Advanced Bio‐Membrane Technologies for Water Treatment: Mechanisms, Challenges, and Future Prospects—A Comprehensive Critical Review

ABSTRACT

Bio‐membrane technologies are emerging as promising solutions for sustainable water and wastewater treatment; however, their practical implementation remains constrained by fouling, limited long‐term stability, and performance degradation under real operating conditions. This review critically evaluates recent advances in bio‐functionalized membrane systems, focusing on the interplay between biological activity, membrane structure, and transport mechanisms. Key separation pathways, including bio‐affinity interactions, enzymatic degradation, and coupled diffusion–reaction processes, are analyzed in relation to membrane morphology and surface chemistry. Advanced fabrication techniques such as electrospinning, layer‐by‐layer assembly, and 3D printing are assessed in terms of performance enhancement and scalability limitations. Major challenges including biofouling, biological instability, and material degradation are critically discussed alongside mitigation strategies such as surface functionalization and enzyme immobilization. The integration of artificial intelligence and IoT‐based monitoring is also evaluated, although most applications remain at early development stages. Overall, this review identifies key research gaps and outlines future directions toward scalable, robust, and sustainable bio‐membrane technologies.

Summary

• Bio‐membrane technologies improve sustainable water treatment across municipal, industrial, and healthcare applications.

• Advanced fabrication methods enhance membrane efficiency, durability, and operational performance.

• Surface modification minimizes membrane fouling and scaling during long‐term operation.

• Smart hybrid membranes enable adaptive treatment of complex wastewater streams.

• Membrane composition and pore structure determine separation efficiency and service life.

Bio‐membrane technology provides a sustainable approach to water treatment across municipal, industrial, and healthcare applications. This review highlights recent advances in bio‐membrane materials, structures, and fabrication techniques, emphasizing separation mechanisms, membrane composition, and porosity. It also discusses fouling mitigation through surface modification and self‐cleaning strategies, while exploring smart and hybrid membrane designs for improved efficiency, durability, and environmentally friendly water purification.

1. Introduction

The global water crisis, driven by population growth, rapid urbanization, climate change, and environmental degradation, continues to pose a significant threat to water availability and quality. The increasing imbalance between water demand and supply has intensified challenges in ensuring access to safe drinking water and adequate sanitation, particularly in developing regions, with direct consequences on public health, agricultural productivity, and socioeconomic stability (Foorginezhad et al. 2025). In response to these challenges, advanced water treatment technologies have become essential. Among them, bio‐membrane technologies have emerged as a promising approach due to their potential for integrated pollutant removal, biodegradation, and resource recovery (Zhu et al. 2024). Unlike conventional membrane systems that rely primarily on physical separation, bio‐membranes combine biological functionality with membrane‐based filtration, enabling enhanced treatment of complex wastewater matrices (Ye et al. 2022). Bio‐membranes are typically constructed from natural or synthetic polymeric materials and incorporate biologically active components such as bacteria, fungi, algae, or immobilized enzymes. These biological entities contribute to contaminant degradation, nutrient cycling, and system adaptability under variable operating conditions (Jiang et al. 2025). Consequently, bio‐membranes have demonstrated improved removal efficiencies for organic pollutants, nutrients (nitrogen and phosphorus species), and certain heavy metals compared to conventional membrane processes. Despite these advantages, it is important to distinguish between conventional membrane systems and truly bio‐functionalized or bio‐hybrid membranes (Sun et al. 2021). In many reported studies, the term “bio‐membrane” is inconsistently used, often referring to modified polymeric membranes without active biological functionality, which creates ambiguity in classification and performance interpretation (Calzuola et al. 2024). From an application perspective, bio‐membranes offer advantages such as modular design, compact footprint, and operational flexibility, enabling their use in municipal wastewater treatment as well as industrial sectors including food processing, pharmaceuticals, and textiles (Banerjee et al. 2026). However, their practical implementation remains limited by persistent operational challenges, most notably biofouling, scaling, and long‐term biological instability. Fouling processes resulting from the accumulation of organic matter, microorganisms, and inorganic deposits lead to flux decline, increased energy demand, and higher maintenance costs, while scaling can cause irreversible membrane damage and reduced lifespan (Abdelrasoul et al. 2013). To address these limitations, recent research has focused on surface engineering strategies, antifouling material development, and hybrid process integration combining biological, chemical, and physical treatment mechanisms (Zhao, Mamrol, et al. 2021). In parallel, emerging approaches such as smart monitoring systems, surface functionalization, and process automation have been explored to improve operational stability and performance efficiency (Khoiruddin et al. 2025). However, many of these strategies remain at laboratory scale, with limited validation under real‐world or long‐term operating conditions (Pichardo‐Romero et al. 2020). Nevertheless, a critical gap remains in systematically linking membrane material design, biological functionality, and process‐level performance under realistic conditions. Furthermore, the feasibility of integrating advanced functionalities such as AI‐driven monitoring and hybrid bio‐reactive systems has not yet been fully established from a techno‐economic and operational perspective (Meng et al. 2017). Therefore, this review aims to critically evaluate recent developments in bio‐membrane technologies, with emphasis on bio‐functionalized systems, separation mechanisms, and emerging hybrid architectures. It also highlights key limitations, inconsistencies in terminology, and unresolved challenges, while outlining future research directions toward scalable, stable, and environmentally sustainable bio‐membrane systems for next‐generation water treatment applications. This review specifically focuses on bridging material design, biological functionality, and digital monitoring.

2. Bio‐Membrane Process Technology

Bio‐membrane process technology builds upon the fundamental principles of conventional membrane separation, including size exclusion, charge‐based repulsion, and pressure‐driven transport, while introducing an additional biological dimension that enables coupled physicochemical and biochemical transformation of pollutants. This integration distinguishes bio‐membranes from traditional membrane systems, where separation is primarily a passive physical process. In bio‐membrane systems, microorganisms, enzymes, or bio‐functionalized coatings are incorporated either within the membrane matrix or on its surface to introduce active degradation pathways for organic and inorganic contaminants (Molla et al. 2024). This dual‐function mechanism enables simultaneous separation and transformation of pollutants, which can potentially enhance overall treatment efficiency and reduce reliance on external chemical dosing. However, the long‐term stability of these biological components remains a critical limitation due to deactivation, detachment, and environmental sensitivity. A widely studied example is membrane bioreactors (MBRs), where ultrafiltration (UF) membranes are coupled with activated sludge or biofilm systems to achieve simultaneous solid–liquid separation and biodegradation (Anis et al. 2019a). Although MBRs exhibit improved effluent quality and reduced footprint compared with conventional activated sludge systems, they are still strongly affected by membrane fouling, which remains the primary operational bottleneck. Reported improvements in flux stability are therefore often system‐dependent and highly influenced by operating conditions rather than intrinsic membrane properties alone (Sewerin et al. 2021). Downstream integration of nanofiltration (NF) and reverse osmosis (RO) membranes with biological pretreatment units has been shown to reduce organic loading and mitigate biofouling potential. However, it is important to note that these systems do not inherently become “bio‐membranes”; rather, they function as hybrid treatment trains where biological processes and membrane separation operate in sequence rather than being fully integrated (Maeda 2024). This distinction is often overlooked in the literature and leads to inconsistent terminology. More advanced designs include surface‐functionalized NF membranes modified with bio‐derived polymers such as chitosan and alginate, or enzyme‐based coatings aimed at enhancing selective ion removal (e.g., boron, nitrates) and degradation of micropollutants (Lakshmi et al. 2022). Despite promising laboratory‐scale results, scalability, long‐term chemical stability, and regeneration of these bio‐coatings remain unresolved challenges. Emerging concepts such as bio‐active membrane distillation (MD) and bio‐integrated electrodialysis (ED) systems have also been reported (Li et al. 2020). These approaches explore the use of bio‐inspired hydrophobic layers or bio‐compatible ion‐exchange modifications to enhance performance under high salinity or extreme conditions (Figure 1). However, their practical feasibility is still limited by thermal stability constraints in MD and membrane selectivity degradation under complex ionic environments in ED. Overall, key innovations across bio‐membrane‐related systems can be summarized as follows:

• Biofilm‐functional membranes enabling coupled filtration and biodegradation

• Enzyme‐immobilized surfaces for catalytic degradation of persistent pollutants

• Stimuli‐responsive and hydrogel‐based coatings for adaptive membrane behavior

• Hybrid biological–physicochemical systems integrating membrane and bioprocesses

FIGURE 1.

Classification of membrane processes by driving force (Sahu et al. 2024).

However, it is essential to emphasize that many of these approaches remain at different levels of integration maturity, and true “bio‐membrane systems” require stable, long‐term biological functionality under realistic operating conditions, which is still an open research challenge (Feria‐Díaz et al. 2021; Aloulou et al. 2022). It should be noted that reported performance metrics in Table 1 are highly dependent on operating conditions, membrane configuration, and biological activity stability; therefore, direct comparison should be interpreted with caution.

TABLE 1.

Comparative analysis of conventional and bio‐relevant membrane processes including separation performance and bio‐integration strategies.

