Analysis of the Efficiency and Environmental Impact of Municipal Solid Waste Incineration as a Tool for Sustainability Development in Kazakhstan

Abstract

Municipal solid waste (MSW) disposal is one of the areas of sustainability development of modern countries including the Republic of Kazakhstan. Annually, more than 4 million tons of MSW are generated, and this amount continues to grow. Additionally, approximately 120 million tons of waste have already accumulated in landfills across the country. It is essential to select an MSW disposal technology that is environmentally friendly, minimizes the generation of more hazardous waste, and maximizes energy efficiency. Ideally, the technology should not only reduce energy consumption but also generate energy and valuable by-products that have market demand. The aim of this study is to conduct experimental research to evaluate the efficiency and environmental impact of incinerating both unsorted and sorted municipal solid waste. As a result of the experiment, the volumes of flue gases and the concentrations of harmful substances produced by the combustion of both unsorted and sorted waste were determined. Additionally, an analysis of the slag and ash generated from the combustion of sorted MSW was conducted. The obtained results enable the development of a waste-free technological scheme for a plant designed for the complete utilization of municipal solid waste.

1. Introduction

1.1. Literature Review

The Sustainable Development Program of Kazakhstan includes a number of priorities enshrined in the Kazakhstan-2050 strategy [1]. One of them is “Rational use of terrestrial ecosystems and water resources, climate change”. Annually, approximately 4.5 million tonnes of MSW are generated in Kazakhstan as a result of human activities, with this volume increasing in proportion to the country’s population growth [2]. In addition to current generation rates, nearly 120 million tonnes of waste have already accumulated in landfills throughout populated areas [3]. At present, the Government of Kazakhstan faces the critical challenge of selecting an appropriate waste disposal strategy [4]. MSW disposal is one of the areas of sustainability development of modern countries because solid waste can be useful as a renewable energy source. It is imperative to adopt an MSW disposal technology that minimizes environmental impact, avoids the generation of secondary hazardous waste, and maximizes energy efficiency. Ideally, the technology should be net energy-positive, producing usable energy and marketable by-products rather than consuming energy during disposal [5]. Furthermore, to facilitate implementation and scalability, the selected technology must demonstrate strong investment appeal to attract private capital [6].

There is extensive international experience in the disposal of MSW [7] including methods such as sorting for recovery of secondary raw materials, energy recovery, pyrolysis, bioprocessing, and thermal destruction.

Among these, pyrolysis and energy recovery are considered the most promising technologies [8]. However, according to the Environmental Code of the Republic of Kazakhstan, the energy recovery of certain waste categories is prohibited. These include liquid waste, hazardous explosive, corrosive, oxidizing, and flammable substances, persistent organic pollutants, mercury-containing components, electronic and electrical equipment, metals, batteries, and construction materials [9].

Therefore, prior to the energy recovery of MSW, sorting is essential [10]. This process facilitates the extraction of both components suitable for use as secondary raw materials [11] and those waste fractions prohibited from energy recovery, as previously indicated [12].

As of 2021, approximately 500 waste incineration plants (WIPs) dedicated to waste-to-energy processing were operational within the European Union (see Figure 1), collectively managing an MSW capacity of approximately 100 million tonnes per year.

Table 1. Analysis of solid waste disposal methods in EU countries.

Country	Method of Solid Waste Disposal and Share in Percentage
	Recycling	Backfill for Reclamation	Energy Recovery	Incineration Without Energy Recovery	Landfilling
EU average	37.9	10.7	6	0.7	44.7
Italy	79.3	0.1	5.7	2.5	12.4
Belgium	77.4	0	11.2	3.6	7.8
Hungary	63.2	5.4	6.4	0.5	24.5
Latvia	57.6	4.6	10	0	27.8
Denmark	56.7	18.4	18.9	0.1	5.9
France	55.8	10.4	5.5	1.3	27
Croatia	52.3	3.5	2	0	42.2
Czech Republic	50.9	34.6	3.5	0.3	10.7
Poland	49.3	20.3	3.6	0.4	26.4
Portugal	48.2	6.1	11.1	0.3	34.3
Slovenia	43.8	49.5	2.5	0.5	3.7
Netherlands	43	0	7.2	0.8	49
Germany	42.7	26.4	12	0.5	18.4
Luxembourg	41.1	32.6	2.6	0	23.7
Spain	38.7	10	2.9	0.2	48.2
Slovakia	38.2	14.7	6.7	0.5	39.9
Austria	36	12.7	No data	No data	45.6
Lithuania	34.1	2.8	6.3	0.1	56.7
Estonia	28.9	8.4	1.8	0	60.9
Malta	18.5	65.6	0	0.2	15.7
Cyprus	17	20.4	7.2	0	55.4
Sweden	13.1	2.7	6.8	0.1	77.3
Ireland	11.5	51.4	9.8	0.1	27.2
Greece	10.7	3.5	0.7	0	85.1
Finland	9.2	2.4	5	0.1	83.3
Romania	3.2	0.3	1	0	95.5
Bulgaria	2.9	0	0.5	0	96.6

