Environmental sustainability of two biological treatments for the organic wet fraction of municipal solid waste

The wet organic waste is an important fraction of municipal solid waste (MSW), which in European Countries can reach values as high as 30-40% of the total amount of generated MSW. Its management requires an appropriate household source separation, an efficient separate collection, and a final biological treatment of anaerobic or aerobic digestion. It has been demonstrated that, in a life cycle perspective, anaerobic digestion (AD) process has a higher environmental sustainability than aerobic composting process [1]. The AD of the wet organic fraction of MSW (OFMSW) is in fact able to minimize the greenhouse gas emissions and to produce a biogas for energy recovery. It is also characterized by the absence of emissions of bio-aerosols and bad odours, a limited utilization of land surface use, and a sufficient economic sustainability [2]. An interesting alternative to aerobic or anaerobic process units is that of an integrated anaerobic digestion plant, which includes a final aerobic treatment. This study aims to compare the environmental sustainability of this integrated solution with that of a “stand-alone” anaerobic process. The integrated solution taken as reference is made-up of three phases: pre-treatment, wet anaerobic digestion (with a Continuous-flow Stirred-Tank Reactor), and a final stage of post-composting in bio-cells. The pre-treatment is a mechanical sorting process that efficiently removes the out-of-target material, making the OFMSW a substrate suitable for AD. The thermophilic anaerobic phase generates two main products: a biogas, with a degradation rate of the volatile solids of 75%, and a solid digestate. The biogas, which is assumed to be composed by 60% of methane and 40% of carbon dioxide, is then burned in an internal combustion engine for electricity production, with a conversion efficiency of 34%. The digestate is dried and sent to the final aerobic phase to obtain a compost, which could be used as soil conditioner. The “stand-alone” anaerobic plant includes the same pre-treatment and AD phases, but it is not equipped with a final post-composting unit. The first configuration requires higher energy for the additional post-composting stage (which has been evaluated as equal to 20% of total electrical energy produced by biogas combustion), while the second configuration produces a lower quality stabilized material, then having a limited number of possible utilization. Data collected in two plants in operations in Italy have been utilized to estimate the environmental burdens for the development of an attributional Life Cycle Assessment (LCA) study. The functional unit coincides with the treatment of 200 t/d (then about 60 kt/y) of OFMSW. The system boundaries includes all the activities from the plant entry gate until the management of solid/liquid residues. The “system expansion” method was utilized to include the avoided burdens related to the recovery of energy and materials. It was assumed that the generated electrical energy replaces the production of electricity from the Italian grid. The compost produced in the integrated plant is assumed to substitute an amount of peat, which has been estimated assuming a carbon content of 20% for compost and 60% for peat. The digestate obtained from the “stand-alone” AD plant is not composted, and it is assumed to substitute inert materials for the operation of landfill capping, accordingly with Italian legislation. The LCA results indicate that the “stand-alone” AD plant has better environmental performances. In particular, its larger energy recovery leads to better results in terms of midpoint impact categories of “Global Warming”, “Non-Renewable Energy” and “Respiratory Inorganics” [3]. The integrated plant shows worst results also in terms of “Land Occupation”, due to the necessity to add a non-negligible amount of a bulking agent (i.e. straw) to the digestate in order to guarantee the utilization of compost as soil conditioner. A sensitivity analysis has been carried out assuming that the compost generated by the integrated plant could be used as substitute of a chemical fertilizer, highlighting the importance of compost quality in the comparison between the two configurations. [1] Yoshida, H., Gable, J.J., Park, J.K., 2012. Evaluation of organic waste diversion alternatives for greenhouse gas reduction. Resources, Conservation and Recycling, 60, 1–9. [2] Arena, U., and Di Gregorio, F., 2014. A waste management planning based on substance flow analysis, Resources, Conservation and Recycling, 85, 54-66. [3] Jolliet, O., Margni, M., Charles, R., Humbert, S., Payet, J., Rebitzer, G., Rosenbaum, R., 2003. IMPACT 2002+: a new life cycle impact assessment methodology. Int. J. LCA, 8 (6), 324–330

