Fresh sewage is usually characterized by which color and odor?

Fresh sewage is typically characterized by a gray color and a musty odor. This coloration arises due to the organic materials and the microbial activity present in sewage, which can lead to a grayish appearance. The musty odor results from the breakdown of organic matter by bacteria and other microorganisms in the sewage, which is a normal aspect of sewage composition.

In contrast, clear and odorless sewage would indicate that there are no organic contaminants present, which is not the case in fresh sewage. Additionally, black and foul sewage is usually associated with stagnant conditions or older waste where decomposition has progressed further, leading to more severe odors. A brown and pleasant odor does not accurately reflect the nature of sewage, as sewage generally has unpleasant odors due to its organic and bacterial content. Thus, the choice of gray and musty effectively captures the characteristics of fresh sewage.