Innovative Approaches for Sustainable Wastewater Resource Management

Abstract

Sustainable wastewater management is essential for conserving water resources and reducing environmental pollution. Traditional wastewater treatment methods primarily aim to purify water for reuse, yet they often involve high energy consumption, extensive chemical use, and loss of potentially recoverable resources, which pose sustainability challenges. With approximately 2.2 billion people worldwide currently lacking access to clean water—a number projected to exceed 3 billion by 2025—water scarcity has become an urgent issue. Traditional wastewater treatment processes handle around 330 billion cubic meters of water annually; however, they account for 3–4% of global energy consumption and produce 300 million tons of carbon emissions. This situation underscores the need for more sustainable treatment methods. Innovative wastewater treatment technologies have the potential to facilitate the reuse of approximately 50 billion cubic meters of water each year, helping to alleviate water scarcity. Additionally, energy recovery from these processes aims to achieve an annual energy savings of 20 TWh, in contrast to conventional treatment methods. This article examines recent advances in sustainable wastewater management technologies, specifically focusing on biological, physicochemical, and membrane-based processes. It discusses strategies for optimizing these processes to minimize environmental impact. Furthermore, innovative approaches, such as advanced oxidation processes and energy recovery, are explored for their potential to harness energy and recover nutrients from wastewater. The article concludes that implementing innovative strategies in sustainable wastewater management can significantly contribute to water conservation, energy savings, and a reduction in carbon footprint.

1. Introduction

Water is a limited natural resource essential for human use and survival. For this reason, access to a reliable and clean water source is crucial for human survival and sustainable development [1]. With the rapid increase in population and industrialization in recent years, existing water resources are being depleted and increasingly polluted. As a result, water consumption is rising to meet the growing demand for water and food, leading to escalating water scarcity [2]. According to the International Water Management Institute (IWMI), approximately 1 L of water is required to produce each calorie consumed as food [3]. This excessive resource consumption also leads to an increase in waste. Consequently, our natural resources are under threat, with water being the most critical resource at risk [4]. Estimates from the World Summit on Sustainable Development (WSSD) suggest that more than 3 billion people will face water scarcity by 2025 [5].

It is, therefore, of great importance to re-evaluate wastewater generated through water consumption and make it sustainable through innovative approaches and emerging technologies across various fields. Reusing wastewater—creating sustainable water sources—provides a new means to protect existing water resources and meet the rising demand for water [6]. Recycled water is regarded as an alternative to natural water sources, offering a reliable supply of water [2]. The primary goal of treating and recycling wastewater is to safeguard existing water sources and reduce the strain on clean water resources [6].

Sustainable wastewater management has become a critical agenda item for protecting water resources and supporting environmental sustainability, especially given the rapidly growing population and industrialization. Traditional wastewater treatment methods aim to make water reusable through physical, chemical, and biological processes. However, these methods often fall short of sustainability goals due to high energy consumption, environmental impacts from chemical usage, and the insufficient recovery of valuable resources. Approximately 330 billion cubic meters of water are treated annually using traditional wastewater treatment methods; however, these processes contribute to 3–4% of global energy consumption and generate 300 million tons of carbon emissions. This situation underscores the need for more effective methods that align with sustainability objectives.

In this context, innovative and sustainable technologies—such as biological treatment, membrane technologies, resource recovery, circular economy approaches (integrated systems that recover water, energy, and nutrients), and smart water management systems—are essential for developing more circular and resource-efficient wastewater treatment systems. Innovative wastewater treatment technologies can enable the reuse of approximately 50 billion cubic meters of water annually, helping to alleviate water scarcity. Furthermore, energy recovery from these processes aims to achieve annual energy savings of 20 TWh compared to conventional treatment facilities.

The importance of approaching wastewater management as an integrated circular system—encompassing water, energy, and nutrient recovery—is becoming increasingly evident. The adoption of innovative biological, physicochemical, and membrane technologies plays a crucial role in implementing sustainable practices, such as energy recovery, nutrient recycling, and carbon footprint reduction. These practices not only aid in conserving water resources but also contribute significantly to mitigating energy and environmental challenges for future generations.

2. Innovations in Wastewater Treatment

The increasing environmental demands and water scarcity we face today make it essential to develop new and more effective wastewater treatment technologies [7]. While traditional treatment methods have significantly improved water quality, they fall short of fully meeting the rapidly evolving demands of industrial and urban sectors. Innovative wastewater treatment technologies offer holistic approaches that not only target pollutant removal but also emphasize the recovery of water, energy, and valuable substances. Technologies, such as membrane bioreactors, advanced materials (e.g., silver, nano iron, carbon nanotubes, nanofiltration membranes, photocatalytic titanium dioxide, and graphene oxide), along with other methods, like photocatalytic and electrochemical processes, introduce new possibilities in wastewater treatment by effectively purifying water and supporting both environmental and economic sustainability.

