Agricultural Irrigation Using Treated Wastewater: Challenges and Opportunities

Abstract

Reusing and recycling treated wastewater is a sustainable approach to meet the growing demand for clean water, ensuring its availability for both current and future generations. Wastewater can be treated in such advanced ways that it can be used for industrial operations, recharging groundwater, irrigation of fields, or even manufacturing drinkable water. This strategy meets growing water demand in water-scarce areas while protecting natural ecosystems. Treated wastewater is both a resource and a challenge. Though it may be nutrient-rich and can increase agricultural output while showing resource reuse and environmental conservation, high treatment costs, public acceptance, and contamination hazards limit its use. Proper treatment can reduce these hazards, safeguarding human health and the environment while enhancing its benefits, including a stable water supply, nutrient-rich irrigation, higher crop yields, economic development, and community resilience. On the one hand, inadequate treatment may lead to soil salinization, environmental degradation, and hazardous foods. Examining the dual benefits and risks of using treated wastewater for agricultural irrigation, this paper investigates the complexities of its use as a valuable resource and as a potential hazard. Modern treatment technologies are needed to address these difficulties and to ensure safe and sustainable use. If properly handled, treated wastewater reuse has enormous potential for reducing water scarcity and expanding sustainable agriculture as well as global food security.

1. Introduction

In response to increasingly urgent challenges, such as water scarcity, soil degradation, and climate change, agriculture is under pressure to adopt sustainable irrigation methods. These interconnected issues are crucially important regarding agricultural productivity and food security. More specifically, climate change disrupts the weather, reduces crop yields, and increases the occurrence of extreme weather events. Since 1961, this has led to a dramatic decrease in global agricultural productivity, with the most dramatic consequences being seen in warmer areas of Africa and Latin America [1,2,3,4]. With climate change adding to problems for agricultural systems worldwide, water shortage is increasingly recognized as a leading global issue. Agriculture is the strongest consumer of water resources worldwide; sources attributed to agriculture account for over 70% of the total freshwater withdrawals [5,6]. Both an increasing frequency of droughts and floods and variability in rainfall patterns endanger crop productivity and increase the costs of crop irrigation [7,8,9,10]. Climate change has directly impacted agricultural operations through more uncertain agroclimatic indicators [8,10]. There are a number of issues that need to be addressed caused by climate change using innovative water management techniques and sustainable farming [9,11,12].

Reusing treated wastewater is the most promising solution to mitigate soil degradation and increase agricultural productivity. Addressing water scarcity is a challenging problem in a drought-prone system [13]. Several studies indicate that treated wastewater may supply crops with needed nutrients, improving soil fertility and reducing the use of chemical fertilization [14,15]. Though treated wastewater is treated to minimize the risks of contaminants [16,17], it is important to ensure the water meets health safety standards.

Wastewater generated by human activities has adverse environmental and public health impacts. The content consists of the mixed waste products of home sewage, industrial discharges, and rainwater, although some come with a mixture of contaminants. A diversity of pollutants characterizes wastewater, necessitating advanced treatment systems that can handle such contaminants and which calls for focused but flexible treatment strategies [18,19,20]. The composition and characterization of wastewater vary greatly depending on the sources. For instance, domestic wastewater is high in nutrients and organic matter, while some industrial wastewater contains harmful substances and heavy metals [21,22]. These various types of wastewaters require recommended procedures to be effectively treated and the effluent to meet environmental standards before release or reuse. Recent advancements in wastewater treatment technologies include electrocoagulation, membrane filtration, and ultraviolet treatment, which have shown promising improvement in treatment effectiveness [23,24,25].

Treated wastewater applications in agriculture present both advantages and challenges. On a positive note, treated wastewater is a long-term alternative to typical chemical fertilizers, improving soil fertility, increasing microbial activity, and providing crops with necessary nutrients [26,27]. This is useful in areas with limited freshwater resources since it can increase agricultural productivity while reducing freshwater scarcity [26,28]. However, there are concerns that treated wastewater may be contaminated with pathogens, heavy metals, and antibiotic resistance genes [16,29,30]. Heavy metals such as lead and cadmium, found in some wastewater, are poisonous and can accumulate in soil, endangering human health through the food chain [31]. The existence of antibiotic resistance genes [30], as well as higher heavy metal levels in treated wastewater-irrigated soils and crops [32], raises public health concerns. Mitigating these dangers requires effective technologies and appropriate legislation. Regular evaluations are also necessary to ensure the safe use of treated wastewater [17]. Sustainable agriculture techniques that protect human health and environmental quality necessitate a careful balance between the potential health concerns and nutrient advantages of treated wastewater [17].

This literature review explores recent research on the challenges and potentials of applying treated wastewater to agricultural production. Evidence exists that treated wastewater can dramatically boost agricultural yields and soil fertility, especially in water-short areas [33,34]. This review also highlights the public perception and regulatory issues and highlights the necessity to take strict treatment procedures to curb the hazards generated by heavy metals and other contaminants [35,36]. It also explains technological advances and good practice strategies that facilitate the safe integration of treated wastewater into sustainable agricultural systems [37,38]. This study, unlike the existing literature, comprehensively addresses the environmental, health, socioeconomic, and social dimensions of using treated wastewater for agricultural irrigation. In addition, the public perception of the agricultural use of treated wastewater is often overlooked in studies, yet it plays a crucial role in these practices. In addition to current practices, complete recommendations for the future are presented.

