LCA Method & LCA inventory analysis
The LCA method was used for this study. The four steps for conducting an LCA were followed, namely goal and scope definition, inventory analysis, impact assessment and interpretation.26 Furthermore, sensitivity analysis was applied to evaluate the reliability of the results by varying some of the input data to determine the corresponding changes in the outputs. This helped to determine the significance and influences of selected data and evaluation methods on the LCA results.
Production phase of PET bottles
The PET bottles considered in this study were assumed to be produced from 100% virgin PET resins which are petroleum-based materials. Also, the bottle weight analysed included the weights of both the bottle cap (polypropylene) and label (low-density polyethylene). These assumptions are supported by previous research.7 Actual measurements were conducted to derive the weights of the bottles. The weights of the single-use and reusable bottles are 0.0203 kg (bottle 0.018; cap 0.002; label 0.0003) and 0.060 kg (bottle 0.055; cap 0.005), respectively. The bottle production processes involve the plastic resin production, preforms production and blow moulding into bottles. Considering that a 1-kg PET bottle requires 1.12 kg PET resin7 for production, a singleuse bottle production consumes about 0.0227 kg of virgin PET resins. Similarly, a reusable bottle consumes about 0.0672 kg of virgin PET resins. The data for the blow-moulding process were extracted from the EcoInvent 3.0 database on SimaPro. As reported before, the study adopted a functional unit of per person annually for the bottled water needs of an individual in South Africa. This was 10 single-use 0.5-L PET bottles as supported by use patterns, and an equivalent functional unit of 1 reusable 0.5-L PET bottle per person annually. Transportation of the bottle from the production plant was included in this phase. The transportation is a function of the weight of the goods and distance covered, calculated in kilogram-kilometre (kg-km) for all the routes.14 The bottle manufacturing firm is located in Modderfontein, South Africa. The impact data for the truck transportation were retrieved from the EcoInvent 3.0 database. A distance of 25.8 km was estimated from the bottle factory in Modderfontein to the water factory in Randburg, South Africa, for water filling of single-use bottles. Also, transportation of reusable bottles from Modderfontein to market in Johannesburg’s central business district was estimated at 23.1 km.
Use phase of PET bottles
The impacts associated with the service life of the single-use bottle include the injection of water into the bottle (filling), transportation of bottled water to the market, refrigeration at the market, transportation to homes and initial consumption by end-users. The impact data for the water injection and refrigeration processes were modelled with the EcoInvent 3.0 database. The weight of water to fill the 0.5-L PET bottle is 0.516 kg. The plastic film to package the set of 10 bottles of water weighs 0.0184 kg. Both the weights of the water and plastic film were derived by actual measurement. Furthermore, the refrigeration of the bottled water was set at 0.0374 kWh7 , and the electricity for water filling at 0.0098 kWh (1 BTU = 0.000293071 kWh of electricity). An estimated distance of 18.3 km was covered to transport bottled water from the water factory in Randburg to the market in Johannesburg’s central business district. For the reusable bottles, based on the actual supply chain, the impacts considered include transportation from the market to homes, initial consumption by filling with water, and the subsequent cleaning and reuse by end-users. Impact activities such as electricity for water filling and refrigeration were not considered as the real supply chain for reusable bottle in South Africa involves buying an empty bottle at the store and filling with water (which is usually tap or non-refrigerated water) at home or at designated places. The successive cleaning of the reusable bottle involves washing manually with a small volume of water, thus no electricity is involved. The water consumption for successive cleaning of a bottle is taken as half the bottle volume and the total is 2.5 L for the year. This assumption is supported by other studies.37,38 Also, the consumer vehicle transportation distance from the market in Johannesburg’s central business district to homes was estimated at 3.5 km.
