Systematic Review
Advanced Oxidation Process in the Sustainable Treatment of
Refractory Wastewater: A Systematic Literature Review
Jorge Alejandro Silva
Escuela Superior de Comercio y Administración Unidad Santo Tomás, Instituto Politécnico Nacional,
Mexico City 11350, Mexico; ; Tel.: +52-55-5729-6000
Abstract: More than 4 billion people yearly suffer from global water scarcity amid climate
change, rapid population growth, and growing industrial activity. Due to the high con-
centrations of recalcitrant organic compounds, refractory wastewater is highly resistant
to conventional biological treatment and represents a critical obstacle for water reuse and
sustainable water management. A systematic literature review of 35 peer-reviewed arti-
cles published from 2010 to 2025 is provided to evaluate the utilization and sustainability
potential of advanced oxidation processes (AOPs) for treating recalcitrant wastewater.
Using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Anal-
yses) framework, the review assesses numerous AOPs, such as ozonation, UV/H2O2, Fen-
ton reactions, and photocatalysis, while also evaluating their performance, efficiency, and
integration ability. The results show that AOPs demonstrate pollutant removal rates often
greater than 96%, reduce sludge formation, and improve effluent biodegradability. They
can be applied at different treatment stages, combined with any renewable energy sys-
tems, and therefore can scale and be sustained, thereby aligning with UN Sustainable De-
velopment Goal 6. AOPs provide a technically feasible and eco-friendly solution for
higher quality wastewater treatment. In the face of increasing pressure on global water
resources, and the urgent need for sustainable water resource management, this study
offers valuable insights for policymakers and practitioners aiming to adopt resilient and
circular strategies for water.
Academic Editor: Shervin Hashemi
Keywords: advanced oxidation processes; Fenton reactions; hydroxyl radicals; refractory
Received: 10 March 2025
Revised: 10 April 2025
wastewater; sustainable wastewater treatment
Accepted: 10 April 2025
Published: 12 April 2025
Citation: Silva, J.A. Advanced
Oxidation Process in Sustainable 1. Introduction
Treatment of Refractory Wastewater: Water is an essential natural resource that supports nearly every life form on the
A Systematic Literature Review.
Earth’s surface. Although water covers over 70% of the Earth’s surface, only 2.5% is avail-
Sustainability 2025, 17, 3439.
able for human use [1]. Further breakdown indicates that only 1% of the available fresh-
https://doi.org/10.3390/su17083439
water is accessible and can be used to support domestic needs and commercial purposes
Copyright: © 2025 by the author.
[1]. Studies indicate that freshwater is becoming increasingly scarce, and more than 2 bil-
Licensee MDPI, Basel, Switzerland.
lion people globally have limited access to safe drinking water [1,2]. In 2022 alone, more
This article is an open access article
distributed under the terms and than 4 billion people faced water shortages at least once in 30 days [1,2]. This number
conditions of the Creative Commons would increase significantly if natural freshwater sources were either depleted or become
Attribution (CC BY) license inaccessible. A sustainable solution to the water shortage problems lies in the use of ad-
(https://creativecommons.org/license vanced technologies to convert more wastewater into a valuable economic and social re-
s/by/4.0/).
source.
Sustainability 2025, 17, 3439 https://doi.org/10.3390/su17083439
,Sustainability 2025, 17, 3439 2 of 37
Advanced wastewater treatment is a multidimensional approach aimed at purifying
wastewater and making it available worldwide for either domestic or commercial reuse.
Advanced wastewater treatment relies on sophisticated methods and technologies to re-
move organic contaminants and other complex compounds that would otherwise be dis-
charged back into circulation for reuse [2]. These advanced processes can be considered
tertiary because they purify water that has undergone primary and secondary treatment
processes [2,3]. However, these advanced treatment processes are not just designed for
removing complex compounds of wastewater. According to Amor et al. [3], advanced
wastewater treatment methods and technologies are also designed to meet stringent en-
vironmental standards to protect ecosystems from potentially harmful carbon com-
pounds. A study by Mousset et al. [4] found that sustainability is one of the key consider-
ations behind advanced treatment processes to enhance efficiency and reliability.
