Adsorption of Natural Organic Matter and Phosphorus from Surface Water Using Heated Aluminum Oxide (Predeposited) Dynamic Membrane Adsorber

Round 1

Reviewer 1 Report

see the file for my comments.

Comments for author File: Comments.pdf

Author Response

The author thanks the reviewers for their time and valuable comments. Major changes to improve clarity have been made throughout the manuscript, as well as sections about the interpretation and data analysis added.

Thank you for your letter and the opportunity to revise the paper. All provided suggestions have been immensely helpful. I do appreciate the Reviewer insightful comments on revising the abstract and other aspects of the paper.

Substantial nature

1. The membrane you used for dynamic membrane formation is polyethersulfone (PES)

ultrafiltration (UF) membranes (MicrodynNadir GmbH, Germany), which has no rejection for

phosphorus. In your process, the phosphorus is adsorbed by heated aluminum oxide particles

(HAOPs) that are pre-deposited on the surface of UF membrane. As the phosphorus is not

rejected by primary UF membrane but by sorption on HAOPs. I would suggest to use a

“dynamic membrane adsorber” instead of “dynamic adsorber” (for example, see this

reference https://doi.org/10.1002/jctb.6728).

-Response:  The manuscript has been reviewed and corrected as suggested. An effort has been made to reflect this change throughout the whole text.

 

2. As the phosphorus was eliminated by sorption, then why UF membrane requiring large

applied pressure was preferred over microfiltration? The author shall critically discuss this in

the manuscript.

-Response: The manuscript has been reviewed and corrected. Initial research always used a UF membrane as a support structure, in more industrial systems, nylon meshes are now being tested. A paragraph on filtration and the pressure that occurs during filtration has also been added.

The following passage was added to the article:

The most commonly used support structures for HAOPs were ultrafiltration membranes (UF), but other materials have also been used such as nylon or metallic meshes (pore size 0.2m). So far, the best support structure for HAOPs particles and thus removal efficiency was achieved with application of UF membranes [19, 21-23, 26]. Because of the potential leakage of Al into the permeate, UF was usual used.

Earlier research on HAOPs cake layer indicated that it doesn’t impact the membrane permeation [19, 21-23,26-28, 30]. The TMP before and after HAOPs deposition, when DI water was filtered through the membrane unit, was monitored constantly [28,30], There has been no significant increase in pressure so far after precoating the HAOPs layer on membrane surface.

3. Pressure is a key process parameter in pressure-driven membrane process. Why the pressure

in not measured in this work keeping in view that you have applied a UF membrane?

-Response: The manuscript has been supplemented with the whole chapter on pressure loss and duration of filtration cycles.

Minor suggestions

Abstract

1. Include a sentence on dynamic membrane how it is formed.

-Response: The manuscript has been reviewed and corrected as suggested.

DM filter builds up as a layer of particles deposited via permeation through the membrane’s surface. This study reports the application of Heated Aluminium Oxide Particles (HAOPs) as a dynamic membrane (DM) adsorber

 

Introduction

2. The references are not properly cited according to the order they appear in the whole

manuscript. For example, [1,6], [6] and [1, 3, 6, 13, 37] on the first page.

-Response: The manuscript has been reviewed and corrected as suggested.

 

3. The difference between self-forming and pre-coated membrane is unclear.

-Response: The manuscript has been reviewed and corrected: Basically, two categories of DM have been reported: self-forming and a pre-deposited one. In each case, the continuous process of DM formation helps to protect the underlying membrane. The self-forming DMs are generated by the substances existing in the feedwater unlike to pre-deposited one, where the secondary membrane is created using filtration of solutions containing specific particles or colloids

4. It is stated that “once the DM layer is fouled, it can be replaced by a new one”. How

adsorbent particles placed via permeation drag are removed from the primary/support

membrane?

-Response: In the cartridge system when dead-end is applied the membrane needs to be washed with DI water, in case of application of tubular systems the dynamic membrane adsorber is backwashed with water in conjunction with air pulses [27]. The particle deposition into the cartridge system is with the syringe injection as Cai et al. recommended. In case of tubular system, the plug flow in recycling mode is applied. 

