KORESPONDENSI ARTIKEL

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Judul Paper : Effects of Pretreatment and Ratio of Solid Sago Waste to Rumen on Biogas Production through Solid-State Anaerobic Digestion

Nama Jurnal : Sustainability Volume : 13 (13)

No.ISSN : 2071-1050 DOI : 10.3390/su13137491

H Index : 85

Impact Factor : 3.251 (2020) SJR Index : 0.61 (2020)

Reputasi : Scopus Q1

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Nama Jurnal : Sustainability Volume : 13 (13) No.ISSN : 2071-1050

DOI : 10.3390/su13137491

H Index : 85

Impact Factor : 3.251 SJR Index : 0.61 Reputasi : Scopus Q2

Judul Paper : Effects of Pretreatment and Ratio of Solid Sago Waste to Rumen on Biogas Production through Solid-State Anaerobic Digestion

Item Halaman

Submission Received (23 April 2021) 1-4

Major Revisions (22 Mei 2021) 5-20

Manuscript Resubmitted (31 Mei 2021) 21-30

Revised Version Received (24 Juni 2021) 31

Minor revisions (26 Juni 2021) 32-33

Manuscript Resubmitted (28 Juni 2021) 34

Accepted for Publication (1 Juli 2021) 35

Final Proofreading Before Publication (2 Juli 2021) 36-37

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23 April 2021

Prof. Dr. Marc A. Rosen Editor-in-Chief

Sustainability

Dear Editor:

Please find enclosed our manuscript entitled “Effects of pretreatment and ratio of solid sago waste to rumen on biogas production from solid sago waste using solid-state anaerobic digestion method in an anaerobic digester,” which we request you to consider for publication as an Article inSustainability.

Our study investigated the effects of several types of pretreatments (physical, chemical, and biological) and their combined effect on the biogas production from a mixture of sago solid waste and rumen.

Additionally, the effect of the mixing ratio of the two wastes was investigated. This was achieved by using variations of the parameters under similar conditions. Thus, the effect of each parameter was noted.

The physical, chemical, and biological pretreatments were conducted by milling (±1 mm), NaOH treatment, and microbial consortium. Further, the results were then modeled by non-linear regression numerical methods to determine the kinetics constant of biogas production rate (U), maximum biogas production (A), and minimum time for biogas formation (λ).

All treatments proved to enhance and accelerate the biogas production rate. The optimum sago waste to rumen mixing ratio was found to be 1:1. Therefore, combining the three pretreatments at a 1:1 mixing ratio is recommended for enhanced biogas production from sage solid waste. This study is important, because it clarifies the roles of different pretreatments in the enhancement of biomass digestion and the role of mixing ratio in the co-digestion processes. This will help industries use optimum process conditions and achieve larger biogas quantities.

This manuscript has not been published elsewhere and is not considered by another journal. We have approved the manuscript and agree with submission to Sustainability. There are no conflicts of interest to declare.

We believe that the findings of this study are relevant to the scope of your journal and will be of interest to its readership. The manuscript has been carefully reviewed by an experienced editor whose first language is English and specializes in editing papers written by scientists whose native language is not English.

We look forward to hearing from you at your earliest convenience.

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Sincerely,

Siswo Sumardiono

Department of Chemical Engineering, Faculty of Engineering, Universitas Diponegoro, 50239, Semarang, Indonesia

Phone No: +62-24-7460058 Fax No: +62-24-76480675

Email Address: [email protected]

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REVIEWER 1

English language and style

( ) Extensive editing of English language and style required ( ) Moderate English changes required

(x) English language and style are fine/minor spell check required ( ) I don't feel qualified to judge about the English language and style

Yes Can be improved

Must be improved

Not applicable Is the content succinctly described and

contextualized with respect to previous and present theoretical background and empirical research (if applicable) on the topic?

