LIFE CYCLE ASSESSMENT: A TOOL FOR EVALUATING AND COMPARING DIFFERENT TREATMENT OPTIONS FOR PLASTIC WASTES FROM OLD TELEVISION SETS

In the present work, energy recovery and mechanical recycling, two treatment options for plastic wastes from discarded television sets, have been assessed and compared in the context of the life cycle assessment methodology (LCA). The environmental impact of each option was assessed by calculating the depletion of abiotic resources (ADP) and the global warming potential (GWP). Then, the indicators were compared, and the option with the smaller environmental impact was selected. The main finding of this study was that mechanical recycling of plastics is a more attractive treatment option in environmental terms than incineration for energy recovery.


INTRODUCTION
At some point, all appliances, including television sets (TVs), require some form of end-of-life management.Thus, the question is not "if" we will manage these appliances, but "when" and "how" to reuse, recycle, or properly dispose of them.Figure 1 shows the composition of a TV set (Murakami, 2001) and the production in 2003 (Japan Almanac, 2005).
Generally speaking, good progress has been made in the recycling of discarded TV sets.The panel glass and funnel glass are recycled to make new cathode ray tubes.The steel and other metals are also recycled to make other new products.The plastic materials, on the other hand, are generally incinerated.
Several treatment options are considered when dealing with plastic wastes.At present, there are three main alternatives in addition to landfilling: (1) energy recovery (also know as thermal recycling), i.e. direct incineration of plastic wastes for energy recovery, (2) mechanical recycling (also known as material recycling), i.e. the method by which plastic wastes are recycled into new resources without affecting the basic structure of the material, and (3) feedstock recycling (also know as chemical recycling), i.e. the technique that breaks down polymers into their constituent monomers, which in turn can be used again in refineries or petrochemical and chemical production.
In the present work, the energy recovery (1) and the mechanical recycling (2) of the plastic wastes from discarded TV sets are assessed and compared in the context of the life cycle assessment methodology (LCA).

LCA METHODOLOGY
Life cycle assessment (LCA) is a method for evaluating the environmental performance of a product or process, starting from raw material extraction, through manufacture and final disposal (Fig. 2) (U.S. E.P. A., 1993;ISO 14040, 1997;Curran, 1996).
LCA is generally carried out in four steps: (1) goal definition and scope: (a) defining and describing the subject of the study, (b) determining the so-called "functional unit" f u , i.e. the unit of comparison that assures that the options to be compared provide an equivalent level of function or service, (c) specifying the processes required in the manufacture, use, and eventual disposal of the products, (d) developing a flow diagram of the processes to be evaluated, and (e) identify the boundaries and environmental effects to be reviewed for the assessment; (2) inventory analysis: identifying and quantifying energy, materials usage, and environmental releases (atmospheric emission, waterborne emissions, etc.) for the entire life-cycle; (3) impact assessment: assessing the human and ecological effects of energy, material usage, and the environmental releases identified in the inventory analysis; (4) interpretation: evaluating the results of the inventory analysis and assessing the impact of each option under investigation in order to select the preferred one.

Goal Definition and Scope
The first important step in carrying out the LCA was goal definition.In this work, two treatment options for plastic wastes generated from the efforts to recycle "old" TV sets have been considered: Option 1: incineration of plastic wastes for energy recovery (electricity production) Option 2: separation of plastic wastes for mechanical recycling.
To quantify the environmental impact associated with each recycling option, the functional unit was defined as  A simplified life-cycle of plastics for production of color TV sets, indicating the system boundary and describing the relation between processes involved, is shown in Fig. 3.A look at Fig. 3 shows that the life-cycle of plastics starts with the extraction of resources (crude oil, coal, etc) needed for production of electricity and the production of PS, PVC, and PE.Then, the plastics (PS, PVC, and PE) are used as raw materials in the manufacturing process for color TV sets.After being discarded, the "old" TV sets are collected.It is assumed that the collection rate of the discarded TV sets is 100 %.The discarded TV sets are then dismantled, and their parts are sorted for recycling purposes.The sorting process results in the production of a mixed plastic product.It is also assumed that the sorting process is able to recovery 100 % of plastics being used in TV set production.Finally, there are only two possible treatment options for plastic wastes: (1) direct incineration for electricity production (energy recovery) or (2) separation of plastics according to their types for reuse in production of TV sets (mechanical recycling).
It is important to note that (a) processes for production of steel, copper, and aluminum, (b) the process for production of TV sets, as well as (c) the process for collecting and dismantling TV sets followed by sorting their parts according to the type of materials have not been included in the following inventory analysis, as these processes have the same influence on the life-cycle of plastics, regardless of the treatment option under investigation.A second important simplification is that the landfilling of the incinerator ash was excluded from the analysis because of a lack of data.Moreover, the last important simplification was that transportation was also excluded from the inventory analysis, assuming that the incinerator together with the waste power generated and/or the facility for separation of plastics are located in the vicinity of the collection point for "old" TV sets, which on the other hand is located in the same area with the facility for the production of color TVs.

