A study of optimum aeration efficiency of a lab‐scale air‐diffused system

Ba’ba’a, H. Al; Amano, Ryoichi S.

doi:10.1111/wej.12261

Cited by 12 publications

(4 citation statements)

References 18 publications

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“…This might be due to the effect of the liquid recirculation flow pattern in the ALR resulting in bubble break-up mechanism, as can be seen in the d B value in the BCR and the ALR. Smaller bubbles tended to have lower rising velocity [22]. Moreover, every solid media added resulted in a positive performance in BCR through decreasing bubble rising velocity, mean increasing bubble retention time in a liquid system, especially the ring solid media due to its capability to capture the gas bubble inside.…”

Section: Bubble Rising Velocity (U B )mentioning

confidence: 97%

Relative Effect of Additional Solid Media on Bubble Hydrodynamics in Bubble Column and Airlift Reactors towards Mass Transfer Enhancement

et al. 2020

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Many researchers have focused on multi-phase reactor development for improving mass transfer performance. However, solid particle addition in gas–liquid contactor for better oxygen mass transfer performance is still limited. Hence, this study aims to analyze the relative effect of different types of local solid media on the bubble hydrodynamic characteristics towards mass transfer enhancement in bubble columns (BCR) and airlift reactors (ALR). This was investigated by varying solid media types (ring, sphere, cylinder, and square), solid loadings (0%–15%), and superficial gas velocities (Vg) (2.6–15.3 × 10−3 m/s) in terms of the bubble hydrodynamic and oxygen mass transfer parameters. The result showed that bubble size distribution in BCR and ALR with additional plastic media was smaller than that without media addition, approximately 22%–27% and 5%–29%, respectively, due to the increase of the bubble breaking rate and the decrease of the bubble rising velocity (UB). Further, adding media in both reactors significantly decreased the UB value. Since media increased flow resistance, resulting in decreased liquid velocity, it can also be the moving bed to capture or block the bubbles from free rising. Therefore, oxygen mass transfer performance was investigated. The oxygen transfer coefficient (KLa) in BCR with solid media addition was enhanced up to 31%–56% compared to a non-addition case, while this enhancement was greater at higher solid loading due to its higher effective surface, resulting in a higher bubble break-up rate compared to the lower loading. In ALR, up to 38.5% enhanced KLa coefficient was archived after adding plastic media over the non-addition case. In conclusion, ring and cylinder media were found to be the most significant for improving KLa value in BCR and ALR, respectively, without extra energy.

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Section: Bubble Rising Velocity (U B )mentioning

confidence: 97%

Relative Effect of Additional Solid Media on Bubble Hydrodynamics in Bubble Column and Airlift Reactors towards Mass Transfer Enhancement

et al. 2020

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“…Smaller bubbles (3.14-4.90 mm) regulated by the F-sand diffuser led to having a lower U B value than larger bubbles of using other diffusers. Larger bubbles, basically from larger orifice diffusers, have higher U B as explained through the relationship between gas-liquid contact time and oxygen transfer efficiency [11,29]. In ALR, the values of U B distributes between 1.6 and 6.75 dm/s.…”

Section: Bubble Diameter (D 32 ) and Rising Velocity (U B )mentioning

confidence: 98%

Effective Analysis of Different Gas Diffusers on Bubble Hydrodynamics in Bubble Column and Airlift Reactors towards Mass Transfer Enhancement

