A nanotechnology roadmap for circular wastewater management

Abstract

Circular wastewater management is increasingly recognized as a critical lever for climate resilience, water security, and the recovery of nutrients, energy, and strategic materials. Yet conventional treatment infrastructures remain constrained by limited selectivity, high energy demand, operational inflexibility, and weak coupling between treatment performance and resource valorization. Although nanotechnology has demonstrated substantial potential to address these bottlenecks, real-world deployment remains fragmented due to fouling, regeneration burdens, scale-up uncertainty, and unresolved safety and governance challenges. This review advances a roadmap that moves beyond material-centric assessments toward a decision-oriented, scale-aware framework for integrating nanotechnology into circular wastewater systems. Drawing on recent laboratory advances, pilot studies, and early demonstrations across municipal, industrial, and agro-food contexts, we situate nano-enabled adsorbents, catalysts, membranes, bio–nano hybrids, and nanosensors within integrated treatment–recovery–reuse platforms, rather than isolated unit operations. Techno-economic and life-cycle evidence is synthesized to identify conditions under which nano-enabled process trains deliver net circular value relative to incumbent technologies. The roadmap explicitly couples nanotechnology with digital intelligence, including nanosensing, AI-enabled monitoring, digital twins, and adaptive control, to translate nanoscale functionality into robust system-level performance under variable influent conditions. To support actionable decision-making, we introduce a pollutant-to-valorization decision matrix, a readiness–impact scorecard, and a 2030 research and standards agenda emphasizing safe-by-design materials, scalable regeneration, antifouling interfaces, hybrid bio–nano reactors, and harmonized risk assessment. By integrating materials science, digital process control, and governance, this roadmap positions nanotechnology as a systems enabler for circular wastewater infrastructure rather than a standalone fix.

1 Introduction

The urgency of transforming conventional wastewater management into a circular model is underscored by global resource scarcity and the increasing pollution of natural water bodies. Circular wastewater systems, which focus on the recovery and reutilization of resources, are imperative for achieving sustainability goals. Circular wastewater systems involve the effective management and valorization of material flows. A key aspect is the recovery of water, nutrients, and energy from wastewater streams. Technologies that leverage biological processes, such as anaerobic digestion and struvite precipitation, facilitate the recovery of valuable resources, including phosphorus and nitrogen, thereby enabling the replacement of synthetic fertilizers in agriculture (Mavhungu et al., 2021; Said et al., 2023). Furthermore, the biorefinery approach emphasizes converting wastewater into high-value bioproducts, mitigating environmental concerns associated with waste disposal while enhancing economic viability (Lappa et al., 2019; Bucci et al., 2023).

The incorporation of microalgae into wastewater treatment exemplifies this integrated framework, as microalgal systems can simultaneously treat wastewater and generate biomass for biofuels, fertilizers, and other bioactive compounds, thereby reinforcing circular economy principles (Olguín et al., 2022; Bucci et al., 2023). By applying biorefinery concepts, wastewater is converted into renewable products, thereby addressing both ecological and economic dimensions of sustainability (Smol, 2023; Pan et al., 2024). The integration of digital intelligence into wastewater management enhances operational efficiency and the potential for resource recovery. Digital Twin technology is an essential tool that enables the continuous updating of digital models representing physical treatment systems, based on real-time data captured by Internet of Things (IoT) sensors (Bado et al., 2022). This technology enables predictive maintenance, operational optimization, and scenario analysis, thereby fostering resource efficiency and resilience (Thakuri et al., 2024). Moreover, combining machine learning with sensor networks can enhance the decision-making processes related to treatment and recovery, facilitating real-time adjustments to operational parameters (Ganthavee and Trzcinski, 2024; Škufca et al., 2022).

For instance, Artificial Intelligence (AI)-driven Waste-to-Energy frameworks can streamline resource recovery by optimizing waste management processes in urban settings, increasing adaptability, and mitigating climate risks (Islam, 2025). The adoption of these digital approaches not only resolves operational inefficiencies but also aligns with the overarching goals of climate resiliency and resource management. Valorization pathways are the processes by which resources recovered from wastewater are transformed into marketable products (Nizzy and Ogwu, 2024; Ogwu et al., 2024). The focus should be on high-value products that can significantly improve economic viability, such as biofuels, bioplastics, and agricultural inputs (Lappa et al., 2019; Smol, 2023). For instance, the production of struvite from wastewater offers a sustainable solution for nutrient recovery while reducing environmental pollution associated with excess nutrient runoff (Mavhungu et al., 2021; Smol, 2023).

Furthermore, the economic assessment of these valorization strategies is crucial; a robust understanding of the techno-economic implications helps identify viable pathways for scaling up innovations within the circular economy (Shingwenyana et al., 2021). The interplay between valorization and economic considerations will enable stakeholders to make informed decisions and facilitate the large-scale implementation of these systems. Establishing clear metrics for assessing circularity in wastewater management is fundamental for maintaining and enhancing system performance. Nanotechnology serves as a powerful catalyst for enhancing wastewater treatment across the spectrum. The integration of nanomaterials into membrane systems has demonstrated improved filtration performance, resulting in higher pollutant removal efficiencies and lower fouling rates (Bucci et al., 2023; Ganeshkumar and Arjunan, 2025). In particular, the customization of photocatalytic nanomaterials to target specific contaminants shows promise for advanced oxidation processes that purify wastewater while recovering useful by-products. Moreover, the use of nanotechnology-based sensors can significantly enhance real-time monitoring of effluent quality and operational parameters, thereby providing essential data for adaptive management practices (Hussain, 2025; Pan et al., 2024). By incorporating nanoscale innovations, wastewater treatment facilities can maximize resource recovery while minimizing environmental impacts, ultimately facilitating a robust circular system.

This paper aims to develop a decision-oriented, scale-aware roadmap that synthesizes nano-enabled wastewater technologies with digital process control and governance frameworks to guide the prioritization, deployment, and safe integration of circular wastewater management solutions. The novelty of this paper lies in its deliberate shift away from material-centric reviews toward a decision-oriented, scale-aware roadmap that integrates nanotechnology with digital control systems and governance frameworks for circular wastewater management. Rather than cataloging nanomaterials by synthesis routes or laboratory performance alone, this review systematically evaluates where and under what conditions nano-enabled solutions deliver measurable circular value across full treatment and recovery trains. By embedding materials innovation within techno-economic and life-cycle considerations, linking nano-functional units to AI-enabled monitoring and process optimization, and explicitly addressing scale-up readiness, safety, and regulatory alignment, the roadmap responds to the translational gap that has limited real-world adoption. This integrative perspective enables comparative prioritization, supports evidence-based decision-making for utilities and policymakers, and positions nanotechnology as a systems enabler—co-evolving with digital intelligence and governance—rather than a standalone technological fix.

2 Circular wastewater systems as integrated recovery platforms

Circular wastewater systems aim to minimize waste and enhance resource recovery throughout treatment processes, transitioning from a linear model of disposal to a circular model of reuse and recycling. Traditional methods, such as the Conventional Activated Sludge (CAS) process, often fail to recover sufficient resources, resulting in both economic inefficiency and environmental unsustainability due to their high energy consumption (Kehrein et al., 2020). Kehrein et al. (2020) reported the low resource recovery potential of CAS, thereby advocating the use of advanced technologies to maximize resource extraction from municipal wastewater. Emerging technologies, particularly anaerobic and electrochemical processes, present promising alternatives. For instance, Gu et al. (2022) document the effectiveness of electrocatalytic hydrogenation in simultaneously removing organic pollutants while enabling resource recovery. Likewise, Ghimire et al. (2021) emphasize the importance of integrating anaerobic systems that can efficiently convert organic material into biogas, contributing to energy recovery in addition to wastewater treatment. Such innovative technologies significantly increase resource recovery, aligning with the shift to a cradle-to-cradle bio-based economy espoused by Puyol et al. (2017). Nanotechnology is revolutionizing wastewater treatment by providing novel materials and processes with enhanced capabilities. For example, improved nanomaterials facilitate pollutant adsorption and enhance membrane filtration efficiencies, thus increasing resource recovery from wastewater streams (Sravan et al., 2024). The application of nanomaterials in wastewater treatment not only enhances resource recovery but also reduces environmental impact, providing a dual benefit (Sravan et al., 2024). Figure 1 illustrates circular wastewater systems as integrated recovery platforms, highlighting the transition from conventional linear treatment toward closed-loop systems that couple treatment, resource recovery, valorization, and reuse.

