Effect of Slurry Acidification In-House by a Dynamic Spraying System on Ammonia and Greenhouse Gas Emissions from Pig-Fattening Farms in Hot Summer Climates

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

My main concern in the experimental design and resulting measurements was the description of the gas sampling protocol. Each measurement period was 15 min, and I assume the gas sampling system rotated among (at least) four sampling points. Thus, there was one sample per location per hour (or longer). If my assumption is correct, line 240 is not accurate as written. Were the data collected during a 15-min period averaged, and the average data among measurement periods for a day or night averaged together? Furthermore, was there a stabilization period when switching between monitoring locations? Equation 212 and Figure 1 suggests there were 2 ambient sampling points; these should be mentioned in the text description. Equation 1 could depict the difference with a delta sign.

Please provide better descriptors and images to demonstrate the spray delivery system. Figure 1 shows additive spray at one end of the rooms, whereas Figure 2 suggests spray delivered at both ends. If there were 10 nozzles per side of each room, can you estimate the proportion of surface area covered by the nozzle streams? The connections to the main pump line are not evident in Figure 2.

Section 4.2 suggests the spraying system optimized the use of additive. However, the methodology does not sufficiently describe the conditions for the spray system to turn on, aside from high temperatures. What was optimized? In comparison to Overmeyer et al, which study used less acid? Which study reduced gases (and which gas) more?

Some minor edits:

• Ammonium is frequently presented with the 4 as a superscript, versus a subscript.
• Line 105 - replace "was extended" with "lasted" or "covered". 
• Experimental design - for completeness, mention there are 2 rooms per treatment
• Was the ventilation setpoint adjusted in the rooms over the trial period? 
• Lines 132-133 - were the average weights equal among rooms, but not among pens at the start of the trial?
• Line 290 - Please comment on whether the difference in volume is reasonable considering the volume of acid addition.
• Line 307 - replace sows with shows
• Figure 5 - y-axis label should be L per day. Please specify whether this is consumption per room or total for the system.
• Line 481 - please specify the gas.

 

 

Author Response

Thank you very much for taking the time to review this manuscript. Your comments improve our work. Please find the detailed responses in the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This study investigates the effectiveness of an in-house dynamic spraying system applying a mixture of organic acids to pig slurry in reducing ammonia and GHG emissions during hot summer periods. Its performance was positive to both the environment and pig growth. However, it may be required to add or correct the part of article mentioned as below.

First of all, pig manure would have very high alkalinity, which means a lot of organic acids may be required to decrease pH for preventing NH3 release to the air. Therefore, the article may need to describe the economical aspects of additive spraying. Furthermore, the addition of organic acids into slurry pit may cause the other gases. Generally, the surface of slurry pit was covered with scum and the additives may hardly mix with slurry.

(Abstract) Please provide brief information of organic acids. However, the additives may not be composed of all organic acids.

(Materials & Methods) Is there the pH goal or threshold when spraying begins?

Please provide the limitation of this study and future work.

Author Response

Thank you very much for taking the time to review this manuscript. Your comments improve our work. Please find the detailed responses in the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

General comments:

This manuscript addresses a well-designed experimental study evaluating the impact of in-house slurry acidification using a dynamic spraying system with a mixture of organic acids on ammonia (NH₃) and greenhouse gas (GHG) emissions from pig fattening farms under high summer temperature conditions. The topic is timely and relevant given the urgent need for sustainable manure management practices in the livestock industry. The dynamic and responsive acidifier application system, based on real-time temperature monitoring, adds practical value and novelty to the study. Overall, the manuscript is methodologically sound, the experimental setup is clearly described, and the results are convincingly presented. However, several issues require clarification or elaboration to improve the manuscript’s clarity, scientific rigor, and practical relevance.

 

1. The manuscript would benefit from a clearer discussion on how this study differs from previous slurry acidification research, particularly regarding the use of organic acids and the dynamic spraying mechanism. Please highlight this distinction in the introduction and discussion.
2. While the system responded effectively to temperature, it did not react to NH₃ concentrations. More explanation is needed—was this due to preset thresholds, limitations of sensor placement, or insufficient NH₃ levels? Consider suggesting system improvement measures.
3. Are the devices (e.g., Innova 1412-5) and the measurement intervals (every 15 minutes) used for monitoring NH₃, CH₄, N₂O, and CO₂ adequately validated for accuracy and suitability?
4. Is the analysis of diurnal variation in gas emissions convincingly explained? Is the interpretation of emission differences in relation to animal activity between day and night logical?
5. Please expand the discussion on practical challenges to adopting such systems in commercial settings, including maintenance requirements, cost barriers, or climate limitations (e.g., winter operation).
6. Are the relationships between gas concentrations and animal productivity metrics—such as feed intake, weight gain, and feed conversion ratio—properly examined?
7. Consider re-structuring the conclusions into concise bullet points summarizing the main findings. Additionally, a brief suggestion for future research—such as testing the system in colder climates or with different acid mixtures—would be valuable.

Author Response

Thank you very much for taking the time to review this manuscript. Your comments improve our work. Please find the detailed responses in the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

I find that the authors have adequately responded to and addressed the review points, and therefore the paper will be accepted for publication.