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5 Questions Answered on Designing In-Tank Aeration for THM Removal

Stanly Aeration Spray

Trihalomethanes (THMs) are a type of disinfection byproduct (DBP) that form when chlorine reacts with naturally occurring organic matter in water. THMs are the most common type of regulated DBP that water utilities struggle with. In-tank aeration has been proven to be effective at lowering THM levels in water distribution systems. But choosing an aeration system that balances THM removal with operating cost is not straightforward. Below, we have compiled some common questions we have received on in-tank aeration design.

3 Questions Answered About Ice Formation in Storage Tanks

ice prevention in storage tanks

Water is an unusual liquid. In warm temperatures, the warmer more buoyant water will rise to the top of a tank and the cooler more dense water will sink to the bottom. In the winter, when water cools to its freezing point, it becomes lighter and floats to the top. As you heat up water from its freezing point, it gets heavier for the first few degrees and is at its densest at 4°C above freezing. It can all seem very counterintuitive! If you decide to use a heater inside your storage tank to prevent ice formation, you will have to overheat the water to make it buoyant enough to float to the top. This will require a lot of extra energy. By combining heating with active mixing, you can actually keep the tank ice-free during the winter and use substantially less energy.

3 Design Challenges to Consider Before Mixing Tanks

Tank with mixer illustration

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.

How to Prevent Ice Damage inside Water Storage Tanks

Ice Damage2 LK

In the water distribution system, cold weather can create risks that are hidden from plain sight: ice accumulation inside water storage tanks. Often, when operators realize they have a problem with ice buildup in their tanks, the tank’s interior is already damaged or the wall is punctured. Additionally, traditional methods for reducing ice formation inside water tanks have been expensive, difficult and often only partially effective.

Biomimicry in Action [VIDEO]

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Six years ago, PAX Water Technologies entered the water industry with a novel approach for improving water quality in storage tanks – biomimicry. By examining how fluids move in the natural world, PAX Water Technologies Founder Jay Harman, developed a small yet powerful impeller that mimics the spiral flow patterns found in whirlpools and tornados. This 6-inch “Lily” impeller is not only organic in shape (it resembles a Calla Lily), it can mix a 10 million gallon storage tank using the same energy footprint as three 100-watt light bulbs.

Thermal Stratification Inside Water Storage Tanks [VIDEO]

Stratification thumbnail

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.

Top Five Mixing Questions from ACE12 in Dallas

ACE Booth 12 new

PAX Water Technologies had a great time in Dallas at ACE12 last week – our new THM Removal System (TRS) was featured at the New Product Technology Showcase and we fielded many great questions from ACE12 attendees at our booth. We always appreciate the opportunity to hear directly from operators and engineers about their water quality challenges.   

THM Removal for Stage 2 Compliance [VIDEO]


The Stage 2 DBP rule is here and presenting tough choices for water system operators. Upgrades to the treatment plant are expensive and constrained by existing infrastructure. Changing disinfectants can also be expensive and difficult to sell to a wary board and community.

Five Mixing MythBusters

Active tank mixer

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:

Active vs. Passive Mixers – 3 Common Misperceptions

Active mixing versus passive mixing in storage tanks

Just as electronic technologies have improved with time, technologies in the water distribution system have evolved from large and expensive pieces of equipment into smaller and more efficient solutions. Developed in the ‘80s, passive mixing systems use bulky nozzles with one-way valves to squirt water in different directions during the fill cycle. Because these mixers rely on the momentum of influent water, passive systems do not mix water once the tank is full or during the drain cycle and tanks re-stratify once the infill has stopped. A common workaround is forcing tank operators into a minimum turnover rate (which is both energy-intensive and expensive).

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