Advanced nanocomposite membranes for sustainable water reuse in agriculture

1 Introduction

1.1 Global water scarcity and the growing pressure on agriculture

Freshwater availability per person has been in steady decline for decades, and the trend has continued into the present (Gleick and Cooley, 2021). Food and Agriculture Organization of the United Nations (FAO)’s most recent AQUASTAT (FAO’s global information system on water and agriculture) assessment reports that renewable water availability per capita fell by roughly seven percent over the last decade alone, with the sharpest declines concentrated in Northern Africa, Southern Asia, and Western Asia (Water, 2024). At the same time, agriculture remains overwhelmingly the largest consumer of the world’s freshwater, accounting for approximately 70%–72% of total withdrawals globally, far outweighing municipal and industrial use combined (Water, 2021). UN-Water estimates that more than three billion people already live in agricultural regions experiencing high to very high-water shortages, and roughly 1.2 billion of them live under conditions of severe water constraint (Ingrao et al., 2023). Mekonnen and Hoekstra’s widely cited global assessment similarly found that close to four billion people face severe water scarcity for at least part of the year (Jones et al., 2024).

The imbalance between water supply and agricultural demand is expected to intensify rather than ease. Climate change is altering precipitation patterns and increasing the frequency of prolonged droughts in historically productive regions, while population growth and rising dietary demands continue to push up the volume of water required to produce food (Khalid Mohamed and Mona Othman, 2025). Urban water scarcity, which is closely linked to agricultural competition for the same finite resources, is projected to affect between 1.7 and 2.4 billion people by 2050, roughly double the number affected in 2016 (Falkenmark, 2013). Because irrigated agriculture underpins a large share of global food production, any shortfall in reliable irrigation water threatens not only farmer livelihoods but also regional and global food security (Dark et al., 2016). Figure 1 provides a comprehensive summary of global freshwater dynamics, highlighting declining per capita availability, sector-wise consumption, and the growing scale of human water stress.

1.2 The case for water reuse in agriculture

Given these pressures, reliance on freshwater abstraction alone is no longer a viable long-term strategy for irrigation-dependent agriculture. Water reuse, meaning the treatment and repurposing of water that would otherwise be discharged as waste, has emerged as one of the most practical near-term solutions to close the widening gap between water demand and supply (Christou et al., 2024). Reused water offers several advantages beyond volume alone: treated wastewater streams frequently contain recoverable nutrients such as nitrogen, phosphorus, and potassium that can reduce a farm’s dependence on synthetic fertilizer, effectively turning a waste stream into a resource stream (Saliu and Oladoja, 2021). This aligns water reuse with the broader circular economy principle of resource recovery rather than resource depletion.

However, water reuse in agriculture is not without risk. Wastewater sources can carry pathogens, antibiotic-resistant bacteria and genes, heavy metals, pharmaceutical residues, and elevated salinity, all of which can compromise crop safety, soil health, and long-term irrigation system performance if not adequately treated (Pompa-Pernía et al., 2022; Oliveira et al., 2022). The central engineering challenge, therefore, is not simply reclaiming water in bulk, but reclaiming it to a quality that is both agronomically appropriate and publicly acceptable, while keeping treatment costs and energy demands within reach of the agricultural sector.

1.3 Common sources of water for agricultural reuse

Three broad categories of wastewater are most commonly considered for agricultural reuse:

Municipal wastewater from domestic sewage and treatment plants is the most widely reused source worldwide. After secondary biological treatment, municipal effluent typically still requires tertiary polishing, most often through membrane-based processes, to meet microbiological and chemical standards for irrigation of food crops (Oliveira et al., 2022). Municipal wastewater is attractive because of its relatively predictable composition and its year-round availability near urban and peri-urban farming zones.

Industrial wastewater, including effluents from food processing, textile, and agro-industrial operations such as sugar and ethanol production, represents a second major source. These streams can be highly variable in composition, sometimes carrying high organic loads, dyes, or salts, but they can also be rich in nutrients or organic matter of value to agriculture when adequately treated (Hafiz et al., 2021).

Agricultural wastewater itself, including drainage water, aquaculture effluent, and livestock wastewater, constitutes a third and increasingly important category. On-farm reuse of drainage and runoff water closes the loop within the agricultural system itself, although this water often carries elevated salinity and agrochemical residues that require careful management (Quist-Jensen et al., 2015; Al-Hazmi et al., 2023).

Across all three sources, membrane technologies have become the workhorse of tertiary treatment because of their ability to achieve high selectivity for a broad range of contaminants within a single unit process. The sections that follow examine the membrane technologies currently used for agricultural water reuse, the persistent challenges that limit their broader adoption, and the emerging role of nanocomposite membranes in addressing those limitations.

Figure 2 shoews schematic illustration of the water reuse cycle for sustainable food production. The framework highlights the major sources of reclaimed water, including industrial wastewater, agricultural effluents, domestic wastewater, and hospital sewage, along with the key benefits of water reuse, such as promoting the circular economy, reducing environmental impacts, supporting food security, providing economic benefits, and conserving freshwater resources. It also summarizes the main challenges associated with water reuse, including health risks, public acceptance, economic constraints, and infrastructure limitations that must be addressed for sustainable implementation.

2 Current challenges in membrane-based agricultural water reuse

Despite decades of development, membrane-based water reuse for agriculture continues to face a cluster of interrelated challenges that have slowed its widespread deployment, particularly in resource-limited farming regions.

2.1 Membrane fouling

Fouling, the accumulation of organic matter, colloids, scalants, and microorganisms on or within the membrane structure, remains the single most persistent obstacle to reliable membrane operation (Ahmed et al., 2023). Fouling manifests as a decline in permeate flux over time, an increase in required trans-membrane pressure, and, in the case of biofouling, the formation of biofilms that are notoriously difficult to remove through conventional chemical cleaning (Alhussaini et al., 2024). In membrane bioreactors treating agricultural or municipal wastewater, fouling is widely regarded as the main factor limiting long-term operational stability, driving up cleaning frequency, chemical consumption, and membrane replacement costs (Pervez et al., 2020). Because agricultural wastewater sources are often rich in natural organic matter, proteins, and microbial loads, they are particularly prone to accelerating fouling relative to cleaner feed sources such as groundwater. Corzo et al. (2018) investigated the long-term performance of a hybrid forward osmosis–nanofiltration (FO–NF) system for agricultural wastewater reuse by operating a demonstration plant continuously for 480 days with real wastewater. They evaluated three draw solutions—sodium polyacrylate, magnesium sulfate (MgSO₄), and magnesium chloride (MgCl₂)—to assess their impact on membrane fouling and process performance. The results showed that sodium polyacrylate caused mainly reversible membrane fouling, while MgSO₄ induced severe irreversible fouling on the NF membranes, leading to its rejection as a draw solution. In contrast, MgCl₂ exhibited the lowest fouling tendency, maintained stable membrane permeability during long-term operation, and produced irrigation-quality water, making it the most suitable draw solution for the FO–NF process.

2.2 Energy consumption and cost

Pressure-driven processes such as reverse osmosis (RO) and nanofiltration (NF) require substantial energy input to overcome osmotic pressure, particularly when treating higher-salinity feed streams such as seawater or saline agricultural drainage (Niewersch et al., 2014). Comparative studies of NF and RO for reclaiming tertiary treated municipal wastewater for irrigation have shown that RO permeate can meet FAO irrigation water quality standards, but only within a narrow pressure window, and that pushing pressures higher to improve rejection sharply increases specific energy consumption without necessarily improving usability for irrigation (Hafiz et al., 2021). Because farm-scale water reuse projects are typically far more cost-sensitive than municipal drinking water schemes, the added energy burden of membrane desalination is a major barrier to adoption, especially in developing regions where the sector can least absorb high operating costs (Suwaileh et al., 2020).

