








key: cord-285620-oawrnmhy
authors: Fahimirad, Shohreh; Fahimirad, Zahra; Sillanpää, Mika
title: Efficient removal of water bacteria and viruses using electrospun nanofibers
date: 2020-08-16
journal: Sci Total Environ
DOI: 10.1016/j.scitotenv.2020.141673
sha: 
doc_id: 285620
cord_uid: oawrnmhy

Abstract Pathogenic contamination has been considered as a significant worldwide water quality concern. Due to providing promising opportunities for the production of nanocomposite membranes with tailored porosity, adjustable pore size, and scaled-up ability of biomolecules incorporation, electrospinning has become the center of attention. This review intends to provide a detailed summary of the recent advances in the fabrication of antibacterial and antiviral electrospun nanofibers and discuss their application efficiency as a water filtration membrane. The current review attempts to give a functionalist perspective of the fundamental progress in construction strategies of antibacterial and antiviral electrospun nanofibers. The review provides a list of antibacterial and antiviral agents commonly used as water membrane filters and discusses the challenges in the incorporation process. We have thoroughly studied the recent application of functionalized electrospun nanofibers in the water disinfection process, with an emphasis on their efficiency. Moreover, different antibacterial and antiviral assay techniques for membranes are discussed, the gaps and limitations are highlighted and promising strategies to overcome barriers are studies.

removing bacteria from water supplies which meet the requirement of effective antimicrobial activity, superior filtration flux with acceptable retention potentials (Zodrow et al., 2014) .

Nanofiber membranes, because of their high surface area to volume ratio, nano-sized pores, and high porosity, have been illustrated to improve the efficiency of conventional materials employed for the filtration and separation of particulate materials (Aussawasathien et al., 2008) .

A number of processing techniques including melt-blown, self-assembly, phase separation, template synthesis, and electrospinning have been employed to prepare nanofibers in recent years. Among them, electrospinning is the most promising, efficient method to produce web-like non-woven ultrafine fibers including microfibers (>1 μm) or nanofibers (<1000 nm) from different kinds of polymers. Moreover, incorporation of bioactive, antimicrobial and antiviral agents into nanofiber structure is easily possible through the electrospinning process Fahimirad and Hatami, 2019; Faccini et al., 2015) .

The present work reviews previous studies on the production and application of electrospun nanofibers as antimicrobial water filtration membranes. The merits and demerits of these novel water microfiltration tools are discussed. Moreover, their antibacterial efficiency and disinfection activities are compared with commercial water membrane filters comprehensively. Finally, some points are recommended to be noticed as the subsequent future research plans.

The objectives of this review were to: (i) introduce the different procedures, which have been applied for incorporation of the various antimicrobial agents into electrospun nanofibers (ii) discuss the different antimicrobial tests used for proving antimicrobial activity of the fabricated electrospun water filters (iii) study the efficiency of the produced antimicrobial electrospun application in the water treatment industry.

J o u r n a l P r e -p r o o f

The electrospinning approach was invented by Cooley in 1900 (Cooley, 1900 . This method is easy, cost-effective, uncomplicated, and has the potential for scale-up production. The flexibility in material selection and additive incorporation to obtain appropriate functionality, as well as its considerable capability to produce fibers in the sub-micron range with the high surface-area (up to 40 m 2 g -1 based on the fiber diameter), are prominent privileges of electrospinning process for fabrication of nanofibers. In addition, effective porosity of electrospun nanofibers (almost about 80% with no upper limit) with many small pores, interconnected pore structure directly promote both infiltration rate and contaminant rejection ratio in comparison with conventional materials being used for MF applications (Nasreen et al., 2013; Wang et al., 2013) . In this process, a prepared solution of polymer is loaded into a syringe and fed at a set flow rate to the spinneret.

Due to the needle connected to a high voltage power supply under the electric field with a specific voltage, a Taylor cone is constructed by elongation of the polymer droplet at the end of the syringe into a characteristic conical shape. Enhancing the electrical field causes the formation of a steady jet elongated and whipped consecutively by electrostatic repulsion. The solvent evaporates when electrostatic forces prevail over surface tension and the jet gets finer, so electrospun nanofiber in MF application, such as uniform fiber morphology with controllable pore size, interconnected open pore structure, high porosity, and membrane thickness, turn them to a superior substitute to replace the conventional MF membrane such as the Millipore GSWP MF membrane with an average pore size of 0.22 mm (Wang et al., 2012; Barhate and Ramakrishna, 2007) .