2. Significance of Treated Wastewater in Irrigation

The use of treated wastewater for agricultural irrigation presents great potential as a sustainable farming operation. However, the required treatment levels, monitoring systems, and site-specific factors should be considered before use [39]. Careful planning and administration can maximize the societal and environmental benefits. Treated wastewater provides an excellent source of organic matter and a wide range of nutrients. It is the key micronutrient for supporting plant growth and contains micronutrients such as manganese, cobalt, iron, copper, zinc, and molybdenum [40]. For example, treated wastewater provides large amounts of the essential elements (total nitrogen 5.84–12.00 mg/L, total phosphorus 0.03–0.35 mg/L, chloride 144 to 1770 mg/L) [41]. In a previous study, treated wastewater was characterized and TDS, chlorine, total nitrogen, and total phosphorus contents were reported as 1062 mg/L, 250 mg/L, 20 mg/L, and 2.3 mg/L, respectively [42]. These are nutrients vital to crop growth and can reduce farmers’ reliance on costly chemical fertilizers, lowering a farmer’s production costs through the use of treated wastewater.

The reuse of treated wastewater for agricultural purposes plays a crucial role in ensuring food security and promoting sustainable agriculture. It is an important resource, especially in arid climate zones, that provides a reliable water supply throughout the year, ensuring continuity of irrigation and maintaining the stability of agricultural production. This supports the continuity of the food supply [43], reducing fertilizer use and increasing crop productivity due to its high nitrogen and phosphorus content [44].

In addition to these benefits, treated wastewater provides an inexpensive way to rid excess nutrients and destroy contaminants while meeting our continuing need for agricultural irrigation. This treated wastewater can also be injected into the deep wells to recharge the aquifer and the water reserves [45]. The use of treated wastewater for irrigation facilitates the strategic scheduling of freshwater applications, especially where water scarcity is a concern, and offers better regulation and less dependence on chemical fertilizers. Additionally, the organic components in treated wastewater play a role as irrigation and nutrient sources and as a factor in soil conservation and structural development. This improves soil health, reduces soil erosion, and stabilizes dunes [46].

Despite these advantages, some thresholds of treated wastewater, such as excessive sodium and chloride levels, may contribute to soil salinity [39]. In addition, the chlorine content can cause chlorosis and harm plants. For instance, irrigation water containing more than 180 mg/L chlorine can decrease crop yield [47]. Before the application of treated wastewater, these topics should be considered, and monitoring is required. Thresholds are discussed in Section 2.2 in detail. In the literature, a variety of crops have been irrigated using treated wastewater and the findings are summarized in

Table 1. Irrigation with treated wastewater and its impact on plants.