FIGURE 1

The integration of digital intelligence in wastewater management systems is crucial for optimizing their functionality and assessing their effectiveness in resource recovery. By employing advanced data analytics, machine learning, and real-time monitoring, operators can ensure systems achieve energy neutrality—meaning they produce as much energy as they consume (Ghimire et al., 2021). Smol et al. (2020) proposed a framework encompassing multiple actions to promote circular economy principles in the wastewater sector, including reducing wastewater generation and resource recovery. These metrics are pivotal for evaluating the transition toward sustainability and measuring the performance of integrated recovery systems.

Key circularity metrics relevant to wastewater management include (Figure 2).

FIGURE 2

2.1 Recovery efficiency

This metric assesses the rate at which valuable resources, such as nutrients and energy, are retrieved from wastewater streams. For instance, it can be used to gauge the proportion of water and nutrients effectively reclaimed from the total volume processed. Enhanced recovery efficiency can decrease dependency on conventional resources and improve the sustainability of the water sector (Smol et al., 2020). Enhanced treatment technologies, such as advanced oxidation processes and nanotechnology applications in filtration systems, can significantly improve recovery rates (Ganeshkumar and Arjunan, 2025; Smol, 2023).

2.2 Energy neutrality

Measured by the net energy balance of the treatment process, energy neutrality aims for the establishment of wastewater treatment facilities that are energy self-sufficient or even energy positive (Ghimire et al., 2021). It is critical to assess energy consumption relative to energy produced by the recovery processes. For example, biogas generated from anaerobic treatment processes can provide a substantial portion of the energy needed for the treatment facility’s operations (Said et al., 2023; Bucci et al., 2023).

2.3 Material circularity indicators

These establish the reusability and recyclability of materials recovered from wastewater treatments, which are critical in redefining the output from waste to valuable resources (Smol et al., 2020; Ogwu and Kosoe, 2025). These indicators reflect the extent to which wastewater-derived products are reintroduced into productive cycles, thereby closing material-flow loops. Continuous monitoring and reporting on these indicators can facilitate stakeholder engagement and transparency, which is essential for promoting public trust and investment (Geetha et al., 2025; Hussain, 2025).

The active pursuit of these metrics drives innovation in wastewater management methodologies and results in more resilient water infrastructure. Valorization in wastewater management is a multidimensional approach that seeks to transform waste into economically beneficial resources. This process has significant applications in various sectors, including municipal supply, agriculture, and industrial processes. Puyol et al. (2017) provide a compelling argument for biotechnological solutions that enhance the concentration and transformation of wastewater resources into valuable products. For example, nutrient recovery through biological pathways can significantly mitigate pressures on freshwater systems while contributing to sustainable agriculture (Pausta et al., 2023). In agricultural contexts, treated wastewater can serve not only as irrigation water but also as a source of essential nutrients for crops, thereby enhancing yields while conserving invaluable freshwater resources. The impact of wastewater reuse strategies on agricultural sustainability is well documented, demonstrating that reclaimed water plays a key role in achieving food security, particularly in regions facing water scarcity (Pausta et al., 2023; Ogwu et al., 2025). Energy recovery from waste through advanced biogas systems and thermally driven processes can also contribute to the transition toward a circular economy. For instance, thermal energy in wastewater can be harnessed for building heating, as demonstrated by Cecconet et al. (2019) in their study on energy recovery applications. Such efforts exemplify the model of wastewater facilities as energy producers rather than mere waste disposers, aligning with contemporary sustainability goals.

3 Nanomaterial families and their functional roles in circular wastewater management

Figure 3 conceptually organizes major nanomaterial families by their dominant functional roles in circular wastewater management systems. The core functional mechanisms through which nanotechnology contributes to circular wastewater management, including (i) selective capture and separation of contaminants using nano-adsorbents and functionalized nanoparticles, (ii) transformation and degradation of persistent pollutants via photocatalysts and nanozymes, (iii) barrier and control functions enabled by nano-engineered membranes and antifouling interfaces, and (iv) bio–nano synergies that enhance microbial-driven degradation and resource recovery (Figure 3). Nano-adsorbents and functionalized nanoparticles are shown as selective capture and separation agents, enabling targeted removal of heavy metals, dyes, pharmaceuticals, and other priority contaminants through surface-engineered interactions. Photocatalysts and nanozymes mediate transformation and degradation, facilitating the breakdown of persistent organic pollutants via the generation of reactive oxygen species or enzyme-like catalytic activity. Nano-enabled membranes and antifouling interfaces are depicted as barrier and control elements that enhance size-selective filtration while mitigating fouling and extending operational performance. Bio–nano synergies, including nano(bio)composites and nano-enabled bioreactors, highlight integrated systems in which nanomaterials enhance microbial activity and bioprocess efficiency, accelerating pollutant degradation and resource recovery. In situ nanosensors are depicted as sensing and feedback components that provide real-time monitoring and process control to support adaptive, data-driven wastewater operations.

FIGURE 3

3.1 Selective capture and separation: nano-adsorbents and functionalized nanoparticles

Nano-adsorbents, such as carbon nanotubes, graphene-based materials, and metal-organic frameworks (MOFs), exploit high surface-area-to-volume ratios and tunable surface chemistry to selectively adsorb contaminants from wastewater, including heavy metals, dyes, and pharmaceuticals. Functionalized nanoparticles can be engineered to enhance affinity for specific pollutants through chemical groups that interact with contaminants (Kristanti et al., 2025). Laboratory studies have demonstrated removal efficiencies exceeding 90% for certain heavy metals and organic compounds. For instance, titanium dioxide (TiO₂) nanoparticles can achieve above 95% removal of organic dyes under optimal conditions. However, actual performance in wastewater treatment plants can be significantly lower due to variations in pollutant concentrations and the presence of complex matrices. Regeneration methods typically involve desorption through chemical elution or thermal processes. For example, thermal regeneration has been observed in carbon-based adsorbents but can lead to structural degradation during repeated cycles (Bora and Dutta, 2014). While laboratory experiments show promise, the scalability of nanoparticle applications remains limited. Real-world applications remain limited, necessitating further studies on long-term stability and economic viability (Onotu et al., 2025).

3.2 Transformation and degradation: Photocatalysts and nanozymes

Photocatalysts such as TiO₂ use ultraviolet (UV) light to generate reactive oxygen species (ROS) that promote the degradation of organic pollutants. Nanozymes imitate enzyme activity, catalyzing degradation reactions without requiring the same environmental conditions as traditional enzymes. In laboratory settings, photocatalytic systems have been reported to achieve pollutant degradation rates exceeding 80% within hours. However, in field applications, efficiency declines due to variability in light intensity and the heterogeneous composition of wastewater (Ahmed et al., 2022c). Photocatalysts can be regenerated by washing or by UV irradiation, although their effectiveness diminishes with increasing particle agglomeration over time. For nanozymes, in situ regeneration through environmental conditions can often mitigate the need for external treatment (Hussein et al., 2025). The effectiveness of photocatalysts and nanozymes has been well documented in laboratory settings; however, their deployment at a commercial scale faces challenges related to material stability and their response to real-world environmental conditions.

3.3 Barrier and control functions: nano-enabled membranes and antifouling interfaces

Nano-enabled membranes are engineered at the nanoscale using materials such as polymer nanocomposites, thereby enhancing filtration capabilities by selectively allowing molecules of specific sizes to pass while blocking others. Antifouling surfaces are designed to minimize biofilm growth and fouling through hydrophilic or superhydrophobic coatings. Membranes can achieve contaminant removal rates exceeding 95% under optimal conditions. However, in practice, they often face challenges with fouling, which can reduce life expectancy and performance by 30%–60% (Mbarek et al., 2022). Cleaning protocols often involve backwashing, chemical cleaning, or physical cleaning techniques. While these methods can restore permeability, each cleaning cycle can impact membrane integrity and effectiveness (Saleem and Zaidi, 2020). Nano-enabled membranes are commercially available in some advanced filtration applications, yet they face competition from traditional materials that may not require such stringent maintenance.

