Textile Wastewater Treatment for Water Reuse: A Case Study

Round  1

Reviewer 1 Report

This manuscript focuses on a combined process for the treatment of wastewater from textile industries. All the steps are clearly presented in details and the rationale for the sequence in the process is explained. The economical analysis of the costs related to the process is also reported.

The work is of interest for researchers/technologists working in the field of environment management. It also offers some cues to scientists working in the design of physico-chemical and biological treatments of wastes. The rationale is well explained in the Introduction, references are correctly cited, data collection is logically designed, results are presented in the right sequence. Interpretation is sound. I think that, this article could be published in Processes. There are only some minor points that should to be fixed before the manuscript could be published.

- Differences and advancements with respect to previous works of the authors have to be better highlighted, even in the Introduction. This is specifically true concerning the reference 3 cited in the text.

- Line 42: “100-200 of…” What do the authors exactly mean?

- Equation 2: “removel” should be “removal”

- Equation 3: the parameter P should be better defined and clarified.

- The errors and uncertainties are not correctly handled. In the tables the errors on the reported values should be quoted. In many cases I think that the experimental results have reported with too many figures.

- The Conclusions section appears as a summary of the work. It also quantitatively reports many results that have been already reported in he text, with no added value. It should be completely re-thought and re-written in order to clearly state the advancements this work brings with respect to previous studies, thus clearly stating a take-home message.

Author Response

Dear Prof.:

Thanks very much for your kind comment and assessment. We have done major revision in light of all of the comments. Here we give the detailed illustrations on the revision in the order they were demanded in the comments:

(1)   Differences and advancements with respect to previous works of the authors have to be better highlighted, even in the Introduction. This is specifically true concerning the reference 3 cited in the text.

Answer: The introduction section has been improved as highlighted with underline from the third to the fifth paragraph of Introduction “In integrated treatment systems, pH adjustment, coagulation–flotation [5], and sedimentation are usually employed as primary treatment steps; biological processes (aerobic and anaerobic) are appropriate for organic removal [6, 7]. However, textile wastewater also exhibits high color and low biodegradability [8], thus making it difficult to treat with physio-chemical and biological treatment methods [9]. Advanced oxidation processes are considered a highly competitive water treatment technology for the removal of those organic pollutants not treatable by conventional techniques due to their high chemical stability and/or low biodegradability [10]. Ultrasonic oxidation technology can accelerate the destruction of the dye molecular structure and achieve dye decolorization and mineralization [11]. Visible-light-driven photocatalytic activity of Gd-TiO₂-GO nanocomposites shows improved visible light photocatalytic performance and degradation efficiency over pure TiO₂ [12].Hydrodynamic cavitation is effective in the degradation of ibuprofen [13]. Combined treatments based on UV light appear to be more eco-friendly and with very interesting removal efficiencies [14]. Therein the advanced oxidation processes, ozonation is one of the best options to treat wastewater containing non-biodegradable organic compounds and to achieve the quality of reclaimed water for reuse [15, 16]. It has a wider range of action on micropollutants removal and water disinfection [17]. In addition to chemical oxygen consumption (COD_cr) and biochemical oxygen demand (BOD₅) removal, ozonation attains a high level of color removal, which is advantageous over conventional methods [3]. The potential of ozonation makes it an interesting process for full-scale applications in water reclamation plants [16]. On the contrary, one of its disadvantages is the high investment costs and energy consumption [18]. Furthermore, effluent salinity must be removed for textile wastewater reuse. The typical textile wastewater can contain as much as 6.0 wt% NaCl or 5.6 wt% Na₂SO₄ [19]. Membrane separations may help achieve the water quality for recycling [6] and allows contaminant removal and water reuse for certain applications [20]. Lin et al. [19] designed ultrafiltration (UF)–diafiltration to separate a dye/Na₂SO₄ aqueous mixture and has achieved 98% desalination efficiency and >97% dye recovery. Lara et al. [21] used a UF ceramic membrane for the removal of a reactive dye, RB5, which was removed by up to 95.2%. Lafi et al. [22] pointed out that primary treated textile wastewater with combined UF–electrodialysis presents similar parameter values to those of normal feed water. Amar et al. [23] investigated the coupling of activated sludge treatment with either nanofiltration (NF) or reverse osmosis (RO) to recycle wastewaters from denim fabric production. NF allows a high yield while maintaining the Tunisian standard of water reuse (COD_cr < 90 mg L⁻¹). Jager et al. [24] pointed out that the residual color in the UF permeate can be reduced from an average of 660 ADMI units to 12 ADMI units in the RO permeate; this value is lower than that required for potable water. Although NF shows better COD_cr removal efficiency than RO, its salinity removal efficiency is dissatisfactory [25]. The yield of RO is lower than that of other systems [23], and its concentrate is difficult to treat due to its high concentration of organic matter, inorganic matter, ammonia nitrogen, and salt [26]. Thus, combining membrane technology with conventional systems or with other membrane-based systems in a hybrid configuration is necessary to fulfill technical and economic objectives [27].

