Which material must be removed from wastewater because it can cause flow obstruction in pipes?

• A. Oils and greases
• B. Sand
• C. Nitrates
• D. Bacteria

Answer: (A)

Oils and greases in wastewater form blockages because they are sticky, viscous, and tend to separate from water. When they cool or accumulate with solids, they cling to pipe walls and trap additional debris, growing into large masses that narrow or completely obstruct sewer lines. This is why grease traps or interceptors are used to remove fats, oils, and greases before they reach the sewer system.

Sand can contribute to buildup as grit, but it’s typically handled by grit removal processes and isn’t as prone to forming the same kind of sticky, large obstructions as fats and oils. Nitrates and bacteria are dissolved or biological concerns rather than physical blockages in pipes.