Wastewater treatment technologies significantly contribute to environmental protection and the sustainable management of water resources. The advantages and disadvantages of various treatment technologies encompass numerous factors that must be considered in selecting and optimizing systems for maximum efficiency. Primarily, biological treatment methods are environmentally friendly, enabling the decomposition of organic matter by microorganisms in a nature-compatible process. These technologies are energy-efficient and are particularly preferred for treating industrial and municipal wastewater with high organic content. However, the effectiveness of biological treatment can be affected by environmental factors, such as temperature and pH. Biological processes can also be slow and may not completely remove harmful microorganisms remaining in treated water. Physicochemical treatment methods, on the other hand, are particularly advantageous for removing heavy metals and inorganic pollutants. Some processes, like chemical precipitation, coagulation, and flocculation, can deliver rapid and effective results. However, the chemicals used in these methods may pose risks to the environment and human health. Membrane technologies are capable of filtering out almost all dissolved solids, microorganisms, and other pollutants in wastewater, thereby significantly enhancing the quality of reclaimed water through advanced treatment. Nonetheless, membrane technologies have high energy demands and operational costs. Additionally, membrane fouling and the need for regular maintenance raise operational costs and pose sustainability challenges. Finally, innovative technologies, such as advanced oxidation processes and UV disinfection, are highly effective at removing harmful chemicals and microorganisms. However, these methods are relatively costly and consume substantial amounts of energy, making them less cost-effective for large-scale applications.

Wastewater recycling is feasible as long as appropriate conditions and standards are maintained. Meeting these conditions largely depends on economic factors [6]. The quality of treated wastewater must meet the standards set for its intended reuse. For successful water recycling, several key factors must be considered when selecting the appropriate technology. These include the characteristics of the treated wastewater, water quality standards based on reuse goals, technology reliability, ease of operation, and economic viability. Careful assessment of these factors ensures the safe and efficient reuse of treated wastewater for agricultural, industrial, or environmental purposes [8].

2.1. Membrane Bioreactors (MBR)

Membrane technologies are among the innovative and effective methods that have gained significant attention in wastewater treatment today [9]. These technologies rely on the principle of physical separation, using a semi-permeable membrane to purify water from various pollutants. Different membrane types—such as microfiltration, ultrafiltration, nanofiltration, and reverse osmosis—filter water based on particle size, thereby removing unwanted substances [10]. Microfiltration targets particles in wastewater sized between 1 µm and 100 nm, while ultrafiltration is used for particles between 100 nm and 10 nm. Nanofiltration is suitable for molecules with particle sizes from 10 nm to 1 nm, and reverse osmosis is applied to ions smaller than 1 nm.

Membrane technologies are regarded as an environmentally friendly alternative due to their high treatment efficiency, reduced chemical usage, and potential for water reuse. Their application is increasingly common in various fields, such as wastewater recovery, drinking water production, and industrial water treatment [11]. Information on the pore sizes of particles filtered by different membrane processes and the corresponding treatment methods is illustrated in Figure 1 [10,12].

Membrane bioreactors (MBRs) offer several advantages over traditional wastewater treatment systems. First, MBR systems can operate at high loading rates, allowing for more efficient processing of wastewater flows. Additionally, their ability to handle higher mixed liquor suspended solids (MLSS) concentrations optimizes biological treatment processes, resulting in faster treatment times. The extended solids retention time (SRT) in MBR systems enables microorganisms to remain in the treatment environment longer, thereby enhancing treatment efficiency. Furthermore, the low food-to-microorganism (F/M) ratios in these systems help regulate the organic load, allowing microorganisms to function more effectively.

These factors collectively contribute to producing high-quality effluent (treated water) from MBR systems, making them highly valuable for water recovery and reuse.

2.2. Electrochemical Treatment

Electrochemical treatment is an innovative and effective technology in wastewater treatment. This method enables pollutant removal through electrochemical reactions and is commonly used to improve water quality, eliminate toxic substances, and reduce waste that is harmful to the environment [13]. Electrochemical treatment purifies dissolved pollutants in water via oxidation and reduction processes using an electric field applied through electrodes [14].

One of the main advantages of this technology is its minimal use of chemicals, making it more environmentally friendly than traditional treatment methods. Additionally, electrochemical methods can be easily designed as modular systems and applied at various scales. This approach, which has applications in relevant areas, such as heavy metal removal, organic pollutant degradation, and color removal, is also notable for its energy efficiency and cost-effectiveness [15]. Electrochemical treatment is widely employed to remove heavy metals and organic pollutants from industrial wastewater and to eliminate pollutants, like nitrogen and ammonia, from municipal wastewater.

Recent studies have shown the effectiveness of electrochemical treatment, especially in industrial wastewater, and technological advancements in this area have introduced new perspectives on wastewater treatment as a viable method [16]. In this regard, electrochemical treatment technologies play a crucial role in sustainable and effective wastewater management strategies.

2.3. Advanced Oxidation Processes (AOPs)

Advanced oxidation processes (AOPs) are innovative methods for the effective removal of environmental pollutants from water and wastewater [17]. These processes convert organic and inorganic pollutants into smaller, harmless compounds by generating highly reactive hydroxyl radicals [18]. Various advanced oxidation techniques, such as photocatalytic oxidation, ozonation, the Fenton reaction, and electro-photochemical methods, are particularly favored for the removal of persistent organic pollutants and for disinfection processes in water treatment [19]. These technologies offer effective solutions in cases where traditional treatment methods are insufficient [20].

