Designing a wastewater treatment system for an industrial process that releases high levels of heavy metals, such as lead and mercury, requires a multi-step approach to effectively remove these contaminants and protect the environment. Here are the key steps to consider:1. Preliminary treatment: The first step in the treatment process involves screening and sedimentation to remove large particles and debris from the wastewater. This can be achieved using bar screens, grit chambers, and primary clarifiers.2. Chemical precipitation: In this step, chemicals are added to the wastewater to precipitate heavy metals as insoluble compounds. Commonly used chemicals include lime calcium hydroxide , sodium sulfide, and ferric chloride. These chemicals react with the heavy metals to form solid precipitates, which can then be removed through sedimentation or filtration.3. Coagulation and flocculation: Coagulants, such as aluminum sulfate or ferric chloride, are added to the wastewater to promote the aggregation of fine particles into larger flocs. This process enhances the removal of heavy metals by sedimentation or filtration.4. Membrane filtration: Membrane filtration, such as ultrafiltration or reverse osmosis, can be used to remove heavy metals from the wastewater. These processes involve passing the wastewater through a semi-permeable membrane that selectively allows water molecules to pass through while retaining heavy metal ions and other contaminants.5. Ion exchange: Ion exchange is a process in which heavy metal ions are exchanged with less harmful ions, such as sodium or potassium. This can be achieved using ion exchange resins, which are porous materials that contain charged functional groups that selectively bind to heavy metal ions.6. Adsorption: Adsorption involves the use of materials, such as activated carbon or modified clay, to remove heavy metals from the wastewater. These materials have a high surface area and can adsorb heavy metal ions onto their surfaces, effectively removing them from the wastewater.7. Biological treatment: Certain microorganisms, such as bacteria and fungi, can accumulate or transform heavy metals into less toxic forms. Integrating a biological treatment step, such as a bioreactor or constructed wetland, can help to further reduce heavy metal concentrations in the wastewater.8. Tertiary treatment: The final step in the treatment process involves additional polishing of the wastewater to remove any remaining contaminants. This can include processes such as disinfection, advanced oxidation, or additional filtration.9. Sludge management: The solid waste generated during the treatment process, known as sludge, must be properly managed and disposed of. This can involve processes such as dewatering, stabilization, and landfilling or incineration.10. Monitoring and control: Regular monitoring of the wastewater treatment system is essential to ensure its effectiveness in removing heavy metals and other contaminants. This can involve the use of sensors, sampling, and laboratory analysis to track the performance of the system and make any necessary adjustments.By incorporating these steps into the design of a wastewater treatment system, it is possible to effectively remove heavy metals, such as lead and mercury, from industrial wastewater and protect the environment from their harmful effects.