5. References for “The application of metal oxides for water treatment has been developed

and investigated for the removal of different contaminants from water” are lacking.

Similarly, references for “However, since it can promote the microbial re-growth in water

distribution networks, exploration of more efficient phosphorus removal techniques is of

importance” are lacking.

-Response: The manuscript has been reviewed and corrected as suggested.

However, since it can promote the microbial regrowth in water distribution networks, the exploration of more efficient phosphorus removal techniques is of importance [8-10].

The application of metal oxides for water treatment has been developed and investigated for the removal of different contaminants from water [1].

6. Nanofiltration and Reverse Osmosis are classically used for phosphorus removal from

natural water resources (surface water and lake water). The author shall critically discuss

the benefits of using dynamic membrane ultrafilter over higher pressure membranes.

-Response: The manuscript has been reviewed and corrected: Among the applied in water membrane techniques the nanofiltration and reverse osmosis (RO) are successfully used for ions removal. Unfortunately, the application of this higher-pressure membranes is always linked with trades off between flow and rejection. Although RO is very effective to reduce the salt and ionic content from the feedwater, but it is also prone to fouling, additionally the more foulants accumulate on the membrane surface the higher pressure is required to maintain desire permeate flow. In contrast, to the application of dynamic membrane adsorber where lower pressure in needed thus possible energy savings. Additionally, The DM interferes with NOM transmission through the ultrafiltration membrane pores by increasing the retention coefficient of NOM in UF membranes [31].

7. As iron oxides have superior adsorption affinities for phosphate, why heated aluminum

oxide was preferred over iron oxides in this work?

-Response: First, Kim et al.(2007) reported that iron oxides have superior adsorption affinities for phosphate, compared to HAOPs [20]. But, then, Lee et al. (2019) outlined that use of HAOPs as the adsorbent produces higher-quality treated water using lower adsorbent doses [24]. Verification is needed.

8. The title of the manuscript suggests the phosphorus removal but natural organic matter

is also targeted in this work as stated in the last paragraph on introduction.

-Response: The manuscript has been reviewed and corrected.

Adsorption of natural organic matter and phosphorus from surface water using dynamic membrane adsorber (heated aluminum oxide particles)

Materials and methods

1. Section 2.1 suggests that HAOPs pre-deposited dynamic membrane filter has already

been employed in water treatment for natural organic matter removal. If it is so, what is

new that is investigated in this work.

-Response: Because there are not many studies using HAOPs as a dynamic membrane adsorber and two published papers give different results so verification is needed. The manuscript is focused on both NOM and phosphorus removal from surface water since biological stability of water is a new topic of importance in water technology and concentrations of both carbon and phosphorus compounds are considered to be limiting factors to this phenomenon.

2. The unit of KF on page 4 is incorrect.

-Response: The manuscript has been reviewed and corrected.

3. Section “Dynamic adsorption experiment”: It is thought that a more detailed explanation

is needed for the method of continuous operation test including cake layer formation.

Especially, please mention the experimental information for Figures 4, 5, and 6.

-Response: The manuscript has been reviewed and corrected.

4. Following above point, what is the thickness or mass of HAOPs pre-deposited per unit

area of the membrane.

-Response: The manuscript has been reviewed and corrected.

The HAOPs layer created in this way can be characterized by the resistance across the layer between 1.4 and 1.4 and 2.4 .10¹¹ m⁻¹ [21] and the HAOPs thickness of 5~10 µm [27].

5. What type of natural organic matter is used for filtration experiments?

-Response: The manuscript has been reviewed and corrected.

There have been conducted filtration experiments on surface water (Olesnica river), most batch tests were carried out on synthetic water

Results and discussion

1. What is the effect of HAOPs cake layer on the membrane permeation?

-Response: The manuscript has been reviewed and corrected.

HAOP’s have no impact on the applied flux and permeation. In the dead end tests the TMP was recorder before and after deposition of HAOPs on membrane during filtration of DI water. Flux was also verified before and after HAOPs deposition.  

 

2. Figure 2: the resolution of the images is lacking or not readable.

-Response: The manuscript has been reviewed and corrected.

