Towards Decarbonization: Waste Management Solutions for San Jose

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IN

DEGREE PROJECT ENVIRONMENTAL ENGINEERING, SECOND CYCLE, 30 CREDITS

,

STOCKHOLM SWEDEN 2020

Towards Decarbonization: Waste

Management Solutions for San

Jose

MARIANO VILLALTA

KTH ROYAL INSTITUTE OF TECHNOLOGY

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Abstract

Costa Rica is a small country located in Central America. It is known for its lush forests and a completely renewable electricity grid. However, this country has a highly deficiente waste management problem. The entire waste ends up in landfills, and no economic or energetical value is taken out of it. Furthermore, this system produces high amounts of greenhouse gases which are a problem for a country that is trying to decarbonize its economy.

This thesis studies three different waste management technologies in an attempt to figure out which is the most suitable for San Jose, Costa Rica. The technologies studied are waste incineration, anaerobic digestion, and landfill gas capture. Each technology is assessed under three aspects: the amount of income each generates, the amount of electricity it produces, and the amount of greenhouse gases each emits.

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Acknowledgements

Completing this Thesis Project, and my entire masters degree at KTH University could not have been done without several important people in my life. I would like to thank my mother, Kristen, for her unconditional and unwavering support during these past 2 years. She has always had my back and has always rooted for me no matter what. I would also like to thank my father, Eladio, for his continued support during this process.

Furthermore, I would like to thank FEMETROM for their help with critical information, and understanding of several concepts, during the past 7 months. This project would not have been able to be carried out without their help. I hope them the best in their continued efforts to create a better waste management system in San Jose, Costa Rica.

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1. Introduction

Costa Rica’s current waste management system is outdated and relies on landfills as the only source of disposal (Ministerio de Salud, 2016); no treatment or material and energy recovery is being done. Currently, 29 municipalities located in San Jose’s Greater Metropolitan Area (GAM) deposit their Municipal Solid Waste (MSW) in privately owned landfills. Two other municipalities located in the GAM deposit their MSW in landfills owned by the state. Moreover, outside of the Greater Metropolitan Area, waste is managed similarly, but with several issues. Some municipalities do not offer waste management services, which forces its citizens to burn the waste or dump it in illegal places, semi controlled dump sites, or uncontrolled dump sites. The waste collection system only recovers approximately 75% of the municipal solid waste (Ministry of Health, 2010). The remaining waste ends up as trash on the street, rivers, and parks.

According to the Ministry of Health (2016), the generation of waste tripled between 1990 and 2006. They state that in 2014, approximately 4000 tonnes of waste was generated by day across the entire country. This is equivalent to 1,460,000 tonnes of waste per year that is not taken advantage of for material or energetical purposes. Furthermore, approximately 12 of the landfills are close to being capped, including the most important one in San Jose’s Greater Metropolitan Area (FEMETROM, 2019).

Furthermore, according to the Ministry of Health (2016), the main reasons for this outdated system are due to an unclear understanding of which governmental entity was in charge of waste management until 2008, a mishandling of funds, no intermunicipal cooperation, and a very little control and monitoring of waste strategies.

However, the latest policy calls for a complete transformation on how the country views waste. Instead of viewing it as a burden that must be dealt with, the Costa Rican society must understand that waste has intrinsic value which must be taken advantage of. The waste must be assessed in order to recover its material, economic, and energetic value

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1.1 National Decarbonization Plan

The national Decarbonization Plan 2050 (National Decarbonization Plan, 2018) sets the ambitious goal of completely freeing the Costa Rican society and economy from carbon emissions. It aligns with the 2015 Paris agreement’s goals, and lays the ground for a nationwide economic shift into a sustainable society by promoting the use of modern technologies and improving resource efficiency. Furthermore, the plan is broken down in 3 phases: the Initial phase (2018-2022), the Inflection phase (2023-2030), and Massive Implementation phase (2030-2050).

This Decarbonization Plan identifies 4 areas of improvement and outlines the opportunities available and necessary actions to be taken in order to reach the ultimate goal. The plan calls for a complete modernization of the current waste management system by improving waste separation, reutilization, and energy recovery. Furthermore, final waste disposal into landfills must be done with extreme efficiency and in order to reduce greenhouse gas emissions and to control land, water, and air pollution.

The plan states that the following actions related to waste must be taken (National Decarbonization Plan, 2018):

1. The entire country will have the necessary infrastructure to collect, separate, reuse, and properly landfill waste by 2050.

2. A societal and business shift that generates less waste and is focused on circular waste solutions.

3. A national strategy by 2022 that will outline the best technologies to reduce methane caused by organic waste.

Moreover, the Decarbonization Plan 2050 indirectly influences the national waste system by seeking to improve the country’s electricity generation capabilities in order to supply the entire nation with renewable energy at a competitive price. Finally, a lifecycle perspective on consumption patterns and business models is said to be necessary in order to decarbonize the national economy.

1.2 Executive Decree 39136

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several forbidden activities and required characteristics any incineration facility in Costa Rica must follow.

1.2.1 Equipment Characteristics

The equipment used to build the incinerator cannot be over 3 years old at the time of purchase, and must be designed and built according to the local waste characteristics. The facility must have at least 2 incinerating chambers: a primary one used for combustion, where the organic material is volatilized, and a secondary chamber used to oxidize the resulting gases (Ministry of Environment, Energy and Telecommunications, 2013). Furthermore an automatic temperature control system must be installed to maintain temperatures at the desired levels. The system feeding waste into the primary chamber must be capable of handling liquid and solid waste, and must be designed to prohibit any gases from escaping through it. Finally, a continuous emission control system must be installed in order to eliminate fugitive emissions and odors.

