A review of membrane approaches and technologies for the removal of heavy metals from water and wastewater

Removing heavy metals from water and wastewater is one of the most important steps in the purification process, which has a direct impact on human and nature health. Daily, a large amount of heavy metals and various ions enter the underground water table in factories and processing and agricultural units. The entry of these ions into the water and their excessive increase over time leads to many diseases such as kidney diseases, damage to the liver and nervous problems and a decrease in the strength of the body's immune system. In general, the separation of heavy metal ions from wastewater, especially wastewater from industries and mines, has been investigated more and more in recent years. There are heavy metals in the water and wastewater of many industries, including metal plating, mining operations, tanneries, wood and chipboard factories, industrial paint factories, textile factories, oil refining and refining, etc. Therefore, removing heavy metals from water and wastewater is very necessary. The process of removing heavy metals from industrial water is also called industrial water desalination. The process of removing heavy metals is also used for soil in addition to water and waste water and waste from industries and factories. One of the most prominent heavy metals in industrial wastewater is lead. The maximum permissible amount declared by EPA and WHO for lead in drinking water is ۱۵ and ۵۰ µg/L, respectively. Alternative methods are used to remove lead from water and wastewater. Chemical sedimentation, ion exchange, reverse osmosis, membrane filter and absorption methods are among the lead removal methods. These methods have the same mechanism for the removal of other metals. Entering the industrial revolution and the significant growth of various industries faced an increase in the amount of heavy metals in underground water, which eventually became a big challenge. Because the entry of heavy metal ions such as arsenic, mercury, lead, nickel, copper, chromium and cadmium into the body leads to many diseases in humans, animals and aquatics. According to the standards provided by several organizations such as WHO, the maximum allowable amount of heavy metals in drinking water is equal to: Mercury: ۰.۰۰۰۰۳ mg/L Lead: ۰.۰۰۶ mg/L Arsenic: ۰.۵ mg/liter Cadmium: ۰.۰۱ mg/liter Chromium: ۰.۰۵ mg/liter Copper: ۰.۲۵ mg/liter Nickel: ۰.۲ mg/liter Zinc: ۰.۸ mg/L. Unfortunately, the effluents of various industries such as metal processing and plating factories, textile, agriculture, dyeing, refineries and petrochemicals, food processing and manufacturing factories, metal corrosion and rusting, as well as mines contain a large amount of heavy metals. So that water extracted from underground water tables may contain metal ions more than the standard size. As a result, the only solution will be to use methods to remove heavy metals from water and wastewater in the water purification stages. In this research, membrane approaches and technologies for removing heavy metals from water and wastewater are reviewed.