2.3 Nutrient removal versus nutrient retention

A challenge specific to agricultural (as opposed to potable) water reuse is that conventional RO and tight NF membranes are highly effective at removing dissolved nitrogen, phosphorus, and potassium salts, precisely the nutrients that would otherwise reduce fertilizer demand (7). Overly aggressive purification can therefore strip water of agronomic value that it would otherwise retain. Balancing adequate rejection of pathogens, salts, and emerging contaminants against the retention of beneficial nutrients requires membranes with more finely tuned, rather than simply maximized, selectivity (Cosenza et al., 2022).

2.4 Water quality complexity and emerging contaminants

Reclaimed wastewater is a chemically complex feed, frequently containing antibiotic-resistant bacteria and resistance genes, pharmaceutical and personal care product residues, and trace organic contaminants that conventional secondary treatment does not remove (Pompa-Pernía et al., 2022). Tertiary nanofiltration has demonstrated the ability to substantially reduce total bacteria and resistance gene concentrations, but complete removal is not guaranteed, and residual risk in reused irrigation water remains a subject of ongoing public health concern (Oliveira et al., 2022).

2.5 Salinity management

Elevated salinity, whether from seawater intrusion, industrial effluent, or agricultural drainage, poses a distinct challenge, since electrical conductivity above roughly 3,000 μS/cm is generally considered high risk for crop yield and soil structure (Pompa-Pernía et al., 2022). Recycled and repurposed membranes have shown promise for treating such saline wastewater streams at lower cost, but salinity management generally still requires either high-pressure RO or hybrid processes combining several membrane technologies, both of which add complexity and cost (Pompa-Pernía et al., 2022).

2.6 Regulatory, economic, and social barriers

Beyond the purely technical challenges, adoption of membrane-based agricultural water reuse is shaped by regulatory standards that vary widely between countries, uncertain economics for smallholder farmers, and public perception concerns about the safety of food grown with reclaimed water (Suwaileh et al., 2020). These non-technical barriers mean that even a technically superior membrane will see limited uptake unless it is also affordable, robust under variable field conditions, and supported by clear water quality guidelines.

2.7 Water reuse regulations and irrigation water quality as design targets

Assessment of membrane performance for agricultural water reuse should be linked not only to irrigation-water quality guidelines but also to the regulatory framework governing reclaimed water in the intended jurisdiction. The FAO irrigation-water guidelines remain highly relevant for assessing agronomic suitability because they address parameters such as electrical conductivity, sodium adsorption ratio, chloride, boron, and selected trace elements that can affect soil structure, crop productivity, and phytotoxicity under repeated irrigation (Minhas et al., 2024). However, these guidelines represent only one component of the broader water-reuse regulatory landscape. Different jurisdictions place different emphasis on microbiological safety, physicochemical quality, monitoring frequency, exposure pathways, and risk management.

The WHO framework adopts a health-based risk-management approach rather than prescribing a single universal set of physicochemical limits for all agricultural applications (Calliera et al., 2025). Its guidelines distinguish vulnerable groups including agricultural workers, nearby communities, and consumers, and emphasize health-based targets, risk assessment, and multiple barriers for controlling microbial hazards. This approach complements agronomic criteria because it recognizes that the acceptable quality of reclaimed water depends on the exposure scenario and intended crop use rather than solely on the measured concentration of individual contaminants.

The European Union provides a more prescriptive framework through Regulation (EU) 2020/741, which establishes minimum requirements specifically for agricultural irrigation (Ricciardo Calderaro et al., 2024). Four reclaimed-water quality classes (A–D) are defined according to the type of crop and irrigation conditions. For the highest-quality Class A water, the requirements include Escherichia coli ≤ 10 CFU/100 mL, BOD5 ≤10 mg/L, TSS ≤10 mg/L, and turbidity ≤5 NTU, together with additional requirements for Legionella and intestinal nematodes where applicable (Ricciardo Calderaro et al., 2024). Less stringent microbiological requirements are permitted for Classes B–D depending on the intended agricultural use. The regulation also specifies routine and validation monitoring, making treatment reliability and process control explicit regulatory requirements.

In the United States, there is no single nationwide agricultural water-reuse standard equivalent to the EU Regulation 2020/741. Instead, requirements vary among states and are supplemented by federal guidance. The U.S. EPA’s Guidelines for Water Reuse provide a technical framework and describe agricultural reuse practices, while individual states establish enforceable requirements (Ritter, 2021). California provides one of the most developed examples through its Title 22 Water Recycling Criteria (Wong and Gleick, 2000). Depending on the intended agricultural application, recycled water may be subject to different treatment and microbiological requirements. For disinfected tertiary recycled water, for example, California specifies a 7-day median total-coliform concentration of ≤2.2 MPN/100 mL, a maximum of 23 MPN/100 mL in more than one sample during a 30-day period, and stringent turbidity requirements; when membrane filtration is used, the filter effluent turbidity requirement can be ≤ 0.2 NTU for more than 5% of the time and ≤0.5 NTU as a single-sample maximum (Reyes et al., 2026).

These regulatory frameworks show substantial convergence in their emphasis on pathogen reduction, suspended-solids control, and reliable treatment performance, but they differ in the parameters used to define acceptable reclaimed water. FAO guidance places comparatively greater emphasis on agronomic parameters such as salinity, sodium, chloride, and boron; WHO emphasizes health-based risk assessment and multiple barriers; the EU establishes explicit reclaimed-water classes with numerical microbiological and physicochemical requirements; and U.S. requirements are more decentralized, with state-specific regulations such as California Title 22. This distinction is particularly important for membrane technology because membrane design directly influences several regulated parameters. MF and UF can provide strong removal of suspended solids and turbidity but may require additional barriers for dissolved salts and pathogens, whereas NF and RO can provide substantially greater rejection of dissolved ions and organic contaminants. The choice of nanocomposite modification therefore needs to be evaluated against the actual quality parameters required by the applicable reuse framework rather than against a single universal performance target. Table 1 compares the major frameworks and highlights their relevance to nanocomposite membrane development.

TABLE 1. Comparison of selected water-reuse and irrigation-water quality frameworks and their relevance to nanocomposite membrane design.

From a nanocomposite-membrane perspective, an important regulatory gap remains. Existing water-reuse frameworks generally regulate the quality of the reclaimed water rather than prescribing specific limits for nanoparticle release originating from the membrane itself. Consequently, a membrane may produce water that satisfies conventional microbiological, turbidity, organic, and salinity requirements while still requiring a separate assessment of nanoparticle or dissolved-metal release. This issue is particularly relevant for membranes incorporating Ag, CuO, TiO2, graphene-based materials, carbon nanotubes, or metal-organic frameworks. Therefore, future regulatory evaluation of nanocomposite membranes should combine conventional reclaimed-water parameters with membrane-specific leaching measurements, nanoparticle characterization, and toxicological assessment. The comparison demonstrates that regulatory compliance for agricultural water reuse cannot be reduced to achieving a single set of irrigation-water limits. Instead, successful membrane deployment requires simultaneous consideration of agronomic quality, microbiological safety, physicochemical quality, exposure scenario, monitoring requirements, and potential contaminants introduced by the treatment technology itself. This multidimensional regulatory landscape represents an important consideration when translating laboratory-scale nanocomposite membrane performance into field-scale agricultural water-reuse applications.

