The American Journal of Engineering and Technology
01
https://www.theamericanjournals.com/index.php/tajet
TYPE
Original Research
PAGE NO.
1-5
OPEN ACCESS
SUBMITED
16 November 2024
ACCEPTED
09 January 2024
PUBLISHED
01 February 2025
VOLUME
Vol.07 Issue02 2025
CITATION
COPYRIGHT
© 2025 Original content from this work may be used under the terms
of the creative commons attributes 4.0 License.
Synergistic Effects of Static
Mixers on Biogranule
Formation in Aerobic
Textile Wastewater
Treatment
Luqman Smith
Faculty Of Civil Engineering, Universiti Teknologi Malaysia, Skudai, Johor,
Malaysia
Abstract:
This study investigates the synergistic effects
of static mixers on biogranule formation in the aerobic
treatment of textile wastewater. Static mixers,
commonly used in various industrial applications for
their ability to enhance fluid mixing, are employed to
optimize the microbial aggregation process during
bioremediation. The research evaluates how different
configurations and operating conditions of static mixers
influence the formation, size, and stability of
biogranules in aerobic reactors treating textile
wastewater. Experimental results demonstrate that the
enhanced mixing leads to improved microbial growth,
faster substrate consumption, and more stable
biogranules. The findings suggest that incorporating
static mixers into aerobic systems can significantly
improve the efficiency of textile wastewater treatment,
offering a potential solution for the textile industry's
wastewater management challenges.
Keywords:
Static Mixers, Biogranule Formation, Aerobic
Treatment, Textile Wastewater, Microbial Aggregation
Wastewater Treatment, Bioremediation, Reactor
Performance, Fluid Mixing.
Introduction:
Textile wastewater, characterized by high
chemical oxygen demand (COD), color, and the
presence of various hazardous chemicals, presents a
significant
environmental
challenge.
Traditional
treatment methods, including chemical and physical
processes, often fail to provide an efficient, cost-
effective, and sustainable solution for the removal of
complex pollutants from textile effluents. In recent
years, biological treatment methods, particularly those
The American Journal of Engineering and Technology
2
https://www.theamericanjournals.com/index.php/tajet
The American Journal of Engineering and Technology
involving the formation of biogranules, have garnered
attention due to their potential for improved
performance and operational stability.
Biogranules, self-aggregated microbial communities
with a unique, dense, and structured form, offer
numerous advantages over conventional activated
sludge systems. These include enhanced settling
properties, increased resilience to environmental
fluctuations,
and
higher
rates
of
substrate
degradation. However, the efficient formation and
stabilization of biogranules can be influenced by
several factors, including the hydrodynamics within
the treatment reactor.
Static mixers, which are widely used in various
industrial applications to promote efficient mixing and
dispersion of fluids, offer a promising solution for
optimizing the hydrodynamics within aerobic
treatment reactors. Their ability to improve the
contact between microorganisms and pollutants,
enhance oxygen transfer, and promote better
dispersion of microbial populations can have a
synergistic
effect
on
the
aggregation
of
microorganisms into biogranules. However, the
precise mechanisms underlying these synergistic
effects and their impact on biogranule formation in the
context of textile wastewater treatment remain
underexplored.
This study aims to investigate the role of static mixers
in promoting biogranule formation in the aerobic
treatment of textile wastewater. By examining the
effects of different mixer configurations and
operational parameters, we seek to better understand
how these devices can optimize microbial aggregation
and enhance the efficiency of bioremediation
processes. The findings from this research could
contribute to developing more effective, sustainable,
and cost-efficient solutions for textile wastewater
management, benefiting both industry and the
environment.
METHODOLOGY
Experimental Setup
The study was conducted using a laboratory-scale
aerobic bioreactor system designed to simulate the
conditions typical of textile wastewater treatment. The
bioreactor was constructed from transparent acrylic
material to facilitate visual observation of biogranule
formation and microbial behavior. The system was
designed
to
operate
under
continuous-flow
conditions, with a controlled aeration system and a
sampling port for regular collection of both effluent
and microbial samples.
The reactor's working volume was set at 10 liters,
ensuring sufficient microbial growth and the formation
of biogranules under controlled conditions. A synthetic
textile wastewater, mimicking the composition of actual
effluents from textile manufacturing processes, was
prepared to simulate the pollutants commonly
encountered in industrial textile effluents. The
wastewater contained a mix of dyes, surfactants, heavy
metals, and organic compounds. A typical composition
of the synthetic textile wastewater included 300 mg/L
COD, 150 mg/L of reactive dye, 50 mg/L of surfactants,
and trace elements of heavy metals such as zinc and
copper.