Another novel application of electrospun nanofiber in water purification and bacterial rejection is thin-film nanocomposite membrane (TFNC), a major type of reverse osmosis (RO) and nanofiltration (NF) membranes, which compromises of three layers including the first barrier layer of interfacial polymerization, a polyacrylonitrile or poly (vinylidene fluoride) electrospun membrane as the second layer and nonwoven polyethylene terephthalate (PET) as the third layer.

The third layer employed as a substructure layer to provide the whole membrane adequate mechanical strength (Subramanian and Seeram, 2013; Yin et al., 2012; Fig 2) . High water flux, great solute rejection, minimum membrane fouling, and perfect mechanical persistence are main properties of an ideal TFC membrane and turn it into an excellent candidate for microfiltration and ultrafiltration applications (Li and wang, 2010) . Sato et al., (2013) fabricated a novel composite fibrous membranes, consisting of an ultra-fine cellulose nanofibrous infused into electrospun polyacrylonitrile (PAN, with an average diameter of 0.2 μm a mean diameter of about 30 μm as the barrier layer (40-100 μm in thickness) to provide filtration attributes) nanofibrous scaffold on a melt-blown polyethylene terephthalate (PET, with a mean diameter of 30 μm as the support layer (about 100 μm thick) to sustain mechanical strength) non-woven substrate for water purification. The nanostructure showed a retention rate of 99.9999% for E. coli filtering and the high percent of the MS2 virus, with 30 nm sizes, captured in the electrospun PAN scaffold infused with m-UFCNs (Sato et al., 2013) . Recently, Taheran et al. (2019) J o u r n a l P r e -p r o o f fabricated a methodical portable water purification instrument using electrospun nanofiber. The device contained three distinct electrospun membranes. The first membrane was made by electrospinning of Polyacrylonitrile/chitosan solution at 85:15 mass ratio as an antibacterial membrane, the second membrane was produced from Laccase (10 unit g -1 ) immobilized onto PAN/biochar 95:05% electrospun mat for removal of micro-pollutants and the third layer was fabricated by electrospinning of PAN/biochar at 95:05 ratio as an adsorptive membrane. The applied technology led to approximately 99% removal of microorganisms, 83% of micropollutant removal, and more than 77% of turbidity decline during less than 5 min contact time (Taheran et al., 2019) .

The important characteristics of a nanofiber mat membrane for application as filters for the separation of contaminations and pathogens from a continuous fluid phase are wetting properties, permeability, porosity, fiber size distribution, and fiber structure.

For water filtration, a membrane must be wet-table and surface wetting properties are generally specified by the contact angle. A surface with a low contact angle (below 90 degrees) is considered a hydrophilic surface, while a surface illustrating a high contact angle (over 90 degrees) is referred to as a hydrophobic surface. Sessile drop and the Captive bubble method are two common techniques used for measuring the nanofibers' contact angle (Nuraje et al., 2013) .

One of the key parameters in filter design and its performance is porosity. Generally, porosity is calculated from the apparent density and bulk density of the membrane. However, other alternative procedures inclusive of image analysis and mercury porosimeter are frequent methods J o u r n a l P r e -p r o o f applied for the evaluation of porosity in the nanofiber membrane (Ghasemi-Mobarakeh et al., 2007) . Electrospun nanofibers are highly porous with interconnected pores in the size range of just a few times the fiber diameter. The small pore size of the nanofibrous membrane introduces a higher retention rate, the interconnected pores leads to better tolerance against fouling and the high porosity defined a higher permeability capability (Homaeigohar et al., 2010) .

Clean water permeability (CWP (l/m2 •h•bar)) illustrates the highest amount of attainable flux dependent on the membrane condition. It can be assayed by calculating the flux at various trans membrane pressures (TMP). The slope of the eventuated curve is regarded as the CWP (Bjorge et al., 2009) . The high CWP grants high flux operation to the membranes, introduces the nanofiber mat as an energy-saving membrane, and means that if fouling does not happen, enormous volumes can be treated (Daels et al., 2011; He et al., 2018) .

The surface charge on membranes is related to affinity corresponding interactions and considered as a significant parameter influencing the disinfection capabilities of the membrane. Surface charges can qualify the strength of biomolecular or even pathogen affinity on a material surface.

