A wastewater from tanning industry was tested for BOD and following test data was found as given in Table below: Volume of waste water used 2.5 ml, DO of waste 0.25 mg/L, D0 of Dilution water 9.7 mg/L Time (in days) DO in Test Bottle (mg/L) |DO in Control Bottle (mg/L) 8.5 7.4 6.5 5.9 4.0 3.7 3.2 9.7 9.7 9.6 9.5 9.4 9.3 9.3 9.3 9.3 10 20 30 3.0 3.0 As an Engineer, you need to decide if the above wastewater can be discharged into the river (described below) A river stream flows at 6.2 m/sec with a velocity of 1.1 m/s, average depth of 2.8 meters and temperature of 15 C. The stream is saturated with dissolved oxygen, has an ultimate Biological oxygen demand of 9.6 mg/L. The wastewater from the above tanning industry is to be discharged to this river stream with a bed activity coefficient of 0.2. The wastewater is at 26C with a volumetric flow rate of 0.55 m'/sec. The local water quality control board requires that the DO of water can never go below 5.0 ppm. What could be the minimum dissolved oxygen concentration, and where can it occur