Technical and environmental performances of alternative treatments for challenging plastics waste

The recovery of resources from streams of mixed plastics waste is a technological and economic challenge since they contain various (and generally non-compatible) polymers, different (and often hazardous) additives, as well as multilayer structures and fiber-reinforced composites. Only a too limited part of these plastics - such as those coming from waste of electric and electronic equipment (WEEE), end-of-life vehicles (ELV) and construction and demolition waste (C&DW) - can be treated by mechanical techniques in the conventional recycling facilities, and a still smaller part is reintroduced into the market. Some innovative treatments have been recently proposed and appear suitable for these challenging waste streams. The paper describes technical characteristics of some of them, and compares their environmental performances with those of currently adopted management options. An environmental life cycle assessment was developed by taking into account the substitutability factor of obtained products and technological readiness level of the analyzed resource recovery processes. The focus is on new treatments of dissolution/precipitation, supercritical fluid extraction, catalytic pyrolysis, and waste-to-energy (WtE) equipped with carbon capture and storage unit (CCS). The results highlight the promising performances of some of these new options, quantify their potential environmental advantages, and suggest to take them into account in the definition of sustainable management schemes for the examined challenging plastics wastes. In particular, physical recycling by dissolution/precipitation process applied to one tonne of WEEE plastics, not treatable by mechanical recycling, can save up to about 2 tCO2,eq. with respect to landfill disposal and WtE with CCS, and more than 3 tCO2,eq. with respect to WtE without CCS. The performances of WtE with CCS appear of interest, particularly for WEEE and ELV mixed plastics, allowing to save up to 0.5 tCO2,eq. and 1.7 tCO2,eq., with respect to pyrolysis and WtE without CCS, respectively

A preliminary social assessment of innovative management options for mixed and hazardous plastics waste

Recyclability of plastics from waste of electric and electronic equipment (WEEE), end-of-life vehicles (ELV) and construction and demolition waste (C&DW) is a technological and economic challenge. It is complicated by their composition, which includes many polymers with high levels of contamination, as well as the large costs of treatments and the continuous evolution of the related legal framework (Ardolino et al., 2021; Cardamone et al. 2022). Innovative treatments able to remove contained contaminants, so generating secondary plastics of good quality and reducing adoption of improper strategies, were recently proposed in a H2020 project (Nontox, 2021). The good environmental performances of management schemes utilising these treatments for WEEE/ELV/C&DW plastics were quantified by means of Environmental Life Cycle Assessments (E-LCAs) as described by Ardolino et al. (2021) and Cardamone et al. (2022). The potential social impacts of these management schemes have been the focus of the preliminary Social Life Cycle Assessment (S-LCA) described in this study. It was developed in agreement with UNEP guidelines (2020) and ISO standards (ISO 14040-44). The analysis maintained the basic assumptions of the E-LCAs, in particular saving the management of WEEE/ELV/C&DW plastics annually collected in Europe as the functional unit. The current management scheme of each of them, including waste-to-energy (WtE) by combustion, sanitary landfilling and substandard options, were compared with the possible future scheme, implementing also innovative treatments of physical recycling (CreaSolv® and Extruclean), plastic upgrading and catalytic pyrolysis. Please click Additional Files below to see the full abstract

Environmental impacts of a material recovery facility in a Life Cycle Perspective

The study aims to evaluate the environmental performances of an integrated material recovery facility (MRF), which has a crucial role in the waste management plan of a region in the middle of Italy, characterized by a low level (less than 20%) of household source separation and separate collection [1]. The facility, which is able to treat about 30 kt/y of mixed waste, has three main units: a mechanical sorting platform, bio-cells for tunnel composting, and a landfill. The output streams of the sorting platform are the ferrous metals and mixed plastics, which are sent to the recycling processes, the solid recovered fuel (SRF), which is utilized in an external combustion-based waste-to-energy plant, and a low-quality organic fraction, which is treated in the on-site composting unit. The solid residues generated by these processes are about a half of the input stream, and are disposed in the annexed landfill. The bio-cells for tunnel composting are in operation since 2014, and so far produces just a low-quality compost, utilized for landfill capping, and a leachate, sent to an external wastewater treatment plant (WTP). The landfill produces a leachate, which is treated in the WTP, and a biogas, which is collected (with an efficiency of about 60%), and sent to a gas engine, having an electric energy conversion efficiency of 38%. Please click Additional Files below to see the full abstract

