Answer:
c.advanced—physical and chemical processes
Explanation:
Sewage treatment is done to remove contaminants from municipal wastewater. This wastewater usually has household wastes but can also contain industrial wastes. The treatment is divided into stages which are: primary, secondary, tertiary(advanced).
Advanced stage is sometimes included in tertiary stage and sometimes considered a separate quaternary stage. It is the final stage of treatment where the contaminants are present just in part per million or billion level of concentration. These remaining contaminants can not be removed from normal processes so more advanced physical and chemical techniques like fine filtration, disinfection or oxidation are used. After this final treatment, the effluent can be discharged to the environment.
