Several researchers have explained the concept of sustainability with a Venn diagram encompassing three elements: Environment, Society, and Economy. Of much concern about the concept of sustainability is striking a balance between these three elements. Necessity is being regarded as the mother of invention according to the quote made by the ancient Greek philosopher Plato. The quest of man to satisfy his diverse needs brings about the advent of technology as we have it today. Sustainable development is defined as the development that meets the needs of the society of today without compromising the ability of future generations to meet their own needs [1
]. A sustainable society is founded on equal access to health care, nutrition, clean water, shelter, education, energy, economic opportunities, and employment. In this ideal society, humans live in harmony with their natural environment, conserving resources not only for their generation but also for their children’s children. As humans derive satisfaction in natural products and resource utilization to meet their needs, a need then arose for proper disposal/treatment/reuse of their continuously generated waste (i.e., municipal solid waste, agricultural, and industrial waste).
Municipal Solid Waste (MSW), more commonly known as trash, comprises various items being thrown away daily. MSW materials can be broadly categorized into three viz: biomass (such as paper, food waste, grass clippings, leaves, wood, and leather products); non-biomass combustible materials (such as plastics, petroleum-based); and non-combustibles materials (such as glass, metals). A new study has revealed that the United States is at the top of the list of countries that are driving the global waste crisis, producing three times the global average of waste for 4% of the world population [2
]. In 2015, a total of 262.4 million tons of MSW was generated in the USA, among which 52.5% was deposited in landfill, 25.8% recycled, 12.8% burnt for energy recovery, and the rest 8.9% was composted [3
]. In 2017, the United States produced 258 million metric tons of MSW, followed by China and India which produced 220.4 and 168.4 million metric tons, respectively [4
The idea of using waste as an energy source is not new. While Waste-to-Energy (WTE) has been slow to take off in the USA (i.e., converting a lesser amount of these enormous waste to energy), it is a big business in Europe, driven largely by EU waste legislation. Figure 1
shows the proportion of total solid wastes generated to the amount converted to energy in 2020, with USA having the least conversion rate of 12%. European countries and Japan convert large amounts of waste generated to energy due to the unavailability of open space for landfills [5
]. In Asia, the Chinese government plans to build 300 waste-to-energy plants over the next three years, including the world’s largest plant in Shenzhen, which, when open in 2020, is estimated to burn 5000 metric tons of trash every day. According to [6
], the USA had 71 waste-to-energy plants that generated electricity in 20 states with a total generating capacity of 2.3 gigawatts. In 2019, 67 WTE plants generated about 13 billion kilowatt-hours of electricity from burning nearly 25 million tons of combustible MSW. Biomass materials accounted for about 63% of the weight of the combustible MSW and for about 47% of the electricity generated [5
]. The global waste-to-energy market is increasing, it is expected to reach USD 37.64 billion by 2020 growing at a compound annual growth rate of 5.9 percent, up from USD 25.3 billion in 2013 [7
Virtually every resident, organization, and human activity in the United States generates some type of waste. Different types of waste generated include municipal solid waste, agricultural and animal waste, medical waste, radioactive waste, hazardous waste, industrial non-hazardous waste, construction, and demolition debris, extraction and mining waste, oil and gas production waste, fossil fuel combustion waste, and sewage sludge. The total generation of municipal solid waste in 2017 was 267.8 million tons of MSW, approximately 5.7 million tons more than the amount generated in 2015. MSW generated in 2017 increased to 4.51 pounds per person per day. This is an increase from the 262.1 million tons generated in 2015 and 208.3 million tons in 1990 [8
]. In 2012, the total solid waste generated by Maryland’s twenty-two counties is 12.3 million tons with Baltimore county generating the highest amount of solid waste [9
]. This total solid waste was reduced to 11.9 million tons in 2016 with Prince George county generating the highest amount of solid waste. In 2018, Maryland counties and Baltimore City generated 14,310,933 tons of solid waste, much higher than the previous years as shown in Figure 2
. Out of the total waste generated, only small percent is converted to energy.
