The correct answer is C. Less than 7.
Sewage is a mixture of human waste, wastewater, and other materials. It is typically acidic, with a pH of around 6.5. This is because human waste contains acids such as urea and ammonia. The pH of sewage can vary depending on the source of the sewage and the treatment that it has undergone. For example, sewage from industrial areas may be more acidic than sewage from residential areas.
A pH of 7 is considered neutral. A pH below 7 is acidic, while a pH above 7 is alkaline. The pH scale is logarithmic, which means that a change of one pH unit represents a tenfold change in acidity. For example, a pH of 6 is ten times more acidic than a pH of 7.
The pH of sewage is important because it can affect the growth of bacteria. Bacteria that thrive in acidic environments are different from bacteria that thrive in alkaline environments. The pH of sewage can also affect the toxicity of heavy metals. Heavy metals are more toxic in acidic environments.
The pH of sewage can be adjusted by adding chemicals such as lime or soda ash. This is done to control the growth of bacteria and to reduce the toxicity of heavy metals.