presents a comparative analysis of MSW disposal methods and technologies employed across EU member states [13,14,15,16,17,18,19,20].

Over the past decade, more than 120 new waste incineration plants have been commissioned across Europe, resulting in a 40% increase in energy generation from waste. The expansion of such facilities continues, exemplified by the commissioning of the largest waste incineration plant in Europe by capacity, which began operations in November 2021 in Istanbul, Turkey [21]. At the legislative level, MSW is recognized as a renewable energy source, and most EU countries apply a “green tariff” to incentivize energy production from these plants.

China has advanced in this direction at an even faster rate [22]: over the past decade, 285 new waste incineration plants have been constructed, increasing the total number to approximately 400. During this period, the volume of energy generated from waste has increased fivefold, while the amount of solid waste requiring disposal has been reduced by more than 50%.

The vast majority of existing waste incineration plants have a significant drawback: they utilize unsorted MSW as feedstock. This practice results in emissions not only of conventional pollutants such as carbon dioxide, carbon monoxide, sulfur oxides, and nitrogen oxides, but also of hazardous compounds including phenols [23], dioxins [24], formaldehyde [25], hydrogen chloride, hydrogen fluoride [26], and heavy metals [27]. Additionally, the combustion process generates slag and ash residues that require disposal in specialized containment facilities [28]. Incomplete oxidation of organic fractions such as food waste can further lead to the formation of fats, oils, organic acids [29], carcinogenic substances [30], and trace amounts of ozone [31], posing additional environmental and health risks.

1.2. Theoretical Basis

Municipal solid waste is a source of gases, which can be classified into landfill gases and combustion flue gases:

1

Landfill gases are gaseous products generated by the bacterial decomposition of the solid organic components of waste. These gases primarily consist of methane and carbon dioxide, with minor amounts of hydrogen sulfide and other gaseous compounds, many of which are greenhouse gases.

2

Combustion flue gases are produced during the direct oxidation of MSW. They are characterized by high temperature, highly variable composition (due to the diverse range of materials combusted), and typically exhibit significant toxicity. This toxicity arises largely from the presence of inorganic substances of undefined chemical composition introduced into the incinerator or furnace, especially when unsorted waste undergoes thermal treatment.

Incinerators are employed when the transportation of waste to landfill or other disposal sites is challenging or impractical. These furnaces demonstrate notably high efficiency in the decomposition of materials such as PVC, polystyrene, and polyethylene. This approach constitutes a high-temperature thermal treatment method for unsorted municipal solid waste, typically conducted without energy recovery, and is often utilized alongside the destruction of hazardous waste.

Primary flue gas emitted from the combustion of unsorted MSW can contain a wide range of gaseous, aerosol, vapor, and particulate pollutants, including soot, ash, and carbon black. Among the most hazardous constituents are furans, dioxins, benzopyrene, carbon disulfide, aldehydes, halogenated compounds, heavy metals, and acidic vapors.

