Start-Up Evaluation of a Full-Scale Wastewater Treatment Plant Consisting of a UASB Reactor Followed by Activated Sludge
, Andrea Pérez-Vidal 2, David Vargas-Nuncira 3, Olga Usaquén-Perilla 4, Ximena Jiménez-Daza 5 and Claudia Rodríguez 6Round 1
Reviewer 1 Report
General comment:
In this research article, the authors evaluated the treatment efficiency of UASB + Activated sludge treatment of sewage wastewater. The reported work shows some fascinating results related to organic and biological pollutants removal in terms of BOD, COD, etc. This work is considered to be published in this journal; however, it has some minor issues that need to be solved before being accepted. The detail is as follow.
· In line number 17 author used the USAB for the first time. It is necessary to abbreviate the first used in the manuscript (similar through out the manuscript).
· To further improve the manuscript quality, it is suggested that the authors add some comparative results in performance evaluation from previous studies in tabular form.
· In addition, from my point of view, Figure 9 of the manuscript is considered for the graphical abstract of this paper.
Author Response
Reviewer #1 - General comment:
In this research article, the authors evaluated the treatment efficiency of UASB + Activated sludge treatment of sewage wastewater. The reported work shows some fascinating results related to organic and biological pollutants removal in terms of BOD, COD, etc. This work is considered to be published in this journal; however, it has some minor issues that need to be solved before being accepted. The detail is as follow.
Author’s response:
The authors appreciate reviewer #1 comments and accepted his recommendations
Point 1:
In line number 17 author used the USAB for the first time. It is necessary to abbreviate the first used in the manuscript (similar throughout the manuscript).
Author’s response:
Corrected
Point 2:
To further improve the manuscript quality, it is suggested that the authors add some comparative results in performance evaluation from previous studies in tabular form.
Author’s response:
Table 6 was included. It presents previous full scale studies. Besides, a comparison with this research was included. See page 16
Point 3:
In addition, from my point of view, Figure 9 of the manuscript is considered for the graphical abstract of this paper.
Author’s response:
The general aspects of Figure 9 were included in the graphical abstract.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors suggest the strategy for the treatment of sludge which involves UASB reactor followed by treatment by activated sludge system. Although many studies report the strategy like this, I would urge the authors to justify the novelty of the work and consider following points for the revision.
1. Add some reviews on similar works involving anaerobic and aerobic wastewater teatment/sludge.
2. Lines 71-74 (Introduction) should be deleted as you didnot carry out any cost analysis.
3. Section 2.1: What is m.a.s.l in 2750 m.a.s.l? is it some standard abbreviation?
4. "Affluent" is not proper term, please replace it with "influent".
5. "Flowsheet of the Tunja STP" , is not enough, please elaborate this title.
6. " Each UASB reactor 124 had a volume of 2895 m3" what was working volume of UASB?
7. Table 1: For a UASB reactor in start up phase, HRT of 6 hours is too less, it should be 12 hours. What is justification for 6 hours?
8. Lines 144-145: (Raw wastewater; UASB effluent; effluent) why "effluent" repeated?
9. Table 2 can be narrated in the text.
10. Kg should be written with small k.
11. for COD and BOD, unit "mg O2/L" is not proper, it is mg/L.
12. Last paragraph of conclusion should be shifted to Discussion.
Author Response
English revision
As recommended by the reviewer the manuscript received an extensive English revision. It was done by the mdpi author service.
Reviewer #2 - General comment:
The authors suggest the strategy for the treatment of sludge which involves UASB reactor followed by treatment by activated sludge system. Although many studies report the strategy like this, I would urge the authors to justify the novelty of the work and consider following points for the revision.
Author’s response:
There are limited published studies related to full scale sewage treatments that combine UASB reactors with activated sludge postreatment aimed to identify and avoid start up and operational problems. The novelty of this research is focused on the identification of the relevant operative aspects that affect the start up and the operation of the combined system. This is particularly important due to the influence of the anaerobic effluent on the aerobic system. In order to highlight the novelty of this research the introduction was improved and news references were added.
Please also see first lines of page 4.
Point 1:
Add some reviews on similar works involving anaerobic and aerobic wastewater treatment/sludge.
Author’s response:
Similar studies supported with new references were included in the introduction section. Please see page 3 paragraphs 2, 3, 4 and 5. Also, Table 6 (page 16) was included showing a comparison with other reported full scale experiences.
Moreover, in the results and discussion section (see new table 6, page 16) a comparison with those studies was done.
Point 2:
Lines 71-74 (Introduction) should be deleted as you did not carry out any cost analysis.
Author’s response
Corrected. Lines were deleted
Point 3:
Section 2.1: What is m.a.s.l in 2750 m.a.s.l? is it some standard abbreviation?
Author’s response:
The abbreviation was deleted and changed by 2750 m above the sea level
Point 4:
"Affluent" is not proper term, please replace it with "influent".
Author’s response:
It was corrected throughout the document
Point 5:
"Flowsheet of the Tunja STP", is not enough, please elaborate this title.
Author’s response:
It was improved.
Point 6:
" Each UASB reactor 124 had a volume of 2895 m3" what was working volume of UASB?
Author’s response:
It was corrected. It corresponds to working volume.
Point 7
Table 1: For a UASB reactor in start up phase, HRT of 6 hours is too less, it should be 12 hours. What is justification for 6 hours?
Author’s response:
It was clarified. Please see last paragraph of page 16
In Table 1 the value of HRT is not related to the operation of the system in the start up phase. It corresponds to the adopted design values.
See new Table 6 (page 16): the operational values of HRT applied to the UASB and Aeration tank in Tunja and in different full scale systems. As can be seen in the mentioned experiences the UASB-AS combination uses UASB reactors operating in low HRT.
Point 8:
Lines 144-145: (Raw wastewater; UASB effluent; effluent) why "effluent" repeated?
Author’s response:
It was corrected. Final effluent
Point 9:
Table 2 can be narrated in the text.
Author’s response:
This comment was not accepted. The authors believe that this table is important because gives methodological clarity, especially in the frequency and sampling sites.
Point 10:
Kg should be written with small k.
Author’s response:
It was corrected in the text and in figures 2, 4 and 5.
Point 11:
for COD and BOD, unit "mg O2/L" is not proper, it is mg/L
Author’s response:
Corrected throughout the document
Point 12:
Last paragraph of conclusion should be shifted to the Discussion section .
Author’s response:
The paragraph was moved to the discussion (see section page 10 paragraph 5). Moreover, the second conclusion was improved including the recommended raw water by-pass to the aeration tank.
Also, the following conclusion was added (see page 21 paragraph 3):
The performance of the combined systems at the end of the evaluation period showed that, as expected, and because of the low-sludge-age operation, there was no nitrification. The BOD effluent was less than 30 mg/L, a value that is widely recognized as a valid quality criterion for conventional activated sludge system effluents. The influent settleable solid concentrations were between 2.8 and 7.0, but their effluent concentrations were less than the method DL (0.1 ml/L). The heavy metals that were present in the influent were aluminum, zinc, and copper, with effluent concentrations less than their DLs. The iron removal efficiency was 82%. Hydrocarbons were present in the influent, but their effluent concentrations were less than their DLs.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
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