Effect of Hydraulic Retention Time on the Treatment of Real Cattle Slaughterhouse Wastewater and Biogas Production from HUASB Reactor

Round 1

Reviewer 1 Report

The manuscript presents, in a very detailed form, the influence of the HRT in a HUASB through different parameters. The use of low-cost biofilm carrier is a good point.

The manuscript is very well written, and results well presented, but offers expected results: that an increase on HRT increase de COD removal and the biogas production, among others. Here there are a lack of novelty, that is compensated by the detailed results showed.

To overcome this issue, and with the results presented, I suggest to introduce an analysis/ discussion To what extent is it worthwhile to increase the HRT (more volume, higher cost) by 50% or 100%, to improve the% COD removed, or biogas production, with lower ratios? .

So to increase the impact and interest of the manuscript I recommend to include a discussion/analysis about which would be the optimal/feasible HRT?

Author Response

Thank you for the wonderful comments. Sincerely we found your comments very interesting and knowledge impacting.

Author Response File: Author Response.docx

Reviewer 2 Report

This manuscript described the effect of prolonged hydraulic retention time on the treatment of cattle slaughterhouse wastewater in a HUASB reactor. Biogas with high methane content was produced. Total suspended solids, fats, oil and grease, volatile suspended solids, chemical oxygen demand were efficiently removed from the stream. The analysis is very detailed and sound. I recommend this manuscript to be accepted for the publication after addressing the comments below.

 

Comments:

The morphology of the microbe is different in Figure 14. Do they have same activity? The authors need to explain this.  The manuscript did a modification of UASB reactor to get a HUASB reactor. Therefore it is necessary to compare the performance of the two types of the reactor.  In section 2.4, why does the author use synthetic wastewater and where was it used?

Author Response

We sincerely thank you for the wonderful and knowledge impacting comments. This really adds value to our understanding.

Author Response File: Author Response.docx

Reviewer 3 Report

In this study, the performance of the HUASB reactor consisting of synthetic grass media as attached growth surface was investigated for the treatment of cattle slaughterhouse wastewater under mesophilic condition. The focus of this study is to applying of the UASB reactor by modifying it using synthetic grass. In this work, the UASB reactor was modified by coupling a round synthetic grass in the sludge zone to serve as an attached growth surface. Also, a flat round plastic mesh attached with SG has introduced at the center to counteract the effect of sludge washout and suspended solid due to upflow velocity.

 

Point 1 : Line 18 – 20 : Proper use of parentheses is required ex) total suspended solids (TSS), volatile suspended solids (VSS)

The system attained a maximum COD removal efficiency of 97 %, total suspended solids TSS, volatile suspended solids VSS, fats, oil and grease FOG

 

Point 2 : Line 32 : Proper use of parentheses is required

Point 3 : Line 36 dissolve oxygen → dissolved oxygen

 

Point 4 : Line 51-61 : The sentence should be edited to make it easier to understand. Overall use of parentheses is inappropriate

Point Line 112  A laboratory-scale hybrid UASB reactor →  A laboratory-scale hybrid HUASB (HUASB) reactor, hereinafter referred to as HUASB.

 

Point 5 : Line 132 : reference [17] : This part should be changed with the author's information. It is not appropriate to include only the reference numbers.

 

Point 6 : Line 138 .Continuous study operation condition

The performance of the HUASB reactor treating raw cattle slaughterhouse wastewater was monitored at constant OLR and varied HRT

One cycle must be supplemented by operating in the following ranges for up to 70 consecutive days.ex) at a fl ow rate of x – y  mL/h(or upflow velocity m/hr) with a HRT of x - y h for 3 days, called one cycle.

 

Point 7 : Line 179-180 : Legend effluent COD must have the same meaning as the graph right axis (COD removal efficiency(%))

 

Point 8: Line 195-197 : The text and pictures seem different. After 2 days of HRT is not included in the graph, and the average value of HRT 2 days is not 38L.

 

Point 9 : Line 200-201 : These are not the average value of each condition. Use the exact representation if it represents the last measurement date of the period under each experimental condition.

 

Point 10: Line 204-206 : This paper also requires additional evidence or data that the effects are the same. No data about LCFA can be found in this paper.

 

Point 11 : Line 254 ; VFA - Need explanation for this abbreviation. Volatile fatty acids

 

Point 12 : Line 303 R2 : Need explanation for this abbreviation

 

Point 13 : Line 339 : “The images demonstrate, the abundance of mainly Methanosarcina-like acetoclastic methanogens”

: SEM images alone should not be used as “demonstrate” without chromosome analysis or 16S-RNA analysis. Therefore, it is appropriate to label methanogens that are assumed to be Methanosarcina from spherical and grow in colonies or granule forms.

Point 14 : The scientific name of the microorganism (family, genus, species) should be italicized according to academic rules.

Point 15 : Line 353 Table 4

These values are not averages.: Biogas, Methane(%), COD, VSS

 

Point 16 : Line 366 : SEM images alone is hard to specify bacterial species.

 

Point 17 : Line 366-369 : This does not appear to be the finding of this paper. Particularly resistant to salts and acetates is not represented in any data in this paper.

Point 18 : 367-369 : “Compared to other methanogens like Methanosaeta sp, the methanosarcina is quite robust toward different impairments. These include high tolerant to ammonium nitrogen concentration, salts, pH shocks, and high acetate concentrations”

: This study is not based on the results of ammonium tolerant, salts, pH shock, etc., but it is not relevant to the conclusion of this study.

Author Response

Sincerely speaking your comments are really knowledge impacting. we found this very interesting and added value to our manuscript. We have also added some attachments with respect to comments on volatile fatty acids (VFA).

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Many of my review comments have been faithfully corrected.
Thank you for your effort.
However, I am somewhat unsatisfied with this part [These include the molecular method involving fluorescence in situ hybridization (FISH) and scanning electron microscopy (SEM) method.].
However, at the current level of correction, I am satisfied because it does not interfere with the overall content of this study.