A trickling filter plant at Cape Fear Public Utility keeps churning out quality effluent through sound maintenance and judicious upgrades.
Maybe you can’t teach an old dog new tricks, but that doesn’t mean an old treatment plant can’t keep up with the times.
In fact, the Cape Fear Public Utility Authority’s M’Kean Maffitt Wastewater Treatment Plant produces exceptional effluent, withstands frequent hurricanes, and wins awards, even though its original trickling filter and other equipment are 45 years old.
“Our trickling filters are pretty robust,” says Milton Vann, supervisor of the plant in Wilmington, North Carolina. “The original one dates to 1972, and the second one was added in 1986. Through all those years, we’ve never been out of compliance, except for high flows during storms.”
A meticulous operations and maintenance program, implemented daily by a dedicated staff, is the key to longevity. “We’ve had the insight not to just apply Band-Aids,” says Vann. “We do it the right way and repair things to last another 40 to 50 years. We’ve received budgeting from upper management to take care of issues when we see them.”
Old but effective
The Maffitt plant, named for former engineer M’Kean Maffitt, is one of two main wastewater treatment plants in greater Wilmington. It serves 68,000 people on the south side of the city, plus Wrightstown Beach and a portion of New Hanover County. Its design capacity is 12 mgd; flows average 6 to 7 mgd.
Collected through a 1,000-mile sewer system, wastewater enters the plant through mechanically raked bar screens, a grit rake and degritter. Then it passes through a distribution chamber that controls the flow to one of two circular primary clarifiers. Treatment continues in one of two trickling filters.
The older unit uses rock media, while synthetic media fills the newer trickler. Bed depth is 6 feet, and the sprinkler arms extend 180 feet end to end. The two media types perform similarly.
“We’ve run lots of tests, and the performance of each filter is about the same — both very good. There are only marginal differences.
“While the primaries and chlorination date back to the beginning, most of the mechanisms are not original, we’ve replaced them with newer equipment. The filters have provided good service over the years and are excellent at handling shock loads. They’re our first line of biological treatment.”
Trickling filter effluent is given a biological polish in a small aeration basin before disinfection with chlorine gas. The basin occupies a former secondary clarifier and is equipped with coarse-bubble diffusers. After disinfection, effluent is dechlorinated with sodium bisulfate and discharged to the Cape Fear River.
Effluent quality is excellent. The plant has a permit of 25 mg/L for CBOD, and reports a level of 5-6 mg/L. Likewise, the TSS limit is 30 mg/L and the effluent is in the range of 4-5 mg/L.
“That’s absolutely amazing for a trickling filter plant,” says Vann.
Anaerobically digested biosolids (digester capacities 500,000 gallons to 1 million gallons) are sent to gravity thickeners (Ashbrook Simon-Hartley) and pressed to a dry cake on belt presses (Andritz). The Class B material is spread on farmland. A lime stabilization system is on standby and can be used to produce Class A biosolids if necessary.
A second treatment plant on the city’s north side, named after another former engineer, James Loughlin, is rated for advanced treatment at 16 mgd capacity. Some flow diversion between the two plants keeps the Maffitt plant flows at or below design. The plant is staffed around the clock. The operations team is assisted by a central maintenance crew employed by the Cape Fear authority. A SCADA system monitors and controls plant processes.
This old-timer will get some new looks in the future. An expansion and upgrade is in the works. A design by the firms of McKim & Creed, and Hazen and Sawyer is about 90 percent complete. “It was scheduled earlier, but the recession reduced building and growth in the area and the project was postponed,” says Vann. The improvements will increase plant capacity to 16 mgd and enable future expansions to 24 mgd.
Like human beings, treatment plants need checkups from time to time to maintain good health, and the Maffitt plant has an exceptional program. The emphasis is on predictive maintenance, which calls for daily, monthly, semi-annual and annual monitoring. “As an older plant, we have to be more conscious of predictive maintenance,” Vann says.