3. The physical and chemical characterization of the applied adsorbent is missing. It can be

taken from literature as it has been widely studied by different research groups.

-Response: The manuscript has been reviewed and corrected.

6. Table 1: The unit of KF is incorrect.

-Response: The manuscript has been reviewed and corrected.

7. Page 5: It is stated “The adsorption kinetics of phosphorus removal could be described

well by the Langmuir isotherms with a correlation value of R2 = 0.9894 which indicated

that chemisorption was the dominant process and suggested the monolayer adsorption.”

Adsorption kinetics are not described by Langmuir or Freundlich isotherms. Additionally,

the nature of the adsorption process cannot be predicted by the fitting of adsorption

isotherms of adsorption kinetics. Generally, thermodynamics parameters are determined

for this purpose.

-Response: The manuscript has been reviewed and corrected.

The adsorption process was better represented by the pseudo-second-order kinetics and the Langmuir isotherm adequately described in revised manuscript. Thermodynamic of Adsorption and the impact of the temperature is not possible to evaluate right now. It will probably confirm the spontaneous nature of the adsorption process, a physisorption process as well as the exothermic nature of the process. 

8. Separation parameter is documented in section 2 but it is not determined in section 3.2.

-Response: The manuscript has been reviewed and corrected.

9. “For the initial concentration between 0.32 to 1.3 mg/L the removal efficiency was up to

77% but when the concentration in the feed increased the removal efficiency also

increased, and it was 99.9% for 18.2 mg/l.” At what filtration time or volume time, these

removal efficiencies were measured? And also pH. I am expecting a concentration profile

of phosphorus against time for these results.

-Response: The manuscript has been reviewed and corrected.

The Olesnica river was reported previously as a highly contaminated. Unfortunately during this research, the concentration of phosphorous was less than 2mg/L. It was therefore decided to carry out tests on synthetic water where an increase in phosphorus content was simulated. The figures were inspired from https://doi.org/10.3390/separations8030032

New chapters have been added to clarify the difference.

 

10. Figure 5 and 6: What are the experimental conditions for results? For figure 6: the NOM

concentration is missing.

-Response: The manuscript has been reviewed and corrected.

Reviewer 2 Report

The manuscript is about the phosphorus sorption on a synthetic aluminium hydroxide (HAOP).  The idea is that this HAOP is suitable for P removal from polluted surface waters due to it binding capacity and due to the size of the particles which make use possible in filters. Re-use or waste aspects are not discussed. I would advice the editor to reject the manuscript on the basis of:

-the experiments and results are performed at a very simple level (some data are missing but this can be improved).

-The amount of data is very small for a manuscript in a scientific magazine. 

-Much more simple data are needed to evaluated this material, to compare it to other materials, and to evaluate the effects on waste, and therefore I would urge the authors to gather more data before publishing their results. 

Some additional comments:

“0.9894”.  Please add info.

“best removal”. This is not clearly defined, and does not match with a Langmuir isotherm. In case of a Langmuir isotherm you always have a strong binding at low concentrations while there is a plateau at P high concentrations. Please be more clear.

“natural water” is mentioned in the title. Please also use this in the abstract or please clarify this aspect when writing about variation in pH and ionic strength. Please add some info in the methods that you use synthetic solutions to mimic the pH and ionic strength of natural waters. Natural water is not a good term, the word natural suggests water in a nature reservation. I think you mean surface waters.

Introduction

“The” dynamic membrane. Please remove “the”. Please check the whole manuscript.

The aspect of waste from HAOP is not discussed. It is strange to suggest a new technique while not discussing the potential drawbacks. Also other problems, if they exist, should be mentioned in the introduction.

2.4

The ionic strength and ionic composition of the solutions is not mentioned.

Please add some info why you think that different phosphorus concentrations (28.7 to 3.28 mg P/L) mimic natural water. Norms for many EU surface waters are lower than 0.5 mg P/L.

After reading the materials and methods, it is not clear how you can write “natural waters” and why you write that this study is needed because it differs from other studies that studied waste waters. You did not check the competition with DOC, SO4, HCO3, and did not check the effects of Ca and Mg etc., all ions that are normal in “natural waters”.

