Application of Bottom Ash as Filter Media for Construction Site Runoff Control

Round 1

Reviewer 1 Report

General comments:

This paper concerns the use of bottom ash in filters for the removal of suspended solids from construction site runoff. Both lab scale and larger (pilot-scale) experiments were conducted. The paper is well written and the results are generally well presented (see my comments below). I have two major issues with the paper, which from my reading of it, are unclear: (1) no replication appears to have been carried out in the lab and pilot-scale experiments (2) no reference is made to destructive sampling of columns between hydraulic loading regimes. As the main focus of the paper is on the performance of filters under different volumetric/hydraulic loading regimes, this is a serious – and fatal – flaw.

Specific comments:

L34 – define KEEI

L38 – change to ‘continue to play’

L44 – no need for semi-colons

L45 – change to ‘the most widely used…’

L50 – delete ‘beneficial’

L52 – change to ‘the reuse of BA has decreased to…’ Are these figures per year or per decade?

L64 – have you got any reference for the comparison to agricultural lands?

L74 – ‘Thus, BA has the potential application for stormwater filtration…’ – I can’t see how this follows on from the previous sentence.

L77 – this is a result of the study. It should not be included in the Introduction section.

Delete L 77 – 80.

L84 – no need to repeat definition of acronym.

L87 – change to ‘…were to (1) investigated…’ [you can then delete the ‘to’ in the following aims]

L98 – delete ‘BA’.

L100 – ‘… 3mm contained most pollutants’ – was measured in the current study?

L121 – ‘S city’  - typo?

L127 – particle size defined as ‘D’ above. Should delete ‘D’ and ‘d’ in both cases.

L140 – change to ‘Detailed specifications…are summarized…’

L140ff – were the columns replicated? From the table/text, this appears not to be the case. The authors need to defend the apparent non-replication of the experiments.

L142 – why were multi-layer columns used in the pilot scale, but not in the lab scale?

Gen comment on M&M: you mention about different volumetric flow/loading rates being applied, but you do not tabulate them. Perhaps these could be incorporated into Table 2? Also, how were they selected? Were the volumetric loading rates the same for the lab and pilot-scale filters, or were they selected to ensure that the empty bed or pore volume retention time was the same? It would be very important to explain clearly the rationale for the selection of the loading rates. I would like to see them displayed as m/d or m3/m3 filter/d. Was the retention time calculated for every column (using a conservative tracer)?

L 250ff: If only one filter column was used in the lab scale experiments and different loading rates were applied, how did you ensure that the results in terms of removal efficiency (Fig 3) were truly independent? Surely, the performance of the columns were impacted by the preceding loading regime? I note that there is no reference in the text to the destruction of the columns after each loading regime.

Figure 3: when you say ‘linear velocity’ and give units of m/d, is this the same a hydraulic loading rate? Is this for the lab or pilot scale unit? If it is for the pilot scale unit, I assume that it is based on the c.s. area and not the cumulative c.s. area of the different columns used?

Author Response

Please see the attached below for the response letter.

Thank you so much!

Author Response File: Author Response.docx

Reviewer 2 Report

1. The author should compare with the existing material to prove that the new material is excellent.These comparisons should include at least the overall operating costs, as well as operational efficiency.

2. The author needs to revisit the grammar of the article. It is best to have someone with a native English background to review and modify this article.

    In my opinion, this article can be published in this journal if the authors offer enough new data. Also, the authors should recheck and correct the errors of typos and grammar before sending out this manuscript. By all the aspects enumerated above, the author should make a minor revision of the paper before its publication.

Author Response

Please see the attached below for the response letter.

Thank you so much!

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I have read the authors' response to my comments. I still have very grave concerns about this ms, and in particular the lack of replication, which is a serious shortcoming. 

To address this, I think that the authors need to add a caveat to the paper, stating that 'due to the lack of replication of the laboratory and pilot-scale filters, the results reported in this study are only indicative of performance.' This text should be placed around L 208 in the ms. I think that the authors should modify the text in the Results/Discussion to reflect this issue. Therefore, the phrasing should be changed to 'appear to' and 'suggest that' when discussing the results. Definite statements such as those in L 412ff ('...since TSS removal efficiencies were significantly affected by particle size, porosity....') need to be removed from the text. 

Author Response

Please see the file attached below.

Thanks for your time and effort.

Author Response File: Author Response.docx

Round 3

Reviewer 1 Report

I am happy that the authors have addressed my main issue with this paper (the lack of replication). However, I have a suggestion to the English used in the crucial line (Ln 207), which is currently clumsily written. It should read:

Due to the lack of replication of the filtration experiments, the results in this study only indicate a preliminary evaluation of BA for construction site runoff filtration and infiltration systems as an alternative filter media.  

Author Response

The authors appreciate the reviewer’s perceptive comments. The authors comply with the reviewer’s comments and modify the sentence.

(see the response letter below)

Author Response File: Author Response.docx