Process and control today | New mixers are lighter to handle and less energy intensive at Fairfield

Replacing anoxic zone mixers with much more energy efficient units provides a water pollution control facility (WPCF) in Connecticut with annual savings of $22,433.

As it strides towards its goal of reaching Net Zero Carbon, the city of Fairfield (population 60,000) wanted to reduce the operating costs of its blenders, which operate 24/7, in the part of a major capital improvement plan (CIP) to replace assets with more modern and energy-efficient equipment.

“Like all sewage treatment plants,” said John Bodie, Superintendent at Fairfield WPCF, “We’ve been a very heavy consumer of electricity, but when we looked at our energy use and came up with a comprehensive plan, it gave us a great opportunity to adopt design standards ecological”.

And like most processing plants, there often isn’t the budget available to fully upgrade equipment at the pace that would suit best practice. However, as many wastewater treatment facilities are discovering to their considerable advantage, help is now at hand with grants and incentives available from energy providers; in this case in Fairfield with United Illuminating (UI), a subsidiary of Avangrid, which owns and operates a portfolio of renewable energy generation facilities.

“Smart energy upgrades that would give us the best performance at the lowest cost”

John Bodie, who has worked at Fairfield WPCF for 30 years, added: “When we plugged in the numbers, it all added up; smart energy upgrades that would give us the best performance at the lowest cost, as well as great savings for many years to come. The help we received from United Illuminating to cover investment costs spurred us on. The 12 existing mixers we had were never the most efficient, and we also found them very difficult to work with; mainly because of their weight.

At the 8.5 million gallon per day facility, mixers continuously suspend solids and mix sludge back into the influent flow. The existing mixing energy input met industry standard recommendations, but single point submersible propeller mixers left dead zones in the denitrification process, as well as the formation of scum and foam – and required also high levels of maintenance and frequent rebuilds.

“Much friendlier”

John Bodie continued: “After looking at several options, we first invested in six mixers manufactured by Landia, which came highly recommended as the best solution. At 2.4 HP each, compared to the previous 6.5 HP units, we of course expected a reduction in power consumption, but the added benefit is that, despite being smaller, they do a better job than older mixers (from another manufacturer). Landia’s first six mixers have now been installed for just over three years without any problems. It used to be that when servicing a mixer that weighed considerably more than a Landia, we had to have three or sometimes four men handling it to lift it, and even then it was very easy for someone to suffer ailments back. Now, with a Landia blender, it’s so much more user-friendly; easy for one person, so it’s also a big saving in maintenance”.

Following the success of Landia’s first half-dozen mixers, six more were installed 15 months ago in Fairfield, replacing units from another manufacturer, but which consumed too much energy and were time-consuming to maintain.

“Substantial savings can be made in energy”

“Annual blender electricity savings of more than $22,000 equates to a reduction in energy consumption of 182,383 kilowatt hours (kWh),” said John Bodie. “The WPCF was built here in 1950, with upgrades carried out in 1968, 1972 and 2001. It has always been a very well run factory, but now the Capital Improvement Plan (CIP) from years ago four years can show other processing facilities what is very important energy savings can be achieved We are very pleased with the Landia mixers which provide many cost and operational benefits to Fairfield WPCF “.

In addition to the 12 new mixers, long-term energy efficiency improvements also included a 2 MW solar system in the nearby old landfill and a 400 kW fuel cell. A new 1.3 MW natural gas generator was also installed, along with interconnecting switchgear, allowing the WPCF and surrounding city facilities to operate independently in the event of a power outage.

For Landia (established in 1933), this facility at Fairfield WPCF follows a large number of projects, where its submersible mixers have replaced inefficient or failing mixers from other manufacturers. In some cases, Landia agitators have been installed in aeration basins, to ensure the mechanical mixing of the sludge, while reducing the aeration to just what is necessary for the biological process. In Chinook, Montana, two 5 HP Landia mixers were purchased so that an energy-intensive 50 HP surface rotor aerator could be turned off during nighttime low BOD load hours. As a result, the submersible mixers now save the sewage treatment plant $18,000 per year in electricity, helping to pay for the entire facility in just over four years.

The switch to Landia mixers has also paid off at the American Falls, Idaho wastewater treatment facility. Here, the original mixers failed to displace solids from the factory MBR – and there were constant seal failures. Now, despite drawing only half the amps of previous units, Landia mixers, truly designed for mixing sewage sludge, responded immediately to the application – dramatically reducing energy consumption and running smoothly. are also much easier and more cost effective to maintain.

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