Ain Shams Engineering Journal 15 (2024) 102701
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Full Length Article
Biofilm formation monitoring using SEM in synthetic wastewater pollutant
removal by combination of DAF and modified MBBR
Sazan Mohammed Ali *, Shoukr Qarani Aziz
Civil Engineering Department, College of Engineering, Salahaddin University, Erbil, Erbil, Kurdistan Region, Iraq
A R T I C L E I N F O
A B S T R A C T
Keywords:
DAF
MBBR
Wastewater
Treatment
Biofilm
SEM
Nowadays, moving bed biofilm reactors (MBBR) and dissolved air flotation (DAF) are frequently used in com­
bination for the biological and physical treatments of synthetic oily wastes. The efficiency of the biocarriers
utilized in MBBR is crucial since it has a big impact on the system’s overall performance. A study was carried out
utilizing a DAF-MBBR technique to treat synthetic oily wastewater in order to evaluate this. Two different kinds
of biocarriers were used in this modified MBBR: polyethylene and plastic bottle caps. The result showed the DAFMMBBRs process demonstrated excellent removal efficiencies for a range of parameters. Moreover, it seemed
that DAF had higher COD, nitrite, nitrate, and turbidity removal efficiencies. For COD, the average removal
efficiency was 39.62%; for oil and grease, it was 77.05%; and for ammonia, it was 39.71%. In the same way,
MBBR1 is effective at eliminating phosphate, ammonia, TSS, and oil and grease. For COD, the average removal
efficiency was 39.12%; for oil and grease, it was 94.10%; and for ammonia, it was 85.42%. The average removal
efficiencies for COD, oil and grease, and ammonia in MMBBR2 were 38.76%, 84.95%, and 86.49%, respectively.
Furthermore, Scanning electron microscopy (SEM) was used to assess the biofilm within the system. This
revealed a well-developed biofilm layer on the interior surfaces of the biocarriers, improving the effectiveness of
synthetic wastewater treatment. Excellent removal efficiencies were shown by the DAF-MBBR system for a range
of parameters during a ten-day operational period.
1. Introduction
The main reason oily wastewater is challenging to treat is that it
consists of two phases: a continuous phase (the medium of suspension)
and a dispersed phase (the suspended droplets of water or oil) (Barambu
et al., 2021) [1]. Nowadays, dissolved air flotation (DAF) technology has
been widely used in many industries to treat various types of waste­
waters such as oil refineries, laundries, paper making, car washings,
metal processing and many other industries. Four basic steps are
involved in the DAF process, including generating bubbles in waste­
water. Water bubbles contact suspended particles. Gas bubbles attach to
suspended particles. In addition, floated material is skimmed off the
surface as the air/solid combination rises (Shammas et al., 2010) [2]. In
addition, an extremely effective biological treatment process is the
Moving Bed Biological Reactor (MBBR). Based on conventional acti­
vated sludge and bio filter processes, it is designed to reduce wastewater
discharge by MBBR. This is a continuous operation biological reactor
that is completely mixed that involves growing biomass on little carrier
elements with a little lighter density than water and keeping them in
motion along with a water stream inside the reactor. MBBR provides a
more specific volume than any other biological system with a similar
apparent volume. Currently, modern MBBR methods involve the utili­
zation of mobile submerged biocarriers within aeration tanks, effec­
tively amalgamating two distinct processes. The technology involves
both attached and suspended biomass growth processes, enabling the
biodegradation of organic pollutants, nitrification, denitrification, and
ammonia removal to be efficiently executed (Banti et al., 2023) [3]. The
thickness of the biofilm stands as a key parameter in assessing MBBR
performance. Research indicates that when the biofilm exceeds 700 μm
in thickness, it becomes challenging to sustain nitrogen removal due to a
deficiency of substrate in the deep anaerobic layer. An essential factor
that influences the effectiveness of MBBR technology is the proper
design of the biocarrier. Ideal biocarriers should possess a substantial
specific surface area per unit volume. Other biocarrier attributes that
have a notable impact on MBBR performance encompass their material
composition, surface characteristics, orientation, pore spacing, and ge­
ometry (Elliott et al., 2017) [4]. Moreover, lower sensitivity to toxic
compounds, higher biomass levels, and an appropriate sludge-settling
* Corresponding author.