This study explores one of the most sustainable ways of treating refractory
wastewater to make it more viable for reuse. Refractory wastewater contains organic com-
pounds that are highly resistant to various biodegradation mechanisms [2,4]. This makes
it difficult to remove using conventional wastewater treatment mechanisms, where bacte-
ria are mostly used to break down organic compounds. Refractory organics mostly origi-
nate from pharmaceutical factories, paper-making factories, textiles factories, and even oil
refineries [4]. Refractory organic compounds can also be dangerous when released into
landfills or nearby rivers and lakes. For instance, when absorbed into lakes, refractory
organics can release harmful chemicals that destroy marine vegetation and could signifi-
cantly cause irreparable harm to aquatic life [2,4,5]. The removal of refractory organics
calls for innovative and sustainable mechanisms to prevent their causing potential envi-
ronmental damage.
Biological and physicochemical systems are often insufficient when applied to the
treatment of industrial effluents with persistent pollutants, despite conventional
wastewater treatment advances. Conventional processes like activated sludge and trick-
ling filters are mainly meant for biodegradable organics and lack the ability to break down
high-strength, chemically complex constituents [6]. These limitations lead to incomplete
treatment, excessive sludge production, and an inability to meet stringent regulatory dis-
charge standards. Additionally, traditional methods are not flexible enough to respond to
changing contaminant loads and newly identified pollutants, limiting the effectiveness of
wastewater treatment approaches and impeding progress towards water security on a
global scale [7].
AOPs overcome some of these limitations effectively by generating ·OH during non-
selective oxidation mechanisms to mineralize pollutants [8]. AOPs mineralize recalcitrant
species to carbon dioxide and water and improve the quality and biodegradability of out-
coming effluents [9]. At the same time, high removal efficiencies of pollutants and a de-
crease in the production of sludge have been achieved with technologies such as ozona-
tion, UV/H2O2, Fenton reactions, and photocatalysis [10]. Thus, AOPs can contribute to
meeting the main objectives of Sustainable Development Goal 6 (Clean Water and Sanita-
tion), through effective strategies for reducing toxic material emissions from point
sources, enhancing wastewater reuse, and removing chemical contaminants to achieve
water quality targets set by international sustainability agendas [11].
Challenges such as high capital and energy costs, operational complexity, and the
need for advanced monitoring hinder largescale implementation of AOPs [12]. The per-
formance of EC is also affected by the water matrix composition and the selection of the
reagent [13]. These barriers highlight the need to consider AOPs not only in terms of their
technical efficiency, but also their economic and environmental sustainability, especially
as countries seek to adopt long-term strategies consistent with SDG 6 [11].
,Sustainability 2025, 17, 3439 3 of 37
The treatment of refractory wastewater can occur through disposal filters and mem-
branes, electrochemical removal, and AOPs. Disposal filters and membranes are often
used to remove micro-organic compounds that may still be present after wastewater un-
dergoes primary and secondary treatment processes [4]. Mechanisms such as reverse os-
mosis can be applied to a selective barrier to allow smaller molecules to pass while retain-
ing larger ones [4,5]. Wastewater then undergoes other examination processes to remove
other potential contaminants. Depending on the types of suspected molecules in
wastewater, membrane filtration can take many forms, including microfiltration, ultrafil-
tration, and reverse osmosis [5]. Nanofiltration often targets the tiniest molecules that can-
not be removed through microfiltration or ultrafiltration [2,5]. Membrane filtration is often
used in cleaning wastewater from food and beverage factories, municipal wastewater, and
seawater desalination.
Electrochemical removal involves passing wastewater through electric currents to re-
move organic and inorganic contaminants. The treatment process often occurs through
various steps, including electrocoagulation, electro-flotation, electrodialysis, and electro-
lytic metal separation [3–5]. Electrocoagulation is where precipitates of dissolved ions can
be moved downstream as solids or liquids to separate them from other water particulates.
