Teknomekanik, Vol. 6, No. 2, pp. 122-135, December 2023
e-ISSN: 2621-8720 p-ISSN: 2621-9980

The effectiveness of the multi-soil-layering system in reducing pollutant
parameters of crumb rubber industrial wastewater
Sri Rizki Putri Primandari1, Mulianti1, Gusni Sushanti2*, Mohamed Gabbasa3 and
Muneer M. Ba-Abbad4
Department of Mechanical Engineering, Faculty of Engineering, Universitas Negeri Padang,
Padang, INDONESIA
2
Chemical Engineering Program, Graduate School of Advanced Science and Engineering,
Hiroshima University, Hiroshima, JAPAN
3
Department of Chemical & Process Engineering, Higher Institute of Science & Technology of
Zawia, Tripoli, LIBYA
4
Gas Processing Center, College of Engineering, Qatar University, Doha, QATAR
© The Author(s)
Published by Universitas Negeri Padang.
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1

* Corresponding Author: d220842@hiroshima-u.ac.jp
Received Oct 22nd 2023; Revised Dec 04th 2023; Accepted Dec 06th 2023
Cite this

https://doi.org/10.24036/teknomekanik.v6i2.27672

Abstract: Multi-soil-layering (MSL) is well-known as an emerging technology for wastewater
treatment. However, limited studies have been conducted on the crumb rubber industry. Thus,
this study aims to reduce the crumb rubber industrial wastewater using MSL system. Four models
of MSL conducted it. They are (1) constructed by body size of gravel with a mixture of andosol soil
and fine charcoal; (2) body size of gravel with a mixture of andosol soil, fine charcoal, sawdust, and
iron particles; (3) tube size of gravel with a mixture of andosol soil and fine charcoal; and (4) tube
size of gravel with a mixture of andosol soil, fine charcoal and sawdust. The construction models
were installed in the variance of the box and each of them was flowed by the Hydraulic Loading
Rate of wastewater. Aeration treatment is given to the maximum hydraulic loading rate. The result
showed that MSL systems significantly minimize the crumb rubber industrial wastewater under
requirements that cover Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD),
Total Suspended Solid (TSS), Total Nitrogen (T-N) and Total ammonia (T-NH3). It also
significantly neutralizes the power of Hydrogen (pH) up to 6. The highest reduction was obtained
by the MSL 3 system (tube size of gravel with a mixture of andosol soil and fine charcoal). The
aeration significantly decreased the BOD, COD, TSS, and ammonia from 85% to 99%. Although
the aeration process enhanced the performance of MSL system, however, MSL without aeration
successfully treated the wastewater to meet the required standard. This study provides new insight
into the effectiveness of MSL system in reducing pollutant parameters of crum rubber industrial
wastewater.
Keywords: Adsorption; Wastewater treatment; Aerobic process; Anaerobic process.
1.