et al. 2021

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Even bubble column reactors (BCR) and airlift reactors (ALR) have been developed in terms of various related aspects towards mass transfer enhancement, the effective analysis of gas diffuser types on mass transfer and gas–liquid hydrodynamic characteristics is still limited. Therefore, the present study aims to analyze the relative effect of different types of air diffusers on bubble hydrodynamics and mass transfer performance to understand their behaviors and define the best type. The experiments were conducted by varying different diffuser types, reactor types (BCR and ALR), and superficial gas velocity (Vg) (0.12 to 1.00 cm/s). Five air diffusers including commercial fine sand (F-sand) and coarse sand (C-sand) diffusers, and acrylic perforated diffusers with orifice sizes of 0.3 mm (H-0.3), 0.6 mm (H-0.6), and 1.2 mm (H-1.2), were used in this study. For every condition, it was analyzed in terms of bubble hydrodynamics and oxygen mass transfer coefficient (KLa). Lastly, the selected diffusers that provided the highest KLa coefficient were evaluated with a solid media addition case. The results of both reactor classes showed that F-sand, the smallest orifice diffuser, showed the smallest air bubbles (3.14–4.90 mm) compared to other diffusers, followed by C-sand, which larger about 22–28% on average than F-sand. ALR exhibited a better ability to maintain smaller bubbles than BCR. Moreover, F-sand and C-sand diffusers showed a slower rising velocity through their smaller bubbles and the tiny bubble recirculation in ALR. Using F-sand in ALR, the rising velocity is about 1.60–2.58 dm/s, which is slower than that in BCR about 39–54%. F-sand and C-sand were also found as the significant diffusers in terms of interfacial area and gas hold-up. Then, the KLa coefficient was estimated in every diffuser and reactor under the varying of Vg. Up to 270% higher KLa value was achieved from the use of F-sand and C-sand compared to other types due to their smaller bubbles generated/maintained and longer bubble retention time through slower rising velocity. After adding 10% ring shape plastic media into the reactors with F-sand and C-sand diffusers, a better performance was achieved in terms of KLa coefficient (up to 39%) as well as gas hold-up and liquid mixing. Lastly, ALR also had a larger portion of mixed flow pattern than BCR. This eventually promoted mass transfer by enhancing the mixed flow regime.

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“…The aeration process is typically accomplished in large tanks, with compressors specifically sized to the hydro-static head and airflow required to facilitate aerobic treatment [18,20,27]. The compressors have to deliver large amounts of air during the aerobic cycles, consequently, the aeration process is an energy demanding process responsible for up to 75% of the total electric power demand at a WWTP [27][28][29][30]. However, electricity consumption should not be considered solely, as the discharge of nutrients is object to taxation, e.g., 30 DKK/kg discharged in Denmark [26].…”

Section: The Aeration Processmentioning

confidence: 99%

“…The compressors have to deliver large amounts of air during the aerobic cycles, consequently, the aeration process is an energy demanding process responsible for up to 75% of the total electric power demand at a WWTP [27][28][29][30]. However, electricity consumption should not be considered solely, as the discharge of nutrients is object to taxation, e.g., 30 DKK/kg discharged in Denmark [26]. Therefore, cost-analysis suggests aeration should be minimized while ensuring a satisfactory extent of nitrification [26,31].…”

Section: The Aeration Processmentioning

confidence: 99%

Compressor Scheduling and Pressure Control for an Alternating Aeration Activated Sludge Process—A Simulation Study Validated on Plant Data

Hansen

Veng

Durdevic

2021

Water

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Aiming at reducing their emissions, wastewater treatment plants (WWTP) seek to reduce their energy consumption, where a large amount is used for the aeration. The case plant, Grindsted WWTP uses an alternating aeration strategy, with a common air supply system facilitating the process in four aeration tanks and thus making optimisation challenging. In this work, a nonlinear model of the air supply system is designed, in which multiple key parameters are estimated by data-driven optimization. Subsequently, a model-based control strategy for scheduling of compressors and desired airflow is proposed, to save energy without compromising the aeration performance. The strategy is based upon partly static- partly dynamic models of the compressors, describing their efficiency in terms of system head and volumetric airflow rate. The simulation study uses real plant data and shows great potential for improvement of energy efficiency, regardless of the aeration pattern in any of the four process tanks, and furthermore contributes to a reduction in compressor restarts per day. The proposed method is applicable to other WWTP with multiple compressors in the air supply system, as this study is conducted using first principle models validated on data from the daily operation.

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A study of optimum aeration efficiency of a lab‐scale air‐diffused system

Cited by 12 publications

References 18 publications

Relative Effect of Additional Solid Media on Bubble Hydrodynamics in Bubble Column and Airlift Reactors towards Mass Transfer Enhancement

Relative Effect of Additional Solid Media on Bubble Hydrodynamics in Bubble Column and Airlift Reactors towards Mass Transfer Enhancement

Effective Analysis of Different Gas Diffusers on Bubble Hydrodynamics in Bubble Column and Airlift Reactors towards Mass Transfer Enhancement

Compressor Scheduling and Pressure Control for an Alternating Aeration Activated Sludge Process—A Simulation Study Validated on Plant Data

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