Experiments without any background should be use with much care. In figure 5 data are presented usign 0 mol/l. This is unclear and is difficult to repeat because you do have salt because you have not washed the HAOP after precipitation and you have added acid/base. The ionic strength should at least be mentioned or estimated.   

3.6

It is not clear which humic acid is used, and how it has been prepared for use. It is not clear which humic acid concentration is used in the competition experiment., and how much is adsorbed.

Author Response

The manuscript is about the phosphorus sorption on a synthetic aluminium hydroxide (HAOP).  The idea is that this HAOP is suitable for P removal from polluted surface waters due to it binding capacity and due to the size of the particles which make use possible in filters. Re-use or waste aspects are not discussed. I would advice the editor to reject the manuscript on the basis of:

-the experiments and results are performed at a very simple level (some data are missing but this can be improved).

-Response: The manuscript has been reviewed and corrected. New chapters on HAOPs filtration and NOM removal were added.  Major changes to improve clarity have been made throughout the manuscript

-The amount of data is very small for a manuscript in a scientific magazine.

-Response: The manuscript has been reviewed and corrected; new chapters have been added to the manuscript.

-Much more simple data are needed to evaluated this material, to compare it to other materials, and to evaluate the effects on waste, and therefore I would urge the authors to gather more data before publishing their results.

-Response. Earlier studies have been dedicated to compare HAOPs efficiency with other materials especially PAC.  This method was developed as a membrane protection (pre-treatment step) and widely researched due to the variety of NOM and in search of the key factor causing fouling.

The results presented here are proof of concept if this technology is applicable to the removal of phosphor compounds and NOM from surface water. There are only two reports in the literature on phosphorus removal and they concern wastewater. Cai reported that iron oxides have superior adsorption affinities for phosphate, compared to HAOPs. On the other, Lee observed a very high phosphorus removal efficiency when there is between 4 and 9 mg/l phosphorus in the feewater.

Verification of the effectiveness of phosphorus removal from surface water is therefore important. In addition, the amount of phosphorus in the water determines its biological stability. Therefore, from a practical point of view, the use of HAOPs for simultaneous removal of NOM and phosphorus can be an interesting solution. HAOPs have so far been mainly used in pre-treatment systems before actual membrane unit. Further studies on application of RO and phosphorous removal are planned.

Practical application of HAOPs shoud be tested on pilot plant. Recent reports on the development of this technology come from work of Manamperuma et al (https://doi.org/10.3390/membranes9110151) in which an aspect of waste nor economics of tested pilot plant was not touched. They are planning to test in pilot plan optimization of HAOPs dose, sludge quality and sludge treatment methods, re-use/recovery of HAOPs and re-use of NOM, HAOPs-NOM bond/adsorbing strength, energy consumption for synthesis of HAOPs.

The presented studies show that HAOPs works well in highly contaminated waters, especially wastewater (which were simulated by creating water with elevated phosphorus content), while in surface waters it is not as effective as conventional methods in removing phosphorus. Greater removal is possible with a membrane that is assumed to be behind the HAOPs unit.

Some additional comments:

“0.9894”.  Please add info.

-Response: The manuscript has been reviewed and corrected. The information that R2 is a correlation coefficient is provided.

“best removal”. This is not clearly defined, and does not match with a Langmuir isotherm. In case of a Langmuir isotherm you always have a strong binding at low concentrations while there is a plateau at P high concentrations. Please be more clear.

-Response: The manuscript has been reviewed and corrected

“natural water” is mentioned in the title. Please also use this in the abstract or please clarify this aspect when writing about variation in pH and ionic strength. Please add some info in the methods that you use synthetic solutions to mimic the pH and ionic strength of natural waters. Natural water is not a good term, the word natural suggests water in a nature reservation. I think you mean surface waters.

-Response: The manuscript has been reviewed and corrected. New information of surface water quality and syntetic water have been added to the manuscript.

Introduction “The” dynamic membrane. Please remove “the”. Please check the whole manuscript.

-Response: The manuscript has been reviewed and corrected

The aspect of waste from HAOP is not discussed. It is strange to suggest a new technique while not discussing the potential drawbacks. Also, other problems, if they exist, should be mentioned in the introduction.

