Nitrogen Removal for Low Concentration Ammonium Wastewater by Adsorption, Shortcut Simultaneous Nitrification and Denitrification Process in MBBR

Round 1

Reviewer 1 Report

Journal: Water

Title: Nitrogen removal for low concentration ammonium wastewater by adsorption, shortcut simultaneous nitrification and denitrification process in MBBR

 

1             General Remarks

Summary: In this manuscript, the authors attempted to evaluate the feasibility MBBR adsorption-shortcut SND process. Moreover, the operational parameters of the adsorption-shortcut SND process were explored. Furthermore, the effects of experimental parameters such as HRT, agitation rate, alkalinity and DO were investigated to understand the denitrification performance. Finally, the authors elucidates the mechanism of the migration, transformation and regeneration mechanism of ammonia nitrogen in the MBBR adsorption-shortcut SND process.

The topic well falls within the scope of Water. It is critical to developing an innovative method for the treatment of oily wastewater. Overall, the authors have conducted many experiments with good experiential designs. Only a minor revision is needed before publication. Some issues are listed below for authors to consider for the revisions.

 

2             Comments

1.     In figures 2 and 3, error bars are missing.

2.     In Figures 4, 5, and 7, I would suggest the authors use the same symbols, such as bars, dots, or box plots for comparison purposes. It is not a good practice to mix them.

3.     The Conclusion section of a manuscript should include a summary of the results, the potential limitation of this research, and the recommendation of future research directions for peers. However, only a summary of the results was covered in the Conclusion section of this manuscript. It would be great to add the potential limitation of this research and the recommendation of future research directions for peers.

4.     Please proofread the authors’ manuscript before the final submission. There are some typos and grammar errors in the manuscript.

Author Response

Response to Reviewer 1 Comments

 

Point (1): In figures 2 and 3, error bars are missing.

Response (1): Thank you for your insightful comments. We have added error bars in figures 2 and 3.

 

Point (2): In Figures 4, 5, and 7, I would suggest the authors use the same symbols, such as bars, dots, or box plots for comparison purposes. It is not a good practice to mix them.

Response (2): We agree that mix them was not a particularly good choose. But, there are many indicators that need to be represented and they have similar change trends. If using the same symbols such as bars, dots, or box plots to comparison purposes, it may be not easy to distinguish for reader.

 

Point (3): The Conclusion section of a manuscript should include a summary of the results, the potential limitation of this research, and the recommendation of future research directions for peers. However, only a summary of the results was covered in the Conclusion section of this manuscript. It would be great to add the potential limitation of this research and the recommendation of future research directions for peers.

Response (3): We sincerely appreciate the valuable comments. Through research, it was found that the studies remain the superficial phase of positive research and descriptive analysis, and they fail to reveal the deeper mechanism of MBBR adsorption-shortcut SND process. Many Future studies on the contribution and improvement of the MBBR adsorption-shortcut SND process are needed to do. 1) The MBBR adsorption-shortcut SND process should focused on the change of microbial communities in shortcut SND process to Clarify the microbial mechanism of nitrogen removal. 2) Establishing activated sludge model 3 mathematical model which can accurately describe the short-range SND nitrogen removal process of MBBR, that is helpful to accurately find out the key factors affecting the nitrogen removal efficiency. 3) N₂O/N₂ production during MBBR adsorption-shortcut SND process should be explored, and the nitrogen balance of the reaction process also should be studied. In general, by much more exploration MBBR adsorption-shortcut SND process are expected to be a preferred N-removal approach to treating aquaculture wastewater in the future.

 

Point (4): Please proofread the authors’ manuscript before the final submission. There are some typos and grammar errors in the manuscript.

Response (4): This manuscript has been edited by a senior scientist with extensive publication experience. We believe it is improved greatly both in terms of the English writing and the layout, fonts and format of different sections.

Author Response File: Author Response.docx

Reviewer 2 Report

The article “Nitrogen removal for low concentration ammonium wastewater by adsorption, shortcut simultaneous nitrification and denitrification process in MBBR” represents the preparation of ceramsite material from sediment, zeolite, and bentonite for ammonia nitrogen removal. Although the study objective is clear, some points should be considered:

1.   In Table 1, what are the wastewater properties such as COD, TSS, N, TDS, etc.

2.   How ceramsite was inserted in the solution, how to be mixed and collected?

3.   The title “3. Results and discussion” should be added.

4.   What about the reusability/regeneration of spent material?

5.   Compare the ceramsite with sponge used previously in https://doi.org/10.1016/j.eti.2020.101327; https://doi.org/10.1016/B978-0-12-822933-0.00014-0; https://doi.org/10.1016/j.jwpe.2020.101415;

6.   Characterization of the ceramsite by SEM/EDX, XRD, FTIR is required

 

Author Response

Response to Reviewer 2 Comments

 

Point (1): In Table 1, what are the wastewater properties such as COD, TSS, N, TDS, etc.