Electro-flotation helps in separating microbubbles of solids from water by suspending or
floating them using electric currents [5]. The materials that remain in situ can then be re-
moved from wastewater using chlorine as a disinfectant, a process known as hypochlorite
electrolysis [14]. Electrochemical removal has several advantages, including the ability to
adapt quickly to wastewater fluctuations by switching to lower or upper currents depend-
ing on the water volume [6,7]. However, electrochemical treatment is a high-energy con-
sumption process and may generate intermediate metabolites that may not be safe for
consumption.
One of the most common mechanisms used in treating refractory wastewater is
AOPs. The study by Spiniello et al. [14] describes advanced oxidation as a chemical pro-
cess that breaks down complex contaminants using highly reactive oxygen species such
as hydroxyl radicals (·OH). The core principle behind advanced oxidation processes
(AOPs) is the generation of a highly reactive species (hydroxyl radicals) that has proven
more effective against highly resistant organic and inorganic contaminants [2,5,14,15].
This gives AOPs greater advantages over conventional wastewater treatment processes
because they are capable of removing even the most stubborn organic compounds, in-
cluding pesticides and contaminants from oil refineries [15]. Moreover, AOPs consume
less energy compared to the electrochemical treatment processes, making it easier to inte-
grate into modern wastewater treatment facilities used by municipalities to clean
wastewater.
Unlike other wastewater treatment methods, advanced processes are designed to tar-
get the most complex or challenging contaminants that would be impossible to eliminate
using conventional methods. Examples of these complex contaminants include personal
care products, pesticides, pharmaceuticals, and endocrine-disrupting chemicals [15].
These contaminants are often embedded into water particles, making it difficult to remove
using traditional wastewater treatment mechanisms. AOPs are designed to eliminate
these stubborn contaminants and make refractory wastewater safer for commercial con-
sumption or reuse at home [5,15,16]. AOPs have been hailed for their efficiency, minimal
chemical use, and reduced sludge production [16]. Moreover, AOPs can be integrated into
existing water treatment plants as tertiary mechanisms to remove the most persistent or-
ganic contaminants [15,16]. Some of the most common AOPs that will be discussed in this
study include ozonation, Fenton reactions, UV/H2O2 combination, photocatalysis, wet air
oxidation (WAO), and ultrasonic irradiation.
, Sustainability 2025, 17, 3439 4 of 37
The number of people reporting severe water scarcity has been growing steadily due
to climate change and pollution. While water makes up more than 70 percent of the Earth’s
surface, only a small portion is accessible for human consumption or industrial use [1].
Ocean water, for instance, must undergo a complex desalination process to make it avail-
able for human and commercial use. The United Nations estimates that more than 700
million people globally will be displaced from their homes due to severe water scarcity
[1]. Moreover, the United Nations estimates that at least 1 in every 4 children will be living
in areas affected by acute water shortages by 2040 [1]. If not addressed, water scarcity may
also expose a huge portion of the human population to various diseases and premature
deaths.
Demand-driven water scarcity is a common problem usually experienced in densely
populated areas such as cities and major urban centers. However, population-driven wa-
ter scarcity often occurs when the number of people living in a particular area exceeds the
water supply, leading to per capita water scarcity [2,16]. While factors such as population
and demand can be controlled, the world is facing a more complex challenge in the form
of climate change [2,4,5]. According to Mirza et al. [15], climate-driven water shortage
may occur due to increased cases of droughts and fluctuations in rainfall patterns even in
places that were once considered cool and wet zones. South Africa, for instance, is a nota-
ble case of a water-scarce country. The country’s annual precipitation is down to 450 mm,
significantly lower than the global average of 850 mm [1]. Apart from South Africa, there
are more than 190 countries facing water scarcity challenges.
