Municipal Solid Waste
Waste management is a complex process that aims to reduce the adverse effects of waste on public health and the environment (Stewart, 2010). Every year, billions of tons of municipal solid waste (MSW) are produced worldwide, making waste management processes a significant concern (Abdel-Shafy & Mansour, 2018). Municipal solid waste includes combustible and non-combustible materials, such as food waste, glass, plastic, paper, major home appliances, and other non-hazardous materials (Stafford, 2020). In this article, waste management specifically pertains to the waste management process of hazardous combustible and non-combustible MSW collected from commercial organizations and households (Iqbal, Liu, & Chen, 2020).
The collection, transportation, treatment, and disposal of waste should be undertaken under the regulation, control, and prevention of waste production through reusing and recycling processes. There are different steps in an ideal waste management process (Gonzalez Martinez, Brautigam, & Seifert, 2012). Waste that are generated during the production, distribution, and consumption of different types of products must be collected and processed safely and sustainably under relevant regulations. Such processes, which include waste sorting, product dismantling, and Refuse Derived Fuel production, are either aimed at waste recycling or treatment. After collection and processing, waste that can be recycled are sorted according to type and made into secondary materials. Hazardous wastes that cannot be recycled undergo thermal, mechanical, biological, and chemical treatments. Some treated waste are then used as industrial elements, while others are transported to landfills.
The world is currently producing more waste, with each individual and country contributing to this process (Ferronato & Torretta, 2019). To reduce the amount of waste, it should be considered for use as a source of energy before being disposed. Most untreated waste are disposed in landfills that are not regulated by environmental health safety standards (Ferronato & Torretta, 2019). Waste disposed this way can mix with groundwater because it is mostly deposited in sites located in depressions or valleys without adequate protection.
Landfilling is the most abundant waste management method that involves depositing waste in compacted layers in excavated land or on land surfaces (Vaverkova, 2019). It has been adopted globally due to the availability of undeveloped land, and remains the most economical form of short-term waste disposal (Danthurebandara, Passel, Nelen, Tielemans, & Van Acker, 2013). Up to 95% of solid waste worldwide is disposed through landfilling with other types of waste (Assamoi & Lawryshyn, 2012; Vaverkova et al., 2018). Landfilling is a viable technique because most residual materials from other forms of waste disposal end up in landfills. In contrast, other waste management technologies are currently unable to eliminate hazardous waste (T. U. S. E. P. Agency, 2020). One advantage of landfilling is that landfills can be used for the temporary storage of waste in some instances, while plans are made on how these landfilled waste materials can be repurposed (Wagner & Bilitewski, 2009). The treatment of waste before landfilling is mandatory in most developed countries, though such policies are often poorly applied in developing countries (Ferronato & Torretta, 2019).
Incineration is a form of thermal waste treatment involving the combustion of organic substances in waste materials and their conversion into ash, heat, and flue gas (Iadarola, Bareschino, & Pepe, 2018). The inorganic substances in waste that form the ash following combustion may come in the form of solid lumps or particles (Council, 2000). The temperature for combusting organic waste should be greater than 850°C, with more than two seconds of residence time. The high temperature destroys organic contaminants; accordingly, raw materials are preserved, and inorganic substances become concentrated. There should be an ample supply of air to perform maximum combustion of MSW while eliminating carbon monoxide (CO) and dioxin formation. The heat produced by this process can be used as a source of electrical power. Flue gas produced by incineration is free of pollutant gases produced by incineration using incinerator flues. Although incineration does not fully replace landfilling as a waste disposal method, it reduces waste mass and volume by 80% and 90%, respectively (Yong et al., 2019). Incineration is also beneficial for biomedical waste treatment, such as pathogen elimination, volume reduction, sterilization, and energy production (Gautam, Thapar, & Sharma, 2010).
Environmental impact of solid waste
Inappropriate waste disposal has severe environmental health consequences, including pollution and the spread of diseases (Alam & Ahmade, 2013). Landfilling without appropriate treatment can pollute the surrounding air, soil, and groundwater environments. When organic landfilled wastes decompose, they create methane gas (CH4), which comprises 20% of all anthropogenic methane emissions; CH4 is very explosive, flammable, and can replicate oxygen (O2) in confined spaces. Another significant landfilling concern is leachate management, which is correlated with rainfall volume (Giang, Kochanek, Vu, & Duan, 2018). Leachate can become mixed with surface waters and groundwater, particularly in older landfills without liners. Poor landfill management also attracts mice and flies that carry infectious diseases. Many developing countries use dumps for waste disposal, which are commonly found in metropolitan areas. However, they can be malodourous, reducing property values for local populations (Njoku, Edokpayi, & Odiyo, 2019). The adverse effects of landfilling can be controlled using appropriate designs and engineering, although such measures are rare especially among developing nations.
