1. Analysis of Oxygen Diffusion Models in Water Aeration Systems ME447/547 Spring 2015 Taylor Rice

2. Background Aeration System Types ▫Splashing – Rotating paddle systems ▫Bubbling – Subsurface gas release systems Standard Applications ▫Agriculture – Some use in fertilizer application and growing techniques, soil aeration ▫Aquaculture – Sustaining plant and fish life ▫Water treatment – Decarbonization, oxidation of iron and manganese in wells, bacterial control Figure 1. Floating paddle aeration system for Agricultural use Figure 2. Bubbling pond aeration system for use in aquaculture.

3. Mechanisms Bubble Effects ▫High surface area with smaller bubbles ▫Transfer of O 2 and Nitrogen across bubble membrane Surface Effects ▫Increased surface area due to ripples on liquid surface ▫Large surface contact with atmospheric air

4. The Standard Model American Society of Civil Engineering (ASCE) standard test procedure ▫Developed to test effectiveness of bubble diffusers in water treatment ▫Develops quantities:  Standard Oxygen Transfer Rate (SOTR)  Standard Oxygen Transfer Efficiency (SOTE)  Standard Aeration Efficiency (SAE)

5. Development of Standard Model

6. Development of Standard Model Cont.

7. Problems With ASCE Standard Model Does not separate bubble and surface diffusion Does not account for changes in diffuser depth below the surface Analyzes bulk changes in concentration Does not account for diffusion of other gases (mainly Nitrogen) Simplifies or ignores important parameters for enhancing diffusion: ▫Bubble diameter ▫Bubble velocity

8. Problems with ASCE Model Cont. The ASCE model is functionally useless for designing aeration systems. However, ▫ASCE model standardizes testing procedure for aeration systems ▫Gives baseline parameters which evaluate aeration systems effectively: SOTR, SOTE, SAE

9. The Separated Model Developed by Connie DeMoyer et al. (2002) Separates bubble and surface interactions for subsurface diffusers. Indicates where transfer occurs Gives insight to the effects of important design parameters Accurate for differing diffuser depths (Standard: 3m-5m)

10. Development of Separated Model

11. Development of Separated Model Cont.

13. Determining Parameters

14. The following snip from DeMoyer shows the how to evaluate this quantity:

15. Results of Separated Model Figure 1. Fitted vs. Measured DO concentrations (Demoyer et al.)

16. Results of Separated Model

17. Effects on Mass transfer Coefficient

18. Special Considerations Figure 3. Schematic of bubble aeration system. (Demoyer et al.)

19. References Boyd, Claude E. "Pond Water Aeration Systems." Aquacultural Engineering: 9-40. Print. DeMoyer, Connie D, Erica L Schierholz, John S Gulliver, and Steven C Wilhelms. "Impact of Bubble and Free Surface Oxygen Transfer on Diffused Aeration Systems." Water Research: 1890-904. Print. McWhirter JR, Hutter JC. Improved oxygen mass transfer modeling for diffused/subsurface aeration systems. AIChE J 1989;35(9):1527–34. Stenstrom, Michael K., Shao-Yuan (Ben) Leu, and Pan Jiang. "Theory to Practice: Oxygen Transfer and the New ASCE Standard." Proc Water Environ Fed Proceedings of the Water Environment Federation (2006): 4838-852. Print.