California Wastewater Treatment Operator Practice Exam 2026 – All-in-One Guide to Master Your Certification

Fixed-film reactors operate by utilizing a specific type of microbial growth where microorganisms develop on fixed surfaces or media, such as rocks or plastic. This method contrasts with suspended-growth systems, where microorganisms are primarily suspended in the wastewater as a free-flowing biomass.

The essence of the fixed-film system is that the microbial colonies adhere to these solid surfaces, allowing the bacteria to break down the organic matter in the wastewater efficiently. This attachment provides a stable environment for the microorganisms, often leading to a higher concentration of biomass compared to what can be maintained in a suspended-growth system. Additionally, because the film develops on a fixed medium, the system can effectively handle variations in flow and loading, which is beneficial in managing certain wastewater treatment processes.

In summary, the reliance on microbial growth on fixed surfaces is what distinctly characterizes fixed-film reactors, setting them apart from other systems that utilize free-floating microorganisms.