Q. How do you remove biofilm?
A. A reliable way to remove biofilm of thermophilic bacilli on stainless steel process piping and tanks is to use a two-step process entailing an alkaline cleaner, such as our Solujet® Low-Foaming Phosphate-Free Liquid, followed by an acidic cleaner, such as Citrajet® Low-Foam Liquid Acid Cleaner/Rinse. In our experience we get the best results when the first 3% Solujet (alkaline cleaner) at 75C is applied for 30 minutes and is followed by a cursory rinse. The second step of 3% Citrajet (acidic cleaner) at 75C applied for 30 minutes is followed with a final thorough rinse with water. This two-step process produces a very clean result on stainless steel. For PVC or other piping types, lower temperatures may be needed. Check with your manufacturer.
If you are not able to achieve the desired 75C temperature for the cleaning cycle, then it is possible to compensate for reduced temperature by using longer cleaning times. Since the surfactant accelerated alkaline hydrolysis reactions follow first order reaction kinetics, every 10C decrease in temperature corresponds to a doubling of the reaction time to get the same amount of reaction. (The Arrhenius equation.) Consequently, in theory, if you go down to 35C (circa 90F), you would have to clean for 480 minutes instead of 30 minutes at 75C (doubling the time 4x for a 40C temperature reduction). In practice you could probably achieve comparable results at less than 480 minutes.
In summary, if you cannot get to temperatures above 35C, then one way to clean biofilm form tanks and centrifuges would be to clean with 3% Solujet cleaner at 35C for 480 minutes (or somewhat less per above), rinse, then clean with 3% Citrajet cleaner at 35 deg C for 480 minutes (or somewhat less) and then rinse thoroughly. Of course this long a cleaning regimen and may not be practical in a manufacturing environment. Whatever can reasonably be achieved with regard to raising temperature will shorten the cleaning times. And this is certainly a heavy biofilm scenario. Subsequent cleaning, prior to a robust biofilm forming can be far shorter cycles.
Additionally, you may want to consider trying an enzymatic cleaner like our product Tergazyme® Enzyme-Active Powdered Detergent that contains both protease and surfactants. The protease addresses both the cells and any proteins bound up in the polysaccharide biofilm, whereas the surfactants improve wetting and penetration through the hydrophobic polysaccharide biofilm.
This is advantageous because efficiently removing the biofilm will lengthen the amount of time until it returns. We recommend that Tergazyme detergent be used as a maintenance step between alkaline/acidic cleaning described above. This intermittent use as a maintenance procedure will completely remove all dead cells and traces of polysaccharide biofilm which in turn slows down the formation of biofilm and allows the regular cleaning cycle to clean effectively for more cycles.
Also, please note that Tergazyme detergent is a powder that you typically mix 1-3% in cool to warm water (35C would be fine, do not exceed 55C – to ensure integrity and activity of the enzyme). Tergazyme detergent is a high foaming cleaner and would not be suitable for a spray-in-air clean-in-place system. You can pump and gently agitate Tergazyme solutions; however you cannot employ high agitation at an air/solution interface without getting excessive foam. If you have an old biofilm, you might want to do a 30 minute 1-3% Tergazyme clean (soak/recirculation) at 35C before the 3% Solujet/3% Citrajet cleaning above.
This approach with Tergazyme detergent can also be reliably used in manual surface cleaning and biofilm removal, such as in cleanrooms.
Certainly we believe that incorporating an alkaline cleaner and/or an enzymatic cleaner will improve the results as compared with some that try just bleach. In our experience, bleach alone when used at concentrations that are suitable for food contact surface does have some efficacy on thermophilic bacilli biofilms, but the efficacy is not persistent. Possibly this is because the bleaching mechanism breaks down membranes at the sulfhydryl groups and unsaturated side chains. This mechanism can often fail as you use up all exposed labile sites to attack. The biofilm might then persist underneath. Furthermore, many prefer to minimize the use of bleach to minimize chloride stress cracking on stainless steel.
We are always pleased to discuss your particular application further.
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