There are many wastewater treatments for textile wastewater reuse, such as constructed wetland [28, 29], activated carbon [30, 31], ion exchange [32, 33]. However, the constructed wetland has poor removal effect on color and the occupation area of it is very large. Activated carbon has a high removal rate on water-soluble dyes, but it cannot adsorb suspended solid (SS) and insoluble dyes. Besides, the activated carbon is difficult to regenerate and thus the operating cost of it is high. Although ion exchange treatment has great removal rate on some specific dissolved pollutants, it is not suitable for the treatment of a large number of multi-component textile wastewater. UF is a good pretreatment process [19]. RO has great effects on the residual color and remaining salt [34].Ozone is one of the best treatment method in advanced oxidation methods [35], and it is a suitable alternative specially when integrated with biological treatments [10]. However, the industrial application of O₃/UV or O₃/UV/H₂O₂ is not recommended because the investment and operating costs are too high [35]. Therefore, in this research, ozonation + UF + RO combination sequence was developed to treat and reuse textile wastewater. The ozonation process mainly aimed to reduce follow-up membrane pollution. Furthermore, specific preprocesses, such as flocculation precipitation, sand filtration, self-cleaning filter, and security filter, were added before ozonation and membrane processing to reduce the operating costs. Besides, the reuse rate of recycled water was subsequently increased through the secondary water reuse system.

The objective of this research is to find an effective method of treating and reusing wastewater from the textile industry, and analyze its elimination effect and operation cost in different stages with the best operative conditions. Although the ability of ozonation and membrane technologies for the treatment of textile wastewater is well known, most studies focused on synthetic wastewater prepared in laboratories and used laboratory-scale plants over limited periods. Comparing to the existing work, this research used detailed field studies, pollutants monitoring and electricity log processing to investigate the elimination effect and operation cost in different stages. To the best of our knowledge, this is the first time to analyze the operation cost of two-stage ozonation + UF + RO combination sequence with engineering data.”

(2)   - Line 42: “100-200 of…” What do the authors exactly mean?

Answer: The unit of the 100-200 has been supplemented as highlighted with underline in line 41 “100–200 L of”.

(3)   - Equation 2: “removel” should be “removal”

Answer: The Equation 2 has been amended as highlighted with underline in line 236 “, (2)”.

(4)   - Equation 3: the parameter P should be better defined and clarified.

Answer: The parameter has been defined and clarified as highlight with underline in line 241 and 242 “P is the inlets of the primary RO tank and the secondary RO tank”.

(5)   - The errors and uncertainties are not correctly handled. In the tables the errors on the reported values should be quoted. In many cases I think that the experimental results have reported with too many figures.

Answer: The errors and uncertainties have been improved in the Tables. The figures have been improved.

(6)   - The Conclusions section appears as a summary of the work. It also quantitatively reports many results that have been already reported in the text, with no added value. It should be completely re-thought and re-written in order to clearly state the advancements this work brings with respect to previous studies, thus clearly stating a take-home message.

Answer: The conclusion has been re-thought and re-written “A combined two-stage water reuse treatment was developed to obtain quality water for reuse in industrial processes. The elimination effect and operation cost of the combined two-stage water reuse treatment were investigated.