Introduction

Many crumb rubber industries are located on the side of rivers. The industry uses a lot of water and
chemicals, producing a lot of wastewater and effluent [1], [2]. The discharge of untreated
wastewater into waterways or rivers causes water pollution, which has a negative impact on human
life [3], [4]. With the new global trend toward sustainable development, the industry must focus
on cleaner production technologies, wastewater reduction and minimization, water recycling and
utilization, and resource recovery [5], [6], [7]. The crumb rubber industries produce wastewater of
an average of 50-100 m3/hour after a chemical treatment process. The wastewater could not be
disposed of directly into the river since it has many pollutants [4]. According to the results of
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periodic monitoring and preliminary analysis of the quality of wastewater disposal by the industry,
it does not comply with the quality standard of environmental requirements [8], [9].
Wastewater in the crumb rubber industry is sourced from raw materials and processes. The crumb
rubber industry uses a lot of water to wash raw materials obtained from tappers, which are still
dirty and even deliberately filled with wood, metal, and sand [10]. The wastewater becomes liquid
and odorous waste [11], [12]. Generally, industrial wastewater from crumb rubber is acidic,
containing dissolved and deposited suspended solids [13] The Biochemical Oxygen Demand (BOD)
and Chemical Oxygen Demand (COD) values are quite high, the nitrogen content is mainly from
ammonia which is used as a latex-fixing ingredient [14]. High BOD and COD in wastewater show
high levels of organic matter [15]. Increasing levels of organic matter will further disrupt the
environmental ecosystem that receives wastewater because oxygen is used by decomposing bacteria
to destroy these organic materials. Lack of oxygen, the death of living things and the presence of
organic material in wastewater generated the emergence of various microorganisms that have the
potential to cause disease [16].
The discharge of liquid waste by land can take place in physical, chemical and biological processes,
it has been known from the past as an effective method and has been used as one of the natural
wastewater treatments [17]. Processing of this method is very cheap, but it requires a large area of
land when compared to modern systems [18]. Where this land is unlimited and the price is cheap,
this system can easily be applied for wastewater treatment. However, processing with this system
has serious problems with permeability, where the processing capacity is limited per unit area.
Sandy soils have high permeability with an infiltration rate of 1.8 to 3.6 m 2/day, but the chemical
and biological ability is not as well as clay soils which have an infiltration rate of only 0.9-0.3 m2/day
[19]. An example of the average flow rate in a treatment system using land is 10-40 l/m2 /day for
traditional trench systems and 1-8 1/m2/day for slow-rate land treatment systems [8].
Biological methods and mechanical methods have been used in the crumb rubber industrial
wastewater treatment. Several studies have focused on biological methods that use microorganism
like Pseudomonas sp., Arthrobacter sp., native purple nonsulfur bacteria (PNSB), and
Rhodopseudomonas palustris specifically aimed at treating wastewater from the rubber industry
[20]–[23]. Although biological methods, particularly anaerobic, aerobic, and facultative ponds, are
widely used for the treatment of rubber wastewater, vast areas are required. Meanwhile,
mechanical methods such as rotating discs, anaerobic filter beds, and aerated lagoons require little
land, but the concentration of pollutants remains high [24]. Biological treatment presents a straight
forward approach to address nitrogen compounds within rubber industry wastewater. However, it
necessitates substantial space for installation and prolonged retention time. Conversely, membrane
treatment offers a compact setup, yields high-quality water, and consumes minimal energy. Yet, it
grapples with membrane fouling, impeding its broad and large-scale implementation [25]–[28].
