An aeration basin is used to oxygenate wastewater at 283 K. The basin is filled to a depth of 4.55 m with 283 m³ wastewater of 0.050 mmole/L initial dissolved oxygen (O₂) concentration. The filled basin is then aerated with six spargers, with each sparger delivering compressed air to bottom of the basin at a volumetric flow rate of 7.08 × 10^-3 m³/s. The dissolved solids content will be low enough that Henry’s law will be obeyed, with a Henry’s law constant of H = 3.27 × 10⁴ atm (p_A = H · x^*_A) at 283 K. For purposes of this calculation, it may be assumed that the rate of O₂ transferred to the liquid is small relative to molar flow rate of O₂ in the aeration gas. 

a. Determine the dissolved oxygen concentration after a 5.0 min aeration time. 

b. Determine the time required to bring the dissolved oxygen concentration up to a concentration of 0.20 mmole/L (1 mmole/L = 1 gmole/m³).