Compared to coal- and fuel oil-fired power plants, MSW combustion results in significantly lower emissions of certain pollutants, including:

• Sulfur oxides: This reduction is primarily due to the relatively low sulfur content of MSW, which ranges from 0.05% to 0.3% of the total mass. Additionally, a portion of the sulfur compounds present in MSW is converted into sulfates during combustion, which remain immobilized in the slag;
• Nitrogen oxides: The concentration of nitrogen oxides in flue gases depends largely on combustion temperature. In MSW incineration units, operating temperatures typically range between 850 and 1000 °C, whereas substantial nitrogen oxide formation generally occurs only at temperatures exceeding 1100 °C

Among the highly hazardous gaseous toxicants present in the flue gases of MSW incineration plants, aldehydes and organic acids formed by incomplete oxidation of food waste, fats, oils, and other MSW components should be highlighted. Additionally, carcinogenic polycyclic aromatic hydrocarbons (PAHs) such as benz[a]pyrene, benz[e]pyrene, benz[a]anthracene, kerosene, phenanthrene, and pyrene are notable contaminants. However, modern dust collection technologies capture up to 99% of fly ash–which adsorbs a significant portion of these carcinogens–and the dispersion of fly ash through stacks further reduces their concentrations at ground level to values well below current maximum allowable concentrations (MAC). Beyond these pollutants, flue gases may also contain trace amounts of ammonia, ozone, and other harmful substances, but their concentrations are typically negligible

A significant challenge in the incineration of solid municipal waste is the formation of dioxins and furans. Organic chemistry recognizes 75 congeners within the class of polychlorinated dibenzo-p-dioxins (PCDDs) and 135 congeners of polychlorinated dibenzofurans (PCDFs). These compounds constitute a diverse group of polyhalogenated heterocyclic aromatic substances, predominantly chlorinated and brominated derivatives, characterized by substantial structural variability.

The formation of dioxins originates from chemical reactions occurring during the combustion and thermal treatment of raw materials containing chlorinated hydrocarbons, including wood, fuel briquettes, coke, oils, and electric transformers filled with polychlorinated biphenyl-containing oils.

Unsorted MSW contains both pre-existing dioxins (for example, in waste oils and certain other materials) as well as precursor substances capable of generating dioxins during the cooling phase of flue gases following waste combustion. Notably, these precursor substances include polyvinyl chloride (PVC), coal, wood, sodium chloride (NaCl), and hydrogen chloride (HCl).

The slag generated during the incineration of unsorted MSW does not contain dioxins, attributable to the presence of excess air and rapid quenching of the molten residue. In contrast, cooled flue gases at approximately 450 °C contain dioxins, which become adsorbed onto particulate matter, primarily fly ash. Additionally, fly ash is enriched with heavy metals. Consequently, the fly ash collected from MSW incineration flue gases must be managed with stringent environmental controls, including containment in engineered landfill sites designed to prevent exposure to moisture and wind erosion, or subjected to specialized stabilization treatments. Such treatments aim to immobilize toxic constituents by converting them into chemically bound, insoluble forms, for example, through vitrification processes.

During combustion, it is essential to consider that unsorted MSW contains potentially hazardous elements characterized by high toxicity, volatility, and elevated concentrations. These include various halogenated compounds (fluorine, chlorine, bromine), nitrogen-containing species, sulfur compounds, and heavy metals such as copper, zinc, lead, cadmium, tin, and mercury. Under incineration conditions, halogens predominantly exist as hydrogen halides (e.g., hydrogen chloride (HCl), hydrogen bromide (HBr)), which represent the most thermodynamically stable combustion products. Sulfur is primarily partitioned into non-volatile sulfate compounds (up to approximately 70%), which are retained in the slag, and volatile sulfur dioxide (SO₂) gas. All volatile reaction products are emitted via the flue gases. In untreated flue gases, typical emission concentrations range approximately between 300–1000 mg/m³ for HCl and 100–500 mg/m³ for HBr.

Dry MSW contains approximately 1% nitrogen by weight. The primary nitrogen oxidation product generated during combustion is nitric oxide (NO), with typical concentrations in raw flue gas ranging from 200 to 400 mg/m³.

Certain heavy metals present in MSW, such as iron, chromium, and nickel, do not form volatile species during combustion and predominantly partition into the slag. Conversely, lead and cadmium form volatile chloride compounds that are transported with the flue gases. Upon cooling of flue gases to approximately 200 °C, these metal chlorides condense and are subsequently captured together with fly ash during the wet stage of gas cleaning. In contrast, mercury and its compounds, which are among the most toxic heavy metals, largely remain in the gas phase even at reduced temperatures.

Over the past decade, the concentration of heavy metals in unsorted MSW has significantly increased, primarily due to the presence of spent dry galvanic cells, batteries, incandescent and fluorescent lamps, synthetic materials such as dyes and stabilizers, as well as metal coatings on leather products.

