Techno-Economic Analysis on an Industrial-Scale Production System of Polyhydroxyalkanoates (PHA) from Cheese By-Products by Halophiles

Round 1

Reviewer 1 Report

• The “Materials” section needs to be completed by the specifications of chemicals and materials used in this study.
• Please explain some units before using their abbreviations, such as MT/day or gal/min.
• Line 159, “The salinity of MSM was measured to be 18.8 parts per thousand (ppt), correspondingly the saltwater density is around 1.13 kg/L [18]”. If this sentence is a result of this study, why the authors are using reference??
• What is “LOD”? please explain the concept. Why LOD 5% is the best?
• Figure 1-3 need to increase the quality of the figures.
• I suggest using the following references in this study:

Sabbagh, F., & Muhamad, I. I. (2017). Production of poly-hydroxyalkanoate as secondary metabolite with main focus on sustainable energy. Renewable and Sustainable Energy Reviews, 72, 95-104.

Muhamad, I. I., Sabbagh, F. A. R. Z. A. N. E. H., & Karim, N. A. (2017). Polyhydroxyalkanoates: a valuable secondary metabolite produced in microorganisms and plants. Plant Secondary Metabolites, Volume Three: Their Roles in Stress Eco-Physiology, 185.

• Some references are too old such as ref.15. please replace with recently published articles.
• Some references are not reliable and understandable such as 20, 21, 22, ….

Author Response

Author’s Reply to the Review Report (Reviewer 1)

The authors appreciate the reviewer’s thoughtful and helpful review, comments, and suggestions. The detailed point to point responses to the comments are shown below and the manuscript has been revised accordingly.

 

The ‘Materials’ section needs to be completed by the specifications of chemicals and materials used in this study.

The names and the prices of the raw chemicals and materials used in the techno-economic models of this study have been described extensively in Table 1 of the Section ‘Economic evaluations’ (Lines 264-165). For instance, the table listed all the salts, water, target product (PHBV), and the specific materials used in the utilities including steam, cooling and chilled water, standard electricity, membranes, and cleaning supplies. In addition, in the Section ‘Specification of unit operations in all scenarios’ (Lines 141-253), the authors have demonstrated how the raw chemicals and materials were utilized in specific unit operations of the production system, to provide a clear overview on the dynamic flows of the production lines.

Besides, the overall mass balances have been conducted in the models for all the materials involved in the calculations, and the mass of input and output streams of the three different production scenarios have been demonstrated in Table 3 of Section 3.1 ‘Mass and energy flows in the model’ (Lines 322-323).

 

Please explain some units before using their abbreviations, such as MT/day or gal/min.

The authors have confirmed that all unit abbreviations were explained with full name at their first appearance. Some changes have been made to Lines 38, 145, 148, 154 for MT/a, and gal/min units.

 

Line 159, ‘The salinity of MSM was measured to be 18.8 parts per thousand (ppt), correspondingly the saltwater density is around 1.13 kg/L [18]’. If this sentence is a result of this study, why the authors are using reference??

Both parameters of the MSM, 18.8 ppt and 1.13 kg/L, were measured data. A change has been made to Lines 162-163: the reference [18] has been removed.

 

What is ‘LOD’? please explain the concept. Why LOD 5% is the best?

As mentioned in Lines 232-233, the LOD is loss on drying, which describes the loss of water and volatile compounds under specific drying conditions. In this study, the LOD is equivalent to moisture content since there is minimum amount of other volatile compounds in the PHBV product. 5% is a measured moisture content of the PHBV powder sample in our research lab, which is good for long-term storage.

 

Figure 1-3 need to increase the quality of the figures.

As suggested, the authors have increased the resolution of Figures 1-3, as demonstrated in Lines 346-352.

 

I suggest using the following references in this study:

Sabbagh, F., & Muhamad, I. I. (2017). Production of poly-hydroxyalkanoate as secondary metabolite with main focus on sustainable energy. Renewable and Sustainable Energy Reviews, 72, 95-104.

