Saving energy in clean-water plants often starts with the efficient use of air.

Dale Clark and his team at the lagoon-based clean-water facility in Clare, Michigan, have achieved about $22,000 in annual electricity savings on average — roughly 19% — by making changes to the aeration system that cost only a few hundred dollars.

They did it by reconfiguring air piping, taking one of two blowers offline, shutting down the aerators in one of three lagoons for the winter and taking other measures to fine-tune air delivered to the process. The modest investment paid for itself in the first month.

The team earned a Sustainable Energy in a Small Facility Award from the Michigan Water Environment Association, based on a nomination by the Consumers Energy electric utility.

Diverse operations

Clare (population 3,100) is a mostly residential community in the heart of Michigan’s Lower Peninsula. The five-member Clare Water team splits time operating the water plant (1.5 mgd capacity), two water towers, a water booster station and four wells; handling the NPDES permit for the water plant’s filter backwash discharge; and operating seven wastewater lift stations.

The clean-water plant (1.35 mgd design, 0.6 mgd average) was built in 1952 as a primary treatment facility. In 1965, aerated lagoons were constricted at the present plant site, and a major 1984 upgrade added headworks screens, clarifiers with chemical phosphorus removal, UV disinfection and the current plant building.

“Then in 2011, we had to do an upgrade for ammonia reduction,” says Clark, who has been with the facility for 25 years, the past six as director of water treatment. “That’s when we added Webitat modules (Entex Technologies) and a SCADA system and did some sludge removal in the lagoons.”

The three lagoons operate in sequence. Influent passes through a 0.030-inch microscreen (Aqseptence Group Inc. - Johnson Screens). The first lagoon (Cell 1) contains seven mechanical surface aerators (Aeration Industries International) and six Webitat modules that provide a substrate for growth of a biofilm. “The primary purpose of Cell 1 is to knock the BOD down,” Clark says.

Cell 2, which contains eight surface aerators, continues biological treatment and removes most of the ammonia. The flow them proceeds to Cell 3, which has 10 Webitat modules and provides final ammonia removal. (Fine-bubble diffusers in that cell are no longer used.)

From the lagoons, the flow travels to two 60-foot-diameter clarifiers, which provide both settling and phosphorus removal. Ferric chloride is added in a mixing tank; polymer is added in the first clarifier. After the second clarifier, the water passes through the UV disinfection unit (Katadyn). The effluent easily meets the dissolved oxygen permit limit of 3.0 mg/L for discharge to the South Branch of the Tobacco River, a trout stream. “We are hardly ever below 10,” Clark says.

Eye on energy

The push to boost energy efficiency began after the addition of the Webitat units during the 2011 upgrade. “We added a 60 hp blower for the Webitat modules, and it raised our energy costs a little more than we liked. We had the large blower for the Webitats, and we had a blower for our chemical mixing and the fine-bubble diffusers.

“We decided to do some piping reconfiguration, run all the air off of one blower and shut the other blower off completely. The 60 hp blower (Aerzen) is on a variable-frequency drive, so we figured if we needed to, we could just turn up the frequency and eliminate that other 15 hp blower. That was a decent way to save some money.”

Next, attention turned to the mechanical aerators in the lagoons. “Previously, we just ran all the aerators all winter, because if they would freeze in the ponds, we couldn’t get them running again. With the addition of the new blower, I thought it might be worth rolling the dice and shutting some of them off for the winter. The blower would enable us to adjust the oxygen level to make up for it.

“It turned out we were able to shut the aerators off in Cell 2 and let them freeze in. It doesn’t affect our permit compliance at all. There are eight 7.5 hp aerators in that pond, and we were able to eliminate the use of those all winter. We were also able to eliminate the fine-bubble diffusers in Cell 3, so we no longer run that blower.”

Some of the mechanical aerators in Cell 1 still operate through the winter to provide mixing.

“The Webitat modules are more or less for the cold-weather months, so in Cell 1 we try to keep some constant movement around those,” Clark says.

“In summertime we run all seven aerators. As the weather cools off, we start dropping those aerators off, too. We might run only four aerators in the winter, and we alternate them. The influent to that lagoon stays relatively warm, so it’s got to get super cold for that pond to freeze. That’s why we can shut three aerators off and rotate which ones we use.”