There are two principal mechanisms for the formation of dioxins and furans during the thermal processing of municipal solid waste (MSW):

• Primary formation, which occurs during the combustion of MSW at temperatures ranging from 300 to 600 °C;
• Secondary formation, which takes place during the cooling phase of flue gases containing hydrogen chloride (HCl), copper and iron compounds, and carbonaceous particulate matter, typically within the temperature range of 250 to 450 °C. This secondary formation is facilitated by a heterogeneous oxychlorination reaction involving carbon particles.

The decomposition of dioxins commences at temperatures exceeding approximately 700 °C, whereas the lower temperature threshold for their formation lies between 250 and 350 °C.

To ensure that the concentrations of dioxins and furans are reduced to regulatory limits (e.g., 0.1 ng/m³) during flue gas treatment, primary control measures must be implemented during the combustion process. A key operational guideline, commonly known as the “two-second rule”, stipulates that the combustion chamber geometry and operating conditions must guarantee that flue gases remain within the high-temperature zone for a minimum residence time of two seconds at a temperature of at least 850 °C, with an oxygen concentration of no less than 6%.

The pursuit of achieving the highest possible combustion temperatures and the establishment of additional afterburning zones alone do not fully resolve the issue of reducing dioxin concentrations in exhaust gases. This is primarily because such measures do not address the propensity for dioxin reformation during subsequent cooling of flue gases. Furthermore, elevated combustion temperatures lead to increased volatilization of heavy metals and higher concentrations of these metals in fly ash, particularly when the waste contains significant amounts of chlorinated organic compounds

Theoretically, two primary strategies exist to inhibit the formation of dioxins during the combustion of solid waste:

• Neutralization of hydrogen chloride (HCl) produced during combustion using alkaline reagents such as sodium bicarbonate (soda), calcium hydroxide (lime), or potassium hydroxide, thereby reducing the availability of HCl for dioxin synthesis;
• Inactivation of catalytically active transition metal ions, particularly copper and iron, by converting them into chemically inert forms–for example, through complexation of copper ions with amine-based ligands–thereby diminishing their catalytic role in dioxin formation

During the combustion of various components of unsorted MSW, a range of toxic and reactive gaseous substances are generated. Among the most abundant and chemically active combustion products are ammonia (NH₃), carbon dioxide (CO₂), and carbon monoxide (CO). The concentrations and emission profiles of these gases are detailed in Figure 2, Figure 3 and Figure 4 [32].

Process-technological methods aimed at suppressing the formation of toxic substances within the boiler furnace play a significant role in reducing the emission of harmful gases into the atmosphere. These methods encompass various strategies to optimize the fuel combustion process in the furnace [33,34].

The most effective approach to achieving a maximal reduction in toxic substance concentrations in flue gases is the operation of high-temperature municipal solid waste (MSW) combustion regimes, typically within the temperature range of 1800–2000 °C.

The Figure 5 illustrates the relationship between the concentration of key toxic substances in flue gases and the temperature within the combustion zone.

Analysis of the dependencies indicates that with increasing temperature, there is a marked reduction in the concentrations of highly toxic substances such as furans, benzopyrene, carbon monoxide, and nitrogen oxides. Accordingly, the developed system incorporates an initial flue gas treatment stage within the synthesis gas afterburning chamber, operating at temperatures exceeding 2000 °C. This high-temperature process facilitates the complete thermal degradation of toxic organic compounds. Subsequently, combustion products exit the afterburning chamber and enter the superheater, where their temperature is lowered to approximately 900–1000 °C, allowing for primary recovery of thermal energy.

High temperatures within the combustion zone result in an increased concentration of nitrogen oxides (NO_x) in the flue gases, thereby necessitating the incorporation of a nitrogen oxide reduction stage within the integrated flue gas cleaning system.

Traditionally, aqueous ammonia solutions have been employed for NO_x reduction; however, the high toxicity of ammonia presents operational challenges related to its handling and storage at waste incineration facilities. A more effective and safer alternative involves the use of decomposition products derived from the thermal breakdown of a non-toxic aqueous urea solution for the reduction of nitrogen oxides to molecular nitrogen. Figure 6 illustrates the relationship between the degree of nitrogen oxide reduction and the temperature within the reaction zone during this process.

