Neco Model Questions Vol1 2022 Chemistry Question 33

Practice objective / multiple choice question 33 from the 2022 Neco Model Questions Vol1 Chemistry examination.

Neco Model Questions Vol1 2022 Chemistry Objective / Multiple Choice Hard Difficulty
Question 33 NECO_MODEL_QUESTIONS_VOL1 • 2022 • CHEMISTRY • objective

A wastewater treatment plant receives 5 000 m³ day⁻¹ of effluent containing phenol at a concentration of 200 mg L⁻¹. The treatment consists of two stages: (i) an aerobic biodegradation stage that removes 70 % of the phenol, and (ii) a chemical oxidation stage that removes 80 % of the phenol remaining after stage (i). (a) Calculate the phenol concentration after each stage and the final concentration after stage (ii). (b) Determine the total mass of phenol removed per day (in kg) and the overall removal efficiency (%). (c) The discharge limit for phenol is 5 mg L⁻¹. Does the plant meet this limit? If not, what minimum removal efficiency must the second stage achieve (as a percentage of the phenol entering that stage) to meet the limit?

Answer Options

A. a) 80 mg L⁻¹ after stage (i); 16 mg L⁻¹ after stage (ii). b) 800 kg removed; 80 % overall efficiency. c) No, the limit is not met; stage (ii) must achieve at least 85 % removal (≈5 % more than the present 80 %).
B. a) 50 mg L⁻¹ after stage (i); 10 mg L⁻¹ after stage (ii). b) 960 kg removed; 96 % overall efficiency. c) Yes, the limit is met; no further removal needed.
C. a) 70 mg L⁻¹ after stage (i); 14 mg L⁻¹ after stage (ii). b) 880 kg removed; 88 % overall efficiency. c) No, the limit is not met; stage (ii) must achieve at least 95 % removal (≈15 % more than the present 80 %).
Correct Answer D. a) 60 mg L⁻¹ after stage (i); 12 mg L⁻¹ after stage (ii). b) 940 kg removed; 94 % overall efficiency. c) No, the limit is not met; stage (ii) must achieve at least 91.7 % removal (≈11.7 % more than the present 80 %).
Correct Answer
D
Correct Option:
a) 60 mg L⁻¹ after stage (i); 12 mg L⁻¹ after stage (ii). b) 940 kg removed; 94 % overall efficiency. c) No, the limit is not met; stage (ii) must achieve at least 91.7 % removal (≈11.7 % more than the present 80 %).

About This Question

This is Neco Model Questions Vol1 2022 Chemistry Question 33. It is one of the objective questions from the 2022 Neco Model Questions Vol1 Chemistry examination.

Difficulty level: Hard .

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