Review Reports

Round 1

Reviewer 1 Report

A very interesting work showing the potential of using rubber waste. The research goal set by the authors was achieved. However, I am concerned that further long-term studies are needed to test the effect of rubber additives on soil toxicity. In Europe, under the influence of environmental protection, it is forbidden to bury rubber waste in the ground. Such treatments were used in the case of utilization of rubber conveyor belts, where the waste was covered with overburden on the heap. Now mines can't do that.

Minor editing of English language required: correct line 336 "Office3"

Author Response

1. A very interesting work showing the potential of using rubber waste. The research goal set by the authors was achieved. However, I am concerned that further long-term studies are needed to test the effect of rubber additives on soil toxicity. In Europe, under the influence of environmental protection, it is forbidden to bury rubber waste in the ground. Such treatments were used in the case of utilization of rubber conveyor belts, where the waste was covered with overburden on the heap. Now mines can't do that.

Response : We totally agree with the reviewer’s comment. In this study, we could only investigate the short-term effect; a long-term effect should be carefully studied before implementation. In addition, it can be predicted that the addition of rubber crumb to soil inevitably causes microplastic problems. We therefore added this concern to the revised manuscript so that readers would be aware of this issue. (see in lines 45, 80)

 

2. Minor editing of English language required: correct line 336 "Office3"

Response : Correction has been made as kindly suggested, as shown in lines 352.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this study Pattanawanichai et al. investigated the utilization of waste tires crumb rubber for the reduction of compaction in soil, it’s a novel study and lies within the scope of the journal “sustainability”.

Overall, this manuscript is well written and briefly arranged throughout all the sections. The authors did extensive work, and several different experiments were conducted. However, the results section is not very clear and needs to be explained clearly and in more detail.

I would like to see a better version of the result. The current version lacks enough information particularly there is no information regarding the role of rubber tires crumb as how much percentage (%) it improved water permeability, and reduced bulk density.

I would like to see the statistical analysis table of these figures, and provide as supplementary data set.

I would also recommend the following minor corrections before its final publication.

Peer Review Comments Sheet

Line number 42: What is “lateritic soils”.

Line number 124: check “L-crum.b”

Line number 374, 379: recheck the reference style.

The English is fine and undestanable.

Author Response

1. I would like to see a better version of the result. The current version lacks enough information particularly there is no information regarding the role of rubber tires crumb as how much percentage (%) it improved water permeability, and reduced bulk density.

Response : The relationship between rubber crumb content and water permeability is given in Figure 7. With increasing crumb content, water permeability increased regardless of the crumb particle size. Obviously, the small crumb sample showed greater water permeability than the large crumb sample when compared at the same crumb rubber content. An explanation is also given, as shown in lines 260. Similarly, the relationship between crumb rubber content and bulk density is given in Figure 6. Clearly, the bulk density of the compacted soil diminished gradually with increasing crumb rubber content, indicating the reduction of soil compaction in the presence of crumb rubber. An explanation is given as shown in lines 234. Overall, the % improvement in water permeability and the % reduction in bulk density depend greatly on the rubber crumb content, as shown in Figures 6 and 7.

 

2. I would like to see the statistical analysis table of these figures and provide as supplementary data set.

Response : In this study, the average values from three measurements were used to plot the graphs. The standard deviation (SD) was also given as an error bar. A supplementary data set is given below.

Table 1 Bulk density of the compacted soils at various water contents.

Water content (%wt.)	Bulk density (g/cm3)
	Test no. 1	Test no. 2	Test no. 3	average	std.
2	1.775	1.793	1.736	1.77	0.029
4	1.890	1.893	1.871	1.88	0.012
6	1.943	1.969	1.946	1.95	0.014
8	1.948	1.933	1.957	1.95	0.012
10	1.904	1.833	1.836	1.86	0.040

 

Table 2 Bulk density of the soil matrix in the unfilled and filled specimens.