1.2.2 Operation Conditions

A set of mandatory guidelines for the operation of a waste incinerator are also given. The burners must only be used during certain situations: to reach a chamber temperature of 900 ºC (before waste is fed), as a support combustion when the secondary chamber temperature levels falls below 900 ºC, during shut down phase to treat any remaining waste, and as a regulator of vapor production. The combustion gases must reach 900 ºC for at least 2 seconds. Waste with halogen content of more than 1% must reach 1100 ºC for more than 2 seconds. The waste cannot be fed to the chambers during startup phases, when temperatures are not at the required levels, or if the emission control system is having problems. Moreover, an air heater must be used to dry waste with a high water content, and the chambers must maintain a below atmospheric pressure. Finally, a pre-treatment area must be created with storage capabilities of up to 4 days worth of waste, and must have a crushing machine to homogenize the waste.

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1.3 FEMETROM

In response to the previously stated national intention to improve the national waste management system, FEMETROM is pursuing the first waste to energy facility in Costa Rica (FEMETROM, 2019). The bid is open to any type of technology that is capable of transforming municipal waste into energy. It is not biased towards any particular technology and does not state that the entire waste stream must be used. FEMETROM is an inter municipal federation made up by the following 10 municipalities: Alajuelita, Aserrí, Curridabat, Escazú, Goicoechea, Mora, Moravia, San José, Santa Ana, and Tibás; all of them are located in Costa Rica’s Greater Metropolitan Area. The efforts made by FEMETROM can be seen in the creation of a project profile for electricity generation with municipal solid waste and in the creation of an International Bid to select a company that will design, build, test, and operate a waste to energy facility. Finally, the bid intends to have a fully operational facility by 2023.

1.4 Aim and Objectives

Costa Rica as a country is aware of its outdated waste management system that relies completely on landfills. No energy or materials are being recovered leaving great potential for economic and electrical value untapped. The aim of this project is to assess which waste management technology, or combination of technologies, is best suitable for San Jose’s municipal waste. The assessment will be done on an environmental and economic perspective. The environmental perspective will be based on the amount of excess greenhouse gases each technology emits, while the economic perspective will be based on the amount of electricity produced by each technology and the amount of income can be generated by each technology. Given the fact that FEMETROM plans to have a functional waste to energy facility by 2023, the entire paper will be based on projections for year 2023. This paper looks to bring understanding to the Costa Rican society on which waste management technologies are best suited for its local context.

Given the overarching aim of this paper, the objectives are to understand which technologies treatment phase emits less greenhouse gases. This will be done by quantifying the amount of excess greenhouse gases emitted. The amount of electricity, in MWh, for each waste technology will also be calculated. Based on this, the potential income generated from selling such technology will be projected. Once this is done, a comparison of the waste treatment technologies will be done based on electricity yields, greenhouse gas emissions, and income generation.

1.5 Limitations

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be the following: Waste Incineration, Anaerobic Digestion, and Landfill Gas Capture. The reason for this is that they are the most widespread used waste to energy technologies.

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2. Technology Description and

Requirements

The 3 waste management technologies assessed in this paper are Anaerobic Digestion, Waste Incineration, and Landfill Gas Capture. This section explains several operational parameters and waste characteristics required by each technology.

2.1 Waste Incineration

Waste incineration is a waste management process which looks to burn waste at high temperatures in order to produce electricity and heat, while reducing the waste’s overall volume by up to 90% (Williams, 2005). An important characteristic of this process is that it produces no methane, a powerful greenhouse gas. However, not all types of waste can be treated by this process, and several controls systems must be installed in order to reduce the emission of hazardous pollutants. Nonetheless, several pollutants and greenhouse gases end up in the atmosphere, land, and water.

The waste used during incineration has a direct influence on the combustion process and the emissions it releases. One of the most important characteristics of waste is it’s lower calorific value. This is the energy contained within the waste, and is a very important parameter in determining the ability of waste to maintain combustion without the need for extra fuel. The average lowest acceptable level of this parameter is 6 MJ/kg during each season and the annual average must be at least 7 MJ/kg (The World Bank, 1999).

Waste incineration facilities have very little control over the composition of waste used. While incinerators are designed to manage a wide variety of waste, they are also limited to the waste’s moisture content, ash, and combustible fraction. The ranges of these three variables can be seen in Figure 1. The shaded region encloses the permissible values: Moisture content must be in between 0 and 50%. According to The World Bank (1999), the percentage of ash present in waste must not surpass 60%, and the combustible fraction must be at least 25% of the total waste stream.

Pre-treatment of waste before it is fed to the incinerator may significantly influence each value. For example, paper and plastic have high calorific values. Removing these from the waste stream for recycling purposes would decrease the waste’s overall calorific value. On the other hand, glass and metals have a low calorific value. Removing them from the waste stream would increase the overall calorific value. Organic waste has a high moisture content. Removing them for other activities, such as anaerobic digestion, would reduce the waste stream’s moisture content (Williams, 2005). Furthermore, the fossil carbon stored in the waste has a direct influence on the amount of carbon dioxide emitted into the atmosphere. The entire fossil carbon present in the waste stream will be assumed to convert to CO2 during the process, and will ultimately end up as a carbon

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Most waste incineration facilities include the following processes in their operations (Waste Incineration Public Health, 2000):

1. Waste storage and pretreatment: Waste must be properly stored and pre-treated once it has reached the facility. The waste at this phase must be handled with caution in order to reduce any fugitive emissions into the environment and to reduce any furnace performance issues. 2. Combustion process: The waste is fed into a furnace where it meets air at high temperatures

to produce a combustion reaction. In order to ensure proper combustion, the furnace, including the waste and gases, must reach certain temperatures for sufficient periods of time; usually 1-2 seconds. Furthermore, turbulence is needed to ensure a proper mixing between the combustible gases and oxygen to properly oxidate the waste. Several design specifications can be taken into account to reach optimal combustion and reduce emissions. For example, arches and bull noses can be installed to delay the gases from escaping the chamber before the time needed.

