Comparison of the Performance of Internal and External Loop Air-lift Reactors for Water Treatment by Activated Sludge

Subject Areas : Environment Pullotion (water and wastewater)

Mohammad Ali  Salehi ¹ (استادیار مهندسی شیمی، گروه مهندسی شیمی، دانشکده فنی مهندسی، دانشگاه گیلان، رشت، ایران *(مسوول مکاتبات))
Nasrin  Hakimghiasi ² (MSc of chemical engineering/ Guilan University)

Received: 2016-12-03 Accepted : 2017-10-25 Published : 2019-11-22

Keywords: superficial gas velocity, Gas holdup, Airlift reactor, Mass Transfer,

Abstract :

Background and Objective: In This study the impacts of operating conditions such as aeration rate, the downcomer-to-riser cross-sectional area ratio (Ad/Ar), and liquid phase properties on the hydrodynamics and volumetric mass transfer coefficient in three-phase airlift reactors was investigated. Method: Experiments were conducted in external loop air-lift reactor with downcomer to riser cross-sectional area ratio (AD/AR=0.14) and internal air-lift reactors with downcomer to riser cross-sectional area ratios 0.36 and 1. Air and Water were used as gas and liquid phases, respectively and activated sludge is used as the solid phase. Findings: The liquid circulation velocity, gas holdup and mass transfer coefficient increased with an increase in the superficial gas velocity, decrease the sludge concentration and decrease downcomer to riser cross-sectional area ratio. The maximum amount of gas hold up, 0.178 in external air-lift reactor with 1%(w/w) activated sludge in superficial gas velocity 0.24(m/s) was observed. A model to predict the effect of activated sludge concentration, the superficial gas velocity and the downcomer-to-riser cross-sectional area ratio on the mass transfer activated sludge airlift reactors provided which with the experimental results are in good agreement. Discussion and Conclusion: The evaluation of internal and external reactors performance at different concentration and superficial gas velocity show that the air-lift reactor with external loop has better performance in comparison with internal airlift reactors.

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