3.4 Bio–nano synergies: nano(bio)composites and nano-enabled bioreactors

Nano(bio)composites combine biological materials with nanomaterials to improve the efficiency of wastewater treatment processes. These systems leverage the advantages of nano-enhanced surface areas to promote microbial growth and enzymatic activity, enhancing the degradation of complex organic molecules. Laboratory settings have shown that these systems can process waste at rates significantly higher than conventional methods. Nano-enabled bioreactors have increased degradation rates by 50%–70% for organic pollutants (Theron et al., 2008). These systems often rely on a balance between microbes and nanomaterials, with regeneration primarily occurring through the natural recovery of microbial communities, thereby allowing them to adapt to changing conditions. While promising results have been documented in pilot studies, the integration into full-scale systems remains limited by uncertainties regarding microbial-nanoparticle interactions and the long-term stability of the nano-enabled systems.

3.5 Sensing and feedback: in situ nanosensors

In situ nanosensors utilize nanoscale materials with high surface area and reactivity to detect pollutants at low concentrations. These sensors can be configured to detect specific chemical signatures, thereby providing real-time feedback. Nanosensors can detect contaminants at low parts-per-billion concentrations, with response times of seconds to minutes. However, real-world applications can vary significantly due to environmental interference (Epelle et al., 2022). Regeneration strategies may include chemical or thermal treatments to restore sensor function; however, the durability of these nanosensors typically degrades under prolonged exposure to harsh environmental conditions, reducing reliability. While laboratory prototypes are functional and exhibit high sensitivity, issues related to field deployment, such as drift and stability, remain unresolved, limiting their widespread adoption.

4 Pollutant classes to valorization pathways: a circular mapping

Nutrient pollutants predominantly include nitrogen and phosphorus, which are integral components of fertilizers and critical for agricultural productivity. However, their excessive presence in wastewater can lead to environmental problems, including eutrophication. Sustainable recovery practices can mitigate these effects while capitalizing on nutrient valorization. Table 1 provides a decision-oriented mapping linking pollutant classes to nano-enabled solution archetypes and downstream valorization products.

4.1 Nanotechnology solutions for nutrient recovery

4.1.1 Adsorption technologies

Advanced nanomaterials, including carbon-based adsorbents like biochar, activated carbon, and graphene oxides, show promise in adequate nitrogen and phosphorus recovery. The high surface area and porous structures facilitate extensive absorption, enhancing nutrient retrieval from wastewater streams (Qadir et al., 2020; Mannina et al., 2021a).

4.1.2 Electrochemical strategies

Recent studies indicate that nanostructured electrodes can catalyze the electrochemical transformation of ammonium ions back into nitrogen gas, thereby recovering nitrogen while mitigating the environmental impact (Das et al., 2025). Nanomaterials, such as conductive polymers and metal nanoparticles, are incorporated into these electrodes to enhance efficiency and selectivity (Azzam et al., 2023).

4.1.3 Biological innovations

Employing nanotechnology to enhance the activity of nitrogen-fixing bacteria in wastewater systems exemplifies an innovative method of nutrient recovery (Ikhajiagbe et al., 2021). For example, nanoparticle-coated carriers can facilitate the cultivation of these bacteria, thereby supporting the biological transformation of nitrogen compounds into valuable products (Ali et al., 2019).

The emphasis here is not merely on nutrient capture but on downstream integration into fertilizer production or biogas generation, showcasing high-value chains that contribute to sustainable agricultural practices (Liu et al., 2017).

4.2 Metals: recovery enhancements through nanotech

Heavy metals, often arising from industrial discharges, pose significant environmental and health hazards. Prominent examples include lead, copper, nickel, and cadmium. Efficient recovery techniques not only address environmental concerns but also facilitate resource reallocation. Nanotechnology solutions for metal recovery include.

4.2.1 Nanomagnetic adsorbents

Nanoparticles, particularly magnetic composites, leverage their unique properties to attract and capture heavy metals effectively from wastewater. Iron oxide-based magnetic nanoparticles exhibit a strong affinity for metals such as lead and cadmium, with the added advantage of easy recovery via magnetic separation (Tripathy and Gupta, 2023).

4.2.2 Metal-organic frameworks (MOFs)

MOFs represent a novel class of materials with high surface areas and tunable pore structures. Their application results in substantial increases in adsorption capacities for various metals, significantly enhancing recovery rates (Rodríguez-Sánchez et al., 2025). They can also be engineered to target specific metal ions, thereby reducing competition and increasing selectivity during recovery.

Valorization pathways for recovered metals extend to their reintegration into manufacturing and construction, thereby forming closed-loop systems that uphold circular-economy principles focused on sustainable production and consumption (Rando et al., 2024).

4.3 Organics: valorization through advanced nanotechnologies

Organic contaminants in wastewater, including pharmaceuticals, personal care products, and industrial chemicals, can adversely affect human health and ecosystems. Their persistence challenges traditional treatment systems, underscoring the need for innovative solutions. Nanotechnology solutions for organic recovery.

4.3.1 Photocatalytic degradation

Photocatalysis featuring semiconductor nanoparticles can effectively degrade organic pollutants upon exposure to light. Materials such as TiO₂ nanoparticles have been extensively studied for this purpose, as they facilitate the breakdown of complex organic molecules into benign byproducts (Serrano-Lázaro et al., 2024).

4.3.2 Membrane technologies

Nano-enabled membranes, particularly those enhanced with nanomaterials like carbon nanotubes, improve filtration capabilities against organic pollutants. These membranes exhibit not only improved permeation rates but also enhanced contaminant rejection, thereby facilitating both removal and concentration for subsequent valorization (Khajeh et al., 2013).

Organic pollutant recovery can be further processed to produce valuable byproducts, such as biofuels or activated carbon, thereby contributing to energy sustainability and resource reclamation (Mannina et al., 2021b).

4.4 Pathogens: nanotechnology interventions

Pathogens in wastewater, including bacteria, fungi, viruses, and protozoa, pose direct threats to public health (Ogwu and Izah, 2025a; Ogwu and Izah, 2025b). The removal of these microorganisms is crucial for ensuring safe water reuse and environmental protection. Nanotechnology solutions for pathogen management include.

4.4.1 Nanocomposite materials

The incorporation of nano-silver and copper nanoparticles into filtration systems enhances antimicrobial properties, significantly reducing pathogen concentration in treated wastewater. These materials inactivate microbial cells upon contact, thereby facilitating effective pathogen removal.

4.4.2 Advanced oxidation processes (AOPs)

Utilization of nanomaterials in AOPs, such as photocatalytic or electrochemical oxidation processes, has been shown to inactivate pathogens effectively. Nanostructured TiO₂ provides a surface for reactive species to form, enabling the destruction of bacteria and viruses.

By effectively addressing pathogenic contamination, treated effluents can be safely reused for non-potable uses, irrigation, or industrial applications, creating significant value from previously contaminated water sources.

4.5 Emerging contaminants: challenges and opportunities

Emerging contaminants, including microplastics, heavy metals, and pharmaceutical residues, pose significant challenges for conventional wastewater treatment. Their increasing prevalence in the environment necessitates innovative and adaptable solutions. Nanotechnology solutions for emerging contaminants include.

4.5.1 Advanced sorbents

Nanomaterials with high aspect ratios and tunable chemical properties can be engineered to capture emerging contaminants effectively. For example, functionalized nanoparticles designed to attract and isolate microplastics from water streams can efficiently reduce their concentration.

4.5.2 Dual-function photocatalytic/adsorptive systems

Innovative hybrid systems combining both adsorption and photocatalytic degradation leverage the strengths of various nanomaterials to combat emerging contaminants while promoting recovery of energy via catalytic activities.

The processing of recovered emerging contaminants can lead to novel raw materials for the production of biodegradable products or energy sources, underscoring the transformative potential of nanotechnology in waste treatment. When analyzing these nanotechnology solutions across various pollutant classes, it is evident that while some areas exhibit pronounced advances (such as nutrient and metal recovery), others, particularly regarding organic pollutants and emerging contaminants, may benefit from incremental enhancements rather than revolutionary changes.

Figure 4 illustrates a circular mapping framework linking major wastewater pollutant classes to nano-enabled solution archetypes, recovered products, and downstream circular values. Nutrient pollutants, such as nitrogen and phosphorus, are removed by nano-adsorbents, electro-nanocatalysts, metal–organic frameworks, and nano-precipitants to generate fertilizers, ammonia, and struvite for agricultural reuse and nutrient circularity. Metal contaminants are selectively captured using magnetic nanoparticles and MOFs, enabling recovery of copper, nickel, and other valuable metals for reintegration into manufacturing value chains. Organic pollutants are transformed via photocatalytic and nanomembrane systems into energy carriers, such as biogas and volatile fatty acids, thereby supporting energy recovery pathways. Pathogens and emerging contaminants are addressed through nano-enabled advanced oxidation processes and hybrid nanocomposite systems, enabling safe water reuse, public health protection, and pollution prevention.