E-mail addresses: sazan.mohammed91@gmail.com (S.M. Ali), shoker71@yahoo.com (S.Q. Aziz).
https://doi.org/10.1016/j.asej.2024.102701
Received 25 October 2023; Received in revised form 26 January 2024; Accepted 12 February 2024
Available online 22 February 2024
2090-4479/© 2024 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Ain Shams University. This is an open access article under the CC
BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
S.M. Ali and S.Q. Aziz
Ain Shams Engineering Journal 15 (2024) 102701
Table 1
Wastewater characteristics.
Pollutants
Characteristics of
real refinery ww
Characteristics of
real car wash ww
Characteristics of
synthetic ww
COD (mg/L)
Oil and
grease
(mg/L)
TSS (mg/L)
196–2496
6–1600
144–970
0.4–1250
1500 ± 500
1500 ± 150
200–10,000
200–5800
10,000 ± 100
Table 2
Specifications Aquaflex BIOAQUA for MBBR1.
Descriptions
Technical details
Diameter of BioAQUA MBBR
Width of BioAQUA
No of inner departments
Approximate dia. of inner deprt
Surface Area of BIOAQUA MBBR
Material of BIOAQUA MBBR
Color of BIOAQUA MBBR
Media fill rate range % fill of Volume
Life Span
Density
26 mm
10 mm
19 qty
5 mm
650 m2/m3
PE vigrin
Natural white
%30–50
>15 year
0.92–0.96 g/cm3 (bulk density)
Table 3
Properties of disposed plastic caps for MBBR2.
Fig. 1. Prepared synthetic wastewater used in this study.
period are the main benefits of the MBBR method (Abdel-Shafy et al.,
2023)[5]. On the other hand, scanning electron microscopy (SEM)
proves to be a valuable method for examining the surface morphology of
biological specimens (Aneke and Adu, 2023) [6]. In the early days of
biofilm monitoring, which were predominantly in the 1980s, micro­
scopy played a significant role, with scanning electron microscopy
(SEM) being a prominent method. SEM was previously employed to
provide a detailed portrayal of bacteria within biofilms, offering the
ability to visualize individual bacteria and illustrate the biofilm’s
connection to the underlying surface (El Abed et al. 2012) [7]. The
integration of wastewater technologies is innovative and provides a high
level of adaptability, making it possible to treat effluents that are heavily
contaminated with organic substances. The main objective of this study
is to use integrated method of combined DAF-MMBBR as physiobio­
logical method to treat synthetic oily wastewater. Moreover. to char­
acterize the impact of biofilm on the surface of biocarriers before and
after experimental runs, the study focuses on evaluating the efficiency of
the biocarriers used in the modified MBBR by utilizing SEM to assess
biofilm formation and its impact on the treatment process.
Descriptions
Technical details
Diameter
Length
Surface area
Void ratio
Color
Density
3.1 cm
0.8 cm
3686 m2/m3
85%
blue
0.92 gm/cm3
oil and grease (O&G). Sieved soil played a role in determining the total
suspended solids (TSS) value. Additionally, synthetic wastewater solu­
tion was prepared using tap water (Fig. 1). Table 1 explained the char­
acteristics of real and synthetic wastewaters.
2.2. Properties of biocarriers used in MMBBR
In this study, two different types of media were introduced into
MBBR reactors: polyethylene and plastic bottle caps. Tables 2 and 3
provide the physical specifications of the MBBR media.
2.3. DAF disk diffusers
The DAF process causes particles to float because bubbles lower the
density of bubble-particle clusters, causing them to rise to the surface.
