Tennessee Wastewater Operator Practice Exam

Why are rotary screw blowers referred to as "hybrid" blowers?

1. Because they use both gas and liquid

2. Because they use mechanical and electrical drive

3. Because they combine positive displacement and internal compression

4. Because they vary speed and pressure regulations

The correct answer is: Because they combine positive displacement and internal compression

Rotary screw blowers are referred to as "hybrid" blowers because they combine two distinct technological principles: positive displacement and internal compression. In this context, positive displacement refers to the method where the blower moves air by trapping a fixed amount of it in a cavity and then forcing it out, while internal compression involves the compression of the air as it passes through the machine's internal geometry. This combination allows rotary screw blowers to achieve high efficiency and pressure, making them suitable for various applications in wastewater treatment. The design of rotary screw blowers leverages both of these principles, optimizing performance and energy usage, which is why the term "hybrid" is applicable. They can provide consistent air output even under varying load conditions, contributing to their advantages in processes that require stable aeration, such as in biological treatment systems. The other options refer to distinct features that do not accurately capture the reason behind the "hybrid" terminology in relation to the design and operation principles of these blowers.