3 Membrane technologies used for agricultural water reuse

A range of membrane processes, differing in pore size, driving force, and separation mechanism, is currently applied to agricultural water reuse. Each occupies a distinct niche depending on feed water quality and the desired characteristics of the product water.

3.1 Microfiltration and ultrafiltration

Microfiltration (MF) and ultrafiltration (UF) use relatively large pore sizes and operate at low pressure, making them well suited to removing suspended solids, colloids, and larger microorganisms as a pretreatment step ahead of tighter membranes (Eykamp et al., 1995). Because MF and UF rely on physical size exclusion, they are not an absolute barrier to bacteria and viruses, and their disinfection performance can be inconsistent unless supplemented by chemical or nanomaterial-based antimicrobial enhancement (Castro-Muñoz et al., 2022). Their low energy requirement, however, makes them attractive as a first-stage treatment for agricultural reuse schemes operating under tight cost constraints. Figure 3 presents the separation capabilities of the major pressure-driven membrane technologies used in water and wastewater treatment, illustrating the relationship between membrane pore size and the size of contaminants retained. As membrane pore size decreases from microfiltration (MF) to reverse osmosis (RO), the ability to remove smaller species progressively increases. Microfiltration primarily removes suspended solids and particulates, ultrafiltration retains macromolecules and colloids, nanofiltration rejects dissolved organic molecules and multivalent ions, while reverse osmosis effectively removes dissolved salts and monovalent ions, producing high-purity water suitable for demanding reuse applications, including agricultural irrigation.

3.2 Nanofiltration

Nanofiltration occupies the selectivity range between ultrafiltration and reverse osmosis, rejecting multivalent ions and larger organic molecules while allowing a greater fraction of monovalent ions and, importantly, some nutrient ions to pass through (Suhalim et al., 2022). This partial selectivity makes NF particularly attractive for agricultural reuse, since it can reduce excessive salinity and remove pathogens and larger contaminants while retaining a useful nutrient load in the permeate. Comparative studies of NF against RO in reclaiming tertiary treated wastewater have found that NF membranes can achieve good removal of nitrates, phosphates, and organic contaminants at considerably lower applied pressure and specific energy consumption than RO, although at some cost to overall salt rejection. NF has also demonstrated the capacity to substantially reduce total bacterial counts and antibiotic resistance gene concentrations when used as tertiary treatment for municipal effluent (Oliveira et al., 2022). Amiri et al. (2026) synthesized imine-based covalent organic framework (COF) nanoparticles and incorporated them into the polyamide selective layer of thin-film nanocomposite (TFN) membranes to enhance water purification performance. The incorporation of COFs increased membrane hydrophilicity and surface roughness, leading to a significant improvement in water permeability while maintaining high salt rejection at optimal COF loading. The optimized membrane (TFN2) achieved excellent heavy metal rejection (>99% for Cu²⁺ and Mn²⁺ and 96.1% for Pb²⁺) and demonstrated superior antifouling performance, exhibiting the highest flux recovery ratio and the lowest irreversible fouling compared with the pristine membrane. These findings indicate that COF incorporation effectively enhances permeability, contaminant removal, and fouling resistance, making TFN membranes promising for wastewater treatment and heavy metal removal. Gorjizadeh et al. (2024) modified polysulfone (PSF) membranes by incorporating hybrid halloysite nanotubes (HHNTs) and dendrimers for the treatment of petroleum wastewater containing heavy metals. The membrane modification increased surface hydrophilicity (indicated by a lower water contact angle) and significantly enhanced heavy metal rejection. The membrane containing 1 wt% HHNTs (HNT1) exhibited the best performance, achieving rejection efficiencies of 98.79% for Pb²⁺, 83.25% for Cu²⁺, 81.09% for Ni²⁺, and 85.98% for Zn²⁺, while also outperforming the pristine PSF membrane. These results demonstrate that HHNT incorporation effectively improves membrane hydrophilicity and separation efficiency, making the modified membranes promising for industrial wastewater treatment.

3.3 Reverse osmosis

Reverse osmosis remains the benchmark technology for producing high-quality desalinated water from saline sources, achieving near-complete rejection of dissolved salts, pathogens, and most organic contaminants (Qasim et al., 2019). For agricultural applications, RO permeate typically requires blending with untreated or partially treated water to restore the nutrient content and ionic balance suited to crop irrigation, since pure RO permeate lacks the mineral content that plants require (Suwaileh et al., 2020). RO’s principal drawbacks for agricultural use are its high energy demand, sensitivity to fouling and scaling, and the need to manage a concentrated reject brine stream, all of which raise its overall cost relative to less selective membrane processes. Ćurić et al. investigated the feasibility of reusing reverse osmosis (RO) concentrate from textile wastewater treatment for agricultural irrigation by evaluating its effects on basil and bean cultivation under greenhouse conditions. They compared irrigation using tap water, untreated textile wastewater, RO concentrate, and a diluted RO concentrate. The results showed that RO concentrate supplied valuable nutrients, significantly increasing nitrogen, phosphorus, and potassium uptake in both crops, although some micronutrient concentrations decreased. Overall, the study concluded that RO concentrate has potential as a complementary irrigation and nutrient source, supporting circular water reuse in agriculture, provided that its application is carefully managed and optimized to avoid adverse effects (Ćurić et al., 2025). Çiftçioğlu-Gözüaçık et al. (2023) investigated two hybrid membrane configurations for recovering irrigation-quality water from alkaloid industry wastewater: an electrooxidation (EO)–NF90/BW30 system and a two-stage NF4–NF90/BW30 membrane process. The two-stage NF4–NF90 system achieved initial and final permeate fluxes of 10.2 and 5.4 L m⁻² h⁻¹, respectively, while the NF4–BW30 and EO–BW30 configurations exhibited initial fluxes of 9.4 and 3.2 L m⁻² h⁻¹, respectively. Increasing the electrooxidation current density from 256 to 768 A m⁻² increased the specific energy consumption from 10.26 to 15.84 kWh kg⁻¹ COD. Membrane autopsy using SEM and EDX was conducted to evaluate membrane fouling. The integrated EO–membrane process effectively minimized fouling while simultaneously achieving disinfection and reducing salinity and heavy metal concentrations to levels that satisfied agricultural water reuse standards.