Below is a general outline of the advanced oxidation process (AOP):

• Pretreatment: This involves the removal of large particles and sediments from wastewater [17];
• Reagent production: Radicals used in advanced oxidation processes are produced, varying according to the specific technology [21]. This includes the following steps:
  • Fenton reaction (using Fe²⁺ and H₂O₂);
  • Ozonation (using O₃);
  • Photocatalytic oxidation (using UV light and catalyst).
• Reaction zone: The radicals produced react with the organic pollutants in the wastewater, oxidizing and breaking them down. At this stage, strong oxidants, such as hydroxyl radicals (OH), are crucial [22];
• Pollutant removal: Organic pollutants are transformed into harmless compounds, such as CO₂ and H₂O, through oxidation [23];
• Final treatment: By-products and residual chemicals formed after the reaction are removed. This may include additional filtration or other treatment methods. Disinfection processes using chlorine, ozone, or UV may also be applied [24];
• Treated water: In the final stage, purified and safe water is obtained, which can be reused for various purposes, such as agricultural irrigation or industrial use [8].

In conclusion, advanced oxidation processes are a crucial component of future environmentally friendly water treatment technologies and are regarded as a powerful tool for achieving sustainable water management goals.

2.4. Biological Treatment

Biological treatment is a method by which organic pollutants in wastewater are removed through natural processes involving microorganisms [25]. In this process, microorganisms metabolize pollutants in wastewater, transforming them into simpler and harmless compounds [25,26]. Biological treatment is widely used as an environmentally friendly and energy-efficient method, especially for domestic and industrial wastewater treatment.

Various biological treatment processes, such as aerobic and anaerobic systems, are effective in breaking down organic matter, and provide an important foundation for sustainable wastewater management. However, the effectiveness of biological treatment can vary depending on system design, the characteristics of the wastewater, and the type of waste being treated.

2.4.1. Flow Chart of Biological Treatment and Traditional Treatment Systems

The flow chart of the biological treatment process outlines various steps involving microorganisms [27]. In the pretreatment stage (screening and grit removal), large solid particles and materials, such as sand, are mechanically separated from the wastewater [28]. This step prevents damage or blockages in the biological treatment system. In the primary sedimentation stage, suspended solids in the wastewater settle [29]. These substances are separated from the upper part of the wastewater and accumulate as sludge.

The most critical phase, aerobic or anaerobic biological treatment, involves microorganisms biologically treating the wastewater in oxygenated or anaerobic environments [30]. Two main biological systems are used at this stage.

Aerobic biological treatment:

• Activated sludge process: Microorganisms consume organic matter in wastewater as oxygen is introduced from the air. The presence of oxygen allows bacteria to convert organic pollutants into carbon dioxide and water [31];
• Biofilters: Microorganisms attached to a fixed surface decompose organic matter as wastewater flows through. This system is often more compact and cost-effective [32,33].

Anaerobic biological treatment:

• Digestion tanks: In oxygen-free environments, microorganisms convert organic pollutants into gases, such as methane and carbon dioxide [34]. This process can be used for energy recovery through biogas production [35].

In the secondary sedimentation stage, the biomass (microorganism mass) formed during biological treatment settles and is separated from the treated water [36]. This biomass is collected as sludge and can be further processed [36,37]. Tertiary treatment removes dissolved substances, chemicals, or micropollutants that cannot be eliminated during biological treatment [38]. Common methods include advanced oxidation, membrane filtration, or chemical precipitation [39]. In the final stage, the treated water is disinfected, typically using chlorination, UV irradiation, or ozone, to make it safe for reuse [40].

Biological treatment systems are essential methods for removing organic pollutants from wastewater and include various approaches. These systems rely on microorganisms to biologically transform organic substances in wastewater, offering diverse solutions for producing clean water. Biological treatment systems include the following:

• Activated sludge systems: Microorganisms are continuously mixed with water in aeration tanks, where they consume organic matter in the wastewater, improving water quality [41]. This system is particularly effective for wastewater with a high organic load;
• Biofilm reactors: In these systems, microorganisms grow on a fixed surface and wastewater flows over this surface. Organic substances are decomposed by the microorganisms on the biofilm, purifying the water [42];
• Lagoons: Lagoons are natural biological treatment methods in which wastewater is processed by microorganisms in large pools [43];
• Anaerobic digestion: This biological treatment method occurs in an oxygen-free environment. Microorganisms in closed tanks biologically transform organic matter, producing biogas in the process [44]. This method is especially beneficial for energy recovery.

These biological treatment systems offer several advantages, including energy recovery, lower costs, and reduced environmental impact. Each system has unique benefits and application areas, making it possible to select the most suitable solution for various types of wastewater and treatment requirements.

2.4.2. Advanced Biological Treatment Systems

Advanced biological treatment systems are modern technologies that provide high efficiency, energy savings, and resource recovery in wastewater treatment while being environmentally friendly. Going beyond traditional methods, they offer sustainability-focused solutions for the treatment of both urban and industrial wastewater. These systems utilize the biochemical processes of microorganisms to effectively remove organic and inorganic pollutants, thereby enhancing the potential for reclaimed water reuse.