Meanwhile, chemical treatments like coagulation/flocculation and AOPs prove less cost-effective
and carry the risk of causing secondary pollution in water bodies [29]–[32]. Overall, the selection
of advanced wastewater treatment methods hinges on several factors: (1) the extent to which a
method is needed to elevate wastewater quality to an acceptable level, (2) the adaptability of the
control method, (3) the expenses involved in the process, and (4) the compatibility of the method
with environmental concerns. Therefore, this wastewater must be addressed using appropriate
technologies such as Multi-Soil-Layering [24].
Multi-Soil-Layering (MSL) is one method of wastewater treatment that utilizes soil as the main
medium by enhancing its function through its structure to clean wastewater. Soil aggregate
structure is the key to purifying wastewater. The specific area of the aggregate surface area is
between 1-10 m2 [33]. Some advantages of MSL system are: (1) being able to decompose organic
substances such as BOD, COD, nitrogen and phosphate from liquid waste simultaneously; (2) able
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to prevent blockages; (3) able to accept high hydrolysis loading and absorption rates; (4) the
composition of the constituent coating material can be replaced by the available material [34], [35],
[36]. The system was formed in the construction of a soil layers mixture with 10-35% iron particles
and organic material with zeolite film in the form of bricks. Besides being able to prevent blockages,
the system is equipped with two processing zones, namely the aerobic zone in the zeolite layer and
the anaerobic zone in the soil mixture layer [37]. The MSL consists of two main processing zones,
namely the aerobic zone and the anaerobic zone. The aerobic zone is in the zeolite layer as a
permeable layer and the space between the zeolite layer and the mixed soil block. Anaerobic zones
are found in mixed soil layers as unpermeable layers. The liquid waste treatment process in the
Multi Soil Layering system consists of decomposition, fixation, nitrification, denitrification,
adsorption and absorption [38]. The aerobic and anaerobic conditions in the MSL system should be
regulated in such a way that all pollutants can be decomposed efficiently [39].
The efficiency of the MSL system also depends on the properties of the mixture coating material.
Perlite and charcoal have a special area that has the same absorption power as organic material with
zeolite. Gravel has the smallest area compared to other attachments, but organic waste liquid
material can coat the surrounding gravel like a film (thin layer) [40], [41], [42]. Perlite, zeolite and
charcoal have lower cation exchange capacity than zeolite, but higher than pearlite and gravel [43].
Therefore, ammonia and nitrogen absorb, and P fixation by pearlite, zeolite and charcoal is lower
than by zeolite and gravel [44]. The lowest fixation occurs in layers that are mixed with wax and
gravel [45]. If zeolite is replaced with zeolitized perlite, perlite, charcoal or gravel, the efficiency
of the system in purifying wastewater changes depending on the content of the material. Zeolitized
perlite, perlite, and charcoal have high specific areas so that they can absorb organic material as well
as zeolite [46]. Gravel has a smaller specific area compared to the previous material but the organic
material is placed around the gravel particles so that it can purify wastewater [47].
MSL system has been an emerging technology in wastewater treatment either domestic or industrial
bonded with pollutant parameters such as BOD, COD, TSS, T-N, total ammonia, and high acidity
[48]. Theoretically, it is suitable to be applied on crumb rubber industrial wastewater treatment.
However, there is a limited study on crumb rubber industrial wastewater [49]. Therefore, this study
aims to determine the effectiveness of the MSL system on crumb rubber industrial wastewater
treatment. The effectiveness is considered from the effect of hydraulic loading rate, aeration, MSL
model composite structure, and components on pollutant parameters such as BOD, COD, TSS, TN, T-NH3, and pH.
2.

