Forecasting quantities of critical raw materials in obsolete feature and smart phones in Greece: A path to circular economy.

Mobile phones represent an ever-increasing waste stream due to the increasing ownership and short lifetime. In particular, smartphones are among the most valuable e-waste because of their extremely high content of numerous key metals, specifically in the printed circuit board and magnets. As feature and smart phones contain different key metals at different concentrations, it is important to distinguish between the two phone types to make reliable estimations. This study presents estimations of obsolete mobile phones quantities, generated in Greece in 1995-2035 and the Critical Raw Materials (CRMs) and Precious Metals (PMs) embedded in them, making a differentiation between feature and smart phones. The dynamic material flow analysis is adopted, the lifespan is evaluated by the Weibull distribution and future sales are predicted by the logistic model incorporating phases of growth, saturation and decline. Then, the future wastes are predicted by the Market Supply A model. According to the results, the generation of obsolete smartphones is constantly increasing, while the waste flows of feature phones are declining. Efficient recycling of obsolete phones (1995-2020) can cover the demand for key metals (Au, Pd, Co) in the new smartphones for more than a decade in Greece, while the demand for Ag, Sb, Si, Zn, Be, Ti will be covered for more than 15 years. In 2020-2035 the accumulated amounts of CRMs and PMs, only from the smartphone waste, will be 1292.02 and 14.11 tonnes, respectively. The findings can contribute to the management of a valuable e-waste category closing the loop between resources-products-wastes.

Technical and environmental assessment of laboratory scale approach for sustainable management of marine plastic litter.

Laboratory scale recycling of marine plastic litter consisting of polyethylene terephthalate (PET) bottle sorting, pyrolysis and chemical vapor deposition (CVD) was conducted to identify the technical and environmental implications of the technology when dealing with real waste streams. Collected seashore and underwater plastics (SP and UP, respectively) contained large quantities of PET bottles (33.2 wt% and 61.4 wt%, respectively), suggesting PET separation was necessary prior to pyrolysis. After PET sorting, marine litter was converted into pyrolysis oil and multi-walled carbon nanotubes (MWCNTs). Water-based washing of litter prior to pyrolysis did not significantly change the composition of pyrolysis products and could be avoided, eliminating freshwater consumption. However, distinct differences in oil and MWCNT properties were ascribed to the variations in feedstock composition. Maintaining consistent product quality would be one of challenges for thermochemical treatment of marine litter. As for the environmental implications, life cycle assessment (LCA) demonstrated positive benefits, including improved climate change and fossil depletion potentials. The highest positive environmental impacts were associated with MWCNT production followed by pyrolysis oil and PET recovery. The benefits of proposed approach combining PET sorting, pyrolysis and CVD allowed to close the waste loop by converting most of the marine litter into valuable products.

Transformation behaviors and environmental risk assessment of heavy metals during resource recovery from Sedum plumbizincicola via hydrothermal liquefaction.

Environmentally sound disposal of hyperaccumulator harvests is of critical importance to industrialization of phytoremediation. Herein, transformation behaviors and environmental risk of heavy metals were comprehensively examined during subcritical hydrothermal liquefaction of Sedum plumbizincicola. It is concluded that low temperature liquefaction favored resource recovery of heavy oil and hydrochars in terms of higher energy density, improved carbon sequestration and less energy consumption. Heavy metals were mainly distributed into hydrochars and water soluble phase with less than 10% in heavy oil. All metal elements except As could be accumulated in hydrochars by extending reaction time, whereas more than 96% of As was redistributed into water soluble phase. Prolonged liquefaction time facilitated immobilization of Cd, Cr and As in hydrochars, but fast liquefaction favored Pb stabilization. Liquefaction significantly reduced environmental risk level of Cd, Zn and As, but may mobilize Pb and Mn, especially for Mn to very high risk level at 240 ºC. High temperature with long reaction time tended to inhibit leaching rate of Mn, whereas low liquefaction temperature with short reaction time prevented the leaching of Zn and As from hydrochars. Overall, these findings are essential for downstream upgrading of heavy oil and metals recovery from hydrochars.

Environmental impact assessment of converting flexible packaging plastic waste to pyrolysis oil and multi-walled carbon nanotubes.