Membrane type	Separation target	Typical flux (LMH)	Rejection efficiency (%)	Fouling resistance (qualitative)	Driving force	Bio‐integration strategy	Refs.
MF	Coupled with biofilm support or pre‐filtration for MBRs	100–300	~20–50 (TSS removal)	Moderate	Pressure	Coupled with biofilm support or pre‐filtration for MBRs	(Meng et al. 2017)
UF	Biofilm‐coated or enzyme‐immobilized UF membranes in MBRs	50–150	90–99 (proteins, viruses)	Moderate–High	Pressure	Biofilm‐coated or enzyme‐immobilized UF membranes in MBRs	(Molla et al. 2024)
NF	Divalent ions, organics, micropollutants	20–50	85–98 (salts, organics)	Moderate	Pressure	Bio‐derived coatings (e.g., chitosan, enzymatic modification)	(Sewerin et al. 2021)
RO	Salts, heavy metals, micro‐contaminants	20–40	> 99 (salts, micropollutants)	Moderate–Low	Pressure	Often used downstream of BMBRs or with bio‐active pretreatment	(Feria‐Díaz et al. 2021)
MD	Water vapor (separates salts/solutes)	5–15	~99 (non‐volatile salts)	High	Temperature	Bio‐inspired hydrophobic membranes, embedded enzymes	(Aloulou et al. 2022; Yan et al. 2021; Qu et al. 2024; Sharma and James 2022)
ED	Ions (monovalent and divalent)	N/A	~80–95 (ions)	High	Electric Field	Bio‐based ion‐exchange membranes, bio‐active coatings	(Zhang, Yan, et al. 2024; Sharma, Mohammed, et al. 2023; Sahu et al. 2024)

3. Membrane Materials

The selection of membrane materials plays a decisive role in determining separation efficiency, selectivity, and long‐term operational stability. Key performance parameters such as chemical resistance, fouling propensity, thermal stability, and mechanical integrity are strongly governed by the intrinsic properties of the base material as well as subsequent surface modifications (Lee et al. 2016). In the context of bio‐membrane systems, material design has increasingly shifted toward biologically compatible or bio‐functionalized platforms aimed at improving interfacial interactions and enabling coupled biological–physical separation processes (Zhang et al. 2023). However, it is important to note that in many reported studies, the term “bio‐membrane” is inconsistently applied to simply modify conventional membranes without stable or active biological functionality. This section critically examines three major classes of membrane materials: organic, inorganic, and hybrid systems with emphasis on their suitability for bio‐membrane applications in water treatment.

3.1. Organic Membranes

Organic polymeric membranes represent the most widely used category in membrane‐based water treatment due to their low cost, ease of fabrication, and tunable morphology (Hadi et al. 2024). Common polymers such as polysulfone (PSf), polyvinylidene fluoride (PVDF), and cellulose acetate (CA) form the structural backbone of microfiltration (MF), UF, NF, and RO systems. In bio‐membrane contexts, these materials are often used as support matrices for immobilizing enzymes, microbial consortia, or biopolymers. However, their intrinsic hydrophobicity (particularly in PVDF‐based systems) often leads to strong fouling tendencies and weak biological adhesion unless surface modification is applied (Wang et al. 2024). Although PVDF membranes are widely used due to their chemical stability and mechanical robustness, their application in bio‐functionalized systems is inherently limited by their hydrophobic and chemically inert surface (Sahu et al. 2023). These properties lead to weak enzyme adhesion, poor interfacial compatibility, and significant enzyme leaching during operation. As a result, the direct use of pristine PVDF as a support for enzymatic immobilization is often ineffective for long‐term applications. To address these limitations, various surface modification strategies have been proposed. Hydrophilic pre‐treatment methods, such as plasma activation or blending with hydrophilic additives (e.g., PVP), can improve wettability and promote enzyme attachment. More importantly, covalent grafting techniques provide stronger immobilization by chemically binding enzymes to functionalized PVDF surfaces, thereby reducing leaching and enhancing operational stability (Kumar and Chang 2024). However, these modifications introduce additional complexity, including potential alteration of membrane permeability and increased fabrication cost (Kaisar et al. 2025). Therefore, while PVDF remains a promising platform for bio‐membrane development, its successful application is highly dependent on the effectiveness and durability of surface functionalization strategies rather than the intrinsic properties of the base polymer itself (Basile and Ghasemzadeh 2019).

3.2. Inorganic Membranes

Inorganic membranes, including ceramic, metallic, and zeolite‐based systems, offer superior thermal stability, chemical resistance, and mechanical strength compared with polymeric membranes. These characteristics make them particularly suitable for extreme operational environments such as high‐temperature industrial effluents or aggressive chemical wastewater. Ceramic membranes exhibit relatively high fluxes (100–200 LMH) and excellent resistance to irreversible fouling, enabling repeated cleaning cycles without significant structural degradation. Recent research has explored their functionalization with bio‐coatings such as antimicrobial peptides or biopolymers to improve compatibility with biological systems and enable coupling with enzymatic or biofilm‐based degradation processes (Madaeni and Ghaemi 2015). However, the long‐term stability of such coatings under harsh cleaning conditions remains a critical challenge. Zeolite‐based membranes, characterized by well‐defined pore structures (~0.4–0.6 nm), provide precise molecular sieving capabilities and are increasingly investigated in catalytic and bio‐assisted separation systems. They typically achieve > 90% rejection of small organic molecules and multivalent ions, making them suitable for selective separation processes in hybrid bio‐reactive systems (Tufail et al. 2025). Nevertheless, their brittleness and fabrication complexity limit large‐scale deployment.

3.3. Hybrid Membranes

Hybrid membranes represent a key strategy in bridging the gap between organic flexibility and inorganic stability. By combining polymeric matrices with inorganic fillers or bio‐functional components, these systems aim to achieve multifunctional performance including enhanced selectivity, antifouling behavior, and catalytic activity. For example, chitosan–silica hybrid membranes leverage the biocompatibility and antimicrobial properties of chitosan with the mechanical reinforcement provided by silica. While high removal efficiencies (> 95% for heavy metals such as Pb²⁺ and Cd²⁺) have been reported, such results are often strongly dependent on feed composition and experimental conditions (Algieri and Drioli 2021). Similarly, PVDF membranes modified with graphene oxide (GO) or TiO₂ nanoparticles have demonstrated improved photocatalytic self‐cleaning and reduced biofouling. However, the long‐term stability of nanomaterial coatings and potential leaching effects remain important concerns for real‐world applications. Reported flux values (~100 LMH) and pollutant rejection (> 98%) in MBR configurations should therefore be interpreted as system‐specific rather than intrinsic membrane properties (Zhao, Muylaert, and Vankelecom 2021). Despite their advantages, hybrid membranes still face unresolved challenges related to interface stability, scalability of fabrication methods, and reproducibility of bio‐functional performance. Their integration into AI‐ and IoT‐assisted systems remains largely at a conceptual or early experimental stage (Ramezani et al. 2024). It should be emphasized that the performance metrics reported in Table 2 are highly dependent on membrane preparation methods, feed characteristics, and operational conditions; therefore, direct comparison should be interpreted cautiously.

TABLE 2.

Comparative performances of membrane materials in bio‐membrane systems: biocompatibility, fouling resistance, and functional integration.

Membrane type	Materials	Water flux (LMH)	Rejection efficiency (%)	Fouling resistance	Biocompatibility	Typical applications in bio‐membranes	Refs.
Organic membranes	PSf, PVDF, cellulose, chitosan	30–150	70–99 (depends on MWCO)	Moderate	Can be bio‐functionalized; support microbial activity	Enzyme‐immobilized UF/MF membranes, microbial carriers	(Tufail et al. 2025)
Inorganic membranes	Ceramics, Zeolites	50–200	90–99	High	Functionalized with biocoatings; enzyme carriers	High‐temp wastewater, enzyme reactors, biofilm supports	(Algieri and Drioli 2021)
Hybrid membranes	PVDF‐GO, chitosan‐silica, TiO2 composites	40–120	85–99 (tailorable)	High	Ideal for smart, durable, and bio‐reactive systems	Smart membranes, catalytic bioreactors	(Zhao, Muylaert, and Vankelecom 2021)

3.3.1. Photocatalysis Paradox

A critical but often overlooked challenge in hybrid bio‐photocatalytic membranes is the fundamental incompatibility between photocatalytic activity and biological functionality (Verma et al. 2024). Photocatalysts such as TiO₂ generate highly reactive oxygen species (ROS), including hydroxyl radicals (˙OH), which are inherently non‐selective. While these species are effective for degrading organic pollutants, they can simultaneously damage or deactivate biological components such as enzymes and microbial cells embedded within bio‐membranes (Ham et al. 2026). This creates a paradox in system design: the same reactive species responsible for enhanced pollutant degradation may compromise the stability and activity of the bio‐functional layer. Consequently, the proposed “synergy” between photocatalysis and bio‐membranes is not universally valid and must be critically evaluated (Zhang, Yu, et al. 2020). In practice, successful integration requires spatial separation, controlled activation (e.g., intermittent UV exposure), or protective immobilization strategies to minimize direct interaction between ROS and biological agents (Sheng et al. 2023). Therefore, hybrid photocatalytic bio‐membranes should not be assumed to be inherently synergistic; rather, their feasibility depends on careful system design that balances oxidative activity with biological stability.

4. Fabrication Techniques for Bio‐Membranes

Fabrication techniques play a decisive role in determining the structural, functional, and long‐term operational performance of bio‐membrane systems. These methods govern critical membrane characteristics such as pore size distribution, surface chemistry, mechanical stability, and biological compatibility, which collectively influence flux behavior, fouling propensity, and separation efficiency (Shabib et al. 2025). In bio‐membrane development, fabrication processes must balance structural integrity with the preservation of biological activity, particularly when enzymes or microorganisms are incorporated into the membrane matrix. Table 3 summarizes key fabrication techniques and their relevance to bio‐membrane engineering.

