Bioaerosols are airborne particles of biological origin, including viruses, bacteria, fungi, capable of causing infectious diseases, allergies or toxins. In particular, indoor air biological molecules have been found to accumulate in large numbers on the filters of the heating, ventilation and air conditioning (HVAC) systems . It is thought that outdoor air pollution and unhygienic installation of HVAC systems often result in lower indoor air quality. Furthermore, organic or inorganic materials deposited on the filter medium after the gas purification contribute to the growth of microorganisms. WHO estimates that 50% of biological pollution in indoor air comes from air handling systems and the formation of harmless microorganisms such as bacteria and fungi. Pathogens are found in air filters. Most of these pathogens produce mycotoxins, which are dangerous to human health, so the growth of microorganisms in the air filter will be reduced by integrating antibacterial silver nanoparticles. air purifier.
The antimicrobial effect of nano-silver on the bacterial contamination of an activated carbon filter (ACF) was studied by Yoon et al. . The results showed that the silver nano-coated “ACF filter” effectively removes biological impurities. Antimicrobial activity analysis of the silver nano-coated “ACF filter” showed that the two bacteria “Bacillus subtilis” and E. coli were completely inhibited within 10 and 60 minutes, respectively.
It was found that the silver nano-coating did not affect the physical properties of the ACF filter such as pressure drop and filtration efficiency, however, the adsorption efficiency was reduced due to the silver NPs coating. Therefore, the authors also propose that the number of nano-silver on the “ACF filter” should be optimized to avoid excessive reduction of their adsorption properties and to display effective antimicrobial activity.
Recently, Jung et al.  generated carbon Nanotubes (CNT) hybrid nanoparticles coated with silver nanoparticles (Ag / CNTs) using aerosol misting and thermal evaporation / condensation and their applicability was examined. antibacterial gas. The aerosols CNT and AgNPs mix together and attach to form Ag / CNTs.
The antibacterial activity of the Ag / CNT coated filter was tested against Gram-positive bacteria S. epidermidis and E. coli Gram-negative. It was found that when Ag / CNTs were deposited on the surface of the air purifying medium, the antimicrobial activity against the tested bioaerosol bacteria was enhanced, compared with the deposition of CNTs or single AgNP. while the filter pressure reduction and bioaerosol filtration efficiency were similar at almost zero levels of CNT deposition.
It was reported that the surface area of nano-silver was enhanced by CNTs, therefore the main reason for the antibacterial filtration efficiency of Ag / CNTs was higher than that of pure Ag-NPs. Polymer gas filters made of polypropylene and silver nitrate (AgNO3) have been tested for bacterial survival .
Research demonstrates that the addition of AgNO3 antibacterial agent to the filters is effective to prevent the filter bacteria from entering. The presence of the antimicrobial compound AgNO 3 in the air filter reduces the number of bacteria, which has been observed in the case of both Gram-negative and Gram-positive strains, Micrococcus luteus, Micrococcus roseus, B. subtilis and Pseudomonas luteola.
The marked reduction in bacterial cell growth on silver-treated filters makes antimicrobial filter treatment a real necessity for the future.
– Disinfect drinking water
Water is one of the most important substances on Earth and is essential for all living things. About 70% of the Earth’s area is covered with water, but only 0.6% is suitable for human consumption needs.
Safe drinking water is an important social and health problem in many developing countries . According to WHO, at least 1 billion people do not have access to safe drinking water. Drinking water pollution and subsequent outbreaks of waterborne diseases are the leading cause of death in many developing countries .
Furthermore, the spectrum and incidence of some infectious diseases are increasing worldwide, so there is a great need for therapies to control microbial contamination in water and reduce the number of Waterborne disease.
Significant interest has arisen in the use of nano-silver for water disinfection. The silver nanoparticles (AgNPs) can be homogenized onto the porous material to form the nano silver sponge composite, by using 3-aminopropyltriethoxysilane (APTES) as the bonding molecule .
This composite can be stored for a long time and durable during the washing process without losing NPs. The antiseptic properties of the AgNPs foam, as an antibacterial water filter, were tested with E. coli.
It was found that at a flow rate of 0.01 l / min, the output E. coli count was zero while the inlet water had a bacterial count of 105 CFU ml −1. It also confirmed that the bonds between the AgNP molecules and the foam are based on the coordination bonds between the -NH2 group at the top of the APTES molecule and the silver atoms on the surface of the NPs.
This type of connection ensures that the AgNP molecules are tightly fixed to the inner channel wall of the porous ceramic so that they can release enough silver ions to fight bacteria. Such nano-silver porous ceramic composites have been successfully tested in purifying drinking water . In addition, the AgNP molecule can be coated on conventional polyurethane (PU) foam by overnight exposure to the chemical.
Colloidal AgNPs . The NPs are stable on foam and are not washed away with water and the morphology of the foam is retained after coating. The NP bond is due to its interaction with the PU nitrogen atom. When a flow rate of 0.5 l min -1 was reached, after a few seconds the output of E. coli was 0 while the inlet water had a bacterial count of 105 CFUml -1.
AgNP molecules are also successfully formed on macroporous “methacrylic acid copolymers” to disinfect water . This suggests that AgNP is formed on these copolymer grains by chemical reduction method that is stable under water washing and that their stability is due to AgNP’s interaction with the “-COO−” carboxylic functional group on ” copolymer grain ”.
The nano-silver-containing polymers showed a highly effective antiseptic ability against two strains of gram-negative bacteria (E. coli, P. aeruginosa) and two strains of gram-positive bacteria (B. subtilis, S. aureus) . AgNPs conjugated copolymerized particles were effective in reducing the number of bacteria to zero for all strains tested. The adsorption or adhesion analysis of bacteria showed that “copolymer particles” containing nano silver “did not have any adsorption / adhesion of bacterial cells.
– Groundwater and wastewater disinfection by biological methods
The effects of nano-silver on microbial communities in wastewater treatment plants were evaluated  and found that the initial wastewater biofilm had a high tolerance to AgNP treatment.
With the application of 200 mg -1 AgNPs, the biofilm bacterial reduction as measured by the number of heterotrophic plates was negligible after 24 hours. Biofilmcan provides physical protection against bacteria under AgNP treatment and extracellular polymers (EPS) can play an important role in this defense.
Sensitivity to silver nanoparticles is different for all microorganisms in the biofilm community. The study illustrates two implications: (i) nano silver can affect the structure of biofilm microbial communities in wastewater, depending on the characteristics of each strain, for example, the ability to generate EPS and growth and community interaction between strains; and Mpenyana-monyatsi et al. , (ii) the effect of Ag-NPs on plankton cells  differs from the effect of the effluent biofilm.
The bacteria in the biofilm treated as the pure culture medium isolated were much more sensitive to Ag-NP, in contrast to the bacterial mixture in the biofilm. Some time ago, a new, cost-effective filter material coated with nano-silver was developed to disinfect groundwater , thus revealing that nano-silver was successfully deposited on a zeolite resin, sand, fiberglass, anions and cations.
The performance of these media as an antibacterial water filtration system has been tested to remove pathogenic bacteria E. coli, S. typhimurium, S. dysenteriae and V. cholera from groundwater. The results showed the maximum microbial elimination efficiency of the Ag / cation resin filter, with complete (100%) removal of all targeted bacteria and the lowest by the Ag / zeolite filter, with removal rate 8-67%.