Studying of Energy and Environmental Characteristics of Municipal Solid Waste From Shymkent City Polygon

doi:10.21203/rs.3.rs-1944414/v1

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Studying of Energy and Environmental Characteristics of Municipal Solid Waste From Shymkent City Polygon

https://doi.org/10.21203/rs.3.rs-1944414/v1

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Purpose

Study of solid household waste in large cities of Kazakhstan with the determination of the possibility of creating solid fuels based on them for heat and electricity generation. The article presents the results of studies of the morphological composition, physical and chemical parameters and the energetical potential of municipal solid waste (MSW) from the garbage landfill of the city of Shymkent.

Methods

For research, 10 samples were taken from the landfill of the city of Shymkent, which were sorted to extract the combustible fraction from each sample. Subsequently, the combustible fraction of each sample was subjected to averaging and grinding to compile point samples. Water extracts for microbiological studies were taken from three samples containing food waste.

Results

The volume-mass parameters of the samples were determined; the average density was 145.4 kg/m3. The morphological composition of the merged sample is as follows: food waste 11.07%, paper and cardboard 6.67%, polymers 30.23%, glass 2.27%, ferrous metals 6.42%, non-ferrous metals 2.52%, textiles 17.01%, wood 0.12%, hazardous waste 0.2%, leather, bones, rubber 8.8%, municipal waste residue after removal of all other components 14.66%. The humidity of the combustible fraction of samples varies from 0.3% to 2.3%. The average humidity is 1.51%.

The average ash content of the combustible fraction of the samples was determined, its value ranges from 5.9% to 33.3%, the average value is 18.4%. The yield of volatile substances was determined, the average value per the dry state was 78.7%. The gross calorific value was determined and the net calorific value was calculated, the average value of which is 24.15 MJ/kg.

The content of macro-elements in solid residues after ashing was determined. O, Na, Mg, Al, Si, P, K, Ca, Mn, Fe were found in the samples. A high content of Si, Ca, and Al was found: 3.6%, 2.0%, and 1.2% in terms of the mass of the combustible fraction, respectively.

Conclusion

10 spot and combined samples of municipal solid waste from the landfill of the city of Shymkent were studied. Physical and chemical characteristics were determined and it was found, that the average density of MSW is at the level of values, typical for developed countries. Parameters of humidity, ash content of volatile substances and net calorific value are at the world average level. A microbiological study showed that bacterial microflora predominated in the samples of water extracts.

municipal solid waste

garbage landfill

incineration

recycling

processing

fuel

ecology

A new environmental policy has been initiated in Kazakhstan; intentions have been announced to move to modern standards for handling solid municipal waste. At the same time, there are practically no data on the morphological composition and biological hazard of both historical and newly arriving waste. Decision about the method of waste processing requires to have an information about the amount of combustible components, their composition and energy characteristics. To obtain an objective picture, the largest cities of Kazakhstan were selected for research, differing, however, in terms of the average standard of living. It should be noted the importance of microbiological studies, since in the studies of municipal solid waste almost all authors focused on obtaining information about energy indicators.

In recent years, more and more attention has been paid to the development of "green" technologies for the processing and disposal of municipal solid waste for the purpose of reuse and energy production, not only in developed countries, but also in the countries of the Asian region and the Middle East [1–3]. A clear understanding of the finiteness of natural resources and the fact that municipal solid waste is an inexhaustible and predictable source of secondary raw materials and fuel, comparable in energy efficiency to its traditional types, makes the development of such technologies necessary.

According to the US Environmental Protection Agency, there are 75 factories in the country that process municipal solid waste and extract energy by incinerating it. The combustible fraction after sorting allows generating about 550 kWh of energy per ton of waste. At an average price of four cents per kWh, a profit per tonne of solid waste is often between $20 and $30 [4].

The flagship among European countries in the field of waste-to-energy conversion is Sweden, which not only recycles almost all of its garbage, but also exports it from Norway, Ireland and the UK. According to the local waste management association "AvfallSverige", 99% of municipal waste is recycled in Sweden [5, 6]. At the same time, 50.6% of waste is recycled, 48.6% is burned for energy production, and only 0.8% is sent to landfills.