The graph clearly demonstrates that the highest efficiency of nitrogen oxide reduction is achieved within the temperature range of 900 to 1000 °C. Accordingly, in the developed system, flue gases exiting the superheater are directed to the NO_x reduction chamber, where nitrogen oxides are reduced to molecular nitrogen through reactions with the thermal decomposition products of an aqueous urea solution.

The non-catalytic reduction of NO_x occurs at elevated temperatures, during which urea thermally decomposes to produce ammonia and isocyanic acid.

This reduction mechanism is effective only within a narrow temperature window, approximately 900–1000 °C, which presents a risk of “breakthrough” of unreduced nitrogen oxide molecules outside this temperature range. Consequently, maintaining the required temperature within the reduction zone poses significant technological challenges. This non-catalytic NO_x reduction process is typically conducted at atmospheric pressure. However, studies have demonstrated that increasing the pressure within the reduction zone can enhance the efficiency of nitrogen oxide reduction. Elevated pressure broadens the effective temperature range for NO_x reduction, thereby minimizing the risk of nitrogen oxide breakthrough and improving overall process stability.

Subsequent to the reduction of nitrogen oxides, the flue gases undergo a quenching process involving rapid cooling to a temperature between 250 and 200 °C. This rapid cooling helps prevent the reformation of dioxins and furans following their thermal decomposition.

2. Materials and Methods

Equipment

The experiment was conducted on a boiler unit with a fixed grate at a facility under construction located 30 km from the city of Astana (Republic of Kazakhstan) along the Alash highway. The combustion test of sorted MSW was performed on a unit featuring a combustion scheme analogous to that of the MSW plant–an industrial grate boiler situated within a cement plant also under construction at the same location. These studies involved the combustion of solid waste in a layered arrangement on the grate of a hot water boiler.

Combustion was carried out on a fixed grate in a dense layer with manual loading in the boiler (Figure 7). Flue gases were pumped out using a smoke exhauster, automatically drawing the required amount of air under the grate from the boiler room. The qualitative composition of flue gases was studied using industrial gas analyzers at two points: immediately at the outlet of the boiler furnace and at the mouth of the chimney.

These tests were conducted on a KSVR-430 (Karaganda, Kazakhstan) hot water boiler installed in a boiler house operating under an active heat load. The KSVR-430 is a solid-fuel steel boiler equipped with fixed grates; its tube section is vertically oriented, floor-mounted, and constructed as a monoblock unit. The side and upper walls of the boiler firebox consist of pipes welded together with steel strips. The boiler is designed with a manual firing system and is primarily intended for combustion of solid fuels, specifically hard coal and lignite (brown coal).

• Heat output: 0.4 MW (0.34 Gcal/h);
• Grate area: 0.63 m²;
• Estimated fuel consumption at maximum power: 70 kg/h;
• Maximum working pressure: 6 kgf/cm²;
• Exhaust gas temperature: 170 °C;
• Inlet water temperature: 70 °C;
• Outlet water temperature: 150 °C.

The combustion process of both sorted and unsorted municipal solid waste in the boiler unit is illustrated in the figures below.

The flue gas composition was measured using the industrial gas analyzer POLAR (Saint Petersburg, Russia), which quantified the following components:

• Oxygen (O₂);
• Nitric oxide (NO);
• Total nitrogen oxides (NO_x);
• Nitrogen dioxide (NO₂);
• Carbon dioxide (CO₂);
• Sulfur dioxide (SO₂);
• Carbon monoxide (CO);
• Hydrogen sulfide (H₂S);
• Ammonia (NH₃);
• Hydrocarbons expressed as methane (CH₄), propane (C₃H₈), or hexane (C₆H₁₄) equivalents;
• Additionally, measurements included:
• Differential pressure;
• Temperature and either excess pressure or vacuum of the gas flow at the sampling point;
• Excess air ratio and heat loss coefficients.

Flue gas analysis was conducted using industrial gas analyzers by the accredited laboratory of ECO EXPERT LLP (Karaganda, Kazakhstan), specializing in flue gas and atmospheric air composition monitoring, as well as by the research laboratory of the Institute of Thermal Power Engineering and Control Systems at the Almaty University of Power Engineering and Telecommunications named after Gumarbek Daukeev (Almaty, Kazakhstan).

The slag and ash analysis was conducted by the National Scientific Laboratory for Collective Use within the priority research area “Technologies for the Hydrocarbon and Mining and Metallurgical Sectors and Related Service Industries” at the Institute of Metallurgy and Ore Dressing JSC (Almaty, Kazakstan).