TABLE 3.

Fabrication techniques and their relevance to bio‐membrane innovation and performance.

Technique	Key features	Fouling resistance	Water flux enhancement	Bio‐membrane relevance	Refs.
Phase inversion	Simple, scalable, supports asymmetric pores	Moderate	Moderate	Supports microbial loading, enzyme embedding	(Lu et al. 2022)
Electrospinning	Produces nanofibrous membranes with high surface area	High	High (up to 300 LMH)	Ideal for biofunctionalization, high permeability	(Evdochenko et al. 2020)
Interfacial polymerization	Forms thin‐film composites, good selectivity	Moderate–High	Moderate	Enables catalytic or antimicrobial layering	(Yang et al. 2016)
Track‐etching	Precise pore size, uniform distribution	Low–Moderate	Low–Moderate	Useful in sensing membranes, diagnostic filters	(Asad et al. 2020)
3D printing	Custom‐designed, layer‐by‐layer fabrication	High	Variable (design‐dependent)	Smart membranes, bio‐scaffold design, AI integration	(Ji et al. 2022)

4.1. Recent Advances in Self‐Healing and Electrospun Bio‐Membranes

Recent advances (2024–2025) in bio‐membrane engineering have increasingly focused on the development of self‐healing systems and electrospun nanofibrous membranes, aiming to address long‐standing limitations related to mechanical instability, fouling, and loss of biological functionality (Li et al. 2023). These emerging approaches move beyond passive membrane design toward dynamic, adaptive systems capable of restoring performance under operational stress. Self‐healing bio‐membranes represent a particularly promising direction. Recent studies have demonstrated the integration of dynamic polymer networks, reversible covalent bonds, and biomimetic hierarchical structures that enable autonomous repair of microstructural damage (Yan et al. 2024). For example, ultrathin self‐healing nanofibrous membranes with confined architectures have shown the ability to recover structural integrity and electrical functionality after mechanical disruption, indicating strong potential for long‐term operational stability in bio‐integrated systems (Bhardwaj and Kundu 2010). However, a critical limitation remains in maintaining biological activity during repeated healing cycles, as enzymatic components and microbial systems may be sensitive to structural rearrangements and local chemical changes. In parallel, electrospinning has emerged as a key fabrication technique for next‐generation bio‐membranes due to its ability to produce highly porous nanofibrous architectures with tunable surface chemistry. Recent developments have focused on hybrid electrospun membranes incorporating bio‐derived polymers, antimicrobial agents, and cell‐membrane‐functionalized nanofibers (Sharma, Jalaja, et al. 2023). These systems offer enhanced permeability, high surface area for enzyme immobilization, and improved bio‐compatibility. Notably, electrospun membranes functionalized with biological interfaces (e.g., cell membrane coatings) have demonstrated improved selectivity and resistance to biofouling by mimicking natural biological barriers. Despite these advantages, several challenges remain unresolved (Kumar et al. 2024). Electrospun membranes often suffer from poor mechanical durability and structural deformation under long‐term hydraulic operation, limiting their scalability. Furthermore, the integration of biological components into nanofibrous matrices introduces additional complexity in maintaining stability, preventing leaching, and ensuring reproducibility across large‐scale fabrication. Importantly, many reported performance enhancements are derived from controlled laboratory conditions and may not directly translate to real wastewater systems (Ghosh and Pramanik 2024). Overall, while self‐healing and electrospun bio‐membranes represent cutting‐edge advancements, their practical implementation requires further validation in terms of long‐term durability, biological stability, and techno‐economic feasibility (Seah et al. 2020). Future research should focus on coupling self‐healing mechanisms with stable bio‐functionalization strategies, as well as developing scalable electrospinning processes compatible with industrial membrane production.

4.2. Phase Inversion

Phase inversion remains one of the most widely used fabrication techniques due to its simplicity, scalability, and compatibility with a broad range of polymer systems. The process enables the formation of asymmetric porous structures through solvent–nonsolvent exchange, which can be tailored to achieve desired permeability and selectivity (Saleh et al. 2025). In bio‐membrane applications, phase inversion has been used as a platform for embedding bioactive components such as enzymes, nanoparticles, and microbial consortia within polymer matrices (Choi et al. 2017; Mashentseva et al. 2024; Apel et al. 2015). However, it is important to note that the incorporation of biological elements is often limited by solvent toxicity and phase separation conditions, which may reduce biological viability or long‐term stability (Soo et al. 2021). Reported flux values (30–120 LMH) are highly dependent on polymer concentration, casting conditions, and post‐treatment modifications, rather than inherent properties of the technique alone (Azmi 2025; Ehsani et al. 2022; Gordano 2024; Kariuki et al. 2025). Fouling resistance is generally moderate and requires additional surface modification strategies to achieve stable long‐term operation. Figure 2 illustrates a representative phase inversion process for nanocomposite CA membranes.

FIGURE 2.

Preparation of nanocomposite cellulose acetate membrane by Phase inversion (El‐Kaliuoby et al. 2025).

4.3. Electrospinning

Electrospinning enables the fabrication of nanofibrous membranes with high surface‐area‐to‐volume ratios and interconnected porosity, which are favorable for mass transfer and surface functionalization (Baker 2012). These structural features make electrospun membranes attractive for enzyme immobilization and microbial attachment. Although high flux values (up to ~300 LMH) are reported in the literature, such performance is strongly influenced by fiber diameter, membrane thickness, and applied pressure conditions (Eltahan et al. 2025). Therefore, these values should be interpreted as system‐specific rather than universal performance metrics. Natural polymers such as chitosan, gelatin, and lignin have been widely explored to enhance biocompatibility and environmental sustainability (Javed et al. 2024). Nevertheless, mechanical stability and long‐term structural integrity remain key challenges, particularly under continuous operation or high‐pressure conditions (Maroufi and Hajilary 2023).

4.4. Interfacial Polymerization

Interfacial polymerization is a well‐established technique for producing thin‐film composite (TFC) membranes, particularly for NF and RO applications. The formation of a dense selective polyamide layer at the interface of immiscible phases enables high separation efficiency (Lu et al. 2022). Recent studies have explored the incorporation of bio‐derived monomers, antimicrobial agents, and catalytic additives into the selective layer to introduce bio‐functional characteristics (Evdochenko et al. 2020; Upadhyaya et al. 2018). However, achieving stable incorporation without compromising membrane selectivity remains a significant technical challenge. Although high salt rejection (> 98%) and moderate flux (20–50 LMH) are commonly reported, these values are highly dependent on membrane thickness, curing conditions, and substrate properties. Furthermore, scalability is well established industrially, but bio‐functional modifications still lack long‐term operational validation.

4.5. Track‐Etching and Stretching

Track‐etching and stretching techniques provide precise control over pore geometry and distribution, enabling highly uniform membrane structures (Yang et al. 2016). These methods are particularly useful in applications requiring controlled transport, such as biosensing membranes and microfluidic devices. However, their application in large‐scale water treatment systems is limited due to low throughput, high production cost, and restricted membrane area scalability (Asad et al. 2020). Typical pore sizes (0.1–0.5 μm) make them suitable for microfiltration‐level applications, but less effective for advanced pollutant removal without additional functional layers.

4.6. 3D Printing

3D printing is an emerging fabrication approach that enables programmable design of membrane architectures with spatial control over porosity, geometry, and functionality. This technique allows integration of bio‐scaffolds, catalytic materials, and sensing elements within a single structure (Ahmad and Ahmed 2023). Despite its strong potential for customization and smart membrane development, current applications remain largely at laboratory or pilot scale. Reported flux values (30–100 LMH) are highly dependent on printing resolution, material formulation, and post‐processing conditions (Sharma et al. 2018). Additionally, issues related to mechanical durability, material compatibility, and long‐term stability under continuous operation remain unresolved, limiting its industrial adoption at present (Ji et al. 2022). It should be emphasized that performance indicators in Table 3 are highly dependent on fabrication parameters, membrane chemistry, and operating conditions; therefore, cross‐technique comparisons should be interpreted in a qualitative rather than absolute manner.

5. Separation Mechanisms in Bio‐Membranes

Bio‐membranes utilize a synergistic combination of physical sieving, chemical interactions, and biological processes to achieve selective contaminant removal. Unlike conventional polymeric membranes, bio‐membranes incorporate enzymes, microbial communities, or functional biomolecules that actively participate in the separation process (Nguyen et al. 2012). These mechanisms govern the transport and rejection of a wide range of contaminants including nutrients (e.g., nitrogen, phosphorus), heavy metals, organic dyes, pharmaceuticals, and emerging micro pollutants as summarized in Table 4.

$$\mathrm{J}=-\mathrm{D}\frac{\mathrm{dx}}{\mathrm{dC}.}$$

TABLE 4.

Summaries of bio‐membrane separation mechanisms and their functional drivers and the “values are system‐dependent and should be interpreted comparatively rather than absolutely”.

