Long, sluggish-flow, flat-grade sewer lines will likely cause which of the following?

Long, sluggish-flow, flat-grade sewer lines will likely cause which of the following?

• A. All of the above
• B. Oxygen deficiency in the air in manholes, sewers or wet wells.
• C. Concrete and metal corrosion
• D. Toxic gas production

Answer: (A)

When sewer lines have a long, sluggish flow and a flat grade, solids tend to settle and the wastewater stays in the pipe longer. This creates anaerobic conditions because oxygen is used by microorganisms faster than it can be replenished by air exchange. In those low-oxygen environments, gases such as hydrogen sulfide and methane are produced. Hydrogen sulfide is toxic and, once formed and released into manholes or wet wells, contributes to gas buildup. It can also react with sewer surfaces to form sulfuric acid, which attacks concrete and accelerates metal corrosion. The combination of air with depleted oxygen and accumulating gases explains why oxygen-deficient air, toxic gas production, and corrosion are all likely outcomes in such conditions. So choosing all of the above reflects the range of problems that can arise from long, sluggish, flat-grade sewers.

When sewer lines have a long, sluggish flow and a flat grade, solids tend to settle and the wastewater stays in the pipe longer. This creates anaerobic conditions because oxygen is used by microorganisms faster than it can be replenished by air exchange. In those low-oxygen environments, gases such as hydrogen sulfide and methane are produced. Hydrogen sulfide is toxic and, once formed and released into manholes or wet wells, contributes to gas buildup. It can also react with sewer surfaces to form sulfuric acid, which attacks concrete and accelerates metal corrosion. The combination of air with depleted oxygen and accumulating gases explains why oxygen-deficient air, toxic gas production, and corrosion are all likely outcomes in such conditions. So choosing all of the above reflects the range of problems that can arise from long, sluggish, flat-grade sewers.