ANS:E - more than 500

The dilution factor refers to the ratio of the volume of water to the volume of sewage in a water body. It indicates how much the sewage is diluted by the surrounding water. In general, a higher dilution factor implies greater dilution of sewage in the receiving water body. Here's how the dilution factor relates to treatment of sewage:

• Less than 150: If the dilution factor is less than 150, it means that the sewage is not adequately diluted by the receiving water body. In such cases, the sewage can have a significant impact on water quality and may require treatment to mitigate pollution and protect aquatic ecosystems and public health.
• Between 150 to 200: Similarly, if the dilution factor is between 150 to 200, the sewage is still relatively concentrated and may pose environmental and health risks. Treatment may be necessary to reduce the pollutant load and protect water quality.
• Between 200 to 300: As the dilution factor increases to between 200 to 300, the sewage becomes more diluted in the receiving water body. While treatment may still be beneficial for further pollutant removal, the dilution factor suggests that the sewage is somewhat diluted and may have less immediate impact on water quality.
• Between 400 to 500: With a dilution factor between 400 to 500, sewage is significantly diluted in the receiving water body. Treatment may still be beneficial for removing pollutants and protecting water quality, but the diluted sewage is less likely to have a severe impact on the environment compared to lower dilution factors.
• More than 500: If the dilution factor is more than 500, it indicates substantial dilution of the sewage in the receiving water body. In such cases, the sewage is highly diluted, and its impact on water quality and aquatic ecosystems may be minimal. Treatment may still be desirable for further pollutant removal, but it may be less critical compared to situations with lower dilution factors.