6. Exercises VI

 

Sludge is the term used to describe semi-solidssemi-gaseoussemi-liquids, such as waste products that solidify during wastewater treatment. The sludge is filteredseeped removed using a skimmer and then moved to a tank, where anaerobic bacteria ferment it to produce biogascng-gascoal gas. This biogas is a cheap fuel for various uses, such as heating, cooking, etc.