1. Introduction

Water dilutable (latex) paints are widely used all over the world as a backdrop to the campaign against solvent emissions. They are used for surface protection, beautification and rejuvenation. Latex paints are applied in residential and commercial indoor environments. They are also used in the painting of car bodies[1].

About 30 million litres of paint is sold in Alberta, Canada every year. 5-10% of these paints and over 1 million empty paint containers are disposed off annually in Alberta[2]. Similarly, over 16 million gallons of latex paint (WLP) is also disposed off in USA every year[3]. However, increasing awareness of the potential environmental and health risks posed by residual paints necessitated regulation of waste paint disposal. Some of these paints contain combustible materials, volatile organic compounds, lead, mercury, and other heavy metals[4 -7]. Consequently, municipalities are required to collect residual paints from households for proper waste management. For example, waste paint constitutes around 21.7% of the total hazardous waste (HZW) collected by municipalities in Ontario province every year. Waste latent paint alone constitutes 12% of the total HZW[8]. The good news about these waste paints is that many have potentials for reuse, recycling and recovery[9, 10]. Recyclability of waste paints is an indication that their human and environmental risks could be eliminated or minimized by recycling. The largeness of the amount of latex paint disposed annually indicated its high economic potential[11]. As a result of these potentials, a number of organizations are now involved in latex paint recycling. However, recycling of materials also has socio-economic and environmental implications. This necessitates an assessment of the net benefit (or cost) of recycling resources at the end of their useful lives[12]. This case study involved a number of forward looking individuals that sought and experimented how these old paints could be reprocessed, repackaged and reused for various applications. These individuals have been reprocessing and repackaging old paints for about ten years and they wanted to know the environmental worth of their paint recycling effort. They also want to know whether it is more environmentally sustainable to recycle latex paint than disposing it off in a landfill or not.

2. Methodology

Lifecycle Analysis (LCA) method was used for this study because it is a comprehensive and proven analytical tool for evaluating potential environmental burdens resulting from resource consumption and emissions by a product or process. It also enables us to assess product/process environmental impacts and to evaluate improvement opportunities that could be implemented to address areas of concerns[13-19]. The method consists of four iterative steps (Figure 1): goal and scope definition, inventory analysis, impact assessment, and interpretation.

Figure 1. An illustration of LCA process

The main purpose of this LCA study was to determine whether it is more environmentally sustainable to recycle latex paint than to dispose it off in a landfill. Other reasons for the project are:

• To evaluate the environmental burden associated with the monthly production of a recycled paint over their entire process lifecycle in order to identify the stage with the largest environmental impacts (hot spots)

• To identify impact category of greatest concern with the aim of finding ways of reducing the ecological footprint

2.2. Functional Unit and System Boundaries

The functional unit was defined as the mass of a monthly production of 12 colour recycled latex paint in two packages of 4, 10 and 18.9 litres. The company produces 60000 litres of recycled paint every month for sale to the clients. The monthly volume of recycled paint production is approximately 49,800kg by mass.

The system boundaries for the analysis are shown in Figure 2. The entire lifecycle was composed of the following stages:

- Old paint transfer from municipalities to the company’s recycling facility in Calgary

- Sorting and inspection of the paints to oil based paints, reusable latex paint, and unreusable latex paint

- Emptying of reusable latex paints into one of the 12 totes based on the paint colour

- Compression and transportation of metallic and plastic containers for recycling

- High speed mixing of each full tot of latex paint

- Filtration of the paints to remove particles and to comply with industry standard

- Storage tank mixing of the paints

- Packaging of the processed paints into 4, 10 and 18.9 litres containers

- Distribution of reprocessed latex paint to retailers

- Transportation of oil paints and unreusable latex paint for disposal in landfills

Figure 2. General flow scheme of paint recycling process

In addition to these main sequential processes, each stage of the process lifecycle included energy utilization. Allocation is not necessary in this case study because it is a single output process. In order to simplify the study, materials and emissions less than 0.01% of the functional unit were not included in the study. Production, maintenance and disposal of machinery and buildings as well as their environmental burdens were also excluded from the study. Non-material values, economic aspects, and human resources were also not considered.

Two dimensions of impact analyses were carried out: absolute impact analysis and comparative/relative impact analysis. The absolute impact analysis examined the potential environmental impacts of the recycled paint production on its own. The comparative analysis assessed the recycled paint production process in relation to avoided disposal and avoidance of the need to produce same amount of new virgin paint to replace the disposed old paint.

