30.10 A pond containing a suspension of microorganisms is used to biologically degrade dissolved organic materials in wa

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30 10 A Pond Containing A Suspension Of Microorganisms Is Used To Biologically Degrade Dissolved Organic Materials In Wa 1 (163.77 KiB) Viewed 25 times

30.10 A pond containing a suspension of microorganisms is used to biologically degrade dissolved organic materials in wastewater, as shown in the figure (right column). The pond contains 1000 m³ of liquid. Recently, inflow and outflow pipes were installed. The inlet volumetric flow rate of water is 0.05 m³/s, and the outflow is the same to maintain a constant liquid volume. The concentration of dissolved oxygen in the inlet liquid water is 10.0 mmole/m³. The present process uses an air sparger to deliver 2.0 mm air bubbles into the wastewater. The rising bubbles uniformly mix the entire liquid phase of the pond. Only a very small portion of the O₂ gas within the air bubbles (containing 0.21 atm O₂) dissolves into the liquid, where it is consumed by the microorganisms. The Henry's law constant to estimate the solubility of O₂ dissolved in the wastewater that is in equilibrium with the partial pressure of O₂ the aeration gas is H 8.0 x 10-4 atm-m³/mmole (1000 mmole = 1.0 gmole). The interphase mass-transfer area of the bubbles per unit volume of liquid is equal to 10 m²/m³ for this process. The process is 100% liquid film controlling. At the current conditions of operation, the current biological oxygen consumption demand, or "BOD," associated with the microbial respiration in the pond is 0.200 mmole 0₂/m³-s. a. Develop a steady-state material balance model to predict the dissolved concentration of O₂ in the holding pond. b. What is the liquid-phase mass-transfer coefficient ky for O₂? What is the steady-state concentration of dissolved oxygen in the pond? C. Potentially useful data (all at process temperature and pressure): DAB = 2.0 x 109 m²/s (A = dissolved O2, B = water solvent); PB,liq = 1000 kg/m³; Pair = 1.2 kg/m³; Vair = 1.6 x 10-5 m²/s; H = 8.0 x 10-4 atm m³/mmole; MB,liq = 825 x 10-6 kg/m.s. Inlet liquid stream V = 0.05 m³/sec CALO = 10 mmol O₂/m³ Air input Wastewater + aerobic microorganisms dissolved O O O Open Pond % O I O O O O O Effluent CAL = ?