a$)$ Would you expect BOD concentration to be the same, greater or less than COD concentration in raw wastewater? How do you expect the ratio of the two would change after secondary treatment $($by CMAS, trickling filter, MBBR$,$ etc$)?$

b$)$ Identify three key factors that can impact the efficiency of BNR processes.

c$)$ Explain how biofilms can achieve complete nitrogen removal in a single tank without needing separate tanks with oxic and anoxic zones.