Which of the following is/are product(s) of wastewater treatment?

During wastewater, remedy water is allowed to settle in a large tank which is sloped closer to the middle. Solids like feces settle at the bottom and are eliminated with a scraper. This is the sludge. 

A skimmer removes floatable solids like oil and grease. Water so cleared is known as clarified water. The sludge is transferred to a separate tank where it is decomposed with the aid of the anaerobic bacteria. 

The biogas produced in the process can be used as gas or can be used to produce electricity.