Response (1): Thank you very much for these suggestions. The -N concentration of the wastewater was about 26.2 mg/L, COD concentration was about 100 mg/L, and pH was about 7.62. The wastewater was a synthetic aquaculture wastewater, so the quality index of TSS and the TDS were ignored.

 

Point (2): How ceramsite was inserted in the solution, how to be mixed and collected?

Response (2): The agitator was installed on the lid of the reactor. After removing the lid, the ceramsite can be added or taken out directly. The ceramsites were kept in suspension and continuous movement in the MBBR by mechanical mixing of agitator.

 

Point (3): The title “3. Results and discussion” should be added.

Response (3): Thank you for your kind advice. We have added title “3. Results and discussion”.

 

Point (4):  What about the reusability/regeneration of spent material?

Response (4): In this study, the reusability/regeneration of the bio-ceramides was by biochemical regeneration. According to our follow-up research, the regeneration effect of bio-ceramsite after a long operation period was shown in Figure S1. As can be seen from the figure, the regeneration rate of bio-ceramsite in the first 20 cycles was about 71.2 ~ 85.1%. With the extension of running time, the nitrification efficiency gradually decreased, and the biochemical regeneration effect of ceramsite continued to deteriorate. However, in the 21st cycle, by extending regeneration time to 14 h and increasing the stirring speed to 150 r/min to promote aging biofilm shedding, the activity of nitrification functional bacteria was restored. And the regeneration rate of ceramsite was restored to 86.1%, indicating that the bio-ceramsite in the reactor still had a large ammonia nitrogen adsorption capacity, and the MBBR adsorption-shortcut SND process could be continuously used for the denitrification treatment of actual low concentration ammonia nitrogen aquaculture wastewater.

Figure S1. Bio-regeneration rate of bio-ceramsite in multi-cycle operation by MBBR

 

Point (5): Compare the ceramsite with sponge used previously in https://doi.org/10.1016/j.eti.2020.101327; https://doi.org/10.1016/B978-0-12-822933-0.00014-0; https://doi.org/10.1016/j.jwpe.2020.101415;

Response (5): We have compared ceramsite with sponge and added those reference to the manuscript (Ref.12、Ref.15 and Ref.16). We find lightweight ceramsite was similar to sponge, both have a rough exterior and an extensive interior pore network. A wide range of microbial communities can grow on that kind of carrier surface and inside the pores to assemble and degrade various pollutants.

 

Point (6): Characterization of the ceramsite by SEM/EDX, XRD, FTIR is required

Response (6): The characterization of the ceramsite was described in the study that served as the research basis of this article “Optimized utilization studies of dredging sediment for making water treatment ceramsite based on extreme vertex design”.

Author Response File: Author Response.docx

Reviewer 3 Report

General comment:

The manuscript deals with investigations on ammonia nitrogen removal by using a moving bed biofilm reactor through the combination of adsorption and nitrification and denitrification. The effect of operational parameter variation and regeneration mechanism were investigated.

The manuscript is very interesting and suitable to be published in this journal; however, some points should be addressed before publication.

Some minor language mistakes are present that should anyway be corrected.

 

 

1. Introduction

Please, improve the literature overview on the nitrogen removal. Please, consider the following papers:

·      Electrochemical Removal of Nitrogen Compounds from a Simulated Saline Wastewater (2023) Molecules, 28 (3), art. no. 1306.

·      Efficient nitrogen removal through coupling biochar with zero-valent iron by different packing modes in bioretention system (2023) Environmental Research, 223, art. no. 115375.

·      Sustainable nitrogen removal in anammox-mediated systems: Microbial metabolic pathways, operational conditions and mathematical modelling (2023) Science of the Total Environment, 868, art. no. 161633.

2. Materials and Methods

Please, clarify if investigations were carried out in duplicate/triplicate etc.

Please, include a statistical analysis.

Please, specify if pH was kept constant of it was monitored during the tests.

Please, clarify if the equilibrium between nitrogen species was considered.

Please, include the nitrogen balance.

Please, clarify if by-product formation was investigated.

3. Results and discussion

Please, improve comparison between your findings and literature data, in terms of removal efficiency.

Please, include results of statistical analysis.

Please, include the nitrogen balance.

Please, include by-product measurement results.

