Human Health, Economic and Environmental Assessment of Onsite Non-Potable Water Reuse Systems for a Large, Mixed-Use Urban Building

Round 1

Reviewer 1 Report

The manuscript “Human Health, Economic and Environmental Assessment of Onsite Non-Potable Water Reuse Systems for a Large, Mixed-Use Urban Building” analyzed, under different aspects, NPR options in a large building. The manuscript is well written and well structured; minor improvements are necessary before it can be accepted for publication in Sustainability.  Please refer to my comments listed below.

• P2 L92-94: The use of MBR as a NPR treatment of greywater has been recently reviewed in depth (Cecconet et al., (2019), https://link.springer.com/article/10.1007/s10098-019-01679-z); similar conclusions to those reported in Schoen et al. (2018) were drawn. I suggest mentioning the above mentioned paper to strengthen your point.
• Please doublecheck the manuscript for errors (e.g., L137, L141, L164)

 

Author Response

• P2 L92-94: The use of MBR as an NPR treatment of greywater has been recently reviewed in depth (Cecconet et al., (2019), https://link.springer.com/article/10.1007/s10098-019-01679-z); similar conclusions to those reported in Schoen et al. (2018) were drawn. I suggest mentioning the above mentioned paper to strengthen your point.
  • Added text to this effect on line 95. Cecconet only looked at bacteriological indicators, but we agree that their conclusion that a disinfection residual is recommended is in line with Schoen et al.’s (2018) conclusion.
• Please doublecheck the manuscript for errors (e.g., L137, L141, L164)
  • These errors refer to Table/Figure link errors that seem to have occurred when the word document was printed to pdf. We have removed all dynamic links so this should not be a problem anymore.

Reviewer 2 Report

Water scarcity is an important problem at the global scale and any method, tool or activity aiming to save, reuse or recirculate the water is of high interest for humans and economies. Also, the integrated assessment of human health, environment and economy is the most appropriate approach for any performant system. The indices selected and the costs analysis are interested and useful for the presented context.

Please. check the vertical scale of the figures no.3, 4a, 5a and corect/ complete.

Also, check and correct the message (Error! Reference source not found.) which is frequently present in your paper.

 

Author Response

Please. check the vertical scale of the figures no.3, 4a, 5a and correct/ complete.

• The vertical scales have been checked and are correct, note the exponential notation. No change has been made.

Also, check and correct the message (Error! Reference source not found.) which is frequently present in your paper.

• These errors refer to Table/Figure link errors that seem to have occurred when the word document was printed to pdf. We have removed all dynamic links so this should not be a problem anymore.

Reviewer 3 Report

The manuscript entitled “Human Health, Economic and Environmental Assessment of Onsite Non-Potable Water Reuse Systems for a Large, Mixed-Use Urban Building” deals with a holistic approach of a very interesting subject about the applicability of small systems for on-site water reuse. The manuscript is written in a concise yet comprehensive way providing all required data in supplementary material text. This study also addresses an integrated methodology that can be adopted when selecting among various technologies. A few minor remarks are listed below:

• Section 2.1. Please comment about the selection of ozone treatment in case of RVWF, since ozone requires onsite production, might be hazardous and poses many safety related issues. Why not selecting ultra- or nano- filtration techniques? Or other more environmentally friendly oxidation methods prior to chlorination?
• Lines 144-145: this text is part of supplementary material. It should be deleted or altered at this part of the manuscript.
• Figure 2 needs some clarifications. In the box of wastewater generation (after potable water consumption), non-potable demand is included. Since recycled water is considered water source, there should be a separate stream for recycled water (before entering the box). In addition, it seems that when greywater is a separate stream, then black water is discharged to central sewerage system. If this is the case, it shall be clearly stated and further considered in cost & environmental impact analysis. Maybe two figures, one for graywater/blackwater and another one for mixed wastewater collection shall be used instead.
• Section 2.5. Costs for equipment regarding the monitoring of effluent quality and the operation control of the units should also be taken into account.
• Line 267: please correct the numbers of sections
• Section 3.1: risk analysis discussion should also be included, as the selected technologies are rather sophisticated as regards their operation and maintenance.
• Is life cycle of all recommended technologies comparable (same end of lifetime)? Please comment.
• Please comment on potential uses of obtained sludge for all systems, according to cyclic economy principles. Sludge treatment costs is also a critical issue in such systems.