3.4 Forward osmosis

Forward osmosis (FO) is an osmotically driven process that uses a concentrated draw solution rather than applied hydraulic pressure to extract water from a feed stream, offering potentially lower energy consumption and reduced fouling propensity relative to pressure-driven processes (Jamadi-Torab et al., 2025). A variant of particular relevance to agriculture is fertilizer-drawn forward osmosis (FDFO), in which a concentrated fertilizer solution serves simultaneously as the osmotic driving agent and the nutrient source for the diluted product water, which can then be applied directly for fertigation without a separate draw-solute recovery step (Phuntsho et al., 2012). Early studies demonstrated that common fertilizers such as potassium nitrate, ammonium sulfate, and monoammonium phosphate can successfully draw water from saline or wastewater feeds while producing a diluted product suitable, in many cases, for direct irrigation use, although the final nutrient concentration is constrained by the osmotic equilibrium between the feed and draw solutions and can still exceed recommended irrigation limits for some ions (Chekli et al., 2017). Hybrid FO-electrodialysis systems have been reported to reduce specific energy consumption to as low as roughly 0.35 kWh per cubic meter, underscoring the potential of FO-based approaches for low-energy agricultural water reuse (Suwaileh et al., 2020). Tran et al. (2025) evaluated the long-term performance of an integrated electrodialysis–forward osmosis (EDFO) system for nutrient recovery from municipal and dairy digestates and its application in agricultural irrigation. The system demonstrated stable long-term operation with minimal fouling, as indicated by only gradual declines in current density over three treatment cycles, reducing the need for chemical cleaning. Greenhouse experiments showed that irrigation with EDFO-treated wastewater maintained leaf area and shoot biomass comparable to the control, while the growing medium pH remained within the optimal range for blueberry cultivation (4.5–5.5). Although electrical conductivity exceeded the salinity threshold (>2 dS m⁻¹), no visible salt damage was observed. In addition, the EDFO process removed more than 90% of pharmaceuticals and pesticides, demonstrating its effectiveness in recovering nutrients, minimizing emerging contaminants, and providing a sustainable water reuse strategy for agriculture. Abdul Wahid et al. (2021) investigated the use of fertilizer-drawn forward osmosis (FDFO) for recovering water and nutrients from anaerobic palm oil mill effluent (An-POME) using six commercial fertilizers as draw solutions. Among the fertilizers tested, mono-ammonium phosphate (MAP) exhibited the best performance, achieving the highest average water flux, the lowest flux decline, and a water recovery of 5.9% after 4 h of operation. During a 24-h fouling experiment, the membrane experienced an 84% flux decline while recovering 15% of the feed water. Importantly, both hydraulic flushing and osmotic backwashing effectively restored membrane flux, indicating that the fouling was largely reversible. These findings demonstrate that FDFO with commercial fertilizers is a promising approach for agricultural wastewater reuse, although further optimization is needed to reduce reverse salt flux and draw solution dilution.

3.5 Membrane bioreactors

Membrane bioreactors (MBRs) integrate biological treatment with membrane filtration, combining activated sludge digestion with UF or MF membranes to achieve simultaneous organic matter removal and solid-liquid separation (Goh et al., 2022). MBRs are particularly well suited to treating agricultural and municipal wastewater with high organic and nutrient loads, and they have also been adapted into membrane photobioreactors that couple microalgal cultivation with membrane separation, enabling simultaneous nutrient recovery and biomass production in a single system (Goh et al., 2022). As with other membrane systems, biofouling remains the dominant operational challenge for MBRs, motivating much of the research into nanomaterial-enhanced antifouling membranes discussed later in this review (Pervez et al., 2020). Mineo et al. (2025) compared two pilot-scale membrane-based wastewater treatment configurations for water reuse: an Integrated Fixed-Film Activated Sludge (IFAS)–Membrane Bioreactor (MBR) system and an IFAS–ultrafiltration (UF) system, operated under intermittent and continuous aeration. Continuous aeration improved biological carbon removal to 74%, enhanced nitrogen removal, and reduced N₂O emissions to approximately 0.7% of influent total nitrogen. It also lowered the carbon footprint to 1.6 and 1.9 kg CO₂-eq day⁻¹ for the MBR and UF systems, respectively. Membrane fouling behavior differed between the two configurations due to differences in particle size distribution of the treated water. Overall, both membrane systems produced effluent meeting EU water reuse regulations, demonstrating their suitability for agricultural water reuse, although additional phosphorus removal was required to fully comply with updated wastewater treatment standards. Bermúdez et al. (2024) evaluated a pilot-scale membrane bioreactor (MBR) equipped with four ultrafiltration membranes for treating real municipal wastewater to meet the EU standards for agricultural water reuse. The system was operated under hydraulic retention times of 6 and 12 h and mixed liquor suspended solids (MLSS) concentrations ranging from 2,688 to 7,542 mg L⁻¹, while being challenged with increasing concentrations of the emerging contaminants diclofenac, ibuprofen, and erythromycin. A subsequent advanced oxidation process (30 min) further polished the treated effluent. The results demonstrated that the treated water met the required quality standards for agricultural irrigation, while the generated biogas and biostabilized sludge also showed potential for resource recovery, supporting a circular economy approach to wastewater treatment and reuse.

3.6 Membrane distillation

Membrane distillation (MD) uses a hydrophobic microporous membrane to separate vapor from liquid based on a temperature-driven vapor pressure gradient, allowing it to treat highly saline feeds that would foul or damage pressure-driven membranes (Regmi et al., 2024). Because MD can, in principle, be powered by low-grade waste heat or solar thermal energy, it is often highlighted as a promising option for decentralized, energy-efficient desalination in agricultural settings, although wetting of the hydrophobic membrane pores and long-term thermal stability remain open engineering challenges (Foorginezhad et al., 2025). Zarebska-Mølgaard et al. (2022) performed a techno-economic assessment of a hybrid forward osmosis–membrane distillation (FO–MD) process for recovering water from anaerobically digested (AD) effluents. Although the system produced high-quality reclaimed water, the experimental water flux was below 2 L m⁻² h⁻¹, limiting its practical applicability. The process exhibited a low energy consumption of 0.52 kWh m⁻³, approximately 100 times lower than the energy generated from methane produced by 1 m³ of AD effluent. Economic analysis estimated a water production cost of US$1.29 m⁻³, assuming a membrane flux of 10 L m⁻² h⁻¹ and a membrane cost of US$36 m⁻². Sensitivity analysis further showed that membrane cost strongly affected water production costs at fluxes below 8 L m⁻² h⁻¹, while fluxes exceeding 14 L m⁻² h⁻¹ would be required for the FO–MD system to become economically competitive for industrial-scale wastewater reuse. Mukhitdinov et al. (2026) investigated the effect of stage temperature boosting in a solar-powered eight-stage air-gap membrane distillation (AGMD) pilot system for agricultural wastewater reclamation by injecting low-grade agricultural waste heat into intermediate stages. The temperature boosting strategy significantly enhanced membrane performance, increasing the distillate flux by 88%, from 6.5 to 12.2 kg m⁻² h⁻¹ under high solar irradiance and from 2.8 to 9.1 kg m⁻² h⁻¹ under low irradiance. System uptime improved from 67% to 92%, while the gained output ratio (GOR) increased from 3.1 to 8.1 and the total specific energy consumption decreased by 62%–145.0 kWh m⁻³. The process maintained excellent permeate quality, achieving >99.5% TDS rejection with no detectable E. coli, demonstrating that waste heat integration effectively mitigates temperature polarization and enables energy-efficient, reliable agricultural water reuse. Table 2 consolidates representative case studies to illustrate, with concrete reported figures, how each membrane process performs in practice for agricultural water reuse.

TABLE 2. Representative case studies illustrating membrane process performance for agricultural water reuse.

3.7 Comparative overview

Table 3 summarizes the relative characteristics of the principal membrane technologies applied to agricultural water reuse. No single technology is optimal across all criteria: MF and UF are cost-effective for pretreatment but provide limited disinfection; NF offers an attractive balance between contaminant removal and nutrient retention; RO delivers the highest overall water quality but at a significant energy penalty; FO and FDFO reduce energy demand and, in the fertilizer-drawn configuration, add agronomic value directly; MBRs excel at organic load reduction; and MD offers a route to treating very saline streams using low-grade heat. This diversity of trade-offs is precisely why enhancing the underlying membrane material through nanocomposite design, rather than simply choosing between existing process configurations, has become such an active area of research, since improvements to flux, selectivity, and fouling resistance can be layered onto any of these established process architectures.

