Cheese Whey Characterization for Co-Composting with Solid Organic Wastes and the Agronomic Value of the Compost Obtained

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript presents a relevant study on the potential for CW to be repurposed through co-composting with agro-livestock waste. The research aligns well with the scope of Agriculture, as it addresses an important issue related to sustainable waste management. Given the significant environmental impact of whey disposal, particularly in regions where small-scale dairy operations lack access to efficient processing technologies, the study provides valuable insights into an alternative valorization method with agronomic benefits.

The work is well structured, with a well-defined experimental design that includes the characterization of CW samples from various dairy producers, the monitoring of physicochemical parameters during the composting process, and the statistical evaluation of results. The use of PCA effectively identifies correlations among multiple variables and provides a deeper understanding of the variability in whey composition. Additionally, the presentation of results is clear, and the study demonstrates practical applicability, particularly for small-scale dairy farms, by proposing an accessible and cost-effective method for whey management while enhancing soil fertility through composting.

However, despite these strengths, several aspects of the manuscript require improvement.

First of all, I would suggest not using the term "recycling" for composting overall the manuscript, as composting is a biological transformation process rather than a conventional recycling process, which typically refers to the reprocessing of materials into new products. A more precise term would be "valorization" or "reuse".

As far as the abstract is concerned, while informative, it could be refined to better emphasize the novelty of the study and its practical implications.

In the materials and methods section, additional details are needed regarding sample selection. Considering the wide climatic variations in the study area, were seasonal variations in whey composition taken into account? Regarding the experimental design for composting, the selection of ingredient ratios (60% corn residues, 5% bean residues, and 35% cow manure) should be justified more explicitly by the authors. Additionally, the number of compost turnings (only two throughout the process) raises questions about aeration efficiency, therefore a discussion of potential improvements in composting management would be beneficial.

To enhance clarity and improve the reader’s understanding of the survey results presented in Section 3.1. "Situation of the Dairy and Agro-livestock Sectors Studied and Destinations of the Generated Wastes" a summary table could be added.

Furthermore, to ensure clarity, I would recommend expressing the coefficient of variation (CV) as a percentage (%) across all the tables where it is present. Moreover, in Tables 1, 2, and 3, I would suggest separating the list of individual results from the part relating to average and CV with a horizontal line to improve readability.

In the discussion, while the paper acknowledges the potential limitations of CW’s high salinity, it does not offer specific mitigation strategies for reducing salt accumulation in the final compost. Additionally, the role of CW in organic matter stabilization and humification could be explored in greater depth. Furthermore, given that excessive salinity can limit compost application in certain soils, a discussion on the potential impact of CW-based compost on different soils would add practical value.

In the conclusions, the potential for co-composting CW with agro-livestock waste as a sustainable waste management strategy is clearly demonstrated, but additional research is needed to optimize the process, particularly concerning CW dilution to prevent excessive salinity in the final product, therefore, greater emphasis on practical recommendations and future research directions should be added.

Comments on the Quality of English Language

The manuscript is comprehensible, but refinements are needed to improve precision, readability, and flow. Some sentences are overly complex or contain minor grammatical issues that can hinder understanding.

Author Response

The manuscript presents a relevant study on the potential for CW to be repurposed through co-composting with agro-livestock waste. The research aligns well with the scope of Agriculture, as it addresses an important issue related to sustainable waste management. Given the significant environmental impact of whey disposal, particularly in regions where small-scale dairy operations lack access to efficient processing technologies, the study provides valuable insights into an alternative valorization method with agronomic benefits.

The work is well structured, with a well-defined experimental design that includes the characterization of CW samples from various dairy producers, the monitoring of physicochemical parameters during the composting process, and the statistical evaluation of results. The use of PCA effectively identifies correlations among multiple variables and provides a deeper understanding of the variability in whey composition. Additionally, the presentation of results is clear, and the study demonstrates practical applicability, particularly for small-scale dairy farms, by proposing an accessible and cost-effective method for whey management while enhancing soil fertility through composting.

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions in track changes in the re-submitted files

However, despite these strengths, several aspects of the manuscript require improvement.

 

First of all, I would suggest not using the term "recycling" for composting overall the manuscript, as composting is a biological transformation process rather than a conventional recycling process, which typically refers to the reprocessing of materials into new products. A more precise term would be "valorization" or "reuse".

Agree. Consequently, we have changed the term "recycle" to "reuse" or "valorize" throughout the manuscript.

 

In the materials and methods section, additional details are needed regarding sample selection. Considering the wide climatic variations in the study area, were seasonal variations in whey composition taken into account? Regarding the experimental design for composting, the selection of ingredient ratios (60% corn residues, 5% bean residues, and 35% cow manure) should be justified more explicitly by the authors. Additionally, the number of compost turnings (only two throughout the process) raises questions about aeration efficiency, therefore a discussion of potential improvements in composting management would be beneficial.