Among the advanced biological treatment systems, notable examples include anaerobic membrane bioreactors (AnMBRs), microalgae bioreactors, biofilm reactors, photobioreactors, and denitrification filters, all of which provide environmentally friendly and high-efficiency solutions. AnMBRs have the potential for energy recovery by breaking down organic matter in an oxygen-free environment and producing methane. Microalgae bioreactors recover nutrients, such as nitrogen and phosphorus, from wastewater, producing biomass that can be used as an environmentally friendly fertilizer or biofuel. Photobioreactors utilize solar energy to oxidize pollutants, offering a low carbon footprint. Nanotechnology-supported nanobubble generators release microscopic bubbles into the water, increasing oxygen levels. These high-resolution oxygen bubbles support biological activity, facilitating faster decomposition of waste. Due to their small size, nanobubbles remain dissolved in water for extended periods, effectively meeting the oxygen requirements in lagoons and enhancing the efficiency of aerobic processes.

These systems stand out as significant innovative biological solutions for sustainable water management.

2.5. Production of Biofuels from Wastewater

Wastewater biofuel production is an innovative approach that significantly contributes to environmental sustainability by integrating waste management with energy production processes. Organic matter in wastewater is transformed through biochemical processes into a valuable resource for biofuel production [45]. Technologies, such as anaerobic digestion, microbial fuel cells (MFC), and biogas production, play a central role in this process [45,46]. Biofuel derived from wastewater is considered an alternative energy source to fossil fuels while aiding in waste disposal and reducing environmental pollution. Thus, wastewater biofuel production is a key element of the circular economy model, offering both economic and environmental benefits.

The production of biofuel from wastewater involves several stages in which organic matter is converted into energy through biochemical processes. The general process includes wastewater collection and pretreatment, biochemical conversion, biogas collection and purification, energy production and utilization, and by-product management, as follows:

• Wastewater collection and pretreatment: Wastewater collected at treatment plants undergoes physical and chemical pretreatment to increase the concentration of organic matter. During this stage, large particles and foreign substances are filtered out [5,47];
• Biochemical conversion stage: Two key technologies are employed, as follows:
  • Anaerobic digestion: Microorganisms break down organic matter in an oxygen-free environment, producing biogas. Methane (CH₄) is the main component of this biogas, which is used as an energy source [48,49];
  • Microbial fuel cells (MFC): Organic matter is biologically degraded by microorganisms, releasing electrons. These electrons are harnessed to generate electricity in the fuel cell [50].
• Biogas collection and purification: The biogas (methane and carbon dioxide) produced in the biochemical conversion stage is purified to increase the methane concentration and separate unwanted gases, like CO₂ [51];
• Energy production and use: The purified biogas is used for electricity and heat production. It can also be converted into transportation fuel in the form of compressed or liquefied methane (CNG/LNG) [52];
• By-product management: Solid waste generated during anaerobic digestion can be repurposed as agricultural fertilizer [48,53]. Additionally, nutrients, like phosphorus and nitrogen, can be recovered from the water.

The process can be summarized by the following equation [54]:

Organic Matter (C₆H₁₂O₆) + Microorganisms → CH₄ (Methane) + CO₂ (Carbon Dioxide) + H₂O (Water) + Energy.

Wastewater biofuel production presents an effective model for both energy generation and sustainable waste management.

3. Strategies for Wastewater Reuse

Strategies for wastewater reuse are designed to support a circular economy approach in water management. These strategies have been developed and continue to evolve to utilize resources more efficiently and reduce waste. The first strategy involves the application of advanced treatment technologies capable of producing high-quality wastewater suitable for agricultural irrigation, industrial production, and even drinking water. The second strategy focuses on local water reuse, such as the purification of greywater used in buildings, enabling its reuse. The third strategy centers on energy and nutrient recovery (e.g., nitrogen and phosphorus) from wastewater, reconfiguring water treatment plants to serve not only as waste disposal facilities but also as centers for energy and resource production.

Globally implemented strategies for wastewater reuse and sustainable water management include the following [55]:

• Use of treated wastewater in agriculture: Many countries utilize treated wastewater for agricultural irrigation, conserving water and protecting water resources [56];
• Wastewater recycling for industrial use: Reusing treated wastewater, especially as cooling or process water, is a common practice in industries [57]. This strategy reduces the demand for clean water resources;
• Greywater recycling: The repurposing of greywater (from showers, sinks, and washing machines) for indoor use, such as toilet flushing or landscape irrigation, is encouraged, particularly in water-scarce regions [58];
• Energy and nutrient recovery: Recovering resources, like biogas, nitrogen, and phosphorus, from wastewater provides energy and recycles valuable nutrients that can be used as fertilizers in agriculture [6,59];
• Constructed wetlands and natural treatment systems: Artificial wetlands and natural treatment systems serve as low-cost, environmentally friendly methods for cleaning wastewater naturally and reintroducing it into water resources [60];
• Obtaining drinking water: In water-scarce regions, particularly in developed countries, advanced treatment technologies convert wastewater into drinking water [61]. This offers a sustainable solution in areas where water resources are limited;
• Policies and regulations: Many countries promote the implementation of these strategies through legal regulations on wastewater recovery and reuse. In this context, economic incentives and strict regulations on water use are applied [2,6,62];
• Urban water cycles: In large cities, local water cycles are established, such as using treated wastewater to irrigate parks and green areas [63];
• Rainwater harvesting: Collecting and storing rainwater provides an important water source, especially in water-scarce regions. This water can be used for various purposes, including drinking, agriculture, landscape irrigation, vehicle washing, and indoor use [64,65];
• Conversion of sewage water into drinking water: Advanced purification technologies are used to transform sewage water into safe drinking water. This method is applied in cities with limited water resources, contributing to sustainable water management and helping to conserve water [61,66]. Singapore’s NEWater project serves as a successful example, employing advanced treatment technologies following conventional treatment methods [67].