Thermal treatment, specifically incineration, has generated opposition from citizens worldwide due to beliefs that it threatens environmental health and is incompatible with waste reduction (Assamoi & Lawryshyn, 2012). However, it would be unwise to neglect incineration in favor of other waste management solutions, including landfilling, if subsequent damaging environmental health impacts are more extensive than those of thermal-treatment techniques (Liu, Ren, Lin, & Wang, 2015). This does not mean that incineration is safe, as scientific evidence indicates that it produces volatile gaseous emissions that can negatively impact environmental health. Furthermore, dust and fly ash from the incineration process can also spread as contaminants.
Significance and objectives
The composition of solid waste varies from one country to another according to location, waste control, and socio-economic status. This means that incineration could be more effective in countries that produce a higher rate of organic waste, which accords with most incineration targets (Ferronato & Torretta, 2019). A report by the European Environment Agency showed the differences in incineration waste disposal methods of European countries, revealing that it is more common among more industrialized and wealthier Western European countries, than Eastern European countries (E. E. Agency, 2016). A previous study clearly illustrated that most wastes are comprised of organic derivatives; therefore, incineration can be an effective waste-reduction method (Cutrim et al., 2019).
The public health issue of MSW management has always been a deeply controversial subject and remains a concern for environmental health practitioners. While there is a lack of studies on MSW management in Saudi Arabia, research on it has been conducted in Middle Eastern countries, allowing for the MSW composition in these systems to be compared to that of Saudi Arabia’s (Maalouf & El-Fadel, 2019; Nabavi-Pelesaraei, Bayat, Hosseinzadeh- Bandbafha, Afrasyabi, & Chau, 2017). The differences between these systems mean that management technology options differ among health systems. Identifying these differences can provide us with more accurate conceptions about the factors that must be considered to establish an environmentally conscious form.
This review compares the environmental health impacts of landfilling and MSW incineration in Brazil, Canada, China, Lebanon, and Iran. We chose countries from different continents to evaluate various health and MSW composition systems (Table 1) to overcome differences in regulation and standards between developing and developed countries, which may affect the results. Additionally, the study considered research from different continents, allowing for various health systems in different parts of the world to be examined. Some countries were chosen from the Middle East (Lebanon and Iran) due to the proximity of the geographical region to Saudi Arabia and the similarity of municipal solid waste sources. Accordingly, this enables a better examination of management forms in different parts of the world under different health systems and provides future research efforts on environmental pollution of the MSW management process in Saudi Arabia and its impact on the national public health.
Life cycle assessment
Our review integrated two different waste treatment plans (landfilling and incineration) and their complementary processes, such as reuse, energy recovery, leachate treatment (LT), and disposal, to reach a comprehensive interpretation about these plans. The solid- waste life cycle includes the collection, transfer, treatment, and disposal steps; however, this study did not assess the collection or transfer processes. Compared with treatment and disposal, the impact of these processes on environmental health is negligible due to the close proximity of waste management facilities with each other, which leads to similar environmental health impacts regardless of the method of treatment.
All papers reviewed in this study discuss four main phases: goal and scope, life cycle inventory, life-cycle impact assessment, and interpretation. This technique provides many advantages, including quantitative analysis, barely miss processes, potential impact evaluation, and a better understanding of the results (Moni, Mahmud, High, & Carbajales- Dale, 2019).
These studies were chosen because they all investigate the life cycle assessment (LCA) technique in waste disposal methods to determine the environmental impact of every MSW management stage, from the generation of raw materials, to treatment and disposal (Mali & Patil, 2016). They start their review with a life cycle inventory analysis, illustrating input and output to treat a large amount of MSW of an average composition for landfilling and incineration scenarios. The authors analyzed life cycle inventory using a combination of LCA- model technical reports, LCA literature, and inventory guidelines on greenhouse gases (GHGs). LCA’s use as an analysis technique is required to avoid missing out on any data output that might affect our analysis while quantifying gas emissions. Air emissions from landfilling and incineration scenarios were estimated through GHGs, acid gases, and Criteria Air contaminants (CACs). The GHGs used here were carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ammonia (NH3), while criteria air contaminants (CACs) include ozone (O3), nitrogen oxides (NOX), sulfur dioxide (SO2), carbon monoxide (CO), volatile organic compounds (VOCs), and particulate matter (PM). Air emissions were mainly classified into three kinds of environmental and public health impact included in the LCA assessment phase (Figs. 1, 2, and 3): acidification potential (AP), global warming potential (GWP), and nutrient enrichment potential (NEP). The LCA has been carried out in all studies according to the ISO 14040/44 guidelines (Standardization, 2006).
