Water insecurity is a pressing issue in dry areas, and it is increased by the fast-growing population and global warming (Amparo-Salcedo et al., 2025). As freshwater resources decline worldwide, it is necessary to find alternative sources of water to sustain agriculture, industry, and economic development (Liu et al., 2024; Dudgeon and Strayer, 2025). One of the possible solution that can reduce the burden on freshwater resources and enhance ecosystem sustainability is the use of treated wastewater (Al-Hazmi et al., 2023; Christou et al., 2024). Although it involves challenges such as social perception, infrastructure, and regulatory challenges, its broader implementation of sustainable agriculture can be achieved through better awareness and effective control systems (Alharbi et al., 2024; Ofori et al., 2025). The application of treated wastewater in irrigation is becoming more acceptable as its advantages to crop yields and soil properties, despite the fact that even with the inappropriate treatment procedures, it remains a threat to the environment (Alayande et al., 2024; Zidan et al., 2024; Areosa et al., 2024; Khokhar et al., 2024).

Application of TWW in irrigation may also influence the properties of the soil including salinity, organic carbon content and enzyme activities (Hoogendijk et al., 2023; Li et al., 2025). The promise of the treated wastewater has also drawn the interest of many researchers, who see its safe use as one of the potential solutions and an alternative resource (López-Serrano et al., 2022; Pratap et al., 2023). Numerous studies have shown that TWW irrigated forage is more water-use efficient compared to freshwater irrigated forage because it results in greater increase in production of biomass, higher nutrient uptake and reduced dependence on freshwater (Cirelli et al., 2012; Licata et al., 2017; Cakmakci and Sahin, 2021). Moreover, the enrichment of plants with minerals, including nitrogen (N), phosphorus (P) and potassium (K) through TWW irrigation may decrease the consumption of fertilizers (Hassena et al., 2018; Khaskhoussy et al., 2022). TWW irrigation enhanced crop growth more effectively than the crops irrigated with normal water (Table 1) due to its higher nutrient content, which improves plant growth and soil fertility (Demir and Sahin, 2017; Seleiman et al., 2021).

The objective of this review was to assess the potential of TWW irrigation in arid areas and to determine how TWW irrigation can alleviate pressure on freshwater resources, enhance soil fertility, increase crop yields, and optimize water-use efficiency.

Freshwater is an essential resource for humans, agriculture, and ecosystem. Fresh water contains less than 500 ppm of dissolved salts and constitutes only 2.5% of the total water on earth. Most is stored in ice caps, soil moisture, and groundwater reservoirs, and only a small percentage is accessible for sustainable uses (Petersen et al., 2017; National Oceanic and Atmospheric Administration, 2023). Water demand has reached critical levels in many regions of the world, especially in the Middle East (Paul et al., 2016; Hameed et al., 2019). The main causes for water scarcity can be summarized as: rapid urbanization, mismanagement of water resources, the lack of infrastructure to supply water, climate change, pollution, and intensive agriculture (Mancosu et al., 2015; Arenas-Sánchez et al., 2016; McGrane, 2016; Bell et al., 2018; Tam and Nga, 2018; AghaKouchak et al., 2020; Ingrao et al., 2023; Tzanakakis et al., 2023).

Food and water security are critical challenges, especially in the Middle East and North Africa regions, which receive only 1.3% of the world’s renewable freshwater and rapid population growth (Karrou and Oweis, 2012; Hameed et al., 2019; Akram et al., 2024). Water scarcity has a direct impact on agricultural production because of high water demand and increasing water costs (Liu et al., 2022; Al Rashed et al., 2023). In response to increasing water scarcity, modern approaches, including desalination and wastewater recycling, have been adopted to reduce pressure on freshwater supplies (Padder and Bashir, 2023; Zolghadr-Asli et al., 2023; Abdou et al., 2024). Desalination technology has limitations because of high energy demands and cost (Al-Addous et al., 2024; Elewa, 2024).