The bubbles are generated by employing a gas that possesses low solu­
bility in the liquid. Nevertheless, in practical applications, air is pre­
dominantly utilized as the gas of choice due to its easy availability,
safety, and cost effectiveness (Hung et al., 2017) [9]. To facilitate the
formation of these bubbles, diffusers were installed at the bottom of the
DAF reactor. These diffusers allowed the controlled flow of air from an
air compressor machine into the reactor. Table 4 presents the specifi­
cations of the disc diffusers utilized in this research.
2. Materials and methods
2.1. Samples and preparation of synthetic wastewater
Raw samples of oily wastewater were collected from Kewrgosek re­
finery and a car wash station in Erbil city, Iraq. The samples were ana­
lysed based on standard method for Examination of Water and
Wastewater (American Public Health Association APHA, 2012) [8]. COD
was measured by a spectrophotometer (Hatch DR3900). Additionally,
separation funnels were used to determine the concentration of oil and
grease inside the samples. Filter paper, muffle furnace, oven and digital
weighing instruments were used to TSS tests. Then based on the real
wastewater quality, a synthetic wastewater was prepared. Three pri­
mary elements, namely organic sources such as starch, diesel derived
from car oil, and finely sieved soil, constituted the wastewater solution.
Starch served the purpose of achieving optimal Chemical Oxygen De­
mand (COD). Car oil diesel was employed to attain the desired value for
2.4. Pilot plant and experimental arrangements
Laboratory setup was created to integrate DAF-MMBBR and a clari­
fier. This system includes a 60-liter container for storing and preparing
synthetic wastewater on a daily basis. Subsequently, a water pump is
employed to transfer the wastewater into the DAF reactor. The DAF
reactor, positioned at the upper part of the experimental setup, has a
2
S.M. Ali and S.Q. Aziz
Ain Shams Engineering Journal 15 (2024) 102701
Table 4
Specifications of disc diffusers used in this study.
Type
Total height
(mm)
Diameter effective/total
(mm)
Perforated area
(m3)
Capacity (m3/
h)
Material of
membrane
Total weight
(kg)
Outlet
ADD80-762
mm
46
60/80
0.002
2–5
EPDM
0.04
190 mm
male
Fig. 2. Experimental setup of combined DAF-MMBBR.
Fig. 3. Pilot plant layout.
3
S.M. Ali and S.Q. Aziz
Ain Shams Engineering Journal 15 (2024) 102701
Fig. 4. Acclimazation phase of DAF-MBBRs reactors.
volume of 55 L and a 10 cm freeboard. Within the DAF reactor, four disk
diffusers generate bubbles to facilitate flotation and push contaminants,
especially oil and grease, to the reactor’s surface. These impurities are
manually removed and skimmed from an open space connected to a
valve.
The flotation process relies on an air compressor linked to diffusers to
supply air. Additionally, an air flow meter device is employed to regu­
late the air flow rate, ensuring that the DAF reactor functions at the
prescribed rate of air flow. To control this rate, a valve is incorporated
into the DAF reactor. Following flotation, the wastewater is allowed to
flow by gravity into two parallel MBBR reactors, each with a 35-liter
capacity. These reactors are equipped with different bio media:
MBBR1 employs polyethylene (PE) media, while MBBR2 uses plastic
bottle caps. Mixers are installed in the MBBR reactors to ensure proper
mixing of the bio media with the wastewater, providing oxygen for
biofilm growth on the bio carriers’ surfaces and distributing bio carriers
evenly within the reactors. Each MBBR reactor is filled with 50% bio
media. Subsequently, the treated wastewater is directed to two identical
clarifier reactors, each with a volume of 35 L. Each reactor is equipped
with a control valve for collecting effluent samples and a sludge
discharge port at the bottom to remove excess sludge. To transport the
effluent from the laboratory setup to the external sewerage system, a
plastic pipe is connected. Additionally, Figs. 2 and 3 in the documen­
tation illustrates specific details of the pilot plant.