Mechanism	Functional driver	Bio‐membrane relevance	Typical rejection (%)	Operating flux (LMH)	Refs.
Size exclusion	Pore size + EPS layer	Dominant in MBRs, biofilm‐enhanced sieving	80–99 (macromolecules)	50–150	(Nguyen et al. 2012; Wang et al. 2021; Wang et al. 2018)
Electrostatic interactions	Surface charge of biofilms/membrane functional groups (e.g., —COOH, —NH2)	Nutrient removal, charged microbial surface effects	70–95 (ions, dyes)	30–100	(Zhang et al. 2016; Ayyavoo et al. 2016; Morsy et al. 2016)
Hydrophilic/Hydrophobic	Surface affinity (hydrophilic or hydrophobic layers)	Oil–water separation, anti‐fouling coatings	90–99 (oils, grease)	20–70	(Shaban et al. 2020; Abd‐El‐Khalek et al. 2019)
Adsorption selectivity	Active groups (e.g., thiol, amine), microbial binding, π–π interactions	Trace contaminant capture, enzyme‐enhanced filters	60–95 (organics, metals)	10–80	(Fadl et al. 2022; Akbari et al. 2015; Zhang, Morsy, et al. 2024)
Solution‐Diffusion	Diffusion across dense matrix + enzyme catalysis or stimuli‐responsive polymers	RO & smart membranes with bio‐active interfaces	> 99 (salts, small solutes)	20–40	(Shaban et al. 2024; Goh et al. 2018)

In bio‐membrane systems, this diffusion‐driven flux is further modified by biological reactions, leading to a coupled diffusion–reaction model where additional resistance terms must be considered. Bio‐membrane transport cannot be fully understood through qualitative descriptions alone (Wang et al. 2021). The overall mass transfer is governed by diffusion–reaction coupling, where the flux (J) depends on the effective diffusion coefficient (D) and concentration gradient. In bio‐functionalized systems, this relationship is further modified by biological activity, which introduces reaction terms and dynamic resistance layers (Wang et al. 2018). Therefore, separation in bio‐membranes should be interpreted as a coupled transport–reaction phenomenon rather than purely physical filtration (Zhang et al. 2016).

5.1. Size Exclusion

Size exclusion remains dominant in MF/UF systems; however, in bio‐membranes, the effective pore size is not static but dynamically altered by biofilm and extracellular polymeric substances (EPS) formation. While this secondary layer enhances rejection (> 99% for microorganisms), it introduces an additional resistance term in the overall mass transfer model (Shaban et al. 2020). Critically, the enhancement in selectivity is often accompanied by a non‐linear flux decline, indicating that biofilm‐assisted sieving is not purely beneficial but represents a trade‐off between permeability and selectivity (Abd‐El‐Khalek et al. 2019). Therefore, claims of “enhanced filtration” must be contextualized within system‐specific fouling dynamics (Hamdona et al. 2021).

5.2. Electrostatic Interactions

Electrostatic interactions in bio‐membranes are inherently heterogeneous due to the coexistence of membrane functional groups and microbial surface charges (Abd‐El‐Khalek et al. 2021). While rejection efficiencies of 70%–90% are reported, these values are highly sensitive to ionic strength and pH. More importantly, electrostatic repulsion often competes with adsorption and biological uptake, making it difficult to isolate its contribution (Fadl et al. 2022). Thus, this mechanism should be interpreted as part of a multi‐mechanistic coupling system rather than an independent driver (Akbari et al. 2015).

5.3. Hydrophilic–Hydrophobic Interactions

Affinity‐based separation plays a dual role in both fouling mitigation and selective transport. However, many reported improvements (e.g., > 95% oil rejection) are achieved under controlled laboratory conditions (Zhang, Morsy, et al. 2024). A critical limitation lies in coating instability and aging, where prolonged operation leads to loss of surface functionality (Shaban et al. 2024; Goh et al. 2018). Therefore, long‐term performance is governed more by coating durability than initial affinity properties (Voutchkov 2017; Jamaly et al. 2014). This affinity‐based control is crucial for long‐term stability and pollutant targeting in wastewater containing mixed polarities (Figure 3). To move beyond a purely schematic interpretation, mass transport in bio‐membranes can be described using a coupled diffusion–reaction model:

$$\mathrm{J}=-{\mathrm{D}}_{\mathrm{eff}}\frac{\mathit{dx}}{\mathit{dC}}+{\mathrm{R}}_{\mathrm{b}}$$

where $\mathrm{J}$ is the permeate flux, ${\mathrm{D}}_{\mathrm{eff}}$ is the effective diffusion coefficient (modified by biofilm/EPS layers), $\frac{\mathit{dx}}{\mathit{dC}}$ is the concentration gradient, ${\mathrm{R}}_{\mathrm{b}}$ represents the net biological reaction term (e.g., enzymatic degradation or microbial uptake).

FIGURE 3.

The transition from qualitative transport description to a coupled diffusion–reaction framework, where biological activity introduces additional dynamic resistance (${\mathrm{R}}_{\mathrm{b}}$) that evolves with biofilm growth and enzymatic processes, significantly altering conventional mass transfer behavior.

In addition, the overall transport resistance in bio‐membranes can be expressed using a resistance‐in‐series model:

$$\frac{1}{J}={\mathrm{R}}_{\mathrm{m}}+{\mathrm{R}}_{\mathrm{f}}+{\mathrm{R}}_{\mathrm{b}}$$

where ${\mathrm{R}}_{\mathrm{m}}$ intrinsic membrane resistance, ${\mathrm{R}}_{\mathrm{f}}$ fouling resistance, ${\mathrm{R}}_{\mathrm{b}}$ bio‐layer resistance (dynamic and time‐dependent).

This framework highlights that bio‐membrane performance is governed by a dynamic balance between diffusion, fouling accumulation, and biological activity. Unlike conventional membranes, ${\mathrm{R}}_{\mathrm{b}}$ is not constant but evolves with microbial growth and enzymatic reactions, leading to non‐linear transport behavior (Nunes and Peinemann 2010).

5.4. Adsorption‐Based Selectivity

Bio‐membranes often incorporate specific binding sites (e.g., carboxyl, amine, or thiol groups) or microbial communities to adsorb trace pollutants via hydrogen bonding, π–π stacking, and electrostatic attraction immobilized enzymes that degrade pollutants during or after adsorption (Lee et al. 2020). Although adsorption provides high selectivity (> 90%), it is inherently limited by saturation. In bio‐membranes, the integration of enzymes or microbes introduces the possibility of in situ regeneration through biodegradation. However, a key unresolved issue is the difficulty in decoupling adsorption from biodegradation, which leads to overestimation of membrane performance in many studies. This represents a major gap in experimental methodology (Figure 4). This mechanism offers high selectivity but needs integration with cleaning strategies or dynamic bio‐layers for long‐term operation (Wang et al. 2010).

FIGURE 4.

A bio‐membrane functionalized with affinity ligands to selectively capture boron, demonstrating adsorption‐based selectivity (Wang et al. 2010).

5.5. Solution‐Diffusion Mechanism

In dense, nonporous membranes such as RO and some TFC composites, the solution–diffusion model dominates. Contaminants dissolve into the membrane matrix and diffuse across based on concentration gradients. In bio‐functional RO membranes, the active layer is enhanced with responsive polymers that change permeability in response to pH or temperature (Table 4). Enzymes or ligands that catalyze reactions during diffusion, enhancing selective transport (Lee et al. 2010). The solution–diffusion mechanism dominates in RO systems and provides high selectivity (> 99.5%). However, bio‐functionalization introduces competing effects:

• Enhanced selectivity via catalytic or responsive layers

• Reduced permeability due to increased transport resistance

Thus, bio‐modified RO membranes often exhibit a selectivity–permeability trade‐off, which remains a fundamental limitation (Jeong et al. 2012). Bio‐layer benefit incorporation of bioactivity improves selectivity for small organics and micropollutants without compromising salt rejection. This mechanism is central to hybrid systems that aim to combine molecular‐level selectivity with bio‐catalytic action. Despite extensive reporting of individual mechanisms, a unified quantitative framework linking bioactivity, transport resistance, and membrane performance is still lacking, representing a critical research gap.

5.6. Synergistic and Competitive Effects Between Mechanisms

Unlike conventional membranes where a single mechanism dominates, bio‐membranes operate through multiple interacting mechanisms (Yang et al. 2025). These interactions can be either synergistic or antagonistic:

• Synergistic effects

  • ○
    Adsorption + biodegradation → extended pollutant removal
  • ○
    Electrostatic repulsion + size exclusion → enhanced selectivity
• Conflicting effects

  • ○
    Biofilm formation improves rejection but increases hydraulic resistance.
  • ○
    Hydrophobic coatings enhance selectivity but promote fouling.
  • ○
    Reactive species (in hybrid systems) may degrade biological components.

Therefore, the overall performance of bio‐membranes is governed not by individual mechanisms, but by the balance between these competing interactions.

6. Challenges and Mitigation in Bio‐Membrane Systems

Unlike Section 5, which describes fundamental separation mechanisms, this section focuses on operational challenges arising from their interaction under real conditions. Bio‐membranes employ a coupled combination of physical, chemical, and biological mechanisms to achieve selective contaminant removal. Unlike conventional membrane systems, where separation is primarily governed by passive transport phenomena, bio‐membranes introduce active biological participation through enzymes, microbial communities, or bio‐functional coatings. However, the extent to which these biological components contribute to actual separation versus ancillary degradation remains system‐dependent and is still under debate in the literature. A key challenge in bio‐membrane systems is that fouling is not merely a surface phenomenon but a dynamic consequence of the interaction between biological activity and transport mechanisms described in Section 5. In many cases, the same biological components that enhance selectivity (e.g., biofilms, enzymes) simultaneously contribute to increased hydraulic resistance and instability, creating an inherent performance trade‐off.

