Compare the effects of alum and ferric chloride as coagulants with respect to pH change and sludge production.

• A. Ferric chloride typically causes less pH drop and produces less sludge.
• B. Both coagulants increase alkalinity and raise pH.
• C. Alum consumes alkalinity and lowers pH; ferric chloride typically causes less pH drop and can produce more sludge.
• D. Alum has no effect on alkalinity or pH; ferric chloride always decreases sludge production.

Answer: (C)