SS is mainly eliminated in the sand filtration process. Ozone can thoroughly eliminate color. The removal rates of the primary and secondary ozone aeration tanks were 69.4±6.98% and 75.36±7.39%, respectively. The removal rate of color is proportional to ozone dosage. UF mainly eliminates COD_cr, TP, and turbidity. RO treatment shows the highest removal rate. The removal rates of COD_cr, color, and SO₄^2- by RO treatment were higher than 99%. The removal rate of the secondary reuse system of recycled water is higher than that of the primary system due to the high ozone dosage and usage of a new RO membrane.

The proposed sequential system is extremely effective. Effluents of the primary and secondary recycled water processing systems satisfy the reuse standards of recycled water. COD_cr, color, NH₃-N, hardness, Cl^-, SO₄^2-, turbidity, Fe³⁺, and Cu²⁺ satisfy the standards of domestic drinking water. The removal rate of the conductivity with new RO membrane was higher than those during UF-electrodialysis process and UF ceramic membrane, and close to that during UF–diafiltration process. The reuse rate of recycled water in the whole system was 86.8%, higher than that during FO-RO system by 31.8%.

The total operating cost of treating textile wastewater reached 0.44 USD m^-3 reuse water, wherein the cost of sand filtration, UF and RO system was maximum (approximately 0.19 USD.m^-3), followed by that of the ozone production (approximately 0.18 USD.m^-3). In the filtration system, RO claimed the highest cost (0.14 USD.m^-3 reuse water), followed by UF (0.04 USD.m^-3). In RO system, the electricity cost and membrane cost were 0.11 and 0.04 USD.m^-3, respectively. The operating cost of secondary reuse system was approximately 0.086 USD.m^-3 higher than that of the primary system. Electricity cost for ozonation and RO treatment accounted for 64.84% of the total cost.

The operating cost of the proposed sequential system in this research was lower than that of FO-RO system by 0.06 USD.m^-3 reuse water. Although the color removal rate of the electrocoagulation-O₃ process was close to 100%, the operating cost of it was much higher than that in this research, 5.80 USD m⁻³ treated wastewater.”

Author Response File: Author Response.pdf

Reviewer 2 Report

This is an interesting work regarding to textile wastewater treatment for water reuse with a interesting sequence, but some aspects should be revised.

CODcr should be defined before the acronym usage.

More references about ozone and organic contaminants degradation should be added to enhance the introduction section related to ozone aplications for example, Oller et al. 2011, Sci. Total Environ.409, 4141–4166; Gomes et al. 2017, Science of the total environment, 586 (2017) 265–283.

The units of flow rates could be corrected. A flow rate never can be a m/h? Please correct it.

Some minor errors can be found in words. Should be revised, for example on the equation 2 appear “removel”. Please correct all the manuscript.

What authors want to say with output of the reuse water? An explanation should be added for equation 3.

The figure 7 should be improved, too much results for the same graph authors can divide in two.

The units should be uniformized.

The value of 12 kWh/Kg O₃ was just for ozone consumption, or also the ozone production and the stream (air or oxygen to produce)? Please revise it.

Why authors selected this sequence? Ever tried another sequence? The reason for this selection should be exploited on the manuscript.

Author Response

Dear Prof.:

Thanks very much for your kind comment and assessment. We have done major revision in light of all of the comments. Here we give the detailed illustrations on the revision in the order they were demanded in the comments:

(1)   CODcr should be defined before the acronym usage.

Answer: CODcr has been defined before the acronym usage as highlighted with underline in line 63 “chemical oxygen consumption (COD_cr)”.

(2)   More references about ozone and organic contaminants degradation should be added to enhance the introduction section related to ozone aplications for example, Oller et al. 2011, Sci. Total Environ.409, 4141–4166; Gomes et al. 2017, Science of the total environment, 586 (2017) 265–283.

Answer: More references about ozone and organic contaminants degradation have been added as highlighted with underline from line 60 to 66 “Therein the advanced oxidation processes, ozonation is one of the best options to treat wastewater containing non-biodegradable organic compounds and to achieve the quality of reclaimed water for reuse [15, 16]. It has a wider range of action on micropollutants removal and water disinfection [17]. In addition to chemical oxygen consumption (COD_cr) and biochemical oxygen demand (BOD₅) removal, ozonation attains a high level of color removal, which is advantageous over conventional methods [3]. The potential of ozonation makes it an interesting process for full-scale applications in water reclamation plants [16]”

(3)   The units of flow rates could be corrected. A flow rate never can be a m/h? Please correct it.