About the Environmental Sustainability of the European Management of WEEE Plastics

A huge increase of waste of electrical and electronic equipment (WEEE) is observing everywhere in the world. Plastic component in this waste is more than 20% of the total and allows important environmental advantages if well treated and recycled. The resource recovery from WEEE plastics is characterised by technical difficulties and environmental concerns, mainly related to the waste composition (several engineering polymers, most of which containing heavy metals, additives and brominated flame retardants) and the common utilisation of sub-standard treatments for exported waste. An attributional Life Cycle Assessment quantifies the environmental performances of available management processes for WEEE plastics, those in compliance with the European Directives and the so-called substandard treatments. The results highlight the awful negative contributions of waste exportation and associated improper treatments, and the poor sustainability of the current management scheme. The ideal scenario of complete compliance with European Directives is the only one with an almost negligible effect on the environment, but it is far away from the reality. The analysed real scenarios have strongly negative effects, which become dramatic when exportation outside Europe is included in the waste management scheme. The largely adopted options of uncontrolled open burning and illegal open dumping produce huge impacts in terms of carcinogens (3.5·10+7 and 3.6·10+4 person·year, respectively) and non-carcinogens (1.7·10+8 and 2.0·10+6 person·year) potentials, which overwhelm all the other potential impacts. The study quantifies the necessity of strong reductions of WEEE plastics exportation and accurate monitoring of the quality of extra-Europe infrastructures that receive the waste

Can plastics from end-of-life vehicles be managed in a sustainable way?

Plastic from end-of-life vehicles (ELVP) are currently managed in European Union without any attention to polymer recovery. The study analyses novel treatments of sorting, dissolution/precipitation, extrusion, catalytic pyrolysis, and plastic upgrading, which could contribute to define a sustainable ELVP management scheme. The environmental performances of each of these treatments have been quantified by an attributional Life Cycle Assessment, allowing to compare a possible innovative recycling scheme with that of the European currently adopted options. The new scheme greatly enhances ELVP management performances, by hugely increasing annual amounts of polymers sent to recycling (from 26 kt/y up to 509 kt/y), drastically decreasing residues to be sent to combustion or landfill (from 984 kt/y down to 232 kt/y), and improving the impact of main environmental categories. Carcinogens, Non-Carcinogens, Global Warming and Non-Renewable Energy reduce of 138%, 100%, 42% and 114%, with reference to the current scenario. These promising results are mainly related to the utilisation of a dissolution/precipitation process (Crea-Solv®), whose introduction could allow recovering large part of target polymers (PE and PP). The recovery of PE in fuel tanks by a supercritical extrusion process (Extruclean) and the treatment of residues and non-target polymers by a catalytic pyrolysis process also contribute to improve the environmental performances. A sensitivity analysis quantifies the role of some key parameters, indicating that the results could be affected by energy consumption of dissolution/precipitation process, oil yield of catalytic pyrolysis treatment, but also by the substitutability factor utilised to quantify the avoided burdens associated to the recycled polymers

An alternative management scheme for plastics from construction & demolition waste