Kazakhstan adopted the Strategy "Kazakhstan-2050: a new political course of an established state", which defines clear guidelines for building a sustainable and efficient model of the economy based on the country's transition to a "green" path of development. According to the Concept for the transition to a "green economy", the state sets itself the task of increasing the share of recycling and disposal by 2030 to 40%.

Despite the measures taken in terms of legislation and real actions, there is still no information about the characteristics of accumulated and newly incoming municipal solid waste at Kazakhstani landfills. The relevance of the work lies in obtaining reliable information about the properties, energetical and ecological parameters of MSW.

Sampling was carried out in accordance with the "Sanitary and epidemiological requirements for the collection, use, application, disposal, transportation, storage and disposal of production and consumption waste" by order of the Minister of Health of the Republic of Kazakhstan dated April 23, 2018 No. 187 [7]. Samples were taken in polyethylene hermetically sealed containers with a volume of 60 liters using bayonet and square-faced shovels.

The morphological composition of municipal waste was determined according to the "Methodology for determining the morphological composition of municipal solid waste" Order of the Agency of the Republic of Kazakhstan for construction and housing and communal services dated January 10, 2012 No. 4 [8].

Samples for further testing were prepared according to ISO 21645:2021 [9]. Two main methods were used in sample preparation: sample weight reduction by separation and sample grinding [10].

Table 1 shows the volume-mass parameters of MSW samples. The average density is 145.4 kg/m³. For comparison, a group of Iraqi scientists cites density data equal to 229.088 kg/m³ for the city of Tikrit [11], for India, the range from 300 to 400 kg/m³ is typical for the city of Bhopal [12], for the capital of Oman, the given data corresponds 311.73 kg/m³ [13]. On average, MSW density values for industrialized countries such as the US and UK range from 100 to 150 kg/m³, while for middle income countries this value is 175–330 kg/m³, for countries with a low income level (Bangladesh, Pakistan, Nepal, etc.), the density value is estimated at 300–600 kg/m³ [14, 15].

Table 1

Volumetric and mass paremeters of MSW samples
Parameter	Sample number
Parameter	1	2	3	4	5	6	7	8	9	10
Volume, L	32	34	54	56	45	51	52	48	57	53
Mass, kg	5.47	4.967	5.399	7.943	5.889	7.98	7.36	8.514	8.569	7.344
Density, kg/m³	170.9	146.1	100.0	141.8	130.9	156.5	141.5	177.4	150.3	138.5

Table 2 shows the species composition of MSW samples. Food waste is represented mainly by inedible remains of vegetables and fruits with signs of decay. Often, this type of waste presented by tied plastic bags, which, combined with high humidity and favorable temperatures in the warm season, contributes to the growth of microorganisms. It is worth noting that it is these wastes are the main source of unpleasant odors.

Paper waste is represented by the remains of printed materials (books, newspapers, magazines), packaging materials (boxes, paper containers) and paper products used for sanitary purposes (toilet paper, paper towels, wipes). Due to hygroscopicity, this type of waste is also a source of moisture in MSW samples.

Polymer waste is represented by the widest range of products. This type of waste is made up of plastic bags and bottles, food containers, plastic scrap from household items, polypropylene construction bags, diapers.

Glass waste is represented by a small number of whole bottles, the main part of this type of waste is broken glass and damaged bottles, as well as containers from pharmaceutical preparations.

Ferrous and non-ferrous metals are represented by cans, fittings, other small construction waste and a small amount of wires from electrical appliances.

Textiles are mainly represented by the remnants of clothing, footwear and cleaning products.

Wood waste consists of remnants of furniture, tree branches and building materials.

Used batteries - hazardous waste.