A solution to low recycling rates of plastic waste is the conversion into multi-walled carbon nanotubes (MWCNTs) that have high value and can create additional revenue for plant operators. The purpose of this study was to perform a life cycle assessment (LCA) of an integrated system that involves flexible packaging plastic waste (FPPW) pyrolysis, oil upgrading, and MWCNTs production. The objectives were to determine the environmental impact of MWCNTs synthesis from non-condensable pyrolysis gases, and to assess the environmental impact of MWCNTs synthesis from different plastic fractions. Integrating MWCNTs synthesis to the plastic pyrolysis process provides various environmental benefits including, reduction of contribution towards climate change, fossil depletion, human toxicity (cancer), and ionizing radiation potentials. Sensitivity analysis of MWCNTs yields provided the range of impacts on the environment and a critical yield of >2% for most impact categories was determined. Comparison of different plastic fractions indicated that using low PET content feedstock had lesser impact on the environment, and demonstrated comparable performance to mixed virgin plastics for most impact categories. The results highlighted the versatility of the integrated pyrolysis process for treating diverse plastic waste fractions with negligible effects from the impurities present in the actual FPPW during thermal processing.

Environmental life cycle assessment of different domestic wastewater streams: policy effectiveness in a tropical urban environment.

To enhance local water security, the Singapore government promotes two water conservation policies: the use of eco-friendly toilets to reduce yellow water (YW) disposal and the installation of water efficient devices to minimize gray water (GW) discharge. The proposed water conservation policies have different impacts on the environmental performance of local wastewater management. The main purpose of this study is to examine and compare the impacts of different domestic wastewater streams and the effectiveness of two water conservation policies by means of life cycle assessment (LCA). LCA is used to compare three scenarios, including a baseline scenario (BL), YW-reduced scenario (YWR) and GW-reduced scenario (GWR). The BL is designed based on the current wastewater management system, whereas the latter two scenarios are constructed according to the two water conservation policies that are proposed by the Singapore government. The software SIMPARO 7.3 with local data and an eco-invent database is used to build up the model, and the functional unit is defined as the daily wastewater disposal of a Singapore resident. Due to local water supply characteristics, the system boundary is extended to include the sewage sludge management and tap water production processes. The characterization results indicate that the GWR has a significant impact reduction (22-25%) while the YWR has only a 2-4% impact reduction compared with the BL. The contribution analysis reveals that the GW dominates many impact categories except eutrophication potential. The tap water production is identified as the most influential process due to its high embodied energy demand in a local context. Life cycle costing analysis shows that both YWR and GWR are financially favorable. It is also revealed that the current water conservation policies could only achieve Singapore's short-term targets. Therefore, two additional strategies are recommended for achieving long-term goals. This study provides a comprehensive and reliable environmental profile of Singapore's wastewater management with the help of extended system boundary and local data. This work also fills the research gap of previous studies by identifying the contribution of different wastewater streams, which would serve as a good reference for source-separating sanitation system design.

Transport of cadmium and assessment of phytotoxicity after electrokinetic remediation.

The use of ethylene diamine tetraacetic acid (EDTA) on the electrokinetic removal of cadmium-contaminated soil was evaluated. A total of four different tests were conducted using EDTA as a washing solution as well as a purging solution at the electrode compartments. The efficiency of electrokinetic extraction was significantly influenced by the pH of the soil medium. The results show that EDTA was effective in desorbing cadmium at a high pH, with Cd-EDTA(-) anion complexes migrating toward the anode. At low pH values near the anode area, cadmium existed as Cd(2+), migrating toward the cathode. Such contradicting directions of cadmium have resulted in its detrimental removal from the soil cell. However, accumulation of cadmium near the cathode was observed at the end of the tests due to the dominating low pH in the soil cell. The phytotoxicity after the electrokinetic process was investigated using Sorghum saccharatum, Lepidium sativum and Sinapis alba plants. The germination index was a major endpoint estimated by measuring seed germination and shoot elongation. The results obtained show that the phytotoxicity was increased after electrokinetic extraction. Despite, the extensive cadmium removal from two-thirds of the cell, the low pH of the soil was the principal parameter exhibiting the phytotoxicity.