Management of the Municipal Waste Stream: Waste into Energy in the Context of a Circular Economy—Economic and Technological Aspects for a Selected Region in Poland

Referee comments

Autors Explanation

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Point 1: The abstract should communicate the key findings of your work, so we know what to expect. Currently it only describes prior work. That is not sufficient. Explain the work you did, why you did it, briefly the methods you used, and finally, what your results are and how it contributes to the field.

Thank you very much for the comment. The amendments have been introduced in the text:

a.

The research section included granulometric, morphological and physicochemical analyses to determine waste parameters.

The biodegradable fraction content analysis in waste – granulation 10 to 20 mm – demonstrated its presence at the level of 80%, which may be used to produce biogas.

The results are a significant research input for a group of municipal waste generated in rural areas, such as Refuse Derived Fuel.ompleted the abstract and added:

b. Removed from abstract:

Municipal waste – at the time of increased demand for energy sources – is one of its alternative disposal option, which results in reducing the use of fossil fuels and limiting climate change.

The available thermal treatment technologies guarantee mechanical durability of the applied systems in order to optimise the technology process and its economic effectiveness.

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  Point 2: Result section 4.2: A lot of the findings here go beyond the morphological analysis. These findings are important and must be presented better – for example, lines 602 to 619 can be an independent section on biodegradability. What I am trying to establish here is that the section contains more information beyond the fact findings of your morphological analysis and the way it is currently written, diminishes the value of your discussion.

Thank you very much for the comment.

Explanation:

Section 4.2. contains a morphological analysis of municipal waste, where the biodegradable fraction constitutes an integral part depending on the granulation size. According to the authors, the addition of a new section may expand the paper even more.

The amendments have been introduced in the text:

Added:

Owing to the specific nature of municipal waste in terms of the  generation site, the biodegradable fraction will always be present in this granulation, and its percentage content will depend on the waste generation site.

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Point 3: The discussion in lines 682 to 764: nothing in these lines is new work or research. You have essentially discussed only prior work in these lines and as a result, should be kept in the background. However, you may create a new “discussion” section as long as you also integrate with some of your findings with the content in these lines so there is a novelty factor associated – otherwise limit to background.

Thank you very much for the comment. The amendments have been introduced in the text:

The title of chapter 4 was changed from: Results into Results and Discussion.

Explanation:

The chapter presents research results along with the analysis and discussion, from line 545 to 828.

The discussion that continues from line 686 to 828 forms the background directly involving the research results.

The amendments have been introduced in the text:

The Residuals and Discussion section has been completed:

Research results presented in the paper demonstrated that municipal waste generated in rural areas – despite the tough conditions of collection and transportation, especially in winter – may be used as fuel for direct energy generation with thermal value ranging from 6.5 to 9.5 MJ∙kg.

The study results based on a case study being a small town (multi-family housing), including single-family houses, with a population of around 14,000, and a rural municipality with a population of around 24,000 showed the need for selective collection optimisation. The above stems from the fact that there is mainly packaging waste in the mixed municipal waste stream.

Humidity analysis of municipal waste generated, inter alia, in rural areas conducted in the study presented humidity to fall within the range of 32.9 to 40.9%. The value may be lower on condition of facilitating the manner of waste collection, transportation to the processing plant and storage prior to the processing on the sorting line.

Drawing conclusions from the study of municipal waste generated in poorly urbanised and rural areas, the conclusion should be that such type of mechanically processed waste may be used to generate Refuse Derived Fuel used in the cement industry.  

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Point 4: There is a large amount of background information provided but most of it is not relevant to the work that has been conducted. It would be fine if this were a review paper, but here the focus should be on the new work conducted and not the literature review – which currently accounts for 30% or more of the your manuscript. The background in the manuscript should be directly relevant to your novel work, otherwise cited and briefly explained only.

Thank you very much for the comment.

Explanation:

The primary goal of the paper was to study municipal waste generated in poorly urbanised areas and rural areas in order to identify the physicochemical properties. The indirect goal was to place the waste in the social dimensions as the source of energy, indicating the technical possibilities of processing, waste stream management systems and economic aspects.  The authors are in agreement with the Reviewer’s remarks that literature overview is vast, yet presenting so many aspects related to a complex municipal waste management in the paper results in loads of data. The third goal – supplementary to the two previous ones - is to present the manners of municipal waste management in Poland compared to other EU states. Waste management transformation in Poland over the past 10 years has shown a significant advancement in complying with the municipal waste management hierarchy, including thermal treatment.

