A 425-m3(15,000 ft3) basin, equipped with 10 gas dispersers of a new design, is to be installed for stripping hydrogen sulfide, H2S, from wastewater. The dispensers, each to use air at a rate of 7:08 × 10-3 m3/s, will be located at a depth of 3.2 m (10.5 ft) below the liquid surface. A preliminary analysis of the 283 K wastewater indicates an initial H2S concentration of 0.3 mmol/L.
In a pilot investigation of the proposed new dispenser, the designated flow rate of 7:08 × 10-3 m3/s was discharged from a single dispenser located at 3.2 m below the surface of the water held in a 28.3-m3 (1000-ft3 ) tank. This water was maintained at 283 K. After 4 h of aeration, the dissolved oxygen concentration increased from 0.04 to 0.25 mmol/L. Based upon this pilot investigation, determine
a. the KLa for oxygen for this new dispenser when it is operated 3.2 m below the liquid surface with the air flow rate of 7:08 × 10-3 m3/s. At 283 K, Henry's law constant for the oxygen-water system is 3.27× 10-4 atm/mole fraction.
b. the KLa for H2S for this new dispenser when it is operated 3.2 m below the liquid surface with the air flow rate of 7:08 × 10-3 m3/s. If the penetration-theory model holds, the capacity coefficient, KLa, is proportional to the liquid mass diffusivity raised to the power of 1/2. The liquid diffusivity of oxygen in water at 283 K is 2.14× 10-5 cm2 /s and of H2S in water at 283 K is 1.4× 10-5 cm2 /s.
c. the concentration of H2S in the 425-m3 basin after 4h of operation if the wastewater's initial H2S concentration is 0.3 m mole/L. Henry's law constant for H2S-water system at 283 K is 0.0367×104 atm/mole fraction.