How are heavy metals typically removed from wastewater?

Heavy metals are commonly removed from wastewater through a process known as precipitation using hydroxide. This method involves adding alkaline substances, like lime or caustic soda, to the wastewater, which raises the pH. When the pH is increased, heavy metals react with hydroxides present in the solution, forming insoluble metal hydroxides. These compounds then precipitate out of the liquid phase, allowing them to be separated from the water through sedimentation or filtration.

Using hydroxide precipitation is advantageous because it is an effective method for treating heavy metal pollution, making it easier to meet environmental discharge standards. The process is not only efficient for metals like lead, cadmium, and copper, but it is also relatively simple and cost-effective compared to some other treatment methods.

The other methods listed—such as filtration through activated carbon, evaporation, and biodegradation—are not primary techniques for removing heavy metals from wastewater. Filtration with activated carbon is more suited for organic contaminants and specific odor compounds, while evaporation is generally used for reducing overall water volume. Biodegradation is not effective for heavy metals, as they do not break down biologically. Therefore, precipitation using hydroxide is the most appropriate choice for the removal of heavy metals in wastewater treatment scenarios.