( ) (x) ( ) ( )

Are the research design, questions, hypotheses and

methods clearly stated? ( ) ( ) ( ) (x)

Are the arguments and discussion of findings

coherent, balanced and compelling? ( ) ( ) ( ) (x)

For empirical research, are the results clearly

presented? ( ) (x) ( ) ( )

Is the article adequately referenced? ( ) ( ) (x) ( ) Are the conclusions thoroughly supported by the

results presented in the article or referenced in secondary literature?

( ) ( ) ( ) ( )

Comments and Suggestions for Authors

Overall, the article is well written and clear, but I am worried about the experimental layout.

Usually, BMP experiments are carried out under mesophilic (or thermophilic) conditions and they are considered to be finished when gas accumulation is negligible. Here we see hardly any sign of plateau and biogas accumulation steadily progressing until the very last day (and the tests lasted way longer than usual: BMP tests typically require 40-45 days). Looking at the experimental conditions adopted, the experiments were carried out under sort of psycrophilic conditions, but the temperature control was rather rough (°T ranged from 20 to 32 °C). The experiment could be acceptable, if only the authors motivated it. Is there any interest in psycrophilic fermentation of sago waste? Why the tested were stopped before reaching stable conditions? Without such a rationale, the manuscript in my opinion is not acceptable for publication.

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REVIEWER 2

(x) English language and style are fine/minor spell check required ( ) I don't feel qualified to judge about the English language and style

Yes Can be improved

Must be improved

( ) ( ) (x) ( )

methods clearly stated? ( ) ( ) (x) ( )

coherent, balanced and compelling? ( ) ( ) (x) ( )

presented? ( ) ( ) (x) ( )

Is the article adequately referenced? ( ) (x) ( ) ( ) Are the conclusions thoroughly supported by the

( ) ( ) ( ) ( )

This article is relative to the “Effects of pretreatment and ratio of solid sago waste to rumen on biogas production from solid sago waste using solid-state anaerobic digestion method in an anaerobic digester”

The content presented in this article needs to be better substantiated, analyses are needed to prove the results of the authors that has been obtained in anaerobic digestion trials. The degradability of the material after treatment was not proven was only grounded with works done by other authors which is not enough. I believe that testing is necessary to prove the delignification of the material (such as, the determination of lignin, cellulose and

hemicelluloses)

Line 56. “In the physical pretreatment of sago solid waste, the raw material size is decreased to reduce the cellulose crystallinity in order to facilitate the enzymatic hydrolysis process [18].” How does a physical process reduce raw material to a cellulose crystallinity? The reference given is not accessible.

Line 94 ...should be written 200 mL and not 200 ml

Line 157-158 formatting problems

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Line 215 “NaOH can separate lignin, hemicellulose, and cellulose, accelerating the microbial decomposition of lignocellulosic biomass”. No analyses have been carried out that provide this statement.

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REVIEWER 3

( ) English language and style are fine/minor spell check required (x) I don't feel qualified to judge about the English language and style

Yes Can be improved

Must be improved

( ) (x) ( ) ( )

methods clearly stated? (x) ( ) ( ) ( )

coherent, balanced and compelling? (x) ( ) ( ) ( )

presented? (x) ( ) ( ) ( )

Is the article adequately referenced? (x) ( ) ( ) ( ) Are the conclusions thoroughly supported by the

( ) ( ) ( ) ( )

Sumardiono et al. have written an interesting paper focused on the effects of pre-treatment (I shredding, II NaOH, III microbial consortium) and ratio of solid sago waste to rumen on biogas production using solid-state anaerobic digestion. In my humble opinion the topic studied, the set of methods used and the results are clear, concise and of scientific interest because the set of pre-treatments carried out allows to increase the biogas productivity. In this perspective, however, I believe (and I ask the opinion of the authors on this matter) that environmental studies should be conducted as a future development to verify the suitability of the process in its interest (pre-treatments + anaerobic bioprocess) and on a large scale. In addition, I report some of my minor considerations by scrolling the text. Thanks for your attention and if you want to consider them.

