Evaluation of a Greenhouse Ecosystem to Treat Craft Beverage Wastewater

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript reports on a proof-of-concept that an accepted method for providing the biological treatment of domestic strength wastewater can be used for the biological treatment of high strength (relative to organic strength) - with the craft beverages being the wastewater source.  This is a harsh environment for biochemical oxidation to take place:  Ethanol is a well-known disinfectant, there are many detergents in this wastewater, and the pH can vary over a wide range.  At issue is whether an aerated greenhouse ecosystem can provide treatment and the will the plants survive the wastewater.  The experimental methods is well planned and executed.  The results provide guidance for how to design this technology for full-scale deployment.

I offer some minor edits.

Line 29:  plants instead of pants

Line 29:  what is the context of "larger"  more root volume, more root length, more root surface area?

What was the lab temperature?  How does this temperature relate to the environment in the Living Machine?

What was the ethanol content - it may be too late to ask this question, but is there a max ethanol content that would destroy the microbes doing the work?

When cold wastewater was transferred from the refrigeration to the treatment system, was there enough thermal mass already in the treatment cell to bring the new water up to temperature without causing a thermal gradient in the treatment cell?

Can you be more descriptive of "plant damage" (Line 260).  Did the damage look like a nutrient deficit or an overall shock to the plant?

Please describe how the plants are physically supported in the test cells - floating plant trays, wire mesh? (section 3.4)

Author Response

Dear Reviewer 1, thank you for the comments.  Your suggestions greatly improved the manuscript.

• Comment 1: Line 29:  plants instead of pants.
  • Corrected (line 29 of revised manuscript with track changes)
• Comment 2: Line 29:  what is the context of "larger" more root volume, more root length, more root surface area?
  • “…plants with large root systems…” has been changed to “…plants with root systems with a higher surface area…”. (line 29 of revised manuscript with track changes).
• What was the lab temperature? How does this temperature relate to the environment in the Living Machine?
  • A paragraph was added at the end of section 3.4 discussing this (lines 543-552 in the revised version with track changes). “The temperature of the lab varied over the course of the experiment. During the colder months, the temperature of the lab was roughly 18 C°. During the warmer months, the temperature was roughly 26 C°. However, all reactors within the system were, on average, 22 C°. There were fluctuations, however, depending on the outside temperature. The lab contained floor to ceiling windows and acted as a greenhouse. The highest temperature recorded within the reactors was 32.7 C° and was taken on 5/12/23 and 10/3/23. The lowest temperature recorded was 15 C° and was taken on 3/20/23. The wastewater transferred into the system from refrigeration did not have a large impact on the water temperature inside of the drums, as all drums had a temperature between 21.9 C° and 22.7 C° for the course of the entire experiment.”
• What was the ethanol content - it may be too late to ask this question, but is there a max ethanol content that would destroy the microbes doing the work?
  • The ethanol content in the wastewater was assumed to be the average as a bottle of wine, ~16% ABV, assuming all the alcohol was in the form of ethanol. Details about how the 16% ABV was found and the formulation for the SWW are now provided (lines 187-200 in the revised manuscript with track changes).
  • This was not studied within the report. In addition to ethanol, there were also cleaning chemicals in the actual wastewater used, which could have an additional impact on the microbes. No specific toxicity experiments were conducted, however.
• When cold wastewater was transferred from the refrigeration to the treatment system, was there enough thermal mass already in the treatment cell to bring the new water up to temperature without causing a thermal gradient in the treatment cell?
  • There was a comment added in lines 548-552 in the revised manuscript with track changes. “The wastewater transferred into the system from refrigeration did not have a large impact on the water temperature inside of the drums, as all drums had a temperature between 21.9 C° and 22.7 C°.:
• Can you be more descriptive of "plant damage" (Lines 288-289 in the revised manuscript with track changes). Did the damage look like a nutrient deficit or an overall shock to the plant?
  • This descriptor was changed to read as “…caused the plants to dry and wither while still maintaining the original leaf color, likely from…” (lines 288-289 in revised manuscript with trach changes).
• Please describe how the plants are physically supported in the test cells - floating plant trays, wire mesh? (section 3.4)
  • A comment on this has been added into section 2.2 on line 148-149 in the revised manuscript with track changes: “The plants were inserted into plastic poultry fence. The fence had extra holes cut into it to allow for the plant roots to be inserted without damage to the plant.”

Reviewer 2 Report

Comments and Suggestions for Authors

The presented material considers the issue of wastewater treatment from craft beverages such as: wine, beer, cider, which contain a lot of phosphorus, nitrogen, which can bring harm to the environment. The authors propose to use a Living Machine® technology for wastewater treatment and its further use for household needs. No doubt, this material is very relevant, useful and will certainly resonate with readers, however, the article needs a major revision: 

1. Introduction
- The end of the introduction looks "not so nice". The information that the authors put forward as objectives looks more like tasks that need to be accomplished in order to reach the purpose. In this regard, request to the authors to clearly formulate the purpose of the research. Also recommend that the sentence on line 64 be changed "The project objectives included the following." on "To achieve this purpose, the following tasks must be accomplished:".

