If you walk the grounds at the Wausau Wastewater Treatment Facility, you might not notice a great deal that looks new.

Those handsome old brick buildings remain, but inside a great deal has changed — and more change is on the way. Last year, work was completed on an $80 million upgrade that boosted wet-weather treatment capacity and improved treatment effectiveness and efficiency.

Many improvements took place inside existing buildings, but the project also added a new administration building, a solids facility with a thermal dryer to produce Class A Exceptional Quality biosolids for beneficial use and more.

The outdoor spaces also saw improvements, including updating of the primary and secondary clarifiers, the addition of a fourth secondary clarifier for greater wet-weather capacity and multiple improvements to the aeration process.

“It was actually a huge maintenance project,” says Ben Brooks, superintendent of the Wastewater Division of the Wausau (Wisconsin) Water Works. “There hadn’t been any upgrades since 1991. We were still meeting permit, although there were some low-pH violations. And in wet-weather events, inflow and infiltration would overcome what the plant could handle.”

Today the plant (8.2 mgd design, 5.0- 6.0 mgd average) consistently meets permit limits for effluent discharged to the Wisconsin River.

In Midstream

Wausau (population 40,000) is the economic and cultural center of central Wisconsin. The Wisconsin River is a centerpiece, a scenic and recreational resource. The downtown Wausau Whitewater Park hosts canoe and kayak competitions and is an attraction for casual paddlers.

Brooks arrived in Wausau in December 2021, around the halfway point of the plant upgrade. Previously he had been plant superintendent at Medford, a city about one hour northwest and his first job after he earned an associate degree in water and wastewater resources from Vermilion Community College in Ely, Minnesota.

The plant receives about 10% industrial flow, mainly from metal plating industries and food and dairy processors. “We take in holding tank waste, septage and some grease trap waste,” says Brooks. “Right now we’re not accepting any landfill leachate.” Waste haulers unload at a receiving station designed as part of the upgrade by the Becher Hoppe engineering firm.

Brooks came on board midway through the upgrade. He calls managing that and stepping up to a much larger plant “a huge challenge,” although the two plants have basically similar activated sludge processes.

Brooks has his office in the new administration building, which includes a multifunction laboratory, training and meeting facilities, a control room with SCADA (created by Donohue & Associates engineers), a break room and locker rooms. An eight-stall vehicle garage is attached.

Handling Solids

Arguably the biggest change to the plant is in solids processing. The plant used to produce Class B cake biosolids for land application but now uses a BioCon thermal drying system. 

“Every spring biosolids were hard to get rid of,” says Brooks. “We have a small window when the land becomes dry enough to haul on. In winter, biosolids cake is frozen, and when it thaws it gets mushy. It’s just not a good product to deal with. Now we can haul out our biosolids in about a week where before we were looking at a month of hauling.”

The storage building is required to provide at least 180 days of storage through winter. “With the dry product, we’ve seen an 80-90% reduction in volume,” Brooks says. “We now have probably two to three years of storage.” Plant team members haul about 1,400 dry tons per year to farms in tandem-axle trucks equipped with spreaders that apply it at agronomic rates. About 2,500 acres within a 20-mile radius are permitted for application.

Brooks has received inquiries about bagging the product for sale as fertilizer: “Right now our biosolids are technically not Class A, even though they meet all the requirements. It just takes time for the DNR to approve it. With recent concerns about PFAS, we have chosen to keep track of the biosolids so we know its disposition. We’ve done some testing and our numbers look very good, so we will pursue other options once we become certified with Class A biosolids.”

(2) BP17.61; 1.7M 2-Belt Horizontal Press (BP6000) from Charter Machine Company

The biosolids dryer takes in primary and waste activated sludge after thickening, screening and anaerobic digestion. The material is first dewatered to 18-22% solids on two belt filter presses (Charter Machine Co.). Inside the BioCon system, the biosolids are dried by indirect convective heating. The drying air is recycled in a closed loop to minimize odor and make-up air requirements.

After about 90 in the dryer, the finished material at 95-96% solids is conveyed into trucks in a fully automated process. The trucks transfer the product to a three-sided storage building on the plant property.

The drying process is fueled by natural gas, but Brooks hopes eventually to feed high-strength waste to the digesters to boost production of biogas and replace at least some of the purchased gas, which was budgeted at $250,000 for 2024.

As it is, biogas fuels a pair of 65 kW microturbines. The electricity typically offsets $8,000 to $10,000 in utility power each month. Remaining biogas fired two dual-fuel boilers for digester heating.

More Work to Come

On top of all those improvements, the upgrade included a host of projects throughout the facility, including among others:

(2) RB822.3; 2.2M Gravity Belt Thickeners from Charter Machine Company

• An upgraded and more efficient TrojanUVSigna UV disinfections system (Trojan Technologies)
• New pumps for primary sludge, return and waste activated sludge, and other materials
• A new primary sludge gravity thickener
• Two gravity belt thickeners (Charter Machine Co.) for waste activated sludge
• New roofs on the primary and secondary digesters and all existing buildings
• A new digester gas handling room and rotary vane digester gas storage compressor (Rolair)
• Two new 1 MW diesel-fueled emergency generators (Caterpillar) that are equipped with a soft transfer that doesn’t disrupt line power during monthly nighttime exercising and in anticipation of storm events.

Order From Chaos

Brooks and Wendtland recall the upgrade as a challenging process enabled by effective communication among facility team members and construction workers under general contractor Miron Construction. At the peak of activity, some 90 electricians and construction workers were on site.

“The wastewater operations team played a crucial role during the upgrade,” says Brooks. “The team ensured that the plant continued to function smoothly and collaborated daily to minimize disruptions to the treatment process. The team collaborated to ensure that all regulatory standards and safety protocols were met.”

Wendtland adds, “There was a lot of communication to make sure everybody was clear. Nothing was left up to, ‘We thought this’ or ‘We assumed that.’ When anything looked like an issue, we brought it up and hashed it out.”

To the greatest extent possible, the contractors worked around plant processes to minimize interference. For example, the new UV disinfection system upgrade was undertaken during fall and winter when the facility is not required to disinfect.

Training was essential. As each new device or process came online, team members received a walk-through followed by classroom and hands-on instruction. The training regimen also included:

• Documentation with detailed operation and maintenance manuals and standard operating procedures that explained the new systems and technologies in a clear and accessible manner
• A support system so that team members could seek help and clarification when needed from plant management, engineers and vendors
• Daily feedback sessions to gather observations from team members about operation of the new technology and systems
• Ongoing discussions about trials and errors with the new equipment to helped team members optimize performance

In all, the upgrade was demanding, but very rewarding. Brooks observes, “Although the team was resilient in most aspects, they were torn in every direction imaginable and became worn out toward the end of the project. But they maintained a positive attitude throughout and did what they do best: Protect human health and the environment.”

More to Come

Next on the agenda for the Wausau facility is a headworks upgrade that went out for bid last fall; the estimated cost is $3.0 million. A new headworks building was planned as part of the 2020-24 upgrade, but it was delayed for budget reasons.

The work will include replacement of existing step screens and various improvements to make the facility more maintenance-friendly. One challenge is fitting the new equipment within the small footprint of the existing headworks building,

When all is said and done, plant visitors might not readily see everything that is new. But the plant team will be operating a more efficient and effective plant that delivers clean effluent to the Wisconsin River.