One of the sustainability issues with desalination is its high energy demand and its negative effect on the environment, even though it plays a critical role in addressing water scarcity (Gude, 2016; Ayaz et al., 2022). Therefore, an innovative water management strategy should be developed, together with the promotion of conservation practices and effective regulation of water supply. In addition, measures water sustainability demands the development of effective adaptation, new monitoring techniques, and long-term adaptive strategies (Al Rashed et al., 2023; Hargrove et al., 2023).

Irrigation with TWW is increasingly practiced, especially in areas where water scarcity is at its peak. Wastewater irrigation is currently practiced in more than 50 countries, with an estimated volume of approximately 15 million m³/day used for crop irrigation (Elgallal et al., 2016). In India, approximately 73,000 hectares are irrigated with wastewater (Singh et al., 2022; Surinaidu et al., 2023). Mexico irrigates approximately 260,000 hectares using largely untreated wastewater (Singh et al., 2020). In North Africa, Tunisia was the first country to implement policies on water reuse, using about 25% of its produced wastewater in agricultural irrigation (Ait-Mouheb et al., 2018). The amount of treated wastewater reuse is 10–29% in Europe, China and US; while 41% in Australia (Aziz and Farissi, 2014).

Proper treatment and management of wastewater are also necessary for food security as they provide agricultural support in regions facing water scarcity (Obaideen et al., 2022; Boularbah et al., 2024). Health safety concerns and the uncertainty about chemical contamination have posed significant obstacles to the successful adoption of wastewater treatment technologies (Msaki et al., 2022; Alzahrani et al., 2023). To gain public acceptance for treated wastewater, effective education programs are needed to raise awareness about safety measures (Carvalho et al., 2022). The World Health Organization (WHO) has developed safety measures for wastewater treatment plants to ensure human health and establish suitable development procedures (Drechsel et al., 2022).

The above practical applications suggest that there is a growing global need to consider wastewater treatment as a sustainable long-term solution to water scarcity in agricultural production. With the development of new treatment technologies and supportive policies, countries might be able to integrate wastewater reuse in their water managements plans, supporting both environmental sustainability and food security.

Multiple outcomes produced through wastewater processing that can contribute to ecological development while also posing various environmental threats (Chowdhary et al., 2018; Saravanan et al., 2021). Wastewater treatment is one of the strategies for addressing water scarcity worldwide (Pedrero et al., 2010). Additionally, organic matter and nutrients contained in treated wastewater enhance soil properties by reducing fertilizer use and encouraging sustainable farming practices (Abou Jaoude et al., 2025). The establishment of wastewater reuse operations aims to reduce fresh water consumption and achieve water conservation goals.

Wastewater poses serious threats to the agricultural systems due to the accumulation of hazardous substances, including heavy metals and pharmaceuticals, which can negatively impact crops and pose risks to human health (Dickin et al., 2016; Karri et al., 2021). The inadequate management of wastewater causes eutrophication in water bodies, which reduces the available oxygen in the water and destabilize the local ecosystems (Rathore et al., 2016; Turki and Maktoof, 2019). Conventional wastewater treatment facilities are relatively ineffective in removing persistent micropollutants, such as pharmaceutical residues and perfluoroalkyl substances (PFAS) (Mosharaf et al., 2024). These chemical substances damage soil and water resources, disrupt ecosystems, and pose environmental threats. Moreover, TWW irrigation affects both the chemical composition and microbial community structure of soil (Becerra-Castro et al., 2015; Ibekwe et al., 2018).

The quality of wastewater depends on the nature of the influents entering wastewater treatment facilities, including domestic waste, atmospheric deposition, urban drainage, or agricultural drainage (Koul et al., 2022). Industrial wastewater increases the variety of contaminant loads in raw water entering wastewater treatment facilities (Katsoyiannis and Samara, 2005). Recent research indicates that wastewater effluents contain emerging organic pollutants such as persistent organic pollutants, brominated flame retardants, perfluorinated compounds, and pharmaceutical residues that are not fully removed during the wastewater treatment process (Mahmood et al., 2022; Morin-Crini et al., 2022).