FIGURE 4

5 Nano-enabled process trains and hybrid systems

The shift towards integrated treatment-recovery systems emphasizes a combination of biological and nanotechnological methodologies. For example, submerged membrane electro-bioreactors have been identified as a promising technology that combines membrane filtration with electrochemical processes to enhance wastewater treatment while minimizing fouling (Bani-Melhem and Elektorowicz, 2011). The modifications to traditional systems enable higher contaminant removal rates, thereby achieving compliance with increasingly stringent regulatory requirements (Ahmed M. et al., 2022). Additionally, polymer nanocomposite membranes are gaining traction due to their high efficiency in pollutant removal (Agboola et al., 2021). These innovations can improve performance and reduce energy consumption throughout the treatment process. By employing hybrid systems that integrate bio- and nanotechnological processes, municipalities can achieve significant resource recovery from wastewater while addressing environmental concerns. Numerous case studies exemplifying integrated systems underscore their effectiveness in resource recovery and contaminant removal. Recent research has demonstrated that combining advanced oxidation processes (AOPs) with biological treatments yields superior performance for high-strength wastewater, improving both removal efficiencies and system robustness (Baghban, 2025). Such hybrid configurations have shown promise, particularly as they can be tailored to local conditions, thereby enhancing modularity and scalability (Madeira et al., 2023).

Hybrid systems offer greater versatility than traditional centralized treatment systems. Their modular nature facilitates retrofitting of existing wastewater treatment facilities, enabling the incorporation of new technologies without extensive overhauls (Waly et al., 2022). This adaptability is especially crucial in decentralized settings where resource constraints may limit the feasibility of large-scale solutions. Such flexibility is essential for modern water management, particularly in developing regions facing growth pressures (Rajakumar et al., 2010). Moreover, integrating these hybrid systems enables communities to remain aligned with circular economy principles, reclaiming valuable resources such as nutrients and treated water for agricultural or industrial use (Mbarek et al., 2022). The modular approach can significantly enhance operational resilience, allowing systems to dynamically adapt to fluctuations in influent characteristics and flow rates. Pilot-scale submerged membrane electro-bioreactors have been tested in municipal wastewater treatment systems, demonstrating simultaneous fouling mitigation and enhanced organic matter removal under continuous operation (Bani-Melhem and Elektorowicz, 2011; Ahmed Z. et al., 2022).

As the field evolves, continuous innovations in nanotechnology are anticipated to further refine wastewater treatment processes. Recent studies emphasize the potential of novel nanomaterials, including graphene oxide and mesoporous titanium dioxide, which exhibit superior properties for pollutant adsorption and catalytic activity (Mustafa et al., 2022; Zhou et al., 2014). The continuous evaluation of these materials for efficacy and environmental impact will be crucial for their integration into existing systems. Adapting regulatory frameworks to support the advancement and implementation of nano-enabled systems will be crucial. Policymakers must consider environmental safety concerns regarding nano-scale materials while also creating incentives for their adoption in wastewater treatment infrastructures (Bui et al., 2016). This involves establishing standards and guidelines that promote the safe use of nanotechnology in the treatment process, ensuring that both public health and environmental safety are maintained.

5.1 Illustrative pilot-scale applications of nano-enabled circular systems

As nano-enabled wastewater technologies transition from laboratory research to practical implementation across diverse operational contexts, pilot-scale studies have provided significant insights into their effectiveness in municipal, industrial, and agro-food applications. The use of nano-enabled systems for wastewater treatment and valorization underscores a shift toward circular economy principles in water management (Table 2). For example.

5.1.1 Municipal applications: enhanced nutrient recovery

In municipal wastewater treatment, nano-enabled membrane bioreactors (MBRs) have been explored as advanced solutions for nutrient recovery and fouling mitigation. MBRs use nanostructured materials that enhance the separation of microorganisms from treated water, thereby improving the removal of nitrogen and phosphorus. Studies demonstrate that these systems can achieve higher nutrient removal efficiencies than conventional activated sludge processes, primarily due to differences in microbial populations and floc sizes between the two methods (Joss et al., 2004; Kehrein et al., 2020). Furthermore, the stable hydraulic performance under continuous operation indicates that nano-functionalized membranes integrate effectively into existing infrastructure while also promoting resource recovery (Kehrein et al., 2020).

5.1.2 Industrial applications: photocatalysis for micropollutant degradation

Nano-enabled photocatalytic systems utilizing titanium dioxide and other semiconductor nanomaterials have shown significant promise in industrial wastewater treatment, particularly for the degradation of micropollutants such as pharmaceuticals and endocrine-disrupting compounds. These studies indicate that effective removal rates can be achieved under real wastewater conditions, facilitating the safe reuse of treated water (Alfonso-Muniozguren et al., 2021; Gao et al., 2024). Advanced oxidation processes provided by these photocatalytic systems complement traditional biological methods, thereby increasing the capacity of wastewater treatment facilities to handle hazardous microcontaminants (Busca et al., 2008). The integration of such technologies into pilot-scale applications underscores the potential of nano-enabled systems to address emerging water quality concerns effectively (Miège et al., 2009).

5.1.3 Agro-food contexts: bio–nano hybrid systems

In the agro-food sector, pilot-scale bio–nano hybrid reactors have been successfully evaluated for their capability to valorize organic-rich waste streams, particularly in anaerobic digestion processes. These systems combine nanomaterials with microbial communities to enhance biogas production and nutrient recovery. Notably, the interactions between nanostructured surfaces and microbial systems lead to enhanced performance in biogas yield and nutrient remobilization, illustrating a significant advancement in bioprocess engineering (Bacab et al., 2020;; Paulo et al., 2024). The ability to generate renewable energy while simultaneously recovering nutrients aligns with the principles of circular agriculture, showcasing how wastewater treatment can facilitate resource regeneration (Kumar et al., 2021).

Nano-enabled technologies in wastewater treatment reflect a promising advancement in enhancing the efficiency and sustainability of resource recovery. Significant improvements in nutrient recovery and micropollutant degradation will continue, indicating a substantial shift towards a circular systems approach in wastewater management. The effective use of nanomaterials not only addresses critical environmental concerns but also transforms traditional wastewater treatment facilities into resource-recovery hubs.

6 Digital intelligence for nano-enabled circular systems

Digital twins are comprehensive virtual replicas of physical systems that enable real-time monitoring, simulation, and predictive analysis. In the context of wastewater management, digital twins can encompass all components of treatment facilities, from influent quality to effluent discharge. Applications in wastewater management include.

6.1 Monitoring and diagnostics

Digital twins facilitate continuous monitoring of critical parameters such as pH, dissolved oxygen, and chemical oxygen demand. They enable the simulation of “what-if” scenarios, allowing operators to anticipate system behavior under various conditions (Zaveri et al., 2025).

6.2 Predictive maintenance

By utilizing digital twins, systems can predict and diagnose failures before they occur, leading to reduced downtime and increased operational efficiency. For example, predictive maintenance models can analyze trends in equipment performance, allowing for timely interventions (Ünal et al., 2022).

6.3 Optimization of treatment processes

Digital twins provide insights into process dynamics, enabling the optimization of chemical dosages and energy consumption. This has proven essential in enhancing the efficiency of biological nutrient removal (BNR) processes while ensuring compliance with environmental regulations (Prabu et al., 2025).

Soft sensors, or virtual sensors, use algorithms and mathematical models to estimate unmeasurable variables from measurable ones. Their deployment is critical to ensuring quality control in wastewater treatment operations, where real-time capabilities are necessary. Soft sensors have been shown to reliably estimate parameters such as sludge concentration and respiration rates. For instance, models constructed using the generalized damped least squares methodology have improved dissolved oxygen control performance, which is essential for aerobic biological treatment (Animashaun, 2025).

