Enhanced Wet Oxidation of Excess Sludge from Pharmaceutical Wastewater Treatment by NaOH

Round 1

Reviewer 1 Report

The authors present the study of enhanced wet oxidation of excess sludge from pharmaceutical wastewater by NaOH as an alkaline homogeneous catalyst.

The topic is of relevant scientific interest, however, making a very general review of the manuscript, aspects can be observed, which it is necessary to be corrected.

 

Materials and Methods

Line 102, It is suggested to improve the quality of Figure 1

Line 104. It is necessary to enter a reference for the determination of SVV and COD, or else, it is necessary to move here the description of line 111-112…. Detailed information on the analysis can be found elsewhere [21,22]….

Line 111-112. You need to move these lines to line 104

Line 111. It is necessary to put a description or reference for the determination of VFAs, because the references [21,22] have not described this analysis

Results and Discussion

Line 140, It is necessary to change Effect of reaction temperatur by Effect of reaction temperature.

Line 211, It is suggested to improve the description and discussion of figure 6. Figures 6a and 6b are very similar and only a slight difference can be seen in region V of both figures.

Line 221, It is necessary to change thermal-hydrolyzed  by thermal-hydrolyzed.   

Line 223, It is necessary to change sewage sludge…  by Sewage sludge   

It is suggested to describe the equation for Removal rate (%)

It is necessary that report the pH final

The conclusions could be improved

 

 In any case, the manuscript is of relevant scientific interest, however, aspects can be observed, that the authors must correct.

 

Author Response

Please see the attached file. 

Thanks!

Author Response File: Author Response.pdf

Reviewer 2 Report

This research paper deals with the treatment of excess sludge from pharmaceutical wastewater by NaOH as an alkaline homogeneous catalyst. In my humble opinion, the manuscript is well organized and the result look like novel. However, the following comments should be addressed by author to consider the publication of the manuscript in Catalysts Journal:

·         The text should be revised, not only because of English grammar, but also because some parts are not well described (scientific soundness should be improved).

·         Authors describe the wet oxidation as an advanced oxidation process (AOP). However, AOPs comprise the use of hydroxyl radicals (not hydroxyl anion) to oxidize organic compounds in aqueous matrixes. Could authors corroborate that WO can be categorized as AOP? The difference among WAO and WO should be identified in the introduction of the manuscript.

·         Which “free radical oxidative agents” (line 439) are generated during WO? Please, introduction should be more descriptive.

·         Wet oxidation (WO) is more known as Wet Air Oxidation (WAO). Could author explain whether any difference exists between WO and WAO? Which is the oxidant source in the process studied in this work? If air or oxygen is not the oxidant use to promote the degradation of the compounds, is NaOH? In this case, NaOH plays a role as catalyst or as oxidant?

·         An additional run without oxygen, means purging with nitrogen (at inert atmosphere), with NaOH should be performed in order to study the real contribution of the NaOH (as oxidative or catalyst agent).

·         How NaOH could impact in the selectivity of the oxidation reactions? (lines 66-67). Please, consider your explanation in a new improved version of the manuscript.

·         What authors mean with “carboxylic acids, which could be used as carbon source for the wastewater treatment” (line 77)? Likely, they refer carbon source for the treatment of wastewater by biological treatment, but this should be better specify.

·         Technical analysis used for the characterization of the wastewater should be better describe, including the methodology to determine VSS and COD. Also, a description of 3D-EEM should be added.

·         The volume of sludge load to the reactor and the volume of the reactor must be specified in the methodology to know the quantity of oxygen loaded into the system.

·         In the figures a removal rate is reposted, but rates is expressed in times units (e.g. mol/second). Please, revise it.

·         The decrease in COD removal adding higher quantities of NaOH must be deeply study as follows: 1) reporting pH of aqueous media in each run; 2) verify the increased in soluble COD because VSS is dissolved as a result of NaOH addition at mild conditions; 3) Bulk COD and soluble COD must be measured in all experiments; and 4) BOD/COD ratio should be reported. If (2) and (3) cannot be reported/performed, then VSS should be removed prior to assess WO in order to verify that higher removals of COD are achieved by increasing NaOH loads.

·         In the manuscript, it is described “Comparing with other heterogeneous catalyst, the merit of NaOH is that is can be dissolved to the sludge solution easily, which induced the fast catalytic effect. In addition, there is no need to consider the filter process which is necessary for the heterogeneous catalyst”. However, author should explain how is expected recovering the catalyst after process for sustainable issues.

·         In addition, the manuscript should explore ways to neutralize pH of the sludge.

·         In the section regarding the effect of the temperature, the reached autogenous pressure must be reported in each experiment at different temperature, since pressure affect the oxygen solubility. In addition, an additional run at 180 ºC and the pressure reached at 260 ºC should be performed in order to verify whether the effect under studied is the temperature indeed, or both pressure and temperature.

·         In some parts of the manuscript, NaOH load is expressed as 0.5 g and in other parts as 0.5 g/L. Please, the text should be revised.

Author Response

Please see the attached file.

Thanks!

Author Response File: Author Response.pdf