**4.4 Microalgal**

Nanoparticles can be utilized for a variety of applications, including medical treatment, solar and fuel cells for efficient energy generation, water, and air filters to minimize pollution, and as catalysts in existing industrial processes to remove the usage of harmful ingredients. Wet techniques are the most traditional and widely utilized ways of producing nanoparticles (physical and chemical). These strategies are classified into two approaches: top-down and bottom-up. Growing nanoparticles in a liquid medium containing reducing and stabilizing agents such as potassium bitartrate, sodium dodecyl benzyl sulfate, methoxypolyethylene glycol, polyvinyl pyrrolidone, or sodium borohydride are how nanoparticles are created chemically. In addition, physical processes include pyrolysis and attrition. Unfortunately, the physical and chemical procedures utilized in both approaches have some implications due to their poor environmental effect, lengthy manufacturing methodology, and prohibitively high cost. According to research, nanoparticles attract atoms and molecules owing to their high surface energy, modifying their surface characteristics. As a result, they are unable to live in their natural habitat in their naked state. Nanoparticles are not suitable for therapeutic use due to these environmental

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

interactions. This mechanism of action has raised awareness about the importance of developing nontoxic and environmentally friendly procedures for the assembly and synthesis of nanoparticles.

Physical processes also include pyrolysis and attrition. Unfortunately, both systems' physical and chemical procedures have some issues because of their bad environmental impact, delayed production methodology, and excessively expensive cost. Nanoparticles, according to study, attract atoms and molecules due to their high surface energy, changing their surface features. As a result, they are unable to survive in their native habitat while nude. Because of these environmental interactions, nanoparticles are not suited for therapeutic usage. This mechanism of action has increased awareness of the importance of developing nontoxic and environmentally friendly procedures for nanoparticle assembly and synthesis and mode of action as shown in **Table 1** [59].


To make gold nanoplates, the microalgal biomass is lyophilized and then exposed to RP-HPLC, or reverse-phase high-performance liquid chromatography, until the gold shape-directing protein (GSP), which controls the shape of nanoparticles, is separated. Furthermore, this protein is exposed to an aqueous HAuCl4 solution, resulting in the formation of gold nanoparticles of various forms. In the case of silver nanoparticles, PLW (proteins with low molecular weight) and PHW (proteins with high molecular weight) found in microalgae biomass is responsible for converting silver ions into their metallic counterparts. Tang et al. biosynthesized silver and gold nanoparticles using a fine powder of *Spirogyra insignis* (Charophyta) [58].

Many studies on the fate of NPs and their effects on biological wastewater treatment have been conducted, and many successes have been reported [60].


organic contaminants. Under most situations, the effects are dose-dependent, and exposure length (short-term or long-term) also plays a role in unfavorable consequences.