6.1. Fouling in Bio‐Membranes

Fouling in bio‐membranes is fundamentally different from conventional systems due to the active role of biological components. Rather than being a purely detrimental process, biofouling may initially enhance selectivity through the formation of biofilms and EPS layers. However, this effect is transient, as continued accumulation leads to excessive hydraulic resistance, pore blockage, and eventual decline in system performance. This dual role highlights a critical paradox: bioactivity simultaneously improves and degrades membrane performance, depending on operational time scale and environmental conditions. It results from the accumulation of microbial products (EPS, SMPs), interaction between the bioactive layer and contaminants (e.g., oil, salts, and heavy metals), and biofilm overgrowth leading to uncontrolled biological resistance or decay (Figure 5). Bio‐membrane fouling leads to increased transmembrane pressure (TMP), decreased biocatalytic efficiency, and selectivity loss, particularly in MBRs and enzyme‐functionalized membranes (Hakami et al. 2020; Zhao, Jin, et al. 2021; Gu et al. 2018).

FIGURE 5.

Conceptual illustrations; actual fouling behavior is system‐dependent and dynamic.

6.2. Types of Fouling and Their Relevance to Bio‐Membranes

The main types of fouling remain consistent (particulate, organic, inorganic, and biofouling), but their behavior in bio‐membranes is influenced by biological activity (Table 5). Biofouling is especially complex in MBRs and bio‐functional membranes where both active biomass and external invaders coexist (Monnot et al. 2016; Anis et al. 2019b).

TABLE 5.

Common fouling types and cleaning strategies.

Fouling type	Relevance	Cleaning	Bio‐specific limitation
Biofouling	Active biomass growth	Enzymatic/biocides	Risk of killing beneficial microbes
Organic	Affects enzymes	Alkaline	May deactivate enzymes
Inorganic	Scaling	Acid	pH shock to bio‐layer

Unlike conventional membranes, fouling types in bio‐membranes are strongly interdependent. For example, organic fouling often acts as a precursor to biofouling by providing nutrients for microbial growth, while inorganic scaling can inhibit biological activity. Therefore, classification of fouling into discrete categories may oversimplify the actual system behavior. Despite the effectiveness of surface modification strategies for fouling mitigation, long‐term coating stability remains a critical challenge. Under continuous cross‐flow filtration, hydraulic backwashing, and aggressive chemical cleaning conditions, coating delamination and surface deterioration may occur, leading to a gradual decline in membrane performance. Future research should focus on covalently anchored coatings, self‐healing surfaces, and durability testing under realistic operational conditions.

6.3. Mitigation Strategies Tailored for Bio‐Membranes

Mitigation strategies in bio‐membranes cannot be directly adopted from conventional systems, as aggressive cleaning or chemical dosing may compromise biological functionality. Therefore, mitigation must balance fouling control with preservation of bioactivity.

6.3.1. Pretreatment for Bio‐Systems

Pretreatment in bio‐membrane systems must achieve dual objectives: minimizing foulant load and preserving microbial viability. Ozonation or UV pretreatment can damage microbial activity if not controlled. Biological pretreatment (e.g., anaerobic filters) can reduce organic loading while maintaining microbial balance (Table 6). Non‐conventional methods like UF/NF are favored in MBR‐based hybrid systems, where microbial growth rate and oxygen demand are also key operational variables (Talaeipour et al. 2017; Rivero‐Falcón et al. 2025; Morgante et al. 2024). However, excessive pretreatment (e.g., strong oxidation or UV exposure) may reduce microbial viability, leading to diminished bio‐functional performance. This creates a design trade‐off between feedwater conditioning and biological preservation.

TABLE 6.

Pretreatment strategies differ when bio‐activity in the membrane system. Higher energy demand is often offset by improved permeate stability and reduced chemical usage.

Aspect	Conventional pretreatment	Membrane pretreatment (bio‐compatible)
Capital cost	Capital cost lower than non‐conventional membrane‐based methods	Higher than conventional methods but new developments are causing costs to decline
Carbon footprint	High	Low
Energy requirements	Low	High
Chemical costs	High	Low
Quality of permeate	Variable, SDI < 4, Turbidity < 1 NTU	Stable

6.3.2. Operational Optimization in Bio‐Membranes

Operational optimization in bio‐membrane systems requires a more nuanced approach compared with conventional membranes, due to their sensitivity to biological and environmental conditions. Key operational factors such as hydraulic shear, temperature, and flux rate play a critical role in maintaining system stability and performance. Excessive cross‐flow velocity (CFV), for example, can disrupt biofilm integrity or damage immobilized microbial cells, thereby reducing bioreactor efficiency (Al‐Hajouri et al. 2013). Temperature variations directly affect microbial metabolism and the production of EPS, which in turn influence membrane fouling behavior and overall separation performance (Zhang, Soliman, et al. 2024). Furthermore, the initial flux rate must strike a balance between sufficient mass transfer and the retention of active biological components (Aziz and Ojumu 2020). In hybrid systems such as RO membranes integrated with anaerobic membrane bioreactors (AnMBRs), this balance becomes even more delicate, as operators must account for both salinity tolerance of microbial communities and the structural resilience of the membrane itself. As summarized in Table 7, effective operational strategies must be tailored to the specific bio‐functional configuration in order to optimize long‐term performance and minimize biological fouling. Operational parameters therefore define a narrow “optimal window” where sufficient mass transfer is achieved without disrupting biological stability. Outside this window, either fouling dominates (low shear) or bioactivity is compromised.

TABLE 7.

Evaluations of conventional pretreatment methods for bio‐membrane applications (Zhang, Soliman, et al. 2024; Aziz and Ojumu 2020; Aktij et al. 2020; Tupe et al. 2025).

Conventional pretreatment method	Advantages	Disadvantages
Coagulation/flocculation	Removes organic and colloidal substances, thereby limiting biofouling.	Ineffective at preventing scale formation, with strict limits on coagulant and flocculant concentrations to avoid damaging RO membranes
Chlorination	Effectively removes bacteria while also helping to minimize odors.	Provides ineffective removal of protozoa and endospores, and may compromise the integrity of RO membranes
Media filtration	Suitable for highly turbid feedwaters and high concentrations	Highly sensitive to feedwater conditions and inefficient in biofouling inhibition
Acidification	pH reduction, which inhibits scale formation and rejection of boron at low alkalinity conditions.	Corrosion propensity increases at low alkalinity conditions and pronounced precipitation‐related problems at high alkalinity
Ozonation	Does not affect the integrity of the feed in terms of odor or taste	Because of storage and transportation difficulties, ozone must be produced in the field and difficult to monitor changes in ozone concentration.
DAF	Cost‐effective	Scraper‐related issues.
Scale inhibitors	Inhibits crystallization‐induced scale formation.	Overdosing of scale inhibitors can cause detrimental damage to RO
UV	Low cost and easy to implement	Can lead to biofilm formation.

6.3.3. Cleaning in Bio‐Membrane Systems

Cleaning in bio‐membrane systems represents one of the most critical operational challenges, as conventional aggressive cleaning strategies are often incompatible with biological components. Enzymatic cleaning agents are more compatible with enzyme‐based membranes. Canary cells and ultrasonic time‐domain reflectometry (UTDR) provide non‐invasive monitoring of early fouling in real time. UTDR is especially useful for early biofilm detection in bio‐MBRs. Biocompatible cleaning protocols are being adopted in bio‐artificial systems, such as enzyme membranes for boron or nitrate capture (Gowayed et al. 2025). Even biocompatible cleaning methods may gradually alter microbial community structure or enzyme activity, leading to long‐term performance drift.

6.3.4. Surface Modification for Bio‐Fouling Control and End‐of‐Life Considerations

Surface engineering in bio‐membranes focuses on dual functionality promoting beneficial bioactivity while resisting undesired biofouling. Techniques such as “coating‐to” or “coating‐from” allow for the deposition of functional layers that enhance flux, selectivity, and biofouling resistance (Woo et al. 2018). Woo et al. applied alternating layers of positively charged PDDA and negatively charged PSS on RO membranes, resulting in improved flux under fouling conditions (Li and Li 2020). Similarly, Li et al. used layer‐by‐layer (LbL) assembly of polyelectrolytes to enhance salt rejection and biofouling resistance. Other notable modifications include, PEI and GO incorporated via LbL spraying into polyamide membranes (Halakoo and Feng), achieving salt rejection rates as high as 99.9%.Sulfonated PVA‐modified TFC membranes achieving 99.17% salt rejection. Gum Arabic‐conjugated PVA membranes exhibiting improved chlorine resistance and antibacterial performance. Additionally, the incorporation of nanomaterials (e.g., zeolite‐Y, GO nanosheets) has shown enhancements in water flux, antifouling behavior, and chemical durability (Halakoo and Feng 2020). Despite promising short‐term improvements, many surface modification strategies suffer from poor long‐term stability due to coating delamination, chemical degradation, or nanoparticle leaching. Consequently, reported antifouling performance is often not sustained under real operating conditions.

