Question

$A20mg/l$ solution of a fluorescent dye was discharged into a stream at a constant rate of $10c{m}^3/sec.$.The background concentration of the dye in the stream water was found to be zero. At concentration of 5 parts per billion. The discharge will be
[Use constant rate injection method]

• A. $0.040m^3/s$
• B. $0.038m^3/s$
• C. $0.035m^3/s$
• D. $0.032m^3/s$

Answer 1

The correct option is A $0.040m^3/s$

$Q=Q_t\frac{C_1-C_2}{C_2-C_0}$
$Q_t=10c{m}^3/sec=10\times {10}^{-6}{m}^3/s$
$C_1=20mg/l=20ppm=20\times {10}^{3}ppb$
$C_2=5ppb,$
$C_0=0$
$Q=10\times {10}^{-6}\times \left(\frac{20\times {10}^3-5}{5-0}\right)m^3/s=0.040m^3/s$