Author Response

• Section 2.1. Please comment about the selection of ozone treatment in case of RVWF, since ozone requires onsite production, might be hazardous and poses many safety related issues. Why not selecting ultra- or nano- filtration techniques? Or other more environmentally friendly oxidation methods prior to chlorination?
  • Ozone was ultimately selected for its effective removal of both viruses and protozoans. The UV dose could have been increased to meet this need, however due to the low LRV of the wetland process, a second barrier of protection was desired for protozoans (i.e. UV and Ozone). A sentence to this effect has been added to the SI file.
  • Only traditional disinfection processes were considered as candidates. Membrane processes are extremely effective but are expected to be costly and energy intensive. They also provide pathogen log reductions well beyond what would be necessary especially when considering the desire for multiple barriers of protection.
  • The ozone generator is a commercially available pre-fabricated system and was assumed to be capable of safe operation.
• Lines 144-145: this text is part of supplementary material. It should be deleted or altered at this part of the manuscript.
  • This comment looks like it was motivated from one of the table/figure link errors that cause some text to go missing. The correct lines refer to a manuscript figure, and point to the source of the LRVs illustrated in Figure 1 (i.e., Table S3). No change has been made aside from removing table/figure errors.
• Figure 2 needs some clarifications. In the box of wastewater generation (after potable water consumption), non-potable demand is included. Since recycled water is considered water source, there should be a separate stream for recycled water (before entering the box). In addition, it seems that when greywater is a separate stream, then black water is discharged to central sewerage system. If this is the case, it shall be clearly stated and further considered in cost & environmental impact analysis. Maybe two figures, one for graywater/blackwater and another one for mixed wastewater collection shall be used instead.
  • Thank you for the detailed critique of the figure. We have responded to each point individually below
    • Non-potable demand is intentionally included in the same box as wastewater generation, under the umbrella of “Large Building Onsite NPR”. The NPR arrow is intentionally made to be a single color, as it a single, indefinite recycle loop. The source and endpoint are, however, intentionally different. No change has been made.
    • The inclusion/omission of blackwater is addressed with footnote 1, in that blackwater discharge is only a component of the graywater systems. We have tried to minimize the number of figures necessary and as this would be the only distinguishing feature between the two separate figures, we opted to address with a footnote. No change has been made.
    • With respect to considering cost and environmental impact of additional wastewater or blackwater, see lines 166-168, specifically “Centralized treatment of wastewater sludge and the untreated fraction of building wastewater is included in the LCI for all scenarios”. No change has been made.
  • Section 2.5. Costs for equipment regarding the monitoring of effluent quality and the operation control of the units should also be taken into account.
    • This is a good point and highlights an important lack of discussion. Given the lack of data in the literature regarding general O&M and effluent monitoring and control, we relied on centralized treatment cost curves and cost factors for each system. Costs for instrumentation and control units specifically were estimated using a contingency factor of 0.08 (8%) of direct costs (see section S4, Table S19). Labor has been assigned to each unit process in the background LCC model. We have added new text in Section 4.1 discussing this general limitation (lines 474-477) and added Table S27 to the SI that shows detailed net present value results broken out by cost category.
  • Line 267: please correct the numbers of sections
    • Printing error, this has been addressed.
  • Section 3.1: risk analysis discussion should also be included, as the selected technologies are rather sophisticated as regards their operation and maintenance.
    • The risk analysis, which was limited to pathogen exposures, captured the expected treatment performance of the selected systems under nominal operation and maintenance conditions. We have also included discussion in Section 4.1 (lines 471-473) that points to the risk of improper or insufficient maintenance. No change has been made.
  • Is life cycle of all recommended technologies comparable (same end of lifetime)? Please comment.
    • Yes, thank you for highlighting an important omission. We did not highlight this clearly enough in the manuscript for LCA models. We have added text in Section 2.2 (lines 164-165) where we describe LCI development, noting that each component has its own lifetime and is provided in Table S21.
  • Please comment on potential uses of obtained sludge for all systems, according to cyclic economy principles. Sludge treatment costs is also a critical issue in such systems.
    • Sludge treatment costs were taken into account in LCA and LCCA results (see lines 166-168). Sludge treatment and reuse beyond centralized treatment is outside the scope of this study. No changes have been made.

Reviewer 4 Report

This manuscript describes a methodology to evaluate the impact of a non-potable water reuse system on human health, economics, and the environment. I strongly agree that the usefulness of the NPR system should be evaluated with various categories as authors suggested. The effect on the health, cost, and CO2 emission was evaluated separately in this study. I understand that it is not easy to integrate all aspects together, but it is still valuable information to understand the different impacts of different treatment processes. 

 

1. Why did the authors choose AeMBR, AnMBR, and RVFW as model processes? Is it because it is widely used in the current NPR system? I recommend providing the reason to choose the processes in the introduction. I guess authors can provide statistics of current technologies used in this field
2. How about the effect of size? I guess that different calculations can be done with different size of building or complex. The discussion on this will be beneficial for further use of the suggested method in a different scenario.

Author Response

1. Why did the authors choose AeMBR, AnMBR, and RVFW as model processes? Is it because it is widely used in the current NPR system? I recommend providing the reason to choose the processes in the introduction. I guess authors can provide statistics of current technologies used in this field
• We moved some justification text from the beginning of the Methods section to the Introduction section. See new text in the final paragraph of the introduction section (lines 117-123).
2. How about the effect of size? I guess that different calculations can be done with different size of building or complex. The discussion on this will be beneficial for further use of the suggested method in a different scenario.
• This is a good point. We partly get at it with our three different scenarios but we agree that it warrants additional discussion. Please see new text added to Section 4.1 (lines 483-486) specifically second to last paragraph.