Irrigated Crop/Plant	Irrigation Source	Findings	Reference
Carrot	WWTP effluent, ozonized effluent, and accumulated effluent	The maximum CEC accumulation was observed in WWTP effluent. No important changes were observed in the physicochemical properties of carrots, except for a reduction in chlorophyll and carotenes with ozone treatment.	[48]
Tomato	Biosolar photocatalytic treatment effluent	No important changes were detected in the total yield, properties, and nutritional data among crops irrigated with reclaimed, control, and polluted water. Pharmaceutical and pesticide residues were analyzed in tomatoes. Venlafaxine and chlorotriazines were detected in tomato samples. Pesticides and pharmaceuticals accumulated in the soil.	[49]
Pepper	Treated wastewater	Possible leaching of nitrate, salt, and E. coli into groundwater was researched. Treated wastewater irrigation did not cause significant groundwater pollutant except salt. Crop irrigation with treated wastewater can successfully prevent important leaching of E. coli and nitrate, while it can cause a small leaching of salt. Nitrate in the treated wastewater may fulfill the nitrogen requirement of pepper. Irrigation water used for pepper crop showed 90% of nitrate and 50% of salt.	[50]
Mandarin tree	Treated wastewater and fresh water	Using treated wastewater increased soil salinity. Mandarin tree yield increased by 29.5%. Combining fresh water and treated wastewater is viable option. Mandarin quality was not affected by the water source.	[51]
Lettuce	Treated wastewater (Conventional activated sludge or membrane bioreactor)	Seven and two CECs were detected in treated wastewater and lettuce, respectively. The composition of irrigation water impacts crop metabolomic and transcriptomic profiles. CECs were only detected in lettuce irrigated with conventional activated sludge-treated wastewater. The lettuce tissues irrigated with MBR-treated wastewater presented the highest number of metabolic changes. Salinity is an important factor for plants. Azithromycin and clarithromycin were detected in the soil but not in the lettuce. Carbamazepine and diclofenac were detected in lettuce.	[52]
Melon	Treated wastewater	CEC accumulation in cucumber and melon was found to be 27.8 μg/kg f.w. and 12.4 μg/kg f.w., respectively. The level of CECs accumulation follows this order: root < stem/leaf < fruit < soil. CECs accumulation in melon harvesting soil was higher than in cucumber harvesting soil. No human risk was observed from eating these foods.	[53]
Pomegranate	Treated wastewater	The polyphenol content of pomegranate decreased slightly. Plant yield, nutrient values, and properties did not change. Using treated wastewater caused early ripening in pomegranate.	[54]
Alfalfa	Treated wastewater	Different irrigation methods were investigated. Sprinkler irrigation resulted in the lowest alfalfa yield. High pathogen risk can occur with sprinkler and surface irrigation. Subsurface-drip irrigation decreases E. coli and fecal coliform accumulation on alfalfa.	[55]
Sorghum	Treated wastewater	Plant synthesizes protein metabolites to defend against stress conditions. Treated wastewater was adequate for nutrient supply. Irrigation with treated wastewater positively impacted plant growth and yield. Using treated wastewater and fertilizer had similar effect on plants.	[56]
Papaya	Treated wastewater	Cumulative fruit yield increased. Subsurface drip irrigation was more effective than drip irrigation. Fruit weight was not significantly affected by irrigation type. Treated wastewater irrigation is safe and cost effective.	[57]
Olive orchard	Treated wastewater	Using treated wastewater decreases the fertilizer application. A mobile application was created to control the irrigation and fertilization schedule. Treated wastewater for irrigation is safe for human health. Using treated wastewater is a productive and suitable method.	[58]
Eggplant	Treated wastewater	Nonylphenol spiked soil was used. Nonylphenol accumulation in eggplant was determined. Nonylphenol accumulation follows the order: leave > steam > root > fruit. Little health risk occurred for adults and children.	[59]
Rice	Treated wastewater	Rice plant growth and grain quality were not detrimentally affected. Low concentrations of antibiotics can help rice plant growth. Antibiotic resistance genes, virulence factors, and human bacterial pathogens were investigated in paddy soil. High antibiotic concentrations can increase protein synthesis.	[60]
Maize	Treated wastewater, Treated wastewater + groundwater (1:1)	Pharmaceutical and personal care product content of crops were determined. Three repetitions for each treatment showed almost no significant changes in each PPCP concentration in the topsoil among the three-irrigation treatment. Little potential health risk for toddles and adults. The bioaccumulation factor of maize was higher than of wheat.	[61]
Wheat
Lettuce	Treated wastewater	Two years drip irrigation applied. Limited CEC accumulation in plant and soil. Sorption and degradation in soil possibly diminished contaminant uptake by leek and lettuce. The longer harvesting period can contribute to the low accumulation of CECs.	[62]
Leek
Lavender	Treated wastewater	Irrigation with treated wastewater increased plant biomass. Soil microbial structure and stability were affected by treated wastewater irrigation. Zea Mays yield increased using treated wastewater. Lavender released volatile oils that impact the fungal species in irrigated soil.	[63]
Zea Mays

.

2.1. Environmental and Societal Drivers of Using Treated Wastewater for Irrigation

Treated wastewater irrigation is driven by various factors, primarily environmental preservation and societal well-being. For farmers, it provides a steady water supply and, in some cases, nutrient-rich wastewater, leading to higher crop yields and financial gains. This increased productivity can improve food availability and reduce malnutrition in underserved regions, ultimately enhancing living standards and social welfare. Environmentally, treated wastewater irrigation reduces the reliance on natural surface and groundwater resources and minimizes wastewater discharge into sensitive ecosystems, such as coastal and aquatic systems. The use of treated wastewater for irrigation may primarily be motivated by the growing demand for water in urban areas, which causes increased return flows that are occasionally released into natural water bodies, contaminating traditional irrigation sources. This can be linked to the growing demand for food production near urban centers, where water sources are frequently harmed by pollution, and the lack of accessible, dependable, or safer alternative water sources, which makes the use of treated wastewater a feasible solution.

In developing countries, the fundamental challenge in the reutilization of treated wastewater may be the lack of advanced treatment plants. However, the root issues are poverty, weak governance, limited technical capacity, regulatory gaps, and prioritization issues within national and local government planning [64]. This situation restricts the development of urban infrastructure and its capacity to address the pressures of urbanization, including the need for comprehensive wastewater treatment systems. To understand the factors driving treated wastewater agriculture, it is essential to examine the level of sanitation and the methods used for collecting and disposing wastewater in urban areas. Eighty percent of the cities in underdeveloped countries have some sort of sewer system. However, just 1/3 of the cities achieved an 80% home coverage rate. Only closed sewers were present in half of the cities that responded, whereas 33% of them had both closed and open sewer systems [65].

2.2. Barriers/Challenges in Using Treated Wastewater in Irrigation

Reusing treated wastewater has been acknowledged as a sustainable and safe water source for the irrigation of vegetables since the early 20th century, when modern wastewater treatment plants were developed [66]. Treated wastewater quality can exhibit considerable variation depending on the extent of treatment. Generally, it contains higher proportions of organic and inorganic components in contrast to freshwater. Inadequate management of these constituents may result in unintended environmental and agronomic consequences [67]. Increased microbiological hazards, heavy metal buildup in plants and soils, deterioration of soil qualities, increasing pathogen levels, and increased food contamination have all been linked to insufficient or untreated wastewater irrigation. Knowledge of sewage characteristics, proper treatment, storage, distribution, crop selection, and regulation are all necessary for the efficient management of agricultural wastewater reuse, emphasizing the health of people and the environment. In some areas, wastewater that is properly treated in accordance with regulations may even be of higher quality than traditional water sources [68]. In addition, comprehensive monitoring is essential to ensure its safety for agricultural use, especially for high-risk crops.