Fig. 5. Observing biofilm formation during adaptation phase.
air flow rate. As for MBBRs, acclimation is with mixing time of 15 min
and HRT of 12 h. The removal efficiencies of COD, oil and grease,
ammonia (NH3-N) and TSS were conducted for both DAF and MBBRs.
The following equation was employed to calculate the removal
efficiency:
Removal% =
3. Results and discussions
Ci − Cf
× 100
Ci
(1)
where: Ci: initial concentration of the parameter, Cf: final concentration
of the parameter.
The initial startup of reactors involved acclimating them to allow
more biofilm to grow around the media during a 6 days operation
period. The same concept of acclimation is adapted by (Sayyahzadeh,
et al. 2016; Magdum and Kalyanraman, 2019; Majid and Mahna, 2019;
Wang, et al. 2020) [11–14]. Fig. 4 demonstrate the outcomes of the
adaptation phase for the DAF-MBBRs. It is noteworthy to mention that
during the adaptation days, the performance of the MBBRs showed a
near parallel trend. After 6 days of operation, the optimum experiments
3.1. Adaptation phase of DAF-MBBR
The start-up operation of DAF-MBBR were carried out after adapta­
tion phase for a few days. Startup stage was aimed at facilitating system
adaptation to the new conditions, promoting a robust biofilm to be
formed on the MBBRs’ prepared media for treatment of synthetic
wastewater derived from DAF reactor effluents, and ensuring thorough
treatment (Shahriari and Shokouhi, 2015) [10]. In this phase, DAFMBBR was acclimated with 35-minute aeration duration and 60 L/min
4
S.M. Ali and S.Q. Aziz
Ain Shams Engineering Journal 15 (2024) 102701
Table 5
Removal efficiencies of DAF-MBBRs operation.
DAF
NO.
Parameters (%)
Day 1
Day 2
Day 3
Day 4
Day 5
Day 6
Day 7
Day 8
Day 9
Day 10
Min.
Max.
Avg.
1
2
3
4
5
6
7
8
9
COD
Oil and grease
Ammonia (NH3-N)
TSS
NO2
NO3
PO-3
4
Color
Turbidity
45.00
36.28
64.29
56.41
30.00
62.96
12.50
53.10
1.94
47.98
83.26
64.29
63.00
35.00
44.44
0.00
53.08
1.35
42.50
86.51
52.68
69.51
35.00
53.70
20.00
53.08
1.91
40.28
88.37
52.68
54.48
35.00
62.96
20.00
53.98
41.69
30.94
67.91
26.96
51.38
23.75
49.07
32.20
66.37
14.16
35.43
87.91
26.96
50.59
41.67
49.07
20.00
73.03
10.31
35.43
79.07
26.96
43.08
63.33
25.93
25.00
48.67
2.24
39.46
79.65
28.57
43.08
53.33
53.70
35.00
48.67
2.24
43.77
82.56
26.96
45.06
46.67
62.96
29.00
52.18
10.31
35.43
79.07
26.79
43.08
50.00
72.22
30.00
48.67
2.24
30.94
36.28
26.79
43.08
23.75
25.93
0.00
48.67
1.35
47.98
88.37
26.79
69.51
63.33
72.22
35.00
73.03
41.69
39.62
77.05
39.71
51.96
41.38
53.70
22.37
55.08
8.84
MBBR1
1
2
3
4
5
6
7
8
9
COD
Oil and grease
Ammonia (NH3-N)
TSS
NO2
NO3
PO-3
4
Color
Turbidity
43.13
99.27
79.50
94.92
7.14
25.00
82.86
62.53
95.69
45.10
97.22
80.00
87.45
48.72
16.67
81.00
66.05
75.61
40.93
93.10
82.26
95.90
43.59
56.00
90.88
47.94
95.98
42.66
92.00
82.26
