Final answer:
Preventative maintenance on an upflow clarifier mainly includes cleaning filter media, which is vital for the removal of contaminants such as bacteria and viruses.
Step-by-step explanation:
Preventative maintenance on an upflow clarifier involves regular activities to ensure the efficient operation of the system and to prevent issues such as the growth of biofilms. An essential aspect of maintenance is Cleaning filter media which removes small particles, such as dust, parasites, bacteria, and viruses, by passing water through layers of sand, gravel, and charcoal. This aligns with the option A offered in the question, as maintaining a clean environment in the clarifier is crucial to its function. Options such as increasing flow rate, reducing chemical dosing, or lowering temperature are not typically part of preventative maintenance for an upflow clarifier.
In addition to cleaning, other maintenance steps that are important include monitoring and optimizing the oxygenation levels and keeping the nutrient levels in check to prevent excessive bacterial or algae growth. Understanding that the purpose of an upflow clarifier is to remove contaminants through a process of sedimentation and filtration, followed potentially by disinfection, underscores the importance of regular maintenance to prevent eutrophication or dead zones formation within water treatment systems.