In virus removal, surface charged nanofibers adsorb virus via electrostatic interactivity between the nanofibers and the counter-charges of virus and signify virus remediation improvement (Cho et al., 2012) . A series of studies have confirmed that electrostatic attraction between the cationic membrane and the anionic surface of bacteria may lead to morphological defects in consequence of ROS generation and cell membrane destruction. Indeed, anionic membranes act as powerful non-adhesive site of bacteria attributable to electrostatic repulsion (Mukherjee and De, 2018; Kolewe et al., 2016) .

Operating conditions influence the antibacterial activity performance of the nanofibrous membrane. As proved by several experiments, bacterial cells are able to decline their size at higher operating pressure, hence resulting in enhancing permeation through the filter. Therefore, less trans membrane pressure (TMP) is usually desired, to retain antibacterial activity during long term application of the membrane. The TMP is described as the mean feed pressure minus the permeate pressure that is essential to push down water through a membrane (Mukherjee and De, 2017; .

Different factors including surface area, surface roughness, pore diameter, zeta potential, and inclusion of biocides or antibacterial agents determine the antimicrobial performance of membrane (Rahaman et al., 2014; Mukherjee and De, 2018) . Accordingly, the employing of electrospun polymeric membranes in bacterial and virus removal from water is performed in two procedures including size exclusion and adsorption (Lee et al., 2016) . In most cases, the diameter of water-borne bacteria is more than 0.2 μm. For example, the E. coli size is 0.5-2.0 μm and Brevundimonas dimimuta dimension is 0.3-0.9 μm. Previous studies have confirmed that using a 0.45 μm pore sized MF leads to a 2 log-4 log bacteria reduction (Gómez et al., 2006; Ghayeni et al., 1999) . Thus, based on the degree of exclusion, the electrospun membrane should have an average pore size of fewer than 0.2 μm. In addition, the narrow pore size distribution is requisite for achieving a high retention rate (Ma et al., 2014) . There is a direct relationship between the pore size and the fiber diameter of a porous nonwoven structure. The relationship has been confirmed as the average pore size was approximately 3±1 times the mean fiber diameter, and J o u r n a l P r e -p r o o f the greatest pore size was about 10±2 times the mean fiber diameter. Thus pore size of electrospun fiber generally grows with increasing fiber diameters (Ma et al., 2011) . Various conventionally employed membranes for the application as micro-filters have 0.2 μm theoretical pore sizes. The advantage of electrospun nanofiber membranes in comparison to conventionally used membranes are the simplicity of manufacture, adjustable size of the pores and high porosity (Saleem et al., 2020) . In view of the fact that the membrane pore sizes can be controlled by adjusting the electrospinning parameters and besides the fact that the most aquatic bacteria dimensions are more than 0.2 mm, electrospun nanofibers can be designed efficiently with smaller pore dimensions suitable for MF applications (Wang and Hsiao, 2016) . For instance, accelerating the flow rate raises the pore diameter by enhancing the fiber diameter. Moreover, increasing polymer solution concentration and using higher molecular weight polymer increases fiber diameter. Employing a secondary ring electrode circling the nozzle cause reducing the fiber deposition and consequently decrease the density of the membrane, the parameter which reduces the pore size. In addition, controlling fiber distribution, post electrospinning modification and using temporary spacers can be utilized for controlling pore size (Dong et al., 2015; Haider et al., 2018) . As discussed above and based on the size exclusion process, microfiltration larger sized bacteria are substantially seized by the membrane but it is not efficient in separating small sized viruses within 0.01-0.1 µm range size (Mi et al., 2014a; Barhate and Ramakrishna, 2007) . So, rejection of bacteria smaller than membrane pores or viruses needs the incorporation of antiviral or antibacterial agents into the membrane. Also, after size-exclusion microbial removal of the membrane, intercepted bacteria can be released and induce membrane biofouling during subsequent filtration. Therefore, antimicrobial agents are commonly used to prohibit bacterial J o u r n a l P r e -p r o o f growth and biofoul formation that would decline filter efficiencies (Botes and Cloete, 2010; Wen et al., 2017) .

Various bioactive agents with different fundamental properties may have consequential impacts on bacteria removal. Plus, nanofiltration membranes or ultrafiltration membranes with a positive charge on the surface are able to remove viruses selectively (Mukherjee and De, 2017).

