Recycled Fraction Research Articles

Modelling Recycling Targets: Achieving a 50% Recycling Rate for Household Waste in Denmark

Within the European Union (EU) a paradigm shift is currently occurring in the waste sector, where EU waste directives and national waste strategies are placing emphasis on resource efficiency and recycling targets. The most recent Danish resource strategy calculates a national recycling rate of 22% for household waste, and sets an ambitious goal of a 50% recycling rate by 2020. This study integrates the recycling target into the FRIDA model to project how much waste and from which streams should be diverted from incineration to recycling in order to achieve the target. Furthermore, it discusses how the existing technological, organizational and legislative frameworks may affect recycling activities. The results of the analysis show that with current best practice recycling rates, the 50% recycling rate cannot be reached without recycling of household biowaste. It also shows that all Danish municipalities will need to make efforts to recover all recyclable fractions, and that the increased recycling efforts of only selected municipalities will not be sufficient to reach the target.

The Influence of Extrusion Conditions on Mechanical and Thermal Properties of Virgin and Recycled PP, HIPS, ABS and Their Ternary Blends

Abstract A recyclable plastics waste stream of electrical and electronic equipment has previously been found to contain acrylonitrile-butadiene-styrene copolymer (ABS, ∼40 wt%), high impact polystyrene (HIPS, ∼40 wt%), polypropylene (PP, ∼10 wt%) and a rest fraction consisting mainly of other styrene-based thermoplastics. In this work, one virgin and one recycled ternary blend consisting of these three components were melt-blended in an extruder to study the influence of processing conditions on the mechanical and thermal properties. The aim of the work has been to understand the inherent compatibility between ABS, HIPS and PP without added compatibilisers, in order to investigate the recycling potential of a real recyclable WEEE plastics fraction. Favourable processing conditions with respect to tensile properties of the virgin blend were found at intermediate screw rotations (40 to 80 min−1) and relatively low barrel temperatures (170 to 220°C), which can be understood from the low onset of thermo-oxidative degradation at 200°C. The recycled blend and recycled ABS, HIPS and PP showed higher stiffness and yield stress, but lower elongation at break than the corresponding virgin materials. The stiffness and yield stress of the blends were found mainly to follow the rule of mixtures of their components while the elongation at break exhibited adverse characteristics indicating incompatibility between ABS, HIPS and PP. The significant variations in the elongation at break of the blends appeared to be due to the ABS component. Differential scanning calorimetry showed an additional melt peak for the recycled blend compared to the virgin blend, otherwise the transitions were similar. The additional peak could be assigned to polyethylene in the PP component. The onset of the thermo-oxidative degradation was found to be at almost 190°C in the case of the recycled blend, which was high considering that it was close to that of the virgin blend and higher than expected from the rule of mixtures of the recycled components.

Stochastic solution of population balance equations for reactor networks

This work presents a sequential modular approach to solve a generic network of reactors with a population balance model using a stochastic numerical method. Full-coupling to the gas-phase is achieved through operator-splitting. The convergence of the stochastic particle algorithm in test networks is evaluated as a function of network size, recycle fraction and numerical parameters. These test cases are used to identify methods through which systematic and statistical error may be reduced, including by use of stochastic weighted algorithms. The optimal algorithm was subsequently used to solve a one-dimensional example of silicon nanoparticle synthesis using a multivariate particle model. This example demonstrated the power of stochastic methods in resolving particle structure by investigating the transient and spatial evolution of primary polydispersity, degree of sintering and TEM-style images.

Physical properties of simulated galaxy populations at z = 2 – II. Effects of cosmology, reionization and ISM physics