 

Please, clarify if the pH was monitored and the effect of the pH variation was taken into consideration.

Author Response

Response to Reviewer 3 Comments

1. Introduction

Point (1): Please, improve the literature overview on the nitrogen removal. Please, consider the following papers:

Electrochemical Removal of Nitrogen Compounds from a Simulated Saline Wastewater (2023) Molecules, 28 (3), art. no. 1306.

Efficient nitrogen removal through coupling biochar with zero-valent iron by different packing modes in bioretention system (2023) Environmental Research, 223, art. no. 115375.

Sustainable nitrogen removal in anammox-mediated systems: Microbial metabolic pathways, operational conditions and mathematical modelling (2023) Science of the Total Environment, 868, art. no. 161633.

Response (1): Thanks for your sincere suggestions. These suggestions are very important for the revision of this paper and the guidance of our follow-up research. According to the above paper, we supplement the introduction and added those citation and reference to the manuscript (Ref. 5、Ref. 23 and Ref. 24). Fundamentally, proper DO levels could suppress nitrite-oxidizing bacteria (NOB) activity escorted by maintaining ammonia-oxidizing bacteria (AOB) and ammonium-oxidizing bacteria (AnAOB) activities to prevent the build-up of NO_3^--N in systems [23]. Besides, the environment with high DO was unfavorable for the growth of denitrifying bacteria and unable to form a subsequent anaerobic condition suitable for denitrification [24].The pH and FA/FNA can influence the microbial activity in MBBR nitrogen removal system, including AOB, NOB, AnAOB and heterotrophs [23]. The optimal control of FA could improve the TN removal efficiency in wastewater treatment systems [23].

 

2. Materials and Methods

Point (1): Please, clarify if investigations were carried out in duplicate/triplicate etc.

Response (1): The effluent samples were taken in triplicate every time for the assessment of wa-ter quality parameters (mean ± SD follow).

 

Point (2): Please, include a statistical analysis.

Response (2): We added a statistical analysis part in materials and methods. Data are presented as means ± SD (n = 3). All statistics were conducted in SPSS 19.0. The figures were made by Origin 2021 software.

 

Point (3): Please, specify if pH was kept constant of it was monitored during the tests.

Response (3): The variation of pH in the reactor was affected by the different dosage of alkalinity. The -N, TN, -N, -N and pH were monitored per hour during the tests. The results of the experiment have been shown in Figure 5.

 

Point (4): Please, clarify if the equilibrium between nitrogen species was considered. Please, include the nitrogen balance.

Response (4): We agree that more study would be useful to understand the equilibrium between nitrogen species and the nitrogen balance. However, when designing the test, we do not have the necessary tool-set to collect the N₂O/N₂ gas. So, we only considered the nitrogen balance between -N, TN, -N, -N, which was not perfect. We hope, in the future, to explore the production process of N₂O/N₂ in MBBR adsorption-shortcut SND process, and understand migration and transformation pathways of nitrogen. The literature that you recommended has inspired us, and we will take it as a reference to design the follow-up research.

 

Point (5): Please, clarify if by-product formation was investigated.

Response (5): We're very sorry. In this experiment, we only consider the change of -N, TN, -N, -N, COD and DO. The by-product formation was not investigated.

 

3. Results and discussion

Point (1): Please, improve comparison between your findings and literature data, in terms of removal efficiency.

Response (1): Compared with the traditional nitrogen removal systems, the MBBR adsorption-shortcut SND process provides up to 80–90 % nitrogen removal, which significantly improved the removal efficiency of ammonia nitrogen [25]. The MBBR adsorption-shortcut SND process allows for an energy savings in aeration compared with nitrification/denitrification process, which significantly reduces the operating costs of the system [52]. The other benefit of the MBBR adsorption-shortcut SND process is that there is reducing the need for carbon sources due to the nitrosation process, and less sludge is produced compared with the nitrification/denitrification process [53]. The operational cost was far less than common nitrification/denitrification process, which showed particular potential of MBBR adsorption-shortcut SND process for engineering application of low-strength ammonium aquaculture wastewater.

 

Point (2): Please, include results of statistical analysis.

Response (2): But in results and discussion part, we can see data are Mean ± SE (n = 3). The figure described the Mean ± SE (n = 3) and trend of the data.

 

Point (3): Please, include the nitrogen balance.

Response (3): We are very sorry that in this experiment we didn't collect the N₂O/N₂ gas. So, we only considered the nitrogen balance between -N, TN, -N, -N, which was not perfect. We hope, in the future, to explore the production process of N₂O/N₂ in MBBR adsorption-shortcut SND process, and understand migration and transformation pathways of nitrogen.

