Which type of bacteria has no known function in sewage treatment?

Pathogenic bacteria are associated with causing diseases and pose a threat to human health and the environment. In the context of sewage treatment, these bacteria typically do not contribute positively to the biological processes involved in treating wastewater. While they may be present in sewage due to their association with human waste, their role in the sewage treatment process is not beneficial. The goal of sewage treatment is to reduce the quantity of harmful pathogens, making pathogenic bacteria irrelevant in the functional context of effective sewage treatment.

In contrast, non-aerobic bacteria, facultative bacteria, and aerobic bacteria play significant roles in the breakdown of organic matter and the treatment of sewage. Non-aerobic (or anaerobic) bacteria thrive in environments without oxygen, where they decompose waste and release methane. Facultative bacteria can function in both aerobic and anaerobic conditions, making them versatile in different wastewater environments. Aerobic bacteria require oxygen and efficiently break down organic pollutants, contributing to the purification of sewage. Thus, while pathogenic bacteria are present in sewage, they do not have a function in its treatment, making them the correct answer in this context.