Heat Recovery from Wastewater—A Review of Available Resource

Round 1

Reviewer 1 Report

The manuscript concerns a review of literature on wastewater heat recovery and its potential at different scales within the sewer system. The following remarks should be referred to: In what way this review will help the research community, policymakers, and other stakeholders? To clarify some aspects, I would suggest that the authors write the bibliography evenly: the abbreviation, the DOI number. In what way the publications were chosen to perform the analysis? Are they indexed in Wos or Scopus? In what way this review will help decision-makers to prioritize criteria based on the objective of planning?  The abstract must be rewritten in a more precise style (a review of literature, how many publications?). It should be expanded to include the important results. Different methods of WWHR should be compared together, the advantages and disadvantages should be illustrated.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Overall:

Please use the journal template. It is not the correct one.

The article is well written. Authors put a lot of work to summarize the potential of heat recovery from wastewater.

Abstract:

Line 1, please revise first sentence “wastewater heat as a renewable heat source”. I suggest to use “wastewater as a renewable heat source…”. Please verify it in all text.

Introduction:

Line 29, “The utilized water (wastewater)…” water and wastewater cannot be treated equally.

Well-written, it provides the most important elements, as background, research gap, objective and scope of paper.

Materials and methods:

Lack of this section. In the review papers, the specific methods should be includes, as for example desk research. Please add this section.

2. Wastewater Heat Recovery:

Please specify the definition of wastewater. It is not just a contaminated water, but water that has been used for specific purposes.

Source of equation (1) should be added.

3. Energy Recovery Options:

It is a review paper, therefore, sources of Figures should be added. Why Figure 1 appears after Figure 2 in the manuscript?

Conclusions:

Please provide the conclusions, not repetition of the results.

References:

Should be adapted to journal template.

Author Response

see attached response

Author Response File: Author Response.docx

Reviewer 3 Report

This review study provides a comprehensive and critical review on the heat recovery from wastewater. Overall the document is very interesting, well-structured and written clearly. I would recommend its publication after moderate revision and considering the following comments:

Major comments:

• I miss a section regarding future research, required improvement, new alternatives
• The discussion of existing papers is sometimes a bit lengthy and with long sections. Might be good to synthetsiez a bit more and make some recapitulative tables to give a better overview and have more impact.

Also the following comments:

• Introduction:
  • L29-32: missing ref
  • L29-36: missing general numbers and TºC range
  • L50-52: what was assessed in those reviews and the aspects they did not cover??
• Wastewater heat recovery:
  • L70: what is ‘’reasonably high’’: please precise, numbers…
• Energy recovery options:
  • A table with heat exchanger technologies, applications and pro/cons would be valuable
  • L175-176: do nit understand the statements which seems contradictory. 5.5% loss after 10 minutes, same after 2 years?
  • I know this is explained more in details in following sections but some values of TºC range would be quite informative already in this section.
  • L254: 40-119 per?
  • 2.3: what about fouling prevention system? Also what about the consideration of heat recovery only in certain flows/separated system (where there is hot water). Might be considered also in the context of building water reuse for joint heat and water recovery.
  • 3.1: biofouling is only considered in sewer pipe but should also be an issue at the element/building level, no?
  • L365: healing or heating?
• Section 6: legal framework: indeed this is key to consider the minimal temperature. But on the other hand, discharging WW with higher temperature to the environment might have an impact, no? Probably not a legal limitation but I think that should be mentioned/discussed somewhere in the paper as a potential environmental benefit.

Author Response

see attached response

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Accept in present form.