Brazil’s waste management system
Mendes et al. (2004) conducted a cross- sectional study using LCA to compare landfilling and incineration’s environmental health impact in Sao Paulo City, Brazil (Mendes, Aramaki, & Hanaki, 2004). The study assessed the treatment and disposal of MSW, comparing three different scenarios on incineration, which differ in ash-treatment system (disposal, meting, and reuse); and two scenarios on landfilling, one with and one without energy recovery. From these scenarios, Mendes et al. (2004) obtained values to calculate the total amount of chemicals entering waste management facilities (landfills and incinerators) in Sao Paulo (Mendes et al., 2004).
Canada’s waste management system
Another study by Assamoi and Lawryshyn (2012) also used LCA to evaluate the environmental health effects of incineration and landfilling of MSW prepared for disposal in Toronto, Canada (Assamoi & Lawryshyn, 2012). Specific parameters, such as diversion rates, changing waste-generation quantities, and waste composition, were considered. The authors chose two scenarios for the evaluation process: status quo (landfilling) and incineration with only electricity recovery. Industrial, commercial, and institutional residual waste were detailed in both scenarios to detect environmental emissions. The authors considered some general emissions, such as incineration plants’ stalk, the transport of solid residues to the management facility, and landfill operations emissions (Assamoi & Lawryshyn, 2012).
China’s waste management system
The third study was conducted in Suzhou city, China by Hong, Li, and Zhaojie (2010), who used LCA to prevent and control MSW. It estimated the environmental health impact of landfilling and incineration (Hong, Li, & Zhaojie, 2010). Hong et al. (2004) chose the management of one ton of MSW as a functional unit and included specific processes in both scenarios, such as infrastructure, road transportation of slag to landfill, LT, direct emissions, material production, electricity recovery, and energy production. The authors also used yearly averages for the operation processes, including the raw consumption of gas, water, and soil emissions, and energy from two scenario sites (Cutrim et al., 2019).
Lebanon’s waste management system
The fourth study was conducted in Beirut, Lebanon by Maalouf and El-Fadel (Mali & Patil, 2016). The authors used LCA to compare two scenarios on landfilling and one on incineration, and assessed their environmental impacts. The management of one ton of waste generated in the test area was used as a functional unit. Maalouf and El-Fadel (2019) selected it as a functional unit. The authors considered emissions from the system’s operation related to energy generation, waste degradation, operating equipment, materials substitution, residues management, and carbon storage (Mali & Patil, 2016).
Iran’s waste management system
A case study was carried out in Tehran, Iran by Nabavi-Pelesaraei et al. (Nabavi-Pelesaraei et al., 2017) who aimed to assess the environmental performance of landfilling and incineration of MSW. The functional unit for this study was based on 8,500 tons of daily MSW produced in Tehran. The researchers considered direct emissions from incineration and landfilling and indirect emissions from producing and consuming electricity and diesel fuels (Nabavi-Pelesaraei et al., 2017).
Incineration showed more energy recovery and emissions from CO2, NO2, and N2O, while landfill facilities presented higher levels of hydrogen sulfide (H2S), nitrogenous compounds, and CH4. The studies showed impact potentials for landfilling and incineration as final and intermittent stages using primary treatment (MT), ash treatment, LT, energy recovery, and materials recovery values.
Please insert fig. 1 here Global Warming Potential
At various MSW management stages, MT contributed the major part of GWP in both landfilling and incineration. The GWP, represented and expressed as Kg of CO2, in landfilling and incineration was found to be mainly due to CH4 generation and plastic burning, respectively. Studies conducted in Brazil, China, Lebanon, and Iran found that the GWP in landfilling was greater than that in the incineration process due to direct methane-gas emissions as shown in Figures 1 A, C, D, and E. On the other hand, Assamoi and Lawryshyn (2012) indicated higher CO2 emissions in incinerators than in landfills in Canada, suggesting that landfilling is more environmentally friendly than incineration (Fig. 1 B).
