Yuma, Ariz., has installed solar-powered mixers in its three potable water tanks to help ensure water quality continues to meet regulations and the community’s expectations. The mixers from Dickinson, N.D.-based SolarBee help distribute disinfectant uniformly, eliminate thermal stratification and prevent stagnation and short-circuiting.

Because of inadequate mixing, the city’s tanks had problems with short-circuiting and stratification. The problems led to uneven water age and inconsistent chlorine residuals in the tanks. Each of the tanks has a maximum storage capacity of 3 million gallons.

“We never had a problem meeting compliance regulations, nor were taste or odor an issue,” said Bill Barbieri, chief plant officer for Yuma’s water department. “But we were creeping up on our levels of THMs (trihalomethanes, a disinfection by-product) and we knew the tanks had stratified. Because of short-circuiting, we didn’t have full use of the capacity of the tank.”

At first, city officials considered installing diverters on the inlets. Instead of directing water straight into the tank, a 45-degree elbow would divert it higher up into the tank. However, upon further study, officials concluded that such a solution would be cost-prohibitive and ineffective.

The city opted for a solution using SolarBee mixers after observing the performance of the mixers in the Las Vegas water system. The city installed one SolarBee SB2500v12 unit in each of the three tanks.

The floating mixers in Yuma’s water tanks operate day and night with a permanent-magnet, low-voltage motor and an onboard battery system for continuous water quality improvement. The SolarBee flow pattern ensures consistent dispersion of disinfectant throughout the tank volume, including constant replacement at the walls, in the bottom three feet of the tank and at the floor, where bacterial growth would otherwise flourish because of lack of disinfectant.

In addition, the well-mixed tanks eliminate the need for energy-intensive deep-cycling or tank flushing. “We liked the greener approach of solar-powered mixing,” said Barbieri. “The tanks are in an isolated area with a limited amount of electrical power. We also liked the fact that the SolarBee mixers are capable of stand-alone operation.”

With the mixers, the city has SolarBee’s BeeKeeper service program, which provides on-site maintenance, power system upgrades and repair of damaged equipment, even if the damage is caused by an act of nature.

Since the SolarBee mixers were installed, the city’s monitoring has confirmed that water temperatures are uniform throughout each tank, stratification issues have been resolved, and there is no longer any short-circuiting. The city uses less chlorine for disinfection, and chlorine residuals are now more consistent. Average concentrations of THMs dropped from 71 to 46
micrograms per liter in the first two years since the SolarBee mixers began circulating tank water. With the mixers, Yuma water officials are assured that the water supply is safe, good-tasting and sustainable.