Moreover, incorporating antimicrobial agents into electrospun nanofibers enhance the antimicrobial activity of fabricated nanofibrous membrane (Nasreen et al., 2013; Park and Kim, 2017 ). An ideal bioactive agent incorporated into the functionalized membrane should be nontoxic, water insoluble with no or slight leaching property. Also, the functionalization process should not cause adverse influences on the quality and overall performance of the membrane.

Based on the majority of researches studied in this review, blending and post-modification strategies are two commonly used techniques to incorporate biocide agents into nanofibers aiming for water disinfection application (Shalaby et al., 2018; He et al., 2018; Makaremi et al., 2016) .

Blend electrospinning is an easy one-step procedure, mostly used for agents' incorporation into nanofibers (Shabafrooz et al., 2014) . Using the same solvent, the bioactive agent is dissolved directly into the polymer solution and a homogeneous blended solution of the incorporating agents in the polymer solution is prepared for the electrospinning step (Pillay et al., 2013;  Fahimirad and Ajalloueian, 2019).

J o u r n a l P r e -p r o o f

The agents incorporation into electrospun fibers can be performed after the electrospinning process by physical or chemical treatments. Covalent and non-covalent immobilizations are fundamental methods for molecules attached to the fiber surface. Non-covalent immobilization is performed by immersion of electrospun mats in a solution compromising the bioactive molecules. By treating with plasma the surface gets activated for subsequent modification using specified ligands like active amine groups. The affinity of incorporated agents to the electrospun nanofiber surface improves by covalent immobilization (Wang and Windbergs, 2017; Kurusu and Demarquette, 2019) .

Some commonly used antimicrobial or antiviral agents in electrospun nanofibers are discussed in this section.

Silver nanoparticles (AgNPs) are considered the most efficient nanoparticles for biological applications and the most extensively applied antibacterial agent for water disinfection Mukherjee and De, 2018) . AgNPs are capable to puncture the microorganisms' cell walls, interact with their nucleic acids and attach to their enzymes, which cause the cell membrane destruction and finally growth inhibition. Different feasible interactions of Ag + ions with various bacterial biomolecules are documented. Furthermore, the extended range of antibacterial activities and virulence effects of Ag + ions toward several microorganisms (e.g. bacteria, viruses, and fungi) at only a few mg mL -1 are confirmed in previous studies. Thus, silver nanoparticles are recognized as potent disinfection agents (López-Heras et al., 2015) . In water purification, nanosilver materials have been mainly applied to prevent the formation of There are three main methods for AgNPs incorporation into electrospun nanofibers including 1) blending of prepared synthesized AgNPs solutions to the polymer solution, 2) AgNP synthesis in the polymer solution by employing a precursor, and 3) Post-treatments of the electrospun nanofibers for AgNP synthesis by reduction of the precursor that has been spun along with the electrospinning solution (Fahimirad and Ajalloueian, 2019).

There are three main approaches to produce iron oxide nanoparticle-nanofiber composites, including (1) electrospinning of solution containing prepared IONPs, (2) in-situ synthesizing of IONPs during the electrospinning process or in the solution to be electrospun and (3) 

It has been indicated that due to electrostatic interaction, CuNPs illustrate antibacterial functions on the bacterial cell through different mechanisms, such as adhesion to the bacterial cell wall, lead to detrimental impacts on protein structure within the cell membrane, denaturation of J o u r n a l P r e -p r o o f proteins in inertial parts of the cell , and adverse effects on phosphorus-and sulfur-containing compounds like DNA (Raffi et al., 2010) .Recently, CuNPs have gained considerable interest because of their broad-spectrum and acutely effective antibacterial activity with comparatively low cost and high scalability (Taner et al., 2011) .

Recently, zinc oxide (ZnO) has received much attention due to its non-toxic profile, effective antibacterial activity, adsorptive properties, mechanical, chemical, and thermal stability while encountering diverse environmental conditions (Tiwari et al., 2018) . ZnO particles have illustrated antimicrobial activity against both Gram-positive, Gram-negative bacteria and even against spores Wagner et al., 2016) . ZnO NPs are considered bio-safe, nontoxic, and biocompatible (Hameed et al., 2016; Farrokhi et al., 2019) . In comparison with bulksized particles, nanoparticles can pass through bacterial cell walls more simply. The release of Zn 2+ ions from NPs destroy the cell membrane and subsequently enhance cellular internalization of the nanoparticles. It is also confirmed that the antimicrobial function of ZnO can be ascribed to photocatalytic activity. By receiving UV light which promotes its interaction with bacteria, ROS, which has a phototoxic effect on bacteria, will be produced (Dimapilis et al., 2018) . 

