**3.2 Metallic nanoparticles**

Metallic nanoparticles have a great deal of potential for many forms of environmental cleanup because of their adaptability. One, two, or three metals and their oxides can be found in a variety of nanostructures. The shape-controlled, stable, and monodispersed properties of metal-based nanomaterials have been thoroughly studied using physical and chemical methods. Water treatments such as adsorption, photodegradation, membrane separation, and chemical disinfection can all benefit from these positive qualities. They have been utilized for self-cleaning surfaces, air purification, and water disinfection because of their noteworthy antibacterial, antifungal, and antiviral activity, which is employed as water disinfectants [26, 27].

### **3.3 Nanoparticles based on oxidation**

Inorganic oxide-based nanoparticles are often created by combining metals and non-metals. The removal of harmful contaminants from wastewater makes considerable use of these nanoparticles. There are also ferric oxides titanium oxides [28], titanium oxide/dendrimers composites [28–30], zinc oxides [31], magnesium oxides, manganese oxides [32, 33] and ferric-oxide [34]. High BET surface area, less environmental impact, less solubility, and lack of secondary pollutants are the characteristics of oxide-based nanoparticles [35].

## **3.4 Silver based nanoparticles**

Due to its low toxicity, water-based microbial inactivation, and well-documented antibacterial action, silver is the substance that is utilized the most frequently.

Silver salts like silver nitrate and silver chloride are used to make silver nanoparticles, which are known to be excellent biocides. Smaller Ag nanoparticles (8 nm) were the most effective, despite the fact that the antibacterial action is size dependant; increasing particle size (11–23 nm) resulting in reduced bactericidal activity.

Additionally, truncated triangular silver nanoplates outperformed spherical and rod-shaped nanoparticles in terms of antibacterial efficacy, demonstrating the importance of shape.

Ag nanoparticles' bactericidal effects can occur through a variety of methods, such as the production of free radicals that damage bacterial membranes, interactions with DNA, adherence to cell surfaces that change the characteristics of the membranes, and damage to enzymes.

Immobilized nanoparticles have become more significant because of their potent antibacterial properties. Gram-positive and Gram negative bacteria have been observed to be particularly sensitive to embedded Ag nanoparticles. In a study, cellulose acetate fibers that had been directly electrospun with silver nanoparticles incorporated in them were demonstrated to be efficient against both types of bacteria. Ag nanoparticles are also added to several kinds of polymers to create antibacterial nanocomposites and nanofibers. In a study, antimicrobial nanofilters made of poly (−caprolactone) based polyurethane nanofiber mats with Ag nanoparticles were created.

Ag nanoparticles are included in several types of nanofibers that have been manufactured for antimicrobial applications and have shown excellent antibacterial capabilities [36–39].

Ag nanofiber-coated polyurethane foam water filters have demonstrated effective antibacterial activities against *Escherichia coli* (*E. coli*). Other examples of inexpensive drinkable microfilters made with Ag nanoparticles exist and can be applied in rural areas of developing nations [40].

Ag nanoparticles are also used in water filtration membranes, such as polysulfone membranes, where they are effective in reducing biofouling and are effective against a wide range of bacteria and viruses. These membranes with Ag nanoparticles demonstrated effective antibacterial properties against *E. coli*, Pseudomonas, and other microbes. The efficiency of Ag nanocatalyst alone and in combination with carbon covered in alumina for the destruction of microbiological pollutants in water has been proven.

Although Ag nanoparticles have been successfully employed to destroy bacteria, viruses, and reduce membrane biofouling, their long-term effectiveness against membrane biofouling has not been observed. This is mostly because silver ions are lost over time.

Therefore, additional efforts to stop this loss of silver ions are needed in order to permanently control membrane biofouling. As an alternative, the problem can be resolved by doping Ag nanoparticles with other metallic nanoparticles or its composites with metal-oxide nanoparticles. This may also result in the simultaneous removal of inorganic and organic substances from water and wastewater [41].