Material dan methods

2.1 Material
Sampling was collected from crumb rubber industrial wastewater near Padang, West Sumatera,
Indonesia. The sampling is conducted according to SNI 6989.59:2008. Each treatment was taken
triplo sample (inlet and outlet) every day. Each sample was taken before treatment (untreated) and
after treatment by using MSL system (treated). The experimental model and its mechanism are
presented in Figure 1.
The samples were then placed into the MSL system from the upper side. The treated wastewater
output from bottom MSL system was collected and subjected to testing for pollutant parameters:
BOD, COD, TSS, total nitrogen (T-N), total ammonia (T-NH3), and pH specified in data analysis.

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Teknomekanik, Vol. 6, No. 2, pp. 122-135, December 2023
e-ISSN: 2621-8720 p-ISSN: 2621-9980

Treated wastewater

Figure 1: Laminate composite preparation
MSL system is classified into 4 models with different sizes and structures as follows:
(1) MSL 1, body size 50 x 75 x 100 cm, with gravel size 3 - 5 mm as compiler permeable layer
and a mixture of andosol soil and fine charcoal with a ratio of 2:1 as unpermeable layers.
(2) MSL 2, body size 50 x 75 x 100 cm, with gravel size 3 - 5 mm as a compiler permeable
layer and a mixture of andosol soil, fine charcoal, and sawdust, with the ratio of 2:0.5:0.5
and 10% iron particles as unpermeable layers.
(3) MSL 3, tube size 50 x 15 x 150 cm, with gravel size 3 - 5 mm as a compiler permeable
layer and a mixture of andosol soil and fine charcoal with a ratio of 2:1 as unpermeable
layers.
(4) MSL 4, tube size 50 x 15 x 150 cm, with gravel size 3 - 5 mm as a compiler permeable
layer and a mixture of andosol soil, fine charcoal and sawdust with a ratio of 2:0.5:0.5 as
unpermeable layers.
Each model of MSL system was tested with different hydraulic loading rates of 250, 500, 1000,
2000, 4000 and 8000 l/m2/day. Aeration is carried out for the highest wastewater rate tested. The
results of the analysis are compared with the crumb rubber industrial wastewater quality standards
according to Indonesia Ministry Decree No. 51 / MenLH /10/1995. The tools used in this study
consisted of a set of multi-soil-layering installation equipment, 5.5 mm and 2.5 mm sieves, gloves,
buckets, and laboratory equipment for analysis. Further, untreated and treated crumb rubber
wastewater were analyzed on pollutant parameters: BOD, COD, TSS, total nitrogen (T-N), total
ammonia (T-NH3), and pH.
2.2 Methods
Pollutant parameter BOD is analyzed by Winkler Titrimetric Method (SNI 06-6989.57-2008),
COD is analyzed by Iodometric method closed reflux (SNI 6989.2: 2009), TSS is calculated by
Gravimetric method with Whatman microfiber glass filter no 42 and accordance with SNI
6989.3:2019. Total nitrogen (T-N) and total ammonia (T-NH3) were determined by Nessler using
a spectrophotometer DR 2000/2010. Meanwhile, pH is measured by a pH meter which has been
calibrated by a buffer solution and accordance with SNI 6989.11:2019. The test was conducted
with 3 repetitions. The percentage of reduction (%R) is determined by the percentage of reduction
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between untreated concentration (UC) and treated concentration (TC) as follows:
%R=
3.

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3.1

UC−TC
UC

x 100%

(1)

Results and discussion
Pollutant parameters of untreated wastewater

The results of the analysis of untreated crumb rubber industrial wastewater are shown in Table 1.
None of the pollutant parameters of untreated wastewater comply with quality standards.
Untreated wastewater contains severe organic content BOD of 85-255 mg/l and COD of 259-830
mg/1, and its colour is brown with high turbidity. This result was aligned with [15], [16], [50] and
reported that crumb rubber industrial wastewater has high impurities. Theoretically, this is due to
the source of the ingredients it is natural material containing organic compounds such as proteins,
carbohydrates, lipids and organic salts that will be decomposed by the activity of microorganisms
over time [24], [51].
Table 1: Pollutant parameters of untreated crumb rubber industrial wastewater
Pollutant parameters
BOD, mg/l
COD, mg/l
TSS, mg/l
T-N, mg/l
T-NH3, mg/l
pH

Untreated wastewater
85 - 255
259 - 830
150 - 540
15 - 25
14 - 25
5.0 - 5.5

Quality standard
60
200
100
10
5
6-7

Besides that, it is also due to the addition of lumpy materials and latex stabilizers [50], [52].
Untreated wastewater is acidic liquid due to acetic acid or formic acid utilization during the
clumping process and also because of the formation of free fatty acids as a result of the activity of
microorganisms.
3.2

MSL system on reducing pollutant parameters of treated wastewater

The results of the analysis of treated crumb rubber industrial wastewater by using MSL system are
shown in Table 2.
Table 2: Analysis of treated crumb rubber industrial wastewater by using MSL
Pollutant parameters
BOD, mg/l
COD, mg/l
TSS, mg/l
T-N, mg/l
T-NH3, mg/l
pH