-Response: The manuscript has been reviewed and corrected. New chapter have been added. This technology has no evaluation on sludge quality and sludge treatment methods. From preliminary observations, HAOPs is an easily washable layer during bakwashing. Work is currently underway to develop an effective way of scaling up and sludge management.

Cai reported that iron oxides have superior adsorption affinities for phosphate, compared to HAOPs [20]. On the other hand, Lee et al. (2019) outlined that use of HAOPs as the adsorbent produces higher-quality treated water using lower adsorbent doses [24]. Additionally, Lee at al. reported that sludge generated by DM was extremely easy to dewater and dry with the application of vacuum filtering and drying [24]. Lately, Manamperuma et al. when testing the application of HAOPs in fully automated pilot system observed the significant removal of color for feed water. NOM is a mixture of macromolecules and humic acid is one of them that is responsible for the water colour [29]. In this study the HAOPs were pre-coated/pre-deposited on 10 µm nylon mesh tube in a recycling mode to limit loss of HAOPs [29]. However, it is not stated in this case is it possible to re-use and recovery of HAOPs as well as energy consumption of this process.

 

2.4 The ionic strength and ionic composition of the solutions is not mentioned.

Experiments without any background should be use with much care. In figure 5 data are presented usign 0 mol/l. This is unclear and is difficult to repeat because you do have salt because you have not washed the HAOP after precipitation and you have added acid/base. The ionic strength should at least be mentioned or estimated.  

-Response: The manuscript has been reviewed and corrected

Effects of ionic strength on phosphorus removal efficiency. The background ionic strength was about 2 mM (determined by applying Russell’s factor to the conductivity of the solution. The ionic strength of the background was spiked by adding NaCl. Adsorbent dose = 1 g/L, agitation speed = 200 rpm, temperature = 25 °C ± 2°C, contact time = 60 min.

 

Please add some info why you think that different phosphorus concentrations (28.7 to 3.28 mg P/L) mimic natural water. Norms for many EU surface waters are lower than 0.5 mg P/L.

-Response: The manuscript has been reviewed and corrected

For the study, the Olesnica river was chosen in which large amounts of phosphorous and nitrogen were reported to be found. Unfortunately, during the study period the phosphorus concentration was not as high as expected. During the study period, the maximum concentration in the evaluated surface water was below 2 mg/L. And since earlier studies had shown the technology to be more effective in removing phosphorus at higher concentrations, synthetic water with higher concentrations was created.

After reading the materials and methods, it is not clear how you can write “natural waters” and why you write that this study is needed because it differs from other studies that studied waste waters. You did not check the competition with DOC, SO4, HCO3, and did not check the effects of Ca and Mg etc., all ions that are normal in “natural waters”.

-Response: The manuscript has been reviewed and corrected

Previous studies evaluated the competition with SO4, HCO3, Ca and Mg. Lee reported that the phosphorus removal by HAOPs with addition of anions such as SO42-, NO3-, and Cl- or slats did not impact the removal efficiency even in case of sulfate that is a potential competitor for adsorptive sites on HAOPs [24]. The effects of the concentration of divalent cations were investigated by Liu, and addition of Ca2＋ or Mg2＋ had no effect on removal efficiency of HAOPs [30]. 

It is not clear which humic acid is used, and how it has been prepared for use. It is not clear which humic acid concentration is used in the competition experiment., and how much is adsorbed.

-Response: The humic acid is often used as a substitute of NOM, and since it wasn’t permitted to take original water for tests due to Highly Pathogenic Asian Avian Influenza A(H5N1) Virus, the humic acid was used instead. Effects of humic acid presence on phosphorus removal (adsorbent dose = 1 g/L, agitation speed = 200 rpm, temperature = 20°C, contact time = 60 min).

Reviewer 3 Report

The paper is very important for practice, because global reserves of phosphorus, respectively phosphorus resources are limited and phosphorus is essential nutrient important for agriculture practice. So, it is necessary to look for methods for removal of phosphorus from alternative sources.

I recommend to publish this paper.

Author Response

Thank you very much. The technology is not yet ready for practical use, but is already highly advanced.