The unit wastewater treatment cost depends on the treatment process but is generally reported to be in the range of 0.08 to 0.23 EUR/m³ [69]. The high cost of treatment may act as a disincentive for farmers to use this water as irrigation water. However, this cost will be offset by a reduction in fertilizer use with the use of treated water [70]. Moreover, the size of the treatment plant is a factor affecting the cost, with smaller treatment plants having higher costs than larger plants [71]. On the other hand, in many countries, treated wastewater is offered free of charge or subsidized to farmers [72,73].

To meet health and safety regulations, this method must, however, ensure that wastewater is adequately treated using strict and frequently expensive procedures [66]. Some of the barriers to this are presented in this section.

2.2.1. Impact of pH in Wastewater

When water pH deviates from the recommended range, it can induce severe soil acidity or alkalinity, consequently impacting plant growth and yield. Most agricultural plants thrive within a soil pH range of 5.5 to 7.0, whereas municipal wastewater usually occurs between pH values of 6.5 and 8.5. However, industrial wastewater has the potential to alter soil pH levels significantly. Consistent wastewater application, especially of poorly treated water, alters soil chemistry, influencing factors such as residual nutrient levels and soil pH [74]. Sustained irrigation with wastewater of extreme pH values can lead to imbalances in the soil microbial population, adversely affecting soil fertility. Such conditions may inhibit the activity of essential microorganisms like nitrogen-fixing bacteria, disrupting nutrient cycling and further impairing plant health [54]. Hence, it is advisable to thoroughly examine water quality before applying it to agricultural fields, and any deviation from the suitable pH range should be closely monitored and addressed.

2.2.2. Impact of Salinity on Wastewater

The prolonged use of treated wastewater can result in the accumulation of salts in the soil’s root zone, as treated wastewater typically contains higher salt levels than freshwater, potentially reducing plant water uptake due to osmotic effects [75]. In addition, soil properties such as texture, drainage capacity, and irrigation methods also impact the salinity of soil [76]. Moreover, it is stated that compared to flood irrigation, drip irrigation application decreases soil salinity [77].

The total amount of dissolved solids in municipal wastewater typically ranges from 250 to 850 mg L⁻¹ (0.4–1.3 dS m⁻¹), exceeding levels found in freshwater supplies and potentially being higher in some developing regions and many coastal areas [78,79]. These salts can pose risks to crops, even at moderate irrigation salinity levels [80,81,82] and may leach into groundwater beneath irrigation sites [83,84]. In some developing regions, freshwater sources are already saline [85], necessitating careful planning for treated wastewater reuse to avoid exacerbating salinity issues or, conversely, offering a less saline irrigation alternative.

Salinity in treated wastewater is typically higher than in freshwater, and under these salinized conditions, crops can experience immediate osmotic stress as well as delayed damage from phytotoxins, which may take days to weeks to manifest. Osmotic pressure limits the plant’s ability to absorb water, affecting seed germination and plant growth, potentially leading to reduced yields and lower crop quality [86]. From a mechanistic perspective, phytotoxic elements disrupt vital physiological functions, either directly or indirectly, by disturbing the balance of plant nutrients. For example, the competition between potassium and sodium for absorption can further exacerbate nutrient imbalances, negatively impacting plant health and productivity [87,88]. Prolonged exposure to salinity can irreversibly damage soil structure by causing soil particle dispersion and crust formation, which significantly reduce water infiltration rates. Over time, these changes can make soils unsuitable for cultivation, necessitating expensive reclamation efforts to restore productivity [89].

2.2.3. Microbiological and Chemical Risks

Treated wastewater may contain chemical contaminants, harmful pathogens, and associated risks such as antimicrobial resistance genes. The concentrations of these contaminants vary based on various factors, including industrial waste discharged upstream and the methods used by wastewater treatment facilities. These pollutants have the potential to build up in crops and soils, eventually making their way into surface and groundwater through irrigation [90,91]. Antimicrobial resistance presents a distinct challenge in the context of microbial contamination.