We use hydrodynamical simulations from the OWLS project to investigate the dependence of the physical properties of galaxy populations at redshift 2 on the assumed star formation law, the equation of state imposed on the unresolved interstellar medium, the stellar initial mass function, the reionization history, and the assumed cosmology. This work complements that of Paper I, where we studied the effects of varying models for galactic winds driven by star formation and AGN. The normalisation of the matter power spectrum strongly affects the galaxy mass function, but has a relatively small effect on the physical properties of galaxies residing in haloes of a fixed mass. Reionization suppresses the stellar masses and gas fractions of low-mass galaxies, but by z = 2 the results are insensitive to the timing of reionization. The stellar initial mass function mainly determines the physical properties of galaxies through its effect on the efficiency of the feedback, while changes in the recycled mass and metal fractions play a smaller role. If we use a recipe for star formation that reproduces the observed star formation law independently of the assumed equation of state of the unresolved ISM, then the latter is unimportant. The star formation law, i.e. the gas consumption time scale as a function of surface density, determines the mass of dense, star-forming gas in galaxies, but affects neither the star formation rate nor the stellar mass. This can be understood in terms of self-regulation: the gas fraction adjusts until the outflow rate balances the inflow rate.

Energy recovery or material recovery for MSW treatments?

Whether to recycle the recyclable fraction in the MSW (municipal solid waste) or to incinerate it for energy recovery is a debating issue. In this paper we present a simple criterion to judge what type of waste components should be recycled or incinerated with energy recovery. According to the R1 formula presented by the waste framework directive (Directive 2008/98/EC of the European Parliament), this paper calculates the energy performances of MSW waste-to-energy plants currently operated in Taiwan firstly. By using the assumed value of energy recovery efficiency and carbon emission costs, we compare the treatment methods between recycling (material recovery) and energy recovery by the cost and benefit analysis, and examine the suitability of recycling for waste fractions of paper, food waste, PET, PVC, and plastic bags/films under a variety of scenarios. The results show that food waste is more appropriate to be treated by recycling while plastic bags/films are suggested to be incinerated with energy recovery.

Numerical optimization of steam cycles and steam generators designs for coal to FT plants

In this work, a recently developed optimization methodology for the design of heat recovery steam cycles (HRSCs) and steam generators (HRSGs) is applied to the design of steam cycles for two interesting coal to Fischer–Tropsch (FT) fuels plants: a FT synthesis process with high recycle fraction of the unconverted FT gases (CTL-RC-CCS) to maximize the production of liquid fuels, and a FT synthesis process with once-through reactor (CTL-OT-CCS). The analysis reveals that designing efficient HRSCs for the once-through FT plant is relatively straightforward, while designing the HRSC for plant CTL-RC-CCS is very challenging because the recoverable thermal power is concentrated at low temperatures (i.e., below 260°C) and only a small fraction can be used to superheat steam. In addition, it is necessary to establish whether it is advantageous to burn the FT off-gases in a boiler or in a gas-steam turbine combined cycle. For this reason, a detailed boiler model is developed and included into the optimization methodology. As a consequence of the improved heat integration, the electric efficiency of the two plants is increased by about 2 percentage points with respect to the solutions previously published.

Design of batch chromatography for separation of binary mixtures under reduced purity requirements

Two methods are presented for designing separation of binary mixtures in a batch chromatography column under reduced purity requirements such that no waste or recycle fractions are generated. The first one is based on the equilibrium theory of chromatography and requires adsorption isotherm parameters. The second one is a shortcut method that uses a single experimental or simulated design chromatogram as input and is recommended under strongly non-ideal conditions with significant dispersive effects. Both approaches allow prediction of the injection volume and the cut position that lead to given target purities. In principle, they apply for all systems with convex or concave isotherms. The applicability of the design methods is evaluated by using numerical simulations. Both design methods work the better the higher the column efficiency and the lower the purity constraints are.

An analysis of the composition and metal contamination of plastics from waste electrical and electronic equipment (WEEE)

The compositions of three WEEE plastic batches of different origin were investigated using infrared spectroscopy, and the metal content was determined with inductively coupled plasma. The composition analysis of the plastics was based mainly on 14 samples collected from a real waste stream, and showed that the major constituents were high impact polystyrene (42wt%), acrylonitrile–butadiene–styrene copolymer (38wt%) and polypropylene (10wt%). Their respective standard deviations were 21.4%, 16.5% and 60.7%, indicating a considerable variation even within a single batch. The level of metal particle contamination was found to be low in all samples, whereas wood contamination and rubber contamination were found to be about 1wt% each in most samples. In the metal content analysis, iron was detected at levels up to 700ppm in the recyclable waste plastics fraction, which is of concern due to its potential to catalyse redox reactions during melt processing and thus accelerate the degradation of plastics during recycling. Toxic metals were found only at very low concentrations, with the exception of lead and cadmium which could be detected at 200ppm and 70ppm levels, respectively, but these values are below the current threshold limits of 1000ppm and 100ppm set by the Restriction of Hazardous Substances directive.