6.3.4.1. Chemical Surface Modification.

Chemical modifications such as hydrophilization, radical grafting, chemical coupling, and plasma treatment are widely employed. Hydrophilization (e.g., using PVP with PSf) improves wettability and reduces organic fouling. Radical grafting with ADMH or ZnO improves microbial resistance and salt rejection. Plasma treatments, like dielectric barrier discharge (DBD), increase hydrophilicity and surface energy, reducing biofilm adhesion by up to 85.4% (Tiron et al. 2018). While these strategies offer short‐to‐medium‐term improvements, long‐term stability and coating integrity often degrade with continuous exposure to chemical, thermal, or mechanical stress, highlighting the need to evaluate membrane durability over extended operation cycles.

6.3.4.2. Durability, Degradation, and End‐of‐Life Management.

Despite enhanced initial performance, modified membranes are still susceptible to degradation due to long‐term exposure to physical and chemical stressors. Although surface modification improves performance, it does not eliminate concerns related to membrane aging, chemical degradation, and structural fatigue. Therefore, a comprehensive understanding of membrane end‐of‐life behavior is critical. A critical gap in current research is the lack of standardized protocols for evaluating long‐term degradation and environmental impact of bio‐functionalized membranes. In particular, nanoparticle leaching and incomplete biodegradation may offset the environmental benefits of bio‐based materials.

6.3.4.3. Membrane Degradation.

Prolonged exposure to oxidants (e.g., chlorine, ozone) leads to polymer backbone scission, reducing mechanical strength. UV and thermal degradation can weaken functional coatings, especially in outdoor applications or solar‐driven MD. Enzyme‐functionalized membranes may experience bio‐inactivation or denaturation, reducing long‐term efficacy (Wu et al. 2024).

6.3.4.4. Recycling and Reuse Strategies.

Several approaches are under investigation to extend membrane lifespan or enable reuse, physical regeneration (e.g., back‐flushing, mild acid/base cleaning) for surface‐fouled membranes. Chemical refurbishment (e.g., oxidative cleaning + re‐functionalization) to restore degraded surfaces (Hashmi et al. 2025). Mechanical repurposing, such as downcycling RO membranes for UF or MF roles after loss of tight selectivity. Emerging research also explores closed‐loop systems, where components (e.g., chitosan, CA) are recovered and reprocessed into new membranes, enhancing circularity.

6.3.4.5. Disposal and Environmental Impacts.

Conventional polymeric membranes (e.g., PSf, PVDF) are non‐biodegradable and often end up in landfills or are incinerated, generating emissions. In contrast, bio‐based membranes from materials like polylactic acid (PLA), gelatin, or starch derivatives offer better degradability. PLA membranes, under composting conditions, degrade within 6–2 months, depending on thickness. Chitosan membranes undergo enzymatic degradation in aquatic environments, minimizing ecological impact. However, membranes incorporating nanoparticles or synthetic additives (e.g., GO, AgNPs) raise concerns of leaching and toxicity during disposal (Parcheta and Sobiesiak 2023; AlSawaftah et al. 2021; Cairone et al. 2024). Hence, safe end‐of‐life disposal protocols and regulatory compliance (e.g., TCLP testing, EU Waste Framework Directive) are essential. By addressing both technical and environmental challenges, bio‐membrane systems can transition from niche applications to core technologies in sustainable water treatment infrastructure.

6.4. Trade‐Offs Between Fouling Control and Bio‐Functionality

A defining challenge in bio‐membrane systems is the inherent trade‐off between fouling mitigation and biological functionality. Strategies such as chemical cleaning, high shear operation, or oxidative pretreatment may effectively control fouling but simultaneously reduce microbial activity or enzyme stability. Conversely, preserving bioactivity often leads to increased fouling susceptibility (Taghavimandi et al. 2025). Therefore, optimal system design requires a balance between these competing factors rather than maximizing a single performance parameter. Overall, fouling in bio‐membranes should not be treated solely as a problem to be eliminated but as a dynamic phenomenon that must be managed in relation to biological functionality and system performance.

7. Innovations and Future Directions

Despite rapid advances in smart and bio‐functionalized membrane systems, most innovations remain at laboratory or pilot scale. A critical challenge lies in translating these developments into robust, scalable, and economically viable technologies. In particular, the integration of artificial intelligence (AI) and Internet of Things (IoT) technologies introduces new opportunities for system optimization, but also raises challenges related to data reliability, model generalization, and operational complexity (Othman et al. 2021). Enzyme‐functionalized membranes can self‐regulate catalytic activity and degrade foulants in situ. Smart hydrogels and stimuli‐responsive polymer coatings allow membranes to adjust porosity or surface charge based on specific operating conditions. Additionally, the integration of AI and IoT technologies has introduced real‐time monitoring, process automation, and predictive maintenance into MBRs, improving system reliability and efficiency (Miyoshi et al. 2019). LbL fabrication techniques, combined with nanomaterials (e.g., ZnO, AgNPs), not only enhance antifouling capabilities but also support microbial activity crucial for bio‐reactive processes. However, the future of these technologies hinges on both economic scalability and environmental safety factors addressed in the following subsections.

7.1. Techno‐Economic Analysis of Bio‐Membrane Systems

While bio‐membrane technologies offer notable environmental and operational advantages, their viability for full‐scale deployment is closely tied to economic and technical feasibility. A key limitation in current regulatory frameworks is the absence of standardized testing protocols for bio‐functional stability and nanoparticle leaching under long‐term operation, which complicates certification and commercialization.

7.1.1. Capital and Operational Costs

Although BMBRs entail 10%–20% higher capital costs due to advanced bio‐functional components (e.g., enzymes, nanoparticles), operational cost reductions of 15%–30% are often realized. These savings stem from lower chemical cleaning frequency, enhanced membrane longevity, and self‐regulating fouling control mechanisms. For example, enzyme‐modified UF membranes showed a 40% reduction in chemical cleaning frequency over a six‐month operating period (Yu et al. 2020).

7.1.2. Energy Efficiency

Energy consumption in AI‐optimized BMBRs has been reported as significantly lower than conventional systems, with UF‐BMBR consuming 0.35–0.6 kWh/m³, compared with 1.0–1.5 kWh/m³ for traditional RO systems (Sibiya et al. 2022).

7.1.3. Lifecycle and Sustainability

Life cycle assessment (LCA) analyses conducted over multi‐year operations demonstrate a potential 15%–40% reduction in total greenhouse gas emissions when incorporating biodegradable or waste‐derived membranes. However, it should be noted that most of the reported LCA results are based on cradle‐to‐gate system boundaries, primarily considering raw material extraction, membrane fabrication, and operational phases, whereas end‐of‐life disposal, regeneration, recycling, and resource recovery processes are often excluded from the assessment. Materials like chitosan, PLA, and cellulose offer favorable end‐of‐life pathways through composting or low‐toxicity incineration (Abdulrazzq et al. 2024).

7.1.4. Scalability and Market Readiness

Pilot studies (e.g., 5–20 m³/day AI‐BMBRs) have reported ROI within 3–4 years, especially in high‐load industrial applications. Barriers to scaling include initial customization costs, limited supplier networks, and a lack of standardization for bio‐functional components. A robust techno‐economic framework incorporating lifecycle cost analysis, risk assessment, and policy alignment is essential for accelerating the industrial adoption of bio‐membrane systems. Most published TEA studies focus on capital and operational expenditures during membrane fabrication and operation, while the energy requirements and economic implications associated with membrane regeneration, recycling, resource recovery, and end‐of‐life management are rarely incorporated into mass balance, lifecycle cost, and profitability calculations. Consequently, the reported economic benefits should be interpreted within the context of the selected system boundaries.

7.2. Environmental Risks and Regulatory Considerations

The deployment of bio‐membrane systems must be accompanied by rigorous assessment of their environmental impact and regulatory compliance, particularly when involving nanomaterials, enzymes, or degradable biopolymers.

7.2.1. Environmental Risks

While functional nanomaterials offer enhanced separation, the leaching of ZnO, AgNPs, and TiO₂ at levels exceeding 10 μg/L can pose acute ecotoxicological risks, especially in aquatic ecosystems. Polymer Byproducts: Degradable membranes may release low‐weight acids or saccharides, altering effluent chemistry and potentially disrupting microbial ecosystems. Pathogen and ARG Propagation: Biofilms, if unmanaged, may harbor antibiotic‐resistant genes (ARGs) or pathogenic microbes. Periodic biofilm control and sterilization protocols are critical (Flores‐Iwasaki et al. 2025).

7.2.2. Regulatory Considerations

Lack of Unified Standards there is a regulatory gap regarding the use of bio‐active or nano‐enhanced membranes, especially in potable water applications. U.S. EPA and EU REACH frameworks focus on leach‐ability and ecotoxicity of nano‐materials. Some countries (e.g., Germany, Japan) enforce material certification for membranes in contact with drinking water.

7.2.3. Recommended Practices

• Implement TCLP testing for all bio‐functional additives.

• Conduct Life Cycle Risk Assessments (LCRA)

• Establish compliant end‐of‐life disposal or recycling pathways

• Addressing environmental safety and regulatory alignment from the early design phase is essential for long‐term sustainability and public acceptance.

Aligning innovation with regulatory foresight is not optional; it is imperative for safe and scalable deployment of bio‐membrane technologies.