Inadequately treated wastewater can still contain bacteria, viruses, and protozoa. They can reach people through the food chain when they consume fruits or vegetables that are irrigated with this water, thus causing outbreaks of gastroenteritis, typhoid, cholera, and viral enteritis [92]. In addition, helminth infections can occur, which cause anemia and impaired growth and cognitive development in children [93]. Dermatitis, fungal infections, and conjunctivitis can occur via dermal exposure to inadequately treated wastewater [93]. Additionally, micropollutant residuals remaining in irrigation water can be toxic and carcinogenic [94]. To mitigate microbial risks, irrigated treated wastewater fruits or vegetables should be washed properly before consumption [95]. The disinfection process can be applied as an advanced treatment process, which decreases the microbial risk potential [92]. Additionally, monitoring of treated wastewater should be conducted periodically, and awareness should be raised among farmers and consumers [96]. Using treated wastewater in agriculture can increase soil salinity, acidity, alkalinity, and toxicity. While some risks can be significant, most are manageable with effective strategies. Although the value of treated wastewater is well recognized, its successful use depends on mitigating risks related to salt and nutrient buildup during irrigation. A previous study noted that treated wastewater can lessen reliance on sources of freshwater, thereby mitigating the risk of volume restrictions and their detrimental effects on the agricultural field [97]. Another study highlights that wastewater treatment and its utilization can substantially alleviate the current and future strain on freshwater sources [98]. Overall, the current technical knowledge and regulatory framework allow appropriate management of the potential risks related to water reuse, making this practice safe from an environmental and human health perspective.

2.3. Country-Wise Reuse Trends and Potential of Treated Wastewater in Agronomic Usages

The reuse of treated wastewater in agricultural practices differs from country to country and is mainly governed by water scarcity and infrastructure, regulations regarding water and wastewater, and public acceptance. Treated wastewater reuse has been adopted more in arid countries with scarce freshwater resources than those with comparatively plentiful supply [65,99,100]. Israel, for example, has been a global leader in treated wastewater reuse for agriculture, with approximately 85% of its treated wastewater utilized in this sector. The country has implemented advanced water treatment technologies and efficient distribution systems, ensuring the safe and reliable supply of this alternative water source to farmers. Different countries have different treated wastewater reuse proportions depending on sectoral demands, countries’ priorities and water sources. For instance, Singapore employs approximately 40% of its treated wastewater for different purposes, mostly non irrigation [101]. In Spain, nearly 71% of treated wastewater used in irrigation purpose and this ratio was 11.5% for Australia and 17% for Jordan [65,102,103,104]. Individuals’ income levels and geographical locations significantly influence the generation and treatment of wastewater. Generally, countries with higher income levels tend to produce more wastewater. Conversely, nations in arid regions with low rainfall tend to collect and treat wastewater for reuse more extensively than others. For instance, a mere 16% of the global population residing in affluent countries accounts for 41% of the world’s wastewater production. Notably, regions characterized by arid climates and minimal rainfall, such as the Middle East and North Africa, exhibit high rates of treated wastewater reuse, with approximately 15% of total wastewater being treated and repurposed in these areas. Remarkably, the population of these regions represents only about 5.8% of the global population [100]. Figure 1 shows the impact of treated water irrigation in plant and ecosystem.

2.4. Advanced Wastewater Treatment Technologies for Producing Irrigation-Quality Water

While treated wastewater offers an appealing solution for direct use in farming, it is crucial to effectively employ proper treatment methods to address environmental and health concerns [34]. In addition to encouraging the efficient use of water resources, advanced wastewater treatment can improve the quality of treated wastewater for irrigation. These methods are specifically developed to treat water of different qualities, increasing its appropriateness for reuse by removing organic contaminants, excess nutrients, and pathogens, hence preventing potential risks in irrigation conditions [105]. Incorporating advanced treatment technology into wastewater management provides numerous important benefits, particularly for agricultural irrigation. The main advantage of using advanced treatment methods is that they help enhance water quality. They save nutrients, organic contaminants, and dangerous pathogens that would otherwise damage crops or degrade soil quality. Properly cleaned wastewater can be used for irrigation without threatening human health or crop productivity [97]. Many advanced treatment techniques, including membrane bioreactors and artificial wetlands, have been developed to recover important, lost nutrients such as nitrogen and phosphorus. By repurposing these nutrients into fertilizers, the values can create a closed loop or circular economy which eliminates the need for synthetic fertilizers in agriculture [106]. These technologies are compatible with the sustainable utilization of water resources, namely wastewater cleaning and recycling technology. They contribute to reducing the environmental impact associated with wastewater disposal and conserving freshwater resources, especially in desert regions in which water is scarce [107]. A number of issues hamper the widespread use of cutting-edge wastewater treatment technologies for agricultural irrigation, despite the numerous advantages; advanced oxidation processes (AOPs), as well as reverse osmosis, often require significant energy and infrastructural investments. While costs have dropped over time, many areas, especially in developing nations, cannot afford it and this possess a barrier to its adoption [108].

2.5. Public Perceptions of Treated Wastewater Irrigation

While using treated wastewater for irrigation has numerous benefits, particularly in agriculture, public acceptance is crucial for its successful implementation. Resistance from the public has been a significant factor contributing to the failure of many water reuse projects [109]. As such, policymakers and decision-makers should perform extensive perception assessments before embarking on using treated wastewater for irrigation practices [110]. Negative emotional reactions (yuck factor), disgust, and fear prevent social acceptance of treated wastewater. Strategies including the appropriate use of language, better public education, and the fostering of open discussion can help cut the ‘yuck factor’ and help urge the environmental and social advantages of using treated wastewater [110]. In the United States, the ‘yuck factor’ or general disgust is a barrier to the acceptance of projects that use treated wastewater. Wester et al. [111] found negative emotional reactions toward the reuse of treated wastewater. The results showed that women with less education were more likely to feel uncomfortable with treated wastewater reuse. In the United States, respondents would accept the recycling of treated wastewater if the treated wastewater is not used to irrigate human food crops [112].