Inventory Analysis
Inventory analysis, known as life cycle inventory (LCI), is the second phase in LCA.It consists of quantifying energy and raw material requirements, atmospheric emissions, waterborne emissions, solid wastes, and other releases for the entire life cycle of the plastics for color TV sets.Steps of LCI are as follows: (a) collect data and (b) create a computer model to evaluate the environmental loads related to each option under investigation.The diagram shown in Fig. 3 provides the road map for data to be collected.The data on "manufacturing process of PS," "manufacturing process of PVC," "manufacturing process of PE," "production of electricity," and "manufacturing process of a TV set" were obtained from the LCA database of the Japan Environmental Management Association for Industry (JEMAI) (JEMAI On-line Database, 2005).The initial magnitudes of the flows entering or exiting these unit processes are given in Tables 1 -5.With regard to the incineration of plastics for energy recovery (option 1), the energy generated from the incineration of plastics has been calculated based on their calorific values (Table 6).Power generating efficiency from the incineration of plastics is considered to be 15% (PWMI, 2004).Furthermore, the emission of CO 2 gas during the incineration of plastics is considered to be 2.55 kg CO 2 / kg (MEJ, 2006).On the other hand, a two-stage dry process that combines triboelectric separation and air tabling has been proposed for the separation of plastic wastes prior to mechanical recycling (option 2).It should be also noted that the data on the separation process were from the experimental work carried out by the authors and published elsewhere (Dodbiba, 2003).Figure 4 shows the simplified flowsheet of the process.A triboelectric separator can be employed for the first stage of the process to collect a PS-rich positively charged fraction and a PE/PVC negatively charged fraction.In the second stage, the PE/PVC fraction can be separated by means of an air table, by taking advantage of differences in specific gravities.It was estimated that the electricity requirement for this process, which is able to collect ca.67 % of each plastic with a grade of 96 % or higher, is approximately 0.74 kWh/kg (Table 7).It is important to note that the rest of the plastics (middlings), which have not been recovered (i.e. less than 33 %), is not re-cycled in the system but is incinerated instead.In other words, the authors have chosen to calculate LCI for a mechanical recycling ratio (R M ) of 67 %.This was done in order to simplify the calculation of LCI.Nevertheless, should the recovery of plastics or the ratio of mechanical recycling be higher than 67 %, the middling can be re-processed to fulfill the requirement.
Next, the data on the processes are organized in vector notations in a way that resembles the classical input-output analysis (Leontief, 1970).The material balance principle and matrix algebra are combined to give an explicit formula (Heijungs, 1994): where g is the vector of the environmental loads; the matrix B represents the flow of environmental releases (CO 2 emission, etc.); the matrix A represents the flow of products and materials (electricity, materials usage, etc); the vector f (know as the demand vector) represents a special process where the functional unit (f u ) is the only output; the superscript -1 denotes that the matrix A is inverted.
The outcome of the inventory analysis (Eq. 1) is the vector g, which is a list containing the quantities g i of pollutants released to the environment and the amount of energy and materials consumed during the life-cycle of plastics, i.e.: The results of the inventory analysis for each treatment option under the evaluation are given in Table 8.

Impact Assessment
Impact assessment, known as life cycle impact assessment (LCIA), the third phase in LCA (Fig. 2) is comprised of the following issues: (a) selection of environmental impact categories, such as abiotic resources, global warming, etc., (b) classification: assigning LCI results (the environmental loads g i ) to the environmental impact categories (classifying CO 2 emissions to global warming, etc.), (c) characterization: expressing LCA results in a way that can be compared (comparing the global warming impact of CO 2 and CH 4 , etc.) and calculating the overall impact indicator of each impact category.
In this work, the environmental impact is assessed by calculating the impact indicator I j of the following categories: (1) abiotic resources, and (2) global warming.
The impact indicators I j are characterized using the following equations: In other words, the environmental loads g i of the substances grouped in a category are expressed in terms of equivalent units by multiplying them by a characterization factor ) ( j i k , (Eq. 3) (Guinee, 2002).The resulting impact indicators ) ( j i I are then aggregated to give an overall indicator I j of the environmental impact category,

