Maximum removal of suspended and dissolved impurities from sewage

To achieve the maximum removal of suspended and dissolved impurities from sewage, various treatment processes are employed. These processes aim to remove both the physical and chemical impurities present in the sewage.

Physical Removal Processes:

1. Sedimentation: Suspended solids in the sewage settle down due to gravity when the flow velocity is reduced. This process is known as sedimentation or settling. It can remove up to 70-80% of the suspended solids.

2. Filtration: Filtration involves passing the sewage through a porous medium to remove suspended particles. It can effectively remove suspended solids, colloidal particles, and some dissolved impurities. Filtration processes such as sand filtration, activated carbon filtration, and membrane filtration can achieve removal efficiencies of up to 95-99%.

Chemical Removal Processes:

1. Coagulation and Flocculation: Coagulants like alum or ferric chloride are added to sewage to destabilize the colloidal particles. Flocculants like polyelectrolytes are then added to form larger flocs that can settle or be filtered out more easily. This process can remove suspended solids, colloidal particles, and some dissolved impurities.

2. Chemical Precipitation: Chemical precipitation involves adding chemicals to the sewage that react with dissolved impurities to form insoluble precipitates. These precipitates can then be removed by sedimentation or filtration. Chemical precipitation can effectively remove dissolved metals, phosphates, and other dissolved impurities.

3. Advanced Oxidation Processes (AOPs): AOPs such as ozonation, UV irradiation, and advanced oxidation with hydrogen peroxide can be used to oxidize and degrade organic and inorganic contaminants present in the sewage. These processes are highly effective in removing dissolved impurities.

Conclusion:

The maximum removal of suspended and dissolved impurities from sewage can be achieved by employing a combination of physical and chemical treatment processes. The use of sedimentation, filtration, coagulation and flocculation, chemical precipitation, and advanced oxidation processes can result in removal efficiencies of up to 92%. However, it is important to note that the specific removal efficiency may vary depending on the characteristics of the sewage and the treatment processes employed.