Describe how the following changes in parameters will affect the efficiency of the removal of organic matter $($as BOD$)$ for an aeration basin with cell recycle with the characteristics listed below:

Y $=0\mathrm{.}70$ mg suspended solids$/$mg BOD

X $=1,000$ mg$/$L

k$\_$d $=1\mathrm{.}80/$day

$\backslash$theta c $=5\mathrm{.}0$ days

$\backslash$theta $=0\mathrm{.}12$ days

S$0=400$ mg BOD$/$L

a$)$ Change $1$: Increase the retention time by $10\%.$

b$)$ Change $2$: Removal of half of the biomass concentration.