Answer: The flow rates of the sand filters have been changed to the filtering surfaces, and highlighted with underline in lines 135, 136, 191 and 192 “The filtering surfaces in the primary and secondary sand filters were approximately 450 m² and 700 m², respectively.”, “The filtering surface in the third sand filtration tank was 280m².”

(4)   Some minor errors can be found in words. Should be revised, for example on the equation 2 appear “removel”. Please correct all the manuscript.

Answer: The Equation 2 has been amended as highlighted with underline in line 236 “, (2)”.

(5)   What authors want to say with output of the reuse water? An explanation should be added for equation 3.

Answer: The parameter has been defined and clarified as highlight with underline in line 41 and 242 “P is the inlets of the primary RO tank and the secondary RO tank”.

(6)   The figure 7 should be improved, too much results for the same graph authors can divide in two.

Answer: The figure 7 has been improved as highlighted with underline “Fig. 6 Pollutant changes in the primary UF (a) COD_cr, color, (b) NH₃-N, TN, and TP, (c) Conductivity, SO₄^2-, Cl^- , and (d) Hardness, Total alkalinity, Turbidity”

(7)   The units should be uniformized.

Answer: The units have been uniformized.

(8)   The value of 12 kWh/Kg O3 was just for ozone consumption, or also the ozone production and the stream (air or oxygen to produce)? Please revise it.

Answer: The value of 12 kWh/kg O₃ has been complemented as highlighted with underline in line 403 “The electricity consumption of the ozone and oxygen production was 12 kWh.kg^-1 O₃ power,’’.

(9)   Why authors selected this sequence? Ever tried another sequence? The reason for this selection should be exploited on the manuscript.

Answer: The reason for this selection has been exploited as highlighted with underline in the fourth paragraph of the Introduction “There are many wastewater treatments for textile wastewater reuse, such as constructed wetland [28, 29], activated carbon [30, 31], ion exchange [32, 33]. However, the constructed wetland has poor removal effect on color and the occupation area of it is very large. Activated carbon has a high removal rate on water-soluble dyes, but it cannot adsorb suspended solid (SS) and insoluble dyes. Besides, the activated carbon is difficult to regenerate and thus the operating cost of it is high. Although ion exchange treatment has great removal rate on some specific dissolved pollutants, it is not suitable for the treatment of a large number of multi-component textile wastewater. UF is a good pretreatment process [19]. RO has great effects on the residual color and remaining salt [34].Ozone is one of the best treatment method in advanced oxidation methods [35], and it is a suitable alternative specially when integrated with biological treatments [10]. However, the industrial application of O₃/UV or O₃/UV/H₂O₂ is not recommended because the investment and operating costs are too high [35]. Therefore, in this research, ozonation + UF + RO combination sequence was developed to treat and reuse textile wastewater. The ozonation process mainly aimed to reduce follow-up membrane pollution. Furthermore, specific preprocesses, such as flocculation precipitation, sand filtration, self-cleaning filter, and security filter, were added before ozonation and membrane processing to reduce the operating costs. Besides, the reuse rate of recycled water was subsequently increased through the secondary water reuse system.”

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript title "Textile wastewater treatment for water reuse: A case study" is generally well written but with a few fundamental issues that needs further clarifications:

1. It is not clear what the novelty of this work is. Please improve the introduction with a clearer description of the novelty.

2. There are multiple unit processes as illustrated in Fig.1. It is not clear the purpose of each unit(tin terms of target pollutant). While the primary sand filters for example achieves over 90% SS removal with about 24 mg/l SS; what is the purpose of a second and a third sand filters? Does this not increase cost unnecessarily ? Same argument for a second UF and RO units.

3. It may be better to report color removal in a more standard unit.

4. It is not clear how the cost in Table 6 were estimated. Provide further details or references used.

Author Response

Dear Prof.:

Thanks very much for your kind comment and assessment. We have done major revision in light of all of the comments. Here we give the detailed illustrations on the revision in the order they were demanded in the comments:

1. It is not clear what the novelty of this work is. Please improve the introduction with a clearer description of the novelty.

