The role of waste pretreatment on the environmental sustainability of waste management
Deviatkin, Ivan (2017-10-20)
Väitöskirja
20.10.2017
Lappeenranta University of Technology
Acta Universitatis Lappeenrantaensis
Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-335-130-1
https://urn.fi/URN:ISBN:978-952-335-130-1
Tiivistelmä
The ever-increasing world population has exerted unprecedented pressure on the world’s natural ecosystems through both the production and consumption of various products. Human behaviour is having a destructive impact on the environment, and waste generation and disposal represents one of the key sources of this negative impact. To tackle the problem, a systematic transition towards a circular economy, which is largely built on the possibilities of waste recycling, has been initiated. The continually increasing waste recycling rates can only be achieved by exploiting the advanced waste treatment technologies that are available. However, the operation of such technologies often requires substantial amounts of energy or materials, thereby potentially eliminating the benefits of waste recycling.
The primary goal of the research presented in this dissertation was to examine the contribution of the waste pretreatment (PT) activities on the overall environmental impact of waste recycling. An analysis of this nature has not previously been performed on a systematic basis across a variety of waste types and environmental impact categories. The specific objectives of this research study were as follows: (i) to quantify the environmental impact of waste PT activities, (ii) to identify the factors that make the most significant contribution to the impact of the PT activities, (iii) to compare the cumulative induced environmental impact caused by waste PT activities and the final recovery process versus the cumulative avoided impact caused by the conventional disposal of waste and product substitution, and (iv) to identify the potential conditions in which break-even points can be achieved.
The goal and the objectives set for this research were achieved by conducting six life cycle assessment (LCA) studies in accordance with the ISO 14040 and ISO14044 international standards. The impact of the recycling or recovery of multiple waste types via a wide number of recycling methods was assessed in terms of the global warming potential (GWP), abiotic depletion potential (ADP), and human toxicity potentials (HTP).
The results of the research reveal that, in general, the need to pretreat waste does not increase the environmental impact of waste recycling activities when compared to the conventional disposal in the majority of scenarios and impact categories; however, a significant variation in the relative importance of the PT activities amongst the alternative studies and the impact categories was identified. The lowest relative importance of the PT of 0.44-0.52% was achieved for the carcinogenic HTPC in the scenario in which a mineral fraction from the treatment of the municipal solid waste incineration bottom ash (MSWI BA) was recycled via either a road construction or garden stone production process. On the contrary, the highest relative importance of the PT activities of 64% was recorded for the GWP in the scenario in which phosphorous was recovered from sewage sludge ash.
The results of the GWP analysis revealed that the PT activities incorporating advanced waste treatment methods had a significant contribution of 29-64% to the overall impact of the entire waste management systems. On the contrary, the low contribution of PT activities of 0.3-3.7% to the overall GWP was recorded when conventional disposal processes that have a high impact on the GWP, such as landfilling of organic waste, were avoided. Furthermore, PT activities could have a low impact on GWP when waste recycling results in the substitution of materials that have substantial carbon footprints; e.g., burned lime or cement. In terms of the ADP, the significant importance of the PT, which ranged from 21- 36%, could be expected when the PT activities require a comparatively high amount of fuels, while also having a low impact on conventional disposal and product substitution. On the contrary, the PT activities may have a low contribution of 0.24-1.2%, when waste recycling results in the substitution of materials or fuels that have a high impact on the ADP; e.g., phosphorous or cement. Straightforward results were achieved for the carcinogenic HTPC, in which only a low (0.44-0.52%) and low-to-moderate (3.7-5.0%) share of the overall impact was associated with the PT activities since the toxicity was mainly related to the release of heavy metals during thermal residue recycling processes. On the contrary, a moderate (1.9-9.2%) and a significant (12-41%) share of the non-carcinogenic HTPNON-C was associated with the PT activities in situations in which the major contributors were the consumption of fuels required for transporting and incorporating the waste in the final recovery process.
The factors that have the largest impact on the contribution of PT activities varied across the studies; however, the variation of the factors studied in the sensitivity analysis revealed that break-even points are seldom achieved. One break-even point was achieved for the GWP in the scenario in which nitrogen recovery was incorporated into the thermally drying of sewage sludge. In this case, the GWP increased from the avoided impact of 18% to the induced impact of 2.6%. Another break-even point was identified for the non-carcinogenic HTPNON-C in the scenario in which the mineral fraction obtained during the treatment of MSWI BA in the garden stone production process was recycled. In this scenario, the avoided HTPNON-C of 14% transformed into the additional impact of 17%.
