In our last article we talked about how to eliminate and prevent biofilm build up in watering systems (click here to see article). But it is also important to know that some common practices being used to rid watering system of pathogens are only marginally effective in doing so (sometimes even counterproductive) and should be avoided. The biggest concern, however, is that the misuse of harsh disinfecting chemicals may actually be more effective in damaging a watering system than in stripping away biofilm that sustains the bacteria.
Typically, a disinfecting agent such as chlorine kills suspended and surface pathogens but unfortunately not the ones embedded in the subsurface of the biofilm. To eliminate the embedded threat, an ongoing program that includes the use of a cleaning agent to strip the biofilm off the interior pipe wall combined with flushing will do the job. Without the nutrient enriched biofilm in the drinker lines, pathogens cannot survive.
Following are common disinfecting agents that we DO NOT RECOMMEND using in your watering system for the purpose of biofilm removal:
- Chlorine. While it may kill bacteria suspended in the water, it is generally ineffective in killing bacteria embedded in the biofilm and equally ineffective in stripping it away. Also keep in mind that watering systems can only tolerate chlorine levels up to 1 ppm. Levels greater than 1 ppm will cause corrosion. The higher the chlorine level the sooner the onset of watering system component damage — 5 ppm will result in damage much sooner than a level of 2 ppm. Combining high levels of chlorine and lowering the pH to below 6 (use of acidifiers) makes the chlorine even more aggressive. Unwelcome watering system failure will result.
- Acidifiers. The use of acidifiers follows a similar pattern as chlorine. Aggressively lowering the pH of water will indeed kill surface and suspended pathogens (but again not embedded ones) they are less effective in biofilm removal. Of greater concern is that in order to be marginally effective at either, the pH has to be lowered to levels that can only result in watering system component damage. Some suppliers have recommended lowering the water to 3 pH which is 10,000 times more acidic than neutral water (7 pH) and not far from the pH of battery acid which is around 1 pH. Little wonder that damage to watering systems is the end and unwanted result.
- Citric acid. A weak acid with only limited disinfecting and cleaning properties – thus not very effective killing pathogens nor getting rid of biofilm either. Rather, since it also has a high carbohydrate content, it can actually add nutrients that will increase biofilm formation in the drinker lines. Acids in general are to be avoided when attacking biofilm because of the potential corrosive effect on the watering system.
- Surface Antimicrobials like quats leave much of the biofilm intact and do not remove or destroy endotoxins.
- Chlorine Dioxide is a strong oxidizing agent that reacts with the surface, and kills pathogens on the biofilm, but does not break down or remove the biofilm.
- Peracetic Acid also affects biofilm surfaces, but is quickly neutralized by catalase. There is no hydrolysis or breakdown of biofilm polysaccharides.
- Bleach. Another often-used disinfectant, but it is not a cleaner and does not break up, nor does it assist in biofilm removal.
The clear message with all these disinfectants is: if it does not strip away and remove the biofilm’s sticky host substance, the bacteria will quickly return to the pre-disinfectant level. In 24 hours at 32 degrees C (90 degrees F), a single E. coli organism multiplies into trillions of E. coli.
So producers are wise to consider the potential trade offs involved in whatever they inject into the drinker lines, and to remember that to truly eliminate the threat that biofilm poses, they must eliminate the biofilm itself, not just disinfect the surrounding water. To do this, our recommendation is to use a properly formulated solution of hydrogen peroxide. Click here for our post about this cleaning method.