WILMINGTON — The city’s wastewater department is the “last line of defense” against water pollution, aimed at treating wastewater so it can be returned safely to the environment.
“The main thing is to purify the water before it is reintroduced into the water supply for downstream neighbors,” said Harry McVey, superintendent of Wilmington’s wastewater treatment plant.
McVey said the discharged water goes through Todd’s Fork and eventually into the Little Miami River. Without treated wastewater, those who pursued recreational activities, such as canoeing, in those areas would be exposed to harmful pathogens.
Wastewater undergoes a lot of steps between going down the drain and discharging into Lytle Creek.
McVey said that when wastewater first enters the Wilmington Wastewater Treatment Plant, first the larger debris is removed by a mechanical screen. That debris is typically taken to the landfill as waste. As the wastewater leaves, it goes through another machine that removes smaller grit, typically inorganic waste.
Then, the wastewater enters a circular clarifier, a large round vat with a mechanical arm circling the bottom. About 40 to 60 percent of solids and 25 to 35 percent of the organics are removed by the clarifier and a settling tank.
At this point, two processes emerge – the sludge is removed, while the water continues to receive treatment.
The wastewater will head to trickle filters, the plant’s first biological process. There, aerobic and anaerobic bacteria break down and remove undesired organic substances.
After that, the water will head to a solids contact tank, which reduces the ammonia and organics by using stabilized bacteria from the sludge.
A secondary set of clarifiers and settling tanks will remove further solids from the wastewater, adding it to the sludge. The wastewater will then be disinfected by a ultraviolet system that kills harmful bacteria before the water is finally discharged into Lytle Creek.
Meanwhile, the semi-solid “sludge” gets separated at a settling tank before it enters a thickener. That sludge and sludge from the secondary settling tank will later enter a digester, which stabilizes it before it eventually is applied to farms as a nutrient-rich fertilizer.
“It’s pretty well stabilized by the time we get here,” said McVey, noting that it also is a good way to help a farmer and divert what many wastewater plants throw away.
The plant, constructed in 1936 and last upgraded in 1989, treated 2.56 million gallons per day in 2015, McVey said. It’s designed and regulated to handle an average of three million gallons per day and can discharge up to 10 million in a single day, if needed.
The department’s primary enemy is inflow and infiltration, according to McVey. “I and I,” as he refers to it, is where non-waste water enters the sewer system and must be treated and discharged.
Inflow and infiltration drive up treatment costs and run the risk of increasing contaminants discharged into Lytle Creek.
Snow and rain are likely culprits of inflow and infiltration, sometimes pushing a single day’s volume up to 10 million gallons.
If business picks up or more activity starts to occur, the plant may need to expand, according to McVey. In 2006, the department created a master plan that called for the creation of a 5 million gallon per day plant. The department also bought the Textron building across the street in case the Ohio Environmental Protection Agency says the plant needs to add a retention basin to hold wastewater until flow returns to normal.
McVey said the department has worked to keep inflow and infiltration low to avoid having to make that expansion.
“It’s a major expense,” McVey said. “It only happens when you have a big storm. You might only use it some years one, two, three times. Other years you might use it 10 times.”
McVey said they’re also never built big enough – eventually a rainfall will occur that will be too much for the basin.
The basin could hold the flow until the storm passes and flow begins to return to normal.
Another possible expense coming up is removing phosphorous.
McVey said the plant is currently able to meet phosphorous discharge limits, but in 2030, those limits are projected to tighten even further. When that happens, the plant will have to undergo upgrades in order to meet those requirements.
Like the sanitation and water departments of the city, the wastewater department is an enterprise fund. It charges for its services and uses that revenue to pay for its own expenses, and it doesn’t benefit from taxes.
Reach Nathan Kraatz at 937-382-2574, ext. 2510 or on Twitter @NathanKraatz.