Taking the above clarifications into consideration, we would like for them to be accounted for under Reviewer’s remarks for point no. 4.

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 Point 5: The work is currently lacking a higher degree of emphasis on the economic aspect. You have discussed some of the technological aspects but when you mention economics, a detailed analysis in an independent section must be conducted and it is not done currently. I suggest doing some research and analysis to support the economic aspects of waste stream management as it relates to your findings and not those done by others previously in any capacity.

Thank you very much for the comment.

 Explanation:

The economic aspects of the paper are a supplementary point as regards the municipal waste studies. Economic studies or analyses have not been included in the paper. Such studies are planned by the Authors in the research papers to come, where studies will include municipal waste processing costs for selected technologies and economic support for municipal waste managing units in Poland.

Referee comments

Autors Explanation

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Point 1: The title should reflect the specific country/region being studied for municipal waste flow management.

Thank you very much for the comment. The amendments have been introduced in the text:

In accordance with the Reviewer's suggestion, the title of the paper was changed to:

Management of the municipal waste stream: waste into energy in the context of a circular economy - economic and technological aspects for a selected region in Poland.

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  Point 2: Waste-to-energy (WtE) is a well-established topic. The introduction should highlight the innovation of this paper.

Thank you very much for the comment. The amendments have been introduced in the text:

a. Completed the abstract and added:

The research section included granulometric, morphological and physicochemical analyses to determine waste parameters.

The biodegradable fraction content analysis in waste – granulation 10 to 20 mm – demonstrated its presence at the level of 80%, which may be used to produce biogas.

The results are a significant research input for a group of municipal waste generated in rural areas, such as Refuse Derived Fuel.

The results are an important research contribution for a group of municipal waste generated in rural areas as a fuel from waste.

b. Removed from abstract:

Municipal waste – at the time of increased demand for energy sources – is one of its alternative disposal option, which results in reducing the use of fossil fuels and limiting climate change. The available thermal treatment technologies guarantee mechanical durability of the applied systems in order to optimise the technology process and its economic effectiveness.

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Point 3: How does waste management policy in the study area differ from that in other regions? What insights can be drawn for waste management in other countries?

Thank you very much for the comment.

Explanation:

The primary goal of the paper was to study municipal waste generated in poorly urbanised areas and rural areas in Poland, in the selected region, in order to identify the physicochemical properties. The indirect goal was to place the waste in the social dimensions as the source of energy, indicating the technical possibilities of processing, waste stream management systems and economic aspects. The municipal waste management policy in Poland is identical in all the regions, as defined in the Act on Municipal Waste and Cleanliness and Order in Municipalities. Comparing municipal waste management in Poland and other EU states, Poland may be found to be implementing the provisions of the EU Directives. Waste management transformation in Poland over the past 10 years has shown a significant advancement in complying with the municipal waste management hierarchy, including thermal treatment. Certainly, compared to e.g. Denmark, Sweden or Germany, where thermal treatment dominated waste management, the process is envisaged in Poland for the years to come. A visible progress is observed in the increasing share of municipal waste recycling.

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Point 4: What is the cost associated with waste-to-energy? Please compare the economic performance of different municipal waste stream management methods.

Thank you very much for the comment.

Explanation:

The economic aspects of the paper are a supplementary point as regards the physicochemical studies of municipal waste and own task of the municipality. Economic studies or analyses have not been included in the study for selected waste streams management. Such studies are planned by the Authors in the research papers to come, where studies will include municipal waste processing costs for selected technologies and economic support for municipal waste managing units in Poland.

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 Point 5: Why was 80 mm used as a cut-off point? Please provide references in the relevant sections of the text.

Thank you very much for the comment.

 Explanation:

The granulation ranges adopted in the paper: 10, 20, 80 mm result from the applicable law in Poland. The applicable law is the Regulation of the Minister of Climate and Environment of 28 December 2022 on the Mechanical and Biological Processing of Non-Segregated (mixed) Municipal Waste.

Completed the abstract and added:

Sizes for granulometric composition were selected based on the Regulation of the Minister of Climate and Environment of 28 December 2022 on the Mechanical and Biological Processing of Non-Segregated (mixed) Municipal Waste. The sizes were binding at the time of the study and study results analyses as well as further municipal waste management manners [85].

85 Decree of the Minister of Climate and Environment of December 28, 2022 on mechanical-biological processing of non-segregated (mixed) municipal waste. (in Polish). https://isap.sejm.gov.pl/isap.nsf/download.xsp/WDU20230000056/O/D20230056.pdf (accessed on 14.07.2024)

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Point 5: Besides particle size, are there other significant factors affecting calorific value? It is suggested to analyze this point using multiple regression or machine learning models.