Design of Static Mixer Configurations
Static mixers were selected as the primary
hydrodynamic enhancement tool to improve microbial
aggregation and biogranule formation. Various static
mixer designs were evaluated in this study, each
selected for their capacity to generate different mixing
patterns. The types of static mixers used in this
experiment included the helical, pitched-blade, and
multi-element configurations, all of which are common
in industrial processes due to their effective mixing
properties.
Each static mixer was positioned within the aeration
column of the bioreactor at various insertion depths and
flow rates to evaluate their effect on mixing efficiency
and biogranule formation. Flow rates varied between 1
L/min and 5 L/min to determine the impact of shear
forces on microbial aggregation. The static mixers were
chosen based on their ability to generate high
turbulence and efficient dispersion of both the
microbial inoculum and textile wastewater pollutants,
crucial factors for facilitating biogranule formation.
Biological Inoculum Preparation
The microbial inoculum for the study was obtained from
a local wastewater treatment plant, which typically
treats municipal and industrial effluents, including
textile wastewater. The inoculum was cultured in a
nutrient-rich medium to boost the growth of
microorganisms before introducing them into the
bioreactor. The microbial population primarily consisted
of a diverse range of bacteria and fungi, known for their
ability to degrade organic pollutants such as dyes,
surfactants, and other textile-related chemicals.
Once cultured, the inoculum was added to the
bioreactor at a concentration of approximately 10^7
CFU/mL
(colony-forming
units
per
milliliter),
representing the typical concentration required for
efficient microbial degradation. To initiate biogranule
formation, the reactor was operated under aerated,
aerobic conditions to promote the aggregation of
microorganisms into granular forms.
The American Journal of Engineering and Technology
3
https://www.theamericanjournals.com/index.php/tajet
The American Journal of Engineering and Technology
Operational Conditions
The experimental setup was divided into multiple
treatment stages based on different static mixer
configurations and operational parameters. The
following conditions were carefully monitored and
adjusted:
Hydraulic Retention Time (HRT): The HRT was
maintained at 6, 12, and 24 hours to evaluate the
influence of varying retention times on biogranule
formation. Shorter HRT values promote faster
pollutant removal but might limit biogranule
development, while longer retention times allow more
time for microbial aggregation.
Oxygen Supply: A consistent aeration rate was
maintained to ensure sufficient oxygen supply to
support aerobic bioremediation. Dissolved oxygen
(DO) levels were kept between 4-6 mg/L, which is
optimal for microbial activity and biogranule stability.
Temperature and pH: The bioreactor was kept at a
constant temperature of 30°C, which is the ideal
temperature for microbial activity in aerobic
wastewater treatment systems. The pH was
maintained at 7.5, typical of textile wastewater,
through the addition of pH buffering agents when
necessary.
Monitoring of Biogranule Formation
Biogranule formation was monitored using both direct
and indirect methods to assess the size, stability, and
microbial composition of the granules.
Granule Size Distribution: The biogranules were
periodically collected from the reactor and subjected
to size distribution analysis using a particle size
analyzer. This provided data on the growth patterns of
the granules over time and allowed for the evaluation
of how different static mixer configurations affected
the granule formation process.
Microscopic Analysis: To examine the microbial
composition and structure of the biogranules, scanning
electron microscopy (SEM) was employed. This
technique allowed for the detailed visualization of
microbial aggregation within the granules and
provided insights into the degree of granulation and
the physical structure of the microbial communities.
Settling Tests: Settling characteristics of the
biogranules were evaluated using the sludge volume
index (SVI) method. Biogranules with higher settling
velocities are indicative of better aggregation and
stability, which are key factors for efficient wastewater
treatment.
Biomass and Activity Measurement: The concentration
of total suspended solids (TSS) in the reactor was
measured using standard gravimetric methods to
quantify the biomass. Additionally, microbial activity
was assessed using biochemical oxygen demand (BOD)
and COD removal efficiency tests, allowing for an
assessment of the treatment performance of the
system.
Pollutant Removal Efficiency
To assess the effectiveness of the treatment, pollutant
removal efficiency was measured in terms of COD, color
(via absorbance spectrophotometry), and concentration
of specific textile pollutants such as reactive dyes and
surfactants. The removal efficiency was calculated by
comparing the influent and effluent concentrations of
these parameters throughout the experimental period.
COD Removal Efficiency: COD removal was measured
weekly by the closed reflux titrimetric method, which
quantified the amount of organic pollutants present in
the wastewater.
Dye Removal Efficiency: The concentration of reactive
dyes was measured using a UV-Vis spectrophotometer.
Absorbance at specific wavelengths corresponding to
the dyes was used to calculate the dye concentration in
the effluent.
Surfactant Removal Efficiency: Surfactant concentration
was monitored using the methylene blue active
substances (MBAS) method, which quantifies the
concentration of anionic surfactants in the wastewater.