S-Clumb
Crumb rubber loading (%wt.)	Bulk density (g/cm3)
	Test no. 1	Test no. 2	Test no. 3	average	std.
0	1.91	1.96	1.99	1.953	0.040
20	1.499	1.462	1.495	1.485	0.020
25	1.275	1.387	1.428	1.363	0.079
30	1.409	1.488	1.523	1.473	0.058
35	1.508	1.379	1.427	1.438	0.065
M-Clumb
Crumb rubber loading (%wt.)	Bulk density (g/cm3)
	Test no. 1	Test no. 2	Test no. 3	average	std.
0	1.91	1.96	1.99	1.953	0.040
20	1.584	1.653	1.638	1.625	0.036
25	1.532	1.66	1.635	1.609	0.068
30	1.564	1.733	1.631	1.643	0.085
35	1.658	1.459	1.739	1.619	0.144
L-Clumb
Crumb rubber loading (%wt.)	Bulk density (g/cm3)
	Test no. 1	Test no. 2	Test no. 3	average	std.
0	1.91	1.96	1.99	1.95	0.040
20	1.669	1.86	1.885	1.805	0.118
25	1.733	1.848	1.961	1.847	0.114
30	1.643	1.595	1.835	1.691	0.127
35	1.609	1.78	1.672	1.687	0.086

 

Table 3 Water permeability of the soil matrix in the unfilled and filled specimens.

S-Clumb
Crumb rubber loading (%wt.)	Water permeability (m/day)
	Test no. 1	Test no. 2	Test no. 3	average	std.
0	0.00	0.000	0.000	0.00	0.000
20	0.220	0.220	0.212	0.22	0.005
25	0.274	0.274	0.274	0.27	0.000
30	0.291	0.291	0.286	0.29	0.003
35	0.323	0.307	0.297	0.31	0.013
M-Clumb
Crumb rubber loading (%wt.)	Water permeability (m/day)
	Test no. 1	Test no. 2	Test no. 3	average	std.
0	0.000	0.000	0.000	0.00	0.000
20	0.072	0.072	0.074	0.07	0.001
25	0.074	0.075	0.074	0.07	0.001
30	0.094	0.094	0.097	0.10	0.002
35	0.202	0.210	0.210	0.21	0.005
L-Clumb
Crumb rubber loading (%wt.)	Water permeability (m/day)
	Test no. 1	Test no. 2	Test no. 3	average	std.
0	0.000	0.000	0.000	0.00	0.000
20	0.049	0.053	0.049	0.05	0.002
25	0.058	0.063	0.063	0.06	0.003
30	0.070	0.066	0.066	0.07	0.002
35	0.080	0.080	0.083	0.08	0.002

 

Table 4 Cone index at various depths of the compacted soils.

Plot 1
Soil depth (cm)	Cone index (kPa)
	Test no. 1	Test no. 2	Test no. 3	Test no. 4	average	std.
5	3795.00	3812.00	3760.00	3777.50	3786.13	22.40
10	3829.00	3798.00	3822.00	3815.00	3816.00	13.29
15	3869.00	3871.00	3859.00	3894.00	3873.25	14.80
20	N/D	N/D	N/D	N/D	N/D	N/D
25	N/D	N/D	N/D	N/D	N/D	N/D
30	N/D	N/D	N/D	N/D	N/D	N/D

 

Plot 2
Soil depth (cm)	Cone index (kPa)
	Test no. 1	Test no. 2	Test no. 3	Test no. 4	average	std.
5	3415.33	3553.33	3277.00	3599.33	3461.25	145.60
10	3507.33	3639.50	3530.33	3633.67	3577.71	68.67
15	3496.00	3795.00	3794.67	3570.50	3664.04	154.06
20	3599.33	3346.00	3726.00	3312.00	3495.83	199.94
25	3570.50	3691.00	3829.00	3277.00	3591.88	234.99
30	3605.00	3754.00	3532.00	3415.00	3576.50	141.87

 

Plot 3
Soil depth (cm)	Cone index (kPa)
	Test no. 1	Test no. 2	Test no. 3	Test no. 4	average	std.
5	3208.33	3231.33	3277.00	3288.67	3251.33	37.87
10	3254.33	3254.33	3288.67	3323.33	3280.17	33.02
15	3265.67	3254.33	3312.00	3334.67	3291.67	38.00
20	3265.67	3254.33	3312.00	3369.33	3300.33	52.33
25	3265.67	3254.33	3323.33	3357.67	3300.25	48.77
30	3265.67	3265.67	3346.00	3357.67	3308.75	49.97

 

Table 5 Water permeation rate of various plots.

