Effects of temperature zones on pyrolysis products of mixed plastic waste

Journal of Material Cycles and Waste Management - Five of the most prevalent plastics in the Chinese market (polypropylene (PP), polyvinyl chloride (PVC), high-density polyethylene (PE),...     

Cryo-comminution of plastic waste

Recycling of plastics is a big issue in terms of environmental sustainability and of waste management. The development of proper technologies for plastic recycling is recognised as a priority. To achieve this aim, the technologies applied in mineral processing can be adapted to recycling systems. In particular, the improvement of comminution technologies is one of the main actions to improve the quality of recycled plastics. The aim of this work is to point out suitable comminution processes for different types of plastic waste. Laboratory comminution tests have been carried out under different conditions of temperature and sample pre-conditioning adopting as refrigerant agents CO2 and liquid nitrogen. The temperature has been monitored by thermocouples placed in the milling chamber. Also different internal mill screens have been adopted. A proper procedure has been set up in order to obtain a selective comminution and a size reduction suitable for further separation treatment. Tests have been performed on plastics coming from medical plastic waste and from a plant for spent lead batteries recycling. Results coming from different mill devices have been compared taking into consideration different indexes for representative size distributions. The results of the performed tests show as cryo-comminution improves the effectiveness of size reduction of plastics, promotes liberation of constituents and increases specific surface size of comminuted particles in comparison to a comminution process carried out at room temperature.     

Combination of three-stage sink-float method and selective flotation technique for separation of mixed post-consumer plastic waste

The aim of this research was to separate the different plastics of a mixed post-consumer plastic waste by the combination of a three-stage sink-float method and selective flotation. By using the three-stage sink-float method, six mixed-plastic wastes, belonging to the 0.3-0.5 cm size class and including high density polyethylene (HDPE), polypropylene (PP), polyvinylchloride (PVC), polystyrene (PS), polyethylene terephthalate (PET) and acrylonitrile-butadiene-styrene copolymers (ABS) were separated into two groups, i.e., a low density plastic group (HDPE and PP) and a high density plastic group (PET, PVC, PS and ABS) by tap water. Plastic whose density is less than that of the medium solution floats to the surface, while the one whose density is greater than that of the medium solution sinks to the bottom. The experimental results elucidated that complete separation of HDPE from PP was achieved by the three-stage sink-float method with 50% v/v ethyl alcohol. To succeed in the separation of a PS/ABS mixture from a PET/PVC mixture by the three-stage sink-float method, a 30% w/v calcium chloride solution was employed. To further separate post-consumer PET/PVC and PS/ABS based on plastic type, selective flotation was carried out. In order to succeed in selective flotation separation, it is necessary to render hydrophilic the surface of one or more species while the others are kept in a hydrophobic state. In flotation studies, the effects of wetting agent, frother, pH of solution and electrolyte on separation were determined. The selective flotation results showed that when using 500 mg l(-1) calcium lignosulfonate, 0.01 ppm MIBC, and 0.1 mg l(-1) CaCl2 at pH 11, PET could be separated from PVC. To separate ABS from PS, 200 mg l(-1) calcium lignosulfonate and 0.1 mg l(-1) CaCl2 at pH 7 were used as a flotation solution. Wettability of plastic increases when adding CaCl2 and corresponds to a decrease in its contact angles and to a reduction in the recovery of plastic in the floated product.     

Pyrolysis of plastic packaging waste: A comparison of plastic residuals from material recovery facilities with simulated plastic waste

Pyrolysis may be an alternative for the reclamation of rejected streams of waste from sorting plants where packing and packaging plastic waste is separated and classified. These rejected streams consist of many different materials (e.g., polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS), aluminum, tetra-brik, and film) for which an attempt at complete separation is not technically possible or economically viable, and they are typically sent to landfills or incinerators. For this study, a simulated plastic mixture and a real waste sample from a sorting plant were pyrolyzed using a non-stirred semi-batch reactor. Red mud, a byproduct of the aluminum industry, was used as a catalyst. Despite the fact that the samples had a similar volume of material, there were noteworthy differences in the pyrolysis yields. The real waste sample resulted, after pyrolysis, in higher gas and solid yields and consequently produced less liquid. There were also significant differences noted in the compositions of the compared pyrolysis products.     

Biodegradability of degradable plastic waste.

