Environmental assessment of a novel ionic-liquid based method for recycling of PVC in composite materials.

Waste PVC is scarcely recycled due to its high chlorine content and its use in composite materials, which reduces the applicability of conventional waste treatment methods, including thermal, mechanical and chemical recycling. For this reason, alternative treatment options are being developed to increase the recyclability of waste PVC. This paper focuses on one such option which utilises ionic liquids (ILs) for material separation and dehydrochlorination of PVC contained in composite materials. Taking blisterpacks used as a packaging for medicines as an example of a composite material, the paper presents for the first time the life cycle environmental impacts of this novel PVC recycling method, in comparison with thermal treatment (low-temperature pyrolytic degradation of PVC). Three ILs were considered for the PVC recycling process: trihexyl(tetradecyl)phosphonium chloride, bromide and hexanoate. The results suggested that the impacts of the process using the first two ILs were comparable, while the system with hexanoate-based IL had 7-229 % higher impacts. Compared to the thermal treatment of waste blisterpacks, the IL assisted process had significantly higher impacts (22-819 %) in all 18 categories considered due to the greater heat requirements and the IL losses. Reducing the latter would lower most impacts by 8-41 %, while optimising the energy requirements would reduce the impacts by 10-58 %. Moreover, recovering HCl would increase significantly the environmental sustainability of the process, resulting in net-negative impacts (savings) in most categories. Overall, these improvements would lead to lower or comparable impacts to those of the thermal treatment. The findings of this study will be of interest to the polymer, recycling and related industries, as well as to process developers.

Environmental sustainability in the food-energy-water-health nexus: A new methodology and an application to food waste in a circular economy.

Current studies on the food-energy-water nexus do not capture effects on human health. This study presents a new methodology for assessing the environmental sustainability in the food-energy-water-health nexus on a life cycle basis. The environmental impacts, estimated through life cycle assessment, are used to determine a total impact on the nexus by assigning each life cycle impact to one of the four nexus aspects. These are then normalised, weighted and aggregated to rank the options for each aspect and determine an overall nexus impact. The outputs of the assessment are visualised in a "nexus quadrilateral" to enable structured and transparent interpretation of results. The methodology is illustrated by considering resource recovery from household food waste within the context of a circular economy. The impact on the nexus of four treatment options is quantified: anaerobic digestion, in-vessel composting, incineration and landfilling. Anaerobic digestion is environmentally the most sustainable option with the lowest overall impact on the nexus. Incineration is the second best option but has a greater impact on the health aspect than landfilling. Landfilling has the greatest influence on the water aspect and the second highest overall impact on the nexus. In-vessel composting is the worst option overall, despite being favoured over incineration and landfilling in circular-economy waste hierarchies. This demonstrates that "circular" does not necessarily mean "environmentally sustainable." The proposed methodology can be used to guide businesses and policy makers in interpreting a wide range of environmental impacts of products, technologies and human activities within the food-energy-water-health nexus.

Assessing the economic and environmental sustainability of household food waste management in the UK: Current situation and future scenarios.

The value embedded in food waste is increasingly being recognised, with the UN targeting a 50% reduction in consumer food waste and the EU recycling of 60% of all household waste, both by 2030. Aiming to provide guidance on the most sustainable food waste utilisation routes, this study evaluates the life cycle environmental and economic sustainability of five plausible scenarios for the year 2030. Focusing on the UK for context, these are compared to the current treatment of food waste as well as to its potential future prevention. The scenarios consider a differing share of four widely-used treatment methods: anaerobic digestion, in-vessel composting, incineration and landfilling. The scenario with the highest anaerobic digestion share that recovers both heat and electricity is the best option for seven out of 19 environmental impacts and the second best for life cycle costs. Upgrading anaerobic digestion biogas to biomethane achieves the lowest global warming potential and life cycle costs. Net-negative global warming potential (savings) can be achieved if the heat from anaerobic digestion and incineration or biomethane are utilised to displace natural gas. Displacing a future electricity mix does not lead to significant global warming potential savings due to the expected grid decarbonisation. However, savings are still achieved for metal depletion and human and terrestrial toxicities as they are higher for decarbonised grid electricity due to the increased share of renewables. A greater share of in-vessel composting leads to higher impacts because of the high electricity consumption. Landfill reduction has an economic advantage for all the scenarios, except for the business-as-usual, with life cycle costs 11-75% lower than for the current situation. While future scenarios improve the overall sustainability compared to the current situation, halving food waste by 2030 can save 15 times more greenhouse gas emissions than the best treatment scenario without waste reduction. Therefore, any commitments to improve the sustainability of food waste treatment must be accompanied by an effective waste prevention strategy. The outcomes of this work can help waste treatment operators and policy makers towards more sustainable food waste management. Although the focus is on UK situation, the overall conclusions and recommendations are applicable to other regions.

Environmental and economic implications of recovering resources from food waste in a circular economy.

