Here is the science behind why foam fractionazation is selective with the types/sizes of bacteria that adher to the bubbles.
Whats in the skimmate?
Introduction; in part.
You are here: Home › Volume IX › January 2010 › Feature Article: Further Studies on Protein Skimmer Performance
Feature Article: Further Studies on Protein Skimmer Performance
By Ken S. Feldman, Kelly M. Maers
Department of Chemistry, The Pennsylvania State University, University Park, PA 16802. Many factors contribute to the 'value' of a skimmer to an aquarist, including quality of construction, size, footprint, noise level, ease of cleaning, energy efficiency of the pump, and of course, the ability to remove organic waste from aquarium water.
CONTENTS
The Modified Mathematical Model
The Math Behind It
The Experimental Design
Results
Skimmer Comparison Studies
Conclusions
Acknowledgments
References
We published a paper on skimmer performance in the January 2009 issue of Advanced Aquarist magazine that detailed, for the first time, an experimental methodology to provide meaningful metrics for both the rate at which skimmers removed organics and the extent of the removal of these organics from aquarium water (Feldman, 2009). Highlights of these earlier studies included:
Analysis of these data for four representative skimmers; a EuroReef CS80 needlewheel skimmer, a Precision Marine ES100 venturi skimmer, a Precision Marine AP624 airstone skimmer, and an ETSS Evolution 500 downdraft skimmer.
Conclusions about relative skimmer performance based upon these measurements:
All four skimmers removed both BSA and TOC with similar rate constants; in short, "bubbles is bubbles", and there was no significant difference between these four skimmers in their intrinsic abilities to strip organics from saltwater.
Only about 20 - 30% of the measurable TOC in reef tank water was removed by skimming, whereas almost all of the BSA was removed from saltwater by skimming.
In the last paragraph before the conclusion, Feldmen discribes the selective removal of certain bacteria types at the molecular level due to thermodynamics and hydropobic surfaces.
The discussion is above my pay grade, but I understand the implications.
Patrick
One of the more surprising and important observations to emerge from the earlier skimmer studies was that the four original skimmers tested removed only 20 - 30% of the measurable TOC in the reef tank water examined; the remaining 70 - 80% of the TOC was not removed by skimming. Extension of these measurements to the three new skimmers tested in this study did not add much to the argument. The Reef Octopus' removal amount fell within this range, whereas the Bubble King and Royal Exclusiv skimmers appeared to remove incrementally more of the extant TOC, perhaps up to the mid-30% range. An explanation for this observation was offered in the January 2009 Advanced Aquarist article; in summary, skimmers can only remove what bubbles trap, and bubbles only trap molecules and/or particles (i.e., bacteria, diatoms, etc.) with some compelling thermodynamic reason to adhere to the bubble's surface. On the molecular level, this surface association is typically driven by the molecule/particle having a hydrophobic (= water hating) patch that can be buried in the bubble surface/interior. This arrangement avoids the energetically penalizing juxtaposition of hydrophobic surfaces with (hydrophilic) water, and so overall the system energy is lowered (a favorable occurrence). Some of the molecules/particles in aquarium water will meet this hydrophobic region criterion, and some will not. The ones that do not have a sufficiently large hydrophobic patch will not interact with bubbles, and hence will not be removed by skimming. From, the results of the experiments described here, it appears that only 20 - 35 % of the measurable TOC meets this hydrophobicity criterion (= [TOCl] defined earlier) whereas the remaining 65 - 80 % does not (= [TOCr] defined earlier). In essence, bubbles are a rather poor media for removal of organic nutrients from aquarium water compared to, for example, GAC. However, they do have the distinct benefit of being cheap.
