Pollutant Removal and Energy Recovery from Swine Wastewater Using Anaerobic Membrane Bioreactor: A Comparative Study with Up-Flow Anaerobic Sludge Blanket

Round 1

Reviewer 1 Report

The manuscript is focused on the pollutant removal and energy recovery from swine wastewater using anaerobic membrane bioreactor. The Authors have demonstrated that  the anaerobic membrane bioreactor can intercept particulate organic matter and enhance metabolic processes and achieve much higher COD removal efficiency than the UASB. 

The presented topis is interesting, the work is performed correctly, the methods are adequately described and English is fine. Moreover, it should be emphasized that most of the papers cited were published in the last few years. However, I have many negative comments about the manuscript. Please, see the comments below:

1. The manuscript is not prepared according to the template of Water Journal. It must be prepared once again.

2. Undoubtedly, the introduction does not provide sufficient background and does not include all relevant references. The lierature review should be performed better. For instance:

- Many papers which are directly related to the subject are not cited in this manuscript, for instance:

DOI: 10.1016/j.bej.2015.02.009

- The advantages of AnMBRs are a very broad issue. Unfortunately, the Authors did not pay much attention to it and described it only in a few lines (lines 64-79). This issue is very important and closely related to the work performned, hence, it should be described in more detail, based on a much larger number of cited works. Many review articles on the subject have recently been published and the Authors did not consider them, for instance:

DOI: 10.3390/membranes12030275

DOI: 10.3390/en15144981

DOI: 10.1016/j.cscee.2021.100109

- In the research, the Authors used the flat sheet MF membrane made of chlorinated polyethylene. It is recommended to demonstrate the advantages of polymeric membranes and explain the choice of this membrane type. The introduction lacks a very short literature review on the polymeric membranes properties. A lot of papers on this topic have been published recently, for instance:

DOI: 10.3390/membranes11010044

DOI: 10.1016/j.watres.2022.118269

3. The novelty of this work should be better emphasized.

4.The obtained results should be compared with the results available in the literature. For instance, the energy demand of AnMBRs is widely discussed in the following papers:

DOI: 10.1016/j.seppur.2015.09.047

DOI: 10.1016/j.seppur.2014.02.013

To sum up, the work is interesting and well done, but the manuscript is written very carelessly, there are no citations of many works closely related to the topic presented. The introduction needs a significant improvement.

 

 

Author Response

Manuscript ID: water-1835192

Title: Pollutant removal and energy recovery from swine wastewater using AnMBR: A comparative study with UASB

 

  We would like to thank the editor and the two reviewers for providing us with these constructive comments. Here, we submit an itemized reply to each comment. In the revised version, changes made in response to Reviewers’ comments are typed in red color, while those based on language editing are typed in blue color.

Reviewer 1

The manuscript is focused on the pollutant removal and energy recovery from swine wastewater using anaerobic membrane bioreactor. The Authors have demonstrated that the anaerobic membrane bioreactor can intercept particulate organic matter and enhance metabolic processes and achieve much higher COD removal efficiency than the UASB. 

The presented topis is interesting, the work is performed correctly, the methods are adequately described and English is fine. Moreover, it should be emphasized that most of the papers cited were published in the last few years. However, I have many negative comments about the manuscript. Please, see the comments below:

1. The manuscript is not prepared according to the template of Water Journal. It must be prepared once again.

Response: Thanks very much for the valuable comments. The manuscript has been revised according to the journal template.

2. Undoubtedly, the introduction does not provide sufficient background and does not include all relevant references. The lierature review should be performed better. For instance:

- Many papers which are directly related to the subject are not cited in this manuscript, for instance:DOI: 10.1016/j.bej.2015.02.009

- The advantages of AnMBRs are a very broad issue. Unfortunately, the Authors did not pay much attention to it and described it only in a few lines (lines 64-79). This issue is very important and closely related to the work performned, hence, it should be described in more detail, based on a much larger number of cited works. Many review articles on the subject have recently been published and the Authors did not consider them, for instance:

DOI: 10.3390/membranes12030275

DOI: 10.3390/en15144981

DOI: 10.1016/j.cscee.2021.100109

 

Response: The advantages of AnMBRs were highlighted in Introduction section based on the suggested references as follows;

“As a novel and effective AD process, anaerobic membrane bioreactors (AnMBRs) have attracted increasing interest in recent years due to their high pollutants removal efficiency and energy recovery rate [13-15]. They have many advantages such as smaller reactor size without the need of sedimentation tank resulting in smaller footprint, no limitations on suspended solid content of the mixed liquor, easy control of solid retention time which enhances the quality of the treated water, excluding tertiary treatment, and energy efficient application [15-17].” Please see Lines 69-75

 

- In the research, the Authors used the flat sheet MF membrane made of chlorinated polyethylene. It is recommended to demonstrate the advantages of polymeric membranes and explain the choice of this membrane type. The introduction lacks a very short literature review on the polymeric membranes properties. A lot of papers on this topic have been published recently, for instance:

DOI: 10.3390/membranes11010044

DOI: 10.1016/j.watres.2022.118269

 

Response: The advantages of MF over other kinds were highlighted in Introduction section using the suggested references as follows;

“Ceramic materials and polymeric membranes have been compared for application in AnMBR, where many studies reported a higher overall permeability and efficiency for polymeric membranes [26, 27]. There are three main forms of membranes including hollow fiber, tubular and flat sheet. Compared to other types, flat sheet membranes are more advantageous due to simple cleaning/replacement methods and high efficiency for commercial application; while high cost is their main disadvantage [15, 28]. Therefore, enhancing the flat sheet membranes bioreactor performance could reduce the overall cost and enhances the process economy.  Please see Lines 94-102.