Recycling of rare earths: a critical review

The rare-earth elements (REEs) are becoming increasingly important in the transition to a green economy, due to their essential role in permanent magnets, lamp phosphors, catalysts, rechargeable batteries etc. With China presently producing more than 90% of the global REE output and its increasingly tight export quota, the rest of the world is confronted with a REE supply risk. Mining companies are now actively seeking new exploitable REE deposits while some old mines are being reopened. Because of the absence of economical and/or operational primary deposits on their territory, many countries will have to rely on recycling of REEs from pre-consumer scrap, industrial residues and REE-containing End-of-Life products. REE recycling is also recommended in view of the so-called “balance problem”. For instance, primary mining of REE ores for neodymium generates an excess of the more abundant elements, lanthanum and cerium. Therefore, recycling of neodymium can reduce the total amount of REE ores that need to be extracted. Despite a vast, mostly lab-scale research effort on REE recycling, up to 2011 less than 1% of the REEs were actually recycled. This is mainly due to inefficient collection, technological problems and, especially, a lack of incentives. A drastic improvement in the recycling of REEs is, therefore, an absolute necessity. This can only be realized by developing efficient, fully integrated recycling routes, which can take advantage of the rich REE recycling literature. This paper provides an overview of this literature, with emphasis on three main applications: permanent magnets, nickel metal hydride batteries and lamp phosphors. The state of the art in preprocessing of End-of-Life materials containing REEs and the final REE recovery is discussed in detail. Both pyrometallurgical and hydrometallurgical routes for REE separation from non-REE elements in the recycled fractions are reviewed. The relevance of Life Cycle Assessment (LCA) for REE recycling is emphasized. The review corroborates that, in addition to mitigating the supply risk, REE recycling can reduce the environmental challenges associated with REE mining and processing.

Quantifying recycled moisture fraction in precipitation of an arid region using deuterium excess

ABSTRACTTerrestrial moisture recycling by evapotranspiration has recently been recognised as an important source of precipitation that can be characterised by its isotopic composition. Up to now, this isotope technique has mainly been applied to moisture recycling in some humid regions, including Brazil, Great Lakes in North America and the European Alps. In arid and semi-arid regions, the contribution of transpiration by plants to local moisture recycling can be small, so that evaporation by bare soil and surface water bodies dominates. Recognising that the deuterium excess (d-excess) of evaporated moisture is significantly different from that of the original water, we made an attempt to use this isotopic parameter for estimating moisture recycling in the semi-arid region of Eastern Tianshan, China. We measured the d-excess of samples taken from individual precipitation events during a hydrological year from 2003 to 2004 at two Tianshan mountain stations, and we used long-term monthly average values of the d-excess for the station Urumqi, which are available from the International Atomic Energy Agency–World Meteorological Organization (IAEA–WMO) Global Network of Isotopes in Precipitation (GNIP). Since apart from recycling of moisture from the ground, sub-cloud evaporation of falling raindrops also affects the d-excess of precipitation, the measured values had to be corrected for this evaporation effect. For the selected stations, the sub-cloud evaporation was found to change between 0.1 and 3.8%, and the d-excess decreased linearly with increasing sub-cloud evaporation at about 1.1‰ per 1% change of sub-cloud evaporation. Assuming simple mixing between advected and recycled moisture, the recycled fraction in precipitation has been estimated to be less than 2.0±0.6% for the Tianshan mountain stations and reach values up to 15.0±0.7% in the Urumqi region. The article includes a discussion of these findings in the context of water cycling in the studied region.