The AP was represented and expressed as Kg of SO2. The MT is responsible for most of the AP in landfills, and LT was the most abundant cause of AP in incineration. In Canada, it was found that incineration produced more AP than landfilling (Fig. 1 B). The SO2 emissions in Brazil, China, Lebanon, and Iran indicated higher emissions in landfills than in incinerators, suggesting that the incineration process is more environmentally friendly than landfilling as shown in Figures 1 A, C, D, and E. These results support incineration and make it a better choice for the treatment of waste before disposal in these countries.
Please insert fig. 3 here Nutrient Enrichment Potential
Nutrient enrichment potential was expressed as Kg of NO3. The MT was mainly responsible for NEP in both the landfilling and incineration processes. Hong et. al (2010) and Mendes et. al (2004) found that landfilling was responsible for producing majority of the NEP compared to incineration (Figs. 1 A and C). Assamoi and Lawryshyn (2012) reported higher NO3 emissions in incinerators than in landfills.
This study aims to better understand the impacts of chemical emissions according to three parameters, GWP, AP, and NEP, in three facilities. These parameters are considered substantial environmental issues concerning their connection with MSW management processes. In this review, MSW was targeted to evaluate landfilling and incineration as primary waste-management forms. We analyzed both the main and specific complementary processes—reuse, energy recovery, LT, and disposal—to minimize their effects on our results and provide a more comprehensive and holistic understanding of the LCA process.
Municipal solid waste requires a higher regulation level because it includes hazardous waste, such as batteries, mercury-containing devices, and electronics. Additionally, people are more directly involved in MSW management than management mechanisms used to dispose of other waste types, such as medical and industrial waste, including generators. Therefore, appropriate related education about MSW management is needed. Organic substances involved in MSW represent a significant element of this kind of waste, which incineration is mainly designed to dispose of. Accordingly, this method offers an efficient and valuable means of treating MSW before disposal. The authors focused on the composition changes in MSW due to residential waste diversion because they determine landfilling and incineration methane generation and end energy content, respectively; these changes can then be used to detect the recovered amount of energy from the two scenarios.
In Brazil, China, and Middle Eastern countries, incinerators were more environmentally friendly than landfills. In contrast, landfills in Canada (a model of developed countries) produced fewer emissions. The significant difference in this finding may be because landfills are much better engineered in Canada. Most landfills in the world, especially old ones, are dumps that may support this hypothesis. The incineration process was relatively comparable to landfilling, significantly less engineered, which remains the best waste- management option. According to this review’s findings, incinerators are an excellent treatment option in countries without strong landfill regulations. Despite this finding, well- engineered landfilling is still the best option for MSW management. In Saudi Arabia, policy makers and authorities can choose the best environmentally friendly MSW management option based on the standards used in designing landfilling. Additionally, health policy makers and authorities can improve the design, structure, or regulations imposed by their landfills for a more effective and environmentally-friendly waste management system.
There is a fair amount of literature on MSW management in Saudi Arabia; however, these documents did not specify the environmental impact of using LCA as a tool. We tried to minimize this by including Middle Eastern countries (i.e., Lebanon and Iran) with a similar culture and possibly produce similar types of local solid waste accordingly. Some literatures did not have NEP as one of the environmental impacts of MSW as it tends to focus on GWP and AP. In general, the reviewed studies did not consider some negligible emissions, such as ash disposal, auxiliary fuel requirements, LT in landfills, and the use and transport of the daily cover for landfill emissions. This work is a good starting point for comparative studies regarding the environmental impact of MSW management processes. Further comprehensive research is needed to understand better the environmental effects of different MSW management methods on other health systems.
Municipal solid waste management requires very high-quality standards and policies for the disposal of MSW with minimum environmental health risks, and the application of these policies determines these risks. Until less invasive methods are discovered, landfilling remains the best option for waste disposal because other MSW management forms cannot be used to entirely clear or minimize waste hazards. In countries where landfilling sites undergo strict MSW disposal policies, the method is considered minimally invasive due to proper construction, engineering, and control structures. Accordingly, it is better to adopt landfilling as an MSW management solution, while dumps are being eliminated. This is not the case in countries with weak environmental health standards, where most landfills are dumps that have not been engineered or controlled. Accordingly, MSW management solutions like incineration remain much better options than poorly organized landfills, despite the former’s environmental health damages compared with properly executed landfilling as seen in developed nations. In Saudi Arabia, from an environmental health point of view, further evaluation for the current landfilling organization standards and policies are required from policy-makers before constructing the MSW management system form (i.e., landfilling and incineration).
CONFLICT OF INTEREST
The author has no conflicts of interest to declare.
I want to express my gratitude to Dr. Brady Skaggs from Tulane University, the USA, for reviewing this work.
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