The comparative/relative impact analysis aspect of this study was based on the average composition, resource use and emissions from the various brands of residual latex paints used as input by the company.

Environmental impacts of packaging, distribution and disposal from the paint recycling process were excluded on the premise that new virgin paint production would require the same number and type of packaging. It was also reasoned that environmental impacts of distribution would be the same for the new virgin paints as well as for the recycled paint. This is because the company has the same client base. So, the impact would be the same if the company is to manufacture and/or distribute the same amount of new virgin paints that they are recycling. Furthermore, it was assumed that no other ingredient is added to the old paint materials in producing the recycled paint.

2.3. Lifecycle Inventory

Inventory data compilation was implemented by using database included in Simapro 7.2 software. Process specific data used for the analysis was collected from the paint recycling company. The primary data on material and energy use as well as solid waste emissions was collected from the company in 2011. Secondary data was obtained from literature and eco-invent database. Table 1 is a sample of inventory data for the paint recycling process. This conformed to the recommendation in [18].

2.4. Impact Assessment

Five categories of impact were considered for each dimension of the two impact analyses. The impact categories are global warming potential (GWP), ozone depletion potential (ODP), photochemical ozone creation potential (POCP), acidification potential (AP), and eutrophication potential (EP). All the inventory data that could be found on the available conversion tables and that are greater or equal to 100 mg were mapped into the affected impact categories. 100years time horizon conversion data were used for the characterization of inventory data for global warming and ozone depletion potentials. Conversion factors for average of three European countries were used for the POCP while maximum oxygen conversion data were used for eutrophication potential assessment.

3. Results and Discussion

This study was carried out to determine whether it is more environmentally sustainable to recycle latex paint than disposing it off in a landfill or not. Tables 3 and 4 showed the summary of lifecycle impact analyses of the inventory data collected for this task. Figure 3 showed the percentage contribution of each recycling process stage to individual impact category. Although there were LCA reports on paints, no report was found on LCA of latex paint recycling process that these results can be compared with[20, 21]. In addition, this study was not aim at process comparison. The following interpretation of the study results was based on ISO 14043.

3.1. Interpretation

The standard (ISO 14043) stipulated a three step process for LCA results interpretation: (i) identification of environmentally significant issues from the inventory data and from the lifecycle impact assessment results, (ii) evaluation of those significant issues, and (iii) drawing conclusion from the evaluated significant issues.

3.1.1. Identification Of Significant Issues

In determining environmentally significant issues, Carbon dioxide was found to be the most significant substance emitted. From the impact assessment table (table 2), it was discovered that global warming which causes climate change is the most significant environmental issue in the paint recycling process. The method and the data used for this study were evaluated and found to be consistent with the requirements of ISO 14040s.

3.1.2. Evaluation

Consistency and completeness of the LCA analysis steps taken were evaluated and they were found to be in conformity with the ISO 14043 standard. This was followed by evaluation of the contribution of each process stage to various impact categories. Figure 3 showed percentage contribution of each recycling process stage to various impact categories. One could see from table 3 that distribution stage of the process has an overwhelming influence on the total potential global warming impact of the process. Packaging is another stage of the recycling process that contributes most significantly to ozone depletion potential and photochemical ozone creation (i.e. photochemical smog) potential of the process.

3.1.3. Environmental Savings

To determine whether it is environmentally better to recycle than to dispose off residual latex paint in the landfill, the difference between total impact of landfilling the residual paint (EI_L) and the impact of the latex paint recycling process (EI_RP) was calculated. A lower value of EI_RP than EI_L showed that it is better to recycle than to landfill the paint. This calculation was done for each impact category. The results of the environmental costs and benefits calculation are in Table 3. The negative values indicate environmental benefits.

These results showed that recycling latex paint by the process brings significant savings in global warming and photochemical smog impacts. Moreover, the results also showed that recycling latex paint by the process leads to slight increase in eutrophication impact.