Round 2

Reviewer 1 Report

The author has worked on the manuscript to improve its quality but the provided revisions are not sufficient to ensure publication in Applied Science Journal. Following are my concerns/suggestions for the manuscript.

1. The title of the manuscript appears to be incomplete or not suitable.  "Adsorption of natural organic matter and phosphorus from surface water using heated aluminum oxide particles pre-deposited dynamic membrane adsorber" might an option.
    I would suggest adding subsections on reagents and chemical analysis in materials and methods
2. In the results and discussion section, separate subsections shall be created to discuss the results obtained through batch adsorption and continuous filtration-cum adsorption tests. In the batch adsortion section, you can discuss adsorption isotherms and adsortion kinetics. In the current version, it is impracticable to combine the results in one subsection. For example, under "Phosphorous removal in filtration experiments", you have discussed the results of batch adsorption along with filtration results.
3. On the page, it is stated that  "In presented studies, the pristine membrane removed up to 74±5% of phosphorous from the feed water.  In the case of PO4, with each dose of HAOPs the concentration in the permeate was recorded below the detection limit (<0.01mg/L) ". It is meant that phosphorus can be removed by pristine UF membrane, which is not true. 
4. Phosphate is generally measured by a spectrophotometer and not phosphorus. How phosphorus was measured in this work?
5. You need to be consistent with discussing adsorbent doses. Sometimes, you have discussed the mass of adsorbent particles per unit area of the primary membrane, and sometimes, adsorbent mass is given in mass per unit volume of solution (Figure 6 and 8,9,10). The concentration of humic acid is missing? Was humic already present in raw feed water?
6. Following the above point, Figure 8-10, what do you mean by agitation speed, contact time?  The contact time between phosphorus-carrying solution and adsorbent pre-deposited cake layer would be less than 1 min.
7. I would suggest discussing the effect of three adsorbent doses on membrane permeability. 
8. Unit of KF is still wrong. see https://doi.org/10.3390/w10070957 for the correct unit of KF
9.  It is stated that "the HAOPs removal capacity was proportional to
   the thickness of the layer (of 5 um)". How the thickness of the deposited cake of adsorbent particles are determined?

 

Author Response

1. The title of the manuscript appears to be incomplete or not suitable. "Adsorption of natural organic matter and phosphorus from surface water using heated aluminum oxide particles pre-deposited dynamic membrane adsorber" might an option. I would suggest adding subsections on reagents and chemical analysis in materials and methods

Response:  The manuscript has been reviewed and corrected as suggested. New title of the manuscript is: Adsorption of natural organic matter and phosphorus from surface water using heated aluminum oxide particles as a pre-deposited dynamic membrane adsorber

2. In the results and discussion section, separate subsections shall be created to discuss the results obtained through batch adsorption and continuous filtration-cum adsorption tests. In the batch adsortion section, you can discuss adsorption isotherms and adsortion kinetics. In the current version, it is impracticable to combine the results in one subsection. For example, under "Phosphorous removal in filtration experiments", you have discussed the results of batch adsorption along with filtration results.

Response: the manuscript was reformulated according to the reviewer's recommendations and paragraph numbering was introduced; the text is also reorganized accordingly.

3. On the page, it is stated that "In presented studies, the pristine membrane removed up to 74±5% of phosphorous from the feed water.  In the case of PO4, with each dose of HAOPs the concentration in the permeate was recorded below the detection limit (<0.01mg/L) ". It is meant that phosphorus can be removed by pristine UF membrane, which is not true.

Response:  The manuscript has been reviewed and corrected. The chapter has been reformulated to emphasize that HAOPs removed PO4 below detection limits not the membrane itself.

4. Phosphate is generally measured by a spectrophotometer and not phosphorus. How phosphorus was measured in this work?

Response:  Phosphates and total phosphorus concentration were measured by Standard Methods 4500-P with the vanadomolybdophosphoric acid in compliance with Standard Methods.org

5. You need to be consistent with discussing adsorbent doses. Sometimes, you have discussed the mass of adsorbent particles per unit area of the primary membrane, and sometimes, adsorbent mass is given in mass per unit volume of solution (Figure 6 and 8,9,10). The concentration of humic acid is missing? Was humic already present in raw feed water?

