Question 12.6: ACTIVATING POLYMERS BEFORE CHEMICAL FEEDING Polymers (includ...
ACTIVATING POLYMERS BEFORE CHEMICAL FEEDING
Polymers (including non-ionic polymers and ionic polyelectrolytes) can be fed as dry product or as a liquid. If liquid polymers are used, it is sometimes necessary to activate the polymers prior to feeding. Activating consists of mixing a diluted solution of polymer.
This allows the long molecular chains that make up the polymer to “unravel” and thus activate. In general, the polymer manufacturer should be contacted to determine an appropriate dilution at which a polymer should be fed to aWTP. Recommend a procedure which can be followed to prepare a polymer dilution assuming (a) polymer density = 12.1 lb/gal (1.45 kg/L); (b) 500 gal (1892.5 L) of 0.5% by weight of polymer is to be prepared.
1 (US Customary System):
The amount of concentrated polymer that must be added to prepare any dilution may be calculated by using a mass balanced method.
1. Determine the weight of 500 gal of water.
Water weight = 500 gal × 8.34 lb∕gal
= 4,170 lb
2. Determine the weight of polymer required to prepare a 0.5% by weight solution.
Polymer weight = (0.5∕100) × 4,170 lb
= 20.85 lb
3. Determine the volume of polymer required.
Polymer volume = 20.85 lb × (gal∕12.1 lb)
= 1.72 gal
Therefore, the diluted and activated polymer solution is made up by placing 1.72 gal of concentrated liquid polymer into a 500-gallon barrel and filling the barrel with water to the 500-gallon mark. Alternatively liquid polymer can also be weighed, and 20.85 lb of polymer can be diluted with 500 gal of water.
2 (SI System):
The amount of concentrated polymer that must be added to prepare any dilution may be calculated by using a mass balance method.
1. Determine the weight of 1,892.5 L of water.
Water weight = 1,892.5 L × 1 kg∕L
= 1,892.5 kg
2. Determine the weight of polymer required to prepare a 0.5% by weight solution.
Polymer weight = (0.5∕100) × 1,892.5 kg
= 9.46 kg
3. Determine the volume of polymer required.
Polymer volume = 9.46 kg × (1 L∕1.45 kg)
= 6.52 L
Therefore, the diluted and activated polymer solution is made up by placing 6.52 L of concentrated liquid polymer into 1,892.5-L barrel and filling the barrel with water to the 1,892.5-L mark. Alternatively liquid polymer can also be weighed, and 9.46 kg of polymer can be diluted with 1,892.5 L of water.