3. The gases must then be cooled to about 150°C in order to properly treat them. Furthermore, the gas cooling techniques have considerable implications on emissions of pollutants such as mercury and dioxins and furans.

4. An air pollution control system removes particulate matter, acid gas, dioxin, and mercury from the flue gas.

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2.1.1 Global Warming

The process of waste incineration also has the potential to emit greenhouse gases. During incineration, biogenic and fossil carbon dioxide can be emitted. Furthermore, the fossil carbon present in the waste stream and the amount of electricity that can be produced by it are critical factors when assessing a waste incinerator.

Greenhouse gas emissions can be classified as direct, indirect upstream, and indirect downstream emissions. Direct contributions represent the gasses emitted directly at the facility during incineration. The amount of fossil carbon in the waste stream, in comparison to biogenic carbon, is a critical factor for determining greenhouse gas emissions (Astrup et al, 2009). Incinerating biologically based material will release biogenic carbon into the atmosphere. This means that incinerating organic waste has no impact on incrementing global warming since it recycles carbon already stored in the environment. These emissions have a GWP of 0. On the other hand, fossil carbon emissions do increase the total greenhouse gases in the atmosphere by releasing carbon that was not part of the natural carbon cycle, usually by incinerating plastics and certain textiles. These emissions do have an incremental effect on greenhouse gases in the atmosphere (UC Davis, n.d.).

2.1.2 Energy Production

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2.2 Anaerobic Digestion

Another technology used for treating large scale waste streams is Anaerobic Digestion. This is an effective process for treating organic waste, such as leftover food, agricultural waste, and sewage sludge (Khalid et al, 2011). During the process, the waste goes through a similar process as it does in landfills. The organic waste degrades with the presence of microorganisms, and without the presence of oxygen. This leads to the formation of carbon dioxide and methane, of which latter is a powerful greenhouse gas. However, this process is done in a closed and controlled reactor, meaning that the gases aren’t directly emitted into the atmosphere and can be used as clean and renewable energy sources. The following subsections will elaborate on the processes by which the waste stream goes through, the waste composition requirements for such a process, and the effects it might have on global warming.

2.2.1 Waste Composition and Operational Parameters

Anaerobic Digestion is a process that is strictly used to treat organic waste. This can be the organic fraction of MSW, sewage sludge, agricultural waste, and manure from livestock. Other waste factors also play an important role in generating a maximum product yield. A low C:N ratio between 20:1 and 25:1 is preferred since it yields more amounts of methane. Mixing the organic fraction of MSW with different organic waste types, such as leftover food or cow manure, is recommended in order to achieve the desired levels (Khalid et al, 2011). Furthermore, a high methane yield is seen at a pH level between 6.8 and 7.2, with 7 being the most desirable level (ibid). Moreover, the water level in the reactor during digestion is a critical factor. A high moisture content often leads to better digestion. Approximately 60%-80% moisture content is needed to produce the best yields (ibid).

2.2.2 Global Warming

The methane produced during anaerobic digestion is a powerful greenhouse gas. The biogas can be combusted to generate power and electricity. The process of combustion releases carbon dioxide into the atmosphere. The CO2 emitted has no contribution to global warming since it’s

also part of the short term carbon cycle. This source of energy can be used as a substitute for fossil fuels for powering automobiles, and can also be used to generate heat and electricity with the help of a gas powered generator (Shah, 2019). According to Timonen et al (2019), carbon dioxide emissions resulting from energy production are less when they use biogas from anaerobic sources than from conventional fossil fuel sources.

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2.2.3 Energy Production

The biogas, assumed to contain 50% methane, produced by anaerobic digestion can be combusted to produce electricity which can be sold to a national grid. To determine the electrical output, it is first necessary to obtain the biogas yields from an anaerobic digestion facility. After this is obtained, a calculation to determine electricity yields from combusting a unit of biogas is required. Both of these calculations will be further explained below.

While the numbers are not exact, biogas production yields depend on several factors, such as organic matter digestibility, kinetics, digestion time, temperature, microbial activity and waste properties (De Mes et al, 2003). Theoretically, the biogas potential yield ranges from 6 to 270 m³

of biogas per tonne of organic municipal waste. However, the typical range goes from 125 to 310 ms/tonne of waste. Aguilar-Virgen et al (2014) concluded a 180-220m³ production of biogas per ton of municipal organic waste. This study captured the biogas yields of codigesting municipal organic waste with cow manure for 8 weeks, with maximum pH level of 8. Another study conducted by Cecchi et. al. (2011), demonstrated that an organic waste stream that has been collected by door to door schemes has a biogas yield of 200m³ per tonne of municipal organic waste. The reason for this high yield is the organic purity in the waste stream due to the collection system. Finally, Stan et al (2018) state that anaerobic digestion has the potential to generate between 80 and 160m³ of biogas per tonne of organic waste. Finally, the United States Environmental Protection Agency states a value of 170m³ of biogas produced per tonne of biodegradable waste (Aguilar-Virgen et al, 2014). This last value will be used to calculate biogas yields for this project due to the fact that it is used by the US EPA, which is a respectable institution that deals with these topics at a national level.