TABLE 3. Comparative overview of membrane technologies for agricultural water reuse.

4 Nanocomposite membranes: concepts and design strategies

4.1 The nanocomposite membrane concept

A nanocomposite membrane is formed by embedding, coating, or otherwise integrating nanoscale materials, typically in the range of 1–100 nm, into or onto a base polymeric or ceramic membrane matrix (Sahu et al., 2023). The underlying rationale is that nanomaterials can impart properties that neither the base polymer nor the nanomaterial could achieve alone: nanoscale fillers offer an extremely high surface-area-to-volume ratio, tunable surface chemistry, and, in many cases, intrinsic catalytic, antimicrobial, or hydrophilic functionality that can be transferred to the surrounding polymer matrix at very low loading fractions (Musa et al., 2025). Compared with pristine membranes, nanocomposite membranes have been shown to improve water permeability, salt and contaminant rejection, and selectivity, while simultaneously enhancing intrinsic properties such as hydrophilicity, porosity, antifouling behavior, antimicrobial activity, and mechanical, thermal, and chemical stability. This dual improvement, in both separation performance and membrane robustness, is what distinguishes nanocomposite membranes from earlier generations of purely polymeric membranes, whose performance envelope was largely fixed by the intrinsic properties of the base polymer (Rahbari-Sisakht et al., 2026).

4.2 Classification of nanomaterials used in membrane design

Nanomaterials incorporated into membranes are commonly classified by dimensionality, a framework that also reflects how they interact with the surrounding polymer matrix and water molecules (Nayeri and Jafari, 2024).

Zero-dimensional (0D) nanomaterials, including metal and metal oxide nanoparticles such as titanium dioxide (TiO₂), silver (Ag), zinc oxide (ZnO), and iron oxide, are the most widely studied class. TiO₂ nanoparticles are particularly valued for their photocatalytic activity, which enables the degradation of adsorbed organic foulants under UV or visible light exposure. Silver nanoparticles are prized primarily for their broad-spectrum antimicrobial activity, which suppresses bacterial attachment and biofilm formation on the membrane surface (Mecha et al., 2023).

One-dimensional (1D) nanomaterials, chiefly carbon nanotubes (CNTs), offer a combination of exceptional mechanical strength, high aspect ratio, and, in the case of aligned or functionalized CNTs, favorable water transport channels that can enhance flux while resisting fouling and enabling composite reinforcement (Ma et al., 2017).

Two-dimensional (2D) nanomaterials, most notably graphene oxide (GO) and reduced graphene oxide (rGO), have attracted substantial attention because their layered, sheet-like structure creates sub-nanometer interlayer channels that can enable size-sieving separation with very high water flux, alongside inherent antifouling and, in some formulations, antimicrobial character (Zhan et al., 2025).

Three-dimensional (3D) nanomaterials, including zeolites and metal-organic frameworks (MOFs) such as zeolitic imidazolate frameworks (ZIFs), contribute highly ordered, tunable porosity and large internal surface area, which can be exploited for molecular sieving, catalytic degradation of pollutants, and, in some ZIF formulations, additional biocidal activity from the metal center (Kadhom et al., 2017).

More recently, bio-based and green nanomaterials, such as cellulose nanocrystals, chitosan, and biogenic (plant- or microbially synthesized) metal nanoparticles, have gained traction as more environmentally benign alternatives that align nanocomposite membrane design with broader sustainability goals (Kadhom et al., 2017; Rana et al., 2026).

4.3 Fabrication strategies

Several fabrication routes are used to integrate nanomaterials into membrane structures, each offering different trade-offs between simplicity, control over nanomaterial location, and long-term stability.

Blending (dope modification) via phase inversion is the most common and scalable approach, in which nanomaterials are dispersed directly into the polymer casting solution prior to non-solvent induced phase separation (Osman et al., 2024). This technique is relatively simple and compatible with existing membrane manufacturing infrastructure, but achieving uniform nanomaterial dispersion without agglomeration, and controlling where nanoparticles ultimately reside within the resulting asymmetric membrane structure, remain persistent fabrication challenges (Osman et al., 2024).

Interfacial polymerization for thin-film nanocomposite (TFN) membranes embeds nanomaterials within the thin polyamide selective layer formed during interfacial polymerization, a strategy widely used for NF and RO membranes. Incorporating nanofillers such as MOF nanoparticles or zeolite crystals into this thin layer has been shown to increase water permeance substantially, in some reported cases more than doubling permeance relative to conventional TFC membranes, while maintaining or improving rejection (Yang et al., 2017).

Surface coating and post-synthesis modification deposit nanomaterials onto an already-formed membrane surface, for example, through dip-coating, plasma deposition, or in situ reduction of metal precursors on the membrane surface. This approach can achieve high surface concentrations of functional nanomaterials, such as silver nanoparticles for antimicrobial activity, without altering the bulk membrane structure, though surface-bound nanoparticles can be more prone to detachment and leaching under prolonged operation (Razavizadeh et al., 2025).

Electrospinning produces nanofibrous membranes in which nanomaterials such as TiO₂ can be directly incorporated into the polymer nanofiber during fiber formation, yielding high-porosity structures well suited to photocatalytic and microfiltration applications (Al-Husaini and Haddabi, 2025).

In-situ growth and hydrothermal synthesis approaches, used, for example, to grow GO/TiO2 or MOF nanostructures directly on or within a support membrane, can achieve strong interfacial bonding between the nanomaterial and the substrate, improving long-term stability relative to simple physical blending (Zhang et al., 2025).

4.4 Key design considerations

Several design variables govern the ultimate performance of a nanocomposite membrane, and effective design requires balancing them rather than maximizing any single one in isolation.

Nanomaterial loading and dispersion. Performance generally improves with nanomaterial loading up to an optimum point, beyond which excessive loading causes particle agglomeration, pore blockage, or mechanical weakening of the membrane structure (Ogwu et al., 2026). Uniform dispersion, often achieved through surface functionalization of the nanomaterial to improve compatibility with the polymer matrix, is essential to realizing the intended performance gains.

Location within the membrane matrix. Where a nanomaterial resides, whether embedded in the bulk support layer, concentrated at the membrane surface, or distributed within a thin selective layer, has a direct bearing on its functional effectiveness. For example, studies on silver nanoparticle location in nanocomposite membranes have shown that antibacterial performance depends strongly on whether the nanoparticles are positioned to maximize the diffusion and release of biocidal silver ions into the surrounding aqueous environment (Sile-Yuksel et al., 2014).

Nanoparticle immobilization and leaching resistance. Because weakly bound nanoparticles can detach from the membrane matrix over time, robust immobilization strategies, such as embedding within a stable polymer network or encapsulating nanoparticles within a protective shell, are increasingly emphasized in nanocomposite membrane design, both to preserve long-term functional performance and to limit the environmental release of nanomaterials, a concern discussed further in Section 6 (Sile-Yuksel et al., 2014).

Compatibility with existing fabrication infrastructure. From a practical standpoint, fabrication strategies that can be integrated into existing phase-inversion or interfacial polymerization production lines, rather than requiring entirely new manufacturing processes, are more likely to see near-term commercial adoption (Osman et al., 2024).