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TiO 2 is a biocompatible chemical thermally stable compound with high photocatalytic activity and has shown good antimicrobial activities with wide spectrum function against microorganisms (Gram-negative and Gram-positive bacteria, fungi, and virus). The generation of reactive oxygen species (ROS) is the major mechanism of TiO 2 . Due to its photocatalytic nature, antimicrobial activity of TiO 2 NPs enhances by exposing UV light on its surface (de Dicastillo et al., 2020; Levchuk et al., 2018b; Levchuk and Sillanpää, 2020) .

It is proved that lanthanum compounds, such as lanthanum hydroxide (La(OH) 3 ), lanthanum carbonate (La 2 CO 3 ), and lanthanum hydroxide (La(OH) 3 ) can attach to phosphate so firmly that they can generate LaPO 4 and remove redundant phosphate in a bacterial cell. According to the very significant band to phosphate, Nano-Lanthanum (La) species represent high effectiveness adsorption and suppress microbial growth by inhibition of the microorganism growth Liu et al., 2017) .

Carbon is the chemical element with atomic number 6 and six electrons situate 1 s 2 , 2 s 2 , and 2p 2 atomic orbital. Graphene is a one-atom-thick hexagonal structure consisting of a 2-dimensional Bhatnagar et al., 2013) . Furthermore, the existence of these functional groups advances the interactions with biomolecules and leads to bacterial death with no intracellular process. GO nano-sheets with Sharpe edges hurt the bacterial cell membranes, lead to leakage of the intracellular matrix and eventually cause inactivation of bacteria. Plus, GO generate oxidative stress by producing ROS and lead to DNA damage and mitochondrial dysfunction (Kumar et al., 2019) . In addition, the antiviral activity of GO is confirmed by several experiments (Ye et al., 2015) .

Single-walled carbon nanotubes (SWNTs) are nanometer diameter cylinders fabricated of rolled up graphene sheet in the form of a tube. Generally, SWCNT length is in the micrometer range and their diameters vary from 0.4 to 2 to 3 nm (Eatemadi et al., 2014) . SWNTs have presented strong and board spectrum antimicrobial activities. The antimicrobial activity of SWCNTs has been confirmed to be varied by several factors. For instance, longer length nanotubes exhibited superior antimicrobial activity, SWCNTs having surface groups of -OH and -COOH illustrate more strong antimicrobial activity in comparison with SWCNTs-NH 2 , also the diameter of nanotubes is an important factor governing their antibacterial effects (Dong et al., 2012) . 

Chitosan [poly-(b-1/4)-2-amino-2-deoxy-D-glucopyranose] is

Quaternary ammonium cations are positively charged polyatomic ions. These ions contain a positively charged nitrogen "head" binding four bonds R including an alkyl group or an aryl group. Quaternary ammonium compounds are salts of quaternary ammonium cations (Tezel and Pavlostathis, 2012) . Because of their positively charged sites, they are able to generate electrostatic bonds with the negatively charged sites on bacterial cell walls, resulting in disruption of a cell wall, defect cell membrane permeability and consequently sever leakage of intracellular low-molecular-weight materials (Chen et al., 2014) . QACs target bacterial cell membranes. Therefore, they illustrate extended-spectrum antimicrobial activity and have been widely employed to construct an antibacterial surface (Jennings et al., 2015) . Quaternized poly benzalkonium chloride (BAC) are some important kinds of QACs (Zhu et al., 2018) .

Easy release of biocides from the membrane improves their exposure rate to bacterial cell. There is a challenging point since the leaching profile of incorporated biocides determines long term bactericidal efficiency of the membrane. Leaching of bactericidal agents resulted in the diminution of the membrane antimicrobial performance over time. Gradual leaching of the blended biocides during the filtration process not only declines the antibacterial activity, but may J o u r n a l P r e -p r o o f also lead to secondary pollution (Fu et al., 2014) . Besides chemical contamination and cytotoxicity issues, the continuous release of bactericidal agents causes the development of bacterial resistance due to being exposed to sub-inhibitory concentrations of biocides (Sile-Yuksel et al., 2014; Mukherjee and De, 2018) . Thus, there is a challenge to provide process eluding leaching of toxic materials while illustrating rapid pathogens killing ability. Nanofiber coatings based methods which promote contact pathogen-killing capacity are promising and can be obtained by chemical modification with tethered biocides functionalities. These strategies may be successful by regarding the right control over the binding quality between the active agent and the underlying biomaterial surface (Zhang et al., 2016; Bazaka et al., 2015; Hilpert et al., 2009) . Despite there are numerous researches on application of antibacterial electrospun nanofiber membrane in water filtration, the leaching pattern and durable bactericidal efficiency of the membranes have not been studied comprehensively. 

