A Life Cycle Assessment to Compare Composting Schemes for the Treatment of Municipal Solid Waste in Mumbai, India

A LIFE CYCLE ASSESSMENT TO COMPARE COMPOSTING SCHEMES FOR THE TREATMENT OF MUNICIPAL SOLID WASTE IN MUMBAI, INDIA

BHUPENDRA K. SHARMA, MUNISH K. CHANDEL*

Centre for Environmental Science and Engineering, Indian Institute of Technology Bombay, Powai, Mumbai, INDIA. *Corresponding author: [email protected]

SUMMARY: Most of the municipal solid waste (MSW) in India is disposed in uncontrolled dumpsites, posing a serious challenge to environment and sustainable development. Mumbai, which generates over 9000 tonnes of MSW daily and having largely the organic fraction (~40%) in its MSW composition, dispose of most of its waste in open dumps. Composting could be the one option to treat organic fraction of MSW in Mumbai. The aim of this study is to evaluate emissions from windrow composting and in-vessel composting of organic fraction of MSW using life cycle assessment (LCA) approach. The LCA was done using GaBi v6.0 Sustainability software with 1 tonne of organic waste as a functional unit and both direct and indirect emissions were evaluated. The results are presented based on the Centre for Environmental Studies of the University of Leiden method (CML-ULM, 2015) characterization method. The direct emissions from both the composting systems were calculated based on the carbon (C) and nitrogen (N) balance present in the MSW composition of Mumbai city. The environmental impact categories considered for this study were global warming, acidification, eutrophication and human toxicity. For the treatment of 1 tonne of organic waste, these environmental impacts for windrow composting were obtained as 137 kg CO2 eq/tonne, 0.198 kg SO2 eq/tonne, 0.087 -3 kg PO4 eq/tonne and 0.451 kg 1,4-DB eq/tonne while for in-vessel composting the impacts -3 were obtained as 219 kg CO2 eq/tonne, 0.621 kg SO2 eq/tonne, 0.089 kg PO4 eq/tonne and 17.3 kg 1,4-DB eq/tonne. The LCA results show that the windrow composting system poses a lesser burden in all the environment impact categories considered and found to be the preferable composting system.

Keywords: Life cycle assessment, Municipal solid waste, Composting, Impact categories

1. INTRODUCTION

MSW management has become one of the major environmental problems in Indian megacities (Bundela et al., 2010). In India, due to the rapid industrialization and population increment, people are migrating from villages to cities which generates thousands of tons of MSW daily. Uncontrolled dumping of MSW is the most common disposal method in most cities

Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017 of India. Mumbai, which generates over 9000 tonnes of MSW daily and having largely the organic fraction (~40%) in its MSW composition (Table 1), dispose of most of its waste in open dumps (Deonar and Mulund) resulting in the degradation of the environmental quality. The scientific management of MSW includes segregation of MSW into bio-degradable and non- biodegradable fractions at the source. Organic waste can be treated biologically (aerobic and anaerobic process) to give compost or energy, the combustible fraction can be treated thermally for energy recovery and inorganic residual can be landfilled and recovered. Composting is a one of the best-suited, low cost treatment method to degrade biodegradable fraction of MSW. Composting is a biological process in which readily biodegradable organic fraction of MSW is decomposed by microbes under controlled aerobic conditions. This process stabilizes the organic matter, after a period of weeks or months to a product is which is called compost (de Bertoldi et al., 1983). The decomposition occurs naturally, however it can be accelerated and improved by human intervention. There are different types of composting technologies available: windrow composting, aerated static pile composting and in-vessel composting. In windrow composting, the biodegradable waste placed in a long narrow piles or rows. These rows are generally turned through a turner to mix the composting material and to improve the porosity and moisture on a regular basis. The turner simply lifts the material from the windrow and spills them down again, mixing the material and reform the mixture into a loose windrow. As the turner moves through the windrow, releases trapped heat, gases, mixes the materials, breaks up the large particles and allow entry of fresh air injected into the compost (Ruggieri et al., 2008). The aerated static pile composting takes the piped aeration system. The pipe is connected to a blower which provides aeration either by forcing or sucking of air through the compost pile. The piles are covered with a layer of bulking agent, such as finished compost or wood chips. The layer of finished compost protects the surface of pile from drying and prevents the releasing of odorous compound to the atmosphere generated within the pile (Mousty et al., 1984). In this composting, continuous oxygen supply eliminates formation of anaerobic conditions and thereby potential odour problems. In in-vessel composting, compostable material is enclosed in a drum, bin, container or vessel. This method relies on a variety of forced aeration and mechanical agitation to control conditions and to speed up the composting process. Mechanical systems are designed to minimize odour and to reduce the process time by controlling environmental conditions such as airflow, temperature, and oxygen concentration, thereby eliminates the odour problems (Cabaraban et al., 2008). Life Cycle Assessment (LCA) is an environmental management tool which can be used to assess the potential environmental burdens from the waste management (Ekvall et al., 2007). LCA has been used, more so in the last decade, to assess the performance of MSW management systems (Chaya and Gheewala, 2007; Mendes et al., 2003). Mendes et al. (2003) studied the management of biodegradable fraction of MSW in Sao Paulo, Brazil: composting, biogasification and landfilling. It was concluded that both composting and biogasification can reduce considerably the environmental impacts compared to the landfilling of waste. Abduli et al. (2011) compared the landfill and combination of composting and landfill in Tehran, Iran. The study shows that combination of composting and landfill has a larger environmental impacts compared to the landfilling. Chaya and Gheewala (2007) examined incineration and anaerobic digestion as the MSW-to-energy schemes in Thailand and found anaerobic digestion superior to the incineration. The goal of this LCA study is to assess the direct and indirect burdens resulting from two different types of composting of organic waste of MSW: windrow composting and in-vessel composting for Mumbai’s waste. The impact categories analyzed are: global warming (GW), Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017 acidification, eutrophication and human toxicity (HT).

