When summer temperatures rise, chlorine demand inside storage tanks increases and water quality can degrade. Warm water temperatures, particularly at the top of the tank, increase biological growth, deplete residual disinfectant and increase the formation rate of disinfection by-products (DBPs). Thermal stratification also creates hot and humid conditions inside the headspace, greatly accelerating corrosion rates inside steel tanks. One effective solution to combat stratification and maintain disinfectant residual levels is active mixing. A powerful mixer eliminates thermal and chemical stratification inside tanks and reduces the growth of biofilms and DBPs. Below, we answered three common questions on maintaining residual disinfectant levels inside water storage tanks.
Q: Compared to other solutions, why is active mixing a more effective way to maintain chlorine residual in tanks?
Active mixing works by continuously circulating the cool, residual-rich water entering the tank - ensuring consistent temperature and chemistry throughout the entire volume. Having a well-mixed tank slows the rate of biological growth and maintains a velocity that reduces sediment accumulation on the floor of the tank. Less biofilm and sediment accumulation in the tank will help maintain chlorine levels. Strategies such as deep-cycling and separating the inlet and outlet are insufficient methods for mixing tanks and have proved to be ineffective for maintaining chlorine residual.
Q: If I get an active mixer, why is tank cleaning also important for maintaining chlorine residual?
Cleaning and inspecting your tank periodically, as well as repairing and touching up interior tank coatings, is critical for reducing biological growth and maintaining chlorine residual in your tank. Mixing is not a silver bullet: placing an active mixer inside a dirty tank will not magically improve water quality. You need a comprehensive approach to tank asset management, and we recommend restoring the tank interior to its original, as-built condition before you install a mixer. However, maintaining a clean tank does require a mixer: it keeps biofilm formation under control and reduces sediment accumulation. Cleaning and mixing together are like a one-two punch for improving water quality in the distribution system.
Q. If I have high DBP levels in my tank and need in-tank aeration, will it reduce my chlorine residual?
The in-tank aeration technologies we use do not have a large effect on chlorine residual. Trihalomethanes, the most common regulated disinfection by-product, are a volatile compound and are removed at a much faster rate than chlorine residual. The amount of chlorine residual loss from aeration is small, approximately 10% or less.