Advanced machine learning frameworks, including recurrent neural networks (RNNs), have demonstrated superiority in estimating hard-to-measure parameters based on historical and real-time data (Yoo and Lee, 2004). Such methodologies facilitate adaptive control strategies that respond effectively to changing operational conditions (Moghadam et al., 2019). Predictive maintenance strategies are crucial for ensuring the functionality of wastewater treatment systems, minimizing unplanned downtime, and extending the lifespan of critical infrastructure components. Stochastic state-space models have been employed to predict system operational states, enabling timely maintenance interventions to be planned and executed (Bertret et al., 2024). The integration of AI with predictive maintenance technologies enables intelligent monitoring systems that can learn from historical performance data and adjust operational parameters accordingly (Thuruthel et al., 2022). These systems can optimize maintenance schedules, thereby aligning operational practices with environmental sustainability (Hyatt et al., 2020).

Adaptive control refers to control systems that adjust their parameters in real time to improve system stability and performance based on real-time data. Using real-time data from soft sensors, adaptive controllers can modulate chemical feed rates or airflow to maintain optimal treatment conditions despite fluctuations in wastewater characteristics (Sabelhaus et al., 2022). Implementation of model reference predictive adaptive control in large-scale wastewater treatment systems has been shown to improve response times to disturbances and mitigate operational inefficiencies (Balseca et al., 2025). A balanced circular transition will require the strategic integration of nano-enabled innovations with mature non-nano solutions, ensuring that technological advancement reinforces, rather than replaces, proven biological and nature-based recovery pathways.

6.4 Nano-enabled versus non-nano circular pathways

The debate over circular pathways in wastewater management often pits traditional advanced non-nano technologies against emerging nano-enabled innovations. Non-nano technologies, including optimized biological treatments such as anaerobic digestion and microbial fuel cells, and nature-based solutions such as constructed wetlands and algal systems, have formed the backbone of sustainable wastewater treatment practices due to their inherent low cost, low energy consumption, and community acceptance. In contrast, nano-enabled technologies, while promising enhancements in selectivity and efficiency, are fundamentally complementary to established methods rather than replacements.

6.4.1 Non-nano circular technologies

Advanced non-nano technologies, particularly anaerobic digestion, have been recognized for their potential to convert organic matter in wastewater into biogas, thereby producing a renewable energy source. According to Speece (1983), anaerobic digestion has been effectively utilized in industrial wastewater treatment to exploit readily degradable organics from various sources, such as food processing. McCarty et al. (2011) emphasize that the shift in perspective from viewing wastewater as waste to a resource has significant implications for water resource management, highlighting the dual benefits of energy recovery and nutrient reclamation. Moreover, assessments indicate that systems such as constructed wetlands can achieve high removal efficiencies, making them valuable for resource recovery and environmental sustainability (Sengupta et al., 2015). Microbial electrochemical systems showcase additional benefits in resource recovery. They facilitate the generation of bioelectricity from bacterial metabolism while simultaneously treating wastewater. This dual functionality indicates their potential as a viable technology for sustainable urban wastewater management, as they effectively convert waste into energy (Fei et al., 2011). Research has shown that coupling these technologies can enhance nutrient and energy recovery from wastewater, advancing circular economy principles in the water sector (Ghimire et al., 2021).

6.4.2 Nanotechnology in circular pathways

Nano-enabled technologies are increasingly viewed as enhancing traditional systems rather than functioning independently. For instance, the integration of nanoparticles, such as zero-valent iron, into anaerobic digestion processes has been reported to significantly improve methane production efficiency, thereby increasing overall system efficacy (Liu et al., 2015). The incorporation of nanomaterials can offer novel opportunities to enhance traditional wastewater treatment processes through superior antimicrobial properties and catalytic actions that traditional approaches lack (Yang et al., 2013). Moreover, advancements in forward osmosis technology, which utilizes nano-materials to concentrate waste streams, have shown promising results in simultaneously treating wastewater and recovering water for reuse (Ansari et al., 2017). These innovations are particularly beneficial in resource-constrained contexts, where optimizing existing infrastructure with nano-enhanced solutions can yield notable improvements in cost-efficiency and process reliability.

6.4.3 Complementarity of nano and non-nano solutions

The key message in assessing nano-enabled versus non-nano pathways is their complementarity rather than competition. As noted by Guerra-Rodríguez et al. (2020), integrating circular economy principles in the wastewater sector requires a comprehensive approach that leverages both existing and cutting-edge technologies. Non-nano solutions provide established frameworks and community trust, while nano-enhancements can optimize processes and improve performance metrics such as resource recovery rates and pollutant reduction efficiencies. The economic viability of these technologies will depend on supportive policies and incentives. For instance, while anaerobic digestion has been recognized for its potential to contribute to energy sustainability, its economic competitiveness against fossil fuels remains a barrier (Kehrein et al., 2020). Thus, ensuring that both non-nano and nano-enabled solutions are synergistically applied could lead to a more resilient and far-reaching implementation of circular pathways in wastewater management.

7 Techno-economic and life-cycle performance of nano-enabled circular pathways

The incorporation of nanotechnology into wastewater management systems has created new paradigms that support the realization of circular economy goals. In this context, the techno-economic assessments (TEAs) and life cycle assessments (LCAs) play a pivotal role in understanding the performance of nano-enabled systems. Table 3 synthesizes comparative trends from published TEA and LCA studies, emphasizing dominant cost drivers, scaling sensitivities, and conditions under which nano-enabled systems may deliver net circular benefit. Nanotechnology introduces a suite of enhancements to traditional wastewater treatment processes, often leading to improved efficacy, reduced resource usage, and higher recovery rates. When evaluating the performance of nano-enabled systems against these critical metrics, one must consider both the benefits and potential pitfalls. For example.

7.1 Energy demand and recovery yield

Nanomaterials can significantly reduce energy demand in wastewater treatment by improving the efficiency of separation and conversion processes. For example, nanofiltration and membrane technologies have been shown to reduce operational energy costs by enabling faster and more efficient removal of contaminants (Sravan et al., 2024). Recent advances in nanostructured materials demonstrate potential for energy efficiency while increasing the recovery yields of valuable resources such as nitrogen and phosphorus. The use of engineered nanoparticles in biological treatments can enhance microbial activity, thereby optimizing the degradation of organic matter and maximizing overall recovery yields (Liu and Zhang, 2025). However, as illustrated in various studies, some nano-enabled processes may have energy-demand implications that offset their benefits. The energy performance must be evaluated comprehensively, accounting for ancillary energy requirements associated with nanoparticle synthesis and operational considerations (Heo et al., 2025). Such analyses can reveal whether specific technologies yield net energy savings when perceived lifecycle energy costs are accounted for.

7.2 Regeneration burden

The regeneration burden reflects the environmental impact and usability of the materials used in the treatment process. Some nanomaterials, while effective in therapeutic applications, may also pose risks during regeneration and disposal. The synthesis of nanomaterials can involve significant chemical inputs, which, if not properly managed, can lead to adverse effects, including toxicity and environmental degradation (Kuppan et al., 2023). Furthermore, the life-cycle implications of nanoparticle regeneration cannot be overlooked. Considerable energy may be required to recover, regenerate, or replace nanoparticles—especially when dealing with nanoparticles designed for enhanced catalytic performance in waste streams (Lam et al., 2022). It is thus imperative that any significant recovery processes using nanomaterials be coupled with comprehensive waste management strategies to mitigate potential drawbacks (Ogwu et al., 2024; Izah and Ogwu, 2025).

7.3 Emissions

The deployment of nanotechnology in wastewater treatment is often associated with reduced emissions, as enhanced pollutant removal reduces emissions. However, an evaluation of the indirect emissions associated with the manufacture, transport, and deployment of these technologies is equally crucial. Studies have suggested that while direct emissions from wastewater treatment processes can be significantly reduced, accurate accounting of emissions must also consider the cradle-to-grave lifecycle (Zhao and Chen, 2025). Emerging assessment frameworks are designed to rigorously determine the effectiveness of emission reductions at each stage of the nano-enabled treatment process, thereby facilitating the identification of the most sustainable practices available (Arjun et al., 2025). This necessitates a balance between immediate operational impacts and longer-term lifecycle emissions captured through broader system dynamics.

The potential of nanotechnology to enhance circularity in wastewater management is contingent on multiple factors. Such as:

7.3.1 Technological maturity

The readiness of nano-enabled technologies for widespread adoption tends to correlate highly with established performance metrics. Innovations at lower technological maturity levels often face challenges in commercialization, thereby limiting their contributions to the circular economy (Urban et al., 2007).