Treated wastewater
0.1 – 13
3 -76
15 – 80
0.2 – 9.4
0.04 – 4.9
6

Quality standard
60
200
100
10
5
6-7

All of the pollutant parameters of treated wastewater comply with quality standards. MSL systems
can reduce pollutant parameters of crumb rubber industrial wastewater, especially BOD and COD,
which are the most critical in wastewater by more than 90%. Other parameters of TSS, T-N and
T-NH3 also showed a high decrease and an increase in pH to the specified limit and fulfilled the
quality standard requirements. The comparison of MSL system’s effect on minimizing wastewater
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between the crumb rubber industry and domestic waste is almost the same but higher than the palm
oil industry [20], [21]. The decrease in BOD and COD of palm oil wastewater by MSL was 80%
and 65%, respectively [53], [54]. The high ability of the MSL system in treating industrial crumb
rubber wastewater is due to crumb rubber industrial wastewater containing only organic substances
and suspended solids but not containing oils and fats such as those contained in the oil palm industrial
wastewater, so the process of biodegradation of organic substances by microorganisms decomposers
that live in a layer of soil mixture, the layers of gravel can run perfectly, as well as the process of
absorption of suspended solids by other constituent components in the MSL installation. This is
supported by the statement of [33] which states that the presence of fat oil along with dissolved
suspensions tends to accumulate and cover the surface of the condenser while the substance is
insoluble which results in blocking the activity of microorganisms [55]. Further comparison
between untreated and treated wastewater, and the percentage of reduction is shown in Table 3.

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Table 3: Analysis of treated crumb rubber industrial wastewater by using MSL
Pollutant
parameters
BOD, mg/l
COD, mg/l
TSS, mg/l
T-N, mg/l
T-NH3, mg/l
pH

Untreated
wastewater
85 - 255
259 - 830
150 - 540
15 - 25
14 - 25
5.0 - 5.5

Treated
wastewater
0.1 – 13
3 -76
15 – 80
0.2 – 9.4
0.04 – 4.9
6

% Reduction
94.90 - 99.88
90.84 - 98.84
85.18 - 90
62.4 - 98.67
80.4 - 99.71
Comply the standard

Table 3 shows that the MSL system effectively reduces all pollutant parameters in crumb rubber
industrial wastewater, especially BOD and COD. This is supported by the study [11], [24]. The
change in pH from 5.0 - 5.5 to 6 is due to the presence of a soil layer on the MSL system.
Theoretically, soil can neutralize pH due to the soil's ability to hold basic cations such as Ca 2+, Mg2+,
Na+, K+ and acidic cations such as H+ and Al3+, thus when the soil is in an acidic condition, there
will be an exchange of acidic cations with basic cations and vice versa [56]. The existence of the
exchange can cause a change in pH, both a change in pH caused by the soil itself and a change in soil
pH caused by the presence of other substances in the soil or passing through the soil. This study is
supported by [57] that soil has a high buffering capacity against changes in chemical and physical
conditions due to the activity of microorganisms and physical reactions caused when the liquid waste
treatment mechanism occurs in the MSL system.
The effectiveness of the MSL system in reducing all pollutant parameters because the MSL
mechanism consists of two treatment zones, the aerobic zone and the anaerobic zone. The aerobic
zone is found in the rock layer (gravel) and the space between the rock layer and the andosol soil
mixture block, while the anaerobic zone is in the soil mixture layer. The wastewater treatment
process in the MSL system consists of decomposition, fixation, nitrification, denitrification,
filtration, adsorption, and absorption [11]. The process of decomposition of organic material
occurred in the aerobic and anaerobic zones. The adsorption process is on the surface of the
energetic mixed layer in the aerobic zone and the rock layer while the absorption process is in the
anaerobic zone in the soil mixed layer. The organic material of the wastewater is adsorbed in the
upper layer of the andosol soil mixture and the surface of the rock layer will then be decomposed
by the aerobic microorganisms that stick there. While adsorbed into the soil mixture layer will be
decomposed by anaerobic microorganisms that live in the soil mixture layer. Filtration of suspended
and dissolved substances occurs when liquid waste enters the layer of the MSL system. The
reference states that the organic material of the liquid waste is adsorbed in the top layer of the
andosol soil mixture as well as the surface of the gravel. Microorganisms in the soil and in the
biofilm formed on the zeolite decompose the adsorbed and absorbed organic material [58], [59].
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3.3 Effect of hydraulic loading rate on pollutant parameters
The results of the analysis of the effect of variations in Hydraulic Loading Rate (HRL) on the
percentage of decreasing levels of parameters (BOD, COD, TSS, T-N, and T-NH3) and pH are
presented in Figure 2.
100

