ABSTRACT

From observations of bundle media with a clear plastic front section, Hinton and Stensel5 concluded that while sheet flow is the predominant type in that media, droplet flow is also important and leads to significant fluid intermixing. Droplet flow results from protrusions in the biofilm. Although the cause of protrusions is unknown, they act as sites of droplet formation, allowing droplets to bypass portions of the media before intersecting it and the sheet flow again. The points where the droplets hit are highly turbulent, resulting in significant intermixing. Thus, while the majority of the flow moves without intermixing, this behavior is frequently interrupted by fluid that has bypassed treatment, causing fluid with a higher substrate concentration

to be mixed back in. The net result is less substrate removal than predicted by models like the one in the preceding section.