TITLE

Have you thought about summarizing the title of the article? Because “from solid sago waste”

it could be implied having already mentioned it before and also “in an anaerobic digester”

speaking of anaerobic digestion and biogas production --> Effects of pretreatment and ratio of solid sago waste to rumen on biogas production through solid-state anaerobic digestion (it's just an example title).

CHECK THE ENTIRE TEST

• I would write °C with the space with the number: eg 14) 25°C --> 25 °C

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• I would write Figure N(letter) always attached: Figure 1 (a) at 124) --> Figure 1(a) as you write at 150) with Figure 3(b).

ABSTRACT

In my humble opinion the abstract is clear, well written and well summarizes the information contained in the paper: aim of the work, study carried out and main results obtained for the optimization of the anaerobic bioprocess. However, I report some of my brief considerations by scrolling the text:

• 12) What do you mean with “microbial consortium of lignocelluloses”? A consortium already adapted to lignocellulosic biomass or a special one that easily degrades

lignocellulosic biomass? Please clarify, eventually rewrite this part if you agree.

• 18) To offer more details, I would add also here the specific of NaOH that you reported at 86): 4% NaOH g/g TS. I would do the same here for microbial consortium of 89): 5% v/v.

INTRODUCTION

• 25-26) I would add also the other common feedstock that can be used for biogas production, eg: agricultural waste, sewage sludge, organic fraction of municipal solid waste, etc (it's just an example sentence).

• 26) If you agree, I would add a small sentence on the description of the anaerobic digestion, eg: “in which the microorganisms degrade the organic matter in four main steps, etc." (it's just an example sentence).

• 31) I would briefly add the description of biomethane and upgrading, if you are referring to this with “special treatment”.

• 34-36) I certainly agree, it would be interesting to expand the sentence and list what the benefits of co-digestion are (eg C/N optimization, etc; it's just an example sentence).

• 36) After “productivity of biogas” I would add a sentence that makes clear that an environmental study on the entire process (eg LCA) could be necessary to understand if it is convenient or not, if you agree with this perspective.

• 64-65) I would add what kind of microbial consortium (eg: lignin-degrading or hydrolysing microbial consortium; it's just an example sentence).

General considerations:

1. Since you are also talking about anaerobic co-digestion and in particular co-digestion with lignocellulosic feedstock, it would be interesting to also mention (if you agree and where you deem it most appropriate, clearly): "Anaerobic co-digestion of municipal solid wastes with giant reed under mesophilic conditions, Journal of Material Cycles and Waste Management 21.6 (2019): 1332-1340”.

2. Since you are talking about lignocellulosic feedstock and also about the difficulty of degradation for which pre-treatments are provided, I would add (where you think more appropriate) a brief description with references of why there are some difficulties in the anaerobic digestion of lignocellulosic feedstock (I noticed that you well described it then in “4. Discussion”, I will write a short summary here too).

MATERIALS AND METHODS

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• 76) I would write in plural --> 2.1 Materials

• 82) You use rumen as an inoculum, but seems to be using enough (even if there is still the difference of TS to be considered, right?) of it given the ratios (especially in the test 1:1). Did you then calculate the contribution of the rumen inoculum to actually understand the net productivity of biogas from sago waste? Please, clarify.

• 93) Why do you add urea? Please, clarify.

General consideration:

1. I would also explicitly write that wt% you are working on in this anaerobic digestion tests. If you do, I would add it also to the abstract at 14) near “the anaerobic

digestion”.

RESULTS AND DISCUSSION

• 154) Typo: write 1:1 without space.

General considerations:

1. Have you not calculated the composition of the biogas produced? Wouldn't it have been interesting to also understand how the percentage of methane (also hydrogen for future development of this study) in the biogas produced varies according to the pre- treatments you have carried out?

2. The reasons for the increase in productivity are well reported in 4., also referring to scientific literature. As a future development, do you find it interesting to complete this work with other experimental activities (eg on the liquid phase taken from the anaerobic bioreactor) that further confirms those interpretations?

CONCLUSIONS

I would also briefly add the reason for these results, which you well write in “4. Discussion”.