In the materials and methods section, an explanation has been included about the period where the CW samples were sampled, indicating that the sampling was performed during the same time period (January 2022) to reduce the climatic effects on the composition of the samples (See lines 127 and 128). Also, the selection of the initial waste proportions for the preparation of the pile has been justified (See lines 142-144). Regarding the turning of the piles, these were carried out when the temperatures did not correspond to the thermophilic stage (< 40ºC), which indicates a drop in the activity of microorganisms due to the need for aeration or due to the exhaustion of substrates that are easy to degrade. This was indicated in section 3.4. Co-composting Cheese Whey with Agro-livestock Wastes and now it has also been included in section 2.3. Design of Co-composting Experiment to be explained in the Material and Methods section (See lines 160 and 161).

 

To enhance clarity and improve the reader’s understanding of the survey results presented in Section 3.1. "Situation of the Dairy and Agro-livestock Sectors Studied and Destinations of the Generated Wastes" a summary table could be added.

Done. See Table 1. All other tables have been renumbered

 

Furthermore, to ensure clarity, I would recommend expressing the coefficient of variation (CV) as a percentage (%) across all the tables where it is present. Moreover, in Tables 1, 2, and 3, I would suggest separating the list of individual results from the part relating to average and CV with a horizontal line to improve readability.

Done. See Tables 2, 3 and 4.

 

In the discussion, while the paper acknowledges the potential limitations of CW’s high salinity, it does not offer specific mitigation strategies for reducing salt accumulation in the final compost. Additionally, the role of CW in organic matter stabilization and humification could be explored in greater depth. Furthermore, given that excessive salinity can limit compost application in certain soils, a discussion on the potential impact of CW-based compost on different soils would add practical value.

Strategies or recommendations to reduce the accumulation of salts in the final compost when CW is added are given in the Conclusion section. This section indicates that more studies are needed to optimize the amount or dilution of CW to reduce the salt content of the final compost, as this was the main limiting factor of using this liquid waste as a moisture source during the co-composting of solid organic wastes. On the other hand, we cannot make a further discussion on the role of CW in organic matter stabilization and humification because a control pile, irrigated only with water, was not performed for comparison. Also, a discussion on the potential impact of CW-based compost on different soils has not been made because the effects of compost on soil properties have not been studied, as it was not one of the objectives of this work. The objectives of this work were to determine the composition of CW generated in different small cheese companies in Canton Mocha (Tungurahua-Ecuador) to evaluate its potential reuse through co-composting with agro-livestock residues. We consider this comment interesting and will take it into account for new experiments where the effects of agricultural use of this compost on soil properties and crop development are evaluated.

 

In the conclusions, the potential for co-composting CW with agro-livestock waste as a sustainable waste management strategy is clearly demonstrated, but additional research is needed to optimize the process, particularly concerning CW dilution to prevent excessive salinity in the final product, therefore, greater emphasis on practical recommendations and future research directions should be added.

In the Conclusion section, practical recommendations and future lines of research are indicated. At the end of this section, it is indicated that further studies are needed to optimize the amount or dilution of CW to reduce the salt content in the final compost, since this was the main limiting factor in the use of this liquid waste as a source of moisture during co-composting of solid organic waste.

 

Comments on the Quality of English Language

The manuscript is comprehensible, but refinements are needed to improve precision, readability, and flow. Some sentences are overly complex or contain minor grammatical issues that can hinder understanding.

Different explanations have been included throughout the manuscript on various topics that the reviewers have considered for improvement. The authors hope that these explanations will make the text more understandable. In addition, the manuscript has been reviewed by a native English speaker.

Reviewer 2 Report

Comments and Suggestions for Authors

The article "Cheese whey characterisation for its co-composting with solid organic wastes and the agronomic value of the compost obtained" presents relevant research on the use of surplus dairy whey for the production of compost in small-scale enterprises, while preserving the environment and soil. 

Observations:

1. The article presents a good idea to use the milk whey for compost production, but does not go into more detail about where the compost would be produced - on the premises, on a common site, by bringing in materials for composting etc.
2. The research methodology should explain how the composting mass, used at different ratios, is evenly mixed? It should be made more clear how the milk whey is evenly distributed in the overall mass.
3. Manure and milk whey collected from different companies and farms will have different chemical compositions, and it would be interesting to know how this will be controlled.
4. The values of the coefficient of variation should be given in the first, second and third tables.
5. The conclusions should also mention the economic benefits of producing compost using traditional methods and using milk whey collected from different farms. 

Author Response

The article "Cheese whey characterisation for its co-composting with solid organic wastes and the agronomic value of the compost obtained" presents relevant research on the use of surplus dairy whey for the production of compost in small-scale enterprises, while preserving the environment and soil. 