As communities and companies around the USA pursue zero-waste-to-landfill and look for renewable energy sources, waste-to-energy plays a major role in sustainable waste management and thereby impacts positively the health of the people in the community and environment at large, which is coupled with social and economic benefits. The incineration of waste is the most stringently regulated and controlled industrial activity. Waste-to-Energy plants are equipped with sophisticated filtering devices to deal with the pollutants that arise from the incineration process and minimize emissions released into the atmosphere. Some of these gaseous pollutants can be hazardous to people and the environment if they are not properly controlled. The U.S. Environmental Protection Agency (EPA) applies strict environmental rules to waste-to-energy plants, which require thermal plants to use pollution control devices such as scrubbers, fabric filters, and electrostatic precipitators to capture air pollutants. Direct industrial CO2
emissions rose 0.3% to reach 8.5 Gt CO2
in 2017 amounting to 24% of global emissions, this is a rebound from the 1.5% annual decline during 2014–2016 [11
Before the advent of incineration technology in the United States, landfills had been in major use since the country has large land mass, unlike European or Asian countries. The major problem with landfills approach is the release of methane gas (i.e., a source of greenhouse gas (GHG) directly into the atmosphere, causing greater environmental havoc to the society. Another adverse effect is pollution to water bodies due to erosion and stormwater run-offs. Global concern with the landfill approach is that the world cannot keep dumping the waste on land forever because land space will soon be filled up. The incineration process was developed as an alternative to landfills. Incineration is a better waste management option; it can burn up to 90% of the total waste generated in a chosen area, saves on transportation cost for waste, as well as producing energy, among others. The conversion process comes with so many advantages as well as disadvantages, the problem arises based on the drawbacks that the waste-to-energy conversion process creates. The process of burning waste to generate energy has been a better option when compared with its counterpart—anaerobic digestion, but of serious concern is the release of harmful gases (CO2
and NOx) into the atmosphere, causing a direct impact on public health such as the spread of diseases, etc., which relate to environmental, economic, and social issues of sustainability [12
The objective of this research work is to assess the sustainability impacts of the thermochemical conversion processes of MSW-to-energy in terms of environmental friendliness, economic and social benefits. This is done by analyzing existing MSW incineration plants in Baltimore Maryland, to determine if the waste conversion process with the current operating technology is sustainable.
3. Results and Discussion
The life cycle assessment was performed using Simapro software. All data used were obtained from the company and EPA publication about the environmental concerns of the incineration plant. All materials and processes were calculated based on yearly usage, production, and consumption. A municipal waste scenario contained in the database demo7 was used for comparison.
3.1. Global Warming Potential (GWP)
The impact assessment analysis of the incineration plant was calculated with the Municipal waste/NL S demo7 scenario. The incineration process generated more greenhouse gases resulting in high impact expressed as the global warming potential with a value of 6.46 × 1017
eq which is 6.46 × 108
Gg of CO2
equivalence over one year as shown in Table 1
. The combustion of MSW normally generates both biomass and fossil CO2
. Biomass CO2
is higher because of the higher fraction of organic waste such as food waste, yard waste, and paper than plastics that come from fossil fuel. This fraction does not contribute to global warming in contrast to fossil CO2
since it is part of the global carbon cycle. Although the combustion of biomass helps reduce the generation of greenhouse gases in particular of CO2
, during the combustion process other fuels, for instance diesel, are used to help to burn MSW because it has high moisture content. A cleaner approach of burning the waste using other fuel sources could result in less GWP
impact by the incineration plant.
According to the study by [18
], three waste management scenarios were analyzed using both CML 2001 and Eco-indicator 99 methods in the SimaPro software. Waste incineration (Scenario III) has very high environmental impacts compared to the other waste treatment processes in many categories, and especially regarding the global warming potential. This agrees with the result obtained in Table 1
3.2. Acidification Potential (AP)
Acidification Potential (AP
) is a consequence of acids being emitted to the atmosphere and subsequently deposited in surface soils and waters. AP
classification factors are mainly based on the contributions of SO2
, NOx, HCl, NH3
, and HF and expressed as SO2
]. According to an LCA study by [22
] on landfills vs. incineration, the incineration option performed more poorly from an environmental perspective than the landfill option in terms of AP
. From this study, the AP
impact is 1.66 × 1017
mmole eq, it gives less impact when compared with the GWP
and EP as shown in Table 1
. Similarly, the study by [18
] indicated that landfilling (scenario 0) and waste incineration (scenario III) have the highest contributions for the acidification impact category because of the SO2
, NOx, HCL, and HF emissions to the air.
