The Mix

A standpipe is a ground-supported storage tank with a height that is greater than its diameter. Its design helps generate storage and pressure with a low upfront cost compared to elevated tank geometries. While there are cost advantages to standpipes, its geometry is a liability: tall and skinny tanks naturally promote thermal stratification and harm water quality. Standpipes have a higher surface area to volume ratio – meaning that more surface area is exposed to heat from the sun, and there’s less volume inside the tank to absorb that heat. Additionally, the limited cross-sectional area of a standpipe makes it difficult to exchange heat between the hot water at the top of the tank and cold water at the bottom, resulting in thermal stratification. Below we have compiled four signs that indicate your standpipe is thermally stratified.

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.

There are many design factors for operators and engineers to consider when specifying mixers for water storage tanks – ranging from tank size and geometry to obstructing tank internals like columns and baffles. Below are the three of the most common questions we’ve received regarding mixing and storage tank design.  Feel free to add your own tank design challenge to the list by leaving a comment below.

Record-setting heat waves are sweeping the country this summer, placing higher-than-usual demand on water utilities. High water use by consumers typically translates into high turnover in water storage tanks, giving water less time to age and stagnate within the tank. However, areas with large capacity tanks or low summer demand can suffer from thermal stratification inside water storage tanks and serious water quality problems.

Charles Fishman (author of The Big Thirst) wrote a piece for the Washington Post last month on “Five Myths About Water.” Number two on Charles’ myth list is “bottled water is better than tap water,” where he unveils that tap water is actually MORE closely monitored than bottled water and that in blind taste tests “people can’t reliably pick bottled from tap.” At PAX Water, Charles’ article got us thinking about some of the myths we’re trying to bust in the drinking water industry. Here are our top five:

Temperatures are expected to top 100 degrees across much of the Eastern seaboard this week and municipalities large and small will be contending with managing their water quality. 

Are you going to ACE10 next week in Chicago? PAX Water Technologies will be there.

Because mixing in water storage tanks is a new concept, many people don’t realize that there are actually two different types of mixing: active mixing and passive mixing. Most state regulators don’t appreciate the difference either.

Active mixing has been shown to eliminate thermal stratification, prevent the formation of dead zones, reduce disinfectant residual loss and improve overall water quality in potable water storage tanks. 

Welcome to the PAX Water Technologies' Web Log! Four years ago, we entered the water industry with a new approach to product development: biomimicry. Biomimicry is the process of studying natural systems and adapting Nature's best designs to solve engineering challenges. We saw a great fit with the water industry: Nature has been transporting, treating and distributing water since the formation of the planet. And over all those millions of years Nature has developed some ingenious ways of improving process efficiency and saving energy.