This method is generally used for testing the inherent antibacterial performance of fabricated electrospun nanofibers as a membrane. This assay generally consists of qualitative detection and quantitative measurement techniques (Zhu et al., 2018) . 

The inhibitory activity of electrospun nanofibers is assayed by the inhibition zone diameter or agar diffusion method toward the considered bacterial sample, based on the Clinical and Laboratory Standards Institute (CLSI Document M02-A12) (CLSI, 2015) . For this reason, 100 μl overnight culture of the tested bacteria (10 6 CFU/mL) is spread across the surface of an appropriate agar plate, the electrospun nanofiber is cut to disk with about 10 mm diameters, sterilized under UV light for 20 min and then incubated on the plates for 18-24 h at 37 °C. Then, the area of bacteria growth is detected, and the diameter of the inhibition zone around the electrospun nanofiber is measured. This procedure modifications are also used (Santos et al., 2016; Jatoi and Al Mamun, 2020; Fig.3 a) .

The antibacterial function of the membrane will lead to changes in the bacteria cell morphology. 

This method is a shaking flask method. Briefly, an appropriate amount of sample sterilized nanofiber is weighted, dipped into a flask containing PBS buffer with a cell concentration of 1-4 × 10 5 CFU mL -1 . The flask is incubated with continuous shaking at 37 • C for a determined time.

After serial dilutions by the phosphate buffer, the bacterial suspensions are plated in the agar plate. The inoculated plates were incubated at 37 • C for 24 h and the viable bacterial cells are counted by a colony counter (Kleyi et al., 2015) . Also, the number of bacteria after incubation for a determined time can be indirectly measured by spectrometric optical density at 625 nm . Then, the reduction rate is calculated with the following equation:

Where R is the reduction rate, A is the number of bacteria isolated from the inoculated electrospun nanofibers after defined time contact time, and B is the number of bacteria isolated from the inoculated electrospun nanofibers at zero contact time (Yao et al., 2016) .

J o u r n a l P r e -p r o o f

The AATCC 100 test method quantitatively evaluates the bacteriostatic (growth inhibition) or bactericidal (killing of bacteria) ability of textiles over a 24 hours contact. For this test, firstly a defined weighted of nanofiber is cut (about 3 mg), get sterilized by UV light, then inoculated with 0.1 ml microbial suspension (1-1/5 × 10 5 CFU mL -1 ) and finally overnight incubated at 37 • C. Over determined contact period, 10 mL PBS buffer is added to the falcon tubes containing the inoculated treated electrospun nanofiber. After 1 min shaking, 10 µl of the solution is cultured on nutrient agar plates and incubated for 24 h (Ardekani et al., 2019). ASTM E2149 is another antimicrobial standard method used for evaluating the antibacterial function of immobilized antimicrobial nanofibers under dynamic contact conditions. The antibacterial efficiency is evaluated depending on the contact time from several mints to 24 h between the bacterial solution and the sample (Ungur and Hrůza, 2017) . For both methods, the percentage of growth reduction is calculated with the R equation, mentioned above.

In this method, some known dyes are been used to probe if the entrapped bacteria are inactivated by membranes and quantify surviving bacteria, representing an operative, visual and precise antibacterial assay (Zhu et al., 2018) . For example, a common dye-based method is detecting the optimal analytical parameters for fluorescence measurements from the dyes SYTO and propidium iodide (PI). The basis of this approach is the attachment of SYTO to live-cell and propidium iodide (PI) to dead cells or cells with defected membranes. The optimal analytical parameters are used for measurement fluorescence by evaluating the intensity of emissions at 505-515 nm for SYTO and 600-610 nm for PI which interpret to quantify of the live cells 