Answer: The introduction has been improved as highlighted with underline in the fourth and fifth paragraphs of the Introduction “There are many wastewater treatments for textile wastewater reuse, such as constructed wetland [28, 29], activated carbon [30, 31], ion exchange [32, 33]. However, the constructed wetland has poor removal effect on color and the occupation area of it is very large. Activated carbon has a high removal rate on water-soluble dyes, but it cannot adsorb suspended solid (SS) and insoluble dyes. Besides, the activated carbon is difficult to regenerate and thus the operating cost of it is high. Although ion exchange treatment has great removal rate on some specific dissolved pollutants, it is not suitable for the treatment of a large number of multi-component textile wastewater. UF is a good pretreatment process [19]. RO has great effects on the residual color and remaining salt [34].Ozone is one of the best treatment method in advanced oxidation methods [35], and it is a suitable alternative specially when integrated with biological treatments [10]. However, the industrial application of O₃/UV or O₃/UV/H₂O₂ is not recommended because the investment and operating costs are too high [35]. Therefore, in this research, ozonation + UF + RO combination sequence was developed to treat and reuse textile wastewater. The ozonation process mainly aimed to reduce follow-up membrane pollution. Furthermore, specific preprocesses, such as flocculation precipitation, sand filtration, self-cleaning filter, and security filter, were added before ozonation and membrane processing to reduce the operating costs. Besides, the reuse rate of recycled water was subsequently increased through the secondary water reuse system.

The objective of this research is to find an effective method of treating and reusing wastewater from the textile industry, and analyze its elimination effect and operation cost in different stages with the best operative conditions. Although the ability of ozonation and membrane technologies for the treatment of textile wastewater is well known, most studies focused on synthetic wastewater prepared in laboratories and used laboratory-scale plants over limited periods. Comparing to the existing work, this research used detailed field studies, pollutants monitoring and electricity log processing to investigate the elimination effect and operation cost in different stages. To the best of our knowledge, this is the first time to analyze the operation cost of two-stage ozonation + UF + RO combination sequence with engineering data.”

2. There are multiple unit processes as illustrated in Fig.1. It is not clear the purpose of each unit (tin terms of target pollutant). While the primary sand filters for example achieves over 90% SS removal with about 24 mg/l SS; what is the purpose of a second and a third sand filters? Does this not increase cost unnecessarily? Same argument for a second UF and RO units.

Answer: The purpose of each unit has been complemented as highlighted with underline “The second sand filtration tank mainly aimed to eliminate the suspended matters, which generate in the ozone aeration, and some residues falling from the ozone aeration tank.”, “In order to remove part of the turbidity and COD_cr and then protect the follow-up RO system, primary UF system was set.”, “In order to increase the reuse rate of recycled water, a secondary water reuse system, which included secondary ozone aeration tank, third sand filtration tank, secondary UF system and secondary RO system, was set to treat the primary RO concentrated water.”, “The third sand filtration tank mainly aimed to eliminate suspended matters and some residues falling from the tank during ozone aeration to maintain the stability of follow-up procedures.”

The SS removal rate was achieved by the primary sand filtration and secondary sand filtration: “As shown in Fig. 2, the removal rate of SS was the highest (99.34±0.92%), followed by color (74.01±8.68%), COD_cr (39.85±7.51%), NH₃-N (27.35±31.78%), TP (13.25±15.94%), and TN (-4.39±25.02%) after treatment by the reaction, precipitation, primary sand filtration, ozonation oxidation and secondary sand filtration.”. Besides, as shown in Fig.2, the sand filtration not only remove the SS, but also the COD_cr, TP, turbidity, and TN and so on. So, the second and third sand filters are necessary.

The second UF and RO mainly aimed to reuse the primary RO concentrated water and increase the reuse rate of recycled water.

3. It may be better to report color removal in a more standard unit.

Answer: Dilution ratio method is more suitable for the wastewater with high color, so “times” was used to report the color removal.