94.88
10.26
65.00
94.13
51.73
91.68
43.25
97.10
88.51
95.52
30.00
23.64
79.38
45.26
97.10
41.56
92.31
88.51
93.80
14.29
23.64
80.00
31.76
96.13
30.42
91.11
88.26
88.54
9.09
41.00
65.33
52.41
95.78
40.00
91.43
90.00
88.89
10.71
40.00
55.00
52.41
95.76
25.03
93.33
89.49
94.46
31.25
25.00
61.97
48.93
95.38
30.56
95.06
88.54
93.06
33.33
16.67
57.14
52.41
95.76
25.03
91.11
79.50
87.45
7.14
16.67
55.00
31.76
75.61
45.10
99.27
90.00
95.90
48.72
65.00
94.13
66.05
97.10
39.12
94.10
85.42
92.71
22.78
35.10
76.73
51.00
93.23
MBBR2
1
2
3
4
5
6
7
8
9
COD
Oil and grease
Ammonia (NH3-N)
TSS
NO2
NO3
PO-3
4
Color
Turbidity
49.62
99.27
78.00
94.71
7.14
25.00
85.43
63.77
95.69
41.12
97.22
80.50
73.64
48.72
16.67
72.50
63.77
75.61
49.62
86.21
83.77
94.97
43.59
56.00
92.13
63.77
95.98
40.84
80.00
83.77
91.75
7.69
67.00
88.13
63.77
91.68
41.82
92.75
89.73
94.94
40.98
23.64
77.50
63.77
96.63
27.78
69.23
89.73
93.00
37.14
23.64
87.50
63.77
95.50
35.00
82.22
89.73
88.54
9.09
55.00
66.67
63.77
91.76
29.63
81.71
90.00
88.89
25.00
50.00
69.23
63.77
91.76
42.02
78.67
89.98
88.67
28.13
37.50
70.42
63.77
91.02
30.17
82.22
89.76
88.54
20.00
16.67
57.14
63.77
91.76
27.78
69.23
78.00
73.64
7.14
16.67
57.14
17.98
75.61
49.62
99.27
90.00
94.97
48.72
67.00
92.13
64.16
96.63
38.76
84.95
86.49
89.76
26.74
37.11
76.66
48.89
91.74
were 41.38% and 53.70% respectively. Removing PO-3
4 in wastewater
was another goal in this study. PO-3
4 removal was 22.37%. According to
Kim et al. (2015) [19], DAF reactor could remove %53 of total phos­
phate. This depends on the operating condition of the reactor. Moreover,
the highest color removal of %73 was attained by DAF. This result close
to the result gained by Palaniandy et al. (2010) [20] resulting in 70%
color removal using DAF with coagulant inside the reactor. Removal
efficiency of turbidity ranged from 1.35 to 41.69%. the highest of 42%
was achieved by Palaniandy et al. (2010) [20]. TSS was another
pollutant that need to be treated effectively. In this study, the average
removal efficiency of TSS was 51.9%. This result is higher than the result
obtained by Wilinski and Naumczyk, (2012) [21] where TSS removal
was 45.2% by DAF and dissolved ozone floatation process.
were conducted to the reactors to observe the removal efficiency of the
pollutants, namely COD, oil and grease, TSS and NH3-N. During first few
days, the removal of pollutants was fluctuated then from 4th day of
operation the values became constant and close to the target removal
efficiencies. Additionally, a thin yellowish layer of biofilm was also
observed encompassing the media (Fig. 5). These obtained results were
also supported by Capodici et al. (2017) [15] and Abdulgader et al.
(2020) [16] where the systems were run as an approach to acclimatize
the microorganisms in the reactor.