The reuse of wastewater offers a vital solution for protecting water resources and supporting sustainable management strategies. Advanced treatment technologies enable the utilization of wastewater across various sectors, particularly for agricultural irrigation, industrial processes, and, in some cases, as drinking water.

Wastewater reuse reduces environmental impacts and generates economic savings by improving water and energy efficiency. These practices promote ecosystem health by encouraging the rational and efficient use of resources.

4. Wastewater Reuse Studies

The successes achieved in wastewater management in recent years demonstrate that significant strides have been made toward sustainable environmental management. Many countries worldwide have begun implementing innovative technologies and strategies to address the growing challenges of water scarcity and environmental pollution.

The first step in the reuse of wastewater occurred in the United States in 1940 when chlorinated domestic wastewater was utilized in the steel industry. By the end of the 20th century, water reuse gained importance in industrialized countries, including those in Europe and America. In 1951, treated wastewater from the Mikawashima wastewater treatment plant in Tokyo, Japan, was repurposed as process water for a paper mill [68].

Ensuring the successful sustainability of wastewater reuse is directly linked to the quality of the treated wastewater, which is influenced by the advancement of wastewater reclamation technology [6]. Recycled wastewater may contain hazardous pollutants, such as salinity, heavy metals, and pathogens [69]. Therefore, the technologies and methods employed in the treatment process are crucial. Reverse osmosis treatment technology is particularly significant for removing salinity from wastewater. Oron et al. [70] achieved an 81% reduction in the initial electrical conductivity of wastewater (2020 μS/cm) using reverse osmosis. They also managed to decrease the sodium (Na⁺) concentration from 280 mg/L by 83% and the chloride (Cl⁻) concentration from 48 mg/L by 80%. Reverse osmosis is recognized as an effective method for reducing the sodium adsorption ratio because it can effectively remove sodium ions and divalent cations. This feature provides a substantial advantage in terms of improving water quality [6,70]. These results demonstrate that reverse osmosis is an effective technology for wastewater treatment. In Singapore, domestic wastewater is purified using advanced membrane systems under the NEWater initiative, which is one of the country’s pioneering projects. This process produces high-purity water through reverse osmosis technology, which is then reintegrated into the network system for use as drinking water [71]. NEWater employs a comprehensive purification process that exposes used water to ultraviolet rays and advanced dual membrane technologies, such as microfiltration and reverse osmosis. The purified water obtained at the end of this process is mixed with reservoir water and subsequently directed to conventional water treatment plants, making it available for drinking water production [72]. This system plays an essential role in supplying safe drinking water and supporting sustainable water resource management.

The reuse of wastewater in agricultural activities presents an alternative and sustainable approach to managing water resources. In this context, the effects of four different concentrations of wastewater on three corn varieties were investigated [73]. The study utilized treated domestic wastewater, and the results indicated that this water stimulated germination rates and seedling development in the corn varieties by 25% and 75%, respectively. Furthermore, using treated wastewater for irrigation contributes to plant growth while potentially reducing groundwater pollution due to decreased fertilizer use, thanks to the nutrients present in the irrigation water [73].

Pedrero et al. [74] conducted a study in Spain to investigate the effects of treated wastewater on citrus trees. The research compared two fields irrigated with wastewater from different treatment plants in the Murcia region of southeastern Spain. The Cartagena field received secondary treated water, while the Campotajar field was irrigated with a mixture of well water and tertiary treated wastewater. The treated wastewater from Cartagena exhibited higher values of electrical conductivity (EC), turbidity, and total dissolved solids than that from Campotajar. Consequently, admixture with well water improved the agricultural quality of the treated wastewater. In both plots, the elevated electrical conductivity levels were attributed to excess chlorides and boron. While fecal coliform, E. coli, and helminth eggs were not detected in the treated wastewater or soil in Campotajar, fecal coliform was found in the treated wastewater from Cartagena at a level above health standards. The study concluded that the use of treated wastewater in both fields did not increase the levels of macronutrients and organic matter in the soil; thus, the wastewater does not serve as a nutrient source under these conditions [74].

To minimize the potential effects of treated wastewater on the environment and public health during agricultural use, advanced treatment methods should complement biological treatment to ensure the complete removal of pathogens and harmful microorganisms from the water [75]. In a study where treated wastewater was used for irrigation via sprinklers at a biological wastewater treatment plant with activated sludge and nitrogen and phosphorus removal units in Clermont-Ferrand, France, the hepatitis E virus was detected at varying rates in both the treated wastewater and the air in the irrigated area [76]. While maturation ponds and UV applications were effective in removing pathogenic microorganisms, ultrafiltration membrane technology significantly enhanced purification efficiency for virus removal [77]. Helvacı [78], in a study evaluating data from four treatment plants using a membrane bioreactor (MBR) system, found that heavy metals and toxic elements did not exceed permissible limits in irrigation waters based on analyses of instantaneous wastewater samples taken from the Iznik wastewater treatment plant. Additionally, it was noted that biochemical oxygen demand (BOD₅), total phosphorus, and suspended solids (SS) values complied with discharge standards, although total nitrogen levels exceeded established limits on certain days. It was emphasized that in MBR systems, treated wastewater can be considered a safe resource due to a 2–3-log reduction in pathogens and viruses [78].

