Ontario Operator-in-Training (OIT) Practice Exam

What does attached growth refer to in wastewater treatment?

1. Microorganisms suspended in water

2. Microorganisms attached to inert materials

3. Microorganisms living in soil

4. Microorganisms that are killed during treatment

The correct answer is: Microorganisms attached to inert materials

Attached growth in wastewater treatment specifically refers to microorganisms that adhere to surfaces of inert materials. This method of treatment utilizes the natural processes of these organisms to break down organic matter in the wastewater. The inert materials, often called carriers or media, provide a habitat for the microorganisms to attach to, facilitating a greater surface area for biological activity compared to suspended growth systems where microorganisms are free-floating in the water. In this context, the effectiveness of attached growth systems, such as biofilters or trickling filters, is due to the stability and resilience of microbial populations that can form biofilms on these surfaces. This allows for efficient biochemical reactions to occur, leading to the breakdown of pollutants in the wastewater. The other options do not accurately describe attached growth. Suspended microorganisms (the first option) involve organisms that are not attached to any surface and are instead dispersed throughout the water. The third option describes microorganisms in soil, which is unrelated to the concept of attached growth in wastewater treatment. Finally, the fourth option concerns microorganisms that are killed during treatment, which is contrary to the goal of the attached growth process, where the aim is to sustain and utilize living microorganisms for the treatment.