 

Point (4): Please, include by-product measurement results.

Response (4): In this experiment, we only consider the change of -N, TN, -N, -N, COD and DO.  The by-product formation was not investigated. At this point we do not have the necessary tool-set to study the by-product formation. Monitoring of by-products will be considered in our future studies.

 

Point (5): Please, clarify if the pH was monitored and the effect of the pH variation was taken into consideration.

Response (5): The -N, TN, -N, -N and pH were monitored per hour during the tests. The results of the experiment have been shown in Figure 5. The pH was not set as a factor in this study. But the different dosage of alkalinity will affect the pH value in MBBR, and the effect of PH on FA was analysed. It can be found that there was a complex connection between the variation of these nitrogen forms and pH as well as FA concentration. The pH of each reactor showed a trend of increasing to the maximum value first and then decreasing after a period of time. The reasons for the increase of pH at the beginning stage may be related to the following factors: on the one hand, the high concentration of organic matter at the beginning of the reaction, the number of heterotrophic bacteria is much more than that of autotrophic bacteria such as AOB and NOB, and the decomposition and metabolism of COD by heterotrophic microorganisms will produce CO₂, while the constant aeration will blow off CO₂, which leads to the increase of pH in MBBR [37]. On the other hand, the alkalinity produced by denitrification in the reactor is larger than that consumed by nitrifying bacteria, which causes a further increase in pH [38]. When the alkalinity produced by denitrification, the alkalinity produced by aeration blow-off and the alkalinity consumed by nitrification are equal, the pH of the system will reach the maximum value and remain unchanged for an extended period of time. Ultimately the pH in the MBBR will start to decrease with the enhancement of nitrification and weakening of denitrification and the reduction of CO₂ blow-off in the later stage of the reaction.

Author Response File: Author Response.docx

Reviewer 4 Report

Well done, comprehensive critical analysis, enjoyed reading the article. Please address the following:

Can you please check figure 2, red legend should be the influent and the blue should be the effluent?

Figure 8, total nitrogen seems to increase at the beginning and then end up higher than the point of start, please explain? not clear what happening her?

Figure 10, on what basis you have identified the Nitrification and denitrification regions on/in the particles? 

Add nomenclature, many of the abbreviations are not identified,

I did not understand, is the regeneration happen in a separate process? NO, then what the benefit of adsorbing and releasing the ammonia N during regeneration?

can you, if possible add a table to summarise the optimum conditions, including TN, ammonia, nitrate, and nitrate in the influent and effluent?

Author Response

Response to Reviewer 4 Comments

 

Point (1): Can you please check figure 2, red legend should be the influent and the blue should be the effluent?

Response (1): Thank you very much for your suggestions. The problem in Figure 2 has been modified.

 

Point (2): Figure 8, total nitrogen seems to increase at the beginning and then end up higher than the point of start, please explain? not clear what happening her?

Response (2): In the adsorption stage, the ceramsite adsorbed a lot of ammonia nitrogen. However, in the shortcut SND denitrification and regeneration stage, those ammonia nitrogen were desorbed by biochemical regeneration effect, which increased the initial TN concentration. With the shortcut SND process, the TN concentration decreased gradually. However, due to the lack of a carbon source, even if a stable shortcut nitrification process was achieved, there were still a lot of -N residues at the end of the reaction, which caused the final TN concentration higher than the point of start.

 

Point (3): Figure 10, on what basis you have identified the Nitrification and denitrification regions on/in the particles?

Response (3): Based on previous references such as “Nitrite accumulation stability evaluation for low-strength ammonium wastewater by adsorption and biological desorption of zeolite under different operational temperature” and “Effect of alkalinity on bio-zeolite regeneration in treating cold low-strength ammonium wastewater via adsorption and enhanced regeneration”, we drew a conceptual map of the mechanism of nitrogen removal.

 

Point (4): Add nomenclature, many of the abbreviations are not identified.

Response (4): Thank you very much for your suggestions. Those abbreviations have been identified such free ammonia (FA), free nitrous acid (FNA), ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), ammonium-oxidizing bacteria (AnAOB) and hydraulic retention time (HRT).

 

Point (5): I did not understand, is the regeneration happen in a separate process? NO, then what the benefit of adsorbing and releasing the ammonia N during regeneration?