It is important to acknowledge an anticipated variation in the inventory data used in the study, which might alter the results achieved. Furthermore, some significant environmental areas of concern were not considered in the research due to limitations in the scope of the study and the inventory data available. Finally, the impact of the system boundaries on the relative importance of the PT should be studied in more depth to achieve comprehensive insights into the relationship between PT activities and environmental impact throughout the entire life cycle of a product.
The primary goal of the research presented in this dissertation was to examine the contribution of the waste pretreatment (PT) activities on the overall environmental impact of waste recycling. An analysis of this nature has not previously been performed on a systematic basis across a variety of waste types and environmental impact categories. The specific objectives of this research study were as follows: (i) to quantify the environmental impact of waste PT activities, (ii) to identify the factors that make the most significant contribution to the impact of the PT activities, (iii) to compare the cumulative induced environmental impact caused by waste PT activities and the final recovery process versus the cumulative avoided impact caused by the conventional disposal of waste and product substitution, and (iv) to identify the potential conditions in which break-even points can be achieved.
The goal and the objectives set for this research were achieved by conducting six life cycle assessment (LCA) studies in accordance with the ISO 14040 and ISO14044 international standards. The impact of the recycling or recovery of multiple waste types via a wide number of recycling methods was assessed in terms of the global warming potential (GWP), abiotic depletion potential (ADP), and human toxicity potentials (HTP).
The results of the research reveal that, in general, the need to pretreat waste does not increase the environmental impact of waste recycling activities when compared to the conventional disposal in the majority of scenarios and impact categories; however, a significant variation in the relative importance of the PT activities amongst the alternative studies and the impact categories was identified. The lowest relative importance of the PT of 0.44-0.52% was achieved for the carcinogenic HTPC in the scenario in which a mineral fraction from the treatment of the municipal solid waste incineration bottom ash (MSWI BA) was recycled via either a road construction or garden stone production process. On the contrary, the highest relative importance of the PT activities of 64% was recorded for the GWP in the scenario in which phosphorous was recovered from sewage sludge ash.
The results of the GWP analysis revealed that the PT activities incorporating advanced waste treatment methods had a significant contribution of 29-64% to the overall impact of the entire waste management systems. On the contrary, the low contribution of PT activities of 0.3-3.7% to the overall GWP was recorded when conventional disposal processes that have a high impact on the GWP, such as landfilling of organic waste, were avoided. Furthermore, PT activities could have a low impact on GWP when waste recycling results in the substitution of materials that have substantial carbon footprints; e.g., burned lime or cement. In terms of the ADP, the significant importance of the PT, which ranged from 21- 36%, could be expected when the PT activities require a comparatively high amount of fuels, while also having a low impact on conventional disposal and product substitution. On the contrary, the PT activities may have a low contribution of 0.24-1.2%, when waste recycling results in the substitution of materials or fuels that have a high impact on the ADP; e.g., phosphorous or cement. Straightforward results were achieved for the carcinogenic HTPC, in which only a low (0.44-0.52%) and low-to-moderate (3.7-5.0%) share of the overall impact was associated with the PT activities since the toxicity was mainly related to the release of heavy metals during thermal residue recycling processes. On the contrary, a moderate (1.9-9.2%) and a significant (12-41%) share of the non-carcinogenic HTPNON-C was associated with the PT activities in situations in which the major contributors were the consumption of fuels required for transporting and incorporating the waste in the final recovery process.
The factors that have the largest impact on the contribution of PT activities varied across the studies; however, the variation of the factors studied in the sensitivity analysis revealed that break-even points are seldom achieved. One break-even point was achieved for the GWP in the scenario in which nitrogen recovery was incorporated into the thermally drying of sewage sludge. In this case, the GWP increased from the avoided impact of 18% to the induced impact of 2.6%. Another break-even point was identified for the non-carcinogenic HTPNON-C in the scenario in which the mineral fraction obtained during the treatment of MSWI BA in the garden stone production process was recycled. In this scenario, the avoided HTPNON-C of 14% transformed into the additional impact of 17%.
It is important to acknowledge an anticipated variation in the inventory data used in the study, which might alter the results achieved. Furthermore, some significant environmental areas of concern were not considered in the research due to limitations in the scope of the study and the inventory data available. Finally, the impact of the system boundaries on the relative importance of the PT should be studied in more depth to achieve comprehensive insights into the relationship between PT activities and environmental impact throughout the entire life cycle of a product.
Kokoelmat
- Väitöskirjat [1102]