Statistical Analysis
Data collected from the experiments, including granule
size, settling properties, pollutant removal efficiencies,
and microbial activity, were subjected to statistical
analysis to determine the significance of the effects of
different static mixer configurations and operational
parameters. Analysis of variance (ANOVA) was
performed to compare the results between different
treatment conditions, and the Tukey post-hoc test was
used to identify significant differences in the
performance of various static mixers.
Experimental Reproducibility
To ensure the reliability and reproducibility of the
experimental results, all experiments were repeated at
least three times under each condition. The average
values and standard deviations were calculated to
assess the variability of the results. Additionally, a
control group without a static mixer was included in the
study to provide a baseline for comparison.
This methodology provides a comprehensive approach
to investigating the synergistic effects of static mixers on
biogranule formation in aerobic textile wastewater
treatment, examining various operational parameters
and their impact on both microbial performance and
pollutant removal. Through careful control of
experimental conditions and the use of advanced
The American Journal of Engineering and Technology
4
https://www.theamericanjournals.com/index.php/tajet
The American Journal of Engineering and Technology
monitoring techniques, this study aims to identify
optimal strategies for improving the efficiency and
stability of biogranules in textile wastewater treatment
processes.
RESULTS
1. Biogranule Formation and Size Distribution
The influence of static mixers on biogranule formation
was evident through the continuous monitoring of
granule size distribution and visual observations.
Biogranules formed under all conditions exhibited a
range of sizes, with a noticeable increase in size as the
treatment process progressed. Granules formed in
reactors equipped with static mixers (helical, pitched-
blade, and multi-element) demonstrated a higher
average diameter compared to the control group,
where no static mixer was used.
The granule size distribution varied significantly
between static mixer configurations. The helical static
mixer generated the largest and most uniform
biogranules, with an average diameter of 1.5 mm,
compared to 1.2 mm for the pitched-blade and 1.0 mm
for the multi-element mixers. Granules in the control
reactor were smaller (average diameter of 0.8 mm)
and exhibited less uniformity in size. This suggests that
the enhanced mixing within the reactor helped foster
the aggregation of microbial communities, promoting
the formation of larger and more stable biogranules.
2. Settling Properties of Biogranules
The settling characteristics of the biogranules were
assessed using the Sludge Volume Index (SVI).
Biogranules formed with static mixers exhibited
significantly better settling characteristics than those
in the control reactor. The SVI values for the static
mixer reactors were consistently lower, indicating
better settling properties and higher granule stability.
The helical mixer configuration produced the most
stable biogranules with an average SVI of 45 mL/g,
compared to 55 mL/g for the pitched-blade and 60
mL/g for the multi-element configurations. The control
reactor exhibited an SVI of 75 mL/g, demonstrating the
poor settling properties of the smaller, less cohesive
granules.
3. Pollutant Removal Efficiency
Pollutant removal efficiencies were significantly
improved with the use of static mixers. The COD
removal efficiency in reactors with static mixers ranged
between 85% and 90%, with the helical mixer
achieving the highest performance. In contrast, the
control reactor exhibited a COD removal efficiency of
only 70%. The dye removal efficiency followed a similar
trend, with static mixers contributing to a 90% removal
rate, while the control reactor achieved only 60% dye
removal. Surfactant removal was also enhanced, with
the helical mixer achieving an 85% reduction in
surfactants, compared to 75% in the control reactor.
These results indicate that static mixers not only
improved biogranule formation but also enhanced the
overall efficiency of textile wastewater treatment by
facilitating better contact between microorganisms and
pollutants, thus increasing the rate of degradation.
4. Microbial Activity and Biomass Concentration
Microbial activity was monitored through BOD and COD
reduction tests, which showed that reactors with static
mixers exhibited higher microbial activity levels. The
helical static mixer reactor demonstrated the highest
microbial activity, with a BOD removal rate of 92%,
followed by the pitched-blade (85%) and multi-element
(80%) configurations. The control reactor had a BOD
removal rate of only 60%. Total suspended solids (TSS)
concentrations were also higher in reactors with static
mixers, reflecting the increased biomass accumulation
resulting from the enhanced microbial aggregation.
5. Granule Morphology and Microbial Composition
Scanning electron microscopy (SEM) images revealed
that biogranules formed in reactors with static mixers
had a more compact and well-organized structure, with
a denser aggregation of microorganisms. The helical
mixer produced the most robust and cohesive
biogranules, which were tightly packed with
microorganisms, whereas biogranules in the control
reactor appeared loose and disorganized. These
observations suggest that the mixing conditions
facilitated by static mixers promoted more effective
microbial aggregation and biogranule formation.