4.5 Characterization of nanocomposite membranes

Because nanocomposite membrane performance depends so heavily on how uniformly and stably nanomaterials are integrated into the matrix, a standard suite of characterization techniques is used across the literature to verify successful fabrication before performance testing begins. Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) are routinely used to confirm the chemical identity and crystalline structure of both the base polymer and the incorporated nanomaterial, verifying that the expected nanophase is present in the finished membrane (63). Scanning electron microscopy (SEM), often combined with energy-dispersive X-ray spectroscopy, is used to visualize nanomaterial distribution, membrane cross-sectional morphology, and pore structure, while thermogravimetric analysis (TGA) tracks changes in thermal stability associated with nanomaterial loading (Zare et al., 2024). Contact angle measurement and porosity analysis quantify the hydrophilicity and pore-level changes that underpin flux improvements, and zeta potential measurement characterizes the surface charge that governs both fouling propensity and selectivity toward charged contaminants such as heavy metal ions and nutrient salts (Bashiri et al., 2026). Taken together, this characterization toolkit allows researchers to connect specific fabrication choices, nanomaterial type, loading level, and integration method, to the resulting membrane microstructure, and in turn to the separation and antifouling performance discussed in Section 5, closing the design loop between concept and measured outcome.

Together, these classification frameworks and fabrication strategies provide the conceptual toolkit from which application-specific nanocomposite membranes are designed. The next section examines the concrete performance gains these design choices have produced, with particular attention to properties most relevant to agricultural water reuse.

5 Performance enhancement by nanocomposite membranes

The design strategies described above translate into measurable improvements across several performance dimensions that are directly relevant to agricultural water reuse: permeability and flux, fouling resistance, selectivity and contaminant rejection, mechanical and thermal durability, and self-cleaning capability. This section reviews the evidence for each in turn.

5.1 Permeability and water flux

Incorporating hydrophilic nanomaterials into a membrane matrix generally increases water flux by improving surface wettability and, in some cases, by creating additional nanoscale transport pathways. Graphene oxide membranes exploit sub-nanometer interlayer channels to achieve rapid water transport alongside high salt rejection, although GO layers can suffer from limited structural stability in aqueous media, causing interlayer spacing to swell and salt rejection to decline over time; stabilizing the GO gallery structure with a secondary polysaccharide such as chitosan has been shown to maintain a fixed interlayer spacing while also imparting a favorable surface charge for cation exclusion (Bashiri et al., 2026). In carbon-nanotube-based membrane distillation systems, incorporating multi-walled carbon nanotubes together with silica nanoparticles into a PVDF membrane has been shown to increase vapor flux substantially relative to the unmodified polymer membrane, with the synergistic combination of the two filler types outperforming either filler alone, while still achieving salt rejection above 99.9% (Ragunath et al., 2018). Similarly, TiO₂ nanoparticle incorporation into mixed-matrix nanofiltration membranes has been found to increase porosity and mean pore size, contributing to improved flux without a proportional sacrifice in separation performance.

5.2 Fouling resistance and antimicrobial activity

Antifouling enhancement is arguably the performance dimension most extensively documented in the nanocomposite membrane literature, and it addresses the single largest operational cost driver identified in Section 2.

Photocatalytic nanomaterials, chiefly TiO₂ and its composites, enable a self-cleaning mechanism in which adsorbed organic foulants are degraded in situ under light exposure rather than simply accumulating on the membrane surface (Zhang et al., 2020). A hydrogenated TiO₂ ceramic ultrafiltration membrane, for instance, demonstrated substantially improved humic acid removal and fouling resistance relative to an equivalent pristine TiO₂ membrane after ultraviolet pretreatment (Aoudjit et al., 2021). Visible-light-responsive photocatalytic composites, such as GO/TiO₂ and g-C₃N₄/TiO₂ nanotube array membranes, extend this self-cleaning function beyond the ultraviolet range, broadening its practical applicability under natural sunlight, a particularly relevant consideration for outdoor agricultural water treatment systems (Aoudjit et al., 2021).

Silver nanoparticle-modified membranes achieve fouling control through a distinct, antimicrobial mechanism: by suppressing bacterial attachment and biofilm formation at the membrane surface, they reduce the biofouling that would otherwise progressively block flow channels and degrade permeate quality over time (Mecha et al., 2023). A review of biogenic silver nanocomposite membranes reported consistent improvements in permeability, selectivity, and long-term fouling resistance when biologically synthesized silver nanoparticles were embedded into polymer membranes (Chauke et al., 2025). Green-synthesized silver nanoparticle-enhanced nanofiltration membranes have similarly shown the lowest irreversible fouling and highest flux recovery at an optimized loading level, attributed to both the antimicrobial action of the silver and favorable changes in surface hydrophilicity (Bashir et al., 2025).

Graphene-based nanocomposites can combine several antifouling mechanisms simultaneously. Functionalized graphene oxide membranes incorporating both antimicrobial nanoparticles and photocatalytically active components have demonstrated a dual antifouling effect, in which reactive oxygen species suppress microbial attachment while photocatalytic activity degrades adsorbed organic matter, outperforming single-mechanism antifouling coatings in dye wastewater treatment trials (Zhan et al., 2025). Electrochemically modified reduced graphene oxide membranes have also shown that applying a modest electric potential across the membrane can enhance flux recovery after fouling by promoting electro-oxidation of foulants at the membrane surface (Edokali et al., 2024).

In membrane bioreactor applications specifically, incorporation of alumina nanoparticles into polysulfone membranes has been reported to reduce membrane fouling by roughly 83%, alongside high dye rejection, illustrating the magnitude of improvement achievable in biologically active treatment environments prone to severe fouling (Pervez et al., 2020).

5.3 Selectivity and contaminant rejection

Nanocomposite membranes have demonstrated enhanced rejection across a wide range of contaminant classes relevant to agricultural reuse, including salts, heavy metals, dyes, and pathogens.

MOF-based nanocomposite membranes have achieved high rejection of dye contaminants; one such membrane combining a metal-organic framework with graphene oxide achieved rejection above 98% for Congo red and above 92% for methylene blue while maintaining useful permeability, and related composite structures incorporating aluminum-based MOF nanosheets into graphene oxide have reported dye rejection exceeding 99% (Jafarian et al., 2023). Zeolite and MOF nanofillers incorporated into thin-film nanocomposite membranes for reverse osmosis have similarly been shown to raise water permeance markedly relative to unmodified thin-film composite membranes while sustaining comparable or improved salt rejection (Kadhom et al., 2017).

Carbon-nanotube nanocomposite membranes, when functionalized with manganese nanoferrite decoration, have shown tunable pore sizes ranging from several nanometers to sub-micron scale depending on nanotube loading, enabling adjustable salt rejection performance for sulfate salts relevant to brackish and saline agricultural drainage water (Ragunath et al., 2018).

Silver-nanoparticle-modified microfiltration and ultrafiltration membranes, while not intended primarily as barriers to dissolved salts, have been shown to markedly improve microbiological disinfection performance relative to unmodified membranes of the same pore size, addressing the specific weakness of MF/UF processes identified in Section 3.1 (Mecha et al., 2023).

For agriculture specifically, the ability of nanocomposite fertilizer-drawn forward osmosis membranes to reject unwanted salts and contaminants from a saline or wastewater feed while allowing controlled passage of draw-solution nutrients into the diluted product water represents a particularly targeted form of selectivity enhancement, one that directly addresses the nutrient-retention challenge discussed in Section 2.3 (Chekli et al., 2017).

