Biological activity in long, sluggish-flow, flat-grade sewer lines will likely

Biological activity in long, sluggish-flow, flat-grade sewer lines will likely

• A. Create oxygen deficiency in the air in manholes, sewers, or wet wells
• B. Decrease line sediment
• C. Stop toxic gas production
• D. Increase the carrying capacity of the line

Answer: (A)

When sewer lines move slowly through a flat grade, there’s not enough turbulence to keep solids in suspension and oxygen in the water is used up by bacteria faster than it can be replenished. The result is an anoxic, or oxygen-poor, environment inside the pipes and especially in the air spaces of manholes and wet wells. Poor ventilation in these areas means the air itself can become oxygen-deficient, so odors and related problems emerge. This is why the most likely outcome is oxygen deficiency in the air in manholes, sewers, or wet wells. Sediment tends to build up in sluggish lines, not decrease; low-oxygen conditions can lead to toxic gas production rather than stopping it; and the carrying capacity of the line does not increase with slow flow—it usually drops due to sediment buildup and a reduced ability to transport wastewater.

When sewer lines move slowly through a flat grade, there’s not enough turbulence to keep solids in suspension and oxygen in the water is used up by bacteria faster than it can be replenished. The result is an anoxic, or oxygen-poor, environment inside the pipes and especially in the air spaces of manholes and wet wells. Poor ventilation in these areas means the air itself can become oxygen-deficient, so odors and related problems emerge. This is why the most likely outcome is oxygen deficiency in the air in manholes, sewers, or wet wells.

Sediment tends to build up in sluggish lines, not decrease; low-oxygen conditions can lead to toxic gas production rather than stopping it; and the carrying capacity of the line does not increase with slow flow—it usually drops due to sediment buildup and a reduced ability to transport wastewater.