Membrane technologies, filtration processes, and electrochemical treatments are employed to minimize potential environmental and public health impacts during the reuse of treated industrial wastewater. A membrane-based treatment process aimed at reusing dyeing wastewater has been developed, investigating the effectiveness of microfiltration (MF), coagulation, and ultrafiltration (UF) methods as pretreatment alternatives. The best-performing pretreatment methods were identified as single-stage 5 µm batch MF and sequential 5 µm batch MF combined with 100 kDa UF, due to high wastewater flows and effective color removal. When comparing these two pretreatment methods with nanofiltration (NF) performance, the 5 µm MF was determined to be the most effective pretreatment process, achieving an 87–92% reduction in color and a 10% reduction in chemical oxygen demand (COD). Following the pretreatment stage, three different NF membranes and two reverse osmosis membranes were tested to obtain reusable water [79]. Test results indicated that the persistent COD and color performance of NF and reverse osmosis membranes were comparable, thereby meeting relevant reusability criteria. Bressan et al. [80] applied catalytic oxidation followed by biological treatment to mitigate the toxic effects of highly polluted olive blackwater, achieving an 80–90% COD removal with the oxidation process and over 90% COD removal with the biological treatment process. Khoufi et al. [81] reported 43% COD, 76.2% phenol, 75% turbidity, 71% suspended solids (SS), and 90% color removal efficiencies with electrocoagulation and precipitation methods applied prior to anaerobic biological treatment [81]. In another study by the same team in 2006, they achieved a 65.8% removal of polyphenolic compounds with the electro-Fenton process while reducing wastewater toxicity by 66.9% with anaerobic treatment [82]. Treated wastewater is utilized in industrial areas as cooling water, boiler feed, process water, and for plant floor maintenance. Among these applications, the most common use is as cooling water, as it enables the reuse of substantial amounts of water in industrial systems and contributes to environmental sustainability by reducing overall water consumption.

There are numerous examples of wastewater utilization across various sectors, including the irrigation of golf courses, parks, and gardens, the production of artificial snow, and the reuse of slaughterhouse wastewater. A study conducted by Ortuno et al. [83] in 2014 indicated that 12% of golf courses in the United States utilize treated wastewater for irrigation. The annual irrigation requirement for an 18-hole golf course varies significantly based on the regional climate, ranging from 52,000 m³ in the Northeast to as high as 566,000 m³ in desert areas. In Kuusamo, Finland, a 2006 study by Sallanko and Haanpää revealed that treated wastewater from the Ruka wastewater treatment plant was employed for artificial snow production [84]. Additionally, Millamena’s 1992 study explored ozonation technology for treating slaughterhouse wastewater. The results indicated that a low concentration of ozone (110 mg/h) was insufficient for effectively removing a significant portion of the organic matter in this type of wastewater. However, when ozonation was combined with pretreatment, the overall efficiency for biochemical oxygen demand (BOD) removal reached 42%, total organic carbon (TOC) removal achieved 34%, and chemical oxygen demand (COD) removal was as high as 58%. This demonstrates that ozonation is particularly effective for COD removal in slaughterhouse wastewater, especially when used alongside pretreatment [85].

Coşkun [86] investigated the mixing of national water obtained from a ready-mixed concrete plant’s recycling unit with wastewater from sedimentation tanks in various proportions. The mixing ratios included 100% wastewater, 20% wastewater and 80% silty water, 40% wastewater and 60% silty water, 60% wastewater and 40% silty water, 80% wastewater and 20% silty water, and 100% silty water. Six different concrete series were prepared using these ratios, and the cube samples from the mixtures underwent testing for slump, unit weight, temperature, air content in fresh concrete, and compressive strength at 2, 7, and 28 days in hardened concrete. The results indicated that silty water did not significantly affect the workability of the mixture; the optimal performance was achieved with a 60% wastewater and 40% silty water mixture, which led to a substantial increase in compressive strength [86]. This suggests that increasing the silty water ratio positively impacts concrete performance, particularly enhancing compressive strength. The reuse of wastewater plays a critical role in mitigating water scarcity by offering sustainable solutions in urban water management. Urban and industrial wastewater treatment systems are becoming increasingly prevalent globally, serving both environmental protection and resource efficiency goals. In Turkey, the Antalya Organized Industrial Zone (OIZ) exemplifies a successful application of industrial wastewater recycling. The wastewater treatment plant in Antalya OIZ operates at a capacity of 20,000 cubic meters per day, employing advanced technologies to dry the sludge produced and incinerate it in cement factories. Studies conducted in 2023–2024 resulted in a 50% reduction in treatment sludge volume and a dryness level of 92% [87,88]. Furthermore, significant strides have been made to enhance water efficiency in the industry through the “Green OIZ Clean Antalya Project”, launched in 2023 [88]. As part of this initiative, companies in the OIZ were encouraged to adopt water recovery techniques and improve energy efficiency [89]. With these water recovery applications, the majority of the wastewater generated in the OIZ is rendered reusable, thereby minimizing environmental impacts in the region.