Public perception can directly impact the acceptance and implementation of treated wastewater reuse in agricultural practices. The perception is impacted by various factors, including health and safety concerns, environmental awareness, economic benefits, and cultural factors [106]. In a survey conducted in Arabia, 77% of respondents supported the use of treated water as agricultural irrigation water due to limited water resources and trust in the authorities responsible for wastewater treatment. Those who did not support it focused on health risks and psychological factors [107]. Education level is also a factor for supporting the reuse of treated wastewater for agricultural purposes. Those with higher education level supported the reuse of treated wastewater [108]. On the other hand, the price of the product is also a factor; since if the price of the product irrigated with treated wastewater is lower, consumers tend to prefer it [109]. In a study conducted in France, although the public was informed about treated wastewater-irrigated crops, 20% of the respondents reported that they would not buy treated wastewater-irrigated crops and the reason for this was lack of confidence in food quality [110]. Environmental risks are also a factor affecting the use of treated wastewater. In Jordan, farmers were concerned that the high salt content of treated wastewater could damage the soil structure [111]. Lastly, in some regions, there is a cultural and religious bias against the use of treated wastewater [112].

Several studies have been conducted to determine the public sentiment on the consumption of crops that are irrigated with treated wastewater. The willingness to pay (WTP) index is commonly used to assess people’s level of satisfaction or dissatisfaction. As shown in a study by Savchenko et al. [113], agricultural products from treated wastewater irrigation sources are not well appreciated by the participants, for whom WTP has little value compared products to irrigated with conventional water. Notably, the WTP for these products was actually lower than for products irrigated with water from an unknown source. These findings are consistent with what was observed by Ellis et al. [114] who conducted a survey among Israeli consumers. When they discovered that an agricultural product was watered with treated wastewater, the consumers significantly cut their demand compared to products irrigated conventionally or sourced from an unspecified location. It is not surprising that despite Israel’s use of treated wastewater for 36 years, there is still reluctance towards crops irrigated with treated wastewater. Despite widespread familiarity with treated wastewater among Israelis, acceptance of it in Israeli homes has been low.

A study of grape and wine irrigation conducted by Li et al. [115] found that consumers prefer to remain ignorant of their irrigation water source than knowing that the water was from treated wastewater. When they found out that treated wastewater was being used as an irrigation source, a lot of consumers lost WTP. Nkhoma et al. [116] also noted that even positive information extolling the benefits of treated wastewater did not change consumers’ inclination to spend more on such products. People are reluctant or averse to treated wastewater due to their disgust for its source and fears of disease transmission and other hazards [114]. So, it is easy to understand why people instinctively prefer clear spring water to treated wastewater. As demonstrated in a study by Savchenko et al. [104,113], the biggest reason why the public are lukewarm on treated wastewater is disgust about the wastewater source. However, consumer acceptance of crops irrigated with treated wastewater will likely increase if consumers are informed of this crop’s negative aspects (i.e., potential risks crops irrigated with treated wastewater may pose to consumers and the positive environmental benefits of using treated wastewater). Some researchers have observed that presenting consumers with a balanced view of treated wastewater, both positive and negative aspects of treated wastewater, can increase their willingness to pay for crops irrigated with treated wastewater [104,116].

3. Environmental, Economic, and Social Benefits

In recent years, treated wastewater has become more popular for crop irrigation. This novel strategy attempts to resolve three interrelated but distinct issues: environmental sustainability, economic viability, and social equality. Water-scarce regions can increase agricultural production by using treated wastewater that would otherwise be discarded. This also plays a role in food security and rural livelihoods and contributes to economic savings by reducing the costs of freshwater extraction and treatment [117]. Economic opportunities for using treated wastewater include cost savings and new sources of income within industries [118]. Using treated wastewater instead of freshwater resources can lower the cost of irrigation, improving the profitability and long-term financial sustainability of agricultural businesses.

It leads to the development of local economies and generates money to pay for infrastructure. Recovered wastewater not only helps improve community resilience and equity, it also provides social benefits [119].

The potential of treated wastewater as a dependable and easily accessible resource for crop production in water-stressed areas calls for more study. Treated wastewater improves food sovereignty in rural communities by lowering their dependency on imported water, raising their standard of living, and stabilizing local economies [120]. The realization of these advantages has some challenges because there is a difference to access to treated water in urban and rural areas. People cannot access this water equally, which can cause social tensions. Also, implementing strong regulatory frameworks and comprehensive governance structures is vital to promote fair distribution, long-term sustainability, and community engagement [121]. It is crucial to have the active monitoring of water resources, regulatory surveillance, and community participation in order to manage questions related to do with quality, health impacts, and perception in a manner that is sustainable and acceptable to communities [122]. However, these challenges and constraints have to be addressed to enhance the potential of using treated wastewater in supporting sustainable agricultural development; this includes strong policy and effective wastewater technologies [123].