Table 2

Species analysis of MSW samples
Type of waste, % wt.	Sample number
Type of waste, % wt.	1	2	3	4	5	6	7	8	9	10
Food waste	10.7	32.0	0.0	0.0	0.0	17.2	0.0	8.8	20.2	22.7
Paper and cardboard	5.5	6.1	13.4	7.9	0.0	5.7	0.7	0.0	14.0	13.2
Polymers	49.8	12.3	33.0	42.1	34.2	26.4	39.6	24.7	14.2	29.6
Glass	0.0	5.8	7.1	2.7	0.0	0.0	1.8	6.5	0.0	0
Ferrous metals	1.6	0.0	0.0	15.4	26.5	10.4	0.2	7.8	0.7	0.3
Non-ferrous metals	4.0	2.8	3.8	0.6	0.6	0.3	6.2	0.0	7.2	0
Textiles	9.3	21.4	0.0	11.8	20.4	8.2	22.9	39.7	20.1	8.9
Wood	0.0	0.0	0.0	0.0	0.0	0.0	1.2	0.0	0.0	0
Hazardous waste	0.0	0.0	0.0	0.0	0.0	2.1	0.0	0.0	0.0	0
Leather, bones, rubber	8.9	0.0	16.3	12.5	1.1	19.7	11.7	3.1	9.4	2.5
Municipal waste residue after removal of all other components	10.2	19.7	26.4	7.1	17.2	10.1	15.7	9.3	14.2	22.8
Total, %	100	100	100	100	100	100	100	100	100	100

The skull of a cow was found in the sixth sample, and bones were also found in the fourth and ninth samples. The rest of municipal waste contains the mineral part of sand, crushed stone, soil, as well as tree leaves.

After sorting the samples, a combustible fraction was formed from paper, polymer textile and wood waste. According to Table 3, the total content of combustible waste is 54.02%, more than half of which is plastic waste. Figure 1 shows the general morphological composition.

Table 3

The percentage composition of the combustible fraction of MSW
	Paper and cardboard	Polymers	Textiles	Wood	Total
Total mass, g	4628	20988	11808	88	37512
% from total mass of MSW	6.66	30.22	17.00	0.12	54.02%
% from total combustible mass of MSW	12.34	55.95	31.47	0.23	100%

Sample moisture content was determined on two samples according to ISO 21660-3:2021 [16]. Table 4 shows the data on the determination of moisture. According to visual determination, the source of moisture in the samples was paper and textile materials, as well as soil particles adhering to the materials of the combustible fraction. The humidity of the samples was in the range of 0.3–2.3%, the average humidity was 1.51%.

Table 4

Moisture of samples
№ of sample	1	2	3	4	5	6	7	8	9	10	W^a avg.total, %
W^a1, %	1.7	1.3	1.7	1.2	0.3	1.8	0.6	1.5	2.1	1.9	1.51
W^a2, %	1.5	1.5	2.2	1.8	0.4	2.0	0.8	1.7	2.3	1.8
W^a avg., %	1.6	1.4	2.0	1.5	0.4	1.9	0.7	1.6	1.7	1.9

One of the important parameters of any solid fuel is the ash content - the mass fraction of ash, the percentage of non-combustible (per anhydrous mass) residue, which is created from the mineral impurities of the fuel during its complete combustion. There is a distinguish between external and internal ash content. External ash content is the result of the fuel's foreign impurities; in the case of MSW samples, the main impurities are sand, dust and soil particles. Also, metal particles and (for example) aluminum foil from combined packages based on glued paper and cardboard will increase the ash content.

Ash content was determined according to ISO 21656:2021 [17]. Table 5 shows data on the determination of ash content. The ash content of the samples was in the range of 5.9–33.3%, the average ash content was 18.4%.

Table 5

Ash content of samples
№	1	2	3	4	5	6	7	8	9	10	A^d avg.total, %
A^d1, %	9.4	12.7	5.9	17.2	28.6	27.9	19.6	33.3	10.0	19.8	18.4
A^d2, %	9.3	12.3	5.8	17.0	28.6	27.8	19.4	33.2	9.9	19.7
A^davg., %	9.4	12.5	5.9	17.1	28.6	27.8	19.5	33.2	10.0	19.8

Another important quality level for fuel is the yield of volatile substances, which characterizes the quality of solid fuels, which is taken into account when determining their rational industrial use. When heated without air access, solid fuels decompose, releasing gas and vapor products, called volatile substances. Depending on the heating temperature, after the removal of volatile substances, a solid residue (kinglet), coke or semi-coke remains.

Volatile substances are not contained in the free form in the fuel, but they are formed when heated, so we can talk only about their yield, but not their content. The yield of volatile substances depends not only on the type of fuel, but also on the conditions of its heating. The composition of volatile substances includes valuable substances that are widely used in industry. So, for example, volatile substances of coal contain benzene, toluene, ammonia, hydrogen, methane, etc. The volatile substances formed during the dry distillation of wood contain methane, carbon monoxide, acetic acid, methyl alcohol, etc.

