Αξιολόγηση βιωσιμότητας τεχνολογιών αξιοποίησης αστικών στερεών αποβλήτων και περαιτέρω διερεύνηση εφαρμογής βιοδιϋλιστηρίου
Authors: Παπαδασκαλοπούλου Χριστίνα 
Published: November 2021

In the framework of the current thesis, the environmental impacts associated with the management of municipal waste in Greece are examined with the use of the Life Cycle Assessment method. The first part of the thesis focuses on the climate change impact incurred by the current status of municipal waste management in Greece, as well as by the new waste management status which is foreseen for 2020 in the latest National Waste Management Plan (NWMP) of 2015. In particular, the new NWMP foresees the separation at source of the different municipal waste streams and sets quantified targets for their recovery. In the second part of this thesis, the case of a biorefinery system is examined for the alternative management and valorization of municipal biowaste with the production of ethanol fuel and other products. The environmental performance of the biorefinery system is assessed compared to different versions of it, as well against the conventional systems for biowaste treatment. Following, the economic sustainability of the application of such a system in full scale is assessed and the values of the critical parameters for which the system may be economically viable, are defined. Finally, the examined biowaste management systems are evaluated against their overall sustainability, based on a set of environmental, technical, economic and social criteria with the use of the MultiCriteria Analysis method. In specific, in the first part of this thesis, the greenhouse gas (GHG) emissions generated by the current municipal waste management system in Greece are estimated for the period 1991-2015. Next, the potential for reducing GHG emissions through the realization of the targets set in the NWMP (2015) with respect to the separation at source and recovery of recyclables. For the estimation of GHG emissions from landfilling, the waste model developed by the Intergovernmental Panel on Climate Change (IPCC) was used, while for the rest management methods, the appropriate emission factors from the scientific literature were selected. The main outcomes of this research are summarized next. The total quantity of municipal waste that is disposed of in landfills during the period 1991-2015 amounts to approximately 110 million tonnes, with the respective quantity being landfilled in the future according to the new NWMP, being 41 million tonnes. The total GHG emissions that are estimated to occur within a 100-year horizon are for the second case 40.9 billion kg CO2eq., which corresponds to 26% of the respective emissions from the current situation. It is thus observed that by reducing the amount of biodegradable waste that is landfilled and collecting the generated landfill gas, the GHG emissions are drastically reduced. The average net emissions from composting are estimated to be approximately 18.8 million kg CO2eq. for the current situation and refer to the treatment of about 46,000 tn organic waste/year on average. With respect to the year 2020 when, according to the NWMP target, it is foreseen that 2,048,000 tonnes of organic waste will be composted, the respective emissions are estimated to be 812.3 million kg CO2eq.. the net GHG emissions from the recycling of recyclable waste are negative, as the avoided GHG emissions related to the substitution of the production of the respective materials from virgin raw materials, are considerable higher compared to the other emissions. On average, the net emissions from the management of recyclable waste during the current period are -342 million kg CO2eq./year, while for the year 2020 the respective emissions amount to -1,689 million kg CO2eq.. Finally, with respect to the overall management of municipal waste in Greece, the net emissions are quite high for the current period, as they are mostly determined by the emissions from landfilling, with the higher total emissions amounting to about 8,200 million kg CO2eq. for2010. The total net emissions from waste management during 2020 are estimated to be about 300 million kg CO2eq., which are 25 times lower compared to 2010, for a managed waste quantity only slightly smaller (-12%) compared to 2010. For the rest of the LCA research conducted in this thesis, an LCA software tool specialized in waste management (EASETECH) was used. In specific, next the available recycling methods for the dry recyclable materials present in the municipal waste were examined and an LCA was conducted on the implementation of a system for the separation at source of four recyclable waste streams (paper, plastic, glass, metal), as foreseen in the new NWMP. In this study, the analysis is further specified with respect to the different materials present in the recyclable streams and to the relevant pretreatment and recycling processes, while the purity and separation efficiency of collected recyclables is also examined. The main results of the research are presented next. In general, the net GHG emissions generated from the treatment of recyclable waste are negative, as the avoided emissions due to the substitution of material production from virgin raw material are higher compared to the emissions generated from the sorting, pretreatment and residue management processes. On average, the stage of recycling of recovered materials contributes 20% and the substitution stage contributes 78%to the total emissions from the management of recyclable waste . The higher negative emissions are observed for the case of paper/carton waste recycling (-313kg CO2 eq./tn), which is attributed mainly to the high share of this waste stream in the collected recyclable waste. High negative emissions are also