The objective of this study is to investigate and assess the use of in situ deposit nanosilver (nAg2O) or nanocopper oxides (nCuO) into nonwoven polyester fabric (NWPF) as a safe and effective antibacterial filter of pollution from domestic wastewater. The bactericidal effect of both nAg2O and nCuO was examined against Gram-negative bacteria (
Municipal wastewater is one of the major sources of aquatic pollution, particularly in developing countries. Microbial contamination of water poses a serious threat to public health. Accordingly, wastewater should be disinfected to prevent the transmission of infectious diseases and to ensure that water is safe for human contact and the environment [
Moreover, the emergence of nanoscience and nanotechnology in the last decade presents opportunities for exploring the bactericidal effect of metal nanoparticles. This has been attributed to their small size and high surface to volume ratio, which allows them to interact closely with microbial membranes, and is not merely due to the release of metal ions in solution [
Furthermore, nanotechnology-derived products that reduce the concentrations of toxic compounds to sub-ppb levels can be used to support the achievement of water quality standards and health advisories [
The objective of this study was to in situ deposit nanometal oxides, such as nanoparticles of silver and copper oxides, into nonwoven polyester fabric, to investigate and asses the capability of nanoparticles, deposited in an innovative fabric, as disinfectants for the removal of bacterial indicators of pollution from secondary treated domestic wastewater.
Nonwoven polyester fabric (NWPF) was purchased from the local market. Silver nitrate and copper chloride were purchased from Merck (Germany). The used hydrogen peroxide (H2O2) and other laboratory chemicals were of analytical grade purchased from Sigma-Aldrich Chemical Company.
The nanometal oxides deposition was performed by padding the polyester fabric samples in an aqueous solution containing 50 mmol of metal salts solution (silver nitrate or copper chloride) and 1.5 wt. % (w/v) of polyvinyl pyrrolidone (PVP) as stabilizing agent. The fabric was then squeezed to a wet pick up 100%. The fabric was padded twice in the reducing-oxidizing bath containing 4 g/L sodium hydroxide and 10 mL H2O2 (35%) at pH 9.5, then squeezed to a wet pick up of 100%. The treated fabric was dried at 50°C for 10 minutes, then thoroughly washed with water for 45 minutes at 50°C and dried for 20 minutes at 50°C.
Treated polyester fabric with nanometal oxides was examined qualitatively and quantitatively using energy dispersive X-ray spectrum (SEM-EDX), coupled with a scanning electron microscope (type JXA-840—electron probe micro-analyzer—JOEL) and a transmission electron microscope (TEM) that gave images of cross-section of treated fabric samples. Total silver concentrations were determined according to Standard Methods for the Examination of Water and Wastewater [
Triplicate samples of one gram of fabric were transferred to shaking bottles with 10 mL de-ionized water. The bottles were then sealed with Para film lids and secured, rotated end-over-end for 48 h at 30 rpm, and then filtered through a 0.45
Two Gram-negative bacterial strains (
A comparison between treated NWPF with nAg2O and nCuO using a disk of 6 mm diameter of fabric was carried out using agar diffusion disk test [
Three overnight grown bacterial suspensions of
Domestic wastewater effluent treated in a Packed bed upflow anaerobic sludge blanket (P-UASB) followed by Inclined Plate Settler (IPS) then Multistage Roughing Fine Sand Filtration (MSRFF) was used as a real source for testing the efficiency of antibacterial filter [
In situ deposition of nanometal oxides into NWPF with a thickness of 1.82 mm was used for disinfection of various microbial strains of Gram-positive and Gram-negative bacteria. Also, disinfection of a real secondary treated wastewater, as a case study, was investigated. Cross-section image of dried fabric was taken with a scanning electron microscope in high vacuum mode after coating with approximately 10 nm of gold to observe fabric asymmetry and its pore structure (Figure
SEM of polyester fabric.
In addition, the X-ray diffraction(XRD) patterns of the NWPF before and after loading with nanometal oxides are shown in Figure
XRD patterns of polyester fabric (A) before loading and (B) after loading with nanometal oxides.