We can use the following basic formulas to calculate efficiency in wastewater treatment systems:

• Wastewater treatment efficiency: This efficiency measures the difference between the incoming wastewater and the outgoing clean water, determining the amount of water recovered. The basic Formula (1) is as follows [90]:

$$\mathrm{W}\mathrm{a}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{w}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r} \mathrm{T}\mathrm{r}\mathrm{e}\mathrm{a}\mathrm{t}\mathrm{m}\mathrm{e}\mathrm{n}\mathrm{t} \mathrm{E}\mathrm{f}\mathrm{f}\mathrm{i}\mathrm{c}\mathrm{i}\mathrm{e}\mathrm{n}\mathrm{c}\mathrm{y}\left(\mathrm{\%}\right)={\displaystyle \frac{\mathrm{A}}{\mathrm{B}}}\times 100,$$

(1)

where A = amount of recycled water (m³/day); B = amount of wastewater entering the facility (m³/day).

For example, in the case of Antalya OIZ, the amount of wastewater entering the facility daily is 20,000 m³. While recovery rates vary by sector, up to 50% of water is typically recovered [88].

Assumptions: B: 20,000 (m³/day), recovery rate: 50%.

Calculating A: A = B × 50%; A = 20,000 m³/day × 0.50 = 10,000 (m³/day);

2.

Sludge reduction and dryness calculation: The drying process aims to reduce the amount of sludge generated during wastewater treatment. In Antalya OIZ, a 50% reduction in sludge volume and a 92% dryness rate have been achieved [88]. If 1% of sludge is produced from 20,000 m³ of treated wastewater, the daily sludge amount is calculated as follows (Formula (2)):

$$\mathrm{D}\mathrm{a}\mathrm{i}\mathrm{l}\mathrm{y} \mathrm{S}\mathrm{l}\mathrm{u}\mathrm{d}\mathrm{g}\mathrm{e}\left({\mathrm{m}}^3/\mathrm{d}\mathrm{a}\mathrm{y}\right)={\displaystyle \frac{\mathrm{20,000} {\mathrm{m}}^3}{0.01}}=200 {\mathrm{m}}^3/\mathrm{d}\mathrm{a}\mathrm{y},$$

(2)

As a result of the 50% reduction, Formula (3) is as follows:

$$\mathrm{R}\mathrm{e}\mathrm{d}\mathrm{e}\mathrm{u}\mathrm{c}\mathrm{e}\mathrm{d} \mathrm{S}\mathrm{l}\mathrm{u}\mathrm{d}\mathrm{g}\mathrm{e}\left({\mathrm{m}}^3/\mathrm{d}\mathrm{a}\mathrm{y}\right)=200 {\mathrm{m}}^3/\mathrm{d}\mathrm{a}\mathrm{y}\times 0.05=100 {\mathrm{m}}^3/\mathrm{d}\mathrm{a}\mathrm{y},$$

(3)

when a 92% dryness is achieved, the remaining sludge is calculated as follows in Formula (4):

$$\mathrm{D}\mathrm{r}\mathrm{i}\mathrm{e}\mathrm{d} \mathrm{S}\mathrm{l}\mathrm{u}\mathrm{d}\mathrm{g}\mathrm{e}\left({\mathrm{m}}^3/\mathrm{d}\mathrm{a}\mathrm{y}\right)=100 {\mathrm{m}}^3/\mathrm{d}\mathrm{a}\mathrm{y}\times 0.08=8 {\mathrm{m}}^3/\mathrm{d}\mathrm{a}\mathrm{y},$$

(4)

3.

Wastewater treatment efficiency result and remaining sludge amount after treatment: A = 10,000 m³/day, B = 20,000 m³/day. Wastewater treatment efficiency is calculated by the following Formula (5):

$$\mathrm{W}\mathrm{a}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{w}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r} \mathrm{T}\mathrm{r}\mathrm{e}\mathrm{a}\mathrm{t}\mathrm{m}\mathrm{e}\mathrm{n}\mathrm{t} \mathrm{E}\mathrm{f}\mathrm{f}\mathrm{i}\mathrm{c}\mathrm{i}\mathrm{e}\mathrm{n}\mathrm{c}\mathrm{y}\left(\mathrm{\%}\right)={\displaystyle \frac{\mathrm{10,000} {\mathrm{m}}^3/\mathrm{d}\mathrm{a}\mathrm{y}}{\mathrm{20,000} {\mathrm{m}}^3/\mathrm{d}\mathrm{a}\mathrm{y}}}\times 100=50\mathbf{\%},$$

(5)

Thus, the amount of water recovered is 10,000 m³/day, reflecting a 50% recovery rate. The amount of sludge remaining after treatment, with a 92% dryness rate, is 8 m³/day.

These calculations demonstrate that water efficiency and sludge reduction have reached a significant level in the Antalya Organized Industrial Zone. Similarly, in urban areas, advanced treatment technologies enable the recovery of wastewater at levels suitable for agricultural irrigation, park and garden maintenance, and other green area applications. These initiatives contribute significantly to Turkey’s sustainability goals in urban and industrial wastewater management.

The reuse of wastewater offers substantial advantages across various application areas. Treated wastewater is utilized in agricultural irrigation, industrial processes, and even drinking water production, presenting great potential for effective water resource management and sustainability.