Biogas can be combusted to generate electricity. Approximately 1m³ of biogas, with a methane content of 50% and with a 35% electrical conversion efficiency. will produce 2.14 kWh of electricity (Banks, n.d.).

2.3 Landfill Gas Capture

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3. Methodology

Each waste management technology previously explained will be assessed for the MSW of San Jose on their greenhouse gas emissions, electricity production, and income generation. After this is done, a comparison based on the stated elements will be done. Furthermore, the amount of greenhouse emissions created in landfills will also be calculated in order to have a clear baseline in this regard. The following section will give a brief overview of each technology and outline the way in which greenhouse gas emissions, electricity, and income are calculated for each.

3.1 Waste in San Jose

It is necessary to have a clear understanding of the amount of waste expected to be generated, and its characteristics, for year 2023 in order to correctly assess each technology’ potential greenhouse gas emissions and electricity generation. FEMETROM (2019) projected yearly waste generation from 2018 until 2024. The amount of MSW to be generated in it’s 10 municipalities is 393,721 tonnes for year 2023.

However, this study does not break down this waste by type. Another study, carried out for the entire greater metropolitan area of San Jose in 2011 (Herrera et al, 2016), broke down the waste by type. The fractions are shown in Table 2. These values, shown in Table 3, have been applied to FEMETROM’s study resulting in a complete quantification and breakdown of waste for the year 2023. The breakdown of waste will be kept the same since the tendency has been so. According to Ministerio de Salud (2016), the waste breakdown by type was the same as it was in 2011. Because of this, it will be assumed to be the same for 2023.

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The 2023 projections estimated for San Jose’s waste will be used to describe how each technology adapts to, and how suitable each one is for, San Jose’s waste. The 49.79%, or 196,034 tonnes, of biodegradable waste will be used to assess the industrial scale anaerobic digestion process, and the remaining non-biodegradable waste will be assumed to be incinerated. The entire waste stream will be used when assessing the landfill methane capture and waste incineration technologies.

3.2 Fossil Carbon in waste stream

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Total Fossil Carbon per waste type (kg C) = theoretical fossil carbon * weight of waste type Eq. (1)

Furthermore, the total amount of fossil carbon present in the waste stream was calculated by adding the total amount of fossil carbon by each individual

Total Fossil Carbon in entire waste stream (kg C) = SUM of Total Fossil Carbon for all waste

types Eq. (2)

Finally, in order to reach the fossil carbon content for the entire waste stream per tonne of municipal solid waste, the following formula was used:

Fossil Carbon per tonne of MSW (C / tonne MSW) = Result of Eq. 2 / weight of MSW (tonnes) Eq. (3)

3.3 Landfills

Landfills are the least suitable option in the waste hierarchy, and produce no economic, material, or energetical recovery (Williams, 2005). The IPCC default method (Frøiland Jensen & Pipatti, n.d.) for quantifying landfill emission will be used in order to calculate the potential methane released from landfilling the entire waste stream in 2023. This formula was chosen since it is used as a proper guideline to estimate methane emissions resulting from solid waste (Frøiland Jensen & Pipatti, n.d.). Furthermore, it is developed by the IPCC, which is a branch of the United Nations in charge of assessing data relevant to climate change ("IPCC - Intergovernmental Panel on Climate Change," n.d.).

The variables used, and where the data will be taken from, is described below:

MSWT : total MSW generated (Gg/yr). According to FEMETROM (2019), 393,721 tonnes of

MSW will be produced by 2023. This is equal to 393.721 Gg.

MSWF : fraction of MSW disposed to solid waste disposal sites. The fraction of MSW collected

today is approximately 75% (Ministry of Health, 2010), this paper will assume the entire waste fraction is collected and sent to landfills by 2023. Due to this, the value used is 1.

MCF: Methane Correction factor. This fraction accounts for the fact that different landfills

produce different amounts of methane per unit of waste. The default value is 0.6 (Frøiland Jensen & Pipatti, n.d.).

DOC : degradable organic carbon (kg C/ kg SW) found in the waste stream (Frøiland Jensen &

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DOC (kg C/ kg SW) = 0.4*A + 0.17*B + 0.15*C + 0.3*D Eq. (5)

- A (kg of total SW): default DOC of paper and textiles.

- B (kg of total SW): Garden and park waste, and other (non-food) organic discards - C (kg of total SW): Food waste

- D (kg of total SW): Wood and straw waste

The values (0.4, 0.17, 0.15, and 0.3) represent the percentage of degradable organic carbon (DOC) for each waste type.

By using the values presented in Table 2, the formula goes as follows:

DOC (kg C/ kg SW) = (0.4*0.2474) + (0.17*0) + (0.15*0.4979) + (0.3*0.0227) DOC (kg C/ kg SW) = 0.18

It is important to note that this calculation of DOC is slightly under the maximum default limit of 0.21 set by the IPCC (n.d.)

DOCF : represents the fraction of carbon that degrades and is released. The IPCC default value is

0.77 (Frøiland Jensen & Pipatti, n.d.).

F : percentage of CH4 in landfill gas. The IPCC default value is 0.5 (Frøiland Jensen & Pipatti,

n.d.).

16/12 : weight conversion of C to CH4. The IPCC default value is 16/12 Frøiland Jensen & Pipatti,

n.d.).

R : recovered CH4. This value represents any methane that is recovered before being emitted to

the landfill (Frøiland Jensen & Pipatti, n.d.). The value used is 0, since no recovery will take place under this scenario.

