Bioaugmentation Strategies for Enhancing Methane Production from Shrimp Processing Waste through Anaerobic Digestion
and Giulia Massini 1,*Round 1
Reviewer 1 Report
The paper entitled Bioaugmentation strategies for enhancing methane production from shrimp processing waste through anaerobic digestion investigate the possibility of energetic valorization of shrimp processing waste by anaerobic digestion using a fermenting bacteria pool and two strains of Anaerobic Fungi.
The manuscript can be improved, below are some suggestions:
- line 38 “in most regions of the world up to 30-35 percent of global fishery” use %
- in Subsection 2.1. describe in more detail how you determined: total solids, volatile solids, total carbon and total nitrogen of waste substrate;
- in Subsection 2.3: why or how you choose the shrimp processing waste concentrations: 6.5, 9.7 and 13.0 g VS L -1? A Figure or a Table with the experimental conditions may help the reader to understand better your experiment;
- in Subsection 2.4. describe in more detail how you determined volatile fatty acids (acetic, butyric, propionic, valeric and isovaleric acids);
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Review of fermentation-2303257 Bioaugmentation strategies for enhancing methane production from shrimp processing waste through anaerobic digestion
The manuscript addresses the topic of treating shrimp processing waste to produce methane. Converting a waste to biofuel is a worthy goal, but it is not clear that this study makes a meaningful contribution to that effort. Microbial cultures that are adapted to a given waste stream through continuous cultivation or repeated subculturing will be efficient in utilizing the waste and will be stable/predictable for use in a process. An adapted culture should have been used as the baseline for comparison with bioaugmentation variables. The anaerobic digestion inoculum (sometimes called M) was derived from cheese whey processing waste, and the mixed bacterial culture F210 was derived from coastal sediment. In other words, none of the cultures used in these anaerobic digestion tests were in any way adapted to shrimp processing waste. Accordingly, it is expected that the composition of the microbial communities will be different at the start of the experiments reported here, and that the composition of all microbial cultures are expected to change over the course of a 145 day incubation. The relevance of this study to treating shrimp processing waste is dubious. How is shrimp processing waste treated now? What percentage of shrimp processing waste is currently treated using anaerobic digestion? Is there a need for bioaugmentation? Operators of facilities treating shrimp processing waste would not choose to use bioaugmentation unless it showed a clear benefit.
Anaerobic digestion of organic waste is generally regarded to consist of two phases: the breakdown of organics to smaller molecules (hydrolytic phase) and the conversion of small organic molecules into methane (methanogenesis). Some anaerobic digestion processes are designed specifically as a two phase process to optimize separately for these digestion steps. The study reported here included two anaerobic fungi. The abstract did not make it clear that these fungal cultures were selected because of their possible contribution to the hydrolysis of chitin, nor was this clarified in the introduction. Were these fungal cultures necessary? Why were these cultures never tested to quantify chitinase activity? Did these fungal cultures survive during the 145 day incubation?
What environmental regulations need to be met when treating shrimp processing waste and how do the results reported here relate to those regulations? Is 145 days a reasonable incubation time for a process?
What is the maximum theoretical value for the conversion of chitin to methane using anaerobic digestion and how do the results in this study compare? How do the results reported in this study compare with the literature regarding anaerobic digestion generally and the degradation of chitin specifically?
Acetoclastic methanogens predominated versus hydrogenotrophic methanogens in this study. How do these data relate to the probable biodegradation pathway for chitin, and how do they compare with the literature generally concerning anaerobic digestion.
The design of the experiments did not allow for data relevant to an actual process for shrimp waste treatment to be obtained. Neither is it clear that the data reported here provide meaningful insights into the anaerobic digestion process.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
This part of the text in the methodology should be changed. It is suggested to describe in accordance with the indication of what it is actually about and not using the citation number:
The AF cultures were then individually reactivated as reported in [26] and in line with [20].
The same applies to the description:
The quantity of the biogas produced was measured using a water displacement device [27].
The description of the methodology should be more concise so that the relationship between introduction, discussion method and presentation of results is optimal.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors made changes and improved the quality of the article.
Reviewer 2 Report
When the authors did not agree with a comment they choose to place an excuse in their response to reviewers without modifying the appropriate regions of the text. Since reasoned scientific rebuttal of the comments was not provided, this is unacceptable. I continue to recommend for rejection of this manuscript.
