What is a common cause of oxygen deficiency within a sewer manhole?

A common cause of oxygen deficiency within a sewer manhole is due to bacterial action that replaces oxygen with other gases. In wastewater environments, bacteria play a crucial role in the decomposition of organic matter. As these bacteria act on the organic waste, they consume the dissolved oxygen present in the water, which can lead to an oxygen deficiency in the system.

When oxygen is depleted through bacterial metabolism, the byproducts can include gases such as carbon dioxide, methane, and hydrogen sulfide. This shift from an aerobic (oxygen-rich) environment to anaerobic (oxygen-poor) conditions not only affects the water quality but can also pose risks to human health and safety due to the accumulation of these hazardous gases.

In contrast, factors like chemical oxygen demand increases, excessive rainfall, and temperature fluctuations do not directly lead to a deficiency of oxygen created through the biological processes happening within the sewer manhole. While they can influence the overall dynamics of the wastewater treatment process and water quality, they are not the primary reason for an immediate depletion of oxygen as bacterial action is.