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The parameter that is least likely to influence sedimentation rates in a primary clarifier is ambient odor.

Sedimentation rates in a primary clarifier are primarily affected by physical and chemical properties of the wastewater and the solids present. Particle size plays a significant role; larger particles tend to settle faster due to gravity, while smaller particles may require more time to settle. The influent flow rate can also impact sedimentation, as higher flow rates can lead to turbulence that may resuspend settled solids, thereby reducing the overall efficiency of sedimentation. Temperature can influence the viscosity of the wastewater, which in turn affects the sedimentation rate—the warmer the temperature, the less viscous the water, facilitating better settling.

Ambient odor, while it may be a concern for operational monitoring or public health, does not have a direct impact on the physical processes involved in sedimentation within a clarifier. Therefore, it is not a parameter that influences sedimentation rates in a meaningful way compared to the other factors listed.