3.2. Performance of DAF-MMBBR
During this stage, both DAF and MBBRs were operated in a contin­
uous mode for an additional 10 days period. The experiments were
undertaken of flotation time of 10 min and air flow rate 72 L/min. in
addition, HRT for both MBBRs was 23.5 hr and mixing time of 13 min
and 22 min for MBBR1 and MBBR2 respectively. The performance of the
reactors was observed based on the removal of pollutants such as COD,
oil and grease, TSS and ammonia. Additionally, further measurements of
parameter removal were conducted including phosphate (PO4), NO2,
NO3, PO-3
4 , color and turbidity. Table 5 presents the efficiency of
pollutant removal during the 10 days operation of the DAF and MBBR.
3.2.2. Performance of MMBBRs
Industrial wastewater was effectively treated by the MBBR. Ac­
cording to the Table 5, the maximum average removal efficiency for oil
and grease in MBBR1 and MBBR2 were (94.10% and 84.95%) respec­
tively. This is because DAF reactor alone cannot remove most of the oil
and grease. Thus, DAF followed by MMBBR can achieve better oil and
grease removal efficiency. The same result recorded by Mahmoudkhani,
et al., (2012) [22]. In addition, COD average removal efficiency for
MMBBR1 and MMBBR2 were 39.12% and 38.76%. It appeared that the
MBBR can remove organic matter in a stable and efficient manner, a
similar point was already made by Ødegaard et al. (2004) [23]. On the
other hand, in a wastewater treatment plant, Total Suspended Solids
(TSS) is a key measure of system performance and the quality of treated
wastewater. Average TSS removal efficiency for both MMBBBRs showed
a good removal efficiency (92.71% and 89.76%) compared to DAF
reactor. This is because at 23.5 hrs of HRT, TSS concentrations gradually
decreased, since the particles had more time to settle and attach to the
surfaces of the media. In another research a TSS removal efficiency of
88% was observed at 12 hr HRT (Zinatizadeh and Ghaytooli, 2015) [24].
In another study using multistage flexible. The average amount of
removal efficiencies for turbidity for both MMBBRs were higher than
90%. This result indicated that the pilot plant performed well during this
3.2.1. Performance of DAF
From Table 5, the maximum average removal efficiency for DAF was
oil and grease (77.05%). While average COD removal was (39.62%).
Because more contact time; flotation time can cause greater removal in
COD and oil and grease. More time cause more air bubbles to dissolve to
pollutants and float them to the surface (Sinaga, et al. 2022) [17]. The
removal of oil and grease was considerably high. The highest oil and
grease removal of 88% was achieved. This is close to the result of Rat­
tanapan et al. (2011) [18]. A removal of 81.65% was obtained by DAF
system for the treatment of biodiesel wastewater. Additionally, as DAF
has aeration inside the reactor, then it allows nitrification happen and
converting more ammonia to nitrite and nitrate. A removal of 39.71%
was recorded for ammonia removal. However, removal of NO2 and NO3
5
S.M. Ali and S.Q. Aziz
Ain Shams Engineering Journal 15 (2024) 102701
Fig. 6. Biofilm formation before and after MMBBRs operation a) MBBR1 B) MBBR2.
Fig. 7. SEM photos of MBBR1 biocarrier (a, b and c): clean biocarrier, (d, e and f): after formation of biofilm.
experiment. In addition, the result of turbidity close to result of El
Moussaoui et al., (2018) [25]. Color was another pollutant in treatment
of synthetic oily wastewater. The average color removal efficiency for
MMBBR1 and MMBBR2 were 51% and 48.89%. longer HRT and
appropriate mixing time can enhance in color removal. Moreover, the
performance of both MMBBRs had a good stability in removing
ammonia. the removal efficiencies were from 79.5 to 90% for MMBBR1
and 78–90% for MMBBR2. The rate of phosphate is related to the mi­
crobial activity and biomass growth which directly related to HRT.