Thank you very much for your valuable comments, which have greatly improved the quality of our work and introduced new values.

Explanation:

Taking into account the fact that studying the thermal value of the waste concerned only 80 and over 80 mm fraction , multiple regression analysis used variables being: two types of granulation and humidity.

The amendments have been introduced in the text:

Fig. 11 presents the relationship between thermal value and the type of granulation and humidity of waste.

Fig. 11 was added. Relationship between thermal value and granulation and humidity.

Municipal waste thermal value is impacted by, inter alia, highly calorific fractions content, e.g. plastic, paper, wood. Moreover, increased humidity that may result from the manner of collection, transportation and storage, may lead to decreased thermal value. Municipal waste generation site also impacts the thermal value, including mineral (ashes) fraction and biomass content in the waste.

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Referee comments

Autors Explanation

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Point 1: The introduction and literature review are too cumbersome and should be simplified.

Thank you very much for the comment. The amendments have been introduced in the text:

1.       Removed from the literature review:

USC furnaces utilise a wide range of Ni-based superalloys, since the common heat-resistant ferritic steel and stainless austenitic steel cannot operate in this range of temperature and pressure. Ni-based superalloys are often used in high-temperature ap-plications due to their mechanical properties and high heat resistance (up to 1150°C).

Other materials used for heat exchangers production are duplex stainless steel. They include two phases of metallurgical structure: austenite and ferrite, in equal quantities. What characterises them is high corrosion-resistance and high pressure inside the system. The majority of heat exchangers share one limitation: welded joints between the elements. The grate in the waste incineration systems is susceptible to damage caused by high temperatures.

-          decreasing public health risks by reducing: physical risks related to the harmful substances released from waste, biological risks related to pathogens inhabiting landfills, non-communicable disease risks, i.e. cancer or other conditions caused by the exposure to harmful substances, psychosocial risks related to people living in the vicinity of improperly stored waste and ergonomic risks related to human activity undertaken to avoid exposure to waste.

-          identify programme options (including technological and political) to reach the goals of the system;

-          carry out an assessment of the identified action programmes in terms of: requirements, resources, responsibilities, environmental impact, individual stakeholders and meas-urement of performance;

-          define economic and resource requirements and determine their availability;

-          define the roles and responsibilities of the various actors, stakeholders and personnel,

2.       Added additions to the introduction:

Based on the statistical data, 13.4 milion tons of municipal waste was generated in Poland in 2022, which on average means 355 kg per capita. Mixed municipal waste prevailed as regards the collected and generated municipal waste, accounting for 60% of the above. More than half (61.1%) of the generated municipal waste was sent for recovery, while over 2.7 milion tons of municipal waste (20.2%) were directed for recovery in the form of thermal treatment with energy recovery. Disposal processes were applied in the case of over 5.2 milion tons of municipal waste, where 5.1 milion tons (38.1% of the municipal waste generated in total) were subject to landfilling. Compared to the leading EU states, the rate of waste sent for landfilling constitutes a huge challenge in the years to come [25].

25.Housing economy and municipal infrastructure in 2022. Central Statistical Office. Statistical Office in Lublin. Warszawa, Lublin 2023. (in Polish).  https://stat.gov.pl/obszary-tematyczne/infrastruktura-komunalna-nieruchomosci/nieruchomosci-budynki-infrastruktura-komunalna/gospodarka-mieszkaniowa-i-infrastruktura-komunalna-w-2022-roku,13,17.html, (accessed on 14.07.2024

3.       Added additions to the literature review:

Municipal waste thermal treatment technologies used in Poland meet the rigorous requirements for such systems, especially as regards gases emission and ash emission standards. The systems are a plant with energy recovery and flue gas treatment, processes control, check and monitoring. Municipal waste processing plant is a complex technical facility, and high rate of composition change in the incinerated waste results in the operator being forced to continuously control the operation and react to any deviations from the optimum parameters. The analysis of the municipal waste market in Poland undoubtedly shows the need to build subsequent thermal treatment plants incinerating the calorific fraction over 80 mm generated in mechanical and biological processing systems. Such decisions should be preceded with a profound economic, technical, environmental and social analysis, taking into account the local dialogue, including society’s participation in consultations. 