5.4 Mechanical, thermal, and chemical stability

Beyond separation performance, nanomaterial incorporation frequently improves the structural durability of membranes, extending their operational lifetime and reducing replacement frequency, a factor directly tied to the economic viability of agricultural water reuse schemes. Thermogravimetric analysis of TiO₂-incorporated mixed-matrix membranes has shown measurable increases in thermal stability with increasing nanoparticle loading, alongside increases in mean pore size and porosity (Ogwu et al., 2026). Carbon nanotube reinforcement has been widely reported to enhance the mechanical strength and thermal stability of polymer membranes, which is particularly valuable in membrane distillation applications operating at elevated temperature (Ragunath et al., 2018). Hydroxyl-functionalized carbon nanotubes incorporated via phase inversion have been shown to enhance the mechanical stability and transport characteristics of polyacrylonitrile membranes, while oxidized carbon nanotube incorporation into polysulfone membranes has produced synergistic improvements in both permeability and antifouling behavior (Majeed et al., 2012).

5.5 Application-relevant performance for agricultural water reuse

When these performance gains are considered together in the specific context of agricultural water reuse, several nanocomposite membrane configurations stand out as particularly well matched to the sector’s needs. Thin-film nanocomposite forward osmosis membranes incorporating antifouling nanomaterials have shown improved resistance to organic and biological fouling under conditions simulating fertilizer-drawn agricultural water recovery, while machine-learning-assisted design approaches are increasingly being used to optimize such membranes for sustainable water recovery applications (Malhotra and Kaleekkal, 2024). Nanofiltration membranes modified with photocatalytic or antimicrobial nanomaterials combine the inherent nutrient-retention advantage of the NF process, discussed in Section 3.2, with active fouling mitigation, addressing two of the sector’s central challenges simultaneously. Bio-based nanocomposite membranes incorporating cellulose nanocrystals or chitosan alongside functional nanoparticles offer a further advantage for agricultural contexts: their biodegradability and comparatively benign environmental profile align well with a sector where end-of-life membrane disposal and nanoparticle release into soil and irrigation water are legitimate sustainability concerns (Marques and Kumar, 2022).

5.6 Illustrative summary of reported performance gains

To consolidate the evidence discussed above, Table 4 draws together representative, illustrative performance outcomes reported for different nanomaterial classes across the studies reviewed in this section. These figures are drawn from distinct studies using different base membranes, feed compositions, and test protocols, so they should be read as indicative of the type and rough magnitude of improvement reported in the literature rather than as directly comparable, like-for-like benchmarks.

TABLE 4. Illustrative performance outcomes reported for representative nanocomposite membrane classes.

Read across these examples, a consistent pattern emerges: nanocomposite modification rarely improves flux, rejection, and fouling resistance through a single universal mechanism. Instead, each nanomaterial class contributes a distinct, complementary function, photocatalytic self-cleaning, antimicrobial suppression, structural reinforcement, or molecular sieving, and the most effective membrane designs are often those that combine two or more of these mechanisms deliberately, as seen in the dual antifouling graphene oxide systems discussed in Section 5.2 (Zhan et al., 2025). This reinforces a broader conclusion of this review: nanocomposite membrane design is best approached as a targeted materials-selection exercise matched to the specific limiting mechanism in a given water reuse application, rather than as a search for a single universally superior nanomaterial.

Taken as a whole, the evidence reviewed in this section demonstrates that nanocomposite membranes do not merely offer incremental improvement over conventional membranes; in several documented cases they address the specific, named limitations, fouling, energy demand, and nutrient-selectivity trade-offs, identified in Section 2 as the principal barriers to expanded agricultural water reuse. The remaining question, addressed in the concluding section, is how these laboratory-scale gains can be translated into safe, affordable, field-scale deployment.

6 Conclusions and future perspectives

6.1 Summary of key findings

Agriculture’s dependence on freshwater, combined with accelerating global water scarcity, makes water reuse an increasingly essential strategy rather than an optional supplement to conventional irrigation supply (Mekonnen and Hoekstra, 2016). Membrane technologies, spanning microfiltration and ultrafiltration through nanofiltration, reverse osmosis, forward osmosis, membrane bioreactors, and membrane distillation, already provide the technical backbone for treating municipal, industrial, and agricultural wastewater to standards suitable for irrigation (Qasim et al., 2019; Mecha et al., 2023). Yet each of these processes carries an inherent trade-off among energy demand, fouling propensity, and the retention of agronomically valuable nutrients, trade-offs that have constrained the pace of adoption, particularly in cost-sensitive agricultural settings (Alhussaini et al., 2024).

Nanocomposite membranes have emerged as a materials-level response to precisely these constraints. By integrating zero-, one-, two-, and three-dimensional nanomaterials into polymeric and ceramic membrane matrices through blending, interfacial polymerization, surface coating, electrospinning, or in situ growth, researchers have demonstrated concrete improvements in water flux, fouling resistance, contaminant selectivity, and mechanical and thermal durability across essentially every major membrane process type reviewed in this paper (Edokali et al., 2024). Photocatalytic and antimicrobial nanocomposites in particular have shown a capacity to actively suppress the organic and biological fouling that represents the largest single operational cost in membrane-based water reuse (Zhan et al., 2025).

6.2 Environmental and safety considerations

The nanoscale properties that provide nanocomposite membranes with enhanced antimicrobial, photocatalytic, and separation performance also create an important environmental-safety consideration: the potential release of nanoparticles or dissolved species from the membrane into treated water. The magnitude of this release is strongly dependent on nanoparticle chemistry, membrane architecture, loading, immobilization mechanism, water chemistry, and operational conditions. Consequently, environmental risk should be evaluated using quantitative leaching measurements rather than by assuming that nanoparticles remain permanently immobilized within the membrane matrix.

Several membrane-specific studies demonstrate that measurable release can occur over both short and extended exposure periods. For example, a study of CuO-incorporated polyethersulfone (PES) ultrafiltration membranes investigated nanoparticle leaching following prolonged exposure of membrane coupons to different aqueous cleaning media. After 840 h (5 weeks), ICP-MS analysis detected Cu concentrations of approximately 65 μg L⁻¹ in water, 80 μg L⁻¹ in 0.1 M NaCl, 196 μg L⁻¹ in 0.1 M NaOH, 241 μg L⁻¹ in 0.5% NaClO, and 589 μg L⁻¹ in 0.1 M HCl. The corresponding average leaching rates ranged from 24.2 to 218.9 μg m⁻² h⁻¹. The authors attributed the release to interactions between the membrane polymer, cleaning medium, and physical/chemical processes that can dislodge nanoparticles from the PES matrix. These concentrations are particularly relevant for agricultural reuse because the FAO recommended maximum concentration of Cu in irrigation water is 0.20 mg L⁻¹ (200 μg L⁻¹), based on the potential toxicity of Cu to plants and its accumulation in soil under prolonged irrigation. Thus, some of the Cu concentrations measured during membrane cleaning (e.g., 241–589 μg L⁻¹) exceed this agricultural-water benchmark, although direct comparison should be interpreted cautiously because the reported experiment used concentrated cleaning solutions rather than continuous irrigation water (Shalaby et al., 2026).

Silver-containing membranes provide another useful example of the importance of membrane architecture and immobilization strategy. In a study of triangular silver nanoparticle-modified polyethylene membranes, cumulative Ag-ion release after 14 days was approximately 4 μg L⁻¹ for one membrane configuration and 5 μg L⁻¹ for another, with the release rate decreasing after the initial period. Approximately 14% of the initially incorporated silver was released from the tested membrane after 14 days. In another study using silver-nanoparticle-modified microfiltration membranes, the Ag concentration in water after 10 months (approximately 7,200 h) was 20 μg L⁻¹ for one membrane configuration, while a second membrane configuration showed approximately 0.1 mg L⁻¹ after 1 month of immersion. Under cross-flow filtration, the Ag concentration in individual permeate fractions was below 100 μg L⁻¹ after 2.75 L of water had passed through the membrane. These results indicate that release can be highest during the initial contact period and may subsequently decline as loosely attached nanoparticles are depleted (Ahmad et al., 2019).