Because longer HRT can extent the contact time between microorgan­
isms and biocarriers to take up and remove phosphates (PO4). From the
Table 5, both MMBBRs removed phosphate of 76%. The same result was
achieved by Al-Zuhairy et al., (2015) [26] for the treatment of sewage
wastewater by hybrid MBBR-activated sludge. The average removal of
ammonia in MMBBR1 and MMBBR2 were 85% and 86%. In the nitrifi­
cation process, ammonia is converted into more oxidized nitrogen
compounds such as nitrite and nitrate, which are then converted into
nitrogen gas by denitrification.
3.3. Biofilm formation in MMBBRs
There is little understanding of the design and operation of biofilm
reactors in the field of environmental biotechnology. Biofilms grow on
carriers float freely within the reactor’s water volume in a moving bed
biofilm reactor. In addition, with an MBBR, the biofilm carrier is
buoyant, free-moving, and requires mechanical mixing or aeration to
distribute throughout the tank (Lewandowski and Boltz, 2011) [27].
In this study, to observe biofilm formation before and after system
operation. Scanning electronic microscopy (SEM) was used before and
after formation of biofilm. The carriers became slippery at the end of the
MMBBR system compatibility period after biofilms formed on their
surfaces. Roughly a week after the adaptation period ended, there was a
noticeable increase in the number of biofilms. Fig. 6 depicts the inner
and outer surfaces of the carriers both before and after the biofilm layers
6
S.M. Ali and S.Q. Aziz
Ain Shams Engineering Journal 15 (2024) 102701
Fig. 8. SEM photos of MBBR2 biocarrier (a, b and c): clean biocarrier, (d, e and f): after formation of biofilm.
formed. It’s important to highlight that for certain media packings, only
a very thin biofilm layer is visible on their outer surfaces.
This occurs as a result of aeration and the carriers colliding, which
leads to the biofilm on their outer surfaces being dislodged and
becoming suspended biomass. Therefore, the inner surface of the media
packings is regarded as a significant area for the development of biofilms
(Majid and Mahna, 2019) [13]. Figs. 7 and 8 illustrated the photos ob­
tained from SEM before and after biofilm formation for both media
carriers (polyethylene and plastic bottle cap). It seems that the micro­
organisms adhering to the carriers primarily consisted of spherical
bacteria. The same result was gained by (Wang et al. 2020) [14].
for various parameters. DAF appeared to have better removal effi­
ciencies for COD, nitrite, nitrate, and turbidity. The average removal
efficiencies were 39.62% for COD, 77.05% for oil and grease, and
39.71% for ammonia. Similarly, MBBR1 performs well in removing oil
and grease, ammonia, TSS, and phosphate. The average removal effi­
ciencies were 39.12% for COD, 94.10% for oil and grease, and 85.42%
for ammonia. MMBBR2 showed average removal efficiencies of 38.76%
for COD, 84.95% for oil and grease, and 86.49% for ammonia.
Furthermore, the SEM analysis revealed a substantial biofilm layer on
the surface of both biocarriers, indicating the effectiveness of the bio­
logical treatment process.
4. Conclusion
Declaration of Competing Interest
In conclusion, the study provides valuable insights into the treatment
of synthetic oily wastewater using DAF-MBBR technologies. The com­
bination of DAF and MMBBR demonstrated efficient removal of pollut­
ants, with the SEM analysis confirming the formation of a welldeveloped biofilm layer on the biocarriers’ surfaces. The results under­
score the potential of this integrated method for effective synthetic
wastewater treatment, offering a promising approach for enhancing
treatment efficiency and resource conservation. In addition, two bio­
carriers were used, for MMBBR1, high-density polyethylene was used as
the bio carrier, while plastic water bottle caps served as the bio carrier
for MMBBR2. The DAF reactor operated with a 35-minute aeration
duration and a 60 L/min air flow rate. In the case of MMBBRs, a 15-min­
ute mixing time and a 12-hour hydraulic retention time (HRT) were
applied. The test results demonstrate the promising potential of this
treatment system in achieving significant average removal efficiencies
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
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