simulation and optimization of an airlift recirculation a

Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences

—— 9th IWA Symposium on Systems Analysis and Integrated Assessment

Simulation And Optimization Of An Airlift Recirculation A/O-MBR Using CFD With

PIV Validation

Presented by: Yang Min 14th-17th, June, 2015

Yang Min*, Yuan Xing*, Wei Yuan-song* , Xu Rong-le*， Luo Nan*, Yu Da-wei*, Zheng Xiang**， Fan Yao-bo* * Research Center for Eco-Environmental Sciences, Chinese Acadamy of Sciences ** School of Environment & Natural Resources, Renmin University of China

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What

How

Conclusion

Background and Why

Acknowledgement

Menu

Outline

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Background & Why

Capacities (m3/d) Numbers

0~10,000 ＞1,000

10,000 ＞60

100,000 5

Table 1 MBRs with different capacities in China by 2015

10.84% 0.43%

36.18%

1.47% 6.66% 3.48%

9.53% 11.99%

0.13% 8.20% 7.22% 3.87%

Feed pump Screen Air compressor Agitation External recirculation Internal recirculation Suction Reclaimed water Non-production Sludge dewatering Sludge drying MCC

Fig. 1. Composition of energy consumption of an A2/O-MBR in China

Approaches for energy saving?

Ø  Intermittent aeration,

Ø  Scaling up,

Ø  ......

Ø  No recirculation pumps

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Pro vs Con

Airlift recirculation A/O-MBR

Energy saving

HQ effluent

Small footprint

DO distribution

Scouring

Mixing

Background & Why

Velocity, TKE, Shear rate CFD&OMT

Hydrodynamics Source term

DO

Innovation:

Methodology:

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What

How

Conclusion

Background and Why

Acknowledgement

Menu

Outline

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Fig.2. Diagram of the Integrated airlift A/O-MBR

Items Parameters Scale 100.0 L/d HRT 14.0h SRT 20.0d Flat sheet membrane

Sinap-25-PVDF, pore size≤0.1µm

Operation flux 10.5LMH

A e r a t i o n intensity

0.5 (SAD 25), 1.0 (SAD 50), 1.5 (SAD 75) m3/h

Connecting hole diameter

10.0mm

Impellers Double straight oar 60 rpm w: d: D= 0.25: 1.00: 1.25

Table 3 Geometry and operation parameters

Ø  What’s new ?

What— Material & Method

Ø  Key concerns ?

Diameter: 10 mm

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Fig. 3. Configuration of the airlift recirculation A/O-MBR


X

Y

Z

Aeration tank

Anoxic tank

Membrane module

Reflow hole

Outflow hole

600mm

Membrane sheet

𝒘↓𝒎 

𝒔↓𝒑  𝒔↓𝒑 

𝒉↓𝒎 

25 (0.5 m3/h) SAD 50 (1.0 m3/h) 75 (1.5 m3/h)

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Ø  PIV (EM3-03M1500, Micro Vec Co., LTD) : (1) 10 mg·L-1 of glass micro-beads, (2)

45.0mm × 30.0 mm of illuminated planar cross-sections, (3) a CCD camera taking 206

pictures per second, (4) 15.0 seconds × 3 times.

Ø  Fluorescence DO meter (Multi 3410, WTW Co. Ltd, German).


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water velocity DO

Fig. 4. Area-weighted average water velocity (left) and DO concentration (right) at the cross section of reflow hole

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Fig. 4. Comparison of dimensionless water velocities measured by PIV and that simulated by CFD

Fig. 5. Simulation vs experiment of DO in the airlift A/O-MBR (S1~S3 positioned in oxic tank, S4~S6 positioned in anoxic tank)


RSD＜ 5.0% RSD＜ 5.0%

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Items Settings

Models & methods RNG k-𝜀 model; Euler-Euler approach; Second order upwind

Phases Gas-liquid phase

Time dependence Average transient state for flow equations & steady state for source term

Membranes Impermeable wall: no-slip (free-slip) boundaries for the liquid (gas) phase

Inlet Velocity inlet

Outlet Degassing boundary

Bubbles Constant diameter and shape

Grid size 98 850, 208 800, and 420 600 hexahedral elements


Ø  Mass conservation:

𝛻(𝛼↓𝑞 𝜌↓𝑞 𝑣 ↓𝑞 𝑣 ↓𝑞 )=− 𝛼↓𝑞  𝛻p+ 𝛻𝜏 ↓𝑞 +𝛼↓𝑞 𝜌↓𝑞 𝑔 +(𝑅 ↓𝑝𝑞 + 𝑚 ↓𝑝𝑞 𝑣 ↓𝑝𝑞 − 𝑚 ↓𝑞𝑝 𝑣 ↓𝑞𝑝 )+(𝐹 ↓𝑞 + 𝐹 ↓𝑙𝑖𝑓𝑡, 𝑞 + 𝐹 ↓𝑣𝑚, 𝑞 )

Ø  Mass transfer:

𝑚 ↓𝑞↑𝑖 𝑝↑𝑗  = 𝑘↓𝐿 a(S↓𝑂↑∗ − 𝑆↓𝑂 ); 𝑅↓𝑖↑𝑞 = 𝛼𝑆↓𝑂 /𝑆↓𝑂 + 𝐾↓𝑂  OUR↓max 

Ø  Momentum equation:

𝛻(𝛼↓𝑞 𝜌↓𝑞 𝑣 ↓𝑞 )= 𝑚 ↓𝑝𝑞 − 𝑚 ↓𝑞𝑝 + 𝑆↓𝑞 

𝛻(𝛼↑𝑞 𝜌↑𝑞 𝑣 ↑𝑞 𝑌↓𝑖↑𝑞 )=𝛻(𝛼↑𝑞 𝐽 ↓𝑖↑𝑞 )+ 𝛼↑𝑞 𝑅↓𝑖↑𝑞 − 𝑚 ↓𝑞↑𝑖 𝑝↑𝑗   𝑘↓𝐿 a=12𝛽𝛼↓𝑏 ∕𝑑↓𝑏  √𝐷↓𝐿 ∆𝑈∕𝜋𝑑↓𝑏   ; source term

sink term

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What

How

Conclusion

Background and Why

Acknowledgement

Menu

Outline

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Ø  𝑠↓𝑝 : 1/1 (1A), 1/2(2A), 1/3 (3A), 1/5 (5A) and 1/7 (7A) (height of diffusers 30mm; ℎ↓𝑚  150mm; SAD 50).

How— Results & Discussion

1A_150_30 2A_150_30 3A_150_30 5A_150_30 7A_150_30

Fig. 6. Effect of diffusers’ interval on flow field in membrane tank

Fig. 7. Shear stress(left) & water velocity (right)

1/1

1/2

1/3

1/5

1/7

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0.10

0.20

0.30

0.40

0.50

0.60

0.70

Shea

r stre

ss (P

a)

1A_150_30 2A_150_30 3A_150_30 5A_150_30 7A_150_30

Fig. 8. Area average shear stress


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Fig. 9. Effect of 𝒉↓𝒎  on flow field of membrane tank

Ø  Mixing height ℎ↓𝑚 (150, 300, 450, 600mm). Aerator tubes 3; SAD 50; height of tubes 30mm.


Fig. 10. Water velocity under different 𝒉↓𝒎 

3A_150_30

3A_300_30

3A_450_30

3A_600_30

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0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

Shea

r stre

ss (P

a)

3A_150_30 3A_300_30 3A_450_30 3A_600_30

Fig. 11. Area average shear stress


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(b) (a)

(c) (d)


4.19 ± 0.22 mg/L

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Fig.14. Volume average dissolved oxygen concentration of membrane tank and anoxic tank in at different aeration intensities (left: SAD25, middle: SAD 50, right:

SAD 75)

[mg L^-1]

2.30 ± 0.13 mg/L 4.19 ± 0.22 mg/L 4.88 ± 0.29 mg/L


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Fig.13. Average DO concentration of membrane (oxic) tank and anoxic tank

Fig.15. IRR and proportion of hypoxia in anoxic tank at different aeration intensities

Ø  The study of DO concentration under different SADs showed an adaptability of this airlift A/O-MBR .


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What

How

Conclusion

Background and Why

Acknowledgement

Menu

Outline

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(1)  The OMT- CFD model was developed for the simulation of DO

concentration. Further work will be done by coupling CFD with

biology-kinetics.

(2)  The new airlift recirculation A/O-MBR was designed and optimized

in terms of shear stress and DO concentration. The operational energy

of this A/O-MBR can be saved by 10%~20%.

(3)  A smaller 𝑠↓𝑝  and a higher mixing height ℎ↓𝑚  helped to get an even

shear stress distribution on membrane surfaces. Better strategies may

be needed for DO concentration control.

Conclusion

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What

How

Conclusion

Background and Why

Acknowledgement

Menu

Outline


Thank you Thank you for your attention!


The authors acknowledge the funds (No. 51278483) by the

National Natural Science Foundation of China.

simulation and optimization of an airlift recirculation a

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