The blower also supplies air for mixing in ferric chloride before clarification, eliminating mechanical mixing. Blower air also mixes the polymer in the clarifier and has the extra benefit of adding oxygen in the water. The chemical feed pumps are now flow-proportional and driven by SCADA, saving labor and providing some chemical savings.

Further fine-tuning

Meanwhile, the Clare Water team took other steps to enhance energy efficiency. That included shutting off the UV disinfection lamps in summer. “Our fecal counts vary based on the temperature of the water,” Clark says. “In September, we might see counts of 20 to 30, but a month or so later, they start climbing.

“When they climb up to 100 to 200, we turn our UV units on and leave them on until April. Then we shut them off. UV light from the sun gives us a lot of pathogen kill because our water is pretty clear. So we stopped running the lamps for a good portion of the year.”

The quest for savings extended to the lift stations in the collections system. Two contained pumps run on single-phase power. “In Lift Station No. 7, we put in VFDs, converted its single-phase power to three-phase and installed three-phase pumps (Flygt - a Xylem Brand). That lowered our energy usage in that station by 15% to 20%.

“We’re also doing some indoor LED light conversions. This year we plan on changing our outdoor lights over to LED. We’re working on that with Consumers Energy.”  

The energy savings are evident in total annual electric bills. Electricity costs from 2012-15 averaged $118,025. Costs from 2015-19 averaged $95,954. Those figures do not include savings on the lift station pump upgrade.

Ample experience

Beyond energy savings, the Clare Water team keeps the plant rigorously maintained. It’s a seasoned team with long tenure in the water department and with the city. Tom Quick, deputy director, is a 32-year department veteran and, like Clark, was a welder by trade before coming to Clare. Both hold associate degrees in water treatment.

Josh Miller, an operator for 11 years, transferred to the water department from the city garage team. So did Mitch Canel, the team’s heavy-equipment operator and a 15-year city employee. Sven Drumhellar, part-time helper, has been on board for two years.

“We’re tightknit; we work together,” Clark says. “We mind our own business, do our jobs and go home.” Those jobs include operating a water and wastewater lab that performs basic compliance and process-control testing. The team also pulls and analyzes samples from monitoring wells around a city-owned abandoned landfill.

“I always tell the guys, ‘There’s nothing you will do that I haven’t already done,’” Clark says. “I’m right there with them. I put myself in their shoes. I put them first as much as I can just to let them know they are valued. If you help people feel valuable and tell them how important they are to you, they’re willing to work for you.”

Meticulous care

“These guys are really good at taking care of the plant,” Clark observes. “Our equipment always lasts longer than the manufacturers say.”

A computerized maintenance management system helps keep planned maintenance on track.

A thermal imaging service visits once a year to image equipment such as starters, bearings, wiring and disconnects to predict impending trouble. “For example, if testing on an aerator shows the amps are high, that is a sign something is wrapped around a propeller, and we need to go out and look at that aerator,” Clark says.

At present, the Clare Water team is going through a water treatment plant upgrade that includes a changeout of three pressure filters, an electrical upgrade, general painting and SCADA modifications.

At the clean-water plant, the main influent lift is aging and so is the UV disinfection system. Recently, exhaust fans have been installed in the blower and electrical room to send heated air into the clarifier room to save energy and provide insurance against freezing. Another lift station is on the table for an upgrade to three-phase power.

Renewable energy isn’t in the immediate future but can’t be ruled out. “It’s a process,” Clark says. “We’re always doing things to try to lower our energy rate. We pick it apart as we go.” It’s one way to amass substantial energy savings.

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Webs of wonder

The lagoons at the clean-water facility in Clare, Michigan, use Webitat biological fixed-media units (Entex Technologies) as part of secondary treatment.

The units are engineered with weblike media to which treatment microorganisms can attach. Besides the media, the modules have integral air diffusers that oxygenate the bacteria and scour the web to make sure the biofilm stays at the optimum thickness. Shrouding of the units creates an airlift pump effect to optimize mixing and eliminate predatory organisms.

In lagoon settings such as Clare, the modules address three primary treatment limitations by providing mixing, aeration and biomass concentration. They are also well suited for oxidation ditches, where they enhance BOD removal and enhance nitrification and denitrification. They can be deployed along the ditch walls to enhance treatment without impeding flow velocity or causing solids to settle. The units can also be used in sequencing batch reactors.