7.3.2 Regulatory framework

The presence of supportive regulatory frameworks can either promote or hinder the adoption of nano-enabled solutions. Guidelines that encourage sustainable practices in wastewater management may enhance circularity by encouraging industries to innovate responsibly.

7.3.3 Cost-benefit trade-offs

Balancing cost implications with potential benefits is critical in determining the economic viability of nano-enabled processes. High initial capital costs may deter investment in promising technologies that lack demonstrable value in operational cost savings or enhanced recovery yields.

A key limitation of current TEA and LCA studies is the lack of harmonized methodological frameworks and standardized system boundaries for nano-enabled wastewater technologies. Differences in functional units, operational assumptions, and data availability across studies restrict direct quantitative comparison with incumbent treatment systems. As such, reported cost and emissions estimates should be interpreted as indicative rather than definitive performance metrics. Despite the potential advantages that nanotechnology provides, several uncertainties cloud the landscape of TEA and LCA for these systems.

7.3.3.1 Material behavior

The environmental behavior of nanomaterials is not yet fully understood, which impairs risk assessments. This includes uncertainties regarding their potential environmental and human health impacts during disposal or degradation.

7.3.3.2 Market dynamics

Fluctuations in material costs and energy prices could drastically affect the economic viability of nano-enabled technologies, further complicating assessments.

7.3.3.3 Public acceptance

Societal perceptions and the readiness for adopting novel technologies present barriers in some regions, which can influence regulatory frameworks and market introduction.

Recent pilot-scale techno-economic assessments of nano-enabled nutrient recovery systems report improved selectivity and recovery yields relative to conventional processes, although with higher capital costs and methodological variability at early deployment stages (Garrido-Baserba et al., 2018; 2022; Mannina et al., 2022).

Figure 5 provides a simplified conceptual overview of how nano-enabled wastewater treatment pathways may be evaluated using TEA and LCA, and highlights the key performance dimensions—energy demand and recovery yield, regeneration burden, and emissions—through which nano-enabled systems may generate circular-economy benefits or introduce trade-offs across the system life cycle.

FIGURE 5

It is important to note that the TEA and LCA components presented here are intended as exploratory and scenario-based assessments rather than harmonized quantitative benchmarks. At present, standardized cost and emissions datasets for nano-enabled wastewater technologies remain limited due to their early-stage development and heterogeneous deployment contexts. Consequently, the analysis focuses on comparative trends, dominant cost drivers, and system-level environmental trade-offs to support strategic decision-making under technological uncertainty.

8 Environmental fate of nanomaterials in wastewater

Understanding the fate of engineered nanomaterials (ENMs) in wastewater treatment systems is vital for the development of safe and effective nanotechnology applications. ENMs can move through various treatment stages and ultimately be released into the environment, impacting both aquatic and terrestrial ecosystems. Table 4 synthesizes known fate pathways and governance needs across the life cycles of nanomaterials. Research has demonstrated that conditions such as pH, ionic strength, and the presence of organic matter significantly influence the stability and behavior of nanoparticles in aqueous environments. For example, the aggregation and dissolution of zinc oxide nanoparticles (ZnO NPs) in various solutions have been shown to vary with these parameters, thereby affecting their behavior throughout the wastewater treatment process (Bian et al., 2011; Lombi et al., 2012; Smeraldi et al., 2017).

Specifically, small ZnO nanoparticles exhibit size-dependent dissolution behavior that can be exacerbated in acidic environments, such as those found in wastewater treatment systems (Smeraldi et al., 2017; Gomez-Gonzalez et al., 2023). Their propensity to aggregate can lead to complex interactions within sludge and influence the overall efficiency of wastewater treatment processes (Smeraldi et al., 2017; Lombi et al., 2012). Studies have highlighted that engineered nanoparticles often aggregate due to attractive particle-particle interactions, leading to sedimentation and reduced bioavailability in ecosystems (Kaegi et al., 2011; Batley et al., 2012). Furthermore, laboratory and field studies have shown that metallic nanoparticles, such as silver (Ag NPs), are frequently adsorbed onto biosolids collected from wastewater treatment plants. Observations indicate that a substantial portion of these nanoparticles can persist in effluents despite treatment, raising concerns about their environmental impact and potential for bioaccumulation (Kaegi et al., 2011; Kent et al., 2014).

8.1 Safety and health risks of nanomaterials

The unique properties of nanomaterials enable their use in wastewater management, yet these same properties can also pose safety and health risks. Nanoparticles can interact with aquatic organisms, potentially causing toxicological effects that warrant thorough investigation (Xuan et al., 2023; Petersen et al., 2015; Casey et al., 2003). A key challenge is assessing exposure risks to human health and determining whether current methodologies are adequate for evaluating the safety of engineered nanomaterials (Bhattacharyya et al., 2017; Meesters et al., 2013).

For example, studies on the fate of silver nanoparticles in pilot wastewater treatment systems provide insights into their bioaccumulation and transformation processes (Kaegi et al., 2011; Kent et al., 2014). Similarly, the effects of coated nanoparticles, such as cerium dioxide and TiO₂, on microbial communities during anaerobic digestion highlight the potential to disrupt treatment efficacy (Yang et al., 2013; Barton et al., 2014). Given that many ENMs have not yet been fully assessed for their long-term effects on human health and ecosystems, regulatory frameworks must evolve to address these uncertainties. A safe-by-design approach is critical; it encourages the incorporation of safety considerations throughout different stages of nanomaterial development and application (Kaushik et al., 2023; Lartigue et al., 2013; Carboni et al., 2021). This initiative focuses not only on minimizing toxicity but also on optimizing the effectiveness of nanomaterials in wastewater treatment. Safe-by-design may be interpreted as a precautionary governance principle rather than as a definitive risk-mitigation solution. Therefore, safe-by-design approaches should aim to reduce potential environmental and health risks through material selection, process optimization, and exposure minimization. Notably they cannot fully eliminate uncertainty associated with long-term toxicity, environmental fate, chronic exposure, and bioaccumulation of nanomaterials. Safe-by-design should therefore be understood as an adaptive regulatory and design framework that supports responsible innovation under conditions of incomplete knowledge, rather than as a guarantee of environmental safety.

8.2 Risk governance frameworks

The governance of nanomaterials in wastewater management is complex, as rapid technological advancements often outpace existing regulatory measures. Current frameworks frequently fail to account for the unique behaviors and risks associated with nanomaterials. Studies emphasize that regulatory gaps can lead to inadequate assessment and management of ENM risks, including those arising from the manufacturing, use, and disposal stages (Lartigue et al., 2013; Carboni et al., 2021; Gottschalk and Nowack, 2011).

Recent assessments suggest that a life-cycle approach to nanomaterial regulation must be more robust, incorporating comprehensive measures to monitor ENM release throughout their lifespan (Layton et al., 2000; Nowack et al., 2011). Additionally, modeling studies provide substantial data on the pathways by which engineered nanomaterials are released into the environment, underscoring the need for stakeholder collaboration to develop effective governance strategies (Batley et al., 2012; Suhendra et al., 2020). International agencies, such as the OECD, have begun to guide on assessing the environmental impact of nanomaterials, but further efforts are needed to establish standardized protocols that adequately address varying exposure scenarios (Xuan et al., 2023; Petersen et al., 2015; Meesters et al., 2013). By engaging a broad range of stakeholders—including researchers, policymakers, and community members—regulatory frameworks can evolve to improve public trust and acceptance of nanotechnology applications in circular wastewater management systems.

Despite increasing attention to environmental fate and safe-by-design strategies, long-term toxicity, chronic exposure pathways, and bioaccumulation dynamics of many nanomaterials remain poorly quantified. Current ecotoxicological evidence is largely based on short-term laboratory assays and species-specific endpoints, limiting the ability to extrapolate risks across ecosystems and human populations. The absence of longitudinal field studies and standardized exposure metrics, therefore, represents a major constraint for comprehensive life-cycle risk assessment of nano-enabled wastewater technologies.