observed from the recycling of plastic and metal waste (-249kg CO2 eq./tn and -150 kg CO2 eq./tn, respectively). With respect to the management of 1 tn waste/material, it was shown that the highest negative emissions (-10,080 kg CO2 eq./tn) are generated from the recycling of non metal waste (aluminum), followed by the net emissions of ferrous metal waste (-2,508 kg CO2 eq./tn) and of plastic waste (-1,248 to -2,205 kg CO2 eq./tn). The management of glass waste results in the lowest negative emissions (-316 kg CO2 eq./tn), with the emissions from the treatment of paper and carton waste ranging also in low levels (-466 to -575 kg CO2 eq./τόνο). In the second part of the current thesis, an LCA was conducted for the identification of the environmental impacts from the implementation, at full scale, of a biorefinery system for the alternative management and valorization of municipal biowaste with the production of ethanol fuel and other products. The system is based on the bioconversion process that was developed in the framework of the LIFE project WASTE2BIO. To this aim, LCA was applied to a number of alternative bioconversion systems concerning the potential process products and system configurations. The basic bioethanol production system includes the following stages: collection and transportation of biowaste; pretreatment; bioconversion; ethanol distillation; anaerobic digestion of stillage; generation of energy from biogas. Besides bioethanol, the potential system products that were also taken into account are the energy from biogas production; the production of soil conditioner from the anaerobic digestate; the production of methane fuel from biogas; and the production of animal feed from the stillage. Furthermore, the available biowaste management methods were examined and compared to the reference biorefinery system, such as the landfilling, composting, anaerobic digestion and incineration methods. The different ethanol production systems and waste management methods were evaluated against thirteen life cycle impact categories. The results of the LCA study show that the reference biorefinery system with biowaste drying at the main plant (central drying) presents very good environmental performance compared to the conventional waste management methods examined. The net emissions to the environment are quite low for all the impact categories examined, while in many of the cases the emissions are negative, meaning that the examined system creates a net benefit for the environment. The highest positive impacts are observed for the impact categories “Ecotoxicity”, “Marine eutrophication” and “Soil eutrophication” and are related to the emissions from the stage where the digestate is applied on land, which is common for most of the examined ethanol production systems. The ethanol production system with decentralized waste drying at municipal level presents low but positive emissions in most of the impact categories, which is mainly attributed to the fact that the heat produced at the bioethanol plant cannot be exploited for satisfying the heat requirements of drying, since the latter takes place remotely. The ethanol production system with waste drying at household level presents higher emissions in all impact categories, with substantially higher emissions in most categories, which is attributed to the fact that household dryers consume more energy and in particular electricity, in contrast to the central/decentralized dryers which use heat. With respect to the alternative/additional products of the bioethanol system studied, it was found that the production of methane transport fuel from biogas instead of electricity and heat presents better environmental performance compared to the reference system in all impact categories. The production of hydrous ethanol for use as heat fuel for fireplaces instead of anhydrous ethanol as transport fuel results in worse performance in all impact categories, while the partial diversion of stillage for the production of animal feed presents worse performance in some categories and better in some others. With respect to the results of the sensitivity analysis, it was shown that the use of catering waste as substrate and the reduction of enzyme dosage due to improvements in their effectiveness leads to further emission savings, as anticipated. The production of energy from the combustion of the solid fraction of process stillage also presents better performance compared to the reference system in many of the impact categories. The increase in enzyme dosage for achieving maximum ethanol production presents worse performance in most impact categories. The reference biorefinery system in general presents very good performance against almost all impact categories compared to the current waste management methods. As regards the impacts in the “Climate change” category, the best performances are observed for the methods of anaerobic digestion, incineration and the reference system, where savings are achieved, while the worst performance with positive emissions is observed for the landfill method. With respect to the rest of the impact categories, relatively high emissions are observed for the composting method in the categories “Acidification, soil”, “Eutrophication, soil” and “Particulate matter” which are related to the air emissions from the composting process, for the anaerobic digestion and the composting method in the category “Human Toxicity, non-carcinogenic” and for all methods except incineration in the category “Ecotoxicity” which are related to the emissions from application of compost/digestate on land or to the emissions from the disposal of effluent landfill leachate to surface waters. Following, the sustainability of the full-scale implementation of the biowaste management system