OX : This value represents the oxidation factor which is the amount of methane oxidized into the

soil. The IPCC default value is 0 (Frøiland Jensen & Pipatti, n.d.).

3.4 Waste Incineration

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waste incinerator, it is necessary to calculate the amount of fossil carbon found in the waste stream. This process has been explained in Section 3.2, and the results will be presented further into the paper. Furthermore, the weight of the total fossil carbon in the waste stream must be converted to CO2. To do so, the resulting total amount of fossil carbon must be multiplied by 44/12 (US EPA,

2020) in order to get the corresponding weight of CO2 emitted. This means that the excess carbon

dioxide emissions due to waste incineration is calculated by multiplying the amount of fossil carbon found in the waste stream by 44/12.

Furthermore, the calorific value of San Jose’s waste will be calculated by using Dahlroth’s (n.d) formula.

Calorific Value (kWh/kg) = Higher Calorific value*(1-Ash content)*(1-Moisture content) -

0.69*Moisture Content Eq. (6)

The higher calorific value, ash content, and moisture content are variables that have been provided by FEMETROM (2019), and can be found in Table 4.

3.5 Anaerobic Digestion

Biogas is mainly made up of methane and biogenic carbon dioxide. For the purpose of this project, it will be assumed to be made up of 50% methane and 50% CO2. The carbon dioxide does not

count as an excess greenhouse gas, and methane is approximately 21 times more powerful than fossil based carbon dioxide (US EPA, n.d.). The emissions that occur as a result of the anaerobic digestion process originate from biogas leakage. Biogas can leak into the atmosphere during production and during the upgrading process. It is assumed that 1% of the biogas produced will be lost and emitted into the atmosphere. This figure is taken from Bolin’s (2009) study which quantifies emissions from Anaerobic Digestion.

Given the electrical conversion efficiency of 2.14 kWh per 1m³ of biogas combusted (Banks, n.d.), it is possible to calculate an approximate electricity output for San Jose’s biodegradable waste using the Anaerobic Digestion treatment method. The weight of the biodegradable fraction of waste, 196,034 tonnes, shown in Table 3, the US EPA 170m³/tonne biogas yield (Aguilar-Virgen et al, 2014) , and the 2.14 kWh per cubic meter of biogas yield Banks (n.d.) will be used.

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3.6 Landfill Gas Capture

As previously mentioned in Section 2.3, landfill gas capturing systems have the potential to capture approximately 20% of the gas generated in a landfill. Because of this, the methane emissions recovered from this system will be calculated based on a 20% reduction from the half of the landfill emissions. Only half of the landfill gas will be used to account for the 50% methane content (the remaining 50% is biogenic carbon dioxide). The formula for doing so is the following:

Landfill Gas Captured (tonnes of methane) = (Landfill emissions/2) * 20% Eq. (8)

The potential electricity produced from the biogas captured will be calculated similarly to how the biogas produced in an anaerobic digestion facility is (explained in section 3.5) The electrical output will be based on 20% of the landfill gas produced in a landfill and the 2.14 kWh electrical conversion efficiency. In this instance, the landfill gas captured represents the resulting value from equation 8. It is multiplied by 2 to include the biogenic carbon dioxide fraction of the landfill gas captured.

Landfill Gas Electrical Output(MWh) = (Landfill Gas captured*2) * Electrical Yield /1000 Eq. (9)

3.7 Income Generation

According to FEMETROM (2019), the waste treatment system has the potential to generate income streams from two sources. Firstly, each municipality has to pay a tipping fee of ₡33,780 for every tonne of waste they want treated. Secondly, with regards to the electricity generating technologies, the electricity generated can be sold to the grid. The 2019 price per kWh generated from already existing electrical facilities was ₡45.2. This value will be used for the electricity generated in 2023.

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4. Results

The following subsections present the results from calculating greenhouse gas emissions, electricity generation, and income generation for all 3 waste technologies.

4.1 Landfills

Currently, landfills are the only waste management option used in San Jose. The entirety of its household waste ends up here and no value is taken out of it (Ministerio de Salud, 2016). As previously mentioned, this produces high quantities of biogas containing methane that ends up in the atmosphere. The formula used to calculate emissions is the following:

Landfill emissions (Gg of CH4/year) = (MSWT * MSWF * MCF * DOC * DOCF * F * 16/12-R)

* (1-OX)

Eq. (10)

The values used are presented in Section 3.3 and in Table 5. The results show that total emissions for 2023 from landfilling the entire waste stream would be approximately 21x10

³

tonnes of methane, which is equivalent to approximately 80x10⁶ kg of CO2 equivalent emissions.

4.2 Biological Treatment Methods

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However, in Costa Rica, the organic fraction of MSW is not separated at the source nor at any other point in the system (Ministerio de Salud, 2016). This means that a separation system is needed to remove any non-organic material in order to make the implementation of a digestion facility feasible. Large scale industrial solutions can be implemented to separate the waste. Some of the most common technologies are the screw press and disc screen to separate the organic fraction from a mixed waste stream, and shredder with a magnet to remove metals from waste that has already been separated at the source. The screw press functions by pressing the waste through narrow slits. The organic fraction of the waste passes through these slits, while the reject (plastic, paper, wood, metal) passes through another chamber into the reject fraction. The disc screen separates nonorganic material from the waste stream using rotating discs. The organic material falls between the discs while the rest is transported on top of them. An industrial bag opener is used to cut open the bags before using a screen press or a disc screen. Finally the shredder and magnet is used to separate metals from the waste stream; plastic cannot be removed from the waste stream. The waste stream is shredded to reduce the size and create a homogenized stream and is next to a magnet that removes metals (Hansen, et al, 2007).

