Modeling Changes in the Composition of River Water with Discharged Wastewater: A Case Study in NW Russia

Round 1

Reviewer 1 Report

The manuscript is interesting but the following changes should be made prior to publication:
- the abstract and conclusions should be more concise and precise
- the description of the first figure should include an explanation of what is shown in figures a and b
- the purpose of the work should be briefly presented and its novelty underlined
- please standardize the units in the tables, also pay attention to the use of dots as separators

Author Response

Dear Reviewer!

My work received a constructive assessment. In the revised version, I have explicitly taken into account all your comments.

Please find below my answers; all proposed changes in the text are highlighted in color.

The manuscript is interesting but the following changes should be made prior to publication:

- the abstract and conclusions should be more concise and precise

In response to this comment I corrected the text in the abstract and conclusions as follows:

Abstract: The technogenic impact of the development of the Lomonosov diamond deposit is associated with the discharge of quarry and drainage waters into the river, which has a special conservation status. Earlier studies of the composition of bottom sediments showed signs of increased accumulation of heavy metals and radionuclides at the wastewater discharge site. The purpose of this work was to predict changes in the composition of surface waters and bottom sediments in the river during the further development of mining operations with the capture by drainage systems of brackish and salty waters, the presence of which was established in the zone of their future influence. For this, the simulation of changes in the composition of water in the river was carried out using the GEOCHEQ software package by minimizing the free energy of the system using a convex simplex algorithm. It was found that the maximum salinity of surface waters can reach 1.51 g/L. In this case, the MPC for fishery watercourses can be exceeded for Cl^-, Na⁺, SO₄^2-, Mg²⁺, Sr, V, U. The genetic basis of the accumulation of these components in solutions for mixing is considered. According to calculations, when about 5000 m³/h of drainage water is discharged into the river, the mass of precipitated chemical elements will be 56-191 t/h, including up to 2.1 t/h of iron, therefore their accumulation in the discharge zone must be controlled.

Conclusions

The purpose of this work was to predict changes in the composition of surface waters and bottom sediments in the river during the further development of mining operations with the capture by drainage systems of brackish and saline waters, the presence of which was established in the zone of their future influence. For this, the modeling of changes in the water composition in the Zolotitsa River was carried out using the GEOCHEQ software package with the calculations of the equilibrium composition of the system by the method of minimizing the free energy of the system using a convex simplex algorithm.

It has been established that the maximum salinization of surface waters occurs as a result of pulling salt water to the system up to 1.51 g/L. At the same time, the MPC for fishery watercourses can be exceeded for Cl^-, Na⁺, SO₄^2-, Mg²⁺, Sr, V, U. The genetic basis for the accumulation of these components in solutions for mixing is considered.

Maximum precipitation from mixing solutions (not counting calcite) is typical for dolomite; then goethite, MnO₂, gibbsite and barite. In general, it should be noted that when about 5000 m³/h of drainage water is discharged into the river, the precipination mass will be from 56 to 191 t/h, including up to 2.1 t/h of iron. Therefore, the outlined tendency for the accumulation of clayey sediments with high sorption properties in the area of ​​discharge of quarry waters may contribute to the continuing accumulation of heavy metals in this zone.

The results of this study provide a better understanding of the dangers of the discharge of saline drainage water from an exploited diamond deposit into the Zolotitsa River. This determines the environmental value of the work.

In the future, it is planned to periodically monitor the state of river water and bottom sediments in the quarry area in order to compare the results of predictive calculations with real values ​​and improve predictive modeling by the method of minimizing the free energy of the system. It is also planned to study the effect of the composition of organic matter in river and groundwater on the mobility of chemical elements in mixed solutions.

- the description of the first figure should include an explanation of what is shown in figures a and b

In response to this comment I corrected the Figure 1 caption as follows:

Figure 1. (“a”) General location of the study site showing the end members involved in the mixing of surface waters of the Zolotitsa River (Z) with fresh groundwater, pumped from dewatering boreholes (DB), brackish and salty groundwater, pumped from the "lenses" in the Vendian Padun Formation (L1 and L2), and (b) with salty groundwater, pumped from the Vendian Mezen Formation (Vmz).

- the purpose of the work should be briefly presented and its novelty underlined

In response to this comment I corrected the text in the Introduction as follows:

The scientific novelty of this work is associated with the calculations of the equilibrium composition of the system by the method of minimizing the free energy of the system using a convex simplex algorithm [37]. Such methods are widely used abroad for calculating metamorphic systems at high temperatures and pressures and are practically not used for aqueous solutions in comparison with methods for calculating equilibria using equilibrium constants [38]. Therefore, their application for solving a specific physical problem of a quantitative description of the ongoing chemical interactions in a near-surface hydrogeochemical system with a forecast of changes in the ecological conditions of a region under further technogenic impact is of undoubted scientific interest.

The purpose of this work was to predict changes in the composition of surface waters and bottom sediments in the river during the further development of mining operations with the capture by drainage systems of brackish and saline waters, the presence of which was established in the zone of their future influence.

- please standardize the units in the tables, also pay attention to the use of dots as separators

In response to this comment I corrected the Tables 2 and 3.

My manuscript professionally edited by MDPI's English editing service.

Thank you very much for your comments and suggestions, they helped to improve the article.

Author Response File: Author Response.docx

Reviewer 2 Report

The paper is interesting.
I recommend publication only if the following issues can be addressed.