Pollution-driven water scarcity is an emerging challenge due to increased industrial-
ization and chemical spillage on existing water bodies. Unlike climate- or demand-driven
water shortages, pollution-driven water scarcity is not a quantity issue [15]. In this case,
water is available in large quantities but is unsuitable for either human or industrial use.
Numerous companies or factories have been accused of discharging their industrial efflu-
ents into nearby water bodies, including creeks and rivers [2,16]. Some factories discharge
their waste into landfills, where they gradually dissolve into the surrounding soils, even-
tually polluting groundwater below [17]. Pollution-driven scarcity remains a significant
concern due to its complex nature and the ability to destroy large volumes of water within
a short duration. Even with strict environmental laws already enacted in various coun-
tries, pollution remains a pervasive issue that requires multifaceted solutions.
Wastewater treatment innovations offer a viable opportunity to save the world from
growing water scarcity. However, due to massive population growth, industrialization,
and stricter environmental laws, wastewater treatment has not achieved its full potential
[1,17]. Some of the most innovative solutions have not been explored fully due to potential
environmental concerns [6,15,17]. Massive population growth and industrialization mean
there is ever-growing volumetric capacity of wastewater that should be cleaned and re-
turned to circulation [17]. Whether there are technologies that can meet the massive de-
mand for water remains debatable. Most municipal wastewater treatment facilities expe-
rience perennial capacity challenges and the inability to scale up quickly to meet urban
needs [3,5]. Researchers are currently working on more sustainable wastewater treatment
mechanisms to increase water supply with a minimal carbon footprint.
Wastewater treatment mechanisms also need to overcome complex contaminants,
especially from chemical processing factories, such as pesticides, pharmaceuticals, tex-
tiles, and pulp or paper manufacturing [5]. Traditional wastewater treatment methods
have proven less capable of removing stubborn contaminants, especially from industrial
effluents [15]. Most of the complex contaminants contain high levels of grease, corrosive
chemicals, and heavy metals. The high amount of sludge produced during wastewater
treatment also remains a significant concern because it leads to pollution [5,17]. Removing
these complex contaminants has proven not just difficult, but also costly for most
Advanced Oxidation Process in the Sustainable Treatment of
Refractory Wastewater: A Systematic Literature Review
Jorge Alejandro Silva
Escuela Superior de Comercio y Administración Unidad Santo Tomás, Instituto Politécnico Nacional,
Mexico City 11350, Mexico; ; Tel.: +52-55-5729-6000
Abstract: More than 4 billion people yearly suffer from global water scarcity amid climate
change, rapid population growth, and growing industrial activity. Due to the high con-
centrations of recalcitrant organic compounds, refractory wastewater is highly resistant
to conventional biological treatment and represents a critical obstacle for water reuse and
sustainable water management. A systematic literature review of 35 peer-reviewed arti-
cles published from 2010 to 2025 is provided to evaluate the utilization and sustainability
potential of advanced oxidation processes (AOPs) for treating recalcitrant wastewater.
Using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Anal-
yses) framework, the review assesses numerous AOPs, such as ozonation, UV/H2O2, Fen-
ton reactions, and photocatalysis, while also evaluating their performance, efficiency, and
integration ability. The results show that AOPs demonstrate pollutant removal rates often
greater than 96%, reduce sludge formation, and improve effluent biodegradability. They
can be applied at different treatment stages, combined with any renewable energy sys-
tems, and therefore can scale and be sustained, thereby aligning with UN Sustainable De-
velopment Goal 6. AOPs provide a technically feasible and eco-friendly solution for
higher quality wastewater treatment. In the face of increasing pressure on global water
resources, and the urgent need for sustainable water resource management, this study
offers valuable insights for policymakers and practitioners aiming to adopt resilient and
circular strategies for water.
Academic Editor: Shervin Hashemi
Keywords: advanced oxidation processes; Fenton reactions; hydroxyl radicals; refractory
Received: 10 March 2025
Revised: 10 April 2025
wastewater; sustainable wastewater treatment
Accepted: 10 April 2025
Published: 12 April 2025
Citation: Silva, J.A. Advanced
Oxidation Process in Sustainable 1. Introduction
Treatment of Refractory Wastewater: Water is an essential natural resource that supports nearly every life form on the
A Systematic Literature Review.