The yield of volatile substances was determined according to the ISO 22167:2021 standard [18]. Table 6 shows the data on the yield of volatile substances per a dry state, with an average value of 78.7%.

Table 6

Yield of volatile substances from solid waste samples per a dry state
№	1	2	3	4	5	6	7	8	9	10	V^d avg.total, %
V^d1, %	87.7	82.6	87.6	77.6	83.6	58.9	81.8	63.4	83.4	80.8	78.7
V^d2, %	87.5	82.3	87.5	78.0	82.8	58.6	81.7	63.7	83.1	80.8
V^davg., %	87.6	82.4	87.5	77.8	83.2	58.8	81.7	63.6	83.3	80.8

The net calorific value is the most important indicator of the quality and energetical properties of fuel and characterizes its value. The gross calorific value was determined according to the ISO 1928:2009 «Solid mineral fuels – Determination of gross calorific value by the bomb calorimetric method and calculation of net calorific value» on an automatic GDY-1A + isoperibol calorimeter. Table 7 shows the values of the gross calorific value without taking into account and taking into account the humidity of the samples.

Table 7

Gross calorific value of MSW samples
№	1	2	3	4	5	6	7	8	9	10
${Q}_{s,V}^{a}$, MJ/kg	26,82	23	23,92	28,795	24,16	23,24	26,54	19,175	29,82	27.34
${Q}_{s,V}^{d}$, MJ/kg	27,26	23,32	24,40	29,24	24,25	23,68	26,72	19,49	30,34	27.86

The net calorific value differs from the gross one essentially only by that the water formed during the combustion of fuel does not condense, but remains in the form of steam and is removed with flue gases. The value of the net calorific value is less than the value of the gross by the value of the heat of condensation of steam, which is formed from the moisture of the fuel and hydrogen of the organic mass, which turns into water during combustion. To calculate the net calorific value, the average hydrogen content in MSW was taken to be 7% [17] from information, presented by different countries of the world; the average value was 24.15 mJ/kg.

Accurate determination of the content of macro elements in solid fuel from municipal solid waste is necessary to solve environmental and technological problems both at the production stage and during combustion. The determination of macro elements is useful for estimation of the behavior of ash during the combustion of solid fuels and slagging of heating surfaces. Direct analysis of solid fuel from municipal solid waste is not possible due to insufficient sample homogeneity, which requires preliminary decomposition, which was carried out in accordance with GOST 55130 − 2012 "Solid fuel from municipal solid waste. Definition of macro elements".

The average content of elements in the combustible fraction is as follows, %: Na − 0.16; Mg − 0.36; Al − 1.22; Si − 3.67; P − 0.04; K − 0.38; Ca − 2.02; Mn − 0.023; Fe − 0.7. Scanning microscopy was used to study the residue after ashing the average sample of the combustible fraction. Figure 2 shows the corresponding micrographs, which shows that the sample contains both large particles with a size of 20–50 µm and very small ones, with a size of 1 µm or less.

To evaluate the biological hazard, a microbiological analysis of water extracts from point samples No. 2, 4 and 6 was carried out. The following groups of microorganisms were studied: heterotrophic bacteria, actinomycetes, microscopic fungi and bacteria of the Escherichia coli group.

According to Table 8, the results of the microbiological analysis of water extracts showed the presence of heterotrophic bacteria in all the samples under study in a significant amount. Their greatest number was found in samples 4 and 6 – hundreds of millions of cells per 1 ml. In sample 2, the number of bacteria was significantly (an order of magnitude) lower.

Table 8 The number of studied groups of microorganisms in samples of water extracts

Sample	The number of microorganisms, colony forming units (CFU)/ml^*
	Bacteria	Actinomycetes	Microscopic fungi		Bacteria of the Escherichia coli group
	Bacteria	Actinomycetes	Filamentous mushrooms	Yeast	Bacteria of the Escherichia coli group
2	(6,95±1,2)×10⁷	units	(6,5±0,7)×10³	not detected	(4,15±0,9)×10⁷
4	(2,2±0,2)×10⁸	not detected	(1,35±0,7)×10⁴	(8,05±0,2)×10⁵	(6,15±0,9)×10⁷
6	(2,09±0,2)×10⁸	not detected	(6,5±0,7)×10³	(4,85±0,3)×10⁴	(2,55±0,3)×10⁷

Actinomycetes were found only in the 2nd sample in a single quantity.