Minimum inhibitory concentration (MIC) represents the minimum amount of antibacterial membrane, which could inhibit bacterial growth. In this method, the defined weighted of nanofiber is dissolved in water (or proper dissolvent), 100 µL of this solution is added to the first well and serially diluted by transferring 50 µL of the well pipetted content to the next well containing 50 µL media. Thereafter, 50 µL of bacterial cultures (1×10 6 CFU mL -1 ) is poured to each well and plate is incubated at 37 ºC for 24 h. To detect the bacterial growth, resazurin or piodonitrotetrazolium chloride is added to wells. The wells that turned pink (if resazurin used) or purple (if p-iodonitrotetrazolium chloride used) represents the surviving of bacteria, hence no growth inhibition. The nanofiber concentration in the last growth inhibited well is considered as the MIC value (Nthunya et al., 2017).

The bacteria retention test can also be performed with a dead-end filtration module using a vacuum filtration cell, a syringe filter holder 25mm, Millipore and a dead-end filtration cell J o u r n a l P r e -p r o o f system (Jabur et al., 2016; Daels et al., 2011; Son et al., 2009) . Before the experiments, the membrane cut diameter and sterilized. All pieces of filtration equipment are sterilized with an autoclave method for 20 min at 121 °C. The membrane is fitted into the device. After passing sterile water from the filter, the bacterial suspension is filtered through the membranes using a pressure.

In this step there are two different techniques for evaluation of bacterial retention:

1)

The filtrate is serially diluted with sterile distilled water and viable counts are assayed by plate counts. The colony count can be facilitated by staining bacterial cells with SYTO 9 fluorescent dye and using a fluorescence microscope . Then the bacterial retention ratio is calculated in terms of LRV (Log Reduction Value) by the equation:

LVR= log (C f /C p )

Where R= (1-(C p /C f )) × 100

Electrochemical disinfection can destroy bacteria and viruses by electroporation and reactive oxygen species (ROS) during a short time. Electrochemical treatment devices electrochemical disinfection regarded as an effective portable water disinfectant. Fabrication of electrospun J o u r n a l P r e -p r o o f porous membrane filter using agents to provide a conducting bed and a strong electric field, facilitate electroporation and production of ROS, which signifies the disinfection process (Hong et al., 2016; Huo et al., 2018) . For testing this ability, an electrochemical filtration device with electrospun nanofiber as a filtration membrane is used. Then, a saline solution containing bacterial suspension flows through the nanofiber filter using low voltages at a defined flow rate.

The bacterial removal efficiency is calculated by the LVR equation (Wen et al., 2017; Tan et al., 2018; Xie et al., 2020) .

In order to determine the deposition of bacteria on a filtrated membrane and the possibility of biofouling, instantly after filtration, the membrane is transferred to an autoclaved beaker filled with PBS buffer and sonicated. The bacteria in the suspended membranes are measured by counting the number of colony cells. Moreover, the morphology of trapped bacteria is investigated using SEM (Xie et al., 2020; Makaremi et al., 2016; Wen et al., 2017) .

Different kinds of electrospun nanofibers have been recently fabricated for bacterial removal from water are illustrated in Tables 1.

Usually, evaluation of the antiviral function of nano-filters is carried out using bacteriophage and Polypropylene nonwoven textile as support layer, the structure shows excellent retention of bacteria and fine solids, with 240 -400 nm pore size and operating pressure < 2 000 mbar. Naked filter is anther novel commercially application of nanofiber in household/bottled water filter with ability to remove 99.9999% of the micro-organic contaminants. Nanotrap is another commercial household water filter produced by Coway company. AstraPool, Fluidra has introduced nanofiber based product applied in filtration system for residential pools (http://electrospintech.com/products.html#.XvS_nm0zbIU).

Liquidity Nanotech Corporation has created electrospun nanofiber membrane made water purification cartridge with superior flow rate, about a cup per minute, good microbiological retention, 6-log bacteria reduction, 4-log virus reduction and 6-log cyst reduction and simple usage process (https://product.statnano.com/product/1981/liquidity-water-purification-cartridge).

PENTAIR company has produced polyethersulfone nanofiber-based cartridge for industrial water purification applications. The cartridge is an absolute barrier to bacteria and viruses: with more than 4-log reduction rate (https://www.directindustry.com/prod/pentair-x-flow/product-71363-1779744.html).

