Assessment of Current Blue Energy Technologies and Their Potential Applications on Romanian Water Resources

Round 1

Reviewer 1 Report

A significant current but also long-term challenge in terms of environmental protection and sustainable development is the orientation towards energy sources with a reduction in the carbon footprint. Modern development trends include environmental technologies that, unlike fossil ones, use clean, also referred to as green energy (solar, wind, geothermal and water), which cannot be accompanied by the production of pollution, such as is produced using fossil fuels, sources of renewable energy, e.g. burning biomass, or biogas production by converting the chemically bound energy content in the organic pollutants of raw urban wastewater, or blue energy, which is dealt with by the authors of the considered work. This study analyzes the possibility of renewable and sustainable energy production by capturing the energy associated with the natural tendency to disrupt the salinity gradients resulting from the contact between salt and fresh water. It also evaluates the potential of obtaining blue energy in Romania based on the processing of historical data on the flows of relevant fresh water sources (Danube) and the salt load in potentially receiving water bodies (salt lakes and the Black Sea). Romania has significant potential for blue energy resources, both for large capacity facilities (Danube River - Black Sea) and for smaller capacity facilities located around 400 salt lakes and salt deposits. The authors describe the principles, advantages and disadvantages of three sustainable energy technologies, namely pressure retarded osmosis (PRO), reverse electrodialysis (RED) and capacitive mixing (CAPMIX), which use the energy potential of the salinity gradient. With the use of salinity gradients, the efficiency of using renewable natural resources increases. These energies maintain a low carbon footprint, thus protecting the environment.

Author Response

Point 1

A significant current but also long-term challenge in terms of environmental protection and sustainable development is the orientation towards energy sources with a reduction in the carbon footprint. Modern development trends include environmental technologies that, unlike fossil ones, use clean, also referred to as green energy (solar, wind, geothermal and water), which cannot be accompanied by the production of pollution, such as is produced using fossil fuels, sources of renewable energy, e.g. burning biomass, or biogas production by converting the chemically bound energy content in the organic pollutants of raw urban wastewater, or blue energy, which is dealt with by the authors of the considered work. This study analyzes the possibility of renewable and sustainable energy production by capturing the energy associated with the natural tendency to disrupt the salinity gradients resulting from the contact between salt and fresh water. It also evaluates the potential of obtaining blue energy in Romania based on the processing of historical data on the flows of relevant fresh water sources (Danube) and the salt load in potentially receiving water bodies (salt lakes and the Black Sea). Romania has significant potential for blue energy resources, both for large capacity facilities (Danube River - Black Sea) and for smaller capacity facilities located around 400 salt lakes and salt deposits. The authors describe the principles, advantages and disadvantages of three sustainable energy technologies, namely pressure retarded osmosis (PRO), reverse electrodialysis (RED) and capacitive mixing (CAPMIX), which use the energy potential of the salinity gradient. With the use of salinity gradients, the efficiency of using renewable natural resources increases. These energies maintain a low carbon footprint, thus protecting the environment.

Response 1

We would like to express our appreciation to the reviewer for the time and expertise provided toward the improvement of our paper.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript entitled,” Assessment of current blue energy technologies and their potential applications on Romanian water resources ” reports the current blue energy technologies and their potential applications on Romanian water resources. This research provides salient insights in relation with the existing green energy technologies of Romania. Hence, this manuscript can be considered for publication after the mandatory minor revision on the given aspects : 

1. Language of the manuscript should be improved.

2.The introduction part should be precise. So far numerous efforts have been reported on the

  Conventional water resource energy technologies in Romania. In this context, it is important to draw clear lines between other  close works and the present work.

3.The fabrication and applications advantages of blue energy technologies over the other region water resources should be provided.

4.Water resources based Fuel cell related activities should be portraited.

5. The activity of prepared materials cited in this manuscript has not been described well.  Hence, the authors are recommended to refer the following significant publications and provide the salient insights of the state-of-the-art of catalysts :

 Applied Biochemistry and Biotechnology, 2020, 192:751–769; Applied Physics A : Materials Science & Processing Journal, 2018, 124, 769 (1-11); Environmental Progress & Sustainable Energy, 2019, 38(6), 13262(1-11)

Language of the manuscript should be improved.

Author Response

We would like to express our appreciation to the reviewer for the time and expertise provided toward the improvement of our paper.

For the specific raised aspects, we offer the following arguments and revisions:

 

1. The language of the manuscript was generally verified, several corrections to the use of English being made.

 

2. Conventional water resources exploitation is not the intended subject of our paper. The general summation of renewable technologies is made just as a general context for the introduction of the blue energy technologies and national potential resources which are the main intended subject of this paper.

In the transition from the summation of general renewable energy to the blue energy subfield, a fragment describing the salient points of advanced nano-structured materials for photo-voltaic microbial fuel cells was inserted in the introduction.

 

3. A comparison between conventional water exploitation and blue energy is not the intended subject for this paper. To do it justice, such a comparison would require a more complex integrated assessment of: capital costs, efficiencies, environmental ecological impacts, land and water use limitations (social, economic), long term effects and so on.

A brief discussion is made before of and in sub-point 4.1 regarding blue energy projects limitations as regards access to both fresh and salty water sources and the need to select the best positions to minimize the eventual environmental impact of the brackish stream reintegration.

 

4. There are many other blue energy technologies that could be described (such as those based on the density difference between fresh and saline water exploited in columns submerged in seawater, or those based on the different water vapor pressure between the saline water and fresh water liquid fazes exploited in vacuum distillation technologies). Fuel cell technologies, although an important part of renewable techniques, are not especially relevant for the main blue energy technologies. The last paragraph of section 2.3 describes particular cases of entropy batteries derived from CapMix technologies which may be regarded as being closer to fuel cell technologies as in it require advanced materials and catalysts for electrodes. Another field in which blue energy techniques would benefit from the research made for fuel cells would be the know-how in minimizing the biofouling of surfaces and membranes. But this will be the subject of future papers, more oriented on the experimental part.

 

5. Although not exactly on the subject of power generation from salinity gradients, the recommended literature proves a valuable point able to illustrate the shift from conventional costly green energy technologies, such as solar panels, towards more integrated and cost-effective technologies that take full advantage of state of the art newly developed nano-structured catalysis to improve both the biocompatibility and the electron transfer from the biological component toward the electrodes. A fragment describing the salient points was inserted in the introduction.

Author Response File: Author Response.docx

Reviewer 3 Report

The present review deals with the assessment of current blue energy technologies and their potential applications on Romanian water resources. The review is well-written and presented. In my opinion, it can be accepted after minor revision. 

comments,

1) Abstract is not attractive, and can be modified.

2) There are some typo and English errors, it should be rectified.

3) Conclusions can be rewritten.

Minor revision is required on the quality of the English. 

Author Response

We would like to express our appreciation to the reviewer for the time and expertise provided toward the improvement of our paper.

 

1. The abstract has been modified to better illustrate the paper’s content.

 

2. The language of the manuscript was generally verified, several corrections to the use of English being made.

 

3. The conclusions have been extended and reorganized.

Author Response File: Author Response.docx