Though the microbes described in the introductory chapter do not corrode the metal in the subway, many microbes influence corrosion and deterioration of metal and stone. Other microbes have other effects on their environment. During wastewater treatment, bacteria are used to reduce the amount of organic and inorganic materials so that the water no longer supports substantial microbial growth. During secondary wastewater treatment, bacteria within sludge digesters break down organic materials into fatty acids, H2, and CO2. These products are fermented to acetate, CO2, and H2. Finally, archaeans ferment acetate to form methane and carbon dioxide. Just by knowing this information, what is true of the bacteria used in sludge digesters?

a. They are capable of anaerobic metabolism.
b. They are sulfate-reducing bacteria.
c. Some are methanogens.
d. They are capable of forming slime layers.

The bacteria used in order to treat wastewater can be classified as anaerobic, aerobic, and facultative. Anaerobic bacteria are able to treat wastewater in low or null oxygen conditions by the process of methanogenesis. Methanogenesis is a metabolic process that involves the formation of methane (CH4) by anaerobic Archaea known as methanogens. The process of methanogenesis occurs in anaerobic environments, such as during waste sludge treatment, where these microorganisms are able to breakdown organic pollutants. Methanogens produce methane during catabolic pathways that involve the breakdown of complex molecules into simpler molecules.