9 Readiness–impact scorecard for deployment prioritization

The increasing pollution of water bodies due to organic contaminants, including pharmaceuticals and antibiotic-resistant bacteria (ARB), necessitates innovative approaches to wastewater management. This roadmap integrates a multi-criteria readiness-impact scorecard to evaluate various nanotechnology solutions for circular wastewater management, considering their technical readiness, circular impact, safety, and scalability. This framework is designed to guide utilities, investors, and policymakers in selecting optimal solutions for enhancing resource recovery in wastewater treatment processes. However, to avoid overstating near-term feasibility, nano-enabled solutions are explicitly stratified according to technology readiness level (TRL) into near-term (TRL 7–9), mid-term (TRL 4–6), and long-term or speculative (TRL 1–3) categories (Table 5). This stratification enables a phased interpretation of the roadmap, distinguishing technologies close to deployment from those still in experimental or developmental stages.

9.1 Multi-criteria scorecard framework

9.1.1 Technical readiness

Technical readiness is an essential component to gauge how prepared a solution is for practical application. Technologies such as microbial electrolysis cells (MECs) are becoming prominent, as reported by Seo et al., who detailed the successful application of combined alkaline-ultrasound pretreatment strategies to enhance methane production and organic matter removal in MECs (Seo et al., 2023). This demonstrates a clear pathway for nanotechnology applications that are already gaining traction. Furthermore, studies indicate that conventional treatment systems integrating advanced oxidation processes (AOPs) can effectively degrade complex organic compounds (Kim et al., 2022).

9.1.2 Circular impact

The circular impact focuses on each technology’s potential to recover resources, mitigate pollution, and minimize waste. Kolpin et al. documented significant occurrences of organic wastewater contaminants (OWCs) in streams, highlighting the need for effective removal technologies that also recover valuable resources (Kolpin et al., 2002). Such findings underscore the importance of implementing circular methodologies that do not merely treat wastewater but enhance its use as a resource. Additionally, Rizzo et al. (2013) demonstrate that urban wastewater treatment plants are hotspots for the dissemination of ARB, underscoring the need to integrate nanotechnology solutions that target these contaminants, promote public health and safety, and enhance wastewater reuse.

9.1.3 Safety profile

Safety profiles of technologies in wastewater management must prioritize public health and ecological integrity. Research by Larsson et al. indicates that the presence of specific contaminants significantly affects microbial communities within treatment facilities, presenting risks to water quality (Larsson et al., 2007). Therefore, solutions must undergo rigorous assessments to ensure they do not introduce additional risks or environmental toxicity. The findings of Larsson et al. (2007) further accentuate the urgency of addressing the toxicological impacts of pharmaceuticals, which inhibit microbial activity and pose long-term ecological risks.

9.1.4 Scalability

Scalability is critical in translating successful pilot projects into broader applications. Practical solutions, such as the adsorption of nitrates and phosphates from wastewater, as discussed by Gizaw et al. (2021), emphasize the potential for rapidly scalable interventions that use low-cost, eco-friendly materials. These advances can be pivotal in adapting treatment technologies to various contexts and operational scales.

9.2 Pathways to deployment

The roadmap identifies distinct deployment pathways ranging from near-term to speculative innovations:

9.2.1 Near-term

Immediate adoption of advanced treatment technologies such as AOPs for pharmaceutical degradation and MECs for resource recovery will enable rapid improvements in wastewater treatment effectiveness (Kim et al., 2022; Seo et al., 2023).

9.2.2 Medium-term

Development of strategies for enhanced nutrient recovery, utilizing existing frameworks, will promote an integrated circular economy approach. Techniques for the effective removal of emerging contaminants, such as ARBs, will gain traction (Rizzo et al., 2013; McArdell et al., 2003).

9.2.3 Speculative

Emerging technologies that incorporate nanoparticles for selective contaminant removal and bioconversion processes represent exciting opportunities that require further R&D investments. These innovative approaches can significantly enhance the value of wastewater as a resource (Berkessa et al., 2019; Pillai et al., 2019).

This scorecard supports deployment prioritization across technical, circular, and governance dimensions (Table 5). Figure 6 presents a staged and asynchronous roadmap for the deployment of nano-enabled circular wastewater systems, integrating technological development, digital integration, and governance pathways across near-term (0–5 years), mid-term (5–10 years), and long-term (10+ years) horizons. The roadmap operationalizes the readiness–impact scorecard by illustrating how nanomaterial innovation, digital intelligence, and regulatory frameworks are expected to mature at different rates, enabling modular and phased system integration rather than requiring simultaneous convergence. This structure supports flexible, context-specific implementation strategies and aligns deployment prioritization with realistic technology readiness and institutional capacity. Several nano-enabled membrane and electrochemical systems have already reached pilot and early demonstration levels, particularly in Europe and East Asia, supporting their classification as near-to mid-term deployable technologies (Bui et al., 2016; Devaisy et al., 2023; Nagy et al., 2023). It is important to recognize that convergence between nanomaterials, digital intelligence, and governance systems is unlikely to occur simultaneously or uniformly across contexts. In practice, technological and institutional components are expected to mature at different rates, leading to asynchronous innovation pathways. The roadmap, therefore, adopts a staged convergence logic, in which individual system elements—such as material platforms, sensing infrastructures, or regulatory frameworks—can be developed and deployed incrementally, without requiring full system integration at early stages.

FIGURE 6

10 A 2030 research, standards, and Innovation Agenda

Figure 7 outlines five interconnected research and innovation domains critical to this transformation: (1) Materials Design and Advanced Oxidation Processes, (2) Regeneration Strategies and Water Reuse, (3) Antifouling Interfaces and Nano-Bio Integration, (4) Digital Monitoring and Regulation, and (5) Circular Business Models. These areas are poised to play a transformative role in achieving the Sustainable Development Goals (SDGs) and the principles of the circular economy.

FIGURE 7

10.1 Materials design and advanced oxidation processes

The development of novel materials through nanotechnology provides significant opportunities to enhance wastewater treatment efficiency. Advanced oxidation processes utilizing nanomaterials, such as TiO₂ and MOFs, have shown promise in degrading a range of emerging contaminants while generating minimal toxic by-products (Cardoso et al., 2021). The use of AOPs in conjunction with nanotechnology not only improves contaminant removal but also aligns with regulatory demands for higher water quality standards (Cardoso et al., 2021). For instance, the integration of AOPs can effectively tackle organic micropollutants that conventional methods struggle to remove (Chauhan et al., 2019). Research efforts to synthesize sustainably designed materials could also reduce costs and environmental risks associated with nanomaterials, thereby making them more accessible for widespread use in existing treatment infrastructure (Qu et al., 2012). Initiatives such as modular treatment systems can be optimized for flexible application, facilitating the retrofitting of aging wastewater plants (Qu et al., 2012).

10.2 Regeneration strategies and water reuse

Circular wastewater management requires innovative regeneration strategies to maximize the recovery of valuable resources from wastewater streams. Studies indicate that efficient recovery of nutrients and water through biological treatment coupled with nanotechnology can significantly enhance sustainability outcomes. Bioaugmentation techniques that integrate nanomaterials can stimulate microbial activity, thereby enhancing the degradation of contaminants and promoting efficient nutrient recovery (Nzila et al., 2016). Moreover, the potential for reclaiming treated wastewater for non-potable uses is crucial for addressing water scarcity. Historical analyses indicate that inadequate wastewater treatment has severe ecological implications, necessitating improvements in treatment efficacy and maximizing water reuse (Grant et al., 2012). The adoption of stringent water reuse guidelines is also essential to safeguard public health while promoting sustainable practices (Rodríguez et al., 2022). In low- and middle-income regions, phased and context-sensitive adoption strategies are essential, prioritizing affordability, institutional capacity, and local governance structures over high-complexity digital infrastructures.

10.3 Antifouling interfaces and nano-bio integration

Fouling remains a critical challenge in membrane technologies employed for water treatment. Innovations in antifouling interfaces using nanostructured coatings can mitigate biofilm formation, thereby enhancing membrane longevity and reducing operational costs (Sinha et al., 2023). Recent advances in the use of nanomaterials to develop smarter antifouling surfaces could further enhance system efficiency while minimizing the need for chemical cleaning agents that pose environmental risks (Hamed et al., 2024). The integration of nano-bio systems, which utilize microorganisms in conjunction with nanomaterials, can foster synergistic effects that enhance contaminant degradation and resource recovery, aligning with both environmental and economic objectives of the circular economy (Chauhan et al., 2019). Hybrid nano–bio configurations, such as nanoparticle-enhanced anaerobic digestion or nanomaterial-integrated wetlands, illustrate how nano-enabled systems can augment existing biological and nature-based platforms without displacing them.