Response (5): Yes, the biochemical regeneration happened in a separate process but in the same reactor. The desorbed high concentration of ammonia nitrogen caused by denitrification and regeneration and the high pH in the liquid phase is the key to realizing the inhibitory effect of high concentration FA on NOB. Maintaining the concentration of FA in the range of 1-10 mg/L can maintain the nitrification reaction in the nitrosation stage, which will reduce the consumption of carbon source in denitrification process. In general, the MBBR adsorption-shortcut SND process base on the regeneration happen in a separate process can realize an effective and energy-saving denitrification process.

 

Point (6): can you, if possible add a table to summarise the optimum conditions, including TN, ammonia, nitrate, and nitrate in the influent and effluent?

Response (6): The optimal operating parameters in the adsorption stage were hydraulic retention time of 8 h and agitation rate of 120 r/min. For the shortcut SND stage, the ideal optimal parameters were 2 times alkalinity and dissolved oxygen (DO) 1.0mg /L. Under optimal operating parameters conditions, the influent TN, ammonia, nitrate, and nitrate concentration were 29.6, 1.7 5.56 and 22.34 mg/L, respectively. And the SND rate, TN removal rate, ammonia removal rate and nitrite accumulation rate were 89.1%, 84.0%, 94.3% and 86.4%, respectively. The data involved in the optimum conditions is relatively small.  Can we use text to present those data?

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The revised article “Nitrogen removal for low concentration ammonium wastewater by adsorption, shortcut simultaneous nitrification and denitrification process in MBBR” seems fine, but some typo errors should be corrected:

Line 21: 1.0mg /L

Line 75: t2270035o

What is the statistical difference between data in Table 2 (based on HRTs variation) and Table 3 (based on stirring intensity variation). This statistical analysis should be conducted, for example, by one-way ANOVA, post Hoc Tukey HSD test, and discussed in the text as well. Same for figures, such as bar chart in Fig. 4.

The Conclusions section should be more concise.

Author Response

Response to Reviewer 2 Comments

 

Point (1): Line 21: 1.0mg /L

Response (1): Thank you for your clear guidance. Such errors in this article have been corrected

 

Point (2): Line 75: t2270035o

Response (2): We are so sorry.We can’t exactly understand the meaning of the numbers.

 

Point (3): What is the statistical difference between data in Table 2 (based on HRTs variation) and Table 3 (based on stirring intensity variation). This statistical analysis should be conducted, for example, by one-way ANOVA, post Hoc Tukey HSD test, and discussed in the text as well. Same for figures, such as bar chart in Fig. 4.

Response (3): Thanks for your valuable suggestions. The data of unit adsorption quantity and -N volume load in Table 2 and Table 3 have been analysised by one-way ANOVA, post Hoc Tukey HSD test. On one line, with the different superscript letters means significantly different (Tukey’s post hoc test, p ＜ 0.05). It can be seen from the data in Table 2 that the differences of unit adsorption quantity and -N volume load between different HRT were significant. The data in Table 3 shown that the differences of unit adsorption quantity and -N volume load between different stirring intensity were significant too.

The bar chart in Fig. 4 and Fig. 7 have been analysised in the same methodology. In those figure, the different superscript letters means significantly different (Tukey’s post hoc test, p ＜ 0.05). We found the differences of regeneration rate and average regeneration speed for 12 h between different addition ratios of alkalinity were significant. The differences of regeneration rate and average regeneration speed for 12 h between 3 mg/L DO and 2 mg/L DO were not significant, but it had significantly different from other DO levels.

 

Point (4): The Conclusions section should be more concise.

Response (4): Thank you for your kind advice. We agree that the conclusions section should be more concise. We have simply summarized the conclusions of the manuscript.

The research focuses on the operational parameters and regeneration mechanism of the MBBR adsorption-shortcut SND process. In the adsorption stage, the -N was adsorbed to the ceramsite surface. In regeneration stage, the adsorbed ammonia nitrogen would be desorbed by biochemical regeneration effect. The shorter the HRT, the greater the -N volume load. To a certain extent, agitation aggravated the diffusion of -N in the ceramisite zeolite component. 2 times alkalinity increased the concentration of FA, which realizes the transition from complete SND to shortcut SND. The more stable shortcut nitrification process could be obtained by combining high concentration FA with low level DO. Under optimal parameters conditions, the removal of TN and -N were improved greatly, and can achieve higher nitrate accumulation rate which significantly reduced the consumption of carbon sources. In general, the MBBR adsorption-shortcut SND process are expected to be a preferred nitrogen removal approach to treating aquaculture wastewater. However, many future studies should focus on the change of microbial communities in shortcut SND process to clarify the microbial mechanism of nitrogen removal. And the N₂O/N₂ production during MBBR adsorption-shortcut SND process also should be explored.

Author Response File: Author Response.docx