Waste Water Characteristics · Environmental Engineering · GATE CE

For wastewater coming from a wood pulping industry, Chemical Oxygen Demand (COD) and 5-day Biochemical Oxygen Demand (BOD₅) were determined. For this wastewater, which of the following statement(s) is/are correct?

Henry's law constant for transferring O₂ from air into water, at room temperature, is 1.3 $${{mmol} \over {liter - atm}}$$. Given that the partial pressure of O₂ in the atmosphere is 0.21 atm, the concentration of dissolved oxygen (mg/liter) in water in equilibrium with the atmosphere at room temperature is

(Consider the molecular weight of O₂ as 32 g/mol)

The theoretical aerobic oxidation of biomass (C₅H₇O₂N) is given below:

C₅H₇O₂N + 5O₂ → 5CO₂ + NH₃ + 2H₂O

The biochemical oxidation of biomass is assumed as a first-order reaction with a rate constant of 0.23/d at 20ºC (logarithm to base e). Neglecting the second-stage oxygen demand from its biochemical oxidation, the ratio of BOD₅ at 20ºC to total organic carbon (TOC) of biomass is _______ (round off to two decimal places).

[Consider the atomic weights of C, H, O and N as 12 g/mol, 1 g/mol, 16 g/mol and 14 g/mol, respectively

A 2% sewage sample (in distilled water) was incubated for 3 days at 27$$^\circ$$C temperature. After incubation, a dissolved oxygen depletion of 10 mg/L was recorded. The biochemical oxygen demand (BOD) rate constant at 27$$^\circ$$C was found to be 0.23 day^$$-$$1 (at base e). The ultimate BOD (in mg/L) of the sewage will be ________. (round off to the nearest integer)