Up until the 1970s many wastewater treatment plants in the US used primary treatment only. Which pollutant most likely decreased the most after secondary treatment began to be used?
Toxic metals
Oxygen-demanding waste
Pathogens
Radioactive isotopes

Question

Up until the 1970s many wastewater treatment plants in the US used primary treatment only. Which pollutant most likely decreased the most after secondary treatment began to be used? ﻿
 Toxic metals ﻿
 Oxygen-demanding waste ﻿
 Pathogens ﻿
 Radioactive isotopes

anonymous · Answer

Toxic metals would be my guess, I am sure that it is either toxic metals, or oxygen demaning waste.

anonymous · Answer

@sammsterz  i think its oxygen demaning waste

anonymous · Answer

@sammsterz yep  B

anonymous · Answer

@sammsterz i'm take  online class so i think keystone

anonymous · Answer

and yes the answer is oxygen demanding waste, the goal of the water treatment is to remove contamination int he water. I'm pretty sure metals won't be much of a bother.