Plastic waste constitutes the third largest waste volume in Malaysian municipal solid waste (MSW), next to putrescible waste and paper. The plastic component in MSW from Kuala Lumpur averages 24% (by weight), whereas the national mean is about 15%. The 144 waste dumps in the country receive about 95% of the MSW, including plastic waste. The useful life of the landfills is fast diminishing as the plastic waste stays un-degraded for more than 50 years. In this study the compostability of polyethylene and pro-oxidant additive-based environmentally degradable plastics (EDP) was investigated. Linear low-density polyethylene (LLDPE) samples exposed hydrolytically or oxidatively at 60 degrees C showed that the abiotic degradation path was oxidative rather than hydrolytic. There was a weight loss of 8% and the plastic has been oxidized as shown by the additional carbonyl group exhibited in the Fourier transform infra red (FTIR) Spectrum. Oxidation rate seemed to be influenced by the amount of pro-oxidant additive, the chemical structure and morphology of the plastic samples, and the surface area. Composting studies during a 45-day experiment showed that the percentage elongation (reduction) was 20% for McD samples [high-density polyethylene, (HDPE) with 3% additive] and LL samples (LLDPE with 7% additive) and 18% reduction for totally degradable plastic (TDP) samples (HDPE with 3% additive). Lastly, microbial experiments using Pseudomonas aeroginosa on carbon-free media with degradable plastic samples as the sole carbon source, showed confirmatory results. A positive bacterial growth and a weight loss of 2.2% for degraded polyethylene samples were evident to show that the degradable plastic is biodegradable.     

塑料废弃物的回收与再生

论述了国内外塑料废弃物回收再生技术的发展现状及各种回收再生方法的原理和特点,并分析了回收再生技术的主要发展方向和前景.     

Debromination of flame-retarded TV housing plastic waste

The thermal stability and degradation kinetics of TV housing plastic and brominated flame retardants were studied by means of thermogravimetry. The effects of the treatment temperature on the removal rate of Br were investigated using a tube furnace reactor under isothermal and vacuum conditions. The results showed that the weight loss of TV housing plastic was divided into two stages: the thermal degradation of brominated flame retardants mainly occurred at 290°–350°C, and the degradation of the high-impact polystyrene resin mainly occurred at 350°–455°C. Nearly 90% of Br can be removed from TV housing plastic when the treatment temperature exceeds 280°C.     

Land treatment and the toxicity response of soil contaminated with wood preserving waste

Soils contaminated with wood preserving wastes, including pentachlo-rophenol (PCP) and creosote, are treated at field-scale in an engineered prepared-bed system consisting of two one-acre land treatment units (LTUs). The concentration of selected indicator compounds of treatment performance included PCP, pyrene, and total carcinogenic polycyclic aromatic hydrocarbons (TCPAHs) was monitored in the soil by taking both composited soil samples at multiple points in time, and discrete soil samples at two points in time. The mean concentration of the indicator compounds and the 95-percent confidence interval (CI) of the composite and discrete samples agreed relatively well, and first-order degradation rate kinetics satisfactorily represented the mean chemical concentration loss of indicator compounds in the LTU. Toxicity of the soil, as measured by Microtox^TM assay of the soil extracts, indicated that toxicity reduction corresponded with indicator compound disappearance. No toxicity effects were observed with time in treated layers of soil (lifts) buried beneath highly contaminated lifts of newly applied soil. This indicated that vertical migration of soluble contaminants from such lifts had little effect on the microbial activity in the underlying treated soil.     

生活垃圾中废旧塑料的二次分选技术

由于城市垃圾中塑料品种繁杂、质量差,回收利用十分困难,国内外对于垃圾中的废旧塑料回收利用甚少。通过技术比选,确定采用多种分选技术的优势组合,以风力分选-X射线分选-光电分选相结合的组合工艺技术,实现对主要塑料品种PO,PS,PVC,PET等的有效分离,以加大废旧塑料的回收利用,减少环境污染,提高资源利用效率。     

Reuse of thermosetting plastic waste for lightweight concrete

This paper presents the utilization of thermosetting plastic as an admixture in the mix proportion of lightweight concrete. Since this type of plastic cannot be melted in the recycling process, its waste is expected to be more valuable by using as an admixture for the production of non-structural lightweight concrete. Experimental tests for the variation of mix proportion were carried out to determine the suitable proportion to achieve the required properties of lightweight concrete, which are: low dry density and acceptable compressive strength. The mix design in this research is the proportion of plastic, sand, water-cement ratio, aluminum powder, and lignite fly ash. The experimental results show that the plastic not only leads to a low dry density concrete, but also a low strength. It was found that the ratio of cement, sand, fly ash, and plastic equal to 1.0:0.8:0.3:0.9 is an appropriate mix proportion. The results of compressive strength and dry density are 4.14N/mm(2) and 1395kg/m(3), respectively. This type of concrete meets most of the requirements for non-load-bearing lightweight concrete according to ASTM C129 Type II standard.     