2. Materials and Methods
- A reference to the sentence located on lines 77-80 is necessary.

3. Tables
- Table 1: column Range: usually the range is specified from the smaller value to the larger value, not the other way around. Please ask the authors to change 320-296 and 800-20,000 on 296-320 and 20-800. In addition, recommend to apply rounding to integer/hundredth values to this Table, i.e., change: 125-130,000, 5,600, 1,200-3,600, 5,100-8,750, 8,000, 6,000, >170,000 on 125-130, 5.6, 1.2-3.6, 5.1-8.75, 8, 6, >170. Also, recommend to the authors to remove units from the name Parameter (mg/l) and add units of measurement to the specific indicators below. pH cannot change in mg/l, so it is not correct to use such units of measurement for all parameters of this column. Please correct it. Pay attention to the authors to the separating sign, somewhere a comma is used, and somewhere a period is used. Recommend using a period as a separator. Please make changes. The use of the abbreviation TSS, which is used only in this Table and nowhere else, is not clear. Recommend to delete this abbreviation.
- Table 2: recommend renaming the column, i.e. change "Hydraulic Residence Time" on "Hydraulic Residence (days)". Accordingly, it is necessary to delete days from the columns below. Also, recommend to the authors to make the following changes to the first column: change "COD Concentration (mg/L) or loading value(kg/m2/day)" on COD Concentration (C_COD, mg/L) or loading value(σ_COD,kg/m2/day). And further modify: change 440+/-217 mg/L*, 392+/-174 mg/L* on startup and 723+/-409 mg/L* once stable, 0.004 kg/m2/d, 0.03 kg/m2/d, 425.7 mg/L*, 0.092 kg COD/m2/d on C_COD 440+/-217, C_COD 392+/-174 on startup and C_COD 723+/-409 once stable, σ_COD 0.004, σ_COD 0.03, C_COD 425.7, σ_COD 0.092. 
- For Tables 4, 6, 7, 9, recommend to the authors to decipher the letters a, b. It is intuitively clear what the authors meant, but one would like to rely on clear notations. Please make changes. 
- Pay attention to the authors that all the Tables are not designed correctly. Request to the authors to familiarize themselves with the template for this journal once again and make all Tables in accordance with its requirements.

4. Discussions
- Part 3. Results and Discussions is now very overloaded. Still, the article would look better and more structured if the authors separated this section into 3. Results and 4. Discussions or shorten the information. Please make the changes. 

5. Conclusions
- The conclusions should be redone. Currently, the conclusions are more like reasoning. The conclusions should be clear and localized, intersecting with the tasks at hand. Please make changes.

6. References
- Pay attention to the authors that at the moment the authors are not referring to references correctly throughout the text. Thus, "General craft beverage wastewater characteristics [10], [12], [13], [14]." should be corrected to "General craft beverage wastewater characteristics [10,12-14]". Request to the authors to be more careful and make similar changes throughout the Manuscript.
- It is necessary to organize the list of references according to the template for this journal. Request to the authors to once again familiarize themselves with the requirements of the template for this journal and in accordance with them to make changes in the formalization of the list of references.

7. Other comments
- Pay attention to the authors that from lines 61-82, 176-219, 222-284, 287-339, 343-374, 382-436, 451-489 the text is necessary to align to the width of the sheet.
- Pay attention to the authors to the separating sign, somewhere in the text a comma is used, and somewhere a period is used. Recommend using a period as a separator throughout the text of the Manuscript. Please make changes.
- A Disclaimer/Publisher's Note section should be added at the end of the reference list.

 

 

 

Author Response

Dear Reviewer 2, thank you for the comments.  Your suggestions greatly improved the manuscript.

• Introduction
  • The ending of the introductory section was edited to improve the flow of the paper. “…. determine possible pollutant removal mechanisms, and determine if this small system is as effective as a larger system.” Was added and the tasks were moved to the beginning of the Materials and Methods section (lines 65-90 in the revised manuscript with track changes).
• Materials/methods
  • The indicated sentence did not come from a reference. This is the standard process for designing a treatment system.
• Tables
  • For the comments regarding Table 1:
    • The numbers in the tables are indeed in the suggested order. For example, 320-296,000 is correct. The lower number is 320 mg/L and the upper number is 296,000. The ranges found in previous studies are incredibly high, as well as not well studied.
    • The numbers within the table are from previous studies, therefore they cannot be rounded.
    • The comment “Pay attention to the authors to the separating sign, somewhere a comma is used, and somewhere a period is used. Recommend using a period as a separator.” Is unclear. It is assumed that it is referring to the commas and periods in the numbers themselves, such as 5.26 or 7.6. These are decimal points as this was the average from the papers referenced.
  • Comments regarding Table 2:
    • The comment regarding changing the units in the heading and next to the numbers was addressed by removing the units in the heading. This is a standard process to display data. mg/L is the standard unit of measurement for a concentration and kg/m²/d is the standard unit of measurement for loading values.
  • Comment regarding superscripts: please refer to lines 238-241 in the revised manuscript with track changes.
  • The comment regarding how the tables are designed is unclear. Please provide specific examples of what needs to be edited and changes will be made.
• Discussions
  • The comment is appreciated, however, it would take more room and time to have it structured in two sections. The discussion refers back to the tables multiple times, which is why it was formatted as such. The consistent flipping from results to discussion to compare the numbers is impractical.
• Conclusions
  • The comment left is unclear as to what specifically should be changed.
• References
  • The references were performed by Mendeley automatically, which does not have the specific in-text referencing requested. This can be changed manually in the final editing.
• Other
  • The disclaimer was added at the very end of the document.
  • The comment regarding the separating sign (comma vs. period) was unclear. Providing specific examples would be beneficial.
  • The comment regarding the alignment of the lines was unclear.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you to the authors for a job well done. After the finalisation, the Manuscript material looks more logical and structured. I think that this article will be of interest to readers.  I recommend this material for publication in the journal MDPI "Sustainability".