The researcher's and industry's attention to research and development of electrospun nanofibrous membranes has been growing because of its simplicity, low-cost, scalable molecules incorporation process on the fabricated non-woven mats, production of membranes with the high surface area.. High surface area to volume ratio, uniform pore size, and high pore interconnectivity and adequate antibacterial property improve the performance of the nanofibrous membrane in water disinfection application (Subramanian and Seeram, 2013) .

However, there are several major concerns to be noticed for the application of electrospun nanofiber in water disinfection. Although high surface area and porosity of the electrospun nanofiber are significant advantages, which enhance permeability and selectivity, they also lead to higher mechanical stresses. Consequently, the membrane might be compacted or deformed through the filtration process, which causes loss the porosity and subsequently decreases the Also, further experimental studies needed to conduct proper control of biomolecules release rate from nanofiber, to ensure a balance between successfully deactivate the bacteria strains and lengthen the period of the function, and minimize contamination. Therefore, fabrication of membrane representing inherent self-cleaning, antiviral, and the antibacterial and anti-biofouling feature has gained immense attention for industrial application. Recently, focusing on the production of smart antibacterial surfaces has led to a promising "kill−release" strategy. This approach proposed the fabrication of dual-functional antibacterial surfaces by incorporating biocides into non-fouling materials. These membranes are able to maintain their long-term antibacterial activity by killing bacteria attached to their surface and subsequently are potent to release the dead bacteria to reveal a clean surface (Wei et al., 2017) . Although these smart membranes are applied for biomedical applications, the strategy can be promising for further J o u r n a l P r e -p r o o f designing of novel electrospun nanofiber with these dual functions and strong long-term functional ability in water disinfection.

As it is illustrated in tables 1 and 2, despite the significant results obtained from the application of electrospinning in water filtration membrane designing, there are some gaps in this research area. For instance, there are no unanimous standard methods for evaluating the antibacterial or antiviral potential of fabricated electrospun water disinfecting filters. Moreover, most of the researchers have used static antibacterial assay approaches that are unable to represent the membrane antibacterial performance under the dynamic water filtration process. Moreover, recent related studies have not investigated comprehensibly the long-term antibacterial or antiviral performance of produced nano-membrane in water disinfection. Due to extensive endeavors aiming to produce novel smart antibacterial and antiviral membranes and, electrospun nanofibers should be developed rapidly as great candidates for a high effective anti-biofouling membrane for water treatment. The water-stable nanofibers was able to bind to two different viruses and achieved a 3.3 LRV for PPV and a 4.2 LRV.

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Recombinant production and antimicrobial assessment of beta casein-IbAMP 4 as a novel antimicrobial polymeric protein and its synergistic effects with thymol

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The effect of soft nanoparticles morphologies on thin film composite membrane performance

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Investigations into the antibacterial behavior of copper nanoparticles against Escherichia coli. Annals of microbiology

Control of biofouling on reverse osmosis polyamide membranes modified with biocidal nanoparticles and antifouling polymer brushes

Fabrication of carbon nanotubes reinforced silica composites with improved rare earth elements adsorption performance

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Evaluation of the physical and chemical characteristics of water on the removal efficiency of rotavirus in drinking water treatment plants and change in induced health risk

Optimization of wastewater treatment processes using molecular bacteriology

Advanced oxidation processes for the removal of natural organic matter from drinking water sources: A comprehensive review

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Nanoparticles composed of Zn and ZnO inhibit Peronospora tabacina spore germination in vitro and P. tabacina infectivity on tobacco leaves

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A novel gravity-driven nanofibrous membrane for point-of-use water disinfection: polydopamine-induced in situ silver incorporation. Scientific reports

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PAN nanofiber web and its antimicrobial and filtration property

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Fabrication of a novel thin-film nanocomposite (TFN) membrane containing MCM-41 silica nanoparticles (NPs) for water purification

Removal and inactivation of waterborne viruses using zerovalent iron. Environmental science & technology

Photo-crosslinked PVA/PEI electrospun nanofiber membranes: Preparation and preliminary evaluation in virus clearance tests. Separation and Purification Technology

Polyvinylidene fluoride membrane blended with quaternary ammonium compound for enhancing anti-biofouling properties: effects of dosage

Progress and challenges in photocatalytic disinfection of waterborne Viruses: A review to fill current knowledge gaps

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Polymeric antimicrobial membranes enabled by nanomaterials for water treatment

Mitigating biofouling on thin-film composite polyamide membranes using a controlled-release platform