A study in Denmark was done in order to compare the efficiency of each waste separation technology in terms of the biomass separated and the methane potential of the separated waste. The resulting biomass waste stream significantly varied for each technology. The screw press’s biomass fraction was 59% of the original waste stream, of which 87.65% was biodegradable material and the rest was ash content. The disc screen resulted in 66% waste reduction consisting of 85.3% biodegradable material and a 14.7% ash content. The shredder with magnet resulted in 98% of the initial waste stream, with a 91.65% biodegradable content and an 8.35% ash content. The reject from each technology shows a significant portion of biodegradable material as well (Hansen, et al, 2007).

4.2.1 Anaerobic Digestion

As it has previously been mentioned, certain characteristics of San Jose’s waste fall within the ideal limits for Anaerobic Digestion; the ones that do not can be manipulated with the use of additives or mixing with other inputs. The following subsections will describe the potential to generate electricity from San Jose’s organic fraction of municipal solid waste (OFMSW) using Anaerobic Digestion as the waste treatment technology, assuming that the waste will already be sorted. Furthermore, the potential greenhouse gas emissions from such a process will also be quantified. The remaining fraction of waste that will not be treated by Anaerobic Digestion will be routed under a scenario in which incineration is used.

Electricity Production

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produce 33,325,727m³ of biogas. This biogas has the potential to produce 71,317 MWh of electricity. Equation 7 including the values are presented here:

Electricity output (MWh) = (Weight of biodegradable Waste (tonnes) * Biogas Yield (m³/tonne) * Electricity conversion (2.14 kWh/ m³))/1000 Eq. (7) Electricity output (MWh) = (196,034 (tonnes) * 170 (m³/tonne) * 2.14 (kWh/ m³))/1000 Electricity output (MWh) = 71,317 MWh

However, typical Anaerobic Digestion facilities use approximately 20% of the electricity they produce (De Mes et al, 2003). After applying this deduction to the previous calculation, an Anaerobic Digestion facility processing San Jose’s entire organic fraction of municipal solid waste will generate 57,054 MWh of electricity.

Greenhouse Gas Emissions

The following steps must be done in order to properly calculate the carbon dioxide equivalent emissions from the 1% of the weight of the biogas leak. Firstly, the volume of biogas in cubic meters must be converted to weight in kilograms. This is done by calculating the volume by methane’s density of 0.657 kg/m³. The result is 21,895,002 kg of biogas produced for the year 2023. Next, it is necessary to calculate the weight of the total biogas produced for every tonne of OFMSW. This is done by dividing the biogas weight by the total OFMSW. The result is 112 kg of biogas produced per tonne of OFMSW. Next, the 1% of this value is taken to represent the 1% leak of biogas. Finally, the result is divided by half in order to represent the fraction of biogas, methane, that has a global warming potential.

These calculations result in total carbon dioxide equivalent emissions of 2,298,986 kg of CO2 eq.

and a GWP of 11.73kg of CO2 eq. for every tonne of OFMSW treated by anaerobic digestion. The

complete values are found in Table 6.

4.3 Treating the Entire Waste Stream

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or energy contained within this waste. Waste incineration is another treatment method that is not waste specific, and, with exceptions to local laws and regulations, can treat the entire waste stream. Furthermore, capturing landfill methane gas is also a non-waste specific option to recover certain value held within the waste that has already been landfilled. The following sections will elaborate on these solutions from a greenhouse gas emission and electricity output point of view.

4.3.1 Waste Incineration

The calorific value of waste is one of the main requirements for waste incineration. As mentioned in the waste incineration sub-chapter, the waste stream is required to have an annual average calorific value of 7 MJ/kg, which is slightly over the value representing San Jose’s waste. However, the moisture content of San Jose’s waste is higher, for its MSW than the 50% recommended limit for improved operational performance. A higher moisture content weakens the combustion process, but reduces CO and NOx concentrations (Li et al, 2008). The ash content from San Jose’s waste stream is way below the 60% limit for incineration. The household and commercial ash percentage is 12.98%. Finally, another positive aspect regarding San Jose’s situation for waste incineration is it’s high fraction of combustible waste. The combustible fraction includes organic waste, paper, cardboard, textiles, and plastics (Omari, 2015). Together, they make up 78% of the household waste and 65% of the commercial waste (FEMETROM, 2019), which is significantly higher than the 25% limit. These fractions of combustible waste have the potential to be higher given the fact that the “Other” category of waste for both sectors is so big.

Fossil Carbon Content and Calorific Value

By following the three formulas presented in Section 3.2, and using Astrup et al’s (2009) theoretical values and the waste weight in tonnes provided by FEMETROM (2019), which is presented in Table 3, the fossil carbon content for San Jose’s waste stream is 111 kg of Carbon per tonne of MSW. The breakdown of this calculation is shown in Appendix B.

Furthermore, the fossil carbon content must also be calculated for the waste stream without the biodegradable fraction. This is to be able to account for the emissions from incinerating the waste stream not treated by the Anaerobic Digestion scenario. The same formulas were used, and the resulting fossil carbon content for the waste stream, minus it’s biodegradable fraction, is 221 kg of C per tonne of solid waste.

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Electricity Generation

The City of San Jose is expecting about 393,721 tonnes of MSW to be produced in 2023 (FEMETROM, 2019). This number is expected to grow yearly. However, according to (Ministry of Environment, Energy and Telecommunications, 2013), which outlines the countrywide regulations for any incineration facility, any waste can be incinerated for electricity production purposes except for hazardous waste. According to FEMETROM (2019), approximately 2% of San Jose’s waste stream is deemed hazardous. This means that 98% of the commercial and household waste is subject to waste incineration with electricity production.