Earth’s surface. Although water covers over 70% of the Earth’s surface, only 2.5% is avail-
Sustainability 2025, 17, 3439.
able for human use [1]. Further breakdown indicates that only 1% of the available fresh-
https://doi.org/10.3390/su17083439
water is accessible and can be used to support domestic needs and commercial purposes
Copyright: © 2025 by the author.
[1]. Studies indicate that freshwater is becoming increasingly scarce, and more than 2 bil-
Licensee MDPI, Basel, Switzerland.
lion people globally have limited access to safe drinking water [1,2]. In 2022 alone, more
This article is an open access article
distributed under the terms and than 4 billion people faced water shortages at least once in 30 days [1,2]. This number
conditions of the Creative Commons would increase significantly if natural freshwater sources were either depleted or become
Attribution (CC BY) license inaccessible. A sustainable solution to the water shortage problems lies in the use of ad-
(https://creativecommons.org/license vanced technologies to convert more wastewater into a valuable economic and social re-
s/by/4.0/).
source.
Sustainability 2025, 17, 3439 https://doi.org/10.3390/su17083439
,Sustainability 2025, 17, 3439 2 of 37
Advanced wastewater treatment is a multidimensional approach aimed at purifying
wastewater and making it available worldwide for either domestic or commercial reuse.
Advanced wastewater treatment relies on sophisticated methods and technologies to re-
move organic contaminants and other complex compounds that would otherwise be dis-
charged back into circulation for reuse [2]. These advanced processes can be considered
tertiary because they purify water that has undergone primary and secondary treatment
processes [2,3]. However, these advanced treatment processes are not just designed for
removing complex compounds of wastewater. According to Amor et al. [3], advanced
wastewater treatment methods and technologies are also designed to meet stringent en-
vironmental standards to protect ecosystems from potentially harmful carbon com-
pounds. A study by Mousset et al. [4] found that sustainability is one of the key consider-
ations behind advanced treatment processes to enhance efficiency and reliability.
This study explores one of the most sustainable ways of treating refractory
wastewater to make it more viable for reuse. Refractory wastewater contains organic com-
pounds that are highly resistant to various biodegradation mechanisms [2,4]. This makes
it difficult to remove using conventional wastewater treatment mechanisms, where bacte-
ria are mostly used to break down organic compounds. Refractory organics mostly origi-
nate from pharmaceutical factories, paper-making factories, textiles factories, and even oil
refineries [4]. Refractory organic compounds can also be dangerous when released into
landfills or nearby rivers and lakes. For instance, when absorbed into lakes, refractory
organics can release harmful chemicals that destroy marine vegetation and could signifi-
cantly cause irreparable harm to aquatic life [2,4,5]. The removal of refractory organics
calls for innovative and sustainable mechanisms to prevent their causing potential envi-
ronmental damage.
Biological and physicochemical systems are often insufficient when applied to the
treatment of industrial effluents with persistent pollutants, despite conventional
wastewater treatment advances. Conventional processes like activated sludge and trick-
ling filters are mainly meant for biodegradable organics and lack the ability to break down
high-strength, chemically complex constituents [6]. These limitations lead to incomplete
treatment, excessive sludge production, and an inability to meet stringent regulatory dis-
charge standards. Additionally, traditional methods are not flexible enough to respond to
changing contaminant loads and newly identified pollutants, limiting the effectiveness of
wastewater treatment approaches and impeding progress towards water security on a
global scale [7].
