Could MBBR Media-Fill Mitigate SOTE Impairment due to High Superficial Velocity?
High Density/Low Flux is a popular design approach for fine bubble diffusers due to efficiency. This means placing a lot of diffusers on the tank floor, and trickling air through them.
High Density/High Flux, on the other hand, is a problem because maximum tank floor airflux rate is a known design constraint for fine bubble aeration systems. It's generally recognized to be somewhere between 15-25 m3/hr-m2 of floor area (per Gillot/Heduit & Frey). Above this rate, oxygen mass transfer either levels off then starts to decline, so if you do it, you are turning up your blowers just to get lower DO's. It's counterproductive.
There are some good reasons why high tank flux impairs mass transfer. Bubbles coalesce. Bubble ascent velocities increase. Spiral flows develop. You can see an example of this in a CFD model we prepared below, representing 2 phase flow (air + water), at a high diffuser density (27%), and a high tank airflux (25 m3/hr-m2 floor area). This spiral develops after approx 100 seconds and remains for the duration of the simulation.
Over the past 6 years since entering the fixed film market, SSI has devoted time and resources to MBBR/IFAS/Media research. We asked ourselves the question, what would the 3 phase flow model (air + water + media) look like, with the same diffuser configuration and airflux? Here is what we saw:
领英推荐
A lot of questions remain, related to gas hold up, shear stress, bubble coalescence, bubble adsorption on the media, etc...
However it looks like it's worthy of further investigation, to see if tanks filled with media are subject to the same upper constraint as tanks without media. If this turns out that they have a higher limit, then it could make sense to consider media for oxygen transfer improvements at the high end of the curve.
This could be particularly interesting for industrial WWTP's or first aerobic zones in BNR's, where OUR's are high and reactor sizes are smaller, thus peak tank flux rates are more often put to the test.
Sales Man
2 年Tom Frankel thanks for sharing this. As mentioned in my earlier comment on your post - you must start a series of such posts in a format to inspire young Waste Water Treatment Professionals and create a knowledge bank for Stakeholders of the Industry. Keep it Up??
General Manager, Clear Water Solutions LLC [Al Shirawi Group]
2 年Very nice, thankyou
Senior Process and Technology Expert at Veolia Water Technologies AB - AnoxKaldnes and Hydrotech AB
2 年Hi Tom At AnoxKaldnes we have done our home work and know which of our different MBBR media types that has how much positive influence on the Oxygen Transfer and how much the Filling degree influence the same.
Parcel Process Officer .
2 年Bubble pattern and sludge colour look bad .
Environmental (Water Quality) Consulting / StarBurst Technology (Water Mixer)
2 年MBBR is an awesome option to obtain additional process treatment for undersized tanks. Especially for industrial wastewater treatment systems with less influent debris.