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions in track changes in the re-submitted files

Observations:

1. The article presents a good idea to use the milk whey for compost production, but does not go into more detail about where the compost would be produced - on the premises, on a common site, by bringing in materials for composting etc.

Thank you for pointing this out. In the Conclusions section, it was indicated that compost would be produced in centralized composting facilities to jointly manage the waste generated by the activities of small and medium-sized cheese, agricultural and livestock farms and thus mitigate their environmental impacts. This aspect has also been included in the Introduction section, after the objectives, so that the reader has a clearer idea from the outset of where the compost could be produced.

 

1. The research methodology should explain how the composting mass, used at different ratios, is evenly mixed? It should be made more clear how the milk whey is evenly distributed in the overall mass.

The procedure used for the homogeneous mixing of the solid organic wastes, in the initial preparation of the pile, and the uniform distribution of the whey in the overall mass has been included in subsection 2.3. Design of Co-composting Experiment. See lines 138-140 and 152-154.

 

1. Manure and milk whey collected from different companies and farms will have different chemical compositions, and it would be interesting to know how this will be controlled.

The variability in the composition of cow manure and whey, which will be treated by composting, will be controlled by periodic analysis of these materials.

 

1. The values of the coefficient of variation should be given in the first, second and third tables.

The values of the coefficient of variation (CV) are given in all parameters shown in table 2, 3 and 4. Only in the case of table 4, CV values were not shown for heavy metals with concentrations below the detection limit of the equipment used to measure them.

 

5. The conclusions should also mention the economic benefits of producing compost using traditional methods and using milk whey collected from different farms. 

Done. See lines 493-495 and 498-501.

Reviewer 3 Report

Comments and Suggestions for Authors

This article explores the feasibility of co-composting cheese whey with agricultural waste in the Mocha region of Ecuador, aiming to address the environmental issues caused by improper management of cheese whey. However, the paper still has some shortcomings that need to be further improved and perfected.

1.Small scale of composting experiment: The 1000 kg of composting material may not be sufficient to represent the actual production situation, suggesting the need for larger-scale composting experiments to verify the repeatability and applicability of the research results.

2.Composting temperature did not meet health standards: The temperature during the composting process did not maintain above 55°C for 15 days, which may affect the hygiene and safety of the compost product. It is recommended to optimize the composting process, such as increasing the number of turning operations and adjusting the addition amount of cheese whey, to raise the composting temperature and ensure the hygiene and safety of the compost product.

3.High salinity in compost product: The salinity content of the compost product exceeded the recommended values of the U.S. Composting Council, which may limit its application in agriculture. It is recommended to optimize the composting process, such as adjusting the addition amount of cheese whey and adding other additives, to reduce the salinity content of the compost product.

4.Lack of assessment of compost product fertility: The authors did not evaluate the fertility of the compost product, which may affect its promotion and application. It is recommended to conduct fertility tests on the compost product to evaluate its application value in agriculture and provide scientific basis for its promotion and application.

5.The discussion section can be more in-depth: The authors can further discuss the application prospects of the compost product, such as which crops to apply, how to apply, how to control the application amount, etc., and explore the impact of the compost product on soil environment and crop growth.

Author Response

This article explores the feasibility of co-composting cheese whey with agricultural waste in the Mocha region of Ecuador, aiming to address the environmental issues caused by improper management of cheese whey. However, the paper still has some shortcomings that need to be further improved and perfected.

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions in track changes in the re-submitted files

 

1.Small scale of composting experiment: The 1000 kg of composting material may not be sufficient to represent the actual production situation, suggesting the need for larger-scale composting experiments to verify the repeatability and applicability of the research results.

The scale at which this experiment was conducted can be considered semi-industrial, as the pile was composed of 1 ton of wastes. The results obtained in the present work are to obtain information on the feasibility of co-composting cheese whey (CW) with agro-livestock solid wastes to obtain compost with possible agricultural use. The data obtained have indicated that these wastes can be treated by composting and obtain a final material with characteristics for use as an organic amendment. Therefore, these results can be transferred to carry out the composting process on an industrial scale.

 

2.Composting temperature did not meet health standards: The temperature during the composting process did not maintain above 55°C for 15 days, which may affect the hygiene and safety of the compost product. It is recommended to optimize the composting process, such as increasing the number of turning operations and adjusting the addition amount of cheese whey, to raise the composting temperature and ensure the hygiene and safety of the compost product.