Around a third of food is wasted globally, requiring significant resources for its treatment and disposal, in addition to wasting valuable resources. Following the circular economy principles, this waste should ideally be avoided, and if not possible, treated to recover resources. This paper considers the life cycle environmental and economic implications of recovering energy and material resources from food waste, focusing on the UK situation. Four treatment methods are considered: anaerobic digestion, in-vessel composting, incineration and landfilling. The results show that per tonne of waste treated, anaerobic digestion has the lowest environmental impacts in 13 out of the 19 categories considered in the study, including net-negative global warming potential. In-vessel composting is the least sustainable option environmentally, in contrast to being preferred over incineration according to the circular economy principles. Incineration has the lowest life cycle costs (£71/t), while landfilling is the costliest option (£123/t). Managing the 4.9 Mt of food waste collected annually from UK households via the four methods generates 340,000 t CO2 eq. and costs £452 m, in addition to causing a number of other environmental impacts. However, it also saves 1.9 PJ of primary energy, primarily due to electricity generation through incineration. If all of this food waste was incinerated, £103 m and 360,000 t CO2 eq./year could be saved compared to current waste management, rendering incineration a carbon-negative technology. This would also result in savings in 14 other impacts, but would increase summer smog by 30% and metal depletion by 56%. The environmental benefits of incineration would be exceeded only if all food waste was treated by anaerobic digestion, which would save 490,000 t CO2 eq./year and produce 50% more electricity per tonne of waste than incineration. Anaerobic digestion would also lead to savings in 14 other impacts compared to the present situation, but would result in a four times higher acidification and three times greater emissions of particulate matter. In addition, it would save £251 m/year compared to the current costs. Nevertheless, prevention of avoidable food waste would realise far greater environmental and economic savings, estimated here at 14 Mt CO2 eq. and £10.7 bn annually.

Environmental sustainability of anaerobic digestion of household food waste.

Consumers are the leading producers of food waste (FW) in developed countries and the majority of household FW is still embedded in general waste where it is incinerated or landfilled. There is increasing awareness in the value of collecting FW as a separate waste stream for production of compost or recovery of energy through anaerobic digestion (AD). This study focuses on AD to evaluate the life cycle environmental sustainability of recovering energy and fertilisers from household FW in the UK. The analysis is carried out for two different functional units: i) treatment of 1 tonne of FW, which is compared to incineration and landfilling; and ii) generation of 1 MWh of electricity, which is compared to other electricity generation options. The former results in net negative greenhouse gas (GHG) emissions (-39 kg CO2-eq./t) and primary energy demand (-2 GJ/t) due to the displacement of grid electricity and mineral fertilisers. AD has lower impacts than both incineration and landfilling across 15 of the 19 impacts. However, the application of digestate to land and the release of ammonia and nitrates lead to higher marine eutrophication (ME), terrestrial acidification (TA) and particulate matter formation (PMF). For the second functional unit, AD electricity emits 203 kg CO2-eq./MWh, compared to 357 kg CO2-eq./MWh for the UK grid mix. Compared to renewables, such as wind and solar, AD electricity has lower energy demand, toxicity potentials and metal depletion. However, it has higher global warming potential, ME, TA and PMF. At the UK level, treating 4.9 Mt of kerbside FW collected annually could provide 0.37% of the national electricity demand and save 190,000 t CO2-eq./yr compared to the grid electricity. The digestate produced could displace 1% of industrial nitrogen fertilisers. Although small fractions of the national demands, they represent a valuable return from a largely unutilised waste stream and help towards implementation of a circular economy.

A novel methodology for assessing the environmental sustainability of ionic liquids used for CO2 capture.

Ionic liquids (ILs) have been proposed as suitable sorbents for CO2 capture because of their high CO2 absorption capacity, thermal stability, negligible vapour pressure and physico-chemical tunability. However, the environmental implications of ILs are currently largely unknown because of a lack of data. The issue is further complicated by their complex chemical structures and numerous precursors for which environmental data are scarce or non-existent. In an attempt to address this issue, this paper presents a new methodology for estimating life cycle environmental impacts of novel ILs, with the aim of aiding synthesis and selection of more sustainable CO2 sorbents. The methodology consists of four main steps: (1) selection of an appropriate IL and synthesis route; (2) construction of a life cycle tree; (3) life cycle assessment; and (4) recommendations for improvements. The application of the methodology is illustrated using trihexyltetradecylphosphonium 1,2,4-triazolide ([P66614][124Triz]), a promising IL for CO2 capture currently under development. Following the above steps, the paper demonstrates how the data obtained from laboratory synthesis of the IL can be scaled up to industrial production to estimate life cycle impacts and identify environmental hotspots. In this particular case, the main hotspots are the precursors used in the synthesis of the IL. Comparison of impacts with monoethanolamine (MEA), currently the most widely-used CO2 sorbent, suggests that [P66614][124Triz] has much higher impacts than MEA, including global warming potential. However, human toxicity potential is significantly higher for MEA. Therefore, the proposed methodology can be used to optimise the design of ILs and to guide selection of more sustainable CO2 sorbents. Although the focus is on ILs, the methodology is generic and can be applied to other chemicals under development.