In the context of water and wastewater treatments, the correct statements are:

particulate matter may shield microorganisms during disinfection
ammonia decreases chlorine demand
phosphorus stimulates algal and aquatic growth
calcium and magnesium increase hardness and total dissolved solids

Correct answer: particulate matter may shield microorganisms during disinfection

Solution

Particulate matter can create a physical barrier that protects microorganisms from the effects of disinfectants, reducing the effectiveness of the disinfection process.

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