Reduction (%)

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98
96
94
92
90
88
0

1000

2000

3000

4000

5000

6000

T-N

T-NH3

7000

8000

HLR (l/m2/day)
BOD

COD

TSS

Figure 2: Effect of HLR on pollutant parameters in reduction percentage
HRL affects the percentage decrease in pollutant parameters (BOD, COD, TSS, T-N, and T-NH3).
The percentage is inversely proportional to HRL, the higher the percentage of decline and vice
versa. This is aligned with [23] that the HRL is inversely proportional to the percentage of reduction
in the treated wastewater. The process that occurs in MSL which consists of the filtration process,
decomposition, nitrification, and denitrification, organic substances and suspended solutions in
wastewater will be filtered and degraded by a population of microorganisms that attach to the
surface of gravel and layers of soil mixture. Further absorbed into the biofilm as a plant food
ingredient. While nitrogen as ammonia will be broken down by the Nitrobacter bacteria in the
nitrification process that occurs in the layers of gravel, nitration will be converted to nitrogen gas
in the soil mixture [58]. The lower the HRL, the process will take place slowly too, so the residence
time will be longer. With longer contact at each layer, the process runs perfectly. Likewise, HRL
is higher, processes are fast and partial. Hydraulic loading rate significantly influences wastewater
treatment, especially in the rate of decomposition and denitrification.
In Figure 2, MSL system is capable of receiving high HRL up to 8000 l/m 2/day and is still able to
reduce the levels of pollutants effectively. MSL system is better compared with other natural
systems wastewater treatment methods such as constructed wetland, overland flow, and septic tank
systems [8], [33]. This is due to MSL structure being made like the arrangement of bricks so that
the permeability becomes high and the processing will take place repeatedly on each layer. The
structure of MSL system (a brick structure) will be able to receive a high loading rate and can
overcome blockages and allow them to occur repeatedly in each layer. However, HRL does not
affect the pH of crumb rubber industrial wastewater. This is due to the nature of the soil can
neutralize, thus, the soil has a high buffering capacity for changes in chemical and physical conditions
due to the influence of micro-organism activity. The physical reactions caused when the wastewater
treatment mechanism occurs in the MSL system, such as changes in pH caused by the quality of
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incoming water or the process of nitrification of ammonium, can be easily neutralized by ion-on Hexchange and other cations in the body and gravel surfaces.

The effect of aeration is considered as the percentage decrease in pollutants parameters of crumb
rubber industrial wastewater showed significant results. The results showed that aeration had a
significant effect on the percentage decrease in pollutant parameters, especially against BOD, COD,
TSS, T-N, and T-NH3. The percentage reduction in pollution levels increases with aeration, ranging
from 85% to 99%. In theory, the MSL system's ability to decompose waste in anaerobic conditions
is affected by aeration. According to [11], sufficient aeration treatment can help aerobic formation,
however after aeration for some time anaerobic conditions will be formed by itself in the MSL
system. This effect is due to aeration assisting in increasing the supply of dissolved oxygen needed
by microorganisms to carry out biodegradation activities on organic substances contained in waste,
especially in the middle and lower layers of the installation. In wastewater systems, aerobic
microorganisms require dissolved oxygen to carry out activities, if oxygen is limited, it can cause
the death of these microorganisms [60].
3.5

Effect of MSL model composite structure and components on pollutant
parameters

95

94.1

97.5

97.2

96

MSL 1

77.1

77.4

81

83.2

94

COD, MG/L

95.1

BOD, MG/L

86

96
95.3

98.6
97

The treatment of various models in the structure and constituent components of MSL on the
percentage of decrease in pollutants parameters (BOD, COD, TSS, T-N, and T-NH3) on the crumb
rubber industrial wastewater in Figure 3.
97.3
96
98.1
98