4. It is not clear how the cost in Table 6 were estimated. Provide further details or references used.

Answer: The further details for the Table 6 have been provided as “For the primary ozone reaction tank, ~90 g O₃.m^-3 wastewater was consumed on average, whereas approximately 118 g O₃.m^-3 wastewater was consumed for the second ozone reaction tank. The electricity consumption of the ozone and oxygen production was 12 kWh.kg^-1 O₃ power [3]. Thus, an operating cost of approximately 0.11 USD.m^-3 wastewater (approximately 8100 USD.d^-1 for 7.5×10⁴ m³.d^-1 wastewater) was calculated for a power price of 0.1 USD.kWh^-1 for the primary zone reaction tank and 0.14 USD.m^-3 wastewater (approximately 3505 USD.d^-1 for 24750 m³.d^-1 wastewater) for the second ozone reaction. Powers of inlet pumps in the primary UF and primary RO system were 340 kW and 2,155 kW, respectively. The total power consumption of primary self-cleaning filter, sand filter, UF, and RO backwash pump was approximately 17 kW. Then, the power consumption of the pumps in the primary water reuse system was 60288 kWh.d^-1, and the electricity cost of the pumps in the primary water reuse system was 6029 USD.d^-1. The total electricity cost in the primary water reuse system was 14129 USD.d^-1.The power consumptions of inlet pumps in the secondary UF and secondary RO system were 110 and 770 kW, respectively. The total power consumption of secondary self-cleaning filter, sand filter, UF, and RO backwash pump was approximately 11 kW. Then, the power consumption of the pumps in the second water reuse system was 21384 kWh.d^-1, and the electricity cost of the pumps in the second water reuse system was 2138 USD.d^-1. The total electricity cost in the second water reuse system was 5643 USD.d^-1.

The PAC dosage was approximately 80 g.m^-3 of wastewater and thus the PAC cost was approximately 644 USD.d^-1. The number of RO membrane and UF membrane were 5280 and 1224, respectively, and the prices of them were 500 and 2167 USD, respectively. So the costs of UF and RO membranes replacement were 53.04 ×10⁴ and 88 ×10⁴ USD.a^-1. The number of workers in the sewage plant were 50, and the annual salary was 25000 USD.person^-1. So the employee cost was 125×10⁴ USD.a^-1. The Machine maintenance cost was approximately 21.91×10⁴ USD.a^-1. The cost of the agentia and the filter-bag were 11.42 ×10⁴ and 3.96 ×10⁴ USD.a^-1, respectively.

The total operating cost of treating textile wastewater is displayed in Table 6, reaching 0.44 USD.m^-3 reuse water, wherein the cost of the ozone production was 0.18 USD.m^-3 (40%), that of sand filtration, UF and RO system was 0.19 USD.m^-3 (43%), and that of machine maintenance, employee cost, agentia, and PAC was 0.08 USD.m^-3 (17%) (Fig.12). In the filtering system, RO claimed the highest cost (0.14 USD.m^-3 reuse water), followed by UF (0.04 USD.m^-3). In RO system, the electricity cost and membrane cost were 0.11 and 0.04 USD.m^-3, respectively. The operating cost of secondary reuse system was approximately 0.086 USD.m^-3 higher than that in the primary system, which was caused by the increased ozone dosage and operating pressure of RO. Based on the above analysis, the electricity cost for ozonation and RO treatment accounted for 64.84% of the total cost. Therefore, the key to reducing the operating cost for reuse of recycled water is decreasing the electricity consumption in ozonation and RO. The operating cost of the proposed sequential system in this research was lower than that of FO-RO system in literature [51] by 0.06 USD.m^-3 reuse water. And it was also much lower than that of electrocoagulation-O₃ process, which was 5.80 USD m⁻³ treated wastewater [50].”

Author Response File: Author Response.pdf

Reviewer 4 Report

General comment:

The manuscript deals with investigations on a combined two-stage wastewater treatment. The primary treatment consists of a flocculation and sedimentation system, two sand filters, an ozonation unit, an ultrafiltration unit, and a reverse osmosis system. The second treatment consists of an ozonation unit, a sand filtration unit, and UF and RO systems.