Response:  The manuscript has been reviewed and corrected. In the case of any coagulant deposition on the membrane surface, the dose is usually provides as mass of adsorbent particles per unit area, in case of batch test where the dose is given as mass per unit volume of solution. An addition has been made to the text to emphasize this difference.

The HA was dissolved in a basic solution (NaOH) and then the pH brought down to 7 by slowly adding an acid solution (HCl) followed by sonication applied in order to prevent the agglomeration. The applied HA concentrations were 3.65mgC/l, 9.65mgC/l, and 15.56mgC/L.

The concentrations of humic acid are traditionally estimated out of concentrations of organic matter (typically from concentrations of total organic carbon (TOC) or dissolved organic carbon (DOC). The UV/Vis absorbance is also used to evaluate the HA concentration. Humic acid is always present in natural water, there are multiple approaches for separating NOM fractions eg. extraction techniques, gas chromatography-mass spectrometry (GC-MS) analysis of water samples which is usually the subject of separate studies http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502009000100015 or DOI: 10.2166/wst.2011.439  and https://doi.org/ 10.3390/w13020146

HA is used very often for simulation of NOM presence in water https://doi.org/10.2166/ws.2017.086

Usually HA is accounting for 60-70% on NOM [https://www.oieau.org/eaudoc/system/files/documents/40/200129/200129_doc.pdf].

6. Following the above point, Figure 8-10, what do you mean by agitation speed, contact time? The contact time between phosphorus-carrying solution and adsorbent pre-deposited cake layer would be less than 1 min.

Figures 8-10 describe the batch tests where the contact time was 60 min, the agitation speed is the speed of stiring plate. It was inspired by https://doi.org/10.3390/ma6052074 and https://doi.org/10.3390/molecules24132357

In the filtration experiment the contact time was less then 1 min.

7. I would suggest discussing the effect of three adsorbent doses on membrane permeability.

Membrane fouling is often characterized in the laboratory by flux decline experiments, where an increase in transport resistance due to accumulation of foulants on and/or in a membrane is manifested as a decrease in permeate flux with filtration time at fixed transmembrane pressure. However, in this case the filtration unit was operated in a dead-end mode at operating conditions of constant permeate flux. Additionally, each time after HAOPs deposition, deionized water was filtered for 30 minutes through the cartridge unit and both the pressure and the flux were verified. No significant changes of pressure or flux change recorded. Additionally, the permeate turbidity was monitored in order to ensure that HAOPs would not leach into it. Turbidity check is a standard operational procedure in this technology

 

8. Unit of KF is still wrong. see https://doi.org/10.3390/w10070957 for the correct unit of KF

-Response:  The manuscript has been reviewed and corrected as suggested.

9. It is stated that "the HAOPs removal capacity was proportional to the thickness of the layer (of 5 um)". How the thickness of the deposited cake of adsorbent particles are determined?

Cai et al. (2008) measured the thickened of the layer by applying SEM imaging and then applying Jmage J.

Reviewer 2 Report

dear author/editor,

 

Very much information has been added to the manuscript. I think this is an improvement. Most importantly, in this manner the manuscript has enough content for a paper. 

A private thought. You currently used raw water. This suggest that you want to used this technique for untreated polluted water. Currently Al flocs are used to clean water after biological removal of N and P from waste water. If the water still does not comply to a certain limit, the last small amount of P is adsorbed using aluminiumoxide.  

I would like to point to some possibilities to improve this manuscript:

-add a conclusion in the abstract

-try to decrease the length of the introduction

-Some parts of the experiments and results are slightly difficult to read. For example: table 1 describes the min and max of the raw water quality. But what was the concentration of the solutions used for figure 3, 4, 5 and 6?

-please get some help with the English language as still some small mistakes are in the text: "the tested water was characterized by an increased content of organic compounds". I guess you mean that the content was relatively high.

-please add the source of the Humic acid: the supplier.

-please do not try to explain the pH effect of PO4 adsorption (pag 15) in this length. The citation offer enough explanations.

-The colours in figure 10 cannot be distinguished. 

 

 

Author Response

The author thanks the reviewers for their time and valuable comments.