10.4 Digital monitoring and regulation

The shifting landscape of wastewater management toward a circular-economy paradigm necessitates the development of sophisticated digital monitoring systems. Implementing IoT-based approaches that leverage real-time data analytics can optimize operational efficiency and support compliance with evolving regulations (Qu et al., 2012). Regulatory frameworks governing the application of nanotechnology in wastewater treatment must evolve to maintain safety and efficacy standards. Developing a comprehensive set of guidelines will facilitate the safe integration of nanotechnology innovations into existing frameworks, enabling scalability (Smol et al., 2020). The deployment of nano-enabled wastewater technologies requires alignment with existing environmental regulatory frameworks governing chemical safety, water quality, and public health protection. Key international instruments, such as the OECD Working Party on Manufactured Nanomaterials and the ISO Technical Committee on Nanotechnologies (ISO/TC 229), and national environmental protection agencies are providing emerging guidelines for risk assessment, exposure monitoring, and material characterization. However, regulatory coverage remains fragmented, and most jurisdictions lack nano-specific compliance standards for wastewater applications. Effective governance of nano-enabled circular systems will therefore require adaptive regulatory approaches that integrate life-cycle risk assessment, precautionary safety thresholds, post-deployment monitoring, and stakeholder engagement. Such frameworks can support responsible innovation by ensuring that technological advancement proceeds in parallel with environmental safety, regulatory oversight, and public trust.

10.5 Circular business models

Transitioning to circular economy practices in wastewater management requires innovative business models that prioritize resource recovery and minimize waste generation. Collaborative efforts among stakeholders—industry, academia, and government—could establish pathways for integrating advanced nanotechnology into market frameworks (Hong et al., 2023). The adoption of business models focusing on the lifecycle impacts of technological interventions will be key to sustainable management practices (Dabare et al., 2025).

11 Implications for policy, utilities, and industry adoption in circular wastewater management

The adoption of circular economy principles in wastewater management is significant, as it aligns with broader sustainability goals and maximizes resource recovery. However, it is important to recognize that access to digital infrastructure is highly uneven across regions, particularly between high-income and low- and middle-income countries. As such, the digital components of the roadmap—such as AI-driven analytics, digital twins, and IoT-based sensing—should be interpreted as modular and adaptive layers rather than universal requirements. In resource-constrained contexts, low-cost sensing technologies, community-based monitoring, and decentralized decision-support tools may offer more feasible entry points into circular wastewater management. Digital twins and AI-based analytics act as translation layers that convert nano-scale process behavior into facility-scale operational intelligence. By leveraging advancements in nanotechnology, stakeholders can enhance treatment efficiency, reduce environmental impact, and recapture resources from wastewater streams. However, effective transitions necessitate well-crafted policies, robust utility frameworks, and collaborative industry engagement tailored to specific socioeconomic contexts.

11.1 Framework for policy and utility adoption

The integration of advanced nanotechnologies into wastewater management requires innovative procurement strategies that prioritize sustainability and circularity. Geissdoerfer et al. (2017) discuss the necessity of systemic change toward sustainability paradigms, which can be framed to include specific requirements for procuring nanotechnology solutions—ensuring that selected materials are both effective and environmentally benign. In low- and middle-income contexts, risk-sharing mechanisms can alleviate the financial burdens associated with implementing new technologies. Jain et al. (2021) indicate that such frameworks not only distribute financial risks among stakeholders but also incorporate the costs of monitoring and assessing the efficacy of new approaches. This model encourages a shift from conventional treatment methods to nanotechnology-enhanced systems, promoting innovative practices even in resource-constrained settings. From a policy perspective, the successful implementation of nano-enabled circular wastewater systems will depend not only on technological maturity but also on the development of coherent regulatory frameworks, international standards, and institutional governance mechanisms to manage long-term environmental and health risks.

Standardization is critical for fostering trust and ensuring the safety of emerging technologies in wastewater management. According to Ghimire et al. (2021), establishing comprehensive guidelines will facilitate the implementation of circular economy principles in wastewater facilities. Efforts to align these standards with global best practices can also spur the development and integration of effective nanotech solutions in treatment processes. Incentivizing utility companies to adopt greener technologies requires comprehensive policy frameworks. As highlighted by Puyol et al. (2017), implementing biological technologies can enhance resource recovery, thereby contributing to the economic feasibility of wastewater treatment. Providing tax incentives or funding opportunities for utilities that demonstrate successful integration of nanotechnology into wastewater treatment can accelerate adoption rates.

11.2 Industry collaboration and stakeholder engagement

Sustainability in wastewater management significantly benefits from cross-sector collaborations. Bhattacharyya et al. (2017) emphasize the regulatory and social dimensions of nanotechnology, necessitating engagement among water professionals, policymakers, and the public. Establishing partnerships that bridge computational modeling, environmental science, and public health can foster holistic approaches to wastewater challenges. Moreover, partnerships with academia can provide ongoing research into innovative materials and methods—for example, Ganjidoost et al. (2022), which demonstrated how performance modeling can optimize existing wastewater collection networks, underscoring the need for partnerships that enhance operational efficiency through research-driven insights.

The practical implementation of circular practices also relies on community engagement and education regarding the benefits of wastewater resource recovery. Community acceptance can be cultivated through educational campaigns that highlight the environmental and economic advantages of adopting innovative wastewater technologies. It is important to stress the value of including public views in policy formulation to ensure acceptance and cooperation. By empowering local stakeholders with knowledge about nanotechnology and its applications, communities are more likely to support related initiatives, enabling a smoother transition toward sustainable wastewater management practices.

12 Conclusion

This roadmap argues that the future of circular wastewater management will not be determined solely by the discovery of ever more efficient nanomaterials, but by the capacity to integrate nanotechnology into system-level architectures that align technical performance with digital intelligence, risk governance, and circular value creation. Although the roadmap is primarily conceptual and systems-oriented, its feasibility is supported by a growing body of pilot-scale and early-demonstration studies across municipal, industrial, and agro-food wastewater contexts, indicating that several nano-enabled pathways are already transitioning from laboratory research to applied implementation. The central challenge facing the field is no longer whether nanotechnology can enhance pollutant removal or resource recovery—this has been convincingly demonstrated—but whether these capabilities can be translated into reliable, scalable, and governable infrastructure that delivers net circular benefits under real-world conditions. By reframing nanotechnology as a systems enabler rather than a standalone intervention, this paper advances the conceptualization and evaluation of innovation pathways in wastewater management. The roadmap highlights that circular performance emerges from the interaction between materials, process design, operational control, and institutional context. Nano-enabled solutions deliver their greatest value when deployed within integrated recovery platforms that combine selective capture, transformation, and separation with real-time sensing, adaptive control, and clearly defined valorization pathways. In this sense, nanotechnology functions less as a discrete technology class and more as a connective layer that enhances selectivity, responsiveness, and flexibility across treatment–recovery–reuse loops.

Also, scale, governance, and digitalization must be treated as co-evolving design constraints rather than downstream considerations. The integration of AI-driven monitoring, soft sensing, and digital twins is not merely an efficiency upgrade; it is a prerequisite for managing the operational uncertainty, fouling dynamics, and safety concerns that have historically limited nano-enabled systems. Similarly, embedding safe-by-design principles and harmonized risk assessment in early-stage development is essential to securing regulatory acceptance and societal trust, particularly as wastewater-derived products re-enter food, agricultural, and industrial value chains. Looking ahead, the roadmap aims to position circular wastewater systems as a critical frontier for integrating materials science, environmental engineering, and sustainability governance. Progress toward 2030 will depend on moving beyond isolated pilot studies toward comparative, decision-relevant evidence that clarifies where nano-enabled pathways outperform incumbent options across techno-economic, life-cycle, and risk dimensions. This requires coordinated efforts in standardization, performance benchmarking, and business model innovation to recognize wastewater facilities as resource-recovery hubs rather than treatment endpoints. Future research priorities should focus on long-term ecotoxicological studies, chronic exposure assessment, bioaccumulation monitoring, and the development of harmonized life-cycle risk frameworks to ensure that nano-enabled circular technologies evolve in alignment with environmental and public health protection. By allowing for asynchronous technological and institutional development, the proposed roadmap is resilient to uneven innovation dynamics and supports flexible, context-specific implementation trajectories.

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