Density Effect of Eisenia sp. Epigeic Earthworms on the Hydraulic Conductivity of Sand Filters for Wastewater Treatment

Round 1

Reviewer 1 Report

The manuscript by Gilibert et al present the methodological study of use of earthworms in prevention of sand filters clloging, an intresting worthy concept although not totaly new (as the authors themself cite some previos work). The experiment were done carfully and the results intresting but the writing  need some language editing as follows:

L35-… “Soil macroinvertebrate communities include many insects and other arthropods, as well as earthworms. Each group has a different impact on soil
physical properties, due to its different burrowing activities which cause an increase of hydraulic conductivity and water infiltration in the soil” I do not see this information in this reference…

L53 “vermicomposting, vermifiltration or constructed wetlands (CW) systems [24-26]” Were is the mention of CW in these references?

L64 “The different burrowing networks made by earthworms influence soil hydraulic properties as well as soil chemical and biological compositions.” Burrowing networks or burrowing behavior?

L73 “sand filters of sewage water.” Unclear, rephrase

76 “the planted filters” It is unclear if the manuscript speaks about sand based constructed wetlands or sand filters which are not commonly planted

89 The “Smart-Clean-Garden Concept” is not a well-known concept. It needs more detailed explanation.

The paragraph in Lines 93-99 is rather meaningless and error prone. For example:

L95 “such as its geology with its mineral composition” – Geology is NOT mineral composition!

L95-96 “water, organic matter and oxygen contents.” Water and oxygen content are changing very fast so are not really a useful factor here.

L100-101 “The hydraulic conductivity is considered as the most important hydraulic parameter as it reflects flow and transport of fluids in porous media” – this is defining a term by itself. Rephrase

L105 “what is the potential influence of …” Why potential influence?

L106-108 What is the “ecological valence” of E. fetida to “chemical composition of the substrate”? And what does this sentence even mean?

L112 “to explain its influence on the chemicals.” What effect? On what chemicals?

L112-114 “So far, very few papers have addressed the link between biodiversity characterized by earthworms and their networks, and the hydrology of the substrate [34,35,39,40].” But this manuscript did not test how different earthworm’s population mix effect the results, so what does biodiversity are we talking about? I suggest removing this sentence unlense you can connect it better.

L133-142 Please refer the reader to Fig. 1a, will make understanding much easier

L145-147 Does “they are close in their aspect and their role in ecosystems” (what “aspects”) explain “however, we were later notified that some earthworms from the species E. andrei were present among E. fetida, as they are close in their aspect and their role in ecosystems”? If it does, how?

L148-149 Before the beginning of the experiment, 35 g of adult Eisenia sp. earthworms were put in the mix of sand and peat bedding for 7 days” What was the mix ratio?

L150 “Then, earthworms were weighted before being introduced in columns” How were the earthworms collected from the sand and peat mixture?

L152 -157 I find the practice of weighting earthworms very weird in the experimental methodology context – “The first density, W100, contained 0.4 ± 0.1 g of fresh earthworms per column (corresponding to 1 earthworm per column) … The density W500 contained 2.2 ± 0.1 g of earth worms per column (2 earthworms per column) or 500 g.m-2 of earthworms. The last density, Wmax, contained 4.3 ± 0.1 g of earthworms per column (3 to 4 earthworms per column) or 1,000 g.m-2 of earthworms.” Why not simply place 1, 2 or 4 earthworms per column and report the avg±SD weight of an earthworm? Indeed I am quite sure that is how the experiment was done! Please report what you did, not what you think you should have done!

L159 “tape water”? I assume you mean tap water?

L164 “filter sand” did you mean sand filter?