5. Conclusions

Research indicates that wastewater management and reuse technologies present significant opportunities for the sustainable management of water resources. Innovative wastewater treatment methods have been developed to address the increasing challenges of water scarcity and environmental pollution in many regions worldwide, yielding both environmental and economic benefits. The findings from various studies suggest that treated wastewater can be successfully reused across a range of applications, including agricultural irrigation, industrial water needs, and even drinking water production.

The development and dissemination of treatment technologies are critical for the recovery and reuse of wastewater. Advanced treatment methods, such as reverse osmosis, ultrafiltration, and ozonation, should be adopted more widely, with continuous improvements made to enhance their effectiveness. National and international standards must be strengthened to ensure the safe and effective reuse of treated wastewater in various applications. These standards should cover water quality, treatment process effectiveness, and the minimization of public health risks. It is essential to combine biological treatment methods with membrane technologies to achieve the complete removal of pathogens, heavy metals, and organic pollutants from treated wastewater. In certain applications, such as irrigation and industrial processes, prioritizing these removal processes is vital for protecting human health and the environment.

Advanced oxidation processes (AOPs) have proven highly effective for the removal of refractory organic pollutants, making them a strong option for treating industrial wastewater. These processes utilize powerful oxidants, such as hydroxyl radicals, to rapidly and effectively break down contaminants. The integration of artificial intelligence and machine learning is crucial for automating treatment processes and enhancing efficiency. These systems continuously monitor and analyze water quality, enabling real-time optimization of operational parameters. Nanotechnology-based filtration systems hold significant promise, particularly for retaining micropollutants and challenging compounds, like antibiotics. Nanomaterials enhance filtration efficiency due to their high surface area and contribute to lower energy consumption. Photocatalytic treatment technologies, which decompose organic pollutants using sunlight, are particularly effective in regions with abundant solar energy. Resource recovery technologies also enable the extraction of valuable materials, such as biogas, phosphorus, and nitrogen, from wastewater, supporting a circular economy by treating wastewater as a resource and promoting both economic and environmental sustainability.

Raising awareness about wastewater reuse and promoting public understanding are essential for enhancing community involvement in wastewater management and facilitating the widespread adoption of recycling practices.

This review examined the existing literature on wastewater reuse and highlighted potential benefits across various application areas. The use of treated wastewater is becoming increasingly important, especially in agricultural irrigation, water recovery for industrial processes, and drinking water production. Utilizing treated wastewater in agriculture promotes plant growth and ensures a more efficient use of water resources, providing critical solutions for sustainable agricultural production in water-scarce regions. Furthermore, advanced membrane technologies and treatment methods, such as reverse osmosis, demonstrate effective results in producing high-quality drinking water.

Recycling industrial wastewater enhances environmental sustainability, reduces water consumption, and improves process efficiency. In industrial applications, such as concrete production, using treated wastewater not only reduces costs but also enhances product performance. These applications illustrate significant potential for protecting water resources and achieving sustainable environmental management, indicating that wastewater reuse can be applied more broadly across various sectors in the future. The cost-effectiveness, energy savings, advantages, and disadvantages of these treatment technologies used for urban and industrial purposes are compiled and presented in

Table 1. Examination of the cost-effectiveness, energy savings, advantages, and disadvantages of treatment technologies [36,91,92,93].

Technology	Application Area	Cost Effectiveness	Energy Saving	Advantages	Disadvantages
Membrane bioreactors (MBR)	Urban and industrial	High recovery rates (90%+), long-term efficiency	Moderate energy consumption (0.3–0.5 kWh/m3)	High water quality (BDO < 5 mg/L), small space requirement, automatic process control	Membrane clogging, high initial costs, frequent maintenance required
Electrochemical treatment	Industrial	Low operating costs (20–30% savings)	High energy consumption (1–4 kWh/m3)	Effective removal of major pollutants (heavy metals, organic matter)	Energy costs, high equipment costs in some applications, electrode wear
Biological treatment	Urban	Low investment costs (200–300 USD/m3)	Low energy consumption (0.05–0.1 kWh/m3)	Natural processes, environmentally friendly, low chemical use	Long process time (12–24 h), poor water quality (space requirement in some cases)
Advanced oxidation processes (AOPs)	Industrial	High effectiveness rates (over 90%)	Moderate energy consumption (1–3 kWh/m3)	Removal of pollutants that are difficult to decompose, short process times	High initial costs, energy costs, need for pH control
Circular economy approaches	Urban and industrial	Long-term cost savings (10–20% annually)	Low energy consumption (0.1–0.5 kWh/m3)	Resource recovery (water, energy, food), waste reduction, environmental sustainability	Difficulty of implementation, need for system integration, initial investment

[36,91,92,93].

Innovative approaches for sustainable wastewater treatment offer promising solutions for the future by combining technologies that enhance resource conservation and energy efficiency with the principles of a circular economy. While different technologies provide complementary advantages in urban and industrial wastewater treatment, the applicability and efficiency of each vary according to specific needs and environmental conditions. Developing integrated and cost-effective methods in wastewater treatment processes is essential not only for the disposal of pollutants but also for energy savings and reducing the carbon footprint, contributing to a sustainable future. In this context, increasing the efficiency of existing and new technologies in their application areas can pave the way for a more effective roadmap to achieve sustainable development goals.

In conclusion, the successes achieved in wastewater management reveal that water resources can be managed sustainably through the use of innovative treatment technologies.