Design of Heavy Metal Wastewater Treatment
Introduction
In today’s world, water is a precious resource which is quickly diminishing. It is essential to conserve and protect water resources and to treat wastewater appropriately before returning it back to the environment. Treating wastewater is important because the wastewater may contain heavy metals, organic matter and other contaminants which can be harmful to the environment if they are not removed properly. This paper will discuss the methods and techniques used to remove heavy metals from wastewater, as well as the design of a heavy metal wastewater treatment system.
Heavy Metal Removal Methods
Heavy metals can be removed from wastewater through physicochemical methods, biological methods, and sorption techniques. Although some of these methods work better for certain metals than others, all of them are effective in removing a variety of metals from wastewater.
Physicochemical methods involve changing the physical or chemical characteristics of the wastewater. These methods include coagulation/flocculation, precipitation, ion exchange, electro-chemical method, and membrane filtration. Coagulation/flocculation is a process that uses chemicals to change the charge on metals in the wastewater, causing them to clump together and form large particles which can be removed by settling. In precipitation, chemicals are added to the wastewater to cause the heavy metals to be insoluble, and then the metal-enhanced liquid is separated from the particulate matter. Ion exchange is an exchange of one type of ion for another, and electro-chemical methods involve passing an electric current through the wastewater, causing the metals to accumulate at the electrode where they are then removed. Membrane filtration is also an option, in which a membrane is used to separate particles from the water.
Biological methods involve using microorganisms to break down pollutants in the wastewater. These methods are more complex, but can be effective in removing a variety of heavy metals. Examples of biological methods include bioremediation and bioaccumulation. Bioremediation uses bacteria or other organisms to break down toxic chemicals in the wastewater, while bioaccumulation uses certain species of bacteria which are able to bind to toxic metals and prevent them from entering into the environment.
Finally, sorption techniques involve using a material to bind to the heavy metal and remove it from the wastewater. Adsorption is the most common type of sorption technique, and involves using activated charcoal, alumina or other materials to bind to the metal and remove it from the solution. Other sorption techniques include chelation and immobilization. Chelation involves using a chemical compound to bind to the metal, and immobilization involves using something like clay to bind to the metal and prevent it from entering the environment.
Heavy Metal Wastewater Treatment Design
The design of a heavy metal wastewater treatment system will depend on the type of metal and the concentration of it, as well as the type of wastewater. Generally, a multi-stage process is used to remove heavy metals from wastewater. A multi-stage system typically includes a pretreatment step to reduce the concentration of contaminants in the wastewater, followed by a treatment step to remove metals and other pollutants, and a final polishing step to reduce the amount of metals which remain in the wastewater.
The pretreatment step is used to reduce the amount of suspended solids and other contaminants in the wastewater, and typically includes screening, flotation and sedimentation. These steps are used to reduce the solid contaminants in the wastewater, which can then be more effectively removed by other methods.
The treatment step is used to actually remove the contaminants from the wastewater, and typically includes coagulation/flocculation, precipitation, ion exchange, electro-chemical treatment, membrane filtration, and biological treatment. Depending on the type of metal and the concentration, one or more of these methods may be used.
Finally, the polishing step is used to reduce the amount of metals remaining in the wastewater. The most common methods used in this step are activated charcoal, alumina, and clay. These materials have a high affinity for metals, and will bind to them to remove them from the wastewater.
Conclusion
Heavy metals are dangerous pollutants which can be harmful to the environment if they are not removed properly. In order to remove these pollutants from wastewater, a variety of methods can be used, including physicochemical methods, biological methods, and sorption techniques. The design of a heavy metal wastewater treatment system typically includes a pretreatment step, a treatment step, and a polishing step. By using these methods and techniques, it is possible to effectively remove heavy metals from wastewater and return clean water back to the environment.