L174, 176,  again “tape water”

L185 “samplings were made” Please check your English

L185-187 “At the end of the experiment, samplings were made at three different depths in the substrate of each column: in the peat bedding layer, in the upper part of the sand layer and in the lower part of the sand layer.” Given that columns are not very long this description is not very clear. Please define more specifically “upper”, “lower”, and “bedding” as approximate height in centimeters. This is highly important as you state yourself “Sampling depth in the sand layer had a significant impact on the OM and moisture contents” (L204-205)

L189-190 “Two samples were used to measure the OM content: samples were put in the oven at 550°C for 2 hours (after 2 hours of temperature build-up), to burn the organic matter weight of samples” – Was this done after drying at 40C or without drying?

Figure 2: Please refer to the the different between the left and right graphs in the caption.

L218 “the 7th day” do you mean D +7 (Fig 1)? Please stick to same nomenclature throughout the text.

L214 “14th day” again, keep nomenclature consistent.

Figure 3: is the hydraulic conductivity before/after addition of bedding? Assuming it is after state this in the panel title, e.g. Day 23 – after bedding addition (are even better D +23 after…)

Figure 4: I am not sure if this figure is really needed as it just show the same results as Fig. 3 in a different way, but if you want to keep it please label clearly on the figure (such as with a dash line) the addition of bedding (i.e. right before D +23) on ALL panels.

L256-257 "Vertical Flow Constructed Wetland (VFCW) sand filter" - is confusing again - are we talking Constructed wetland or Sand filter? A CW is much more then "a filter"... This specific confusion seem to repeat it self throughout the text.

I am woried about possible interpertation of the jump from 3-4 worms/column (what was measured) to density of 500 g/m^-2 (what is stated in the conclusions) - upscaling in real life is rarly as simple as simple multiplication. I urge the writers to rephrase this part of the discussion more carfully as not to confuse readers. I suggest adding after "Density of 500 g/m^-2" the words "(2 earthworms/column)". Same for all other densities.

Same goes for Fig. 1 - Add what you actualy did, i.e. 1, 2, 3-4 earthworms under the "density"

The manuscript is intresting and I recomend accepting it after language and content editing.

Author Response

Dear reviewer,

Please see the attachment for our detailed responses point-by-point.

Author Response File: Author Response.docx

Reviewer 2 Report

I check the paper titled “Density Effect of Eisenia sp. Epigeic Earthworms on the Hydraulic Conductivity of Sand Filters for Wastewater Treatment” where experimental activities were carried out. I suggest minor revisions before publication.

• Two main points are not clear and should be better describer through the manuscript (e.g., Abstract, Intro, Conclusions): What is the main novelty of this work? What can be practical implications of the results obtain in this study? Please, try to better highlight these very important points.
• Why Eisenia was tested on a sand filter for wastewater treatment? Better discussion in this choice should be made.
• Figure 2, 3 and 4. Please, provide the number of data (in the captions of figures) used to create the plots.
• Quality of figures 2, 3 and 4 should be enhanced.
• Please, provide a nomenclature.

Author Response

Dear reviewer,

Please see the attachment for our detailed responses point-by-point.

Author Response File: Author Response.docx

Reviewer 3 Report

Manuscript entitled “Density Effect of Eisenia sp. Epigeic Earthworms on the Hydraulic Conductivity of Sand Filters for Wastewater Treatment” submitted by Océane Gilibert, Magali Gerino, Dan-Tâm Costa, Sabine Sauvage, Frédéric Julien, Yvan Capowiez and Didier Orange, can be considered for publication in Water Journal, after a minor revision.

Here is a list of my specific comments:

1. Page 2, line 77: “The biological processes supplied…”. Add here a reference.
2. Page 2, line 89: “The Smart-Clean-Garden Concept proposes…”. The same observation as above.
3. Page 2, line 91: “This paper aims at demonstrating…”. This paragraph should be reworded.
4. Page 3, lines 105-130: “The main objective of this study was to assess…”. At the end of Introduction, the main objectives of this study should be clearly presented. Avoid repetitions.
5. Page 5, line 185: “at three different depths”. Add here the values.
6. Page 11, References: The number of references is too high and should be reduced. 

Author Response

Dear reviewer,

Please see the attachment for our detailed responses point-by-point.

Author Response File: Author Response.docx