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

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

1. Introduction

Please, improve the introduction by including a short on AOPs, such as photodegradation and cavitation, which are useful for the removal of organic pollutants. Please, consider the following papers:

o   Iovino, P., Chianese, S., Canzano, S., Prisciandaro, M., Musmarra, D., 2016. Degradation of Ibuprofen in Aqueous Solution with UV Light: the Effect of Reactor Volume and pH, Water, Air, and Soil Pollution, 227(6), Article number 194.

o   Musmarra, D., Prisciandaro, M., Capocelli, M., Karatza, D., Iovino, P., Canzano, S., Lancia, A., 2016. Degradation of ibuprofen by hydrodynamic cavitation: Reaction pathways and effect of operational parameters, Ultrasonics Sonochemistry, 29, 76-83.

o   Oppong, S.O.-B., Opoku, F., Govender, P.P., 2019. Tuning the electronic and structural properties of Gd-TiO2-GO nanocomposites for enhancing photodegradation of IC dye: The role of Gd3+ ion, Applied Catalysis B: Environmental, 243, 106-120.

o   Zhu, C., Jiang, C., Chen, S., Mei, R., Wang, X., Cao, J.,  Ma, L., Zhou, B., Wei, Q., Ouyang, G., Yu, Z., Zhou, K., Ultrasound enhanced electrochemical oxidation of Alizarin Red S on boron doped diamond(BDD) anode:Effect of degradation process parameters, Chemosphere, 209, 685-695.

It is not clear what is the scope of the manuscript: did you find the best operative condition of each unit in order to achieve the highest pollutant removal? Did you keep constant the operative condition of each unit and monitored the treatment plant?

2. Materials and Methods

Please, report the variation range of the operative conditions of the treatment plant in a Table, in order to simplify the readability of the manuscript.

Please, specify the wastewater analytical technique.

Please, define the total operating costs.

Please, specify if investigations were carried out in duplicate or triplicate.

3. Results and Discussion

Please, add standard deviation.

Please, improve comparison between experimental findings and literature data.

Please, compare the performance and costs of the proposed treatment with the ones of other treatment systems.

Please, use an international currency for the cost analysis.

Please, include at least ordinary maintenance cost and employees cost into the cost analysis.

Author Response

Dear Prof.:

Thanks very much for your kind comment and assessment. We have done major revision in light of all of the comments. Here we give the detailed illustrations on the revision in the order they were demanded in the comments:

1. Introduction

Please, improve the introduction by including a short on AOPs, such as photodegradation and cavitation, which are useful for the removal of organic pollutants. Please, consider the following papers:

o   Iovino, P., Chianese, S., Canzano, S., Prisciandaro, M., Musmarra, D., 2016. Degradation of Ibuprofen in Aqueous Solution with UV Light: the Effect of Reactor Volume and pH, Water, Air, and Soil Pollution, 227(6), Article number 194.

o   Musmarra, D., Prisciandaro, M., Capocelli, M., Karatza, D., Iovino, P., Canzano, S., Lancia, A., 2016. Degradation of ibuprofen by hydrodynamic cavitation: Reaction pathways and effect of operational parameters, Ultrasonics Sonochemistry, 29, 76-83.

o   Oppong, S.O.-B., Opoku, F., Govender, P.P., 2019. Tuning the electronic and structural properties of Gd-TiO2-GO nanocomposites for enhancing photodegradation of IC dye: The role of Gd3+ ion, Applied Catalysis B: Environmental, 243, 106-120.

o   Zhu, C., Jiang, C., Chen, S., Mei, R., Wang, X., Cao, J.,  Ma, L., Zhou, B., Wei, Q., Ouyang, G., Yu, Z., Zhou, K., Ultrasound enhanced electrochemical oxidation of Alizarin Red S on boron doped diamond(BDD) anode:Effect of degradation process parameters, Chemosphere, 209, 685-695.

Answer: More references about AOPs have been added as highlighted with underline from line 52 to 59 “Advanced oxidation processes are considered a highly competitive water treatment technology for the removal of those organic pollutants not treatable by conventional techniques due to their high chemical stability and/or low biodegradability [10]. Ultrasonic oxidation technology can accelerate the destruction of the dye molecular structure and achieve dye decolorization and mineralization [11]. Visible-light-driven photocatalytic activity of Gd-TiO₂-GO nanocomposites shows improved visible light photocatalytic performance and degradation efficiency over pure TiO₂ [12].Hydrodynamic cavitation is effective in the degradation of ibuprofen [13]. Combined treatments based on UV light appear to be more eco-friendly and with very interesting removal efficiencies [14].”