3.1. Environmental Benefits

Treated wastewater used in agriculture has many environmental benefits if it meets strict quality standards. This brings reduced water shortage, less pollution, more fertile soil, and a healthy ecosystem [97]. The use of treated wastewater in agriculture is excellent for the environment because it conserves freshwater use and reduces nutrient pollution [117]. Another advantage of using treated wastewater is that it reduces the demand for freshwater in lakes, rivers, and groundwater compared to freshwater in rivers and reservoirs. The protection of freshwater supplies is necessary to maintain ecological balance and to meet requirements for different water uses across sectors, especially in water-stressed regions [26]. Treated wastewater is a rich source of plant-building nutrients, including nitrogen, phosphorus, and potassium, and it is an eco-friendly substitute for manufactured fertilizers. Using treated wastewater for irrigation decreases nitrogen loss to neighboring water bodies and keeps them away from the eutrophication of adjacent ecosystems. This method permits crop nutrition while reducing the ecological footprint of nutrient contamination of water sources [27].

Treated wastewater can also be used in agriculture instead of freshwater sources for the benefit of both aquatic ecosystems and animals. This strategy reduces water extraction, maintains environmental flows in streams and rivers, and increases ecosystem services and biodiversity. Healthy agricultural landscapes support different habitats, increase pollinator populations, and provide a home for beneficial insects, all of which strengthen a whole system’s ecosystem resilience [124]. Treated wastewater contains organic materials and micronutrients and helps improve soil fertility and structure. Improved water retention decreases erosion and includes microbes necessary for healthy nutrient cycling and soil health. By creating healthy soils, these methods promote sustainable agriculture practices that further lead to healthy crop development and environmental resilience [125]. Treated wastewater must be carefully managed for agricultural irrigation. It must conform to the applicable water quality standards and undergo continuous monitoring to achieve safety and effectiveness. Given the increased demands on water resources and food production at a global scale, the use of treated wastewater in agricultural practices constitutes one effective way to foster resilient and sustainable food systems [46].

3.2. Economic Benefits

Using treated wastewater in farming practices has financial benefits for farmers, communities, and regions [126]. Treated wastewater contributes to the economic and environmental sustainability of farming by raising crop yields and productivity (Figure 2). It increases soil fertility and health, enhancing overall agricultural productivity. Plants’ use of the nutrients in treated wastewater is improved because organic materials and important micronutrients are already biologically available for uptake. Thus, this leads to healthier crops that the buyers find more valuable. Furthermore, healthier soil and improved water retention help crops withstand stress, ultimately lowering production variations and increasing farmer productivity [127]. Previous research has proved that the use of treated wastewater for the irrigation of agricultural crops could lead to an improvement in crop yields due to the valuable nutrients contained in the treated wastewater [128]. It is stated that increased total nitrogen content in irrigation water enhances the turfgrass yield, and it is recommended that irrigation water contain at least 5 mg/L total nitrogen for maximum yield [129]. A study conducted in Taiwan found that secondarily treated wastewater contains 15–20 mg/L of nitrogen, which is excessive for irrigating rice [130]. Crop yield varied based on crop type and nutrient concentration in treated wastewater used for irrigation [96]. For instance, irrigating with treated wastewater increased the yield of eggplant, cucumber, tomato, and kidney beans by 61, 24, 15, and 7%, respectively, compared to the groundwater as a control group [131].

Ref. [132] compared rice crops that were irrigated with treated wastewater versus conventional water, and the rice yields in treated wastewater irrigation were 15% higher. Similarly, Emongor et al. [133] noted a 115% increase in tomato yield when the plant was irrigated with treated wastewater. Wang et al. [134] sampled 62 crop research studies to understand how treated wastewater affects yields between 1987 and 2021. They concluded that crop yield under treated wastewater irrigation was 19.7% higher than crops irrigated by conventional methods. Treated domestic and livestock wastewaters significantly increased yield, whereas certain treated industrial wastewaters containing plant growth inhibitors were associated with decreased yield. Additionally, the concentration of nutrients in treated domestic wastewater was identified as a key factor influencing product performance [18,134].

Treated wastewater is high in nutrients, particularly nitrogen, phosphorus, and potassium, all of which are essential for plant growth. Wastewater- and treated wastewater-use studies in Brazil, Saudi Arabia, and Poland have shown that it can meet the nutritional requirements for corn, supplying adequate phosphorus, potassium, and some micronutrients [34,135]. A study by Zema et al. [136] also reported a huge increase in those plant metrics due to treated wastewater irrigation, such as biomass yield of up to 63%, plant height of up to 25%, and leaf area index of up to 86%. Likewise, Urbano et al. [137] found yields at least 48% higher than under conventional irrigation practices, indicating that the nutrients in treated wastewater were suitable enough to support plant nutrition. The presence of ammonia in treated wastewater, as indicated by Gatta et al. [138], also caused a 20% increase in artichoke yield. Furthermore, Singh et al. [139] also found that treated wastewater irrigation promoted grain weight and rabi crop yield compared to conventional irrigation methods. Irrigation with this treated wastewater can help farmers reduce the use of synthetic fertilizers. This method reduces the financial burden associated with the inputs and outputs of chemical fertilizer transport and application [107]. The major economic advantage of using treated wastewater in farming is the reduced cost of water supply. Sometimes, treated wastewater is less costly or subsidized than freshwater sources. Most crucially, these affordability levels are especially beneficial in locations where freshwater supplies are scarce or where prices are high due to rising demand and water scarcity [140]. Treated wastewater can be used for irrigation by agricultural businesses to meet strict water rules and sustainability standards.