#### **3.5 Titanium based nanoparticles**

TiO2 nanoparticles have mostly been utilized as a catalyst in organic reaction and wastewater breakdown. Because of their special characteristics and lower tendency to aggregate due to the existence of greater repulsive forces, microorganisms (such as bacteria) are often used in the biosynthesis of TiO2 nanoparticles. The morphological structures of TiO2 nanoparticles, such as spherical titania (TNP), titania nanotubes

*Sewage Treatment Using Nanoparticles DOI: http://dx.doi.org/10.5772/intechopen.109407*

(TNT), and titania nanosheets, have been extensively researched in the field of water purification along with development and improvement. High specific surface area, pore volume, and pore size are typical characteristics of TNP. As a result, TNP offers an active site that is very easy to reach and can be employed for organic pollutant adsorption. The typical hydrothermal method for producing TNT from TNP uses a potassium hydroxide/sodium hydroxide (KOH/NaOH) solution. TNT is anticipated to be more advantageous than TNP because of its tubular structure, which also provides bigger pore volume and a higher interfacial charge carrier transfer rate. TNT also offers the high hydrophilicity qualities of TiO2 [42].

One of the most significant chemically stable nanoparticles, titanium dioxide (TiO2), has attracted the most interest for its use as a photocatalyst and adsorbent in the removal of contaminants from wastewater. Some microorganisms, such as bacteria, can biosynthesize these nanoparticles as reducing agents for nanofactories in order to create nontoxic, environmentally friendly ways to generate nanoparticles [43].

#### **3.6 Iron based nanoparticles**

Ferric oxide is a cheap substance for the adsorption of toxic metals due to the natural abundance of iron and its straightforward production technique. It is an environmentally benign substance that can be utilized in contaminated environments without raising the risk of secondary contamination. The pH, temperature, amount of adsorbent, and incubation period all play a role in how different heavy metals bind to Fe2O3 nanoparticles. Different researchers modified the surface of Fe2O3 to boost its adsorption capability. Recently, there have been multiple publications on the use of magnetic oxides, particularly Fe3O4, as nanoadsorbents to remove hazardous metal ions such Ni2+, Cr3+, Cu2+, Cd2+, Co2+, Hg2+, Pb2+, and As3+ from wastewater. For instance, Shen et al. [44] have found that pH, temperature, the quantity of the adsorbent, and the incubation duration all have a significant impact on the adsorption efficiency of Ni2+, Cu2+, Cd2+, and Cr6+ ions by Fe3O4 nanoparticles. According to Palimi et al. [45], 3 aminopropyltrimethoxysilane was used to modify the Fe2O3 nanoparticles' surfaces.

When it comes to simultaneously removing many contaminants from wastewater, such as Cr3+, Co2+, Ni2+, Cu2+, Cd2+, Pb2+, and As3+, nano-adsorbents have strong affinity.

#### **3.7 Manganese oxide based nanoparticles (MnO)**

Due to their high BET surface area and polymorphism structure, manganese oxide (MnOs) nanoparticles have remarkable adsorption capacity [46]. It has been frequently utilized to remove several heavy metals from wastewater, including arsenic [47]. Hydrous manganese oxide (HMO) and nanoporous/nanotunnel manganese oxides are the most commonly used modified MnOs. HMO was created by mixing MnSO4H2O into a NaClO solution. The inner-sphere is usually responsible for the adsorption of numerous heavy metals on HMOs, including Pb (II), Cd (II), and Zn (II). Divalent metals did, however, adsorb on the surface of HMOs in two stages. Metal ions first adsorb on the outside surface of HMOs, and then intraparticle diffusion occurs .

#### **3.8 Zinc oxide (ZnO) based nanoparticles**

For the adsorption of heavy metals, zinc oxide (ZnO) possesses a porous micro/ nanostructure with a high BET surface area. For the removal of heavy metals from wastewater, nano assemblies, nano-plates, microspheres with nano-sheets, and hierarchical ZnO nano rods are frequently utilized as nano-adsorbents In comparison to commercial ZnO, the aforementioned modified forms of ZnO nano-adsorbent exhibit a high removal effectiveness of heavy metals. ZnO nano-plates and porous nano-sheets were utilized to remove Cu (II) from wastewater. These modified ZnO nano-adsorbents exhibit greater Cu (II) removal effectiveness compared to commercial ZnO because of their distinctive micro/nanostructure. Additionally, nano-assemblies were employed to eliminate a variety of heavy metals, including Co2+, Ni2+, Cu2+, Cd2+, Pb2+, Hg2+, and As3+. Due to their electropositive character, microporous nano-assemblies exhibit strong affinity for the adsorption of Pb2+, Hg2+, and As3+. According to Kumar et al. [48] mesoporous hierarchical ZnO nano-rods have a good removal efficiency for Pb (II) and Cd (II) from wastewater.