AOPs overcome some of these limitations effectively by generating ·OH during non-
selective oxidation mechanisms to mineralize pollutants [8]. AOPs mineralize recalcitrant
species to carbon dioxide and water and improve the quality and biodegradability of out-
coming effluents [9]. At the same time, high removal efficiencies of pollutants and a de-
crease in the production of sludge have been achieved with technologies such as ozona-
tion, UV/H2O2, Fenton reactions, and photocatalysis [10]. Thus, AOPs can contribute to
meeting the main objectives of Sustainable Development Goal 6 (Clean Water and Sanita-
tion), through effective strategies for reducing toxic material emissions from point
sources, enhancing wastewater reuse, and removing chemical contaminants to achieve
water quality targets set by international sustainability agendas [11].
Challenges such as high capital and energy costs, operational complexity, and the
need for advanced monitoring hinder largescale implementation of AOPs [12]. The per-
formance of EC is also affected by the water matrix composition and the selection of the
reagent [13]. These barriers highlight the need to consider AOPs not only in terms of their
technical efficiency, but also their economic and environmental sustainability, especially
as countries seek to adopt long-term strategies consistent with SDG 6 [11].
,Sustainability 2025, 17, 3439 3 of 37
The treatment of refractory wastewater can occur through disposal filters and mem-
branes, electrochemical removal, and AOPs. Disposal filters and membranes are often
used to remove micro-organic compounds that may still be present after wastewater un-
dergoes primary and secondary treatment processes [4]. Mechanisms such as reverse os-
mosis can be applied to a selective barrier to allow smaller molecules to pass while retain-
ing larger ones [4,5]. Wastewater then undergoes other examination processes to remove
other potential contaminants. Depending on the types of suspected molecules in
wastewater, membrane filtration can take many forms, including microfiltration, ultrafil-
tration, and reverse osmosis [5]. Nanofiltration often targets the tiniest molecules that can-
not be removed through microfiltration or ultrafiltration [2,5]. Membrane filtration is often
used in cleaning wastewater from food and beverage factories, municipal wastewater, and
seawater desalination.
Electrochemical removal involves passing wastewater through electric currents to re-
move organic and inorganic contaminants. The treatment process often occurs through
various steps, including electrocoagulation, electro-flotation, electrodialysis, and electro-
lytic metal separation [3–5]. Electrocoagulation is where precipitates of dissolved ions can
be moved downstream as solids or liquids to separate them from other water particulates.
Electro-flotation helps in separating microbubbles of solids from water by suspending or
floating them using electric currents [5]. The materials that remain in situ can then be re-
moved from wastewater using chlorine as a disinfectant, a process known as hypochlorite
electrolysis [14]. Electrochemical removal has several advantages, including the ability to
adapt quickly to wastewater fluctuations by switching to lower or upper currents depend-
ing on the water volume [6,7]. However, electrochemical treatment is a high-energy con-
sumption process and may generate intermediate metabolites that may not be safe for
consumption.
One of the most common mechanisms used in treating refractory wastewater is
AOPs. The study by Spiniello et al. [14] describes advanced oxidation as a chemical pro-
cess that breaks down complex contaminants using highly reactive oxygen species such
as hydroxyl radicals (·OH). The core principle behind advanced oxidation processes
(AOPs) is the generation of a highly reactive species (hydroxyl radicals) that has proven
more effective against highly resistant organic and inorganic contaminants [2,5,14,15].
This gives AOPs greater advantages over conventional wastewater treatment processes
because they are capable of removing even the most stubborn organic compounds, in-
cluding pesticides and contaminants from oil refineries [15]. Moreover, AOPs consume
less energy compared to the electrochemical treatment processes, making it easier to inte-
grate into modern wastewater treatment facilities used by municipalities to clean
wastewater.
Unlike other wastewater treatment methods, advanced processes are designed to tar-
get the most complex or challenging contaminants that would be impossible to eliminate
using conventional methods. Examples of these complex contaminants include personal
care products, pesticides, pharmaceuticals, and endocrine-disrupting chemicals [15].