3. The novelty of this work should be better emphasized.

Response: The novelty of this paper has been emphasized in the introduction section as follows;

“Although AnMBR systems have been extensively used in the treatment of wastewater with high organic matter concentration, research about SW treatment using AnMBR has less been conducted. Despite their advantages, comparing the potential of AnMBR in pollutant removal and methane production from SW with other conventional systems such as UASB was not systematically investigated. In addition, evaluation of energy production from SW in AnMBR and UASB is of great importance. In addition, comparing the microbial communities in both reactors has not been analyzed. Please see Lines 104-110.

 

4.The obtained results should be compared with the results available in the literature. For instance, the energy demand of AnMBRs is widely discussed in the following papers:

DOI: 10.1016/j.seppur.2015.09.047

DOI: 10.1016/j.seppur.2014.02.013

 

Response: Results of the present study were compared with the results of the mentioned references as suggested. References number [19], [35], [36] and [54]. Please see Lines 428-442.

To sum up, the work is interesting and well done, but the manuscript is written very carelessly, there are no citations of many works closely related to the topic presented. The introduction needs a significant improvement.

Response: Thank you very much for your constructive suggestion which enhanced the manuscript.

Reviewer 2 Report

This paper reports pollutant removal and energy recovery from swine wastewater using AnMBR by comparing it with a UASB. The research was done systematically and well organized. The report is also well written. A few minor issues below can be addressed by the authors to improve the manuscript.

Please provide the detail of the membrane. Was there any means of membrane fouling control apart from the intermittent operation?

Data in Table 3 seem too optimistic about the energy for membrane filtration. Please add some justification to the very low energy input assigned for this parameter. Also please include the energy required for maintaining and heating the feed was not included in the balance to obtain a more realistic estimation.

 

Membrane fouling will become an important issue in AnMBR (See: https://doi.org/10.3390/membranes11030203; https://doi.org/10.3390/membranes12060551; https://doi.org/10.1016/j.jwpe.2020.101350). Please discuss/comment on it.

Author Response

Manuscript ID: water-1835192

Title: Pollutant removal and energy recovery from swine wastewater using AnMBR: A comparative study with UASB

 

  We would like to thank the editor and the two reviewers for providing us with these constructive comments. Here, we submit an itemized reply to each comment. In the revised version, changes made in response to Reviewers’ comments are typed in red color, while those based on language editing are typed in blue color.

 

 

 

Reviewer 2

This paper reports pollutant removal and energy recovery from swine wastewater using AnMBR by comparing it with a UASB. The research was done systematically and well organized. The report is also well written. A few minor issues below can be addressed by the authors to improve the manuscript.

Please provide the detail of the membrane. Was there any means of membrane fouling control apart from the intermittent operation?

Response: Thank you very much for the valuable comments on this manuscript. The details of membrane are provided as follows;

“The length and width of the membrane module was 12.8 cm and 7.8 cm, respectively. Membrane on both sides of the module frame was made of chlorinated polyethylene with a normal pore size of 0.22 μm and a total effective area of 0.02 m².” Please see Line 131-133.

Backwash was conducted to remove the foulants and recover membrane permeability when the TMP exceeded 40 kPa. It is mentioned in the text as follows;

“To control the membrane fouling in AnMBR, membrane filtration was intermittently operated (8min-on, 2 min-off) during the whole operating period [29, 30]. In addition, backwash using the effluent was conducted to remove membrane foulants and recover its permeability when the TMP exceeded 40 kPa.”

Data in Table 3 seem too optimistic about the energy for membrane filtration. Please add some justification to the very low energy input assigned for this parameter. Also please include the energy required for maintaining and heating the feed was not included in the balance to obtain a more realistic estimation.

Response: The energy of influent and effluent pump was calculated based on the previous studies and it is in agreement with other researchers. The energy for water bath and substrate mixing were added to Table 3 and text was further explained.

Membrane fouling will become an important issue in AnMBR (See: https://doi.org/10.3390/membranes11030203; https://doi.org/10.3390/membranes12060551; https://doi.org/10.1016/j.jwpe.2020.101350). Please discuss/comment on it.

Response: We agree with you that membrane fouling is a very important issue in MBR systems. However, in this paper, we mainly focused on comparison of pollutant removal performance and energy recovery properties of AnMBR and UASB. The membrane fouling mechanisms and fouling control have been suggested in the conclusion section for future perspectives;

“The membrane fouling properties, mechanisms, and mitigation pathways should be further investigated.” Please see Lines 453-454.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The manuscript has been corrected. Hence, I recommend it for publication in present form.