During the initial 15 min of the experiment, unsorted MSW and coal were combusted simultaneously, leading to the drying and ignition of the MSW. Subsequently, during the combustion of unsorted MSW, the burning waste progressed along the grate, thereby creating space for the loading of additional waste portions for drying and combustion.

The studies were conducted n = 3 ÷ 5 times of parallel determinations. In addition, the number of series of each experiment m is 10 ÷ 15 times. Standard deviations and confidence interval with confidence probability P = 0.95 were calculated for each point indicated on the Figures 8–22 below for each sample of experimental data.

The experiment, including characterization of the MSW and analysis of combustion products, was carried out by personnel from our design company in collaboration with researchers from L.N. Gumilyov Eurasian National University (Astana, Kazakhstan),Almaty University of Power Engineering and Telecommunications named after Gumarbek Daukeev (Almaty, Kazakhstan), and the National Scientific Laboratory for Collective Use in the priority area “Technologies for the Hydrocarbon and Mining and Metallurgical Sectors and Related Service Industries” at the Institute of Metallurgy and Ore Dressing (Almaty, Kazakhstan).

3. Results

During the experiment, flue gas analysis data were obtained. The composition of the flue gases varied depending on the operational conditions, including whether the smoke exhauster was active or inactive, whether the fuel loading door was open or closed, and the characteristics of the solid waste fed into the combustion chamber.

The results of flue gas analysis obtained during the combustion of unsorted MSW in Astana, measured by the gas analyzer installed upstream of the smoke exhauster at the boiler outlet, are presented below (Figure 8, Figure 9, Figure 10, Figure 11 and Figure 12).

During the first 15 min of the experiment, unsorted MSW and coal were combusted simultaneously, after which the MSW dried and ignited. Subsequently, as the unsorted MSW continued to burn, the combustion front progressed along the grate, creating space for the loading of new waste batches for drying and combustion.

The results of the flue gas analysis obtained during the combustion of sorted MSW in Astana, measured by the gas analyzer installed upstream of the smoke exhauster at the boiler outlet, are presented below (Figure 13, Figure 14, Figure 15, Figure 16 and Figure 17).

The results of flue gas analysis obtained during the combustion of sorted municipal solid waste from Astana city, as measured by the gas analyzer installed downstream of the smoke exhauster in the smoke stack, are presented below (Figure 18, Figure 19, Figure 20, Figure 21 and Figure 22).

Variations in the values are attributed to air infiltration in the smoke exhauster, which leads to an increase in the total volume of flue gases due to the additional air.

The analysis of slag and ash produced after the combustion of sorted municipal solid waste was conducted by staff of the National Scientific Laboratory for Collective Use under the priority area “Technologies for the Hydrocarbon and Mining and Metallurgical Sectors and Related Service Industries” at the Institute of Metallurgy and Ore Beneficiation JSC. The analysis was performed using an Axios Ikw X-ray fluorescence wavelength-dispersive spectrometer (PANalytical). Data processing and interpretation were carried out using the SuperQ software (Omnian 37).

4. Discussion

4.1. Technical Aspect

Significant emissions of nitrogen and sulfur oxides were detected during the ignition and co-combustion of MSW with coal. However, following the complete combustion of coal, when only sorted MSW was burned, a marked reduction in nitrogen oxide concentrations was observed, and sulfur oxide emissions approached negligible levels.

The observed discrepancies in measurements are attributed to air infiltration within the smoke exhauster, resulting in an increased total volume of flue gases due to the ingress of air.