Plot area	Water permeability (m/day)
	Test no. 1	Test no. 2	Test no. 3	Test no. 4	average	std.
Plot No. 1	3.381	5.712	5.742	3.916	4.69	1.22
Plot No. 2	5.310	5.480	4.870	5.140	5.20	0.26
Plot No. 3	10.410	9.784	10.504	10.210	10.23	0.32

 

Table 6 Water quality after the extraction.

Test items	Concentration (parts per million: ppm)
	Test no. 1	Test no. 2	Test no. 3	average	std.
Calcium carbonate (CaCO3)	162	172	175	170	7
Sulfate (SO42-)	76	72	77	75	3
Chloride (Cl -)	30.5	30.8	32	31	1
Nitrate (NO3 -)	1.11	1.12	1.16	1.13	0.03
Fluoride (F -)	N/D	N/D	N/D	N/D	N/D
Ferric (Fe)	0.200	0.202	0.207	0.203	0.004
Manganese (Mn)	0.041	0.044	0.045	0.043	0.002
Copper (Cu)	N/D	N/D	N/D	N/D	N/D
Zinc (Zn)	35.72	34.95	35.02	35.2	0.4
Lead (Pb)	0.0022	0.0019	0.002	0.0020	0.0002
Chromium (Cr)	N/D	N/D	N/D	N/D	N/D
Cadmium (Cd)	N/D	N/D	N/D	N/D	N/D
Arsenic (As)	N/D	N/D	N/D	N/D	N/D
Mercury (Hg)	N/D	N/D	N/D	N/D	N/D

 

In the manuscript, it is stated at the end of the manuscript that the data presented in this study are available on request from the corresponding authors, in case readers may want to see them.

 

3. I would also recommend the following minor corrections before its final publication.

Line number 42: What is “lateritic soils”.

Response : Laterite soil is the leached residue resulting from the natural process of laterization in tropical and sub-tropical regions. The laterite soil is generally formed where the parent rock is rich in alumina, iron, and silica. Consequently, laterite soil contains a major portion of alumina and iron sesquioxide. The color of the laterite soil is either purplish or brick red. It is widely used as a pavement material in tropical regions, especially in Southeast Asia. Additional information has been added to the revised manuscript, as shown in lines 42.

Line number 124: check “L-crumb”

Response : Correction has been made as kindly suggested, as shown in lines 133.

Line number 374, 379: recheck the reference style.

Response : Correction has been made as kindly suggested, as shown in lines 390 395.

Author Response File: Author Response.pdf

Reviewer 3 Report

The work concerns rubber crumbs produced from used tires, which can be used to reduce the degree of soil compaction and to improve the porosity, and permeability of the soil. The work is interesting and presents new information. However, the reviewer has very serious concerns about the leaching of heavy metals from the rubber crumbs and the adverse environmental impact. Manuscript should be considered for publication, only after major revisions:

·        Line 130 replace „condition” with conditions.

·        2.1. Materials - How was a representative sample of the rubber crumb obtained?

·        2.5. Determination of contaminated water quality -Please describe in detail the methodology for metal determination using ICP, Shimadzu model ICPMS-2030, and anions using ion chromatography.

·        2.5. Determination of contaminated water quality - Shouldn't authors make rubber crumb extraction repeating several times with different samples? in the tested samples, the content of heavy metals was low in one sample (S-crumb). Why was such a small amount of rubber crumb taken into the study? The water extract usually contains 10% of the tested material. Why was the leachability of impurities from M-crumb and L-crumb samples not tested? According to the reviewer, the study of the extracts should be repeated several times with the content of 10% of each rubber crumb. Only then will it be possible to answer whether impurities are washed out of the rubber crumb.

·        3.1. Characterization of the soil sample- Have other soil properties such as porosity, consistency, structure, viscosity, firmness, and organic content been investigated? If possible, please complete the information in the main text.

·        Is there a natural substance that can be used to improve the porosity, permeability of the soil? If so, compare the results of natural materials with those of soil crumbs.

Minor editing of English language required.