Municipal solid waste management for total resource recycling: a case study on Haulien County in Taiwan

This work presents the enforcement performance of recent Haulien County, Taiwan municipal solid waste (MSW) recycling management programs. These programs include: Mandatory Refuse Sorting and Recycling, Diverse Bulk Waste Reuse, Pay-as-you-Discharge, Total Food Waste Recycling, Restricted Use on Plastic Shopping Bags & Plastic Tableware, Recycling Fund Management, and Ash Reuse. These programs provide incentives to reduce the MSW quantity growth rate. It was found that the recycled material fraction of MSW generated in 2001 was from 6.8%, but was 32.4% in 2010 and will increase stably by 2-5% yearly in the near future. Survey data for the last few years show that only 2.68% (based on total MSW generated) of food waste was collected in 2001. However, food waste was up to 9.7% in 2010 after the Total Food Waste Recycling program was implemented. The reutilization rate of bottom ash was 20% in 2005 and up to 65% in 2010 owing to Ash Reuse Program enforcement. A quantified index, the Total Recycle Index, was proposed to evaluate MSW management program performance. The demonstrated county will move toward a zero waste society in 2015 if the Total Recycle Index approaches 1.00. Exact management with available programs can lead to slow-growing waste volume and recovery of all MSW.

Precious metals and rare earth elements in municipal solid waste – Sources and fate in a Swiss incineration plant

In Switzerland many kinds of waste, e.g. paper, metals, electrical and electronic equipment are separately collected and recycled to a large extent. The residual amount of municipal solid waste (MSW) has to be thermally treated before final disposal. Efforts to recover valuable metals from incineration residues have recently increased. However, the resource potential of critical elements in the waste input (sources) and their partitioning into recyclable fractions and residues (fate) is unknown. Therefore, a substance flow analysis (SFA) for 31 elements including precious metals (Au, Ag), platinum metal group elements (Pt, Rh) and rare earth elements (La, Ce, etc.) has been conducted in a solid waste incinerator (SWI) with a state-of-the-art bottom ash treatment according to the Thermo-Re® concept. The SFA allowed the determination of the element partitioning in the SWI, as well as the elemental composition of the MSW by indirect analysis. The results show that the waste-input contains substantial quantities of precious metals, such as 0.4±0.2mg/kg Au and 5.3±0.7mg/kg Ag. Many of the valuable substances, such as Au and Ag are enriched in specific outputs (e.g. non-ferrous metal fractions) and are therefore recoverable. As the precious metal content in MSW is expected to rise due to its increasing application in complex consumer products, the results of this study are essential for the improvement of resource recovery in the Thermo-Re® process.

Separability studies of construction and demolition waste recycled sand

The quality of recycled aggregates from construction and demolition waste (CDW) is strictly related to the content of porous and low strength phases, and specifically to the patches of cement that remain attached to the surface of natural aggregates. This phase increases water absorption and compromises the consistency and strength of concrete made from recycled aggregates. Mineral processing has been applied to CDW recycling to remove the patches of adhered cement paste on coarse recycled aggregates. The recycled fine fraction is usually disregarded due to its high content of porous phases despite representing around 50% of the total waste.This paper focus on laboratory mineral separability studies for removing particles with a high content of cement paste from natural fine aggregate particles (quartz/feldspars). The procedure achieved processing of CDW by tertiary impact crushing to produce sand, followed by sieving and density and magnetic separability studies. The attained results confirmed that both methods were effective in reducing cement paste content and producing significant mass recovery (80% for density concentration and 60% for magnetic separation). The production of recycled sand contributes to the sustainability of the construction environment by reducing both the consumption of raw materials and disposal of CDW, particularly in large Brazilian centers with a low quantity of sand and increasing costs of this material due to long transportation distances.

Measurement and analysis of carbon formation during diesel reforming for solid oxide fuel cells

Experiments and equilibrium analysis were conducted to study carbon formation during diesel reforming for a solid oxide fuel cell-based auxiliary power unit (APU) application. A photo-acoustic instrument provided direct measurements of solid carbon concentration in the reformer effluent stream, which could be correlated to reformate gas composition (as determined via mass spectrometer) and reformer temperature. These measurements were complimented by equilibrium calculations based upon minimization of total Gibbs free energy. It was determined that oxygen-to-carbon ratio (O/C), fuel utilization fraction and anode recycle fraction all influence the degree of carbon formation, and that once significant carbon concentration is measured, the reformer performance begins to show marked degradation. At a fixed operating point, lowering the reformer temperature produced by far the largest change in effluent carbon concentration. Systematic variation in O/C, fuel utilization and anode recycle revealed the interdependence among reformer temperature, effluent gas composition and carbon concentration, with a strong correlation between carbon and ethylene concentrations observed for [C2H4] > 0.8%. After each experiment, baseline reformer performance could be recovered by operation under methane partial oxidation (POx) conditions, indicating that reformer degradation results at least in part from carbon deposition on the reformer catalyst.

