i Aeration is a critical component of aerobic wastewater treatment processes; in fact, it accounts for...
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i Aeration is a critical component of aerobic wastewater treatment processes; in fact, it accounts for the largest portion (45-75%) of energy costs in a wastewater treatment plant. Bubble diffusers are commonly used for aeration and are called fine bubble or coarse bubble, depending on the bubble size. These devices provide air (or pure oxygen) into the bottom of a wastewater treatment reactor and the bubbles rise through the reactor creating convection mass transfer from the bubble surface to the bulk liquid. In this application, the convection mass transfer rate is typically called the oxygen transfer rate (OTR) and is calculated according to the following equation: OTR = K₁a(Co2,s-C02,00)V OTR = oxygen transfer rate (kg O₂/h) Co2.s = dissolved oxygen concentration in wastewater just outside bubble surface (where oxygen from air or pure oxygen is in equilibrium with wastewater, mg/L) Co2 = dissolved oxygen concentration in bulk wastewater (must be 2 mg/L to maintain aerobic conditions) KLa = volumetric mass transfer coefficient (combines together a convection mass transfer coefficient, KL, in m/h with interfacial area, a, in m²/m³ that describes bubble surface area per reactor volume to give overall units of 1/h) V = reactor volume (m³) For a 50-m³ (50,000 L) wastewater treatment reactor at 20°C, calculate OTR for the following scenarios and discuss which design selection has the largest impact (the type of diffuser used or the type of gas used): A fine bubble diffuser (K₁a = 3.6 h ¹) with air at 101.3 kPa with 21% oxygen (1.38 kg 0₂/h) A fine bubble diffuser (K₁a = 3.6 h¹) with pure oxygen at 101.3 kPa (7.92 kg O₂/h) A coarse bubble diffuser (KLa = 0.6 h¹¹) with air at 101.3 kPa with 21% oxygen A coarse bubble diffuser (KLa = 0.6 h¹) with pure oxygen at 101.3 kPa i Aeration is a critical component of aerobic wastewater treatment processes; in fact, it accounts for the largest portion (45-75%) of energy costs in a wastewater treatment plant. Bubble diffusers are commonly used for aeration and are called fine bubble or coarse bubble, depending on the bubble size. These devices provide air (or pure oxygen) into the bottom of a wastewater treatment reactor and the bubbles rise through the reactor creating convection mass transfer from the bubble surface to the bulk liquid. In this application, the convection mass transfer rate is typically called the oxygen transfer rate (OTR) and is calculated according to the following equation: OTR = K₁a(Co2,s-C02,00)V OTR = oxygen transfer rate (kg O₂/h) Co2.s = dissolved oxygen concentration in wastewater just outside bubble surface (where oxygen from air or pure oxygen is in equilibrium with wastewater, mg/L) Co2 = dissolved oxygen concentration in bulk wastewater (must be 2 mg/L to maintain aerobic conditions) KLa = volumetric mass transfer coefficient (combines together a convection mass transfer coefficient, KL, in m/h with interfacial area, a, in m²/m³ that describes bubble surface area per reactor volume to give overall units of 1/h) V = reactor volume (m³) For a 50-m³ (50,000 L) wastewater treatment reactor at 20°C, calculate OTR for the following scenarios and discuss which design selection has the largest impact (the type of diffuser used or the type of gas used): A fine bubble diffuser (K₁a = 3.6 h ¹) with air at 101.3 kPa with 21% oxygen (1.38 kg 0₂/h) A fine bubble diffuser (K₁a = 3.6 h¹) with pure oxygen at 101.3 kPa (7.92 kg O₂/h) A coarse bubble diffuser (KLa = 0.6 h¹¹) with air at 101.3 kPa with 21% oxygen A coarse bubble diffuser (KLa = 0.6 h¹) with pure oxygen at 101.3 kPa
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To calculate the oxygen transfer rate OTR for each scenario well use the provided equation OTR KaCo2s Co20V Given information Reactor volume V 50 m Co20 dissolved oxygen concentration in bulk wastewat... View the full answer
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Managing Supply Chain and Operations An Integrative Approach
ISBN: 978-0132832403
1st edition
Authors: Thomas Foster, Scott E. Sampson, Cynthia Wallin, Scott W Webb
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