Wastewater contains pathogenic microorganisms, excess nutrients, heavy metals and other organic contaminants that pose serious risks to human health and the environment. Treated wastewater often contains pathogenic bacteria that can cause various infections and diseases, particularly in young, pregnant, immune-compromised, and elderly people (Afolalu et al., 2022). Wastewater must be properly treated before discharge or reuse to avoid contamination of final products and water resources (Gholami-Shabani and Nematpour, 2024). The untreated wastewater is usually released and flows into the downstream water bodies which can affect groundwater (Edokpayi et al., 2015). Treated wastewater has been found to contain several emerging contaminants, including nonconventional pollutants, pesticides and polycyclic aromatic hydrocarbons (PAHs) along with pharmaceutical and personal care products (Chaturvedi et al., 2021; Samal et al., 2022; Zahmatkesh et al., 2022). These pollutants might not be completely eliminated during the treatment process, and can accumulate in soils, particularly heavy metals and persistent organic pollutants (POPs). These contaminants can be absorbed by the plants and transferred through the food chain, leading to health-related problems in both humans and animals (Chen et al., 2005; Bundschuh et al., 2011).

Toxic metals present in wastewater used for vegetable irrigation can be absorbed into edible and non-edible parts (Alam et al., 2003). Persistent and non-biodegradable heavy metals are likely to accumulate in plant and animal tissues, and may be absorbed by humans through the food chain (Chowdhury and Rahman, 2024). The prolonged exposure to these toxins through the diet can cause gradual accumulation in the body and increased the risk of chronic diseases (Bahemuka and Mubofu, 1999). Treated wastewater irrigation initially improves soil productivity and increases crop yields. However, the long-term application may lead to soil salinization and the accumulation of harmful pollutants, which causes soil degradation (Wang et al., 2024). Soil degradation leads to a decline in plant survival and negatively influences agricultural productivity and ecosystem sustainability (Gomiero, 2016).

Therefore, treated wastewater should undergo advanced processing, alongside effective monitoring and strict regulatory control, to ensure environmental protection and ecosystem stability.

Wastewater treatment involves three main steps, primary, secondary, and tertiary, with each step using a specific method of contaminant removal (Figure 1), which contributes to the protection of human health and environmental sustainability (Saravanan et al., 2021). The first step in primary wastewater treatment involves physical separation through screening and sedimentation, along with skimming processes aimed at removing solids, reducing the load on subsequent treatment stages, and improving overall treatment efficiency (Wang et al., 2006; Cristaldi et al., 2020). The secondary treatment via activated sludge is a proven and effective process for the removal of organic matterand lowers contaminants as well as nutrients from wastewater (Verlicchi et al., 2012; Montazeri et al., 2015).

Advanced filtration methods, including chemical treatment, membrane bioreactors and oxidation processes, allow treated water to meet discharge limits and can be applied at large scale (Monteoliva-García et al., 2020; Giwa et al., 2021). Algae-based treatment and phytoremediation are a viable way to remove a pollutants and offers a sustainable approach to address environmental problems (Hong et al., 2024). The biodegradation processes can be enhanced using ultrasonic treatment, particularly for recalcitrant wastewater (Kim et al., 2024; Wen et al., 2024). Moreover, wastewater treatment relies on a combination of physical, biological, and chemical processes to remove contaminants effectively and produce safe water.

Innovative and sustainable wastewater treatment methods are key to lowering pollution and advancing the objectives of the Urban Wastewater Treatment Directive (UWWTD). The European Commission is reviewing the UWWTD as part of the European Green Deal and is also encouraging new water reuse regulations to promote sustainable water management (Interreg Europe, 2014). The Circular Economy Action Plan advocates cost-effective water reuse, whereas the initial UWWTD provided limited provisions on wastewater reuse (European Commission, 2015). The new regulation on water reuse provides minimum requirements for the use of reclaimed water in agriculture to address water scarcity in regions such as Greece, Italy and Spain. Moreover, the supplementary regulation provides technical risk-management guidelines and standardized conditions for safe water reuse in agricultural fields (European Commission, 2023).