Using plastic bag waste to assess the reliability of self-reported waste disposal data

Direct waste analysis (DWA) and the material flows approach are the two standard methods to quantify aggregated waste streams and analyze waste composition. Yet, with the increasing application of producer responsibility measures, product-based waste data rather than aggregated waste data are becoming important. It is over this requirement that both approaches fail to some extent in delivering the type and quality of information that is needed. This study uses plastic bag waste as an illustration to show how self-reported questionnaire survey data may be used to assess disposal quantities of product-based waste types. The estimates from a large-scale questionnaire survey with over 4,100 completed cases were verified against DWA data of the same year in Hong Kong. It was found that self-reported data give systematically lower figures (on the order of 1.3-5 times) than those obtained from standard methods such as DWA for Hong Kong and the UK. However, it is demonstrated that self-reported data can be internally consistent. Also, the magnitude of underestimation may not be as considerable as it appears since the data from DWA are not themselves entirely accurate owing to the difficulties in obtaining a pure load of waste for field analysis and the variable moisture contents or contamination levels in waste material.     

Optimum source segregation bin for household solid waste and waste plastic recycling

Journal of Material Cycles and Waste Management - This research aims to conceptualize a source segregation bin for household waste and demonstrate the recyclability of waste plastic. Various...     

Telerobots for remote disposal of mixed waste

Two remote-controlled robotic submersible vehicles and an automated shredder are helping remove and dispose of highly reactive, sometimes explosive materials, dumped into a water-filled quarry at the U.S. Department of Energy's reservation in Oak Ridge, Tennessee. Human workers never enter the four-acre site, except for well-planned equipment maintenance and to shoot holes from a protected but into the retrieved containers, releasing pressure and exposing the contents to air and water. During its approximately two years of operation, the $8 million project has retrieved more than 15,000 items from the thirty feet of water at the bottom of the quarry.     

废旧塑料回收利用现状及问题

塑料制品在给人类带来便利的同时,也带来了极大的负效应,随着塑料使用量的大幅增加,废旧塑料由于难以自然降解,所造成的环境污染日趋严重。回收利用为处理废旧塑料垃圾开辟了减量化、无害化、资源化的道路。目前各国对废旧塑料回收利用都非常重视,投入大量人力、物力,乃至通过立法,开发各种废旧塑料回收利用的关键技术。综述了废旧塑料的回收和利用现状,以及国内近些年来废旧塑料处理和回收利用技术的研究进展及其发展趋势。     

Technical specifications for mechanical recycling of agricultural plastic waste

Technical specifications appropriate for the recycling of agricultural plastic wastes (APWs), widely accepted by the recycling industry were developed. The specifications establish quality standards to be met by the agricultural plastics producers, users and the agricultural plastic waste management chain. They constitute the base for the best economical and environmental valorisation of the APW.The analysis of the APW streams conducted across Europe in the framework of the European project “LabelAgriWaste” revealed the inherent characteristics of the APW streams and the inherent constraints (technical or economical) of the APW. The APW stream properties related to its recycling potential and measured during pilot trials are presented and a subsequent universally accepted simplified and expanded list of APW recycling technical specifications is proposed and justified. The list includes two sets of specifications, applied to two different quality categories of recyclable APW: one for pellet production process (“Quality I”) and another one for plastic profile production process (“Quality II”). Parameters that are taken into consideration in the specifications include the APW physical characteristics, contamination, composition and degradation. The proposed specifications are focused on polyethylene based APW that represents the vast majority of the APW stream. However, the specifications can be adjusted to cover also APW of different materials (e.g. PP or PVC) that are found in very small quantities in protected cultivations in Europe. The adoption of the proposed specifications could transform this waste stream into a labelled commodity traded freely in the market and will constitute the base for the best economical and environmental valorisation of the APW.     

