The application of LCA to alternative methods for treating the organic fiber produced from autoclaving unsorted municipal solid waste: case study of Catalonia

Highlights

• Autoclaving is a new technology to treat unsorted municipal solid waste (MSW).

• We compare seven options to treat unsorted municipal solid waste.

• This research provides useful information to decision makers about ways to manage unsorted MSW.

• Autoclaving offers the possibility of recovering the valuable portion of mixed MSW.

• Autoclaving plus biological treatments yielded the best environmental performance.

Abstract

Despite efforts to increase the selective collection of municipal solid waste (MSW) in developed countries, the amount of unsorted waste remains high, with the consequent difficulty of material recovery and recycling. In 2010, 61% of the MSW generated in the European Union (EU) ended up in landfill and incineration facilities. Autoclaving is a novel technology that can be used to treat unsorted MSW, producing organic fibers that can be composted. The life cycle analysis (LCA) was used to assess the effectiveness of autoclaving unsorted MSW and various alternative methods for treating organic fibers produced through this process. The alternative methods that were considered included composting in tunnels, composting in confined windrow and composting in turning windrow as well as anaerobic digestion. The environmental assessment results were compared to those associated with incineration and landfill. The results of this study showed that autoclaving with sorting, digesting anaerobically and composting had the lowest impact values for eutrophication and the global warming potential. It was also found that autoclaving is justified only if the products of the process, that is, polyethylene terephthalate, ferrous and non-ferrous metals, are recycled to avoid virgin material production and if the remaining mixed plastic wastes are incinerated for energy recovery.

Introduction

The growing generation of municipal solid waste (MSW) due to population growth and new patterns of consumption is an important issue for European Union (EU) countries. Policies for managing MSW in a sustainable manner have been key components of EU directives. In Europe, policies for reducing the amount of waste sent to landfills have been significantly influenced by EU directives 1994/62/EC and 1999/31/EC (European Commission, 1994, EU, 1999). These directives limit the amount of degradable waste that can be sent to landfills as a proportion of the waste produced in 1995. Despite recent efforts to reduce the amount of solid waste sent to landfills, the landfilled MSW volume remains high. In the EU-27 countries, 37% of municipal waste was landfilled, 24% was incinerated and 39% was recycled or composted on average in 2010 (Eurostat, 2010). In Spain, the amount of waste sent to landfills was even higher; 58% (14 million tons) of the MSW generated in 2010 was deposited in landfills (Eurostat, 2010), and 75% of the total MSW was unsorted. In addition, the quantity of waste collected by selective management in Spain in 2009 was barely 13% (MAGRAMA, 2010). Thus, the development of new, more efficient technologies will be critical in allowing countries to comply with EU guidelines, promoting improved MSW management and reductions in the amount of waste sent to landfills. Such technologies may reduce the quantity of waste sent to landfills. During the last decade, the use of an emerging technology called autoclaving has been investigated for the pre-treatment of unsorted MSW. This technology is based on the autoclaving principles used for the sterilization of healthcare waste (Diaz et al., 2005). Autoclaving offers the possibility of recovering the valuable portion of mixed MSW (i.e., mixed waste that can be exploited for energy or materials after treatment). The first studies on autoclaving were conducted in the early 1980s (Eley et al., 1995). The main features of the autoclaving treatment were described by Papadimitriou (2007). It has been clearly noted that pre-treating unsorted MSW through autoclaving could be a solution for countries or regions where separate waste collection has not yet been implemented. It may also be a good solution for treating the rejected fraction of wastes produced by mechanical–biological treatment (MBT) plants.

Autoclaving can be described as a hydrothermal process, applied in wet environmental conditions at high pressure, whereby waste is treated using heat generated by saturated steam from a reactor. Autoclaving is an alternative to the treatment of unsorted municipal waste. Autoclaving can reduce the initial volume of treated waste, sterilize materials from pathogens, remove liquids, compact plastics, remove stickers on glass and plastic containers and provide other beneficial changes to the properties of treated waste. In addition, all biodegradable waste (e.g., paper and organic matter) is combined into a single fraction called organic fiber (OF). This OF has been recently studied for its biodegradability, following composting and anaerobic digestion (Stentiford et al., 2010, Trémier, 2006).

In this study, the OF produced through autoclaving was processed using aerobic and anaerobic digestion technologies. For this purpose, data from full-scale facilities that treat the organic fraction of municipal solid waste (OFMSW) located in Barcelona, Catalonia, were used. The full-scale facilities' technologies that were studied included composting in confined windrow (CCW), composting in tunnels (CT) and composting in turned windrow (TW) as well as anaerobic digestion of thermophilic and mesophilic ranges (ADC-M and ADC-T). Data on energy and emissions for these full-scale facilities were taken from previous studies by Cadena et al., 2009, Colón et al., 2012 and Pognani et al. (2012). The information from the ecoinvent database v2.2 was adapted to build the models for incineration and landfill technologies as alternatives for treating unsorted MSW.

The objective of this study was to identify techniques for managing unsorted MSW in a sustainable fashion. Therefore, the life cycle analysis was used to assess various biological technologies for treating OFs produced by autoclaving unsorted MSW. These technologies were further compared with two well-known traditional approaches, incineration and landfill.

Fig. 1 shows the different scenarios for waste treatment selected in this study. A total of seven scenarios were considered into the study. The first five are related to systems composed of autoclaving, sorting and the biological process (aerobic and anaerobic digestion) to treat the OF resulting from the autoclaving process. The last two scenarios refer to incineration and landfill technologies which were used as reference system to treat unsorted MSW. Incineration and landfill of 1 ton of unsorted MSW were compared with the first five systems (autoclaving + sorting + biological treatments). A full description of each technology and the main assumptions (i.e. technical considerations, efficiencies for energy recovery, etc.) are presented in the following sections. Many real case studies were found in the literature for the biological technologies (aerobic and anaerobic digestion) to treat the organic matter from MSW (Andersen et al., 2010, Boldrin et al., 2009, Cadena et al., 2009, Colón et al., 2010, Colón et al., 2012, Gentil et al., 2010, Gómez Palacios et al., 2002, Rigamonti et al., 2010, Sonesson and Bjo, 2000) but few related to autoclaving technology. The studies about the autoclaving are focused mainly in the technical conditions of operation and the OF characterization (Banks, 2008, García et al., 2012, Papadimitriou et al., 2008, Papadimitriou and Barton, 2009, Papadimitriou, 2010, Stentiford et al., 2010, Trémier, 2006). According to a literature review the current study is the only related with the environmental assessment of autoclaving technology and the OF resulting from this process. Furthermore several studies of real cases for incineration and landfill technologies, both for MSW treatment, were found in literature (Assamoi and Lawryshyn, 2012, Banar et al., 2009, Bilitewski, 2007, Bovea and Gallardo, 2010, Cherubini et al., 2009, Cleary, 2009, Diaz and Warith, 2006, Eriksson et al., 2005, Fragkou et al., 2010, Fruergaard et al., 2010, Galante et al., 2010, Kirkeby et al., 2007, Manfredi et al., 2011, Morselli et al., 2005).