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REVISION ROUND 1

REVISION NOTE BASED ON REVIEWERS COMMENTS

Journal Name : Sustainability (ISSN 2071-1050) Manuscript ID : sustainability-1213768

Title : "Effects of pretreatment and ratio of solid sago waste to rumen on biogas production from solid sago waste using solid-state anaerobic digestion method in an anaerobic digester"

Author(s) : Siswo Sumardiono * , Gebyar Adisukmo , Muthia Hanif , Budiyono Budiyono , Heri Cahyono

Reviewer 1

1 Comment 1 Overall, the article is well written and clear, but I am worried about the experimental layout. Usually, BMP experiments are carried out under mesophilic (or thermophilic) conditions and they are considered to be

finished when gas accumulation is negligible. Here we see hardly any sign of plateau and biogas accumulation steadily progressing until the very last day (and the tests lasted way longer than usual: BMP tests typically require 40- 45 days). Looking at the experimental conditions adopted, the experiments were carried out under sort of psycrophilic conditions, but the temperature control was rather rough (°T ranged from 20 to 32 °C). The experiment could be acceptable, if only the authors motivated it.

Response Thank you for the suggestion. We have clarified in Number 2 and Number 3 below.

2 Comment 2 Is there any interest in psycrophilic fermentation of sago waste?

Response We did not design this research towards psychrophilic fermentation. The research was carried out in July and August 2020, and fermentation was designed with room temperature ranging from 30.37 ^oC (August) and 30.46

oC (September). The following is attached a link from the central statistics body about Temperature By Months at Semarang Climatology Station, 2020 https://semarangkota.bps.go.id/statictable/2021/03/02/135/suhu-udara- menurut-bulan-di-stasiun-klimatologi-semarang-2020.html

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We use a consortium of microorganisms from a product branded

"Decoprima" which is produced by PT Prima Agrotech Jakarta Indonesia.

https://primaagrotech.com/products/decoprima/ Which consists of

• Streptomyces thermovulgaris strain 09924-c8Ka-50-3: 1 x 10⁶cfu/gram

• Thricoderma virens clone L-1: 1 x 10⁶cfu/gram

• Geobacillus thermocatenulatus strain KNOUC105: 1 x 10⁶cfu/gram The character of the microbes are mesophilic and thermophilic, which can be active at room temperature and high temperature.

According to the article by Rodríguez-Valderrama et al., 2019 entitled

“Evaluation of feeding strategies in upflow anaerobic sludge bed reactor for hydrogenogenesis at psychrophilic temperature”

(https://www.sciencedirect.com/science/article/pii/S0360319918331446) states that psychrophilic microorganisms act at temperatures <25 ° C, so that the process we are doing does not include psychrophilic fermentation.

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3 Comment 3 Why the tested were stopped before reaching stable conditions? Without such a rationale, the manuscript in my opinion is not acceptable for publication.

Response We would like to clarify our experiment that you think stops the observation before reaching a stable state. Apart from being in the form of accumulated production, we also study biogas production by observing the rate of biogas production. Most of the variables in this study showed that on the 54th day, they simultaneously experienced a decrease in the rate of biogas production.

From this phenomenon, we took the initiative to continue the fermentation process until the 60th day. Continuing the fermentation process until the 60th day as a solution to test whether the phenomenon of decreasing the rate of biogas production continued was confirmed to be true.

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Reviewer 2

1 Comment 1 This article is relative to the “Effects of pretreatment and ratio of solid sago waste to rumen on biogas production from solid sago waste using solid-state anaerobic digestion method in an anaerobic digester”

Response You are right. Thank you for the review notes.

