Secondary & Supplemental Treatment: How Do They Compare?

If you’re in the aquatics industry, you probably have come across the terms “secondary” and “supplemental” treatment, but do you really understand what they are and how they differ? Those who aren’t exactly sure aren’t alone, there is considerable confusion about supplemental and secondary equipment for commercial pool water treatment and what each means for public, commercial and other aquatic facility operators.

Why is supplemental or secondary treatment important for aquatic facilities?

Before we define and compare supplemental and secondary treatments, it's important to understand why they are gaining popularity in hotels, recreation centers, water parks and other facilities. Aquatics facilities are installing supplemental and secondary treatments to improve water and air quality, reduce risk and protect swimmers.

Combined chlorine & Crypto

Primarily, supplemental and secondary treatments are used to complement chlorine by reducing harmful combined chlorine and adding protection from chlorine-resistant Cryptosporidium.  When chlorine in the aquatic facility water combines to organic material, like sweat or skin oils, it produces harmful combined chlorine, or chloramines, in the air and water. Combined chlorine can cause irritation, unpleasant "pool" odor, allergies and other health issues. Commonly referred to as “Crypto,” this parasitic infection is transmitted by ingesting contaminated water. Crypto outbreaks can result in hundreds of patrons falling ill from diarrheal disease, facility shutdowns and multi-million dollar lawsuits. In 2016, over 200 people fell ill in Arizona during a Crypto outbreak in local recreational water facilities, and more than 1,000 fell ill in Ohio in a similar event. The CDC's Model Aquatic Health Code, or MAHC, offers specialized guidelines to help aquatic facilities, as well as local and state authorities, offer a healthy and safe water environment. The MAHC recommends that aquatic facilities add Crypto protection with additional supplemental or secondary treatments. Additionally, MAHC contains recommendations that state or county health officials can use to voluntarily select to update their health codes. The code itself is a living document that is open for revision every three years.

Supplemental treatment

Supplemental systems are disinfection processes that are installed in addition to a commercial aquatic facility's primary disinfection method, like chlorine or bromine, which are required by health code. Essentially, supplemental disinfection does what chlorine or bromine can't - reduce combined chlorine and protect against Crypto - so swimmers and staff can enjoy a healthy, clean and safe pool environment.  Typically, supplemental systems are not required by health code but can enhance overall system performance and improve water quality, Centers for Disease Control and Prevention's Model Aquatic Health Code. Often, an NSF 50 certification can qualify a system to be marketed and used in the field as a supplemental treatment technology.

Secondary disinfection

Similarly to supplemental treatment, secondary systems are most often used to imply an additional form of disinfection beyond chlorine or bromine. These technologies often are required to provide science-based evidence proving their ability to reduce the levels of bacteria, viruses and parasites, like Crypto.   The MAHC guidelines recommend secondary disinfection for aquatic venues for children under 5 years old - like wading pools, interactive water play structures, etc. - and therapy pools, where there is a likelihood for bathers with open wounds. Other aquatic facilities that do not require secondary disinfection can install supplemental treatment to improve system performance and water quality.  According to the MAHC requirements, "Secondary disinfection systems shall be designed to achieve a minimum 3-log (99.9 percent) reduction in the number of infective Cryptosporidium parvum oocyst per pass through the secondary disinfection system for interactive water play aquatic venues and a minimum 2-log (99 percent) reduction per pass for all other aquatic venue requiring secondary disinfection." To learn how an independent university lab reduced 99.99% (4-log) of Cryptosporidium in under 60 minutes, download the Crypto Removal Case Study here.