Wastewater treatment performs essential functions to decrease the environmental threats from heavy metals, pharmaceuticals, and microplastics (Zhai et al., 2023). Therefore, proper waste management methods are necessary to protect human health and environmental stability (JeyaSundar et al., 2020). Heavy metals, including lead, mercury, and cadmium, are major toxicological concerns because of their high toxicity and potential carcinogenic effects (Tiwari et al., 2024). Industrial activities generate the most metal pollution that accumulates in aquatic ecosystems, posing threats to both ecosystems and humans health (Hu et al., 2013). Traditional wastewater treatment often result in the release of heavy metal pollutants (Figure 2), that cause environmental pollution (Yang et al., 2018). These factors indicate the need to develop new wastewater treatment processes to remove hazardous substances from the wastewater (Ahmed et al., 2021; Ejairu et al., 2024). Treatment of industrial wastewater systems has major issues in controlling pollution caused by pharmaceutical and personal care products (Alsalihy et al., 2024). The conventional treatment systems fail to completely eliminate these compounds from wastewater and show low efficiency in reducing their concentrations. The spread of residual substances from wastewater into agricultural regions affects human health and natural ecosystems (Wu et al., 2024). This demonstrates that wastewater treatment plants require technological solutions to ensure adequate management of contaminants and minimize environmental impacts (Rout et al., 2021).

Microplastics have gained significant attention as a major environmental problem, especially in wastewater management systems (Amesho et al., 2023), due to the release of millions of microplastic particles into land and freshwater ecosystems (Cheng et al., 2021). The microplastics pose serious threats to aquatic ecosystems, increasing risks to aquatic life health (Issac and Kandasubramanian, 2021). Similarly, other toxic compounds such as pesticides and heavy metals can also contaminate water and soil with harmful effects on crops during irrigation (Jadhav and Medyńska-Juraszek, 2024; Tariq et al., 2024). Concerns regarding bioaccumulation and long-term toxicity of microplastics and other pollutants are intensified by their persistence in the environment (Meena et al., 2025). Standard wastewater treatment plants have a limited ability to remove microplastics and emerging pollutants because their initial purpose is to target organic matter and nutrients (Miino et al., 2024). Current filtration systems require upgrades because they are inefficient in removing these pollutants from water (Shahid et al., 2021). In addition, wastewater treatment is essential for minimizing environmental contamination; however, current technologies show limited efficiency in removing emerging pollutants such as, pharmaceuticals and personal care products, and microplastics. These limitations in wastewater treatment demand further research into innovative and efficient removal approaches to protect both environmental and human health.

Wastewater irrigation has multiple effects on soil characteristics by altering both its physical and chemical properties (Sdiri et al., 2023). The addition of organic matter and nutrients through wastewater irrigation provides benefits but also causes challenges such as soil salinization and heavy metal accumulation while affecting soil microbial populations (Bashir et al., 2021). The effectiveness of wastewater irrigation depends on the standard of water quality and specific characteristics of the wastewater applied (Rezapour et al., 2021).

One significant advantage of using wastewater to irrigate soil is its potential to enhance soil organic carbon. Research has demonstrated that wastewater irrigation can increase organic carbon by a maximum of 20% in comparison to groundwater irrigation (Gurjar et al., 2019; Ankit et al., 2023). Azazy et al. (2022) also found that wastewater irrigation improves soil structure, water retention, and fertility by increasing organic matter in the soil. Wastewater irrigation improves microbial activity and soil quality; however, it can also alter soil salinity and nutrient content, which affect plant growth (Gao et al., 2021; Aguilar-Rangel et al., 2024). Salinization has deleterious effects on the soil structure, hindering the growth of plants, and poses a threat to soil sustainability (Mazhar et al., 2022). Wastewater irrigation has led to severe problems due to the accumulation of heavy metals in soil (Chaoua et al., 2019). Irrigation with wastewater can increase the concentration of heavy metals in the soil, posing risks to soil health and crop productivity due to the bioavailability of heavy metals, which is influenced by the pH and organic matter (Khalid et al., 2018; Alnaimy et al., 2021). The best way to reduce the risk of contamination is to ensure that irrigation practices are well regulated and regularly monitored (Khalid et al., 2018).

