Question

Waste water treatment mechanism of nanoparticles

Answer 1

Nanomaterials for Water and Wastewater Treatment

2.1. Zero-Valent Metal Nanoparticles

2.1.1. Silver Nanoparticles

Silver nanoparticles (Ag NPs) are highly toxic to microorganisms and thus have strong antibacterial effects against a wide range of microorganisms, including viruses [11], bacteria [10], and fungi [12]. As a good antimicrobial agent, silver nanoparticles have been widely used for the disinfection of water.

The mechanism of the antimicrobial effects of Ag NPs is not clearly known and remains under debate. In recent years, several theories have been put forward. Ag NPs have been reported to be able to adhere to the bacterial cell wall and subsequently penetrate it, resulting in structural changes of the cell membrane and thus increasing its permeability [13]. Besides, when Ag NPs are in contact with bacteria, free radicals can be generated. They have the ability to damage the cell membrane and are considered to cause the death of cells [14]. In addition, as DNA contains abundant sulfur and phosphorus elements, Ag NPs can act with it and thus destroy it. This is another explanation for the death of cells caused by Ag NPs [15]. What is more, the dissolution of Ag NPs will release antimicrobial Ag+ ions, which can interact with the thiol groups of many vital enzymes, inactivate them, and disrupt normal functions in the cell [16].

With the development of nanotechnology, Ag NPs have been successfully applied in water and wastewater disinfection in recent years. Direct application of Ag NPs might cause some problems, such as their tendency to aggregate in aqueous media that gradually reduces their efficiency during long-term use [17]. Ag NPs attached to filter materials have been considered promising for water disinfection due to their high antibacterial activity and cost-effectiveness [18].

Via the in situ reduction of silver nitrate, Ag NPs have been deposited on the cellulose fibers of an absorbent blotting paper sheet (see Figure 1). The Ag NPs sheets showed antibacterial properties towards suspensions of Escherichia coli and Enterococcus faecalis and inactivated bacteria during filtration through the sheet. Moreover, the silver loss from the Ag NPs sheets was lower than the standards for silver in drinking water put forward by Environmental Protection Agency (EPA) and World Health Organization (WHO) [19]. Therefore, for water contaminated by bacteria, filtration through paper deposited with Ag NPs could be an effective emergency water treatment. Besides, Ag NPs synthesized by chemical reduction have been incorporated into polyethersulfone (PES) microfiltration membranes. The activity of microorganisms nearby the membranes was observed to be remarkably suppressed. The PES-Ag NPs membranes exhibited strong antimicrobial properties and held great potential in application for water treatment

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