ارزیابی چرخه عمر تصفیه پسماندهای الکترونیکی Life cycle assessment of electronic waste treatment

Abstract Life cycle assessment was conducted to estimate the environmental impact of electronic waste (e-waste) treatment. E-waste recycling with an end-life disposal scenario is environmentally beneficial because of the low environmental burden generated from human toxicity, terrestrial ecotoxicity, freshwater ecotoxicity, and marine ecotoxicity categories. Landfill and incineration technologies have a lower and higher environmental burden than the e-waste recycling with an end-life disposal scenario, respectively. The key factors in reducing the overall environmental impact of e-waste recycling are optimizing energy consumption efficiency, reducing wastewater and solid waste effluent, increasing proper e-waste treatment amount, avoiding e-waste disposal to landfill and incineration sites, and clearly defining the duties of all stakeholders (e.g., manufacturers, retailers, recycling companies, and consumers). ۱٫ Introduction Electronic waste (e-waste) refers to waste generated from discarded electrical or electronic devices (e.g., cell phones, computers, TV, printers). Given the vast technological advancement and economic development in many countries in recent years, the volume of e-waste produced has significantly increased (Qu et al., 2013; Robinson, 2009). The current global production of e-waste is around 25 million tons per year (Robinson, 2009), with the greatest amount of e-waste imported in China (Chi et al., 2014). However, compared with e-waste recycling in developed countries, that in China suffers from a high occurrence of environmental pollution and low energy efficiency. One of the most important mineral resources, e-waste is traditionally recovered in China by workers with the use of open flames or hot plates as a convenient way to remove electronic components (Allsopp et al., 2006). The improper handling of e-waste releases heavy metals (e.g., lead, cadmium, mercury, and beryllium) and hazardous chemicals (e.g., dioxins, furans, polychlorinated biphenyl) that seriously deteriorate the atmosphere, water, and soil quality (Li et al., 2014; Xu et al., 2014) and thus affect human health (Liu et al., 2009). The potential environmental impacts generated by e-waste recycling are complex and involve multi-factorial participation (e.g., process, activity, and substances). In this regard, a systematic consideration of emission inventories and the environmental potential impacts caused by e-waste recycling is highly needed. Life cycle assessment (LCA) is a systematic approach to assess and quantify the environmental performance associated with all stages of a product creation, processes, and activities (ISO 14040, 2006). LCA can simultaneously, systematically, and effectively evaluate and identify environmental inventory, impact, key factors, decisions, optimization, and improvement opportunities associated with all stages of system boundary. Several studies have analyzed the environmental impact of e-waste treatment on the environment via LCA (Song et al., 2012; Niu et al., 2012). Song et al. (2012) investigated e-waste treatment by using emergy analysis combined with the LCA method for a trial project in Macau. Their results showed that recovery of metals, glass, and plastic from e-waste can generate environmental benefits. Niu et al. (2012) compared three cathode ray tube (CRT) display treatment scenarios (i.e., incineration, manually dismantling, and mechanically dismantling) via LCA by using literature review. Their results showed that the incineration of CRT displays has the greatest impact, followed by mechanical dismantling. Despite their scientific contributions, the aforementioned studies are unclear as to whether direct air, water, and soil emissions from the industry site of e-waste recycling are included in the calculation of results. Inventory databases are also variable in terms of regionalization, geography, and uncertainties involved. However, in the aforementioned studies, no regionalized database was selected to determine the environmental effects of e-waste in China. Most data were collected from European database (Ecoinvent centre, 2010). Therefore, accurate results for Chinese case studies are difficult to obtain. The quantification and communication of uncertainties related to LCA results are also vital for their correct interpretation and use. However, most LCA experts, including the authors of the aforementioned studies, still conduct LCA without considering uncertainties. The environmental impact generated from informal recycling processes should also be quantified because substantial e-waste in China is recycled by individual workshops (Lin and Liu, 2012). In this regard, the current study aims to address the aforementioned needs, identify the key factors to improve the processes in the Chinese e-waste recycling industry, characterize and compare two e-waste recycling technologies commonly applied in China, and introduce a Chinese e-waste recycling database. ۲٫ Scope definition ۲٫۱٫ Functional unit In this study, the management of 1 ton of e-waste (i.e., computer and television) is selected as the functional unit to provide a quantified reference for all other related inputs and outputs. All air, water, and soil emissions, raw materials and energy consumption, and waste disposal are based to this functional unit. ۲٫۲٫ System boundary System boundaries were set by application of a gate-to-gate approach. Two scenarios commonly used in China were considered in this study, namely, e-waste treatment with end-life disposal (ET-D) and e-waste treatment without end-life disposal (ET-ND). Fig. 1a presents the system boundary and mass flow for the ET-D scenario. The ET-ND scenario is simpler than the ET-D scenario because the pollutant control system is commonly excluded in the ET-ND scenario in many individual workshops (Fig. 1b). The ET-D scenario involves raw materials and energy production; road transportation of raw materials to the e-waste treatment site; direct air, water, and soil emissions during e-waste treatment processes (i.e., classification, disassembly, crush, electrodialysis, and metal refining); and waste disposal (i.e., on-site wastewater and air pollution treatment, landfill and leachates treatment, incineration). To simplify the LCA analysis of the ET-D and ET-ND scenarios, the common process of e-waste collection to the e-waste treatment site is excluded. The infrastructure (i.e., construction and equipment) process is also excluded because of the lack of information from selected e-waste treatment sites. Moreover, infrastructure provides a minimal overall contribution to the potential environmental impact (Ecoinvent centre, 2010).