Life cycle assessment of a household solid waste source separation programme: a Swedish case study

The environmental impact of an extended property close source-separation system for solid household waste (i.e., a systems for collection of recyclables from domestic properties) is investigated in a residential area in southern Sweden. Since 2001, households have been able to source-separate waste into six fractions of dry recyclables and food waste sorting. The current system was evaluated using the EASEWASTE life cycle assessment tool. Current status is compared with an ideal scenario in which households display perfect source-separation behaviour and a scenario without any material recycling. Results show that current recycling provides substantial environmental benefits compared to a non-recycling alternative. The environmental benefit varies greatly between recyclable fractions, and the recyclables currently most frequently source-separated by households are often not the most beneficial from an environmental perspective. With optimal source-separation of all recyclables, the current net contribution to global warming could be changed to a net-avoidance while current avoidance of nutrient enrichment, acidification and photochemical ozone formation could be doubled. Sensitivity analyses show that the type of energy substituted by incineration of non-recycled waste, as well as energy used in recycling processes and in the production of materials substituted by waste recycling, is of high relevance for the attained results.

Evaluation of Hard Materials Using Eco-Attributes

Hard materials based on Alumina (AN), Silicon Carbide (SC), Boron Carbide/Nitride (BC/N), Zirconia (ZN), and alike are often used to produce abrasive grains and coat cutting tools. These materials improve the performance of grinding/machining operations by providing an enhanced productivity, a longer grinder/tool life, and a better surface finish. On the other hand, they might leave some burdens on the environment. Therefore, eco-attributes (i.e., energy consumption, CO2 emission, NOX/SOX emission, water usage, recycle fraction, etc.) of these hard materials should be used to make an informed decision. This study deals with this issue and provides an evaluation of AN, SC, BC/N, and ZN based hard materials in terms of CO2 emission, NOX emission, SOX emission, and water usage. The outcomes of this study are useful for analyzing grinding and other abrasive processes for achieving eco-manufacturing.

Theoretical analysis of steady state recycling chromatography with solvent removal

The possibility to enhance the process performance of steady state recycling (SSR) chromatography by removing solvent was investigated in the framework of the equilibrium theory. A method was developed to choose a priori the relevant cut times corresponding to arbitrary purity constraints and to predict the steady state of the process without performing dynamic simulations. The amount of fresh feed introduced per cycle and the injection width were identified as the only free operating parameters. A relationship was derived between the amount of fresh feed and the solvent removal capacity required to achieve the chosen purities. The performance of three different process configurations was analyzed: solvent removal applied to (I) the fresh feed, (II) the recycle fraction, and (III) their mixture. It was found that solvent removal facilitates treating more fresh feed per cycle than is possible in a conventional SSR process. In addition, it was shown that the three SSR-SR configurations have identical performance with the same operating parameters. In contrast, the configurations differ with respect to the maximum amount of fresh feed that can be processed per cycle, as well as to the range of feasible injection widths. It was shown that SSR with solvent removal can yield higher productivity and lower eluent consumption than an optimized batch chromatography process that employs solvent removal.

