Always Adaptable

Multiple upgrades and an experienced team help the Salt Creek treatment plant handle variable influent and stay in compliance.
Always Adaptable

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Fred Dale and the Salt Creek Sanitary District

Wastewater Treatment Plant in Villa Park, Ill., have come a long way over the last 38 years.

When Dale entered the wastewater profession in 1972, many considered working at a treatment plant to be a dead-end job. And for many years the plant also had been the site of the community's garbage dump, reinforcing the negative impression. But now, as Dale retires after a long and successful career, he looks back on the many changes that have given the clean-water business well-deserved respect. "I saw the end of that old era and witnessed wastewater treatment becoming an honorable and respectable job," he says.

And at the 3.3 mgd (design) Salt Creek plant, numerous improvements exemplify the evolution of wastewater management. From the days when the old trickling filters struggled to cope with loads from the community's former Ovaltine plant, the facility has kept pace with technological advances and increasingly stringent effluent requirements.

As Dale hands over the district manager job to chief operator Jim Listwan, the plant is due for more upgrading — to replace its tertiary filters and reconstruct the filtration building.

Changing technologies

The Salt Creek Sanitary District traces its roots to 1928, when it was formed as the Salt Creek Drainage Basin Sanitary District, serving Villa Park and four other suburban communities west of Chicago. Quarrels over bond issues and funding gradually prompted the other communities to withdraw from the district. Eventually it took on its current name, serving just the 22,500 residents of Villa Park.

In the early 1970s, two half-million-gallon pre-aeration tanks and two square final clarifiers were built, and the plant converted its old rectangular final clarifiers to chlorine contact basins. The pre-aeration basins were needed to cope with the large BOD and suspended solids loads periodically discharged by the Ovaltine plant. They still serve the plant today, providing temporary storage for sidestream flows as well as flow equalization during wet weather.

The treatment process took on a much different look in an ambitious 1976-78 project that added a third rectangular primary clarifier and one million gallons of activated sludge capacity, along with Hydro-Clear sand filters (Zimpro/Siemens Water Technologies) and a second 450,000-gallon anaerobic digester.

When the operating staff determined that the trickling filters were starving the activated sludge process and degrading effluent quality, they decided to shut them down. "When the tricklers were taken out, our performance improved quite a bit," says Dale. "We kept one pre-aeration tank for extra aeration and converted the other one to sidestream flow equalization, taking supernatant from our solids handling processes and bleeding it slowly back into the normal flow. These pre-aeration tanks have been serving us for years, just plugging away."

A 2-meter belt press was added in 1993 for solids dewatering, and in 1994 a fourth rectangular primary came online. Dale and his staff also oversaw another significant upgrade in 2004-2006 when three new aeration basins added another 0.5 mgd of capacity, and a pair of 14-foot side water depth (SWD) secondary clarifiers replaced the old square units. Also, UV light took the place of chlorine and sodium hypochlorite for disinfection. The plant also got a new SCADA system.

The flow today

At present, Salt Creek flow averages about 3.4 mgd. Two influent pipes bring wastewater into the plant, where WEMCO pumps move it through an Envirex (Siemens) automatic bar screen, which Dale says "has been a workhorse for us." From there, the flow passes to a chain-and-flight grit chamber (Walker Process) and classifier-washer (Weir Specialty Pumps/WEMCO Pump). Four rectangular clarifiers provide primary settling; one tank is used mainly for sidestream flows.

A battery of seven aeration basins are designed to provide flexible biological treatment. They are operated in the plug-flow mode but can be converted to step-feed operation if the need arises. Dale says any one basin can be isolated for maintenance. Fine-bubble disc diffusers from Sanitaire (Xylem) provide aeration.

The secondary clarifiers are center-feed, Walker Process, 75 feet in diameter. In June 2012, the plant began construction of a new tertiary building with disc filters (Kruger). This will replace the 34-year-old Hydro-Clear filters. Filtrate is disinfected in a TrojanUV4000Plus, containing a single channel and two banks of UV bulbs. Effluent discharges through a weir to a pipe outfall in Salt Creek, which flows to the Des Plaines River.

Primary and waste activated solids are thickened, then anaerobically digested before dewatering on a belt press (Ashbrook) that dates back nearly 20 years. "It's been working well," says Dale. The plant staff has replaced belts and one cylinder and roller over time. Pressed cake averages 18 to 21 percent solids, and a dump truck hauls it to a 1,400-cubic-yard-capacity solids holding area. Synagro has a contract to pick up the cake and haul it to area farm fields. Return activated sludge is pumped back to the first aeration basin.

