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

Answer: (B)

When wastewater moves slowly in long, flat-grade sewers, organic matter has more time for bacteria to act and for solids to settle. The microbes consume the available oxygen to oxidize the organics, and because the flow is sluggish, air exchange in the spaces of manholes, sewers, or wet wells is limited. This combination can drive the air in those confined spaces toward oxygen deficiency. That’s why oxygen-deficient atmospheres are likely in these conditions. Sediment buildup is more likely in slow-flow conditions, not a decrease of sediment. Toxic gas production can occur with anaerobic activity, but it isn’t what you’d call a stopped effect here. And the line’s carrying capacity isn’t inherently increased by biological activity; if anything, slow flow reduces carrying capacity for wastewater, not improves it.

When wastewater moves slowly in long, flat-grade sewers, organic matter has more time for bacteria to act and for solids to settle. The microbes consume the available oxygen to oxidize the organics, and because the flow is sluggish, air exchange in the spaces of manholes, sewers, or wet wells is limited. This combination can drive the air in those confined spaces toward oxygen deficiency. That’s why oxygen-deficient atmospheres are likely in these conditions.

Sediment buildup is more likely in slow-flow conditions, not a decrease of sediment. Toxic gas production can occur with anaerobic activity, but it isn’t what you’d call a stopped effect here. And the line’s carrying capacity isn’t inherently increased by biological activity; if anything, slow flow reduces carrying capacity for wastewater, not improves it.