To prevent catastrophic failures, the staff regularly prepares assessment reports, and an engineering firm has come in to give the plant a heads-up on potential problems. The maintenance program is computerized and reports required maintenance items for the operations supervisor, Steve Styers, each morning.
Styers assigns the tasks to operators who conduct checks on their equipment on each shift, listening for noise and looking for abnormal operations. Ben Silvester, central maintenance supervisor, assigns tasks to the maintenance staff. “We do lots of visual inspection, and our maintenance team does a great job of handling the day-to-day operations,” Vann says.
Vann points to a potential bearing failure in one of the secondary clarifiers a few years ago. Through the predictive maintenance program, the staff was able to detect the trouble and rebuild the bearing before it went out.
In harm’s way
Wilmington and its treatment facilities are smack in the middle of Hurricane Alley. Storms frequently roar up the east coast of the U.S. As a result, Vann and his staff have dealt with huge storms. They also spend a good deal of time on emergency preparedness.
Vann says the good thing about hurricanes is that they are predictable. That enables the plant staff to be proactive: “We can see it coming and can track it.” Storm precautions include lowering the levels in the digesters and the wet-end basins to add capacity for storm flows, which have run as high as 30 mgd. “We don’t want solids going over the weirs,” says Vann.
The operators also check the diesel-fired generators weekly to make sure they are ready to go if needed. The plant often switches to generator power in advance of a storm just to make sure everything keeps running if and when the main power supply goes out.
The authority also sets up emergency contact centers, and operators and upper management can communicate via cellphone and radio. In advance of severe weather, additional operators are positioned at the plant and prepared to ride it out. That way, no one has issues trying to get into or out of the plant in bad conditions.
“We’ve been very fortunate in that we’ve had no Category 4 or 5 storms come through,” Vann says. “Probably the worst we’ve had was the combination of Fran and Bertha a few years ago. They hit us back to back and did a lot of damage. Our approach is to be prepared, let it come in and roll out, and keep everything inside our walls.”
The attention to detail and careful planning at the Maffitt plant hasn’t gone unnoticed. In 2015, the facility won the North Carolina Eastern Section WEA-AWWA award for operations and maintenance. And the plant was recently honored with certification under the state Department of Labor’s Safety and Health Achievement and Recognition Program (SHARP). The program honors organizations that develop and maintain good worker safety programs.
“We received these awards in recognition of our record of excellence for such an old facility,” says Vann. “They are a sign of accomplishment and a shot in the arm for everybody. It was the result of having phenomenal support of management and staff, and it showed that good old hard work pays off.”
The Cape Fear Public Utilities Authority was proud to have three of its staff honored recently by the North Carolina AWWA-WEF section:
- Robert Daughtry as Wastewater Collections Operator of the Year
- Jim Tayson as Water Distribution System Operator of the Year
- Michael Richardson for his work in disaster preparedness
A background in construction and piping led Daughtry to a key position in the collections division. His work in operations, maintenance and data tracking led to his award. He was honored for “being diligent about and doing outstanding work in tracking and reporting,” as the utility complies with requirements of a consent decree.
Daughtry, as collections system supervisor, is responsible for more than 1,000 miles of sewers and 143 pumping stations. His team aims to video-inspect 20,000 feet of the system and clean at least 10 percent each year. The utility uses Envirosight cameras and POSM Software.
Tayson, supervisor of water distribution and construction, has been with the city since 2004. Under his leadership, the department has made several changes in operations, notably flushing and valve maintenance practices that have improved performance and produced some of the lowest disinfection byproduct numbers the system has ever recorded. “We’re an older community,” he says. “Our biggest challenges are related to our aging infrastructure and trying to keep up with the latest technologies to hold our system together.”
Richardson is now retired, but his award was noteworthy since the North Carolina section has always honored a utility, not one person, for disaster preparedness. At the time, he was the utility’s water resources manager. The award cited him for advancing disaster preparedness, and thereby strengthening the utility’s ability to withstand a disaster.