Evaluation of the Effect of a Spray Coating Applied on Open-Air-Stored Woodchips

Round 1

Reviewer 1 Report

The research aims to assess the efficacy of an acrylic coating designed for wood chip protection in the coal-energy industry. While the experimental design is notable for treating wood chip piles with the acrylic coating and monitoring moisture content, dry matter, and temperature changes, it lacks treating all piles uniformly. This limitation hinders a comprehensive comparison between treated and untreated piles, which could have strengthened the study's findings. Additionally, further controls should be implemented to address variables like environmental factors and pile composition.

Despite these methodological concerns, the study contributes empirical evidence on the real-world effectiveness of acrylic coatings. However, it falls short in addressing all main questions posed, particularly regarding the coating's performance under various conditions.

The paper's references are relevant, supporting its context and findings in wood chip protection and coatings. Furthermore, the quality of the tables and figures is commendable, providing clear visualization of experimental data. Yet, a deeper analysis and interpretation of this data could enhance the paper's impact and clarity.

In conclusion, while the research presents valuable insights, it requires methodological improvements and deeper analysis to strengthen its contributions to the field. Additionally, conducting an extensive comparison of the study's results with other research would enrich its relevance and significance.

Author Response

1. The research aims to assess the efficacy of an acrylic coating designed for wood chip protection in the coal-energy industry. While the experimental design is notable for treating wood chip piles with the acrylic coating and monitoring moisture content, dry matter, and temperature changes, it lacks treating all piles uniformly. This limitation hinders a comprehensive comparison between treated and untreated piles, which could have strengthened the study's findings. Additionally, further controls should be implemented to address variables like environmental factors and pile composition.

ANSWER: We thank the reviewer for the constructive comments and the support to improve our work. We agree with the reviewer that the temperature monitoring should have been done on all piles to better understand the microbial activity in dry and wet biomass as well as treated and untreated piles. Indeed, we placed a datalogger for each pile (4) plus one for the larger control pile. But, as reported in the manuscript, the dataloggers suffered some unexpected malfunction and just two of them recorded useful data. Regarding the other factors mentioned, all of them were uniformly represented in the piles (two dry vs two wet, two treated vs two untreated). Regarding the non-controlled variables (weather conditions and woodchips composition of the piles) we did not extend the study to a more comprehensive evaluation of these factors due to the industrial focus of the study. In fact:

• In Mediterranean climate, wintertime has relatively low temperatures and high rainfall, while summer is dry and hot. The former poses a challenge to biomass facilities to maintain the quality of fuel within the set threshold, while the latter naturally improves the quality of wood chips with a fast moisture content reduction. As such, just the winter period is worth considering for biomass protection/coating, in summertime, open piles are just the perfect condition for biomass drying.
• Accordingly, the actual biomass fuel consumed by Italian power plant is a mix of several woody species since such is the structure of our forests. A study on specific type of fuel would not represent the real condition. We considered more relevant to perform the study on a representative sample of the typical fuel consumed by the facility.

1. Despite these methodological concerns, the study contributes empirical evidence on the real-world effectiveness of acrylic coatings. However, it falls short in addressing all main questions posed, particularly regarding the coating's performance under various conditions.

ANSWER: we agree with the reviewer that a more complex study, including several climatic and biomass conditions would have provided more data and results to be compared. Nevertheless, as stated above, the main target was to check with a “scouting test” if the coating could be effective in the specific conditions where it is needed, i.e. Mediterranean wintertime on the actual feedstock of the local biomass facilities. In case of promising results, the next study would address more variables. Among these, we consider very relevant also the shape of the pile.

1. The paper's references are relevant, supporting its context and findings in wood chip protection and coatings. Furthermore, the quality of the tables and figures is commendable, providing clear visualization of experimental data. Yet, a deeper analysis and interpretation of this data could enhance the paper's impact and clarity.

ANSWER: thanks for the advice. We integrated the “results” and “discussion” sections accordingly.

1. In conclusion, while the research presents valuable insights, it requires methodological improvements and deeper analysis to strengthen its contributions to the field. Additionally, conducting an extensive comparison of the study's results with other research would enrich its relevance and significance.

ANSWER: thanks for the advice. We found more comparable researches and included them in “discussion”.  

Reviewer 2 Report

The study offers vital insights on the advantages of using an acrylic coating to protect woodchips. However, the results suggest that the protective layer did not demonstrate significant improvements when compared to untreated piles. The experimental design is well-defined and organised, incorporating suitable controls and measurements to track temperature fluctuation, moisture content, and dry matter during the construction of the piles. Several parts could be improved to enhance the paper.

