text: A proposed experimental step to this process would make use of organisms that engage in "dark fermentation.
full_question: A proposed experimental step to this process would make use of organisms that engage in "dark fermentation." The optional, tertiary forms of this process include the use of powdered activated carbon and ion-exchange resins. Early steps of this process often make use of a communitor, a type of shredder, after which a cyclone degritter might be used. During one portion of this process, a material, such as alum, is added to a flash mixer. An optional, late stage of this process involves the use of a mass of microorganisms called "activated sludge" to remove suspended solids. Stages of this process include coagulation and flocculation, in which impurities precipitate out. Ultraviolet light or ozone is used as a disinfectant during the final stage of this process, which is followed with effluent discharge. For 10 points, name this process by which H2O is purified and sent back to the environment.
first_sentence: A proposed experimental step to this process would make use of organisms that engage in "dark fermentation.
raw_answer: waste water treatment [or water reclamation; or sewage treatment]