Study on the Effect of Water Flux in Osmotic Microbial Fuel Cells on Membrane Water Content and Resistance

Round 1

Reviewer 1 Report

The authors present a set of data concerning water (along with protons) flow across a membrane separating anodic and cathodic compartments in an osmotic microbial fuel cell. 
In my opinion the manuscript is not suitable for publication in current version. Major corrections and clarifications are needed.
Selected examples of bad sentences or expressions:

line40
... the waste of MFCs is not able to be achieve direct emissions or neutilization without further disposal[2].

line 46
pervade hydrone

line 102
gegenion

line 103
enhanceosomes 

line 114
were investigation 

line 152 
ampere density

line 172
by the titanium

line 179
Haber-Luggin blood capillaries were utilized as electric pole,
comment:
This capillary does not serve as an 'electric pole'

line 239
In the course of measurements,the electricity in the test is determined by a using a digital multimeter.
comment:
Unnecessary sentence.

line 241
Water transmitted by electro-osmotic drag results in a growth of the negative electrode size and a decline of the positive electrode size that is determined by capillary tubing.
comment:
I can not figure out how the water flux could influence the size of the electrodes.

Table 1
Faraday of current passed
comment:
?

line 308
The net 19 hydrone per H+ ion 
comment:
probably should read: 19 moles of water per ...

line 409
As was anticipated, ampere density growth from 0.05Am-2 to 1.8Am-2 under the circumstance that the extrinsic resistance dropped from 2358 Ω to 117.6 Ω.
comment:
Probably, it was not the sole reason because the current increase is much higher (36 times), than the resistance drop (20 times).

line 432
At low employed ampere density, electro osmotic water transmission which was lower than 4.86 A m-2 is able to surpass osmotic water
transmission due to electro osmosis.
comment:
I can hardly understand this sentence.

line 436
The amount of water is affected primarily by water content.
comment:
?

Author Response

The authors present a set of data concerning water (along with protons) flow across a membrane separating anodic and cathodic compartments in an osmotic microbial fuel cell. In my opinion the manuscript is not suitable for publication in current version. Major corrections and clarifications are needed. Selected examples of bad sentences or expressions: line40 ... the waste of MFCs is not able to be achieve direct emissions or neutilization without further disposal[2]. Although the MFCs is a new wastewater treatment technology capable of simultaneous electricity production and water quality purification, the treated wastewater still cannot be discharged directly. It still needs to be treated in depth with MFC coupled with other processes. Therefore, MFC coupled with forward osmosis technology can be used for the subsequent treatment of wastewater and efficient power generation. line 46 pervade hydrone We modified the manuscript. line 102 gegenion We changed into: counterions line 103 enhanceeosomes The sentence changed into：Phase I also contains the membrane reinforcements or inert fillers in the polymer line 114 were investigation We modified the manuscript. line 152 ampere density We changed into: current density
line 172
by the titanium
We changed into: with titanium coated with platinum
line 179
Haber-Luggin blood capillaries were utilized as electric pole,
comment:
This capillary does not serve as an 'electric pole'
We changed into: These capillaries were filled with the same solution (and same
concentration) as present in the specific compartment and they were connected to a
small reservoir that contains Ag/AgCl reference electrodes.
line 239
In the course of measurements, the electricity in the test is determined by using a digital
multimeter.
comment:
Unnecessary sentence.
We deleted the sentence.
line 241
Water transmitted by electro-osmotic drag results in a growth of the negative electrode size
and a decline of the positive electrode size that is determined by capillary tubing.
comment:
I can not figure out how the water flux could influence the size of the electrodes.
We changed into：Water transported by electro-osmotic drag causes an increase in the
catholyte volume and a decrease in the anolyte volume which is measured by
calibrated capillaries
Table 1
Faraday of current passed
comment:
?
You could find it in Equation (5).
line 308
The net 19 hydrone per H+ ion
comment:
probably should read: 19 moles of water per ...
We changed into：19 water molecules per H+ ion
line 409
As was anticipated, ampere density growth from 0.05Am-2 to 1.8Am-2 under the circumstance
that the extrinsic resistance dropped from 2358 Ω to 117.6 Ω.
comment:
Probably, it was not the sole reason because the current increase is much higher (36 times),
than the resistance drop (20 times).
We changed into：It may be caused by membrane fouling
line 432
At low employed ampere density, electro osmotic water transmission which was lower than
4.86 A m-2 is able to surpass osmotic water
transmission due to electro osmosis.
comment:
I can hardly understand this sentence.
Please refer to Figure 4.At low applied current density, lower than 4.86 A m2 electro
osmotic water transport can exceed osmotic water transport due to electro osmosis.
line 436
The amount of water is affected primarily by water content.
comment: It means water flux mentioned above

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments on(Luke Chen)

Study on the effect of water flux in osmotic microbial fuel cells to membrane water content and resistance

In generals:

1. In this study, the purpose is whether to optimize the water transmission in purifying wastewater or to maximize the current density is not clear. Hence, to minimize the membrane resistance is referred to water transport resistance or current resistance is a vague. 
2. The parameters considered in this study include osmotic pressure, current density, membrane thickness, water content distribution in membrane, water flux, and membrane resistance. The conclusions did not conclude a set of parameters combination that optimizes the studied OsMFC system with least water flux resistance or current resistance.
3. Unlike CEM the OsMFCs system is non-selective for cation, this study did not discussion on the competition of Na⁺ and Cl^- with H⁺ in the pore space of the membrane.
4. A more detailed figure that displays the arrangement and the materials of the electrodes, electrolytes, membrane, in/effluent of wastewater/CO₂ and O_2/H₂O needs to be added to illustrate the experimental setup.
5. The measurement of water content in the membrane is too rough. How to measure the water content in a hydrophobic membrane requires more elaboration on the measurement procedures.
6. In this study, the diversity of some quantities such as osmotic pressure or density was phrased. Is the diversity here is referred to the gradient of the quantities?
7. Many Figures are blurred. The quality of the figures needs to be improved.
8. The references format needs to be confirmed whether they are consistent with the journal format.

In Specifics:

1. In Eq. 1: It’s needed to be replaced with a clear or original drawing.
2. In Eq. 2: The bottom abscissa of the Fig. 2 is the osmotic pressure, while there is no pressure parameter appears in Eq. (3).
3. In Eq. 3: ∆m is not consistent with ∇
4. In Line 77: electro-osmotic “drug” may be changed into “drag”
5. In Line 196: No formula m1-m2 was found in the content.
6. In Line 223: Are C_a and C_c density or concentration?
7. In Line 251: to “be” determined.

Comments for author File: Comments.pdf

Author Response

This manuscript has undergone English language editing by MDPI. The text has been checked for correct use of grammar and common
technical terms, and edited to a level suitable for reporting research in a scholarly journal.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I accept a corrected version of the manuscript