1. Introduction
Nowadays, due to urbanization and vast population growth around the world the environmental issues associated with vast production of different types of biomass and their conversion to value-added products have become more critical than ever [1], [2] and [3]. These environmental issues have different aspects which should be controlled by governments and local authorities. One of these aspects which has imposed a significant pressure on the environment and has turned into a controversial challenge worldwide is municipal solid waste (MSW) [4]. Although, the definition of MSW varies by country, it is generally defined as waste collected by municipalities or other local authorities and typically includes household waste, garden (yard)/park waste and commercial/institutional waste [5]. Accordingly, MSW is significantly under the influence of consumption habits and the patterns of the communities׳ developments and contains a wide variety of materials [6] and [7].
Moreover, since municipal activities yield the largest volume of wastes worldwide [4], therefore, there are many directives and legislation implemented to face this growing challenge. Examples of such legislations are directives of the European Parliament (2008/98/EC) and of the council of 19 November 2008 on waste, the best available techniques (BAT) reference documents that have been adopted under both intergovernmental panel on climate change (IPCC) directive (2008/1/EC) and Industrial emissions directive (IED), the resource conservation and recovery act (RCRA) for proper management of solid waste in U.S., waste disposal and cleaning law in Japan, national waste policy in Australia, etc. Although different by name but all these directives and legislations generally are identical for they include instructions and limitations for prevention (in waste generation), preparing for reuse, recycling, other types of recovery (including energy) and the disposal of waste [8]. In better words, they are aimed at protecting the environment and human health through prevention of harmful effects of waste generation and waste management.
Beside the legislative improvements over the past decades, different waste management options/technologies have also emerged around the world. For example, new methods for biological treatment of MSW, physico-chemical treatment of wastewaters, treatment of combustion ashes and flue-gas cleaning residues, treatment of waste contaminated with Polychlorinated Biphenyl (PCBs), treatment of waste oil/solvents, treatment of waste catalysts and some methods for incineration (grate incinerators, fluidized beds, rotary kilns, pyrolysis and gasification systems, etc.) [5] and [9]. Nevertheless, the lack of public acceptance for the location of new waste disposal and treatments facilities is still a problem due to concern about adverse effects on the environment and human health. This is ascribed to the fact that every step (from handling to final disposal or incineration) in waste treatment causes health issues through releasing pollutants into the air, soil and water [10]. On the other hand, decision making for waste management industry needs assessments in order to reduce the risk associated with human health and the environment.
Therefore, within such contexts, sustainable MSW management needs environmental assessment methods that evaluate waste treatment methods׳ environmental acceptability. Life cycle assessment (LCA) is a methodology capable of evaluating environmental pollution throughout the life cycle of a specific product and/or service on a cradle to grave basis [11]. LCA has been frequently used to evaluate and compare the environmental aspects of different MSW management strategies. The LCA findings have paved the way to sustainable development in waste management and have considered as inputs to decision-making in terms of the choice of waste management strategies. Table 1 summarizes a variety of LCA studies conducted on MSW management systems. However, most of the LCA studies conducted on MSW management suffer from malpractices in several aspects of LCA such as significant deficiencies in terms of their goal and scope definition e.g. unclear delimitation of the system boundaries. Other deficiencies include truncated impact coverage, difficulties in capturing influential local specificities such as representative waste compositions into the inventory, and a frequent lack of essential sensitivity and uncertainty analyses [12].