These contaminants are often embedded into water particles, making it difficult to remove
using traditional wastewater treatment mechanisms. AOPs are designed to eliminate
these stubborn contaminants and make refractory wastewater safer for commercial con-
sumption or reuse at home [5,15,16]. AOPs have been hailed for their efficiency, minimal
chemical use, and reduced sludge production [16]. Moreover, AOPs can be integrated into
existing water treatment plants as tertiary mechanisms to remove the most persistent or-
ganic contaminants [15,16]. Some of the most common AOPs that will be discussed in this
study include ozonation, Fenton reactions, UV/H2O2 combination, photocatalysis, wet air
oxidation (WAO), and ultrasonic irradiation.
, Sustainability 2025, 17, 3439 4 of 37
The number of people reporting severe water scarcity has been growing steadily due
to climate change and pollution. While water makes up more than 70 percent of the Earth’s
surface, only a small portion is accessible for human consumption or industrial use [1].
Ocean water, for instance, must undergo a complex desalination process to make it avail-
able for human and commercial use. The United Nations estimates that more than 700
million people globally will be displaced from their homes due to severe water scarcity
[1]. Moreover, the United Nations estimates that at least 1 in every 4 children will be living
in areas affected by acute water shortages by 2040 [1]. If not addressed, water scarcity may
also expose a huge portion of the human population to various diseases and premature
deaths.
Demand-driven water scarcity is a common problem usually experienced in densely
populated areas such as cities and major urban centers. However, population-driven wa-
ter scarcity often occurs when the number of people living in a particular area exceeds the
water supply, leading to per capita water scarcity [2,16]. While factors such as population
and demand can be controlled, the world is facing a more complex challenge in the form
of climate change [2,4,5]. According to Mirza et al. [15], climate-driven water shortage
may occur due to increased cases of droughts and fluctuations in rainfall patterns even in
places that were once considered cool and wet zones. South Africa, for instance, is a nota-
ble case of a water-scarce country. The country’s annual precipitation is down to 450 mm,
significantly lower than the global average of 850 mm [1]. Apart from South Africa, there
are more than 190 countries facing water scarcity challenges.
Pollution-driven water scarcity is an emerging challenge due to increased industrial-
ization and chemical spillage on existing water bodies. Unlike climate- or demand-driven
water shortages, pollution-driven water scarcity is not a quantity issue [15]. In this case,
water is available in large quantities but is unsuitable for either human or industrial use.
Numerous companies or factories have been accused of discharging their industrial efflu-
ents into nearby water bodies, including creeks and rivers [2,16]. Some factories discharge
their waste into landfills, where they gradually dissolve into the surrounding soils, even-
tually polluting groundwater below [17]. Pollution-driven scarcity remains a significant
concern due to its complex nature and the ability to destroy large volumes of water within
a short duration. Even with strict environmental laws already enacted in various coun-
tries, pollution remains a pervasive issue that requires multifaceted solutions.
Wastewater treatment innovations offer a viable opportunity to save the world from
growing water scarcity. However, due to massive population growth, industrialization,
and stricter environmental laws, wastewater treatment has not achieved its full potential
[1,17]. Some of the most innovative solutions have not been explored fully due to potential
environmental concerns [6,15,17]. Massive population growth and industrialization mean
there is ever-growing volumetric capacity of wastewater that should be cleaned and re-
turned to circulation [17]. Whether there are technologies that can meet the massive de-
mand for water remains debatable. Most municipal wastewater treatment facilities expe-
rience perennial capacity challenges and the inability to scale up quickly to meet urban
needs [3,5]. Researchers are currently working on more sustainable wastewater treatment
mechanisms to increase water supply with a minimal carbon footprint.
Wastewater treatment mechanisms also need to overcome complex contaminants,
especially from chemical processing factories, such as pesticides, pharmaceuticals, tex-
tiles, and pulp or paper manufacturing [5]. Traditional wastewater treatment methods
have proven less capable of removing stubborn contaminants, especially from industrial
effluents [15]. Most of the complex contaminants contain high levels of grease, corrosive
chemicals, and heavy metals. The high amount of sludge produced during wastewater
treatment also remains a significant concern because it leads to pollution [5,17]. Removing
these complex contaminants has proven not just difficult, but also costly for most
