When the Willmar (Minn.) Wastewater TreatmentPlant needed more capacity, better odor control and the ability to meet stricter effluent limits, the city built a new activated sludge plant five miles west of town.

The six-year project, completed in 2010, tested the four operators’ mettle as they ran two plants simultaneously until the new one was online. They also spent three months in classroom training. Along the way they met the challenges of taking part in the planning and design phases, starting up a new laboratory, incrementally taking flow from the old plant to the new over five weeks, and adding seed sludge from the old site. They also decommissioned the old plant.

Throughout the process, the team stepped up to the plate, and their work paid off. The plant has successfully met effluent limits, including those for phosphorus and ammonia. At 5.24 mgd, it will allow residential and industrial growth and accommodate a projected population of more than 27,000 by 2030.

Close involvement in all phases of the project — planning, design, construction and startup — gave the staff an extra measure of pride in the new plant and a deeper understanding of how it works.

History of upgrades

Willmar, the fastest-growing non-metropolitan city in Minnesota, lies 100 miles west of the Twin Cities. It is surrounded by lakes, rolling hills and farmland. Its first wastewater treatment plant was built in 1930 and used fixed-film treatment technology. As the city grew, a 1960 upgrade increased the capacity to 2.5 mgd.

Another upgrade to 5.04 mgd in the early to mid-1980s added rotating biological contactors (RBCs). Then the plant began seeing increased industrial loadings, including grease and feathers from meat and poultry processing plants, that affected RBC performance, created odors, and caused cleaning and maintenance problems.

In 1988, the plant added a new trickling filter ahead of the RBCs, and odor control for the screenings building, primary clarifiers, trickling filter, RBCs, and gravity sludge thickener. Rotary drum fine screens were added to supplement the influent mechanical screen. These removed feathers and other material that had been lodging in the RBCs and reducing effectiveness. In 1996, the plant upgraded the biosolids storage.

The big decision

Still there were issues. The plant’s location near a mall and residential area meant that odor remained a problem. “This was partially caused by a persistent filamentous bacterium, called Beggiatoa, from the large amount of sulfur entering the plant,” says plant superintendent Colleen Thompson.

The plant was also operating at or near capacity for BOD, TSS, total nitrogen and total phosphorus, and the city was expecting new effluent limits for phosphorus and ammonia to take effect in 2010.

In 2004, the city council passed a resolution to relocate the treatment plant. With community support, grants and low-interest loans from the state and federal governments, the city built the new plant on 37 acres purchased in the early 1990s. The site is surrounded by farmland.

“We chose an activated sludge plant based on cost, ease of operation and maintenance, longevity of equipment, and safety to personnel,” says Thompson. “It’s proven technology and it’s robust.” Construction began in September 2008 on the plant, two pump stations, and separate pipelines to convey municipal and industrial wastewater.

Good planning

Long before construction began, Thompson wanted her staff involved. In 2005, she formed a team from the operations staff: operator Terry Thole, working foreman/lab technical manager Jim Gauer, and maintenance mechanic Paul Marcus.

“During the planning phase, the four of us held five workshops with a team from the city and consulting engineer, Donohue & Associates,” says Thompson. “During the design phase, we held 11 workshops and 50 meetings.” In the construction phase, Thompson attended at least three meetings a week for about a year and a half.

Marcus brought the maintenance perspective to the table, and Thole represented the operators’ point of view. Gauer offered his computer and electrical experience. For example, he worked with the engineers on the SCADA system design to ensure compatibility with the SCADA that controlled 25 lift stations in Willmar and Eagle Lake.

Biosolids coordinator Jason Lindahl and lab technician/quality manager Jim Werder attended meetings pertaining to their specialties. “Those meetings took a lot of our time and were just the beginning of what would be a tremendous effort from all my staff,” says Thompson. “This is what makes our team special. We knew we were going to put in extra time during this project, but we were all committed and innovative, and we worked well together.”

Donohue & Associates communicated the plant’s progress to the operations team and the city. “Communication was one of the key components of the program’s success, making sure all stakeholders were on the same page,” says Thompson. “I relied on Terry, Paul and Jim to share information with our staff.”

Transition challenges

Operators and lab technicians faced some challenges during construction and startup. They included developing a transition plan for the new laboratory. “The new lab had to be proven before we started to direct the flow from the old to the new plant,” says Thompson. “We hired Graham Connections to rewrite the standard operating procedures and quality manual before we set up the new lab in the administration building.”

The lab staff worked overtime during the period when both plants were sharing the treatment load with separate discharges. The Minnesota Pollution Control Agency required effluent figures from both discharge points. “That really burdened our lab staff, as it doubled their workload,” says Thompson. “Jim Werder, our lab technician, and assistant Les Lange went above and beyond to keep up with the regulatory requirements and paperwork.”