for the production of ethanol is assessed. In particular, a thorough financial analysis of the biowaste conversion plant for the production of ethanol took place. Three basic scenarios were examined with respect to biowaste drying: (i) municipal level, (ii) home level and (iii) central plant level. Furthermore, for each scenario different sub-scenarios are examined with respect to the system critical/most influencial parameters, such as the enzyme costs, the ethanol selling price, the debt level and loan duration. The results of the financial analysis for each of the examined sub-scenarios indicated the lowest fee at which the municipalities may manage their biowaste which is at the same time feasible for the business investment at the ethanol production plant level. The analysis showed that biowaste drying at central level is more economical for the municipalities (management costs for the municipality: 91-122€/tn wet waste) compared to drying at municipal level (management costs for the municipality: 113-136€/tn wet waste), mainly due to the fact that the thermal energy produced at the biorefinery plant is not fully exploited in the case where drying takes place distantly (at municipal level). On the other hand, the required thermal energy for drying at municipal level is satisfied through the purchase and use of natural gas, thus substantially increasing costs for the municipality. If dried biowaste produced at municipal level are combusted in order to exploit the produced energy for drying, then the management costs are reduced (78-88€/tn wet waste). The biorefinery system with decentralized drying and combustion presents better environmental performance compared to the biorefinery system with decentralized drying, at the impact categories “Climate change” and “Depletion of abiotic resources – Fossil”. This is attributed to the avoidance of fossil fuel use for drying, according to the LCA results. However, it should also be taken into account that combustion and energy recovery from waste is less preferable compared to recycling based on the waste management hierarchy of the Waste Framework Directive, as savings in resources are achieved due to the substitution of mineral fertilizer production. This is reflected through the impact category “Depletion of abiotic resources – Elements and compounds”, where the biorefinery system with decentralized drying and combustion creates net burdens, in contrast to the biorefinery systems with central and decentralized drying, where we have net savings. This is attributed to the fact that less fertilizer is produced, due to the combustion of (part of) biowaste and thus the savings are smaller than the burdens. Finally, drying at household level did not prove to be economical (management costs for the municipality: 152-176€/tn wet waste), mainly due to the high costs for the purchase of the household driers and the high amounts of electricity consumed for drying. However, the sensitivity analysis showed that a reduction in the cost of the household dryer of 50€ (100€ from 150€) may result in a reduction of about 14€ in the total management cost for the municipality. In the last part of this thesis, the multicriteria analysis tool developed for the comparative assessment of the overall sustainability of the examined biowaste management methods, is presented. Sustainability is assessed in terms of economic, environmental, technical and social criteria. The assessment takes into account the whole waste management system, from the production and transportation of waste to their treatment or final disposal and the use of potential products. According to the selected environmental criteria, combustion with energy recovery is the best method from the environmental point of view followed by the biorefinery system with central/decentralized drying. According to the economic criterion which is based on the minimum management fee, the most preferred method is that of composting, followed by landfilling and anaerobic digestion. The methods of combustion and the biorefinery system with decentralized drying and combustion are in fifth place. The alternative biorefinery systems incur higher capital and operational costs, which is attributed to the complex processes involved, the advanced equipment, the costly raw materials (e.g. enzymes) and the specialized personnel. The biorefinery systems however produce higher net revenues, as apart from the sale of excess electricity and of the fertilizer produced, there are significant revenues from the sale of ethanol as well. According to the examined social criteria, anaerobic digestion is considered to be the most preferred method, followed by combustion and the biorefinery system with decentralized drying (without and with combustion). Following, four alternative scenarios were assessed with the multicriteria method, where higher weights were assigned to different criteria groups at the three scenarios (environmental, economic, social scenarios), while at the fourth scenario, equal weights are assigned to all criteria groups (weighted scenario). The results of the multicriteria analysis show that the method of combustion is the most preferred option both for the weighted scenario and the environmental scenario. Anaerobic digestion is the most preferred option according to both the economic and the social scenario. Composting is ranked between the second and the third place in all scenarios, except for the environmental one. According to the environmental scenario, the biorefinery system with central drying and the respective system with decentralized drying and combustion are ranked in the third place. Those two systems are ranked higher compared to the other biorefinery systems which involve drying at decentralized/household level, in all scenarios.