If 98% of this waste is to be incinerated, then the city can expect 385,846 tonnes of waste to be used for incineration purposes. The overall electricity generation per year for incinerating San Jose’s entire waste stream can be seen in Table 7, given the electrical generation yields according to the calculated calorific value.

Fossil Carbon in the Waste Stream

Greenhouse gas emissions from waste incineration are directly linked to the fossil carbon found in the waste input. It is assumed that 100% of the total carbon entering a waste incinerator will be emitted into the atmosphere as carbon dioxide.

It has previously been stated that there is 111 kg of carbon per tonne of MSW; the breakdown of this calculation can be seen in Appendix B. However, this measurement of carbon has to be converted to carbon dioxide weight. According to US EPA (2020), carbon dioxide is 44/12 heavier than carbon, signifying an emission rate of 407 kg of CO2 eq. per tonne of municipal solid waste.

The total emissions for 2023 are calculated to be 157,237,625 kg CO2 eq..

Emissions from incinerating the non-biodegradable fraction of waste

Anaerobic digestion does not treat the non-biodegradable waste fraction. Because of this, the untreated waste will be assumed to be sent to incineration. These emissions must be accounted for. This waste used for incineration includes all the waste except for the biodegradable fraction, which has already been treated by anaerobic digestion.

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eq. released for 2023. This value represents only the waste that does not go to anaerobic digestion, while the value presented in the previous sub-section represents the entire waste stream.

Electricity generation from incinerating the non-biodegradable fraction of waste

The untreated waste fraction from the Anaerobic Digestion scenario has the potential to produce electricity through waste incineration. The electrical output will be calculated following the same formula presented in Section 3.4. This means that the non-biodegradable fraction of waste can produce 102,099 MWh of electricity if incinerated.

4.3.2 Landfill Gas Capture

Landfills contain all types of waste and no pretreatment or sorting is necessary. Landfill gas capture systems prefer sites with higher biodegradable since more biogas will be captured. However, more biodegradable material also implies a higher methane amount not captured and emitted into the atmosphere. This is since these systems only collect approximately 20% of the methane generated. Technical specifications of San Jose’s current landfills are suitable to the necessities to implement such a system (Ministerio de Salud, 2016). However, landfills in the area are nearing full capacity and new ones would need to be opened (Ministerio de Salud, 2016). Furthermore, the power facility using landfill gas must be located nearby the landfill. This is not the case for San Jose’s landfills and would entail larger deficiencies in the system, or the need to build a new power facility on site.

Electricity Generation

Section 4.1 calculated the potential amount of methane gases produced per year if San Jose’s entire waste stream were to be landfilled. This landfill gas can be captured and used to generate electricity. However, as previously mentioned, the entire gas cannot be captured. The 20% landfill gas collection rate benchmark and UNFCCC standard implies that there is a potential to divert 8,737,344 kg, or about 13x10⁶ cubic meters, of landfill gas from directly entering the atmosphere. This is assuming that equal parts methane and biogenic CO2 are emitted from landfills. The landfill

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Greenhouse Gas Emissions

A landfill gas capturing system has the potential to significantly reduce greenhouse gas emissions. A 20% reduction in methane emissions would result in approximately 16x10⁶ kg of CO2 eq.

reduction of greenhouse gas emissions, leaving landfills with a 2023 net emission value of 64x10⁶ kg of CO2 eq.. This breakdown can be found in Table 9.

4.4 Income Generation

As previously mentioned, the income potential due to tipping fees will be the same for each treatment method. This is because, under each scenario, the totality of waste will be treated. The income generated from treating the entire waste is just over 13 billion Costa Rican Colones, or roughly 17x10⁶ Euros.

Furthermore, income generated from selling electricity to the national grid depends on the amount of electrical output produced by each technology. Because of this, a landfill gas capturing system produces the most amount of income, followed by waste incineration. The scenario in which the OFMSW was treated by anaerobic digestion and the remaining waste by waste incineration produced the least amount of electricity. The complete breakdown of electricity output, and income generated from selling it, is presented in Table 10.

4.5 Complete Scenarios

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5. Discussion

One of the most eye opening results is that the impact generated from the waste incineration technology, in terms of greenhouse gas emissions, is greater than landfilling waste. The amount of carbon dioxide equivalent emissions from incinerating the entire waste stream, or incinerating the fraction not used by anaerobic digestion, is significantly higher than those emitted from landfills. Furthermore, the greenhouse gases emitted from the anaerobic digestion and waste incineration scenario are mainly caused by the incineration process.

However, it is also true that waste incineration is the waste management technology that produces more electrical output, and thus generates a higher income stream. In fact, the electricity output from the anaerobic digestion plus waste incineration scenario is significantly impacted by the latter. Approximately 57x10³ MWh were generated from anaerobic digestion, while the remaining 102x10³ MWh were generated from incineration.

It is also true that the landfill gas capturing scenario is the one that generates the least amount of greenhouse gases, in terms of net landfill emissions, but also generates the least amount of electricity and income. However, this technology does not solve other problems related to landfilling waste. However, these problems are out of the scope of this paper.