Processes affecting isotopes in precipitation of an arid region

The isotopic composition of precipitation has been measured in samples simultaneously collected during individual precipitation events at two neighbouring high-altitude stations (Houxia at 2100 m a.s.l. and Gaoshan at 3545 m a.s.l.) in the Tianshan Mts., northwest China. The observed changes of δ18O (δ2H) and deuterium excess with surface air temperature, altitude and season have been evaluated to derive information on the effects of subcloud evaporation and moisture recycling on the formation of precipitation and its isotopic composition under arid climatic conditions. Consulting the long-term monthly averages of ‘d’ excess and temperature of the nearest GNIP station Wulumuqi, a striking similarity was found with the results of the two high-altitude stations concerning the relation between ‘d’ excess and temperature. The ‘d’ excess-temperature plot of the Wulumuqi data shows an hysteresis effect which appears to signify seasonal changes in the interplay between subcloud evaporation and moisture recycling. Finally, for the first time a negative altitude gradient of the d excess has been found for all stations including two more GNIP stations in northwest China but far away from the study area. This ‘inverse altitude effect’ may manifest a decrease of the recycled fraction in air moisture with altitude.

AzTEC/ASTE 1.1-mm survey of the AKARI Deep Field South: source catalogue and number counts

We present results of a 1.1 mm deep survey of the AKARI Deep Field South (ADF-S) with AzTEC mounted on the Atacama Submillimetre Telescope Experiment (ASTE). We obtained a map of 0.25 sq. deg area with an rms noise level of 0.32-0.71 mJy. This is one of the deepest and widest maps thus far at millimetre and submillimetre wavelengths. We uncovered 198 sources with a significance of 3.5-15.6 sigma, providing the largest catalog of 1.1 mm sources in a contiguous region. Most of the sources are not detected in the far-infrared bands of the AKARI satellite, suggesting that they are mostly at z ~ 1.5 given the detection limits. We constructed differential and cumulative number counts in the ADF-S, the Subaru/XMM Newton Deep Field (SXDF), and the SSA 22 field surveyed by AzTEC/ASTE, which provide currently the tightest constraints on the faint end. The integration of the best-fit number counts in the ADF-S find that the contribution of 1.1 mm sources with fluxes >=1 mJy to the cosmic infrared background (CIB) at 1.1 mm is 12-16%, suggesting that the large fraction of the CIB originates from faint sources of which the number counts are not yet constrained. We estimate the cosmic star-formation rate density contributed by 1.1 mm sources with >=1 mJy using the best-fit number counts in the ADF-S and find that it is lower by about a factor of 5-10 compared to those derived from UV/optically-selected galaxies at z ~ 2-3. The fraction of stellar mass of the present-day universe produced by 1.1 mm sources with >=1 mJy at z >= 1 is ~20%, calculated by the time integration of the star-formation rate density. If we consider the recycled fraction of >0.4, which is the fraction of materials forming stars returned to the interstellar medium, the fraction of stellar mass produced by 1.1 mm sources decrease to <~10%.

Wet and dry cooling systems optimization applied to a modern waste-to-energy cogeneration heat and power plant

In Brescia, Italy, heat is delivered to 70% of 200.000 city inhabitants by means of a district heating system, mainly supplied by a waste to energy plant, utilizing the non recyclable fraction of municipal and industrial solid waste (800,000 tons/year, otherwise landfilled), thus saving annually over 150,000 tons of oil equivalent and over 400,000 tons of CO 2 emissions. This study shows how the performance of the waste-to-energy cogeneration plant can be improved by optimising the condensation system, with particular focus on the combination of wet and dry cooling systems. The analysis has been carried out using two subsequent steps: in the first one a schematic model of the steam cycle was accomplished in order to acquire a knowledge base about the variables that would be most influential on the performance. In the second step the electric power output for different operating conditions was predicted and optimized in a homemade program. In more details, a thermodynamic analysis of the steam cycle, according to the design operating condition, was performed by means of a commercial code (Thermoflex ©) dedicated to power plant modelling. Then the off-design behaviour was investigated by varying not only the ambient conditions but also several parameters connected to the heat rejection rate, like the heat required from district heating and the auxiliaries load. Each of these parameters has been addressed and considered in determining the overall performance of the thermal cycle. After that, a complete prediction of the cycle behaviour was performed by simultaneously varying different operating conditions. Finally, a Matlab © computer code was developed in order to optimize the net electric power as a function of the way in which the condensation is operated. The result is an optimum set of variables allowing the wet and dry cooling system to be regulated in such a way that the maximum power is achieved. The best strategy consists in using the maximum amount of heat rejection in the wet cooling system to reduce the operational cost of the dry one.