3.3. Eutrophication Potential (EP)
The major problem faced by the MSW incineration plant under study is nitrogen, which is a key substance in waste and possibly a major contributor to the EP. Fifty percent of total nitrogen in the waste can be found in leachate as NO3−
and contributes a major share to eutrophication [23
]. Moreover, fuel production, collection, and transportation also emit eutrophying substances such as NH3
O, and NO3−
. From the analysis, the overall EP from the total tons of waste the incineration plant processed annually is 2.27 × 1012
kg of N equivalents as shown in Table 1
. This accounts for total phosphorous and nitrogen in the water and the NOx
O emissions in the air. As shown in Table 2
, the inventory analysis shows that oxides of Nitrogen produced are 1.63 × 103
Mtn, which results in a greater impact of eutrophication potential.
3.4. Economic Analysis of Wheelabrator Technologies (WT)
The Economics of Life Cycle Assessment are dominated majorly by the cost and revenue review. Total capital expenditure (i.e., the present value of the investment cost of a particular waste management system); total operation and maintenance costs (that is, costs involved in waste collection and transportation, labor cost, and the costs involved in utilities, operating suppliers, insurance, taxes, etc.); and environmental cost (i.e., monetary value for the environmental emissions) must be incorporated in the LCA economic analysis [24
]. It is important to also consider cost in terms of the area MSW processing plants occupy. WT sits on approximately 12 acres of land and can produce electricity along with by-products and co-products. At the waste collection end of the process, another cost appears in the form of handling and management of waste based on consumers and environmental factors. In the case where a consumer disposes of solar panels and glass, waste disposal trucks collect these non-combustibles and dump them on the tipping floor. WT pays for them to be disposed of, thereby impacting the cost structure (i.e., an unexpected cost that normally would not be included in cost analysis but contributes to the overall economics in the sustainability of the plant).
As shown in Figure 3
, WT generates revenue from both its fuel source and its outputs. The WTE plant processes 2250 tons of waste daily with electricity generation of about 60 MW/h which powers 40,000 homes in Baltimore. An important aspect of electricity generation from waste is the fact that the heat produced from burning the waste at 2500 °F is used to heat water to produce steam. WT produces 110,000 lbs. of steam per hour and makes about $
4000 daily. The plant also makes revenue from sales of electricity at $
30/MW and charge a tipping fee of $
50/ton of waste collected from the city of Baltimore (with a rebate of $
5 to the Baltimore city waste management and $
7.50 to outsiders). In 2018, 690,000 tons of waste was processed by the plant. Another source of MSW plant revenue generation is the sale of Ferrous and Non-Ferrous metals from the recovery process. About 15,000 tons of metals are recovered yearly from the plant and are sold to buyers majorly in Europe and Asia. The price of metal sales is very unstable and can swing up to +/− 300%. According to the plant manager at WT, the plant was able to sell a ton of metals at $
1500 in 2018, but in 2019, only received $
500/ton. This is all based on forces of demand and supply in the market. In general, the cost of MSW operation is in the form of land cost, Operation and Maintenance costs, environmental costs, fuel costs, and labor costs. The revenue, on the other hand, comes from tipping fees, steam sales, electricity sales, and metal sales. According to the plant manager, about 66% of their revenue comes from the sale of steam.
