Neco 2023 Chemistry Question 7

Practice objective / multiple choice question 7 from the 2023 Neco Chemistry examination.

Neco 2023 Chemistry Objective / Multiple Choice Hard Difficulty
Question 7 NECO • 2023 • CHEMISTRY • objective

A wastewater sample has an initial chemical oxygen demand (COD) of 300 mg·L^{-1}. Primary treatment reduces the COD by 40 % of its original value. The secondary biological stage reduces the biochemical oxygen demand (BOD_{5}) by 70 % of the BOD_{5} present after primary treatment. For this wastewater the relationship between COD and BOD_{5} is given by \(COD = 1.5\,BOD_{5}+30\) (mg·L^{-1}).\n\n(i) Determine the final COD after both treatment stages, assuming the COD-BOD_{5} relationship holds after each stage.\n(ii) Calculate the overall percentage reduction in COD.

Answer Options

A. Final COD = 90 mg·L^{-1}; overall reduction = 70 %
B. Final COD = 120 mg·L^{-1}; overall reduction = 60 %
C. Final COD = 105 mg·L^{-1}; overall reduction = 65 %
Correct Answer D. Final COD = 75 mg·L^{-1}; overall reduction = 75 %
Correct Answer
D
Correct Option:
Final COD = 75 mg·L^{-1}; overall reduction = 75 %

About This Question

This is Neco 2023 Chemistry Question 7. It is one of the objective questions from the 2023 Neco Chemistry examination.

Difficulty level: Hard .

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