The form of nanoparticle immobilization is therefore a critical determinant of environmental safety. For example, a casein-coated Ag nanoparticle/polymeric membrane investigated under a 7-day cross-flow experiment released approximately 0.16 ± 0.06 mg L⁻¹ and 0.19 ± 0.04 mg L⁻¹ Ag for two membrane formulations, respectively, when 1 L of water was circulated through the system (Haider et al., 2016). However, approximately 97%–98% of the initially incorporated silver remained associated with the membranes. Under dead-end filtration, Ag concentrations decreased as progressively larger volumes of water were passed through the membranes, indicating that the initially released fraction was associated largely with loosely bound material. Such results demonstrate why nanoparticle loading alone is insufficient to predict environmental release; surface attachment, chemical coordination, encapsulation, and the location of nanoparticles within the membrane structure must also be considered.

The environmental relevance of these concentrations depends strongly on the endpoint used for comparison. For silver, the World Health Organization currently lists a provisional reference value of 0.1 mg L⁻¹ (100 μg L⁻¹) for drinking water, while emphasizing that this is not a formal health-based guideline because the available toxicological database is insufficient for establishing one (Organization, 2021). More stringent values apply when ecological protection is considered. The Canadian long-term guideline for total silver for the protection of freshwater organisms is 0.25 μg L⁻¹, derived using a species-sensitivity-distribution approach based on chronic toxicity data. This illustrates an important point for agricultural water reuse: a leachate concentration can be below a drinking-water benchmark while still being relevant to aquatic ecosystems receiving membrane effluent, particularly when exposure is continuous or when sensitive organisms are present.

Ecotoxicological evidence further supports the need for caution. For example, chronic toxicity data compiled for freshwater organisms show sensitivity to dissolved silver at sub-μg L⁻¹ to low-μg L⁻¹ levels, depending on species and exposure conditions (Ratte, 1999). In addition, recent studies of Ag nanoparticles have reported growth-inhibition effects in microalgae at concentrations in the low-to tens-of-μg L⁻¹ range, with toxicity influenced by nanoparticle aggregation and the release of Ag⁺ ions. Therefore, assessment based solely on total nanoparticle concentration may underestimate risk because particle size, aggregation state, surface coating, dissolved-ion fraction, water chemistry, and natural organic matter can substantially modify bioavailability and toxicity.

For agricultural applications, the exposure pathway is also different from that of conventional drinking-water treatment. Irrigation creates repeated inputs to soil, where nanoparticles and released metals may accumulate or interact with soil minerals, organic matter, microorganisms, and plant roots. Consequently, short-term membrane-leaching measurements should not automatically be interpreted as evidence of negligible long-term risk. Conversely, high concentrations measured during aggressive membrane-cleaning experiments should not be directly extrapolated to normal irrigation operation because cleaning solutions, exposure conditions, and water-to-membrane ratios can differ substantially from field conditions.

Overall, the available quantitative evidence indicates that nanoparticle release from nanocomposite membranes is measurable and can range from sub-μg L⁻¹ to hundreds of μg L⁻¹ depending on the material and test conditions. The environmental significance therefore depends on both release magnitude and exposure duration, as well as the intended water-reuse pathway. Future studies should report nanoparticle and dissolved-metal concentrations separately, include mass-normalized or membrane-area-normalized release rates, characterize release during both normal operation and membrane cleaning, and conduct extended tests representative of realistic agricultural service periods. Coupling these measurements with crop-uptake studies, soil accumulation experiments, and standardized aquatic and terrestrial ecotoxicity tests would provide a more defensible basis for evaluating the environmental safety of nanocomposite membranes. Improved immobilization, covalent or coordinative attachment, and the use of bio-based nanomaterials remain promising strategies for reducing release while retaining the functional advantages of nanocomposite membranes.

6.3 Techno-economic and scale-up challenges

Most of the performance data reviewed in this paper originate from laboratory-scale studies conducted over relatively short operating periods, and a recurring conclusion across multiple reviews is that long-term, pilot- and field-scale performance data remain scarce (Nazari and Abdelrasoul, 2025). High production costs for certain nanomaterials, particularly engineered carbon nanostructures and functionalized MOFs, along with the technical difficulty of achieving uniform, reproducible nanomaterial dispersion at manufacturing scale, remain significant barriers to commercialization. Bridging this gap will likely require closer integration between nanocomposite membrane fabrication and existing large-scale membrane manufacturing infrastructure, favoring fabrication strategies, such as dope blending during conventional phase inversion, that require minimal modification to established production lines over more exotic synthesis routes that are difficult to scale (Ogwu et al., 2026).

6.4 Emerging directions

Several converging trends are likely to shape the next phase of nanocomposite membrane development for agricultural water reuse. Data-driven and machine-learning-guided membrane design is increasingly being used to predict membrane properties, explain structure-performance relationships, and accelerate the screening of candidate nanomaterial-polymer combinations, potentially shortening the historically slow, trial-and-error development cycle for new nanocomposite formulations (Ogwu et al., 2026). Applied specifically to fertilizer-drawn forward osmosis membranes, machine-learning-assisted approaches have already been used alongside experimental testing to optimize membranes for sustainable agricultural water recovery (Van Puffelen et al., 2022). Hybrid process configurations that combine nanocomposite membranes with complementary technologies, such as forward osmosis-electrodialysis or membrane bioreactor-nanofiltration trains, are also likely to play a growing role, since they allow the specific strengths of nanocomposite materials, whether antifouling, photocatalytic, or nutrient-selective, to be deployed at the process stage where they add the most value rather than expecting a single membrane material to solve every challenge simultaneously (Hum et al., 2022). Finally, the continued development of bio-based and green-synthesized nanocomposite membranes reflects a broader recognition that sustainability credentials, not just separation performance, will determine which nanocomposite technologies ultimately gain acceptance in a sector as closely tied to environmental and food-safety considerations as agriculture (Jafarinejad et al., 2019).

6.5 Concluding remarks

Nanocomposite membranes represent a genuinely promising materials-engineering pathway toward more energy-efficient, fouling-resistant, and selectivity-tunable water reuse for agriculture, and the evidence reviewed here shows measurable, reproducible performance gains across a wide range of nanomaterial classes and membrane configurations. Realizing this promise at the scale required to meaningfully offset global agricultural water demand will depend less on further incremental laboratory-scale performance gains and more on resolving the parallel challenges of nanoparticle environmental safety, manufacturing scalability, and cost, so that the next-generation of nanocomposite membranes can move from demonstrated laboratory potential to dependable, field-proven infrastructure for sustainable agricultural water reuse. Table 5 summarizes the principal conclusions of this review, highlighting the key findings, environmental and safety considerations, techno-economic challenges, emerging research directions, and the future prospects of nanocomposite membranes for sustainable agricultural water reuse.

TABLE 5. Summary of the main conclusions and future perspectives for nanocomposite membranes in agricultural water reuse.

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Footnotes

Edited by: Nalan Kabay, Ege University, Türkiye

Reviewed by: Yung-Tse Hung, Cleveland State University, United States

Anupam Singha Roy, Woxsen University, India