3.3. Social and Health Benefits

Using treated wastewater is one of the most significant societal ways of addressing water scarcity. Using treated wastewater can help reduce the demand for freshwater by providing an extra water source for crop irrigation and supplying water to factories and cities. Consequently, this demand reduction lessens the burden of the current freshwater sources and should guarantee a more sustainable water supply for communities [107,141]. The most efficient strategy to redirect treated wastewater from water bodies to sustainable reuse is to treat it correctly, keeping it out of water sources and lowering the danger of waterborne diseases and pollution. Additionally, using treated wastewater for irrigation supplies plants with needed phosphorus and nitrogen, reducing the likelihood of eutrophication from runoff and limiting runoff of nutrients into adjacent water bodies [107,142,143].

Climate change resilience can be enhanced through using treated wastewater [107,144]. Diversification of water sources and decreasing dependence on freshwater protect communities from droughts, water shortages, and other climate-related pressures. In addition, there is an opportunity to use treated wastewater for landscape irrigation, which can enhance esthetics and provide green spaces in communities. As a result, this increases general livability and quality of life by providing people with recreational amenities like parks and gardens [107]. Moreover, participation and community engagement are common in treated wastewater reuse projects [145]. It encourages community members to increase awareness and understanding of water management practices. This develops a sense of ownership and responsibility for water management and its impacts on them. Through active involvement of the community, treated wastewater reuse initiatives can provide the key for people to participate in sustainable water management and the well-being of their communities [145,146]. Thus, the stakeholders can achieve numerous goals through the use of treated wastewater, which is ecologically friendly, economically sustainable, and socially responsible [147].

4. Recommendations for Future Studies

Future studies should focus on understanding the long-term impacts (on the ecosystem and human health) of treated wastewater in agriculture. Thorough monitoring strategies are necessary to assess cumulative impacts on surface water, groundwater, and soil quality systems. Major areas of concern are changes in soil salinity, the persistence of organic contaminants, and the accumulation of heavy metals. Future studies should also investigate such things as the growth of bacteria resistant to antibiotics and the bioaccumulation of toxic compounds in crops resulting from treated wastewater irrigation. The danger of these compounds needs to be evaluated in relation to how well advanced treatment methods, such as membrane bioreactors, UV disinfected, and advanced oxidation processes, can remove them. In addition, studies should determine how treated wastewater affects biodiversity, particularly soil organisms and pollinators that are pivotal to agricultural ecosystems.

Different wastewater treatment and reuse scenarios need to be examined to determine their cost-effectiveness compared to their benefits, which may include cheaper agriculture, reduced wastewater expense, and reduced freshwater usage. Public acceptance remains one of the greatest impediments to widespread wastewater reuse. Therefore, more studies on cultural aspects, societal opinions, and educational initiatives can provide direction to create successful communication strategies, promoting acceptance and trust.

The impact on the agricultural ecosystem should be examined if treated wastewater is used as irrigation water as a long-term application. Mathematical models could be developed, and real-scale systems could be established. Biochemical changes that may occur in plants and soil over time could be examined. Plants affected and plants not affected by treated wastewater could be classified, and treated wastewater could be used to this extent. The durability, product quality, and yield of plants irrigated with treated water for a long period could be examined. To prevent the salinity problem that may occur in the soil, the soil test could be employed before using treated wastewater. Leak to groundwater could be examined and predictions should be made using models. The use of treated wastewater for agricultural purposes could be encouraged in entire region, not only in arid and semi-arid climates. By utilizing smart irrigation systems, the quality of treated wastewater and the amount to be used for irrigation can be monitor continuously. Different types of irrigation methods could be examined. The scope of legal regulations could be improved, and monitoring of micropollutants in irrigation water could be ensured. The use of treated wastewater for agricultural purposes could be strengthened with holistic approaches, and the public should be informed about this issue.

5. Conclusions

Using treated wastewater for agricultural irrigation has substantial opportunities and challenges, making it an important technological and regulatory priority. In water-scarce areas, treated wastewater is an assured water supply, enhancing agricultural productivity and increasing crop yields. However, its effectiveness depends on careful adherence to safety requirements for its physicochemical and microbiological qualities to reduce risks to human health and the environment. Raw or inadequately treated wastewater poses a big threat because it is likely to contain pathogenic bacteria, toxic metals, and hazardous chemicals. Despite treatment, runoff and leaching of nutrients may lower surface and groundwater availability and quality. It is necessary to use thorough treatment technologies and subsequent observation to ensure the safe and sustainable use of treated wastewater. Despite these limitations, treated wastewater is a social, economic, and environmental water scarcity solution. It conserves freshwater supplies, promotes water conservation, and is a low-cost irrigation method, especially in dry areas. Appropriate treatment and management of wastewater are critical to addressing global water issues, ensuring public health, and developing resource and energy-efficient farming systems. The main limitation of this review article is lack of quantitative meta-analysis. In the future, authors will focus on this topic.