Hot lime-soda process preferred over cold lime-soda method:

• When the chemicals are added at higher temperatures (80 to 150 degree C), the process is Hot lime soda process.
• At higher temperature:

1. The reactions are fast .
2. Precipitation is more complete.
3. Settling rate and filtration rates are increased.

• Hence, the precipitate and sludge formed settle rapidly and coagulants, and also chemicals needed are in smaller quantities than that of cold process.
• Dissolved gases are eliminated from water to a certain extent. The softened water recovered has hardness of about 15 to 30 ppm.