What issue can FOG (fat, oil, grease) cause in wastewater systems?

• A. Sanitary sewer overflows due to blockages
• B. Increased nitrification
• C. Improved settling
• D. Lower BOD

Answer: (A)

FOG can cause blockages in sanitary sewer lines. When fats, oils, and greases enter the sewer, they cool and solidify, coating the pipe walls and trapping other debris. Over time this buildup grows into a blockage that restricts flow. During wet weather or high flow, the restricted pipes can back up, leading to sanitary sewer overflows or basement backups. That’s why blockages and overflows are the primary issues associated with FOG in wastewater systems. Nitrification is a biological process in the treatment plant, not driven by grease in the pipes; grease can even hinder settling by forming a floating scum layer, and it doesn’t reduce the organic load measured as BOD—in fact, it can contribute to it.