Table 1. MSW composition of Mumbai (Sharholy et al., 2008)

MSW Components characteristics (% by weight)

Biodegradable 40 Paper 10 Plastic 2 Metals - Glass 0.2 Textile 3.6 Leather 0.2 Ash, fine earth and 44 others

2. METHODOLOGY

2.1 Life cycle assessment

We use International Organization for Standardization (ISO) 14040:2006 methodology for LCA. The methodology comprises of four major phases termed as, goal and scope definition, life cycle inventory, life cycle impact analysis and interpretation of the results (Guinee et al., 2001). The goal of this study is to assess two different types of composting systems using LCA methodology and identify the suitable composting system. One tonne of MSW is selected as the functional unit for comparison of both the composting systems. All the relevant processes within the system boundary are included for the assessment (Figure 1). Within the system boundary, inputs such as energy and mass, and outputs like air and water emission from the treatment process are considered. Direct emissions are the emissions from the foreground system while the indirect emissions are the emissions from the background system. The background system includes the supply of electricity and diesel. (Table 2) required to the foreground system whereas the foreground system includes emissions associated with different composting systems considered in this study. Biogenic carbon dioxide

(CO2) emission from the process is not included in the inventory because it is considered carbon neutral and do not contribute towards global warming (Chandel et al., 2012; Zhao et al., 2009).

Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017

Environment OFMSW System boundary

Windrow/ In-vessel Energy Composting

Emissions Materials

Figure 1. System boundary for composting systems for this study

Table 2. Inventory of resource use in foreground system Unit WC IVC Process inputs Waste treated tonne of OW 1 1 Resources consumed Electricity kWh/tonne 0.88a 37a Fuel litre/tonne 0.47b 1.6a aBoldrin et al. 2009 bKolhapur Composting Plant, 2015

2.1.1 Emissions estimation

The emission calculation from composting process are based on the carbon (C) and nitrogen (N) balance as described in the literature (Sharma and Chandel, 2016; Boldrin et al. 2010; Boldrin et al., 2009; Amlinger et al., 2008; Fisher, 2006; Ham and Komilis, 2003). The systems assessed in these studies is similar to the systems assessed in the present study. For windrow composting system, we assume that 70% of total carbon is released into the air. The CO2 and methane (CH4) emissions were calculated as 66% and 2.5% of the carbon released into the air. We assume that 50% of total nitrogen is released into the air in the form of nitrogen (N2), nitrous oxide (N2O), and ammonia (NH3). N2O emission and NH3 emission were calculated as 1.4% and 2.4% of the total nitrogen released into the air. For the in-vessel composting system, we assume that 70% of total carbon is released into the air. The CO2 and CH4 emissions were calculated as 60% and 3% of the carbon released Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017

into the air. We assume that 50% of total nitrogen is released into the air in the form of N2, N2O, and NH3. N2O emission and NH3 emission were calculated as 1.8% and 0.1% of the total nitrogen released into the air. The total amount of C and N present in compostable waste is 5.76 kg and 0.312 kg as calculated based on the Mumbai MSW composition by using elemental analysis (C, H, O, N, S). Water emissions have not been considered for the composting system as it is assumed that the leachate production is either insignificant or recirculated to the system back (Sharma and Chandel, 2016; Bernstad and Jansen, 2012; Lee et al., 2007; Bjarnadottir et al., 2002). The indirect environmental burdens associated with the diesel consumption during the treatment process have been taken from the GaBi database (GaBi, 2014). However, avoided emissions and indirect burdens resulting from the application of compost on land have not been considered.

