The correct answer is: D. A source of objectionable odour.
Fresh sewage is a mixture of human waste, water, and other materials. It is generally considered to be a source of objectionable odour because it contains a variety of bacteria and other microorganisms that produce volatile organic compounds (VOCs). These VOCs are responsible for the characteristic “sewage smell”.
The odour of sewage can be quite strong, and it can be difficult to get rid of. In some cases, it can even be harmful to human health. For this reason, it is important to treat sewage properly before it is released into the environment.
There are a number of ways to treat sewage. One common method is to use aeration. Aeration involves pumping air into the sewage, which helps to break down the organic matter and reduce the amount of VOCs. Another common method is to use filtration. Filtration involves passing the sewage through a series of filters, which removes solid particles and other contaminants.
Once sewage has been treated, it can be safely released into the environment. In some cases, it may be reused for irrigation or other purposes.