A completely mixed reactor (CSTR or CMRF) is to be used to treat an industrial w

Question

A completely mixed reactor (CSTR or CMRF) is to be used to treat an industrial wastewater. A tracer study is conducted to determine the true hydraulic residence time of the reactor. A slug of tracer (NaBr) is added to the reactor and allowed to wash out over time. The flow to the reactor is 10,000 L/d and the reactor volume is 40,000 L. The tracer data are given below. Using our mass-balance approach, determine the true hydraulic residence time of the reactor.If the pollutant to be removed has a concentration of 100 mg/L and decays by 1st-order kinetics with a rate coefficient (k1 value) of 2.25 d-1, what percent removal is achieved if one uses the theoretical hydraulic retention time of the reactor? What percent removal is achieved using the true hydraulic residence time determined in part (a) of this problem?

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Time (day) Tracer Concentration (mg/L)

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50 1 30 2 18 3 11 4 6.8 5 4.1 6 2.5 7 1.5 8 0.9 9 0.6 10 0.3

Explanation / Answer

Answer:

Initial concentration of tracer at Zero days = 50 mg/L

Concentration of tracer after 10 days = 0.3 mg/L

Percent concentration of tracer after 10 days = (0.3)*100/50

= 0.6%

Thus percentage tracer removal = Initial percentage of tracer - final percentage of tracer)

=(100-0.6)

= 99.4%

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