The physical properties of the soil, such as porosity, hydraulic conductivity, infiltration and water retention, are altered by wastewater irrigation (Gharaibeh et al., 2016; Loy et al., 2018). Irrigation of wastewater alters soil surface microbial communities because it favors dominant groups of bacteria over those that are beneficial, which negatively affects overall soil health (Lüneberg et al., 2018; Gurjar et al., 2019). Wastewater can be effectively used in agricultural production, but it requires proper management practices including regular inspection and appropriate wastewater selection.

New technologies, like advanced oxidation, UV disinfection, membrane bioreactors or AI optimization, are being added to the conventional wastewater treatment techniques, such as activated sludge, chlorination, and constructed wetlands (Shamshad and Rehman, 2025). These processes are costly and energy-intensive, though they are effective in improving the removal of contaminants (Küçükbayrak and Alver, 2025). Renewable sources of energy like solar, wind, and biomass reduce emissions and enhance efficiency (Panwar et al., 2011). Additionally, the bio-electrochemical systems and constructed wetlands as a single system is a sustainable and resource-efficient approach to wastewater treatment although the technologies of wastewater treatment have been one of the most popular topics in recent years. Even though membrane filtration (Nthunya et al., 2021; Molinari et al., 2024), advanced oxidation processes (Adeoye et al., 2024; Long et al., 2025), and biological treatment systems (Ponnusami et al., 2023) have been investigated as wastewater reclamation techniques, their combined effectiveness remains poorly understood (Singh et al., 2023). Moreover, further studies on decentralized wastewater treatment systems are necessary to meet sanitation requirements in rural and remote areas (Kumar et al., 2023; Ribarova et al., 2024). Additionally, Wang et al. (2023) reported that artificial intelligence is still not widely used in wastewater treatment, especially for real-time modeling and optimization with machine learning.

Alternative irrigation methods based on wastewater irrigation have gained significant scientific attention due to their positive effects on crop growth, despite environmental and health risks (Khalid et al., 2018). Initially, wastewater irrigation can improve soil fertility but may lead to long-term soil degradation due to salt and heavy metal accumulation (Friedel et al., 2000; Sánchez–González et al., 2017). Another major problem is the salinization of soil which is most prevalent in the arid and semi-arid regions, where wastewater is often used for irrigation purpose, as it may contain high concentrations of salts that increase electrical conductivity of the soil and reduce water availability to plants. Additionally, wastewater can deposit toxic metals such as cadmium, lead, and nickel in the soil, which may accumulate over time and disrupt nutrient uptake and transport, as well as microbial activities (Ungureanu et al., 2020).

Moreover, irrigation of Zea mays and Glycine max with treated livestock wastewater presents no safety hazards in intercropping systems. Treated wastewater enhances crop production while limiting heavy metal mobilization in soil–plant systems (Kama et al., 2023). Similarly, Fendri et al. (2013) showed that treated domestic wastewater improved seed germination and enhanced seedling growth in Avena sativa plants.