Disposal phase of PET bottles
In modelling the disposal phase of the two PET bottles, the single-use PET bottles are considered to be disposed of after the initial consumption of the contents21, whilst the reusable PET bottles are assumed to be used repeatedly for one year and then disposed of, based on reports of random users. Water quality, bottle damage, aesthetics, new designs, etc. are expected to influence use patterns and shelf life. Approximately 90% of plastic bottle waste in South Africa ends up in landfills.9 The average distance from the waste disposal location to the Robinson Landfill Site in Turffontein Stafford, South Africa is 3.8 km. Furthermore, plastic waste is mostly polymeric and does not degrade for hundreds of years.32,39 However, plastic waste in landfill contributes to pollution and this was modelled in the software. The LCA inventory of all the activities and processes involved in the different phases of the life cycles of the single-use and reusable PET bottles is further presented in Table 2. The total distances covered by the single-use and reusable PET bottles from production to disposal are 51.4 km and 30.4 km, respectively.
LCA Impact Assessment The IMPACT 2002+ assessment
The IMPACT 2002+ assessment method in SimaPro 9 was used for the potential impact assessment of the PET bottles. This method has been used by other similar LCA studies7,38,40, as it gives a comprehensive assessment of the processes examined, and is also among the current and up-to-date LCA methodologies. The impact categories evaluated in this LCA study were carcinogens, non-carcinogens, global warming, ozone layer depletion, aquatic eutrophication, aquatic ecotoxicity, terrestrial ecotoxicity, respiratory organics, respiratory inorganics, terrestrial acidification/nutrification, aquatic acidification, non-renewable energy (primary), and land occupation. The carcinogens and non-carcinogens (kg C2 H3 Cl eq.) are related to the formation of chemical compounds that affect human health and the ecosystem. Global warming (kg CO2 eq.) is related to climate change, which is of public concern, and the environmental impact is assessed using greenhouse gases consisting of carbon dioxide, methane, nitrous oxide and other less prevalent gases. The ozone layer depletion (kg CFC11 eq.) impact is associated with the depletion of the ozone layer by chemical substances, as the ozone shields humans and organic matter from the ultraviolet radiation of the sun. The exposure to phosphorous compounds in the environment can be linked to aquatic eutrophication (kg PO4 P-Lim) and this negatively affects plants and organisms through oxygen deprivation. Respiratory organics (kg C2 H4 eq.) and inorganics (kg PM2.5 eq.) are environmental impact categories related to the formation of tropospheric ozone and are a threat to health and quality of life. Terrestrial and aquatic acidification (kg SO2 eq.) has to do with the release of chemicals such as sulfur dioxides into the environment, causing lower than normal pH, which affects the acidity of the ecosystem. Aquatic and terrestrial ecotoxicity refers to substances that are poisonous to organisms in the ecosystem when emitted. Non-renewable energy (MJ) is primary energy such as coal and petroleum which cannot be reused, within a particular period, after the initial use. Land occupation (m2 org.arable) is associated with land mass that has the capability of being ploughed for useful purposes such as agriculture.
Article TitleLife cycle assessment of single-use and reusable plastic bottles in the city of Johannesburg
Polyethylene terephthalate (PET) bottles of water have experienced huge growth in demand and sales in South Africa. This expansion in use creates challenges as well as opportunities for managing the life cycle impact. The properties that make PET desirable for fluid-containing bottles have also made it highly resistant to environmental biodegradation. Reusable plastic bottles are now marketed as a solution to reduce the impact of single-use plastic bottles. We assessed the life cycle impact of single-use PET bottles and an alternative, reusable PET bottle based on consumption patterns in South Africa and the material flow and supply chain in the urban environment. This robust consideration of local conditions is important in evaluating the life cycle impact. In an examination of 13 impact categories, the reusable PET bottle had lower impact than the single-use bottle in all the impact categories examined. The mass of PET bottle material required to deliver the water needs at any given time is a dominant factor on the environmental burden. Extending the life of reusable bottles and designing lighter weight bottles would reduce their life cycle impact. Information obtained in evaluating alternatives to plastic water bottles can be valuable for providing a foundation assessment for policymakers and plastic bottle manufacturers to make informed choices and to focus on improvements in life cycle impact.