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3.4 Effect of aeration on pollutant parameters

TSS, MG/L

T-N, MG/L

MSL 2

MSL 4

MSL 3

T-NH3, MG/L

Figure 3: Effect of HLR on pollutant parameters in reduction percentage
Results showed that model MSL 3 reduces the highest percentage of pollutant parameters covering
BOD, COD, TSS, T-N, and T-NH3 compared to other MSLs models. MSL 3 is equipped with a
tube size 50 x 15 x 150 cm, with gravel size 3 - 5 mm as a compiler permeable layer and a mixture
of andosol soil and fine charcoal with a ratio of 2:1 as unpermeable layers.

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4.

Conclusion

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In this study, wastewater from the crumb rubber industry has been minimized by using a MultiSoil-Layering system to comply with quality standard requirements. The main findings of this study
are summarized below:
1. MSL systems significantly minimize the crumb rubber industrial wastewater to comply
with the quality standard requirement with pollutant parameters biochemical oxygen
demand (BOD), chemical oxygen demand (COD), total suspended solid (TSS), total
nitrogen (T-N) and total ammonia (T-NH3).
2. Hydraulic loading rate (HLR) affects the percentage reduction in pollutant parameters
(BOD, COD, TSS, T-N, and T-NH3). The percentage is inversely proportional to HLR,
the higher the percentage of decline and vice versa. MSL system is capable of receiving high
HRL up to 8000 l/m2/day and is still able to reduce the levels of pollutants effectively
3. MSL also significantly neutralizes the power of hydrogen (pH) up to 6.
4. The aeration significantly decreased the BOD, COD, TSS, T-N, and T-NH3 ranging from
85% - 99%. However, MSL without aeration has complied with the quality standard
requirement. Although MSL equipped with aeration process has better performance than
without aeration, treated wastewater from the crumb rubber industry by MSL system
without aeration has complied with the quality standard requirements.
5. The highest reduction was obtained by MSL 3 model (a tube size 50 x 15 x 150 cm, with
gravel size 3–5 mm as a compiler permeable layer and a mixture of andosol soil and fine
charcoal with a ratio of 2:1 as unpermeable layers).
In conclusion, MSL system has a significant effect on reducing pollutant parameters such as BOD,
COD, TSS, T-N, and T-NH3 in crumb rubber industry wastewater and complying with the standard
based on Indonesia Ministry Decree No. 51/MenLH /10/1995. However, some recommendations
for further studies could be provided for better results. For further studies, MSL could be applied
to other industrial wastewater and consider another advanced process to improve MSL system to
produce water supply for industrial processes. Another recommendation is physical pretreatment
such as sedimentation or settling tanks prior to the MSL system to decrease the working load of
MSL system, especially TSS. Further studies also could apply other carbon active such as coconut
shell as unpremeable layers.
Author contribution
Sri Rizki Putri Primandari: research conceptualization & writing – original draft. Mulianti: data
gathering; Methodology. Gusni Sushanti: data gathering, writing-result analysis. Mohamed
Gabbasa: Writing – review & editing; Visualization. Muneer M. Ba-Abbad: Writing – review &
editing.
Funding statement
This research received no specific grant from any funding agency in the public, commercial, or notfor-profit sectors.
Acknowledgements
The authors would like to express sincere gratitude to the Department of Mechanical Engineering
and Manufacture Laboratory, Faculty of Engineering, Universitas Negeri Padang. Other, the
authors also would like to express gratitude to Hiroshima University, Higher Institute of Science &
Technology of Zawia, and Qatar University for supporting this study.
130

Teknomekanik, Vol. 6, No. 2, pp. 122-135, December 2023
e-ISSN: 2621-8720 p-ISSN: 2621-9980

Competing interest
No potential conflict of interest was reported by the author(s).
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