Chlorinating before a microstrainer may cause a sticky, jelly-like coating to form on the microstrainer. What is present in the water that causes this problem?

Chlorinating before a microstrainer may cause a sticky, jelly-like coating to form on the microstrainer. What is present in the water that causes this problem?

• A. Soluble iron
• B. Soluble manganese
• C. Slime-producing algae
• D. Filamentous algae or fungi

Answer: (A)

When chlorine is added ahead of a microstrainer, dissolved iron (Fe2+) in the water is oxidized to Fe3+. This ferric form then hydrolyzes to iron hydroxide (Fe(OH)3), which precipitates as a gelatinous, jelly-like coating. That sticky layer readily adheres to the microstrainer surface, causing fouling and reduced flow. So, the presence of soluble iron in the water is what drives the problem. The other options don’t fit as neatly. Soluble manganese can oxidize and precipitate too, but iron’s gelatinous precipitate is the classic slime that coats screens. Slime-producing or filamentous algae would be affected by chlorine rather than cause this coating before filtration.

When chlorine is added ahead of a microstrainer, dissolved iron (Fe2+) in the water is oxidized to Fe3+. This ferric form then hydrolyzes to iron hydroxide (Fe(OH)3), which precipitates as a gelatinous, jelly-like coating. That sticky layer readily adheres to the microstrainer surface, causing fouling and reduced flow. So, the presence of soluble iron in the water is what drives the problem.

The other options don’t fit as neatly. Soluble manganese can oxidize and precipitate too, but iron’s gelatinous precipitate is the classic slime that coats screens. Slime-producing or filamentous algae would be affected by chlorine rather than cause this coating before filtration.