2.1.2 Life cycle impact assessment

In this study, the composting systems were modelled using GaBi v6.0 Sustainability software (Figure 2) and results are presented based on the Centre for Environmental Studies of the University of Leiden method (CML-ULM, 2015) characterization method.

Figure 2. Flow diagram of both types of composting using GaBi software

Four impact categories were investigated: global warming, acidification, eutrophication, and human toxicity by multiplying the emissions (CH4, N2O, and NH3) accounted in the inventory stage with an equivalency factor.

3. RESULTS AND DISCUSSION

The environmental emissions under each composting system are presented in Table 3. Emissions to air from the composting due to degradation of the organic matter are considered as the direct burdens whereas indirect burdens include the emissions from the consumption of diesel and electricity. The emissions of biogenic CO2 is comparatively high because of the organic waste but this biogenic CO2 does not contribute to global warming since it is the part of the global carbon cycle. The air emissions (direct emissions) of CH4, N2O, and NH3 from foreground system are considered for this study. Table 4 and Table 5 show the environmental impacts from windrow composting and in-vessel composting, respectively for 1 tonne of organic waste (OW). Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017

The comparison of the modelled scenarios is presented in Figure 3. Characterisation results are defined for global warming, acidification, eutrophication and human toxicity as kg of CO2 -3 equivalents, kg of sulphur dioxide (SO2) equivalents, kg of phosphate (PO4 ) equivalents, and kg of 1,4-dichlorobenzene (DB) equivalents per tonne of OW, respectively. The global warming effect is mainly caused by the emissions of greenhouse gases such as fossil CO2 and CH4, where the effect of CH4 is more than CO2 due to the high global warming potential of CH4. Acidification is caused by the emission of acidifying substances including nitrogen oxides (NOx), sulphur dioxide, sulphur trioxide, hydrogen chloride (HCl), hydrogen fluoride, sulphur oxides and ammonia. Eutrophication is caused by the release of phosphate, nitrogen oxide (NO), nitrogen dioxide (NO2), nitrates and NH3. Human toxicity is mainly caused by pollutants such as particulate matter (PM), SO2, NOx, arsenic (As), chromium (Cr), cadmium (Cd), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), zinc (Zn) and dioxins.

Table 3. Air emissions (direct emissions) under each composting system Emissions Unit WC IVC kg/tonne of OW 243.9 221.7 CO , biogenic 2 4 6

CH4 kg/tonne of OW 3.36 4.032 kg/tonne of OW 0.171 0.220 N O 2 6 6 kg/tonne of OW 0.113 0.004 NH 3 7 7 Table 4. Environmental impacts from windrow composting Total Impact categories Unit impacts

Global warming kg CO2 eq/tonne 137

Acidification kg SO2 eq/tonne 0.198 -3 Eutrophication kg PO4 eq/tonne 0.0868 Human toxicity kg 1,4-DB eq/tonne 0.451 Table 5. Environmental impacts from in-vessel composting Impact categories Unit Total impacts

Global warming kg CO2 eq/tonne 219

Acidification kg SO2 eq/tonne 0.621 -3 Eutrophication kg PO4 eq/tonne 0.089 Human toxicity kg 1,4-DB eq/tonne 17.3

Figure 3 shows that the in-vessel composting has high global warming effect as compared to the windrow composting. Because in case of in-vessel composting, the electricity consumption and emissions of CH4 and N2O during the degradation process are comparatively high. In India, electricity is mostly produced from the fossil fuels which lead to the high emissions of fossil CO2 and other pollutants like SO2, NOx, heavy metals etc., resulting in high environmental impacts. Similarly, for other environmental impact categories (acidification, eutrophication and human toxicity) also, the in-vessel composting system shows the high impacts as compared to the windrow composting (Figure 3) due to the high electricity consumption.

Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017

Figure 3. Comparison of environmental impacts from both the composting systems

4. CONCLUSION

Life cycle assessment is done to compare windrow composting and in-vessel composting of organic fraction of MSW for Mumbai. For the treatment of 1 tonne of organic waste, these environmental impacts for windrow composting were obtained as 137 kg CO2 eq/tonne, 0.198 -3 kg SO2 eq/tonne, 0.087 kg PO4 eq/tonne and 0.451 kg 1,4-DB eq/tonne while for in-vessel composting the impacts were obtained as 219 kg CO2 eq/tonne, 0.621 kg SO2 eq/tonne, 0.089 -3 kg PO4 eq/tonne and 17.3 kg 1,4-DB eq/tonne. Gaseous emissions from the windrow composting process shows the main contribution to global warming, acidification and eutrophication while the energy consumption shows the highest contribution to human toxicity. Similarly, the gaseous emissions from the in-vessel composting process represents the main contribution to global warming, and eutrophication while the energy consumption shows the highest contribution to acidification and human toxicity. The LCA results show that the windrow composting system poses a lesser burden in all the environmental impact categories considered.

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