Municipal waste management fee per capita is supposed to cover the costs of system functioning. The highest share in the fee may be applied to: collection, transportation, recovery and disposal of the municipal waste. Waste management system assumes all the costs of collection and management to be covered by the inhabitants’ fees. The cost of the system may be reduced by the raw materials sales from waste income - both accepted at the selective waste collection points and collected form the property. Statistical data concerning Poland show that where municipal waste incineration plants function in towns/cities, the fees collected from the inhabitants are lower by approx. 10% compared to those without such plants. Yet, as regards towns, where less waste is generated per capita, the fees are not lower. The fee depends on multiple factors, not only the amount of the waste generated, but also the specific nature of the region in terms of social and economic condition and many others [51].

51. Jędrczak, A.; den Boer, E.; Kamińska-Borak, J.; Szpadt, R.; Krzyśków, A.; Wielgosiński, G. Municipal waste management in Poland. Cost analysis of municipal waste management. IOŚ-PIB, Warszawa 2022 (in Polish). https://ios.edu.pl/wp-content/uploads/2021/11/55848_gospodarka_odpadami_3.pdf, (accessed on 15.07.2024)

One of the main objectives of the EU is pursuing sustainable development in waste management that ultimately leads to decrease in waste generation and the highest possible rate of recovering precious raw materials. These may be achieved with the use of integrated management systems in municipal waste management. Poland is an EU state, where municipal waste management is subject to continuous qualitative and quantitative optimisation. The crucial issue is to increase the waste segregation level at source, thus increasing the recycling level.

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  Point 2: There is no relevant literature in the literature review on the classification of municipal waste by particle size.

Thank you very much for the comment. The amendments have been introduced in the text:

An Act was added which is binding in Poland and concerns the mechanical and biological processing of municipal waste and the contents were enriched with the following:

Sizes for granulometric composition were selected based on the Regulation of the Minister of Climate and Environment of 28 December 2022 on the Mechanical and Biological Processing of Non-Segregated (mixed) Municipal Waste. The sizes were binding at the time of the study and study results analyses as well as further municipal waste management manners. [85].

85. Decree of the Minister of Climate and Environment of December 28, 2022 on mechanical-biological processing of non-segregated (mixed) municipal waste. (in Polish). https://isap.sejm.gov.pl/isap.nsf/download.xsp/WDU20230000056/O/D20230056.pdf (accessed on 14.07.2024)

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Point 3: Figure 5 Horizontal coordinates have no unit.

Thank you very much for the comment.

Explanation:

As regards clusters analysis presented as a dendrogram in Figs. 5 and 6, the bond distance on the horizontal axis is not defined in units of measure in Statistica.

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Point 4: All analyses did not have comparisons with literature results.

Thank you very much for the comment.

The amendments have been introduced in the text:

Owing to the specific nature of municipal waste as regards the  generation site, the biodegradable fraction in this granulation will always be present, and its percentage content will depend on the waste generation site.

Municipal waste thermal value is impacted by, inter alia, highly calorific fractions content, e.g. plastic, paper, wood. Moreover, increased humidity that may result from the manner of collection, transportation and storage, may lead to decreased thermal value. Municipal waste generation site also has an impact on the thermal value, including mineral fraction and biomass content in the waste.

Research results presented in the paper demonstrated that municipal waste generated in rural areas – despite the tough conditions of collection and transportation, especially in winter – may be used as fuel for direct energy generation with thermal value ranging from 6.5 to 9.5 MJ∙kg.

The study results based on a case study being a small town (multi-family housing), including single-family houses, with a population of around 14,000, and a rural municipality with a population of around 24,000 showed the need for selective collection optimisation. The above stems from the fact that there is mainly packaging waste in the mixed municipal waste stream.

Humidity analysis of municipal waste generated, inter alia, in rural areas conducted in the study presented humidity to fall within the range of 32.9 to 40.9%. The value may be lower on condition of facilitating the manner of waste collection, transportation to the processing plant and storage prior to the processing on the sorting line.

Drawing conclusions from the study of municipal waste generated in poorly urbanised and rural areas, the conclusion should be that such type of mechanically processed waste may be used to generate Refuse Derived Fuel used in the cement industry.  

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Referee comments

Autors Explanation

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If anything, I'd recommend removing the "economic" mention from the title given, and to quote the authors, "economic aspects of the paper are a supplementary point as regards the municipal waste studies. Economic studies or analyses have not been included in the paper". Including economics in the title is misleading the way the manuscript is designed

Thank you very much for your comments. We changed the original title following your suggestion.

New title:

Management of the municipal waste stream: waste into energy in the context of a circular economy – economic and technological aspects for a selected region in Poland

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