Which of the following is added during water or sewage treatment to promote flocculation?
a. Sludge
b. PHA
c. BOD
d. Alum

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Understand the concept of flocculation in water or sewage treatment: it is a process where small particles clump together to form larger particles (flocs) that can be more easily removed from the water.

Identify the substances listed in the options and their roles: sludge is the settled solid waste, PHA (polyhydroxyalkanoates) are biopolymers produced by bacteria, BOD (biochemical oxygen demand) is a measure of organic matter, and alum is a chemical used as a coagulant.

Recall that flocculation is typically promoted by adding coagulants, which neutralize charges on particles and help them aggregate.

Recognize that alum (aluminum sulfate) is commonly used as a coagulant in water and sewage treatment to promote flocculation.

Conclude that the correct answer is the substance that acts as a coagulant to promote flocculation, which is alum.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Flocculation in Water Treatment

Flocculation is a process in water and sewage treatment where small particles aggregate into larger clumps called flocs, making them easier to remove. This is typically achieved by adding chemicals that neutralize particle charges, promoting their clumping and sedimentation.

Role of Alum in Flocculation

Alum (aluminum sulfate) is a common coagulant added during water treatment to induce flocculation. It neutralizes the negative charges on suspended particles, allowing them to bind together into larger flocs that settle out of the water, improving clarity and purification.

Distinction Between Treatment Terms: Sludge, PHA, and BOD

Sludge is the solid residue from wastewater treatment, PHA (polyhydroxyalkanoates) are microbial storage polymers, and BOD (biochemical oxygen demand) measures organic pollution. None of these are added to promote flocculation, unlike alum which is specifically used as a coagulant.

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