Transmission electron micrograph of cross-section fabric (a) after loading with nanosilver oxide and (b) after loading with nanocopper oxide.
Silver nanoparticles
Copper nanoparticles
The two types of in situ nanometal oxides fabrics, namely, nAg2O and nCuO were examined for the removal of bacterial indicators of pollution using the disk diffusion test. Table
Effect of nAg2O and nCuO on microbial removal using agar diffusion disk test.
Types of polyester nanoparticles filters | Gram-negative | Gram-positive | ||
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nAg2O | +++ | +++ | ++ | + |
nCuO | ++ | + | ++ | − |
+: low effect (<5 mm diameter); ++: moderate effect (5–15 mm diameter); +++: high effect (>15 mm diameter); −: no effect.
It is recognized that nanoparticles may have undesirable and unforeseen effects on the environment and in the ecosystem [
The morphology of fabric using the SEM micrographs after nano-Ag-oxide (nAg2O) loading is presented in Figure
SEM-EDX analysis of fabric after nAg2O loading.
To confirm the morphology of the fabric used, it was treated with gold (Au) layer and recognized by Scanning Electron Microscopy (SEM). The energy dispersive spectrometer (EDS) spectrum for the fabric after firing was also recorded. The SEM image indicated that Ag was well distributed inside the fabric as shown in Figure
SEM-EDX micrograph with Au layer for fabric after nAg2O loading.
The effect of contact time of nano-Ag2O fabric and three bacterial strains (
Effect of contact time for bacterial reduction using nano-Ag-oxide.
Bacterial strain |
Contact time | CFU/100 mL | % of removal | |
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Control of fabric without nAg2O | Fabric with nAg2O | |||
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15 min |
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30 min |
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60 min |
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120 min |
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180 min |
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24 h |
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15 min |
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30 min |
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60 min |
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120 min |
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180 min |
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24 h |
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15 min |
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30 min |
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60 min |
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120 min |
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180 min |
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24 h |
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Physicochemical and bacterial indicators analyses of raw and secondary treated domestic wastewater effluent are shown in Table
Physicochemical and bacterial indicators of raw and treated wastewater*.
Parameters | Raw wastewater | Treated effluent** |
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pH |
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Total suspended solids (TSS) mg/L |
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Chemical oxygen demand (COD) mgO2/L |
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Biological oxygen demand (BOD) mgO2/L |
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Total coliform (MPN-index/100 mL) |
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Fecal coliform (MPN-index/100 mL) |
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The effect of exposure time of nano-Ag-oxide incorporated in nonwoven polyester fabric, on the bacteria, was investigated. The results depicted in Table
Effect of contact time for reduction of total and fecal coliforms from secondary treated effluent using nano-Ag-oxide.
Time | Control | Nano-Ag-oxide | ||||
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Total coliforms (MPN-index/100 mL) | Fecal coliforms (MPN-index/100 mL) | Total coliforms | Fecal coliforms | |||
Conc. |
% of removal | Conc. |
% of removal | |||
Zero time |
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2 min |
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5 min |
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10 min |
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15 min |
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20 min |
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5.3 |
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30 min |
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5 |
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Also, fecal coliforms were reduced by one order of magnitude (from 260 to 15 MPN-index/100 mL) after 10 min. These residual values are far less than the concentration of coliforms stated in the Egyptian Code of Standards (501-2005) for reuse of wastewater for agricultural purposes (1000 MPN-index/100 mL) [
The results were also confirmed by the image shown in Figure
Cross-sections of treated polyester fabric taken after disinfection.
The results indicated that bactericidal effect of nano-Ag-oxide is a promising alternative technique to the traditional chemical disinfectants which generate harmful disinfection byproducts. Silver nanoparticles are stable and are not washed away by water leaching test after 48 h. In situ deposition of nanometal oxides into nonwoven polyester fabrics proved to be a very effective antibacterial filter against
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors would like to thank the Science and Technology Development Fund and the Egyptian Academy of Scientific Research and Technology for funding this project under Grant no. 1088.