Depletion of abiotic resources
Depletion of abiotic resources is assessed by calculating the ADP indicator (Eqs.3 and 4).The ADP indicator indicates the extraction of non-renewable raw materials such as naphtha, natural gas, petroleum, crude oil, etc.
Figure 5 shows the normalized ADP (i) indicators of various non-renewable raw materials extracted during the life-cycle of plastics needed for production of color TV sets.
A look at Figure 5 shows that the ADP (i) varies with the type of raw material and the treatment option for plastic wastes.It can be seen that naphtha is the resource depleted the most, consequently having the greatest environmental impact.It can also be seen that LNG and coal, which are used for production of electricity, have a relatively great environmental impact.The normalized indicators ADP (i) are then combined to calculate the overall impact indicator of abiotic depletion (ADP) for each treatment option, ADP=ΣADP (i) (Eq. 4).The results are given in Figure 6, which shows that separation of plastic wastes for mechanical recycling (option 2) has a lower environmental impact on the abiotic depletion when compared with incineration of plastics wastes for energy recovery (option 1).

Global warming
Global warming is assessed by calculating the global warning potential, GWP indicator (Eqs.3 and 4).The GWP indicator indicates the amount of greenhouses gases emitted into the Earth's atmosphere.Figure 7 shows GWP (i) indicators of various greenhouses gases emitted during the life-cycle of plastics needed for production of color TV sets.A look at Figure 7 shows that the GWP (i) varies with the type of greenhouse gas and the treatment option for plastic wastes.It can be seen that the emission of CO 2 has the greatest environmental impact.It can also be seen that CH 4 , which is mainly emitted during the production of PE, and NO 2 have a relatively great impact on global warming.
The normalized indicators GWP (i) are then combined to give the overall impact indicator of global warming (GWP) for each treatment option, GWP=ΣGWP (i) (Eq.4).The results are given in Figure 8, which shows that separation of plastic wastes for mechanical recycling (option 2) has a lower environmental impact on global warming.

Interpretation
Interpretation i.e. evaluation of results is the last phase of the LCA.The objective was to analyze results and reach conclusions based on the findings of the preceding phases of the LCA.

CONCLUSIONS
The energy recovery and the mechanical recycling of plastic wastes from discarded TV sets are compared in the context of LCA.The results show that energy recovery is an option that uses more resources and emits a larger quantity of greenhouse gases because of the incineration of plastic wastes.The separation of plastics for mechanical recycling, on the other hand, is a more effective alternative because it consumes less energy and fewer resources as well as having a lower environmental impact on global warming.

Superscripts -1
Indicates that the respective matrix should be inverted

"
10 years use of color TV sets", i.e. f u = 10 years.It is assumed that each TV set (screen: 25 inches; weight: 30 kg) contains 1.8 kg of PS, 1.05 kg of PVC and 0.30 kg of PE.Moreover, the number of discarded TV sets was considered to be 1.2 million sets per year, a number similar to that of the production of color TV sets in Japan in 2002(Japan Almanac, 2005).

Figure 3 .
Figure 3.A simplified life-cycle of plastics for TV sets, indicating the system boundary.

Figure 4 .
Figure 4. Simplified flowsheet of the process for separation of plastics according to their type.

Table 7 .
Electricity requirement for separation of plastics (option 2): system inputs

Table 8 .
Environmental loads, g i

Table 9 .
Table9compares both of the environmental indicators that have been calculated for each treatment option under the assessment.It can be seen that both ADP and GWP indicators of option 2 are smaller when compared with those of option 1.These results indicated that the separation of plastics for mechanical recycling (option 2) is a more environmental-friendly alternative for treatment of plastic wastes from discarded color TV sets.Comparing the environmental indicators for energy recovery and mechanical recycling The Ministry of Environment of (MEJ)(2006), A Manual for Calculation of Greenhouse Gases Emission, pp.VI-5.Available from internet: http://www.env.go.jp/earth/ghg-santeikohyo/manual/ (in Japanese) Guinee, J.B. (2002) Handbook of life cycle assessment.Kluwer Academic Publisher.Heijungs, R. (1994) A generic method for identification of option for cleaner product.Ecol.Econ., Vol. 10, pp.Japan Environmental Management Association for Industry (JEMAI) (2005) On-line Database.Available from internet: http://lcadb.jemai.or.jp/lca/servlet/DefaultLeontief, W. (1970) Environment repercussions and the economic structure: an input-output approach.Rev. Econ.Stat., Vol.52, No. 3, pp.262.Murakami, O. (2001) Technology for recycling plastic materials, Mitsubishi Electric, ADVANCE, pp.6-9.Plastic Waste Management Institute (PWMI) (2004) An introduction to plastic recycling, 2004.Available from internet: http://www2.pwmi.or.jp/ei/index.htm.U.S. Environmental Protection Agency.Office of Research and Development (1993) Life Cycle Assessment: Inventory Guidelines and Principles, EPA/600/R-92/245.