If you are having bacteria or algae problems in your chilled water systems, non-oxidizers are commonly slug fed to kill off the bacteria. The most common products used to kill off the bacteria in your chiller is Glutaraldehyde. Glutaraldehyde is slug fed at 45 to 115 ppm as a routine basis and slug fed up to 225 ppm as a strong effective kill. You should use bacteria slides and keep the bacteria levels below 10^3. When levels get higher, slug feed as needed.
You may also use Isothiazolin as a second option, but keep in mind Isothiazolin is a sensitizer chemical and some people may have severe outbreaks when in contact or even being around the vapor of Isothiazolin. For this reason, we suggest using Glutaraldehyde.
In theory, it is a common belief in the water treatment field that you need to alternate between biocides. This is because in studies have indicated some bacterias can become immune from the non-oxidizer if you only feed one, so by alternating the biocides it will keep a more effective kill. ChemWorld suggests starting with Glutaraldehyde and performing weekly dip slides. If you have problems getting your bacteria under control try alternating biocides.
How do I feed Glutaraldehyde? You need to feed get the chemical into the system as fast as possible. This can be with an AOD pump of by manually pouring the chemical into the basin. The key is you must reach the threshold of around 100 ppm (depending on the bacteria) of active Glutaraldehyde in your process water, in order to have an effective kill. If you slowly pump Glutaraldehyde into the system, you can use excess amount and ultimately never reach a good kill rate which will cost more money and produce poor results.
Does Nitrite cause bacteria in the chilled water? Also, if your chilled water is above 45F, you many not choose to use a nitrite based product. Nitrite may be a food source for bacteria development. If you have above 45F chilled water temperatures, you may consider using a straight Molybdate product. Molybdate is more expensive compared to nitrite, so you will need to determine if the process is critical enough to justify the additional expensive for controlling your corrosion rates. The most concentrated liquid molybdate is 35% sodium molybdate.