Life cycle assessment (LCA) is a methodology to assess all the environmental impacts associated with a product, process or activity. According to ISO (International Organization for Standardization), LCA is divided into four phases: goal and scope definition, inventory analysis, impact assessment and interpretation (ISO, 1997). In this study, we dealt with the first two phases (goal and scope definition, inventory analysis). The impact assessment aims at understanding and evaluating the environmental impacts based on the inventory analysis, within the framework of the goal and scope of the study. In this phase, the inventory results are assigned to different impact categories, based on the expected types of impact on the environment. Finally, the interpretation phase where the inventory analysis and impact assessment results are discussed and the significant environmental issues are identified to reach conclusions and recommendations consistent with the goal and scope definition.
2.1. Goal definition and scoping The goal and scope definition is perhaps the most important component of an LCA since the study will be carried out according to the statements made in this phase. It defines the purpose of the study, the expected product of the study, the boundary conditions, and the assumption. Furthermore, a reference unit (functional unit), to which all the environmental impacts are related, has to be defined.
2.1.1. System boundary In Bangladesh, more than 80% of the rice is processed in villages and the rest is processed in commercial rice mills (Rahaman, Miah, & Ahmed, 1996). Commonly used local parboiling processes are vessel, small-boiler and medium boiler. It was also reported that there might be room to improve the small-boiler process (Roy, Shimizu, & Kimura, 2005). Therefore, among the local parboiling processes vessel and medium-boiler, and the untreated process were considered to evaluate the life cycle of rice. A complete life cycle study should include agricultural production, industrial refining, storage and distribution, packaging, consumption and waste management, all of which together comprise a large and complex system. It has been reported that agricultural LCAs often exclude production processes of medicine and insecticides, machines, buildings, and roads because of a lack of data. In this study, only the post-harvest phases (parboiling, dehusking, milling and cooking) of rice were considered. The life cycle of rice under different processing methods and the system boundary of this study, which are encircled by a broken line.
2.1.2. Functional unit The purpose of the functional unit (FU) is to provide a reference unit to which the inventory data are normalized. Definition of FU depends on the environmental impact category and aims of the investigation. In this study, the FU has been defined as the mass of the product, e.g., 1 ton of rice.
2.2. Inventory analysis and data collection An LCA starts with a systematic inventory, which quantifies the resources use, energy use, and environmental releases throughout the product life cycle being evaluated. The inventory analysis involves data collection on raw materials and energy consumption, emission to air and water, and solid waste generation. In this study, we compiled the data on resources consumption and air emission (CO2) in the rice life cycle.
2.2.1. Life cycle energy consumption The energy consumption in the life cycle of rice produced by local processes (vessel, small-boiler, medium-boiler and untreated processes) has already been reported where the energy consumption in the parboiling processes was measured at Gazole under Malda district in West Bengal, India (Roy et al., 2005). The eastern part of India (West Bengal) and Bangladesh share the same parboiling processes and type of energy for parboiling. In this study, energy consumption in the life cycle of rice produced by vessel, medium-boiler and untreated process were derived from the literature, excluding the energy consumption in the drying process because sun drying is the common practice in Bangladesh.
2.2.2. Air emission The emission factor for CO2 was derived from the literature and the following assumptions have been made to determine the CO2 emission in the life cycle of rice. These are: (i) biomass is the source of primary energy for all types of energy consumed in the life cycle of rice, except the diesel energy, (ii) IGCC technology (electricity efficiency: 43%; Gustavsson, 1997) was used to generate electricity, (iii) improved cookstove (ASTRA; efficiency: 30%; Bhattacharya et al., 1999) was used for cooking, (iv) rice husk used in parboiling and electricity generation was assumed to be the industrial use of biomass and biomass used for cooking is considered to be the domestic use of biomass.
2.3. Production cost of rice The cost and profit are the most important indicators in decision-making on an investment. The installation cost of parboiling plants, the market price of paddy, rice husk, broken grains and labor cost for parboiling treatment, cost of milling and the capacity of the parboiling plants were derived from the literature (Roy, Shimizu, Shiina, & Kimura, 2006). The processing capacity of the untreated process was assumed to be the same as the vessel process. Rice yield is an estimate of the quantity of rice (after milling) which can be produced from a unit of paddy and expressed in a percentage, i.e., milled rice yield = {(weight of rice kernels after milling)/(weight of paddy)} · 100, and head rice yield = {(weight of whole rice kernels after milling)/(weight of paddy)} · 100. The maximum head and milled rice yield were reported to be 68% and 70%, respectively, for parboiled rice, and these were 60% and 68%, respectively, for untreated rice (Roy, 2003), which have been used in this study to determine the production cost of rice produced by the local processes. Based on the monthly production capacities the production cost of rice was calculated by subtracting the value of excess rice husk and value of broken grains from the value of paddy, labor cost for parboiling, cost of milling, and the depreciation cost (straight-line depreciation at 10% interest rate). Saunders and Betschart (1979) reported that parboiled and untreated rice contains 15,440 and 15,190 kJ of energy per kilogram, respectively. Therefore, the production cost of rice was worked out for both per unit mass and energy. The production cost of rice was worked out for two scenarios: milled and head rice.