Evaluating source separation of plastic waste using conjoint analysis

Using conjoint analysis, we estimated the willingness to pay (WTP) of households for source separation of plastic waste and the improvement of related environmental impacts, the residents' loss of life expectancy (LLE), the landfill capacity, and the CO(2) emissions. Unreliable respondents were identified and removed from the sample based on their answers to follow-up questions. It was found that the utility associated with reducing LLE and with the landfill capacity were both well expressed by logarithmic functions, but that residents were indifferent to the level of CO(2) emissions even though they approved of CO(2) reduction. In addition, residents derived utility from the act of separating plastic waste, irrespective of its environmental impacts; that is, they were willing to practice the separation of plastic waste at home in anticipation of its "invisible effects", such as the improvement of citizens' attitudes toward solid waste issues.     

Comparative environmental analysis of waste brominated plastic thermal treatments

The aim of this research activity is to investigate the environmental impact of different thermal treatments of waste electric and electronic equipment (WEEE), applying a life cycle assessment methodology. Two scenarios were assessed, which both allow the recovery of bromine: (A) the co-combustion of WEEE and green waste in a municipal solid waste combustion plant, and (B) the staged-gasification of WEEE and combustion of produced syngas in gas turbines. Mass and energy balances on the two scenarios were set and the analysis of the life cycle inventory and the life cycle impact assessment were conducted. Two impact assessment methods (Ecoindicator 99 and Impact 2002+) were slightly modified and then used with both scenarios. The results showed that scenario B (staged-gasification) had a potentially smaller environmental impact than scenario A (co-combustion). In particular, the thermal treatment of staged-gasification was more energy efficient than co-combustion, and therefore scenario B performed better than scenario A, mainly in the impact categories of "fossil fuels" and "climate change". Moreover, the results showed that scenario B allows a higher recovery of bromine than scenario A; however, Br recovery leads to environmental benefits for both the scenarios. Finally the study demonstrates that WEEE thermal treatment for energy and matter recovery is an eco-efficient way to dispose of this kind of waste.     

Valorization of post-consumer waste plastic in cementitious concrete composites

The sheer amount of disposable bottles being produced nowadays makes it imperative to identify alternative procedures for recycling them since they are non-biodegradable. This paper describes an innovative use of consumed plastic bottle waste as sand-substitution aggregate within composite materials for building application. Particularly, bottles made of polyethylene terephthalate (PET) have been used as partial and complete substitutes for sand in concrete composites. Various volume fractions of sand varying from 2% to 100% were substituted by the same volume of granulated plastic, and various sizes of PET aggregates were used. The bulk density and mechanical characteristics of the composites produced were evaluated. To study the relationship between mechanical properties and composite microstructure, scanning electron microscopy technique was employed. The results presented show that substituting sand at a level below 50% by volume with granulated PET, whose upper granular limit equals 5mm, affects neither the compressive strength nor the flexural strength of composites. This study demonstrates that plastic bottles shredded into small PET particles may be used successfully as sand-substitution aggregates in cementitious concrete composites. These new composites would appear to offer an attractive low-cost material with consistent properties; moreover, they would help in resolving some of the solid waste problems created by plastics production and in saving energy.     

Use of waste plastic in concrete mixture as aggregate replacement

Industrial activities in Iraq are associated with significant amounts of non-biodegradable solid waste, waste plastic being among the most prominent. This study involved 86 experiments and 254 tests to determine the efficiency of reusing waste plastic in the production of concrete. Thirty kilograms of waste plastic of fabriform shapes was used as a partial replacement for sand by 0%, 10%, 15%, and 20% with 800 kg of concrete mixtures. All of the concrete mixtures were tested at room temperature. These tests include performing slump, fresh density, dry density, compressive strength, flexural strength, and toughness indices. Seventy cubes were molded for compressive strength and dry density tests, and 54 prisms were cast for flexural strength and toughness indices tests. Curing ages of 3, 7, 14, and 28 days for the concrete mixtures were applied in this work. The results proved the arrest of the propagation of micro cracks by introducing waste plastic of fabriform shapes to concrete mixtures. This study insures that reusing waste plastic as a sand-substitution aggregate in concrete gives a good approach to reduce the cost of materials and solve some of the solid waste problems posed by plastics.