Reviewer 5 Report

The article is very interesting. Although it does not solve any technical problem, it is actually a development that creates strategies of conduct. However, without a supplement, it is extremely difficult to understand. In addition, the conclusions and suggestions presented in the main article only after looking at the tables in the supplement become understandable and credible. Actually, the article should be printed together with the supplement, or tables from the supplement should be attached to the main article, for example as an appendix.
Without the information contained in the supplement, the article is difficult to understand and loses credibility.

Introduction to the analysis of wetlands solutions raises doubts. In summer, even in temperate climates, not to mention hot areas, wetlands have so much evaporation and evapotranspiration that the possibilities of reusing water are negligible. It happens that the heat period in hybrid solutions (vertical flow and horizontal flow or vice versa) at the outlet flow is zero or close to zero.

In turn, the use of an anaerobic process is difficult for technical and safety reasons. Biogas is flammable and explosive.

Specific comments.
1. Lines 54, 183, 186, 187 - I know these are quotes, but it would be more understandable to other readers if the authors added, for example in brackets: square feet ⇒ square meters; gallons per day ⇒ cubic meters per day.

2. Lines 143, 144 -lack of consistency

3. Fig. 4 - Part a partially covers part b

4. Figures 4 and 5 introduce WW and GW markings. In this case, do they mean WW - sewage, GW - gray water? There is no clear explanation.

5. Fig. 6 - no indication of which drawing is "a" and "b". You can guess that it is, but it should be marked

6. The supplement contains table S245, and there should be table S25

7. Several articles were not cited in the text, e.g. 16, 24, 28, 29, 42, 44 and 47.
8. I don't understand the role of "Error! Reference source not found" in several places. Is it inserted by the Authors or by the Editor

Author Response

The article is very interesting. Although it does not solve any technical problem, it is actually a development that creates strategies of conduct. However, without a supplement, it is extremely difficult to understand. In addition, the conclusions and suggestions presented in the main article only after looking at the tables in the supplement become understandable and credible. Actually, the article should be printed together with the supplement, or tables from the supplement should be attached to the main article, for example as an appendix.
Without the information contained in the supplement, the article is difficult to understand and loses credibility.

            It is indeed a lot of information to conduct an integrated system analysis of various technologies presented in this paper.  The detailed descriptions of the methods, design configuration and inventory are included in the supplemental information to avoid the diversion of the main point of the paper.  It is our understanding that that supplemental document was and will be made available to anyone wishing to read the main manuscript.

Introduction to the analysis of wetlands solutions raises doubts. In summer, even in temperate climates, not to mention hot areas, wetlands have so much evaporation and evapotranspiration that the possibilities of reusing water are negligible. It happens that the heat period in hybrid solutions (vertical flow and horizontal flow or vice versa) at the outlet flow is zero or close to zero.

            While we agree that ET can be a significant flow for natural wetlands, especially in warm or dry environments, the flow rates treated by these systems are orders of magnitude greater than typical ET rates. For example, the target loading rate for these systems is assumed to be 0.60 m³d^-1m^-2, or 219 m/yr. Even in the driest parts of the country, evaporation rates are on the order of 80 inches per year, or 2 m/yr (https://geochange.er.usgs.gov/sw/changes/natural/et/). Additionally, the configuration of the RVFW should serve to limit ET. Water is introduced into the system below the surface and flows vertically downward. And the surface area of these systems is very small in comparison to natural wetlands, which is made possible by the active recirculation of the wastewater/graywater.

In turn, the use of an anaerobic process is difficult for technical and safety reasons. Biogas is flammable and explosive.

            Agreed, and we assume that implementation of any such system would include the requisite safety precautions. Just as we assume, e.g., hazardous chemicals like chlorine will be stored properly, we assume any produced biogas will be handled properly.

Specific comments.

1. Lines 54, 183, 186, 187 - I know these are quotes, but it would be more understandable to other readers if the authors added, for example in brackets: square feet ⇒ square meters; gallons per day ⇒ cubic meters per day.

• Conversions to metric have been provided.

2. Lines 143, 144 -lack of consistency

• This seems to be a printing error (.doc to .pdf). Thank you for bringing it to our attention, we have addressed the source of the error.

1. 4 - Part a partially covers part b
   • Noted, we have addressed the formatting issue.

4. Figures 4 and 5 introduce WW and GW markings. In this case, do they mean WW - sewage, GW - gray water? There is no clear explanation.

• Abbreviations have been defined in the Figure captions (lines 344 and 376-377).

5. Fig. 6 - no indication of which drawing is "a" and "b". You can guess that it is, but it should be marked

• This seems to be a transcription error, we have corrected it, thank you for bringing it to our attention.

6. The supplement contains table S245, and there should be table S25

• This error has been corrected.

 

7. Several articles were not cited in the text, e.g. 16, 24, 28, 29, 42, 44 and 47.

• You are absolutely correct. Something must have happened with our reference manager. Thank you so much for bringing this to our attention! These references have been removed.

 

8. I don't understand the role of "Error! Reference source not found" in several places. Is it inserted by the Authors or by the Editor

• We apologize for this, it appears to be an error that is created when our .doc file was printed to .pdf. We have made all dynamic links static and eliminated the error.

Author Response File: Author Response.pdf