Bacteria is everywhere. Under ideal conditions, these single celled organisms can multiply as frequently as every 30 minutes. In a twelve-hour period, one cell can grow to over 33M. Due to these rapid growth tendencies, choosing the proper disinfection technology is more critical than ever.
At Watertech we rely extensively on biocides to aid in the prevention of biofilm in cooling towers. Additionally, microbicides have become widely accepted in other applications including: healthcare, commercial, food/beverage and wastewater. Below we will outline some common oxidizing microbicides, their benefits, and most common applications.
Choosing the Best Biocide for Your Application
There are a wide array of solutions available to help manage and prevent microbial growth. Identifying the advantages and potential disadvantages of each can help you determine the best treatment for your water system.
Common Biocides and Disinfectants
Chlorine (sodium hypochlorite)
Chlorine is one of the most widely used biocides mainly due to the fact it is relatively inexpensive and readily available. While it is typically the lowest cost option, due to its high volatile and oxidative state, it can be aggressive to the metals that make up your piping systems. It has been known to cause corrosion specifically in domestic water piping and cooling tower systems when not fed at proper dosages. Chlorine can also form THM (trihalomethanes), a cancer-causing by-product.
Stabilized Bromine
Stabilized bromine is used for the disinfection of cooling towers and is a good choice for spas and other situations with warmer water. Bromine is more costly than chlorine, but more stable in the warmer temperatures. It has less odor and is also less irritating to the skin. It works in a wider range of pH levels and dissolves slowly so you can maintain water quality for a longer time period.
Chlorine Dioxide
Chlorine dioxide, a molecule used in both domestic water and process water treatment, is a chlorine-based chemistry. Its ability to be successful in all types of makeup water make it an attractive choice. It can penetrate both sessile and planktonic levels of the biofilm. While it is less aggressive than chlorine, its stability in hot water is less than desirable. Another potential drawback is that a generator may be required to produce the chemical on site.
MANUFACTURING application: Watertech recently used chlorine dioxide in a Whey production facility to disinfect their COW (Condensate of Whey) Water. COW water without disinfection causes microbiological fouling in the reverse osmosis system membranes, ammonia condenser bulk water, and boiler feedwater. The residual ClO2disinfectant removed the organics that caused the fouling, thus the system was able to operate more efficiently.
Monochloramine
Monochloramines are the most stable of the three chlorine-based disinfectants. Not only does the stability help with efficacy and ability to stay in solution for long periods of time, but it is proven to be the least corrosive chlorine-based chemistry. Its primary function is in disinfecting drinking water and penetrating biofilm in healthcare domestic hot water systems.
HEALTHCARE, COMMERCIAL & INDUSTRIAL application: Watertech strongly recommends monochloramine in hot water systems with high bacteria counts. Because most municipalities use chlorine as their primary disinfectant, healthcare facilities need to supplement with monochloramines to help combat waterborne pathogens that are resistant to low free chlorine residuals. Additionally, domestic hot water systems are at temperatures where bacteria thrive (70-110F), adding supplemental disinfection will help prevent bacteria amplification and over time remove the biofilm.
Peracetic Acid
Peracetic acid is a low-cost biocide that kills microbes without leaving residue on your GMP surfaces. It produces little to no toxic by-products. However, its main drawback is that it can be highly corrosive. It is used almost primarily in the food and beverage industry or in hospitals for equipment and instrument sterilization.
FOOD & BEVERAGE application: Peracetic acid is a very strong oxidizer often used in the food industry on processing equipment, and for spray washing food products. It is also suitable for air washers as a disinfectant because it produces no harmful byproducts.
Hydrogen Peroxide
Hydrogen peroxide is used as a biocide to prevent microbial growth in water systems.
WASTEWATER application: One Watertech wastewater customer has seen success feeding hydrogen peroxide into anaerobic solids prior to their screw press. The addition of the hydrogen peroxide causes lysing of the bacteria which releases liquid from the solids and allows for more effective dewatering of the anaerobic solids. The result is lower chemical feed rates and improved cake dryness from the screw press.
Considerations When Selecting Biocides
| Type of Biocide |
Advantages |
Disadvantages |
Common Applications |
| Chlorine |
• Low cost
• Readily available
• Effective in open systems
• Kills planktonic biofilm
(Free floating)
|
• Can form NTM by-products in hot water recirculation systems.
• Corrosive to metals |
• Cooling towers
• Secondary disinfection
• Produce washing
• Breweries |
| Stabilized Bromine |
• More stable than chlorine in warmer temperatures
• More effective at maintaining the correct pH
• Less odor
• Less of a skin irritant |
• More costly than chlorine
• Takes a little longer to activate than chlorine
• Low pH |
• Cooling towers
• Spas and hot tubs |
| Chlorine Dioxide |
• Quick killing
• Effectively penetrates biofilm |
• Generator may be required
• Difficult to maintain residual in hot water systems
• Generates chlorite as a disinfection by-product in domestic water application
|
• Cooling towers
• Secondary disinfection
• Produce washing
• Breweries |
| Monochloramine |
• Most effective against biofilm
• Least corrosive to metals
• Highest stability |
• Generator Required
• Slower kill rate than chlorine/chlorine dioxide
|
• Secondary disinfection
• Cooling tower |
| Peracetic Acid |
• Low cost
• Effective at removing/
killing microbes on surface |
• Can be highly corrosive |
• CIP cleaning
• Produce washing
• Cooling towers
• Breweries
|
| Hydrogen Peroxide |
• Low cost
• Aggressive oxidizer
|
• Regulated by Homeland Security
• Greater safety concerns |
• Cooling towers
• Wastewater
|