Federal stimulus funds paid the bill and the people of Ogdensburg, N.Y., will reap the rewards from a $1.1 million upgrade to its wastewater treatment plant. “It’s not often you get the opportunity to have this kind of efficiency increase,” says Kit Smith, public works director. “Small gains usually mean a lot. These are big, big gains.”

A new style of high-efficiency turbo blower is at the heart of the project, which also includes fine-bubble diffusers and a biogas-to-energy system for heating the digesters. The turbo blowers and fine-bubble diffusers will result in a 25 percent savings on the plant’s annual energy budget. Biogas recovery could double that.

The 1950s-era 19 mgd sludge activated plant has gone through incremental improvements over the years, the last in 1978. Located just downstream from Lake Ontario and across the St. Lawrence River from Canada, the plant has always discharged good effluent to the St. Lawrence Seaway, according to Smith.

 

Aeration upgrade

With money from the American Recovery and Reinvestment Act of 2009, the plant’s coarse-bubble diffuser system was replaced with fine-bubble diffusers as part of the aeration upgrade that went online in October 2010. The project was designed by Tisdel Associates Consulting Engineers and is expected to free up money for needed improvements to the city’s combined sanitary and storm sewer system.

APG-Neuros makes the turbo blower selected for the project. “They are state-of-the-art technology,” says Smith. “We feel they are going to be a very popular blower. To my knowledge, ours are the first in New York.” The manufacturer says there are 368 units operating in the U.S. and more than 1,100 installed around the world.

APG-Neuros says its turbo blowers operate at a savings of up to 40 percent compared to conventional blowers. “We did a lot of research on the blowers,” notes Smith. “The APG-Neuros blowers have been used in Canada for the last five or six years.”

One of the Canadian plants using the blowers is just 40 miles away in Kingston, Ont., so Smith went there to learn more about them. Kingston reported energy savings of 46 to 66 percent, and Smith has seen similar results at his plant.

“We used to run three centrifugal blowers 24 hours a day and a fourth about 11 hours a day with the coarse-bubble diffusers,” he says. “With the fine-bubble, we’re running only one of our four high-efficiency blowers around the clock, and sometimes we use two.”

 

Big reduction

Smith is seeing a 52 percent reduction in electricity use so far, though that could change if a nearby cheese plant goes back into operation. It shut down shortly after the fine-bubble system went into operation. Even if it does go back into operation, Smith expects a worst-case 40 percent electricity savings.

“We’re looking at saving $90,000 to $100,000 a year. It’s been great so far,” he says. The cost of aeration has been nearly cut in half, and that equates to a savings of 25 percent of the plant’s total budget for heat, power and lighting. The changes have also made life easier on the operators because they no longer have to travel around the plant adjusting blowers.

The new blowers have high-speed motors that run on air bearings. “There’s no need for a gearbox or a lubrication system,” Smith says. “They turn at a very high rpm, very similar to a jet engine, and have very few parts to wear out. The efficiency is by far better than anything we could come close to, and we looked at a lot of different blowers.”

They are also clean and quiet. “Anyone who has walked into a room with centrifugal blowers knows that you have to wear hearing protection and be able to read lips,” Smith says. “Even with two of the new blowers running, you can carry on a normal conversation.”

Treatment results have also been good; a combination of the turbo blowers, new dissolved oxygen probes from Hach Co., and an automated dissolved oxygen control system provided through Koester Associates. “We put in variable-speed drives that adjust the blowers automatically according to the amount of air we need to achieve the proper dissolved oxygen,” Smith says.

The blowers, diffusers, and DO system cost just over $800,000 in stimulus funds. The remaining $300,000 went for the biogas system that heats the plant’s three digesters and miscellaneous energy efficiency improvements.

 

Energy recovery

Keeping digesters at 90 degrees year-round requires a lot of gas, especially during winter. The new biogas system will provide digester heating while also heating part of the treatment plant. “We’re expecting at least a 50 percent reduction in our natural gas costs, about $130,000 in annual savings,” Smith says. The system will also provide environmental benefits by ending the flaring of biogas.

The biogas project started two years ago when plant staff and the city’s Highway Division took on the difficult job of cleaning and repairing the digesters on their own rather than hiring a contractor. “That was a big project; they hadn’t been cleaned since the 1960s,” Smith says. “We also removed the old metal roofs, which were rusted and leaking.”

New fiberglass roofs were installed by the plant staff to support capture and storage of the biogas. A gas conditioner from Applied Filter Technology installed in April 2011 will clean the biogas, which will be burned in a new Burnham Commercial boiler that can also use natural gas.

“Gas conditioning wasn’t included in the original system,” Smith notes, “but after reading about it, doing some research and talking to people at other plants, we added it to cut down on the maintenance needed for the boiler.”

 

Exciting time

Ratepayers aren’t the only ones who will benefit. Smith says there are unmet needs for the combined sewer and stormwater system, and the savings will help fund that work. “Our collection system is about 100 years old; we’re a small city and our funding is limited,” Smith says. “We’re planning to take some of the savings and build a capital fund and develop a long-term plan for making upgrades.”

While some separation of the sanitary and stormwater systems has been accomplished, there are still two to four times a year when stormwater overtaxes the sanitary system, causing discharges to the St. Lawrence River.

“We’re under order from the EPA to correct that the best we can, so we’re hoping to take some of the savings and do upgrades without having to finance the whole cost,” Smith says. “We can save a lot of money, increase our efficiencies, make our effluent even better, and limit the number of overflows. It’s been a godsend to us.”