The methods section lacks specificity regarding the procedures used for applying the acrylic solution and selecting the wood chips. Enhancing the reproducibility of the study and improving readers' understanding of the experimental setting can be achieved by including details on the application method, such as the spraying technique employed and the treatment time. Furthermore, information regarding the wood chips' species, particle size, and starting moisture content would be beneficial for understanding the results.

The debate should go deeper into the possible causes for the observed results and examine alternative hypotheses for the lack of substantial differences between treated and untreated piles. The authors noted that the protective barrier might have hindered moisture dispersion from the pile by evaporation. However, it would be beneficial to explain why this process did not effectively prevent moisture penetration from rainfall, particularly in dry material. Additionally, examining alternate methods to shield woodchips from moisture damage beyond the constraints of acrylic crusting would expand the conversation and offer significant perspectives for future research.

The conclusions need to be adjusted to precisely represent the study's findings and their practical consequences. The results indicate that acrylic crusting may not effectively limit moisture intake from rainfall, but they do enhance our comprehension of the difficulties and possibilities related to woodchip preservation. The authors need to recognise the constraints of the existing method and emphasise possible directions for future research, including investigating different coating materials or improving application methods. The study makes a significant contribution to the subject of woodchip preservation, but it might benefit from more detailed discussion and subtlety to enhance its impact and relevance to scholars and practitioners.

Minor English Language corrections required.

Author Response

1. The study offers vital insights on the advantages of using an acrylic coating to protect woodchips. However, the results suggest that the protective layer did not demonstrate significant improvements when compared to untreated piles. The experimental design is well-defined and organised, incorporating suitable controls and measurements to track temperature fluctuation, moisture content, and dry matter during the construction of the piles. Several parts could be improved to enhance the paper.

The methods section lacks specificity regarding the procedures used for applying the acrylic solution and selecting the wood chips. Enhancing the reproducibility of the study and improving readers' understanding of the experimental setting can be achieved by including details on the application method, such as the spraying technique employed and the treatment time. Furthermore, information regarding the wood chips' species, particle size, and starting moisture content would be beneficial for understanding the results.

ANSWER We thank the reviewer for the constructive comments and the support to improve our work.  Concerning the procedures used for applying the acrylic solution, they are described in the paper, mentioning the kind of sprayer and the quantity of acrylic used; woodchips had not previously selected nor characterized by particle size distribution. Our aim was to test the method on ordinary feedstock used by the energy biomass plant, produced by different suppliers using different chippers and even the wood material was a mix of different sources. Nevertheless, we added in Material and Methods section the kind of feedstock was used to make the piles, sometimes named them only by the genus. The starting moisture content is presented in Table 1 and in Table 2. 

1. The debate should go deeper into the possible causes for the observed results and examine alternative hypotheses for the lack of substantial differences between treated and untreated piles. The authors noted that the protective barrier might have hindered moisture dispersion from the pile by evaporation. However, it would be beneficial to explain why this process did not effectively prevent moisture penetration from rainfall, particularly in dry material.

ANSWER We thank the reviewer for the suggestion. We discussed more in detail the possible causes of the observed dynamic of air drying and rainfall-driven remoistening. Yet, being an empirical study conducted open air, it is not possible to control all the variables involved. Thus, our hypothesis are just speculations based on experience, observation, and analysis of previous works. We extended the “discussion” session accordingly.

1. Additionally, examining alternate methods to shield woodchips from moisture damage beyond the constraints of acrylic crusting would expand the conversation and offer significant perspectives for future research.

ANSWER We expanded the “discussion” part mentioning alternatives set by other scientists to protect or enhance the quality of woodchips and stressing the difficult balance between affordability and feasibility in adopting one solution at the other.

1. The conclusions need to be adjusted to precisely represent the study's findings and their practical consequences. The results indicate that acrylic crusting may not effectively limit moisture intake from rainfall, but they do enhance our comprehension of the difficulties and possibilities related to woodchip preservation.

ANSWER We honestly do not know why the crusting agent didn’t work, we just addressed hypothesis on the possible reasons. We tried to present the study's findings and their practical consequences at our best.

1. The authors need to recognise the constraints of the existing method and emphasise possible directions for future research, including investigating different coating materials or improving application methods. The study makes a significant contribution to the subject of woodchip preservation, but it might benefit from more detailed discussion and subtlety to enhance its impact and relevance to scholars and practitioners.

ANSWER We added in the “discussion” part possible directions for future research, according to our knowledge.