**3. Effect of heavy metals on water**

An increase in anthropogenic activity has resulted in the release of numerous dangerous compounds into water resources, endangering aquatic ecosystems and the environment. Heavy metal ions, which are very poisonous, non-degradable, and tend to bioaccumulate and biomagnify, are the most serious contributors to water pollution [15]. Toxic contaminants from anthropogenic businesses, such as mining or agricultural operations that do not use environmentally friendly procedures, or natural phenomena, such as volcanoes, earthquakes, or storms, are virtually always present in wastewaters [52]. Heavy metals are now one of the most important environmental hazards. To safeguard people and the environment, hazardous heavy metals should be eliminated from wastewater. Chemical precipitation, ion exchange, adsorption membrane filtration, electrochemical treatment procedures, and other ways are utilized to remove heavy metal ions [53]. It is regarded as one of the most hazardous to human health among heavy metals. Precipitation, coagulation/flocculation, ion exchange, reverse osmosis, complexation/sequestration, and electrochemical processes are all common ways of removing heavy metal ions from wastewater. These technologies are not commercially viable, and they may result in the production of harmful by-products [54]. As a result, removing unwanted metals from water systems effectively and thoroughly remains critical yet difficult work for environmental engineers. Several strategies for removing heavy metals from water have been presented in recent years [55].

#### **3.1 Treatment of water contaminated with heavy metals**

Because the composition of wastewater is exceedingly intricate, and the characterization of target species will be severely influenced by the many coexisting compounds, current technologies will have a difficult time recognizing the detailed composition. Physicochemical tests such as complexometric titration, ion exchange, and stripping voltammetry were used to evaluate the complexation features in early investigations, making it difficult to obtain the exact coordination condition of heavy metals [56]. Micellar-enhanced ultrafiltration (MEUF) is a newly discovered water treatment technique that has been proved to be an effective technology for removing heavy metals even at low concentrations [7].