The plant recycles a portion of its effluent for internal use. "It's not a lot," says Dale. "Maybe 2,500 to 3,000 gallons a day. We use it for our mechanical seals, lawn watering, hosing down equipment, and running the belt press."

Operational challenges

Varying flows are a special challenge at Salt Creek. "About 30 percent of our town still has combined sewers, so we see large variances in incoming flows," says Dale. Volume can range from very low to as much as 20 percent above the design maximum, and influent values can swing widely, as well. "Last year, we recorded monthly influent ammonia levels from 15.6 to 41 mg/L, BODs from 86 to 484 mg/L, and suspended solids from 159 to 898 mg/L," Dale notes. "The swings can get pretty wild sometimes within the same week."

Creative operations enable Salt Creek to handle the changes. Dale and Listwan point out that the old pre-aeration tank plays a vital role in treating the higher flows by acting as a surge tank when flows exceed 7 mgd. The tank can handle up to 250,000 gallons.

"It enables us to accept a greater first flush without upsetting the system," explains Dale. After a wet-weather event, the excess flow is bled back into the system through the fourth aeration basin, where it mixes with the normal flow.

Through experience, Dale and Listwan have perfected their operation so that these storm surges do not lead to permit violations. "I watch the data from our lab closely, and we keep an eye on our flow and overall process, anticipating the effect of wet weather, or very low flows," says Listwan.

Dale adds, "We'll retain more solids and cut back on wasting if we see wet weather coming our way. We watch a number of different variables and have been tweaking the operation over the last several years, getting better and better."

Sludge age is a key: The target is about 12 days. Both Dale and Listwan credit their new Allen-Bradley SCADA system (Rockwell Automation) for much of their success. A fiber optic cable links secondary treatment with the administration building, operations and maintenance, the pre-aeration building, and the raw sewage area.

Various PLC nodes monitor the different equipment areas of the plant. The secondary control building serves as the central SCADA control station, featuring three main computers that process all system data and display it on 19-inch screens. "It really works well," says Dale. "Many of the pumps are now paced by the computer."

Good performance

Despite the storm surges and the frequent changes in the plant layout, Salt Creek has accumulated an exceptional performance record. Effluent limits for both CBOD and TSS are 10 mg/L (April to October) and 20 mg/L (November to March).

Over the last 12 years, plant effluent has averaged 2.66 mg/L for CBOD (based on annualized monthly averages) and 2.25 mg/L for TSS. Performance has been even better since the 2004-2006 upgrade. The same is true for ammonia removal: Effluent averaged less than 0.8 mg/L before 2006 and has averaged about 0.2 mg/L since. The permit requirement is 4 to 8 mg/L in cold weather and 1.5 to 3 mg/L in summer.

The plant also meets a dissolved oxygen target of not less than 6.0 mg/L (weekly average) during warm weather, and from 3.5 to 4 mg/L during winter. "Our operators use Hach portable units to monitor DO at various points around the plant," says Dale. "We use settleometers to determine settleability every day."

The operators are the key to Salt Creek's success, Dale and Listwan will tell you. The team includes operators John Bach, Chris Dale, Doug Koch and Bob Newland. "I can honestly say this is the best staff I've ever had," Dale says. "It's a veteran team — three of our operators have at least 11 years of experience."

Listwan, who has 20 years under his belt, says, "These guys care about what they're doing. They don't want any violations. They go out of their way to make sure things are right, and they notice if there's even a slight movement in our effluent quality. They do a great job, and everybody pitches in. They all know what they have to do, and it's done correctly."

Dale notes that Listwan and the staff benefitted from the experience of the 2004-2006 plant upgrade. "Everybody got to see how the new clarifier and the extra aeration basins were built," he says. "There's no substitute for that. You can tell people, but if they actually see it being built, they get a much better understanding of how the plant operates."

Making the handoff

With his planned retirement, Dale has had time to create a smooth transition of control to Listwan. "About a year ago, we started going over things here and there," says Dale. "Jim is as diligent as they come."

Adds Listwan, "I have a very strong grasp of operations, but Fred has taught me more about the budget and administration." Listwan has been on the job since 1992, coming over from a stint in manufacturing and machining. "It was a down economy, and I was looking for a job," he says. "I took a wastewater course at a local college, and my brother had worked for Fred."

Since then, Listwan has achieved his Class 1 (highest) certification and has been heavily involved in the major improvements at the plant, including the challenge of maintaining peak performance during two years of construction.

Now, he's in charge as Salt Creek undergoes yet another upgrade, switching to four new disc filters, tearing down the old filter building and replacing it with a new structure, and contemplating a switch to alum for phosphorus removal. "I'll be the one responsible now," he says. "We won't be able to ask Fred."



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