how primary sewage treatment and secondary sewage treatment are used to help
First, primary sewage treatment, a physical process, uses screens and tanks to remove large floating objects, rocks, and sand. Next, secondary treatment, a biological process, uses bacterial to breakdown biodegradable materials, but does not kill pathogens.
Finally, chlorination,ozone, or UV is used to kill pathogens and some viruses. A major problem is inadequate secondary treatment facilities in numerous cities and untreated storm water runoff systems, which allows pollutants to be discharged into coastal waters, lakes, and streams.