Author Response

The work concerns rubber crumbs produced from used tires, which can be used to reduce the degree of soil compaction and to improve the porosity, and permeability of the soil. The work is interesting and presents new information. However, the reviewer has very serious concerns about the leaching of heavy metals from the rubber crumbs and the adverse environmental impact. Manuscript should be considered for publication, only after major revisions:

Response : We also agree with the reviewer’s comment about the long-term environmental impact. We therefore urge readers to be aware of the long-term impact before implementation. Concerning the release of heavy metals, we believe that the amount of released heavy metals is very low because the compounding ingredients in tires do not contain large amounts of heavy metals, except for zinc. However, we have included this concern in the conclusion (see lines 290, 349).

1. Line 130 replace “condition” with conditions.

Response : Correction has been made as kindly suggested, as shown in lines 139.

2. Materials - How was a representative sample of the rubber crumb obtained?

Response : Photographs of the representative rubber crumb samples are added to the revised manuscript as shown in Figure 1.

3. Determination of contaminated water quality -Please describe in detail the methodology for metal determination using ICP, Shimadzu model ICPMS-2030, and anions using ion chromatography.

Response : Additional information about the determination of water quality has been included in the revised manuscript, as shown in lines 155.

4. Determination of contaminated water quality - Shouldn't authors make rubber crumb extraction repeating several times with different samples? In the tested samples, the content of heavy metals was low in one sample (S-crumb). Why was such a small amount of rubber crumb taken into the study? The water extract usually contains 10% of the tested material. Why was the leachability of impurities from M-crumb and L-crumb samples not tested? According to the reviewer, the study of the extracts should be repeated several times with the content of 10% of each rubber crumb. Only then will it be possible to answer whether impurities are washed out of the rubber crumb.

Response : We selected only the S-crumb sample for the extraction because this S-crumb sample showed the greatest potential for solving the hardpan soil problem, and it will be used in the field test. In addition, the crumb producer has informed us that all samples (S-, M-, and L-crumb) were taken from the same production lot by using wasted truck tires as raw materials. Actually, the extraction has been done three times, and the average value is reported. To avoid confusion, the standard deviation of the measurements has been added to the revised manuscript as shown in Table 3. During the extraction, 1,250 g of the crumb sample was immersed in 5 L of water (5,000 g) which is equivalent to 25% w/w (higher than 10%). We increased the percentage of the sample in water because we wanted to make sure that the amount of extracted rubber chemicals was sufficiently high and detectable.

5. Characterization of the soil sample- Have other soil properties such as porosity, consistency, structure, viscosity, firmness, and organic content been investigated? If possible, please complete the information in the main text.

Response : We are afraid that we do not have the requested information. Since we focused on the soil compaction problem, we therefore characterized only parameters significantly affecting or indicating soil compaction, such as particle size, pH, and bulk density (which might be inversely related to porosity). We will keep the reviewer’s comment in mind for our future work.

6. Is there a natural substance that can be used to improve the porosity, permeability of the soil? If so, compare the results of natural materials with those of soil crumbs.

Response : In theory, the addition of organic substances to soil can reduce the degree of soil compaction through a reduction in soil-soil interaction and, thus, alleviate the hardpan problems. Most decomposable natural substances can then be used. However, because most natural substances decompose in a short period of time, they need to be added to the soil regularly. Crumb rubber, on the other hand, takes a very long time to decompose and, thus, less action is needed in the long term. However, a long-term adverse effect must be thoroughly investigated before implementation because there are other issues to be discussed, such as microplastics and the significant release of zinc into the environment.

In the literature, De la Rosa, et. al. revealed the reduction in soil compaction by the addition of olive waste biochar. However, they indicated a reduction in soil compaction due to the significant reduction in resistance to the penetrability of the amended soils. As a consequence, we cannot compare the results with the crumb addition.

José, M.D.L.R.; Paloma, C.; Antonio, D.E. Soil biochar application: assessment of the effects on soil water properties, plant physiological status, and yield of super-intensive olive groves under controlled irrigation conditions. Agronomy. 2022, 12, 2321. https://doi.org/10.3390/agronomy12102321.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors made corrections to the manuscript and answered all questions and concerns. In actual form, the reviewer recommends the manuscript for publication.