points$)$

b$)$ Which are the process steps $x$ and $Y($from figure below$)$ of the wastewater treatment process? $(3$ points$)$

c$)$ Considering that the wastewater at point $A($see figure above$)$ has a BOD equal to $1000mg\frac{O_2}{L},$ what is approximately the BOD value at point $B$ and why? What is the expected value at the output of the plant and why? $(6$ points$)$