The main objective of the study is to develop a technology for MSW incinerating with permissible emissions into the environment. Harmful emissions in Kazakhstan are limited by the CIS interstate standard [35]. This standard sets the “nitrogen oxide emissions (NO_x)” at a level of no more than 150 mg/m³ (73.17 ppm) (under conditions of the exhaust gases temperature and pressure of 0 °C, 0.1013 MPa, respectively, and an oxygen concentration about 15%), and the “maximum emissions of carbon monoxide (CO)” is 300 mg/m³ (240 ppm). Maximum emissions of sulfur dioxide (SO₂) are established individually for each enterprise in Kazakhstan. The strictest standards are set by the U.S. Environmental Protection Agency (EPA)—205 mg/m³ (100 ppm) for nitrogen oxide emissions from equipment with a capacity of up to 3.5 MW. If the capacity is equal to or greater than 110 MW, the emission limit is reduced to 30 mg/m³ (15 ppm) [36]. The maximum carbon monoxide according to EPA is 63 mg/m³ (50 ppm) [37]. The sulfur oxide emissions constitute 220 mg/m³ (75 ppm). The European Union Directive [38] has average values between EPA and CIS. It has following “Air emission limit values for waste incineration plants”: SO₂ = 50 mg/m³ (75 ppm); NO and NO₂, expressed as NO₂ = 200 mg/m³ (97.5 ppm) and CO 100 mg/m³ (80 ppm). The Chinese standard for thermal power plants [39] has average emission concentrations of NO_x and SO₂ during combustion should not exceed 50 mg/m³ (24 ppm) and 35 mg/m³ (8 ppm), respectively. But this standard aims to be reached in the future rather than in the present.

Unsorted MSW incinerating produces the following emissions:

NOx, mg/m3	75
CO, mg/m3	1500
SO2, mg/m3	0–48

Combustion of sorted MSW produces the following emissions:

NOx, mg/m3	75
CO, mg/m3	1000
SO2, mg/m3	0–80

Air infiltration inside of the chimney reduces the harmful emissions to the following values:

NOx, mg/m3	8
CO, mg/m3	160
SO2, mg/m3	0–18

Average values of nitrogen oxides and sulfur oxides do not exceed most current environmental legislation, including Kazakhstan. But carbon monoxide emissions usually significantly exceed permissible limits immediately after combustion. Under conditions of significant dilution of the exhausted gas flow with air (infiltration) in the chimney, CO decreases to the permissible limits in Kazakhstan, but continues to exceed the EU Directive and especially the US EPA limit.

Slag is already used in the construction of road surfaces in Kazakhstan. Fly ash is used to produce building mixtures and in the production of reinforced concrete products, as a component that enhances the action and viscosity of cement, which strengthens the connection of the research with the circular economy concept.

4.2. Economical Aspect

The research results will be used in the design and construction of waste-to-energy power plants in Kazakhstan:

• Power plant in Astana with a capacity of 40 MW.
• Capital construction costs—58 million USD.
• Cost of sold electricity with government subsidies—0.061 USD/(kWh).
• Own needs—16.8%.
• Electricity generation—348 × 10⁶ kWh/year.
• Operating costs—1.6 million USD.
• Annual income minus own needs and operating income—16.062 million USD.
• Annual profit minus income tax—12.85 million USD.
• Payback period of investments—4 years 6 months.

5. Conclusions

The following results were obtained from the experiment:

• The qualitative and quantitative compositions of flue gases produced during the combustion of both unsorted and sorted municipal solid waste (MSW) in Astana were identified;
• X-ray fluorescence analysis was performed using a wave-dispersive spectrometer “Axios” PANalytical.

Analysis of slag and ash generated after the combustion of sorted MSW demonstrated that all constituent components remained below the established maximum allowable concentrations (MAC).

The results obtained enable the selection of optimal technologies for municipal solid waste disposal tailored to each region, alongside forecasting their efficiency and the potential improvement of the environmental situation within those regions according to general priorities of The Sustainable Development Program of Kazakhstan (Kazakhstan-2050 Strategy).

The most suitable and optimal technologies for municipal solid waste disposal are energy-efficient and environmentally friendly methods such as pyrolysis with synthesis gas production, and combustion for the generation of electrical energy and ancillary products.

Pyrolysis is particularly advantageous for treating small quantities of waste, especially in cases where waste streams include types beyond household refuse.

For large volumes of solid municipal waste, the waste-free incineration process developed by the authors is recommended, incorporating technologies for the complete utilization of solid, liquid, and gaseous by-products of the incineration process. Both technologies facilitate the processing of not only fresh waste collected from the population but also waste that has accumulated within landfill cells, thereby supporting the comprehensive remediation of the national territory from solid municipal waste according to sustainability development program in Kazakhstan.

6. Patents

There are patents resulting from the work reported in this manuscript. Source: Glazyrin, S.A. et al. Method for cleaning flue gases of a drum-type power boiler. Patent of Republic of Kazakhstan, No. 5184, 2020 (in Russian) [40].