Mycelial fungi were found in all studied samples of water extracts. Their number in samples 2 and 6 was 6500 cells per 1 ml, and in sample 4 twice as much. Yeast microflora was also found in samples 4 and 6. At the same time, their number exceeded the number of micromycetes by an order of magnitude and amounted to 805 thousand and 48.5 thousand CFU/ml, respectively.

Bacteria of the Escherichia coli group were also found in all the studied samples of water extracts. On the [Chromagar Orientation] medium, their number was tens of millions of cells per 1 ml. The largest number was noted in sample 4. The determination of bacteria of the Escherichia coli group by the fermentation method on a lactose-peptone medium, followed by inoculation on Endo medium, showed that the coli-index of these samples is more than 1100, i.e. there are more than 1100 cells in 1 liter of water. This indicates a strong fecal contamination of the samples. Figures 3, 4 and 5 show images of cultured microorganisms from the studied extracts.

10 spot samples were studied, as well as a number of combined samples of municipal solid waste from the landfill of the city of Shymkent. Physical and chemical characteristics were determined and it was found that the average density of MSW is at the level of values, typical for developed countries. Parameters of humidity, ash content of volatile substances and net calorific value are at the world average level. A microbiological study showed that bacterial micro flora predominated in the samples of water extracts. Bacteria of the Escherichia coli group were detected in a significant amount. Fungal micro flora, represented by filamentous fungi and yeasts, was also found in the studied water samples.

The net calorific value of the combustible fraction of municipal solid waste containing various organic materials is comparable to such values for charcoal and anthracite (~ 27 MJ/kg). At the same time, taking into account these parameters for paper and wood waste, it becomes clear that the main contribution to the calorific value is made by plastic waste.

The low moisture content of the studied samples is caused by favorable climatic conditions, since the sampling was carried out during the warm season for this region; as well as by the storage of waste in the open air, which contributed to natural drying, since plastic waste is not hygroscopic materials.

The average ash content is at a fairly high level, but most likely it is the surplus ash content, as evidenced by the composition of the ash, which has a high content of calcium, silicon, aluminum and magnesium - distinctive elements of the soil. Organizing separate collection in containers, as well as provide intermediate storage on the site, for example, concrete site, the ash content can be significantly reduced when burning such fuel. At the same time, it is also necessary to minimize the release of ash particles into the atmosphere, which, according to the analysis, are very small in size and, accordingly, can be carried away with air currents.

Of the detected micro flora, the greatest danger to personnel involved in the processing and incineration of MSW is caused by bacteria of the Escherichia coli group, since virulent strains, when infected by the alimentary route, can cause gastroenteritis, peritonitis, sepsis, etc. These circumstances emphasize the need for workers to use personal protective equipment and mandatory maintaining of hygiene.

Data Availability

The datasets supporting the conclusions of this article are included within the article and its additional files. The data that support the findings of this study are available from the corresponding and lead authors, upon reasonable request.

Funding

The research was carried out within the implementation of the project AP09058076 "Research of energy potential and environmental safety of the municipal solid waste from Kazakhstani landfills", funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan.

Conflict of interest

The authors have no financial or proprietary interest in any material discussed in this article.

Ethical Approval

Not applicable.

Consent to Participate

Not applicable.

Consent for Publication

Not applicable.

Author contributions

Abilmagzhanov A.Z.: Conceptualization, Project administration, Writing- Reviewing and Editing

Ivanov N.S.: Methodology, Writing- Original draft, Writing- Reviewing and Editing.

Adelbayev I.Y.: Visualization, Investigation, Resources.

Kholkin O.S.: Formal analysis, Visualization

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Studying of Energy and Environmental Characteristics of Municipal Solid Waste From Shymkent City Polygon

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Abstract

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№	1	2	3	4	5	6	7	8	9	10
\({Q}_{s,V}^{a}\), MJ/kg	26,82	23	23,92	28,795	24,16	23,24	26,54	19,175	29,82	27.34
\({Q}_{s,V}^{d}\), MJ/kg	27,26	23,32	24,40	29,24	24,25	23,68	26,72	19,49	30,34	27.86