Singh et al. [49] reported the removal of numerous harmful metal ions from wastewater using porous ZnO nano-assemblies, including Co2+, Ni2+, Cu2+, Cd2+, Pb2+, Hg2+, and As3+. It has been claimed that Hg2+, Pb2+, and As3+ demonstrate superior removal efficiency (63.5% Hg2+, 100% Pb2+, and 100% As3+) because of their stronger attraction to ZnO nano-assemblies due to their high electronegativity.

#### **3.9 Magnesium oxide based nanoparticles (MgO)**

Magnesium oxide (MgO) and iron oxide (Fe2O3) are potential metal oxide nanoparticles (NPs) for the adsorption of textile and tannery wastes. Due to their nanostructure and numerous active sites, these NPs have large surface areas and a high capacity for the adsorption of heavy metals. Ecosystem harm from NP biotreatment is nonexistent. In earlier research, for the purification of textile colors and the eradication of particular heavy metals magnesium oxide (MgO) is utilized. MgO microspheres are a new structure that can increase the removal of heavy metals' adsorption affinity. The shape of NPs has undergone many forms of alteration to boost the adsorption capability of MgO. These include nanorods, nanobelts, fishbone fractal nanostructures, nanowires, nanotubes, nanocubes, and three-dimensional things. Kiran et al. [50], reported that the remediation of Reactive Brown 9 dye was then carried out using MgO-NPs once the reaction's key variables (dye concentration, nanoparticle concentration, pH, and temperature) had been optimized. The highest degree of decolorization (95.8%) was achieved at 0.02% dye concentration, 0.003 mg/L MgO-NP concentration, pH 4, and 40°C. The mineralization of the examined dye samples was evaluated using TOC and COD, and their values were found to be 88.56% and 85.34%, respectively. Other troublesome colors could also be treated using the magnesium oxide nanoparticles in stages. It is imperative to get rid of these harmful colors because they ruin the aquatic environment and spread several diseases.

#### **3.10 Al2O3 based nanoparticles**

Aluminum oxide nanoparticles (ANPs) are used in a variety of industrial and personal care products. *E. coli* has been examined for the growth-inhibitory effect of alumina nanoparticles over a broad concentration range (10–1000 g/mL). These metal oxides' antibacterial properties are ascribed to the production of reactive oxygen species (ROS), which results in cell wall breakdown and eventual cell death. However, alumina nanoparticles might neutralize free radicals. The ability of these

NPs to protect cells from oxidative stress-induced cell death appears to depend on the particle's structure but is unrelated to its size between 61,000 nm [51].

### **3.11 Copper based nanoparticles**

A variety of bacterial pathogens responsible for hospital acquired infections were successfully eliminated by CuO nanoparticles (CuO NPs). However, a significant portion of CuO NPs are scavengers. The ability of these NPs to protect cells from oxidative stress-induced cell death appears to depend on the particle's structure rather than its size between 61,000 nm. It is necessary to produce a bactericidal action [52].

### **3.12 Curcumin-loaded nanocarriers for hospital wastewater treatment**

Water contamination with a wide range of chemical, microbiological, and toxic substances is a growing environmental concern. In a study by (Mozhgan et al), the heated high-speed homogenization process was used to create eco-friendly curcumin-loaded nanostructured lipid carriers (NLC-curcumin). NLC-curcumin had an average particle size of 137.9 3.21 nm and a zeta potential of −23.36 3.5 mV. The nanoparticles' morphology, thermal behavior, antioxidant properties, and infrared spectroscopy were also studied. The potential of NLC-curcumin on bacterial growth reduction in the actual environment of hospital wastewater was evaluated using colony forming unit per milliliter (CFU/ml) analysis. The results show that 0.125 M NLC-curcumin in Mueller-Hinton agar media significantly lowers the proportion of wild bacteria strains in autoclaved wastewater at 37°C. NLC-Curcumin (0.125 M) significantly reduced the percentage of the microbial total count at 25°C in the original hospital wastewater treatment as shown in **Table 1** [53].