7.3. AI and IoT Integration in Bio‐Membrane Systems

The application of AI in bio‐membrane systems is primarily focused on fouling prediction, process optimization, and anomaly detection. Unlike conventional control systems, AI models rely on data‐driven learning from operational parameters such as TMP, flux decline, dissolved oxygen, pH, and temperature (AbuHamra et al. 2025). Commonly applied algorithms include the following:

• Artificial neural networks (ANNs): used for nonlinear modeling of fouling behavior and flux prediction

• Support vector machines (SVM): applied for classification of fouling types and system states

• Random Forest and Gradient Boosting: used for feature importance analysis and predictive maintenance

• Deep learning models (e.g., LSTM): suitable for time‐series forecasting of membrane performance

In parallel, IoT architectures enable real‐time data acquisition through distributed sensor networks measuring key variables such as turbidity, COD, ammonia, and biofilm thickness (Banitaba et al. 2022). These data streams are transmitted to cloud‐based platforms where AI models perform predictive analytics and generate control actions (Table 8). A typical AI–IoT architecture in bio‐membrane systems consists of three layers:

• Sensing layer: embedded sensors for water quality and membrane condition

• Data processing layer: edge or cloud computing for data filtering and storage

• Decision layer: AI algorithms for prediction, optimization, and automated control

TABLE 8.

AI‐ and IoT‐driven bio‐membrane systems in wastewater treatment: technologies, scale, and performance.

Case	Location	Scale	Technology	Key technical approach	Key outcome	Refs.
AI‐based predictive maintenance	China, 2023	Pilot‐scale	Machine learning (ANN)	TMP and flux data‐driven fouling prediction	35% reduction in downtime; 99.2% COD removal	(Aytaç et al. 2024)
IoT‐enabled monitoring	India, 2022	Pilot‐scale	Sensor network (pH, NH3, turbidity)	Real‐time biofilm and nutrient monitoring	Early biofilm detection; improved ammonia control	(Kamali et al. 2021)
Smart Bio‐Membranes	South Korea	Lab–pilot	pH‐responsive membranes + sensors	Stimuli‐responsive bio‐layer regulation	40% reduction in cleaning; stable operation (90 days)	(Ha 2020)
Deep Learning Fouling Prediction	Europe, 2024	Pilot‐scale	LSTM neural networks	Time‐series prediction of fouling evolution	> 90% prediction accuracy; optimized cleaning cycles	(Ahmed et al. 2021)
Hybrid AI–IoT MBR System	USA, 2023	Full‐scale	IoT + Random Forest	Integrated sensor–AI decision system	20%–30% energy reduction; improved system resilience	(Saleh et al. 2020)

However, despite promising results, several limitations remain. AI models often suffer from limited generalization across different feedwater compositions and operating conditions. In addition, sensor drift, data noise, and missing data can significantly affect model accuracy. Furthermore, the complexity of biological systems introduces uncertainty that is difficult to capture using purely data‐driven approaches (Saleh et al. 2020). Importantly, most reported AI applications are trained on short‐term experimental datasets, raising concerns regarding their reliability in long‐term industrial operation.

It should be noted that the outcomes of techno‐economic assessment (TEA) and LCA are highly dependent on the selected system boundaries. Most studies on advanced bio‐membranes adopt a cradle‐to‐gate approach, focusing primarily on raw material extraction, membrane fabrication, and operational performance. In contrast, cradle‐to‐grave assessments that include membrane regeneration, cleaning cycles, material recovery, recycling, and end‐of‐life disposal remain relatively limited. Consequently, future TEA and LCA studies should integrate membrane lifespan, fouling management strategies, regeneration efficiency, resource recovery, and disposal impacts to provide a more comprehensive evaluation of the economic viability and environmental sustainability of emerging membrane technologies.

7.4. Green and Waste‐Derived Materials

Amid the global shift toward circular economy and carbon footprint reduction, bio‐membrane research has increasingly focused on the use of sustainable materials derived from agricultural or industrial waste and biodegradable green polymers (Table 9). These materials not only reduce environmental impact but also offer comparable if not superior performance under harsh operating conditions, as demonstrated by several recent pilot and field studies.

TABLE 9.

Performance analyses of bio‐membranes from recycled and agricultural waste materials.

Source material	Region	Application	Performance	Sustainability benefit	Refs.
Recycled cellulose (paper waste)	Vietnam	UF for industrial effluents	> 90% COD removal	50% cost reduction	(Guo et al. 2022)
Chitosan (shrimp shells)	North Africa	Boron and micropollutant removal	> 70% boron, > 85% MP	90% biodegradable	(Zagho et al. 2018)
Starch (corn waste)	India	Laundry greywater	> 80% surfactant, > 95% phosphate	30%–40% cheaper	(Yu et al. 2025)

The convergence of material circularity and high‐performance bio‐membrane function represents a pivotal direction for sustainable water treatment innovation (Table 10).

TABLE 10.

Comparative analysis of green/waste‐derived bio‐membranes and their practical limitations.

Property	Green/waste‐derived materials	Operational considerations
Biodegradability	High (PLA, chitosan, cellulose)	Sensitive to temperature and humidity
Biofouling Resistance	Enhanced with enzymatic or nanomaterial coatings	Requires routine regeneration of active sites
Reusability	Moderate, depends on degradation rate	Less tolerant to harsh chemical cleaning
Cost	Low to moderate	Dependent on local supply chains
Separation Performance	Comparable or superior in specific applications	May degrade over time without surface protection

7.5. Environmental and Regulatory Implications of Advanced Bio‐Membranes

The deployment of nanomaterial‐enhanced and bio‐functionalized membranes must be accompanied by comprehensive environmental risk assessment and regulatory alignment, especially as these technologies move closer to commercialization.

7.5.1. Potential Environmental Risks

Leaching of nanomaterials, though typically within regulatory limits, can accumulate over time, necessitating improved binding mechanisms and surface stabilization strategies.

• Nanoparticle Leaching.

  • Nanomaterials such as ZnO, AgNPs, and TiO₂ may leach into treated water during extended use.
  • Reported concentrations: Up to 5–15 μg/L, ecotoxicity threshold > 10 μg/L can harm aquatic organisms and micro‐biomes, mitigation: nano‐encapsulation, covalent surface bonding, or matrix immobilization.

• Propagation of Pathogens or Antibiotic Resistance Genes (ARGs)

  • Biofilms supported by bio‐membranes may harbor harmful microbes or ARGs if not properly managed. Prevention: Periodic sterilization, real‐time monitoring, controlled biolayer renewal.

• Lack of Unified Standards

  • Currently, no international standard specifically regulates bio‐active or nano‐enabled membranes in drinking water applications.

7.5.1.1. Relevant Guidelines.

U.S. EPA & EU REACH: Emphasize leachability, biodegradability, and eco‐toxicity. Germany, Japan: Require safety certification for bio‐based membrane materials in contact with potable water.

7.5.2. Recommended Practices for Safe Deployment

• Perform standardized TCLP and LCRA evaluations.

• Prioritize low‐leachability designs during development.

• Ensure end‐of‐life traceability and recyclability.

• Adopt real‐time risk monitoring via embedded sensors.

As bio‐membrane systems transition from laboratory innovation to industrial‐scale deployment, future development must integrate material sustainability, digital intelligence, and regulatory alignment. By merging biotechnology with smart materials and AI‐driven control, the next generation of membranes holds the potential to revolutionize sustainable water treatment.

7.6. Future Work

Future research in bio‐membrane systems should move beyond incremental material improvements toward integrated, system‐level innovation. A key priority is the development of standardized methodologies to quantitatively distinguish between physical separation and biological contribution, as current studies often overestimate performance due to overlapping mechanisms. Another critical direction involves enhancing the long‐term stability of bio‐functional components, particularly enzymes and microbial systems, under realistic operating conditions. This requires the design of robust immobilization strategies and protective microenvironments that can sustain biological activity over extended periods. From a technological perspective, the integration of artificial intelligence with bio‐membrane systems should evolve toward hybrid modeling approaches that combine data‐driven algorithms with mechanistic understanding of biological processes. This is essential to address the inherent variability and uncertainty associated with biological systems. In addition, future work should focus on scalable fabrication techniques, particularly for electrospun and self‐healing membranes, ensuring reproducibility and economic feasibility at industrial scale. Finally, comprehensive techno‐economic and LCAs must be incorporated early in the design phase to ensure that environmental benefits are not offset by hidden costs or material‐related risks. Addressing these challenges will be essential for transitioning bio‐membrane technologies from promising laboratory concepts to reliable, large‐scale solutions for sustainable water treatment.

7.6.1. Emerging Composite Bio‐Membranes for Persistent Pollutant Removal

Recent advances in membrane science have shifted the focus from conventional separation processes toward multifunctional composite membrane systems capable of simultaneously removing and degrading emerging contaminants (Yu et al. 2025). While self‐healing and electrospun membranes have attracted considerable attention due to their enhanced durability and tunable structures, advanced composite membranes integrating catalytic, electrocatalytic, and bio‐inspired functionalities represent a rapidly evolving research frontier. These next‐generation membrane platforms are particularly attractive for addressing persistent organic pollutants (POPs), pharmaceuticals, endocrine‐disrupting compounds, per‐ and polyfluoroalkyl substances (PFAS), dyes, and other recalcitrant contaminants that are often inadequately removed by conventional membrane filtration alone (Yu et al. 2022). Recent studies have demonstrated that coupling membrane separation with electrocatalytic degradation significantly enhances contaminant removal efficiency while mitigating membrane fouling (Yu, Chen, et al. 2026). In these systems, conductive membrane architectures facilitate the generation of ROS, enabling in situ degradation of pollutants directly at the membrane interface. Such integrated processes reduce secondary waste generation and improve treatment efficiency compared with standalone filtration technologies (Table 11). Furthermore, advanced composite membranes incorporating nanostructured catalysts, carbon‐based conductive materials, metal–organic frameworks (MOFs), and bio‐inspired functional layers have exhibited remarkable selectivity toward complex micropollutants while maintaining high permeability and operational stability.