Muhamad, I. I., Sabbagh, F. A. R. Z. A. N. E. H., & Karim, N. A. (2017). Polyhydroxyalkanoates: a valuable secondary metabolite produced in microorganisms and plants. Plant Secondary Metabolites, Volume Three: Their Roles in Stress Eco-Physiology, 185.

Thanks for the reviewer’s suggestions. The reference has been added to this study as shown in Lines 546-547: Sabbagh, F.; Muhamad, I.I. Production of Poly-Hydroxyalkanoate as Secondary Metabolite with Main Focus on Sustainable Energy. Renewable and Sustainable Energy Reviews 2017, 72, 95–104, doi:10.1016/j.rser.2016.11.012

 

Some references are too old such as ref. 15. Please replace with recently published articles.

The reference 15 (Gänzle, M.G.; Haase, G.; Jelen, P. Lactose: Crystallization, Hydrolysis and Value-Added Derivatives. International Dairy Journal 2008, 18, 685–694, doi:10.1016/j.idairyj.2008.03.003) is a classic paper in the diary research field and has been cited for over 300 times in the recent decade and over 20 times in the year 2021 alone. The authors confirm the necessity of this paper as a reference of our study.

 

Some references are not reliable and understandable such as 20, 21, 22, …

The references 20 and 22 were the references where the 2021 market prices of certain chemicals were obtained for the economic analysis conducted in this study. They were the up-to-date market prices for bulky purchases from the reliable international trade platform. Since the production scale of this study was industrial scale (9700 metric ton/year), the authors considered these prices of the raw chemicals and materials over the local wholesale prices.

The reference 21 was for the company which produces the software (SuperPro Designer), and this software was used for technical design and economic calculations of the models in the study.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

 3-hydroxy fatty acid polyesters obtained from the microbial sources have grater industrial applications.

This manuscript deal with the process parameters and improving the industrial production efficiency of the PHA. Different approaches have been implemented for the improvement production of PHA.  Overall, the manuscript is interesting I have a comment

After incorporating all the parameters, the production efficiency of the strain and the approach has been improved and what is the value of the efficiency because it cost much in the industrial level.

 

Also any approach to produce the enzyme by the catalyst and simultaneously increase the production rate of PHA.

Author Response

Author’s Reply to the Review Report (Reviewer 2)

The authors appreciate the reviewer’s thoughtful and helpful review, comments, and suggestions. The detailed point to point responses to the comments are shown below and the manuscript has been revised accordingly.

 

This manuscript deal with the process parameters and improving the industrial production efficiency of the PHA. Different approaches have been implemented for the improvement production of PHA. Overall, the manuscript is interesting I have a comment: After incorporating all the parameters, the production efficiency of the strain and the approach has been improved and what is the value of the efficiency because it cost much in the industrial level.

The authors agree with the reviewer’s opinion that the production efficiency of PHA is of vital importance particularly with an industrial scale of production. Compared to the conventional plastic market and bioplastic market, the current PHA market is still much smaller and has a great potential to increase. The production cost of PHA is found to be the bottleneck for the market growth, and there are many research interests in reducing the production cost through improving the production efficiency and reducing the cost parameters that have major influences on the overall economics of PHA. Therefore, in the industrial level, innovative biotechnologies that can promote the overall production efficiencies will help reduce the production cost and make PHA market penetrate more into the traditional market, which eventually leads to more replacement towards sustainable and environmental-friendly plastic products.

 

Also any approach to produce the enzyme by the catalyst and simultaneously increase the production rate of PHA.

The authors think this comment from the reviewer is very inspiring. The wild-type microbial PHA producer, Haloferax mediterranei, cannot produce the lactase enzyme by itself; therefore, there is always a need to purchase external lactase enzyme to break down lactose into monosaccharides (glucose and galactose) in order to be utilized by the strain as substrate for cell growth and PHBV synthesis. Given that, a strategy to genetically engineer this strain or through catalytical method to make it produce the enzyme under certain conditions would eliminate the cost of purchasing additional enzyme and thus reduce the overall production cost. Although this falls out of the scope of this study, it would be a very interesting topic for further research.

Author Response File: Author Response.pdf