Question

Two representative pollutants are radon (²²²Rn) and benzene. Parameters needed for the estimation are listed in the table below. Answer the following questions.

(a) Estimate the steady-state radioactivity in the station in Bq m^-3.

(b) Estimate the steady-state concentration of benzene both in mg m^-3 and in ppbv. Molecular weight of benzene is 78 g mol^-1. Assume 298 K and 1 atm (= 101,325 Pa).

(c) Although regulatory limit of indoor benzene concentration is 30 mg m^-3 in Korea, researchers argue that it should be as low as 1.3 mg m^-3 considering carcinogenic risk of benzene. Can you lower the benzene concentration as low as for protection of citizens’ health? Suggest potential options to lower benzene concentration in the station.

Parameter	Symbol	Value with units
Volume of indoor air	V	30,000 m3
Air-exchange rate	ke	2.0 h-1
First-order decay constant of 222Rn	kd, Rn	0.00754 h-1
Rate of production of radioactivity of 222Rn inside the station	Ri, Rn	10 Bq m-3 h-1
Outside background radioactivity	Ao	4.0 Bq m-3
Rate of production of benzene inside the station	Ri, benz	3.0 mg m-3 h-1
Outside background concentration of benzene	Co, benz	1.5 mg m-3
Half-life of benzene in the station	t1/2, benz	8.0 h

Answer 1

The Reduction of concentration of banzene in the room can be done by unit operation carried to separate benzene by diffusional mechanism.SOme solvents that are non polar in nature. supercrtical CO2 can be utilise to diffuse benzene and lower the concentration.The whole process can be carried by circulating the air present in room and bring it in contact with supercrtical liquid like Co2 in a column and the outlet stream can be again send to the room.The process can be similar to the working of air conditioner ,only hte thing is there is a physical contact of inffluent (benzene rich air) is required with the solvent.

Benzene can also be separated by adsorption process on zeolite crstals .The researchers have obatined the self diffusiion phenomenon of benzene in Zeolite crstals.Thus adsoption can also reduce the benzene concentration to significant amount.

The above processes discussed above are to reduce the benzene concentartion or to purify the air .they are reliable only if the inffuent concentartion of benzene has some limits.