active recycling coupled with innovative ways of using the bottom and fly ash or the anaerobic digestion residues currently driven to the landfill would need to be put in place to ensure a truly optimized sustainable urban waste management system. Our analysis points out that landfilling is the worst waste management strategy at a global scale. At the same time, the investigated options for waste treatment coupled with energy and material recovery would result in very important benefits in terms of greenhouse gas emission reduction. However, not all options are equally benign to the local environment and to the health of the local population, since both the former and the latter are still affected by non-negligible local emissions. With regard to public health impacts, adverse effects on respiratory health, congenital malformations, low birth weight and cancer incidence were estimated. A significant and not intuitive result is the fact that life cycle analysis produces different conclusions than a simple environmental impact assessment based only on estimated or measured emissions. 

Taking into account the overall life cycle of both the waste streams and of the technological systems and facilities envisaged under the plausible scenarios analyzed herein, alters the relative attractiveness of the solutions considered. Furthermore, waste treatments leading to energy recovery provide an energy output that, in the best case, is able to meet a significant but not high percentage of the urban power demand.