These salt compounds can accumulate and negatively affect your customers’ septic systems.

A “quat” is a shorthand term for a type of chemical known as a quaternary ammonium compound. Put in the simplest terms, a quat is a complex organic salt compound used for multiple applications. Despite the similarity in naming, a quat is not and does not contain either ammonia or ammonium ion. The name comes from the similar chemical structure to these other molecules.

Where will you find them?                                                                                                        
There are literally hundreds of quats in existence and in common use in home, commercial and industrial products. A review of the ingredients of many products will reveal their presence, if you are familiar with the ingredients list. Unfortunately, most of the time the names given do not include the term quat or quaternary ammonium but instead use complex and lengthy chemical names. The amount of quats has been on the rise in homes and businesses primarily due to the requirement to reduce the use of phosphorus in cleaning products. Initially this seems like a good idea, as excess phosphorus in the environment leads to increased algae growth in many water bodies. The problem is that quats can be toxic to the microbes in our septic systems and in the soil. In commercial systems, large amounts of quats can end up in the wastewater stream due to hand dishwashing and toilet cleaning.

Quaternary ammonium salt compounds are commonly used in the following applications:

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  1. Antimicrobial disinfectants commonly found in antibacterial soap, toilet bowl cleaner and other household disinfectants. Examples are benzalkonium chloride, benzethonium chloride, methylbenzethonium chloride, cetalkonium chloride, cetylpyridinium chloride, cetrimonium, cetrimide, dofanium chloride, tetraethylammonium bromide, didecyldimethylammonium chloride, ammonium chloride and domiphen bromide.
  2. Food service establishment sanitizers. Most national restaurants, convenience stores and grocery chains require the use of quat sanitizer.
  3. Surfactants (compounds that make it easier to loosen or dissolve solids into liquids, commonly used in cleaners to release dirt into watery solutions). This includes automatic dishwashing and laundry detergent. 
  4. Fabric softeners (both liquid for use in washing machines and the dry form for use in dryer sheets).
  5. Antistatic agents, usually found in shampoos.
  6. Septic tank additives used to control septic odors by killing bacteria. This objective, however, runs counter to the purpose and function of septic tanks (promoting anaerobic bacterial growth).

It is important to note that the quat used in one application will not necessarily be effective in other applications. For example, dryer sheets (sulfur-containing quaternary ammonium salts) will not act as antimicrobials (long alkyl chain quaternary ammonium salts).  A good resource to find the active ingredient in a product is the Department of Health and Human Services Household Products database.

The problem
It is well understood that disinfectants or sanitizers in high concentrations can kill off the good microbes in our septic systems. Quats compounds are very stable and the chemical bonds are difficult to break, so they have a long biocidal effect. Quats are stable water-soluble organic salts and tend not to break down. In fact, they are used as preservatives due to their bactericidal nature and exceptional chemical stability. In a study of RV wastewater, quaternary ammonia was shown to slow down the rate of oxygen uptake by the microorganisms and be toxic to microorganisms (Hindin, 1994). 

In anaerobic environments, they have been found to be inhibitory at 5-15 mg/L and in aerobic conditions at 10–30 mg/L for BOD and 2–5 mg/L for nitrification. Another study by Gross (1987) evaluated the impacts of several chemicals including Lysol, which contains alkyl dimethyl benzyl ammonium chloride, one of the most widely used quats. The purpose was to determine the amounts of specific household chemicals required to destroy bacteria populations in individual domestic septic tanks using both lab and field studies. A Lysol concentration of 5 mL/L destroyed the bacteria in the domestic septic tanks. This corresponds to 5 gallons of Lysol in a 1,000-gallon septic tank. The bacteria population recovered to its original concentration within approximately 60 hours (2 1/2 days). Although it is unlikely that a property owner would use 5 gallons in a home at one time, the cumulative impact of these chemicals can impact system performance.

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Unlike bleach, quats are odorless and colorless. There are quat test strips that will show if the cleaning products in use contain quats or not and at what concentration. Typically what they will be measuring is benzalkonium chloride, which is used in commercial kitchen sanitation. Most of the test strips are designed for use in sinks to measure concentrations in the range of 200 mg/L, but we are interested in much lower levels. Therefore, be sure to get strips that can read down to 5 mg/L, use a Hach kit or have an analysis done at a lab (ASTM Method D5806-95).

The use of quats should be avoided. For in-home use, natural-based cleaners such as baking soda, vinegar and borax are preferred along with limited amounts of chlorine and/or other biodegradable cleaners.   

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In commercial kitchens, oxidative sanitizers like bleach or iodine are recommended over quaternary ammonia. Another potential option is a botanical disinfectant called Benefect, which is on the EPA registered disinfectant list. Hydrogen peroxide breaks down to water and oxygen and does not leave harmful residues. Peroxide sanitizers offer an alternative to more toxic cleaners, because they do not introduce irritating fumes into the air. High-temperature dishwashers may be another alternative to consider, along with commercial dishwashers using chlorine. Many national or regional chains will not stop using quats. For these sites, consider the use of NeutraQuat, a QAC neutralizer for wastewater systems.

About the Author
Sara Heger, Ph.D., is an engineer, researcher and instructor in the Onsite Sewage Treatment Program in the Water Resources Center at the University of Minnesota. She presents at many local and national training events regarding the design, installation and management of septic systems and related research. Heger is education chair of the Minnesota Onsite Wastewater Association (MOWA) and the National Onsite Wastewater Recycling Association (NOWRA), and serves on the NSF International Committee on Wastewater Treatment Systems. Send her questions about septic system maintenance and operation by email to

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