Thank you for pointing this out. Indeed, the main factors controlling pathogen inactivation during the composting process are temperature and time. However, these are not the only factors that act on pathogen reduction during the composting process. Pathogen inactivation is also favored when the thermophilic process is under alkaline conditions, since the presence of certain compounds, such as ammonia, hydroxide anions, etc. contribute to the reduction of this type of microorganisms. High pH values (> 9) were recorded in the pile during the thermophilic stage, as can be seen in Table 6. Also, the reduction of pathogens during the composting process may be due to antagonism or competition between the bacterial species present in the pile. In addition, it has been observed that lactic acid bacteria can inhibit different pathogenic microorganisms, being this type of bacteria present in CW, through the formation of bacterocin. This indicates the importance of the addition of this liquid residue during the composting process for the potential reduction of pathogenic microorganisms through the production of antibacterial metabolites. Therefore, pathogen reduction in the pile could occur even if temperatures were not maintained ≥ 55°C for at least 15 days. This explanation has been included in the manuscript together with the bibliography from which the information was taken, included in the References section. See lines 370-387.

 

Regarding the recommendations for optimizing the composting process, it should be noted that the turning was carried out when the temperatures did not correspond to the thermophilic stage (< 40ºC), which indicates a drop in the activity of microorganisms due to the need for aeration or due to the exhaustion of substrates that are easy to degrade. This was indicated in section 3.4. Co-composting Cheese Whey with Agro-livestock Wastes and now it has also been included in section 2.3. Design of Co-composting Experiment to be explained in the Material and Methods section (See lines 160 and 161). Regarding the CW addition volume adjustment, this liquid residue was added to the pile throughout the bio-oxidative phase to ensure a moisture within the range of 40-60%. A humidity lower than 40% would reduce microbial activity, while a humidity higher than 60% would cause a reduction of the air/water ratio, not ensuring that the process is aerobic.

 

3.High salinity in compost product: The salinity content of the compost product exceeded the recommended values of the U.S. Composting Council, which may limit its application in agriculture. It is recommended to optimize the composting process, such as adjusting the addition amount of cheese whey and adding other additives, to reduce the salinity content of the compost product.

We agree with this comment and therefore, in the Conclusions section we indicate the need for further studies to optimize the amount or dilution of CW to reduce the salt content of the final compost, as this was the main limiting factor of using this liquid waste as a moisture source during the co-composting of solid organic wastes.

 

4.Lack of assessment of compost product fertility: The authors did not evaluate the fertility of the compost product, which may affect its promotion and application. It is recommended to conduct fertility tests on the compost product to evaluate its application value in agriculture and provide scientific basis for its promotion and application.

In this study, the germination index (GI) test (Zucconi et al., 1981) was performed to determine the evolution of the phytotoxicity of the waste mixture throughout the composting process (Table 6). In the final compost, this parameter reached the value of GI = 90.9% (Tables 6 and 8). This indicates that the agricultural use of compost is safe and that it will not produce adverse effects on the germination or growth of plants.

 

5.The discussion section can be more in-depth: The authors can further discuss the application prospects of the compost product, such as which crops to apply, how to apply, how to control the application amount, etc., and explore the impact of the compost product on soil environment and crop growth.

The objectives of this work were to determine the composition of CW generated in different small cheese companies in Canton Mocha (Tungurahua-Ecuador) to evaluate its recycling potential through co-composting with agro-livestock residues. The results indicated that the composting process could be used for the treatment of these wastes and in addition, the final compost obtained had interesting characteristics for agricultural use due to its significant OM, Nt, and P contents and the final values of Corg/Nt ratio (< 20), CEC (> 67 meq/100 g OM) and GI (>50%), indicating OM stabilization and humification and phytotoxicity reduction during the composting process. However, this work did not include experiments to explore the impact of the compost product on soil environment and crop growth, as this was not one of the objectives of this work. We consider this comment interesting and will take it into account for new experiments where the effects of agricultural use of this compost on soil properties and crop development are evaluated.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have improved the manuscript where possible, and after some minor changes which I suggest below it can be considered for publication.

Section 2.3: Since the residues were mixed based on fresh weight, the moisture content of each residue should be reported.

Line 508: Is “OM” rather than “MO”.

Lines 549-552: This is not a conclusion for this work, this added sentence can be removed.

Comments on the Quality of English Language

The English in the manuscript is generally acceptable, however, I recommend that the journal performs a final language review to refine minor corrections and improve overall clarity.

Author Response

The authors have improved the manuscript where possible, and after some minor changes which I suggest below it can be considered for publication.

Thank you very much for taking the time to review this manuscript again. Please find the detailed responses below and the corresponding revisions in track changes in the re-submitted file.

Section 2.3: Since the residues were mixed based on fresh weight, the moisture content of each residue should be reported.

Done. See lines 145 and 146; 148 and 150.

Line 508: Is “OM” rather than “MO”.

Done. “MO” in table 7 has been changed to “OM”

Lines 549-552: This is not a conclusion for this work, this added sentence can be removed.

Done

Reviewer 3 Report

Comments and Suggestions for Authors

This paper can be accepted.

Author Response

This paper can be accepted.

Thank you very much for taking the time to review this manuscript again.