3.5. Human Health Concerns
Waste incineration systems produce a wide variety of pollutants that are detrimental to human health. Such systems are expensive and do not eliminate or adequately control the toxic emissions from chemically complex MSW. Even new incinerators release toxic metals, dioxins, and acid gases. Far from eliminating the need for a landfill, waste incinerator systems produce toxic ash and other residues. The waste-to-energy program to maximize energy recovery is technologically incompatible with reducing dioxin emissions. Dioxins are the most lethal Persistent Organic Pollutants (POPs) which have irreparable environmental health consequences. Dioxin is a highly toxic compound that may cause cancer and neurological damage, and disrupt reproductive systems, thyroid systems, respiratory systems, etc. [25
The affected populace includes those living near the incinerator as well as those living in the broader region. People are exposed to toxic compounds in several ways: (1) breathing the air which affects both workers in the plant and people who live nearby; (2) eating locally produced foods or water that have been contaminated by air pollutants from the incinerator; and (3) eating fish or wildlife that have been contaminated by the air emissions. According to the operation manager, WT has been working tremendously on reducing the negative impacts. Through the usage of local waste as a fuel to create a local-energy ecosystem, WT diverts waste from landfills and lowers greenhouse gases by recycling metals, offsetting the use of fossil fuels, and reducing methane emissions from landfills. As a significant partner in the City of Baltimore’s revitalization over 30 years, Wheelabrator has helped the city reduce its carbon footprint while providing Tier 1 renewable energy to tens of thousands of Maryland homes and businesses. Furthermore, it has been a supporter and contributor to several green initiatives within the city.
WT is committed to protecting public health and the environment through the use of a Continuous Emissions Monitoring System (CEMS) being monitored every 10 s. The facilities use advanced environmental control systems to meet and exceed some of the most stringent environmental standards in the world while safely producing clean, renewable energy for nearby homes and businesses. Wheelabrator facilities operate with superior environmental performance and are extensively regulated under state and federal air, water and solid waste laws and regulations to protect human health and the environment. All the WT facilities have maintained their environmental permits without exception, since commencing operations over 40 years ago and continue to perform, on average, four to five times better than standards set by the U.S. Environmental Protection Agency.
3.6. Environmental Achievements of Wheelabrator Technologies in USA
It is a known fact that WT was the first waste-to-energy plant in the U.S. to have a materials recovery facility on site. Wheelabrator Falls was the first and only privately owned, waste-to-energy plant to have a materials recovery facility on site.
Similarly, WT is the first to install advanced air pollution control technology. Wheelabrator Millbury was among the first waste-to-energy facilities in the U.S to install advanced air pollution control technology designed to control SO2 and other acid gas under EPA guidance; it has the best available control technology requirements needed to install carbon injection systems. Wheelabrator Falls was the first waste-to-energy facility to install a full-scale powder-activated carbon injection system in the U.S. to improve mercury emission control and to design the most efficient boiler. The WTE plant has the highest temperature and pressure steam conditions of any municipal solid waste-fired boiler in the world.
3.7. Social Concerns
Wheelabrator has been engaged in a tussle with the city of Baltimore and its residents due to environmental concerns majorly from their NOx emissions. The Wheelabrator plant in Baltimore burns the majority of the city’s garbage and is considered its single largest source of industrial air pollution. According to EPA release in 2014, the Baltimore incinerator is the source of so much of the city’s pollution—it produced 82 percent of the sulfur dioxide and 64 percent of the nitrogen oxides emitted by smokestacks within city limits in 2014 [26
]. Maryland State environmental officials are working with Wheelabrator to reduce the incinerator’s emissions stating that a comparable facility in Montgomery County produces less than half as much nitrogen oxide.
In February 2019, the Baltimore Clean Air Act (BCAA) was approved by the city council to checkmate the activities of polluters in the city with Wheelabrator Technologies as number one in the city. The BCAA act requires the incineration plant to install a technology that will reduce the release of NOx to 45 ppm, much less than the current 150 ppm rate. A non-compliance with this standard will result in non-renewal of the company’s license for operation by the end of 2021 [27
]. It is no doubt that the city has benefitted greatly from the plant for the past 34 years as MSW generated in the Baltimore environ is being processed by the plant as opposed to being dumped on land. The two landfills in Baltimore are being said to be filled in 5–10 years with the current intake of waste by these facilities. However, shutting down of WT by 2021 will cause these landfills to be filled much earlier than the proposed years. The impact of shutting this facility down has generated certain concerns in the minds of the researchers such as: (1) a safer option for MSW management in the city after WT shutting down; (2) an alternative source of electricity needed by more than 40,000 homes and steam for heating and cooling by over 200 businesses in the city; (3) employment opportunities for the laid-off workers from the plant. One major hypothesis which is yet to be accepted is that the city will effectively manage its waste after shutting down the incineration plant.