An A2O system is used for biological phosphorus removal and nitrogen removal. Fo

Question

An A2O system is used for biological phosphorus removal and nitrogen removal. For the base case for this evaluation, the internal recycle ratio is 3.0 and the return activated sludge recycle ratio is 0.5. The aerobic SRT (solids retention time) is 16 days and full nitrification is occurring. Indicate whether the following changes in wastewater characteristics, plant operation or treatment goal require an increase (I), decrease (D) or remains the same (S) in the effluent phosphorus concentration. Explain your answer clearly.
a) Influent readily biodegradable COD decreases by 40%.
b) A small amount of dissolved oxygen gets into the first bioreactor.
c) Influent TKN concentration decreases by 30%.
d) The return activated sludge recycle ratio increases to 1.0
e) The secondary clarifier effluent TSS concentration increases by 30%.

Explanation / Answer

Answer:

a) Influent readily biodegradable COD decreases by 40%. - Increase in effluent phosphorus concentration

b)A small amount of dissolved oxygen gets into the first bioreactor - Should not have any impact(Same) in the phosphorus concentration

c) Influent TKN concentration decreases by 30%.- Decrease in effluent phosphorus concentration

d)The return activated sludge recycle ratio increases to 1.0 - same (S) in the effluent phosphorus concentration

e)The secondary clarifier effluent TSS concentration increases by 30% - Increase in phosphorus concentration

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