Steady-State Methodology for Activated Sludge Model 1 (ASM1) State Variable Calculation in MBR
Round 1
Reviewer 1 Report
The paper "Steady-state methodology for Activated Sludge 2 Model 1 (ASM1) states variables calculation in MBR" presents the simplified equations needed for establishing the steady state of the carbon part for a MBR-asm1-based model to be computed given input characteristics.
It is shown on 24 conditions (HRT, SRT and input characteristics) that the proposed expressions are in accordance with the simulations performed with GPSX.
While the objectives in themselves (computing the steady easily for an MBR technology) are interesting the "innovation" is very low. Indeed, it suffers from my viepoint of two main drawbacks : it does not concern the nitrogen part (why?) and today the computation time to find the steady state of a dynamical system for a model including dozen of variables is not a problem anymore.
To summarize, such a work is suited for a conference but for sure the content is not enough for a journal paper.
At least, the paper needs to address i) considerations about (possibly global) stability, and ii) the nitrogen part. It also needs to be completely reread for the Englich (I do not think "operand" means anything in English).
Author Response
Reviewer 1 Comments
- While the objectives in themselves (computing the steady easily for an MBR technology) are interesting the “innovation” is very low. Indeed, it suffers from my viewpoint of two main drawbacks: it does not concern the nitrogen part (why?) and today the computation time to find the steady state of a dynamical system for a model including dozen of variables is not a problem anymore.
Nitrogen treatment was included in the paper. Analytical expressions were also developed for state variables linked to nitrogenous compounds: autotrophic biomass (XBA), ammonia (SNH) and nitrites and nitrates (SNO). However, it is also true that the study of the sensitivity analysis was not extended to these compounds because the main objective was only to explain the steps leading to a complete sensitivity analysis. The following sentence was added in the paper to explain this choice: In the following, the steps of the analytical sensitivity analysis were detailed only for organic compounds in order to minimize the dimension of tables. It should be mentioned that these analysis steps are still applicable for nitrogen treatment compounds (XBA, SNH and SNO).
Analytical expressions developed in this study: state variables and sensitivity coefficients are directly applicable for all aerated ASP processes that can be assimilated to continuously stirred tank reactors in the steady-state conditions. This is a very useful for professionals needing a practical but quite accurate tool for design and control of WWTP.
- At least, the paper needs to address i) considerations about (possibly global) stability, and (ii) the nitrogen part. It also needs to be completely reread for the English (I do not think “operand” means anything in English).
(i) As mentioned above, obtained expressions are applicable for all aerated ASP processes that can be assimilated to continuously stirred tank reactors in the steady-state conditions and (ii) nitrogenous compounds were included in the steady-state approach as expressions of XBA, SNH and SNO were provided.
The paper was reread and corrected by a native English speaker.
Reviewer 2 Report
The article has scientific and practical value. I recommend publishing it in the journal WATER (MDPI).
Author Response
Thank you very much for complimentary remarks
Reviewer 3 Report
Comments
Title: Steady-state methodology for Activated Sludge Model 1 (ASM1) states variables calculation in MBR
This paper is of little significance and lacks of novelty and practicability:
- The summary lacks data support.
- There are many grammatical or spelling errors in this paper,
such as line 89 odel → model.
- The process is very complicated, so it can't be called rapid estimation of the of the sludge operating parameter.
- There is no error line in Figures 4 and 5.
- The discussion is not in-depth.
- There are too few references in recent years, only one article in recent five years.
Author Response
- The summary lacks data support
The summary was extended in order to add some key figures, for example : “A strong match (less than 4% of error overall)” or “ “the SRT effect is lower on XBH, XS at high SRT (˃20 days), while it is more pronounced on XP and XI as their variations with SRT are linear”
- There are many grammatical or spelling errors in this paper
The paper was reread and corrected by a native English speaker.
- 3. The process is very complicated, so it can’t be called rapid estimation of the sludge operating parameters
The objective of this paper was to explain the methodology used to obtain analytical expressions. This work needs to be performed only if the configuration changes. For example, the obtained expressions of this study are applicable for design and control of each ASP process that can be assimilated to a continuously stirred tank reactor in the steady-state conditions, which is a very common configuration in WWTP. Once a different process configuration is set, mass balance equations should be slightly modified to include the configuration impact.
- There is no error line in Figures 4 and 5
Error lines with a percentage error of 5% were added in Figures 3, 4 and 5
- The discussion is not in-depth
The discussion was thorough: “It is noteworthy to mention that the analytical expressions developed in this study have a wide applicability range thanks to the low number of assumptions. This makes it possible to fix the initial condition before starting simulation or to explain the impact of operating parameter on water quality or on mixed liquor suspended solid composition.”
- There are too few references in recent years, only one article in recent five years
Recent years reference were added.
Mannina, G., Ni, B. J., Rebouças, T. F., Cosenza, A., & Olsson, G. (2020). Minimizing membrane bioreactor environmental footprint by multiple objective optimization. Bioresource Technology, 302, 122824.
Demir S., Manav Demir N. Implementation of Activated Sludge Model No. 3 as an educational tool: bioXL3. Computer Applications in Engineering Education, 2020, Volume 28 (5), pp. 1154-1173.
Reviewer 4 Report
I would like you to add your answer to the following questions to the article:
More detailed justification why the simplifying is required,
What is the deviation from the original version of the model,
What this article add to our current knowledge,
Why we simplification, in order to kame models more accurate we need to make them more complicated, add new parameters to the model, ect,
This model is in use any many software such as BioWin, why do you think companies selling these software should be interested in your modification,
It is important to justify your research outcomes.
Author Response
I would like you to add your answer to the following questions to the article:
Our answers were added directly in the text.
More detailed justification why the simplifying is required
More details were added: “These assumptions lead to obtain biomass concentration (XBH, XBA) in relation to their respective substrate (COD and Ammonium) instead of reducing biomass growth due to alkalinity or nitrogen.”
What is the derivation from the original version of the model
There is no derivation from the original ASM1 model.
What this article add to our current knowledge
This article gives the Developed analytical expressions of steady state variables. These expressions were summarized in Table 3. This makes it possible to see directly the impact of operating parameter (HRT and SRT) as the impact of kinetics and stoichiometric parameters. This greatly simplifies sensitivity analyses.
Why simplification, in order to make models more accurate we need to make them more complicated, add new parameters to the model, etc
The simplification allows to obtain simplified expressions of steady state variable. New parameter can be added, or the biological pathway can be upgraded, that should slightly modified the mass balance equation and then new analytical expressions for state variables for this new configuration can be generated.
This model is in use by many software such as BioWin, why do you think companies selling these software should be interested in your modification
Many software allows their users to find the steady state flow. Our simplified expressions can be a way to validate the software programming or just to fix the initial condition : “It is noteworthy to mention that the analytical expressions developed in this study have a wide applicability range thanks to the low number of assumptions. This makes it possible to fix the initial condition before starting simulation or to explain the impact of operating parameter on water quality or on mixed liquor suspended solid composition. Moreover, the steady state equation allow the identification of the most sensitive parameters and provides pointers for initiate the elaboration of procedures for the model parameters determination.”
It is important to justify your research outcomes
Our research outcomes was amended in part 4 discussion and in the conclusion.
Round 2
Reviewer 3 Report
The revised manuscript can be accepted.