Responses to reviewers’ comments

I would like to point to some possibilities to improve this manuscript:

-add a conclusion in the abstract

-Response:  The manuscript has been reviewed and corrected as suggested.

Filtration experiments were conducted with surface water and batch tests were carried out with synthetic water. The outcome of this study highlights HAOPs efficiency in NOM removal up to 92% in filtration experiments. In case of phosphorous, removal efficiency varied. When surface water was a feed, 77% was achieved while synthetic water showed maximum removal efficiency of 99.99%.

 

-try to decrease the length of the introduction

-Response:  The manuscript has been reviewed and corrected as suggested.

 

-Some parts of the experiments and results are slightly difficult to read. For example: table 1 describes the min and max of the raw water quality. But what was the concentration of the solutions used for figure 3, 4, 5 and 6?

Each new portion of raw water contributes to the change of NOM quality, the samples are normalized (UV254 were normalized to their values in the feed) when calculating the removal efficiency.

-please get some help with the English language as still some small mistakes are in the text: "the tested water was characterized by an increased content of organic compounds". I guess you mean that the content was relatively high.

-Response:  The manuscript has been reviewed and corrected as suggested.

-please add the source of the Humic acid: the supplier.

-Response:  The manuscript has been reviewed and corrected as suggested.

-please do not try to explain the pH effect of PO4 adsorption (pag 15) in this length. The citation offer enough explanations.

-Response:  The manuscript has been reviewed and corrected as suggested.

-The colours in figure 10 cannot be distinguished.

-Response:  The manuscript has been reviewed and corrected as suggested.

Round 3

Reviewer 1 Report

See my comments in pdf file.

Comments for author File: Comments.pdf

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

dear Authors, editor, the authors have made various improvements.

 

 

 

 

Author Response

Thank you for the review, If there's anything to improve then I need to know a little bit more what that should be.

Round 4

Reviewer 1 Report

The author has provided the revisions, which are genuinely useful for the readers to understand the content of the paper and can be accepted after addressing the minor issue as 

1. The data presented in Figure 3 is taken from adsorption isotherms. So, the caption of dynamic membrane adsorber is wrong. Write the experimental conditions for Figure 3 like Figure 4.
2. In Figure 4, the legends shall appear in the order as the data appears. For instance,  data of pH 7 shall be on the top followed by 2 and 11.
3. Figure 8. It is suggested to write the initial UV absorbance at 254 nm so that the reader can understand the rejection of 18% with a bare UF membrane. Moreover, The author shall critically discuss why the reduction in UV absorbance at UV 204 at  10 g/m2 is greater compared to larger adsorbent loading of 17 10 g/m2
4. Figure 10. There is no need to add the H with numbers as the x-axis reflects the unit of time.

Author Response

Thank you for giving me the opportunity to submit a revised draft of my manuscript titled: Adsorption of natural organic matter and phosphorus from surface water using heated aluminum oxide (predeposited) dynamic membrane adsorber. I am are grateful to the reviewers for their insightful comments on my paper. I have been able to incorporate changes to reflect the suggestions provided by the reviewer. I have highlighted the changes within the manuscript using Track Changes” function if you are using MS Word.

 The data presented in Figure 3 is taken from adsorption isotherms. So, the caption of dynamic membrane adsorber is wrong. Write the experimental conditions for Figure 3 like Figure 4.
-Response:  The Figure 3 has been reviewed and corrected as suggested. 
2.    In Figure 4, the legends shall appear in the order as the data appears. For instance,  data of pH 7 shall be on the top followed by 2 and 11.
-Response:  The Figure 4 has been reviewed and corrected as suggested. 
3.    Figure 8. It is suggested to write the initial UV absorbance at 254 nm so that the reader can understand the rejection of 18% with a bare UF membrane. Moreover, The author shall critically discuss why the reduction in UV absorbance at UV 204 at  10 g/m2 is greater compared to larger adsorbent loading of 17 10 g/m2
-Response:  The manuscript has been reviewed and corrected as suggested. 
4.    Figure 10. There is no need to add the H with numbers as the x-axis reflects the unit of time.
-Response:  The Figure 3 has been reviewed and corrected as suggested.