According to Seleiman et al. (2021), TWW is a valuable agricultural resource that is effective in irrigation of bioenergy crops, including Sorghum bicolor L. and Pennisetum glaucum L., in arid regions. Moreover, TWW provides essential nutrients and reduces the use of NPK fertilizer by half, thereby sustaining crop growth, biomass production, and contributing to environmental protection. Hashmat et al. (2021) demonstrates that the growth, nutrient uptake, and yield of pea (Pisum sativum L.) plants treated with biologically treated wastewater and 50% dilution of wastewater (WW50) were significantly improved than untreated wastewater. Another study reported that tertiary treated wastewater (H2) from Al Ain Treatment Station had a positive effect on wheat growth, grain production and chlorophyll content especially in SAWYT wheat variety when cultivated in a hydroponic system. When using H2 treatment, the content of Ca, K, and P in wheat kernels increased, without heavy metal accumulation, and this suggests that H2 can be used as an alternative nutrient-rich irrigation source in arid areas to irrigate wheat (Al Hamedi et al., 2021). Baram et al. (2022) reported that drip irrigation using oxygenated nanobubble-treated wastewater (ONB-TWW) has a positive effect on the yield and quality of lettuce (Lactuca sativa) grown in both sandy and clayey soils. Furthermore, using treated wastewater decreased membrane leakage and improved root viability and chlorophyll content, especially in poorly aerated clayey soil. Ochoa-Rivero et al. (2023) found that barley and oats irrigated with treated wastewater or groundwater also accumulated (As, Cd and Pb) in roots and leaves with lower concentrations in grains. Verma et al. (2024) reported that untreated canal wastewater had adverse effects on Pisum sativum because it reduces germination, growth of the seedlings, and causes oxidative stress due to elevated heavy metals concentrations. Nevertheless, tube-well water enhanced plant growth, which indicates that effective treatment and dilution of canal water may help to reduce its toxicity, and at the same time may help to supply crops with essential nutrients during irrigation. Al-Zayadneh et al. (2025) also found an increase in yield, yield components and nutrient content of barley (Hordeum vulgare L.) by irrigation with treated wastewater instead of potable water. Similar findings have been reported in other crops, including maize and vetch (Mohammad and Ayadi, 2004), wheat (Al Hamedi et al., 2023), and barley (Al-Karaki, 2011; Samarah et al., 2020).

Wastewater irrigation poses a challenge when adopted as an agricultural practice. Plants absorb heavy metals from wastewater, leading to potential health risks when contaminated crops are consumed by humans. Ghosh et al. (2012) reported that long-term irrigation with treated sewage water resulted in high levels of heavy metals in vegetables, raising concerns about food safety. Furthermore, Ahmed and Slima (2018) showed that heavy metals may accumulate in the edible part of the crops and frequently exceed phytotoxic levels. Gutierrez et al. (2024) reported that saline wastewater irrigation had a detrimental effect on germination and chlorophyll content in broccoli plants; however, these negative effects were alleviated with magneto-priming treatment.

The toxic effects of untreated wastewater negatively affects plant physiology and human health (Mishra et al., 2023). Further, it impairs key physiological processes, including photosynthesis, respiration, and water balance, leading to increased levels of reactive oxygen species (ROS) and altered enzyme activities (Durán–Álvarez and Jiménez–Cisneros, 2014; Singh and Laura, 2014). The specific impact of wastewater on plant species is influenced by their nutrient uptake capacity and type of wastewater application (Ayoub et al., 2016). In addition, irrigation with industrial and sewage wastewater negatively affected nutrient uptake, biomass accumulation, photosynthetic activity, and yield of Vigna radiata L. and Pisum sativum L. compared with biologically treated wastewater (Singh and Laura, 2014; Yasmeen et al., 2014). Reduced growth and yield were primarily attributed to diminished photosynthetic capacity, and disrupted nutrient uptake (Hajihashemi et al., 2020). Furthermore, wastewater management requires proper treatment and careful handling procedures to safeguard plant health while maintaining agricultural productivity and food safety.

TWW provides a sustainable approach in agriculture to address water scarcity, enhance soil fertility through nutrient inputs, and reduce dependence on chemical fertilizers. In addition, it promotes crop growth and increases yield and nutrient uptake. However, improper handling or inadequate treatment can lead to contamination by heavy metals, pathogens, and microplastics, which may accumulate in soils and enter the food chain. Therefore, maximizing the benefits of TWW requires investment in advanced treatment technologies, stricter regulatory enforcement, and increased public awareness of the safe reuse of wastewater. Addressing these challenges is essential to ensure the long-term sustainability and safety of TWW in agricultural practices.