- Lines 36-38: You should mention that groundwater is polluted while it could be used for potable water (via desalination) or for industrial uses. Cite the following references:

Panagopoulos, A. (2021). Beneficiation of saline effluents from seawater desalination plants: Fostering the zero liquid discharge (ZLD) approach - A techno-economic evaluation. Journal of Environmental Chemical Engineering. 

Panagopoulos, A. (2021). Techno-economic assessment of Minimal Liquid Discharge (MLD) treatment systems for saline wastewater (brine) management and treatment. Process Safety and Environmental Protection, 146, pp. 656-669. 

Panagopoulos, A. (2021). Study and evaluation of the characteristics of saline wastewater (brine) produced by desalination and industrial plants. Environmental Science and Pollution Research, 1-14.

- Please mention the novelty of the current study.

- Conclusion: Discuss the applicability of your findings/results and future study in this field.

- Language editing is recommended.

- Include '2. Hydrogeological Struct' in the '3. Materials and Method' section

Author Response

Dear Reviewer!

My work received a constructive assessment. In the revised version, I have explicitly taken into account all your comments.

Please find below my answers; all proposed changes in the text are highlighted in color.

The paper is interesting.
I recommend publication only if the following issues can be addressed.

- Lines 36-38: You should mention that groundwater is polluted while it could be used for potable water (via desalination) or for industrial uses. Cite the following references:

Panagopoulos, A. (2021). Beneficiation of saline effluents from seawater desalination plants: Fostering the zero liquid discharge (ZLD) approach - A techno-economic evaluation. Journal of Environmental Chemical Engineering. 

Panagopoulos, A. (2021). Techno-economic assessment of Minimal Liquid Discharge (MLD) treatment systems for saline wastewater (brine) management and treatment. Process Safety and Environmental Protection, 146, pp. 656-669. 

Panagopoulos, A. (2021). Study and evaluation of the characteristics of saline wastewater (brine) produced by desalination and industrial plants. Environmental Science and Pollution Research, 1-14.

In response to this comment I corrected the text in the Introduction and References as follows:

Processes for improving water quality can also be considered for drinking use or for technical purposes [11–13].

11. Panagopoulos, A. Beneficiation of saline effluents from seawater desalination plants: Fostering the zero liquid discharge (ZLD) approach - A techno-economic evaluation. Environ. Chem. Eng. 2021₁. 9-4, 105338.
12. Panagopoulos, A. Techno-economic assessment of Minimal Liquid Discharge (MLD) treatment systems for saline wastewater (brine) management and treatment. Saf. Environ. Prot. 2021₂. 146, 656-669. 
13. Panagopoulos, A. Study and evaluation of the characteristics of saline wastewater (brine) produced by desalination and industrial plants. Sci. Pollut. Res. 2021₃. https://doi.org/10.1007/s11356-021-17694-x

- Please mention the novelty of the current study.

In response to this comment I corrected the text in the Introduction as follows:

The scientific novelty of this work is associated with the calculations of the equilibrium composition of the system by the method of minimizing the free energy of the system using a convex simplex algorithm [37]. Such methods are widely used abroad for calculating metamorphic systems at high temperatures and pressures and are practically not used for aqueous solutions in comparison with methods for calculating equilibria using equilibrium constants [38]. Therefore, their application for solving a specific physical problem of a quantitative description of the ongoing chemical interactions in a near-surface hydrogeochemical system with a forecast of changes in the ecological conditions of a region under further technogenic impact is of undoubted scientific interest.

- Conclusion: Discuss the applicability of your findings/results and future study in this field.

In response to this comment I corrected the text in the conclusions as follows:

Conclusions

The purpose of this work was to predict changes in the composition of surface waters and bottom sediments in the river during the further development of mining operations with the capture by drainage systems of brackish and saline waters, the presence of which was established in the zone of their future influence. For this, the modeling of changes in the water composition in the Zolotitsa River was carried out using the GEOCHEQ software package with the calculations of the equilibrium composition of the system by the method of minimizing the free energy of the system using a convex simplex algorithm.

It has been established that the maximum salinization of surface waters occurs as a result of pulling salt water to the system up to 1.51 g/L. At the same time, the MPC for fishery watercourses can be exceeded for Cl^-, Na⁺, SO₄^2-, Mg²⁺, Sr, V, U. The genetic basis for the accumulation of these components in solutions for mixing is considered.

Maximum precipitation from mixing solutions (not counting calcite) is typical for dolomite; then goethite, MnO₂, gibbsite and barite. In general, it should be noted that when about 5000 m³/h of drainage water is discharged into the river, the precipination mass will be from 56 to 191 t/h, including up to 2.1 t/h of iron. Therefore, the outlined tendency for the accumulation of clayey sediments with high sorption properties in the area of ​​discharge of quarry waters may contribute to the continuing accumulation of heavy metals in this zone.

The results of this study provide a better understanding of the dangers of the discharge of saline drainage water from an exploited diamond deposit into the Zolotitsa River. This determines the environmental value of the work.

In the future, it is planned to periodically monitor the state of river water and bottom sediments in the quarry area in order to compare the results of predictive calculations with real values ​​and improve predictive modeling by the method of minimizing the free energy of the system. It is also planned to study the effect of the composition of organic matter in river and groundwater on the mobility of chemical elements in mixed solutions.

- Language editing is recommended.

In response to this comment my manuscript professionally edited by MDPI's English editing service.

- Include '2. Hydrogeological Struct' in the '3. Materials and Method' section

In response to this comment '2. Hydrogeological Struct' included in the '3. Materials and Method' section

Thank you very much for your comments and suggestions, they helped to improve the article.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Accept.