Construction and Demolition Waste (C&DW) is a priority stream in the circular economy agenda, since it accounts for more than a third of all wastes generated in the European Union. About 1.8 Mt/y of these C&DW are plastics, whose valorisation has to overcome several obstacles: i) Current legislation recycling targets are established in terms of total recycled mass (Iodice et al., 2021), hence can be easier obtained by focusing on heavy fractions, i.e. metals and inert materials; ii) Plastics in buildings are often embedded behind walls, under floors and inside roofs: this complicates their gathering and separation (EC, 2021); iii) C&DW plastics often contain substances of concerns, allowed in the past but restricted by the current legislation (Wagner and Schlummer, 2020): the long lifetime of plastics in buildings - from about 15 years up to, sometimes, 100 years – it is thus a further technical obstacle for recycling; iv) Recycling entails high costs and needs specific policy actions to be implemented, such as landfill ban and the creation of a competitive market for secondary raw material (Pantini and Rigamonti, 2020). These constrains make collection and management schemes complex and variable from country to country. Moreover, the rare utilisation of a selective demolition as alternative to a conventional demolition further worsens the quality of recoverable materials. Please click Additional Files below to see the full abstract

Combined Use of an Information System and LCA Approach to Assess the Performances of a Solid Waste Management System

A municipal solid waste information system, named W-MySir, is utilised to acquire high-quality data to implement an attributional life-cycle assessment (LCA) focused on the evolution of the environmental performances of municipal solid waste management in a specific area. The main aim was to investigate how this combined approach can be used for monitoring progress of the management scheme toward important targets, such as being CO2-neutral, increasing the circularity of the service, and planning a transparent approach to cost evaluation. The analysis was applied to the municipality of Procida, one of the three islands of Naples Bay (Italy), and focused on the last ten years of activity of the local solid waste service. The results of the life cycle impact assessment are reported in terms of the main impact categories. They indicate a positive evolution of the environmental performances, with improvements of up to 140% for global warming potential. The positive results are mainly due to the large increase in household source separation and separate collection in Procida during the period under analysis, together with the availability of a more integrated and sustainable regional system of solid waste management. Further improvements may be achieved through better performance at the sorting and remanufacturing stages of dry recyclable fractions and the availability of anaerobic digestion units to produce biomethane from organic fractions of municipal solid waste. The combined approach indicates potential further benefits for both the tools: LCAs could provide reliable results in shorter times; information systems could offer a wider spectrum of services for monitoring and planning waste management systems in a sustainable way

Technical and Environmental Performances of Alternative Thermochemical Treatments for Mixed Plastics Waste

There is a general and important effort to increase circularity of plastics, by proposing new behaviours and styles of life (“how to use and reuse plastics”), new eco-design criteria (“design for recycling” and “design from recycling”), innovative recycling processes able to increase the quantity and quality of recovered resources (“Plastics-to-Plastics” but also “to-Chemicals”, and “to-Fuels”). The attention in mainly focused on mixed plastics waste (MPW) whose treatment shows the major technical difficulties, due to the co-presence of various and generally non-compatible, polymers, with different kinds of additives, pigments and fillers. Please click Additional Files below to see the full abstract

Social life cycle assessment of innovative management schemes for challenging plastics waste

The focus is on current and innovative management schemes of plastics waste coming from electric and electronic equipment, end-of-life vehicles, and construction and demolition waste. Their complex compositions, due to the presence of several polymers, different (also hazardous) additives, and non-plastics fractions, make difficult finding sustainable management options. The study aimed at an assessment of social performances of currentmanagement schemes for these challenging plastics, compared with those of alternative schemes, including advanced innovative process options (dissolution/precipitation, supercritical fluid extraction with CO2, catalytic pyrolysis). A social life cycle assessment was developed at European level, by also exploiting synergies with parallel environmental analyses. The results indicated that innovative solutions could lead to good performances for human health ofworkers, but also for improvement of economies of local communities and society. The still limitedmaturity of proposed technologies would require a sufficiently long period of economic incentives to demonstrate process validity in the recovery of polymers, suitable to be accepted by the market. Accordingly, the estimated potential social effects should be further studiedwhen the proposed innovative processeswill be implemented at larger scale, to include aspects strictly related to the behaviour of a specific company going beyond the single process. Results contribute to define a complete set of environmental and social data and information, which can help European decision makers to define new criteria for sustainable management of the waste plastics of interest