It is not clear what is the scope of the manuscript: did you find the best operative condition of each unit in order to achieve the highest pollutant removal? Did you keep constant the operative condition of each unit and monitored the treatment plant?

Answer: “The objective of this research is to find an effective method of treating and reusing wastewater from the textile industry, and analyze its elimination effect and operation cost in different stages with the best operative conditions.”

2. Materials and Methods

Please, report the variation range of the operative conditions of the treatment plant in a Table, in order to simplify the readability of the manuscript.

Answer: The variation range of the operative conditions of the treatment plant has been reported as highlighted with underline in Table 1.

Please, specify the wastewater analytical technique.

Answer: The wastewater analytical technique has been improved as highlighted with underline in 2.3 Analytical methods “The pH was measured according to the glass-electrode method, using orion 420A+pH meter. COD_cr analyses were performed by the fast digestion spectrophotometric method with DRB200 digester/DR890 chromometer. BOD₅ analyses were determined by the dilution and inoculation method with YSI5100 dissolved oxygen meter. Color was measured according to the dilution times method. NH₃-N was performed by the Nessler’s reagents spectrophotometric method with 722 spectrophotometer, while TP was performed by the ammonium molybdate spectrophotometry with 722 spectrophotometer. TN was determined by the alkaline potassium persulfate digestion UV spectrophotometry with UV-1800 ultraviolet spectrophotometer. SS was measured according to the gravimetric method, using electronic scales. Turbidity, hardness, conductivity, total alkalinity and Cl^- were determined by turbidity meter (PTURB-202), hardness tester (CHCM-210), conductivity meter (GTCON-400C), total alkalinity meter (CHTA-211) and portable chlorometer (CLS-10A), respectively. SO₄^2- was performed by the gravimetric method with electronic scales. Fe³⁺ and Cu²⁺ were determined by the flame atomic absorption spectrometric method with flame atomic absorption photometer.”

Please, define the total operating costs.

Answer: The total operating cost has been defined as highlighted with underline from line 242 to 245 “The total operating cost TOC includes electricity cost of ozone and oxygen production, electricity cost of pumps, agentia cost, machine maintenance cost, PAC cost, cost of UF and RO membrane replacement, employee cost and cost of filter-bag replacement.”

Please, specify if investigations were carried out in duplicate or triplicate.

Answer: The investigations have been supplemented from line 232 to 238“Each sample was determined in triplicate.”, “Each sample was determined in duplicate.”

3. Results and Discussion

Please, add standard deviation.

Answer: The standard deviations have been added.

Please, improve comparison between experimental findings and literature data.

Answer: The comparison between experimental findings and literature data has been improved as highlighted with underline “The removal rates of COD and color in the primary and secondary ozone aeration tanks were all lower than those of electrocoagulation-O₃ process, during which the ozone dose was 280 g.m^-3 and the color removal rate was close to 100% [50].”, “The removal rate of the conductivity with new RO membranes was higher than those during UF-electrodialysis process [22] and UF ceramic membrane[21], and close to that during UF–diafiltration process [19].”, “The reuse rate of recycled water in the whole system was 86.8%, higher than that during forward osmosis (FO)-RO system by 31.8% [51].”

Please, compare the performance and costs of the proposed treatment with the ones of other treatment systems.

Answer: The compare the performance and costs of the proposed treatment with the ones of other treatment systems has been improved as highlighted with underline “The operating cost of the proposed sequential system in this research was lower than that of FO-RO system in literature [51] by 0.06 USD.m^-3 reuse water. And it was also much lower than that of electrocoagulation-O₃ process, which was 5.80 USD m⁻³ treated wastewater [50].”

Please, use an international currency for the cost analysis.

Answer: An international currency for the cost analysis has been used.

Please, include at least ordinary maintenance cost and employees cost into the cost analysis.

Answer: The ordinary maintenance cost and employees cost have been complemented as highlight with underline in Table 6.

Author Response File: Author Response.pdf

Round  2

Reviewer 2 Report

The authors provide significant changes in the manuscript. 

Reviewer 3 Report

The authors have addressed my earlier concerns. I have no further comments.

Reviewer 4 Report

The authors revised the manuscript according to my suggestion. The paper is publishable.