Table 1. Samples of Inventory data for the paint recycling process Data category Substances Unit Quantity Air Emission Ethane, 1,2-dichloro-1,1,2,2-tetrafluoro-, CFC-114 mg 62.422246 Air Emission Ethane, dichloro- mg 16.916128 Air Emission Ethane, hexafluoro-, HFC-116 mg 105.33392 Air Emission Ethanol mg 457.85147 Air Emission Ethene, chloro- mg 2.755309 Air Emission Ethyne mg 97.778655 Air Emission Methane, bromotrifluoro-, Halon 1301 mg 402.67409 Air Emission Methane, dichloro-, HCC-30 mg 1.5286144 Air Emission Methane, tetrachloro-, CFC-10 mg 4.2406896 Air Emission Methane, tetrafluoro-, FC-14 mg 948.00532 Air Emission Methane, trichlorofluoro-, CFC-11 mg 2.3633944 Air Emission Methanol mg 554.26237 Air Emission Acetic acid g 1.0406542 Air Emission Benzene g 39.607146 Air Emission Benzene, ethyl- g 2.2740594 Air Emission Butane g 78.048095 Air Emission Butene g 25.573004 Air Emission Dinitrogen monoxide g 335.09789 Air Emission Ethane g 23.853359 Air Emission Ethene g 775.88079 Air Emission Formaldehyde g 1.838449 Air Emission Heptane g 17.961586 Air Emission Hexane g 37.782941 Air Emission Methane kg 5.6203882 Air Emission Nitrogen oxides kg 32.189457 Air Emission Sulfur oxides kg 7.8781966 Raw materials Baryte, in ground kg 4.5590617 Raw materials Bauxite, in ground kg 9.690721 Raw materials Clay, bentonite, in ground kg 1.3143554 Raw materials Clay, unspecified, in ground kg 19.773079 Raw materials Coal, 18 MJ per kg, in ground kg 193.12426 Raw materials Coal, brown, 8 MJ per kg, in ground kg 107.61832 Raw materials Gas, mine, off-gas, process, coal mining/kg kg 1.4600093 Raw materials Iron, in ground kg 97.440142 Raw materials Lead, in ground kg 3.0827645 Raw materials Marl, in ground kg 105.16653 Raw materials Sand, unspecified, in ground kg 2.8753678 Raw materials Sodium chloride, in ground kg 41.46825 Raw materials Wood, dry matter kg 9.5688289

Table 2. Contribution of each process lifecycle stage to different impact category Process Lifecycle Stages Environmental Impact Categories Global Warming (GWP)kg CO2-eq Ozone Depletion (ODP)kg CFC 11-eq Photochemical Smog (POCP)kg C2H4 -eq Eutrophication (EP)max kg O2 -eq Old paint transfer 13952.4 0.00504 1.0334 198.151 Sorting/inspection 6402.7 0.00939 20.2009 52.46 High speed mixing 1220.9 0.00021 0.02711 7.90668 Filtration 732.5 0.00013 0.01627 4.74401 In-storage tank mixing 87.708 1.60E-05 0.00203 0.59324 Packag-ing 16444.5 0.02751 59.8931 141.647 Distri-bution 62772.9 0.02320 4.75451 907.159 Disposal 21147.2 0.01239 20.9182 168.956 Gross env. impacts of the process 122760.7 0.07789 106.846 1481.62

Table 3. Monthly environmental savings from the recycling process Process Lifecycle Stages Environmental Impact Categories GWP ODP POCP EP kg CO2-eq kg CFC 11-eq kg C2H4 -eq max kg O2 -eq Env. impacts of the process (excluding packag'g & distrib'n) 22396.2 0.01479 21.2797 263.86 Monthly env. savings from metal & plastic recycling -31,113.48 -0.0232 -16.44 -184.78 Monthly env. savings from latex paint recycling instead of disposal -61.905 -5.02E-05 -2963.6 -6.5267 Monthly env. savings from latex paint recycling instead of producing virgin paint -61.905 -5.02E-05 -2963.6 -6.5266 Total env. savings by avoiding landfill disposal, avoiding producing equivalent amount of virgin paint and carrying out container recycling -31237.3 -0.02 -5,943.6 -197.83 Net monthly env. benefits of paint recycling -8,841.1 -0.01 -5,922.3 66.02

Figure 3. Percentage contribution of each process stage to individual environmental impact

4. Conclusions

Considering various stages of the process across the four impact categories shown in Table 2, there is no one single process stage that have the most significant impact across the board. Packaging, distribution and disposal process stages are the three stages that require more urgent attention. This conclusion was based on the significance of their impact potentials in most of the impact categories. Recommended improvements for this process are reuse of recycled paint packaging containers, exploration of possible alternative onsite use of old paint fraction that is disposed off in the landfill, and alternative transportation method for the distribution of the recycled paint. Results of this work showed that paint recycling process has appreciable global warming potential which could cause climate change. Furthermore, it showed that paint recycling is not only economically wise but it is also ecologically beneficial. Recycling old paint has lower ecological footprint than sending old paint to the landfill for disposal and producing the same amount of virgin paint in replacement.