Another challenge was seeding the new facility. For that purpose, the team used a trash pump to deliver solids from the old plant’s gravity thickener into a nearby sanitary sewer manhole, and from there it traveled to the new site.

“By using our conveyance system, we eliminated the need to have seed solids trucked to the new plant,” says Thompson. “Our staff had to start and stop the trash pump daily during this process. We also had to make sure the solids were replenished every day in the thickener. It was a well-thought-out plan by the engineering firm and the city.”

Extensive training

The startup plan included classroom training for plant staff, provided by Donohue and the equipment vendors. Operators had to learn about the activated sludge process, as they had no experience with it. Donohue wrote 30 standard operating procedures for the equipment and conducted training on all of them.

“Our operators spent numerous training hours learning about the new equipment, for which there were about 60 operation and maintenance manuals,” says Thompson. “That translated into about 60 days of training over three months. It was very intense to take in all this information, and it consumed a lot of staff time.”

The engineering firm also conducted hands-on training and, once the plant was started up, the consultants were available to answer questions, even visiting the plant when requested. “Staff attendance at the training sessions was based on workload and whether the session pertained to their job duties,” says Thompson.

Startup demands

Once all the flow from the old plant had been redirected to the new plant, things became a bit easier for the operators and laboratory technicians. They no longer had to operate two plants at once or test effluent at two discharge sites.

Still, there were other demands. “The biggest challenge was going from a trickling filter/RBC digester system with chlorine disinfection to an oxidation ditch/selector basin with UV disinfection,” recalls Thole. “Only one person here had operated that type of system, and that was 20 years ago. It took some book studying and trial and error to understand the new process and to operate and maintain it.”

The team also had to deal with the new SCADA system. “I remember when our operators first went on call after the new system was started up,” says Thompson. “They could just as well have spent the night at the plant for all the instrumentation/control and automation bugs that had to be worked out. It took a good four to six weeks before the operators felt comfortable being on call.”

The majority of issues were related to alarm time-out settings, and which alarms should be classified as critical or non-critical. “Another problem was with the smart devices on our motor control centers, which were tripping out equipment while trying to start,” says Thompson. “That was an occasional problem that took time to identify.”

New plant

The plant went online in August 2010. It includes an administration building that houses maintenance, laboratory, control systems and staff. There is also a biosolids storage/truck loading area and a new electric power building. Equipment includes:

• Three chemical feed systems: ferric chloride for phosphorus removal, magnesium hydroxide for pH control, and sodium hypochlorite for disinfecting recycled effluent.

• Industrial treatment influent selector (634,000-gallon tank and two blowers).

• Municipal pretreatment equipment: EPIC Landustrie Archimedes screw pumps, Vulcan fine screens and washer/compactor, KSB submersible pumps, and a selector.

• Two municipal and two industrial oxidation ditches (WesTech), each with two aerators.

• Two municipal and one industrial clarifier (Walker), five return pumps (Flygt – a xylem brand).

• UV disinfection system (TrojanUV).

• One municipal and two industrial biosolids storage tanks (Aquastore – CST Storage).

• Biosolids belt press (Ashbrook).

The industrial wastewater stream is pumped to the plant in a force main, and the municipal stream flows by gravity. Effluents from the two streams are combined before discharge to Hawk Creek.

Biosolids are applied to farmers’ fields after being tested for parameters regulated by the MPCA and the U.S. EPA. The plant also includes a receiving station for trucked-in wastes such as septage and landfill leachate. There is also a dumpsite for recreational vehicle wastewater.

Problems solved

Today, the plant is operating well and meeting its permit requirements. “We’re starting to feel more comfortable with the new plant now that a year has passed and we’ve experienced the seasonal changes,” says Thompson. The separation of the incoming streams has reduced odors considerably: “That prevents the volatile organic compounds (VOCs) from forming,” says Thompson.

The plant’s four operators keep busy with equipment operations, preventive maintenance and grounds work, while maintenance mechanic Marcus repairs, fabricates and rebuilds major equipment. Operators continue to fine-tune the process by monitoring and observing pH, suspended solids and volatile solids, conducting regulatory and process testing, and modifying equipment.

Two laboratory technicians test for CBOD, TSS, phosphorus, ammonia and fecal coliform in the regulatory lab, and for mixed liquor suspended solids, volatile solids, settleability, alkalinity and percent solids in the process lab.

The operations staff reports jointly to Thompson and Gauer, who helps organize the process and regulatory data and the wasting schedule for solids stabilization. “The operations staff does all the process testing and shares many ideas and solutions to make the plant run smoothly,” says Gauer. “I am very proud of them for their dedication and common effort to preserve and protect the environment.”