It is difficult to determine which solution out of the three waste management technologies is best for San Jose since each poses benefits and drawbacks. Anaerobic Digestion emits the least amount of greenhouse gas emissions. However, the need to treat the entire waste stream makes this scenario incomplete. The

It is clear that the three technologies presented will aid in achieving a better waste management system. However, it is clear that waste incineration will create a higher amount of greenhouse emissions than the current reality. Due to this, the waste incineration technology will not be a tool used to help Costa Rica achieve its objectives set in the National Decarbonization Plan, which was presented in Section 1.2. A landfill gas capturing system, or anaerobic digester, has more potential to reduce overall excess greenhouse gases. If an anaerobic digester were to be implemented to treat San Jose’s OFMSW, then other alternatives can be sought after for treating the remaining waste stream. For example, recycling must be studied as a possible alternative for treating the remaining waste not treated by anaerobic digestion.

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further study that analyzes how such an implementation can be done within the boundaries of this decree.

5.1 Putting the Results into Reality

Moreover, it is important to note that Costa Rica currently has none of the waste management methods studied. The scenario in which the entire city’s waste is separated, and an waste incineration facility and an anaerobic digestion facility are built and fully functional is highly improbable by 2023. However, it does represent a more complete scenario where each waste type is managed accordingly. A more realistic scenario is to have only 1 facility built. If the anaerobic digestion is built, then the remaining waste would ultimately end up in landfills. This scenario would entail a different emission tally and electrical yield output.

The results presented in the previous sections are based on several assumptions. First off, while Costa Rica’s electrical grid is completely renewable, it is naive to say that no emissions occur from it. If the emissions per unit of energy from the country’s electricity mix were to be quantified, then a more complete understanding of overall emissions per technology could be made. This is since each facility uses electricity to power their operations. Furthermore, the results have the potential to change if the system boundaries of this paper were to be expanded. For example, including emissions and energy usage from waste collection and transportation, or including emissions from a waste separation facility. If this was the case, then each technology would have higher emission totals, and a subsequent better understanding for the most sustainable solution could be made. Another critical assumption is the 50% estimated methane content present in biogas. The literature states that this is the most widespread value used for landfills. However, a 60% methane content in biogas would imply very different results. The emissions due to biogas leakage from anaerobic digestion would be significantly higher. However, this would also lead to an increased electricity output and income stream.

Furthermore, the system described in this paper assumes that the entire waste generated in San Jose will be collected and used for treatment. This is a very difficult achievement to obtain since a significant part of the waste stream is lost during the process and ends up in rivers, lakes and beaches. Moreover, it is assumed that the biodegradable fraction of waste is separated with a 100% success rate. A further study must quantify how much of the biodegradable waste can be separated and the percentage, and type, of impurities that will not be sorted out.

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5.2 Further Assumptions

It has been demonstrated how each technology’s projected emissions, electricity production, and income generation are dependent on the waste characterization. The waste characterisation projected for 2023 is based on the assumption that that the characteristics of waste will be the same as they were in 2011. These values have significant influence on the overall results. For example, a greater amount of biodegradable waste would imply more electricity and income for Anaerobic Digestion. The same can imply different values for the fossil carbon content values used to determine emissions from waste incineration.

Much can be done to solve the shortcomings regarding a lack of data on waste characterization for San Jose’s waste. I propose a yearly recurring study of San Jose’s waste to have a clear understanding of its characteristics, tendencies, and how these change each year. If possible, this study must be done for all the municipalities of Costa Rica if possible. This type of studies can be done prior to any waste management technology being implemented and after. It can help to determine which technology is best in accordance with the waste, as this study has done. Furthermore, electrical output projections and income generation can be made once the technologies are implemented.

Moreover, this study accounts for the income stream generated from each method, but not for the costs of producing or maintaining each one. Due to this, a complete economic comparison cannot be done, since a net income is calculated by subtracting expenses, amongst other items, from gross income . In order to have a more complete economic comparison, initial investments and operational costs must be taken into account for each technology in order to have a more complete understanding of the economic expenses and income related to each treatment method.

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6. Conclusion

Costa Rica’s deficient waste management system is a serious problem for the country’s citizens and environment. Furthermore, the country’s aim to position itself as a green and sustainable country has been severely slowed down by its waste problem. However, there is a country wide understanding of this problem and several advances have been made to improve it. This thesis project seeked to gain a deeper understanding of the best waste management technologies available to improve San Jose’s problem at managing its municipal solid waste.

It has been proven that continuing to landfill the waste leads to significant greenhouse gas emissions, and little electrical and economic output. Of the technologies studied, anaerobic digestion, and landfill gas capture have the potential to significantly reduce greenhouse gas emissions and provide a certain level of economic income and electrical output. Anaerobic digestion emits about 2x10⁶ CO2 equivalent emissions. However in a more complete scenario in

which the waste stream not used by anaerobic digestion is treated by a waste incinerator, emissions rose to approximately 159x10⁶ CO2 eq., which is higher than landfill emissions. Furthermore,

emissions from incinerating the entire waste stream are roughly 157x10⁶ CO2 eq., while a landfill

gas capturing system has the potential to divert approximately 16x10⁶ CO2 eq., resulting in a net

landfill emission tally of 64x10⁶ CO2 eq.

Due to the emissions previously presented, and in relation to the country’s National Decarbonization Plan, the anaerobic digestion facility is the most adequate for implementation. However, a solution is needed to treat the waste stream that is not treated by this technology. Landfill gas capturing systems would also be a beneficial solution to reduce greenhouse gases. However,this technology does not eliminate the landfill problem, and produces less electricity and income than an anaerobic digester alone.

Furthermore, waste incineration is the technology that generates the most electricity and income, followed by the anaerobic digestion plus incineration scenario. It is important to note that the anaerobic digester alone generated more electricity than the landfill gas capturing system.

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Appendices

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TRITA TRITA-ABE-MBT-20667