2 Comment 2 The content presented in this article needs to be better substantiated, analyses are needed to prove the results of the authors that has been obtained in anaerobic digestion trials. The degradability of the material after treatment was not proven was only grounded with works done by other authors which is not enough. I believe that testing is necessary to prove the delignification of the material (such as, the determination of lignin, cellulose and hemicelluloses)

Response We strongly agree with your opinion that delignification is an important stage in processing biomass (including sago waste) before the following process. There is one stage that we do not show in the article, that we have tested the substrate (delignification results) before the biogas production process. In this study we used 4% NaOH as a deliginifying agent. The results of delignification of sago waste were then analyzed for the content of lignin, holocellulose and alpha-cellulose using

methods ASTM D 1106-56, ASTM D 1104-56, and ASTM D 1103-60, respectively. There was a decrease in lignin from 7.86% to 3.32%, hemicellulose 21.03% to 15.75%, while cellulose levels increased from 40, 32% to 47, 12%. In our point of view that the delignification process is a control variable, we do not display these results in the article, only mentioning that the sample has gone through the delignification process prior to biogas production.

3 Comment 3 Line 56. “In the physical pretreatment of sago solid waste, the raw material size is decreased to reduce the cellulose crystallinity in order to facilitate the enzymatic hydrolysis process [18].” How does a physical process reduce raw material to a cellulose crystallinity? The reference given is not accessible.

Response We attach a reference which states that mechanical treatment can reduce crystallinity (on google drive link below)

https://drive.google.com/drive/folders/1WmnkmqTNJ4BdlGekAhGgMv dUPNy3cDSI?usp=sharing

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4 Comment 4 Line 94 ...should be written 200 mL and not 200 ml

Response The revised text reads as follows on (line 101 in the revised manuscript) 5 Comment 5 Line 157-158 formatting problems

Response The revised text reads as follows on (line 162-163 in the revised manuscript)

6 Comment 6 Line 215 “NaOH can separate lignin, hemicellulose, and cellulose, accelerating the microbial decomposition of lignocellulosic biomass”.

No analyses have been carried out that provide this statement.

Response The results of delignification of sago waste were then analyzed for the content of lignin, holocellulose and alpha-cellulose using

methods ASTM D 1106-56, ASTM D 1104-56, and ASTM D 1103-60 respectively. There was a decrease in lignin from 7.86% to 3.32%, hemicellulose 21.03% to 15.75%, while cellulose levels increased from 40, 32% to 47, 12%. In our view that the delignification process is a control variable, we do not display these results in the article, only mentioning that the sample has gone through the delignification process prior to biogas production.

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Reviewer 3

Sumardiono et al. have written an interesting paper focused on the effects of pre-treatment (I shredding, II NaOH, III microbial consortium) and ratio of solid sago waste to rumen on biogas production using solid-state anaerobic digestion. In my humble opinion the topic studied, the set of methods used and the results are clear, concise and of scientific interest because the set of pre-treatments carried out allows to increase the biogas productivity. In this perspective, however, I believe (and I ask the opinion of the authors on this matter) that environmental studies should be conducted as a future development to verify the suitability of the process in its interest (pre-treatments + anaerobic bioprocess) and on a large scale. In addition, I report some of my minor considerations by scrolling the text. Thanks for your attention and if you want to consider them.

Author response: Thank you!

1 Comment 1 Title

Have you thought about summarizing the title of the article? Because

“from solid sago waste” it could be implied having already mentioned it before and also “in an anaerobic digester” speaking of anaerobic digestion and biogas production --> Effects of pretreatment and ratio of solid sago waste to rumen on biogas production through solid- state anaerobic digestion (it's just an example title).

Response Thank you for the suggestion about the title. We agree with the revised title in the manuscript “Effects of pretreatment and ratio of solid sago waste to rumen on biogas production through solid-state anaerobic digestion.” The

2 Comment 2 Check The Entire Test

I would write °C with the space with the number: eg 14) 25°C --> 25

°C

Response The revised text reads as follows on (line 14 in the revised manuscript)

3 Comment 3 I would write Figure N(letter) always attached: Figure 1 (a) at 124) --

> Figure 1(a) as you write at 150) with Figure 3(b).

Response We have revised the manuscript 4 Comment 4 Abstract

In my humble opinion the abstract is clear, well written and well summarizes the information contained in the paper: aim of the work,