TABLE 11.

Comparison of emerging composite bio‐membrane technologies for persistent organic pollutant removal and water purification applications (Li et al. 2021; Zhang, Wang, et al. 2020; Wang, Zhou, et al. 2024; Bernardes et al. 2025; Zaffora et al. 2023; Osman et al. 2024).

Technology	Target pollutants	Removal/degradation mechanism	Key advantages
Self‐healing bio‐membranes	Organic foulants, biofilms	Autonomous repair of membrane defects	Extended membrane lifespan and reduced maintenance
Electrospun nanofiber membranes	Dyes, microorganisms, suspended solids	High porosity and enhanced adsorption/filtration	High flux and tunable pore structure
Catalytic composite membranes	Pharmaceuticals, dyes, endocrine disruptors	Catalytic oxidation and degradation	Simultaneous separation and degradation
Electrocatalytic membranes	Persistent organic pollutants (POPs), PFAS, antibiotics	Reactive oxygen species generation and electrochemical oxidation	Reduced fouling and high degradation efficiency
MOF‐based composite membranes	Micropollutants, heavy metals	Selective adsorption and molecular sieving	High selectivity and permeability
Bio‐inspired multifunctional membranes	Emerging contaminants and mixed pollutants	Combined separation, self‐cleaning, and catalytic functions	Integrated treatment and improved sustainability

Despite these promising developments, several challenges remain before large‐scale implementation can be realized. The long‐term stability of catalytic components, membrane regeneration efficiency, catalyst leaching risks, and the economic feasibility of large‐scale fabrication require further investigation. In addition, the long‐term physical and chemical stability of surface‐modified and coated membranes remains a major challenge. Functional coatings may experience gradual delamination, detachment, or performance deterioration under continuous cross‐flow operation, hydraulic backwashing, and repeated chemical cleaning cycles. Therefore, future studies should prioritize the development of robust coating–substrate interfaces and conduct long‐term durability assessments under realistic operating conditions. Additionally, future research should focus on developing multifunctional bio‐membranes capable of combining selective separation, self‐cleaning behavior, electrocatalytic degradation, and resource recovery within a single integrated platform. Such approaches may provide sustainable solutions for water treatment systems facing increasingly complex contaminant mixtures and stricter environmental regulations (Yu, Zhang, et al. 2026).

8. Applications of Bio‐Membranes

While numerous studies report successful applications of bio‐membranes, most available data are derived from pilot‐scale or short‐term experiments. Therefore, a critical evaluation of operational conditions, system limitations, and scalability challenges is essential to assess their real‐world viability. Their real‐world applicability is now well‐documented in diverse fields, particularly in water treatment, healthcare, and environmental safety. Recent pilot‐scale projects and full‐scale implementations have validated their performance in real‐world scenarios, as outlined below.

8.1. Water and Wastewater Treatment

Bio‐membranes are increasingly adopted in MBR systems, especially for treating municipal and industrial wastewater (Table 12).

TABLE 12.

Real‐world applications of bio‐membranes in diverse water treatment scenarios by region.

Location	Technology	Outcome	Challenge
China	AnMBR	> 95% removal	Enzyme stability, fouling
Germany	UF enzyme	80% pharma removal	Limited lifetime
Africa	NF chitosan	Boron removal	pH sensitivity

Despite high reported removal efficiencies (> 90%–95%), system performance is strongly dependent on operating parameters such as hydraulic retention time (HRT), sludge retention time (SRT), salinity, and organic loading rate. For example, enzyme‐modified membranes may exhibit performance decline under fluctuating feed composition due to enzyme deactivation or fouling. Furthermore, long‐term stability beyond 3–6 months is rarely reported, raising concerns regarding scalability and operational reliability. These applications affirm the role of bio‐membranes as a robust alternative in wastewater systems facing variable chemical loads, salinity, and stringent effluent standards (Kapitonov and Ryzhkov 2023; Li et al. 2025).

8.2. Healthcare Applications

Bio‐membranes are widely used in medical fields due to their ability to interact safely with biological tissues and fluids (Table 13). Although bio‐membranes demonstrate excellent biocompatibility in medical applications, their performance is often evaluated under controlled laboratory or clinical conditions. Issues such as long‐term stability, sterilization compatibility, and material degradation under physiological conditions remain critical challenges that limit broader clinical adoption.

TABLE 13.

Medical applications of bio‐membranes in dialysis, tissue engineering, and drug delivery systems.

Use case	Technology	Region	Outcome	Ref.
Dialysis	Vitamin E‐enhanced cellulose triacetate	Japan	Reduced oxidative stress, improved hemocompatibility	(Li et al. 2025)
Tissue engineering	Gelatin–chitosan scaffolds	South Korea	Cell proliferation, angiogenesis in 14 days (animal model)	(Xu et al. 2022)
Drug delivery	PLA‐alginate hybrid membranes	EU (clinical trials)	Controlled antibiotic/anti‐cancer drug release	(Bicket et al. 2024)

8.3. Environmental Protection and Safety

Bio‐membranes contribute significantly to environmental protection and safety through advanced filtration and separation technologies. They are used in protective clothing to shield against chemical and biological hazards, enhancing occupational safety. Functionalized bio‐membranes are effective in removing heavy metals from contaminated water, supporting pollution control and environmental remediation (Table 14). Additionally, bio‐membranes are utilized in gas separation processes, particularly for CO₂ capture, playing a vital role in air purification and reducing greenhouse gas emissions (Maniarasu et al. 2023). The role of bio‐membranes in environmental remediation and safety is expanding through innovative field applications. In environmental applications such as CO₂ capture or heavy metal removal, performance is highly sensitive to process conditions including pressure, temperature, and contaminant concentration. In addition, enzyme‐based systems (e.g., carbonic anhydrase membranes) may suffer from rapid deactivation under industrial flue gas conditions, limiting their long‐term applicability.

TABLE 14.

Environmental and safety applications of bio‐membranes in heavy metal removal, protective equipment, and CO₂ capture.

Application	Location	Technology	Key outcome	Ref.
Heavy metal removal	Peru	Amino‐functionalized membranes	> 90% Cd2+ and Pb2+ removal from acid mine drainage	(Maniarasu et al. 2023)
Chemical hazard protection	Netherlands	Smart bio‐membranes in PPE	Detection & adsorption of toxic vapors (NH3, Cl2)	(Ayinde et al. 2025)
CO2 capture	Norway	Carbonic anhydrase‐integrated membranes	35%–50% CO2 separation under flue gas conditions	(Donato 2025)

Across diverse application domains, bio‐membranes have evolved from theoretical constructs to operationally viable tools. Their ability to integrate with biological, chemical, and digital systems underscores their central role in the transition to cleaner, safer, and more sustainable technologies.

8.4. Cross‐Sector Limitations and Scalability Challenges

Across different application domains, several common limitations can be identified:

• Limited long‐term operational data under real conditions

• Sensitivity of biological components to environmental fluctuations

• Lack of standardized performance metrics across studies

• Scale‐up challenges due to material cost and system complexity

These limitations suggest that while bio‐membranes show strong potential, their transition to industrial‐scale applications remains constrained by stability and reproducibility challenges.

9. Conclusion

Bio‐membrane technology represents a promising paradigm shift from passive separation systems toward integrated, bio‐reactive platforms capable of simultaneous filtration and transformation of contaminants. This review critically evaluated the interplay between membrane materials, biological functionality, and transport mechanisms, highlighting that system performance is governed by complex trade‐offs between selectivity, permeability, and biological stability. Despite significant progress in material design, fabrication techniques, and hybrid system integration, several key limitations remain unresolved. These include insufficient long‐term stability of bio‐functional components, lack of standardized methodologies to quantify bio‐contribution, and limited scalability of advanced fabrication and modification strategies. In addition, the integration of AI and IoT technologies, while promising, is still constrained by data reliability, model generalization, and system complexity. From a techno‐economic perspective, bio‐membrane systems demonstrate potential for reduced operational costs and improved sustainability; however, current analyses are largely based on pilot‐scale data and may not fully capture industrial‐scale variability. Environmental concerns, particularly nanoparticle leaching and end‐of‐life management, further highlight the need for robust regulatory frameworks and lifecycle‐based design approaches. Future research should focus on developing durable bio‐functional materials, establishing unified performance evaluation protocols, and integrating data‐driven optimization with material‐level innovation. Addressing these challenges will be essential for transitioning bio‐membranes from emerging technologies to reliable, scalable solutions for sustainable water treatment and environmental protection.

Author Contributions

Mahmoud Shaban: writing – original draft. Ashraf Morsy: writing – review and editing, writing – original draft. Fatma Fadel: data curation, investigation. Ahmed H. Abdel‐Salam: investigation, formal analysis. Abdullah Akhdhar: writing – review and editing. Zarah Alqarni: writing – review and editing. Mahmoud H. Ebeid: formal analysis, validation. Lovert A. William: investigation, formal analysis. Ahmed Morsy: investigation, software, formal analysis. M. Abdelaty: software. N. S. Yousef: software. Abd El Salam Nasra: investigation.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.