Performance of a Combined Bacteria/Zeolite Permeable Barrier on the Rehabilitation of Wastewater Containing Atrazine and Heavy Metals
, Cassia Z. Pimentel 1,2, Bruna Machado 1,2, Filomena Costa 1,2 and Teresa Tavares 1,2
Round 1
Reviewer 1 Report
The authors present an interesting topic. However, they must attend to the following points before being considered for publication. 1. Introduction, lines 53-76, must use the following current reference ; http://dx.doi.org/10.1016/j.cej.2022.141034 document more about treatment methods to remove metals. 2. The authors should improve the Figure of the FTIRs. 3. Authors should use a scheme on possible separation mechanisms. 4. Authors should compare the performance of these materials with others reported in the literature.
Author Response
Response to Reviewer 1 Comments
Point 1 - Introduction, lines 53-76, must use the following current reference; http://dx.doi.org/10.1016/j.cej.2022.141034
Response 1: The requested reference was added to Introduction.
Point 2 - document more about treatment methods to remove metals.
Response 2: More references which document the removal of heavy metals were added to the text.
Point 3 - The authors should improve the Figure of the FTIRs.
Response 3: The quality of the figures was improved.
Point 4 - Authors should use a scheme on possible separation mechanisms.
Response 4: A schematic representation of the possible separation mechanisms was added to the text.
Point 5 - Authors should compare the performance of these materials with others reported in the literature.
Response 5: A comparison with the performance of other materials was already included in the text (lines 416-464).
Reviewer 2 Report
The authors have done an extensive study on the removal of atrazine and heavy metals containing wastewater using an R. viscosum – zeolite permeable barrier. There are a few following points that need to be addressed by the authors,
1. The authors can clarify the reason for fixing the initial concentrations of pollutants, are there any field data to substantiate the contaminants concentrations?
2. As the authors have done a toxicity study, the impact of Atrazine on human and other environmental components was not clarified.
3. In section 2.8, the details on the permeability of the bio-barrier, how it is checked, and methods used to confirm the permeability and the permeability value can be highlighted.
4. The biodegradation of atrazine is not having following a proper trend in degradation, is there any SD value, if so can be added to the graph? The clear explanation of the biodegradation part is weak.
5. In the PBR reactor, why the C/Co value is increasing after the initial few hours of study, whereas the other pollutants are decreasing? The reason for the such scenario can be elaborated.
6. Conclusion part is weak, and needs to intricate more details about the results and its conclusion can also include the future perspective.
Author Response
Response to Reviewer 2 Comments
Point 1 - The authors can clarify the reason for fixing the initial concentrations of pollutants, are there any field data to substantiate the contaminants concentrations?
Response 1: Regarding atrazine, this herbicide has been detected at µg/L concentration levels in a wide variety of environmental water samples, although higher concentrations can be found in waterbodies within watersheds with a high density of different culture. The authors wanted to demonstrate the capacity of the treatment in study to treat high levels of atrazine (such as 1 mg/L), that could be found on such types of water bodies. Regarding the concentration of heavy metals used (40 mg/L of Cu and 60 mg/L of Zn) these are levels commonly found in different industrial effluents, such as from metal plating facilities, mining operations, fertilizer industries, tanneries, batteries, etc.
Point 2 - As the authors have done a toxicity study, the impact of Atrazine on human and other environmental components was not clarified.
Response 2: The toxicity experiments were performed with the objective to access the ability of R. viscosum to uptake cupper (Cu) and zinc (Zn) and to degrade atrazine when exposed to different contaminants levels. Although this is a quite pertinent issue, the focus of this manuscript was not the assessment of the harmful impact of the studied pollutants on human health and the environment.
Point 3 - In section 2.8, the details on the permeability of the bio-barrier, how it is checked, and methods used to confirm the permeability and the permeability value can be highlighted.
Response 3: The permeable bio-barrier was operated in closed-loop mode (100 % recirculation), since the objective was to evaluate the capacity of the barrier (zeolite + bacteria) to remove/degrade the pollutants. The concentration of metals and atrazine along the time of operation were quantified by ICP and UHPLC, respectively. The authors totally agree with the importance to perform permeability studies under continuous operation simulating more realistic scenarios, which certainly will be the next experiments to be performed.
Point 4 - The biodegradation of atrazine is not having following a proper trend in degradation, is there any SD value, if so can be added to the graph? The clear explanation of the biodegradation part is weak.
Point 5 - In the PBR reactor, why the C/Co value is increasing after the initial few hours of study, whereas the other pollutants are decreasing? The reason for the such scenario can be elaborated.
Response 4 and 5: The removal of atrazine (and heavy metals) over time during the PBR experiment is represented in Figure 7, with the respective error bars (SD values). The explanation of the herbicide degradation trend is presented in lines 463-471. In the present study, due to technical limitations inherent to the diode-array detector used, it was not possible to identify any by-products resulting from the degradation of atrazine. A further study using a MS detector would be crucial to quantify the degradation metabolites and to demonstrate the degradation pathway.
Point 6 - Conclusion part is weak, and needs to intricate more details about the results and its conclusion can also include the future perspective.
Response 6: The Conclusion section was deeper reviewed and new information was added, including future perspectives.