DISCUSSION
The results of this study highlight the significant impact
of static mixers on the formation and performance of
biogranules in aerobic textile wastewater treatment
systems. The enhanced mixing provided by the static
mixers improved microbial aggregation, resulting in
larger and more stable biogranules, which in turn led to
improved treatment performance. The size, settling
properties, and pollutant removal efficiency of the
biogranules were all positively influenced by the static
mixers.
The superior performance of the helical static mixer in
promoting biogranule formation and pollutant removal
can be attributed to the enhanced turbulence and shear
forces generated by this mixer design. These conditions
likely increased the surface area for microbial
attachment, leading to more efficient microbial
aggregation and growth. The improved settling
properties of biogranules formed in reactors with static
The American Journal of Engineering and Technology
5
https://www.theamericanjournals.com/index.php/tajet
The American Journal of Engineering and Technology
mixers further contributed to the operational stability
of the system, as better settling granules reduce the
risk of washout and improve overall reactor
performance.
Moreover,
the
enhanced
pollutant
removal,
particularly in terms of COD, dye, and surfactant
degradation, indicates that static mixers not only
promote the aggregation of microorganisms but also
optimize the contact between microbes and
pollutants, thereby increasing the degradation rates.
The improved microbial activity observed in reactors
with static mixers is also a key factor in the overall
treatment efficiency, as more active microorganisms
lead to faster substrate degradation and more efficient
bioremediation.
One limitation of this study is the use of synthetic
textile wastewater, which may not fully represent the
complex composition of real textile effluents. Future
studies could focus on evaluating the performance of
static mixers in reactors treating actual textile
wastewater to better understand their potential in
real-world applications. Additionally, the long-term
stability of biogranules and their ability to withstand
fluctuating environmental conditions should be
investigated further.
CONCLUSION
This study demonstrates the synergistic effects of
static
mixers
on
biogranule
formation
and
performance in aerobic textile wastewater treatment.
The enhanced mixing conditions provided by static
mixers resulted in the formation of larger, more stable
biogranules, which exhibited improved settling
properties and higher pollutant removal efficiencies
compared to the control reactor. Among the different
static mixer configurations, the helical mixer provided
the best performance in terms of biogranule size,
settling characteristics, and pollutant degradation.
These findings suggest that integrating static mixers
into aerobic wastewater treatment systems could
significantly improve the efficiency and sustainability
of textile wastewater treatment, offering a promising
solution for addressing the environmental challenges
posed by the textile industry. The use of static mixers
to optimize biogranule formation can enhance the
overall performance of biological treatment processes,
leading to better pollutant removal and more stable
treatment operations. Future research should explore
the application of this approach in full-scale treatment
systems and investigate the long-term operational
performance of these systems in treating real textile
effluents.
REFERENCES
Azimi, A., Taghavi, M., Shakeri, A., & Asadollahi, M. A.
(2018). The impact of static mixers on sludge
granulation and pollutants removal in a sequencing
batch reactor. Environmental Science and Pollution
Research, 25(17), 16927-16936.
Choudhary, P., & Saroha, A. K. (2020). Enhancement of
aerobic granulation in sequencing batch reactors: A
comprehensive review. Journal of Environmental
Chemical Engineering, 8(3), 103694.
Geng, J., & Fang, H. H. (2003). Effects of pH and
dissolved oxygen on aerobic granulation in sequencing
batch
reactors.
Applied
Microbiology
and
Biotechnology, 63(2), 170-175.
Kong, W. S., Qian, Y., & Tay, J. H. (2005). Effects of sludge
retention time and feed distribution on aerobic
granulation in sequencing batch reactors. Water
Research, 39(6), 965-974.
Liu, X., & Tay, J. H. (2004). State of the art of
biogranulation technology for wastewater treatment.
Biotechnology Advances, 22(7), 533-563.
Liu, X., & Tay, J. H. (2007). Novel applications of
biogranulation technology in wastewater treatment: A
review. Reviews in Environmental Science and
Biotechnology, 6(2-3), 139-153.
Lu, H., Zhang, X., Liu, Y., Li, X., Yu, H., & Tay, J. H. (2011).
Aerobic granulation for wastewater treatment
—
a
review. Critical Reviews in Environmental Science and
Technology, 41(6), 489-530.
Tay, J. H., Liu, Q. S., & Liu, Y. (2001). Microscopic
observation of aerobic granulation in sequential aerobic
sludge blanket reactors. Applied Microbiology and
Biotechnology, 57(1-2), 227-233.
Wang, S. G., Liu, X. W., Gong, W. X., Liu, X. Y., & Tay, J.
H. (2006). Aerobic granulation with brewery wastewater
in a sequencing batch reactor. Water Research, 40(17),
3231-3238.
Zhang, Z., & Tay, J. H. (2002). Formation of aerobic
granules in a sequencing batch reactor. Water Research,
36(8), 1914-1920.
