Answer: The correct answer for the blank is- C) Digest Sewage.
Bacteria play significant role in the treatment of sewage ( a wastewater that is produced by community) as they decompose the decaying organic matter into inorganic substance and organic byproducts. In other words, bacteria digest the sewage.
This is done in order to remove the suspended waste of solid ( such as faeces) from sewage before it gets discharged back in the environment.
It results in removal or reduction of disease causing microbes in the sewage.
Thus, C) is the right option.