What occurs when air comes into contact with wastewater in the drainage system?

When air comes into contact with wastewater in the drainage system, the interaction primarily leads to the movement of the air along with the wastewater being transported. This process ensures that the system maintains a certain degree of pressure, which is essential for preventing the buildup of gases and odors that can negatively affect sanitation conditions.

In a properly functioning drainage system, air will move with the wastewater as it flows, helping to maintain the necessary airflow and pressure equilibrium within the pipes. This situation underscores the importance of venting in drainage systems, as it allows air to enter and can prevent problems like siphoning or backpressure.

The other options do not accurately describe the common occurrences in wastewater systems when air contacts it. For instance, a sudden vacuum is typically caused by improper venting, leading to other issues rather than being a direct effect of air interacting with wastewater. Flooding of fixtures usually happens due to blockages or overloading, not merely air contact. Circulation of air stopping is not indicative of air's impact on wastewater contact but rather suggests a malfunction or design problem in the drainage system.