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Grease on down the road

Fats and oils clogging up in winter weather
Solon treatment plant needs a low-fat diet

SOLON– Have you heard?
Grease is the word.
And the City of Solon would like you to stop putting it down the drain.
Fats, oils and grease (FOG) are accumulating in the city’s sewer system, and when they reach the treatment plant during cold spells, it’s causing difficulties.
As a result, Public Works Director Scott Kleppe is hoping to educate the public about alternate disposal methods.
“The problem we’re experiencing is poor settling and foaming in the oxidation ditches,” Kleppe said. “In the winter time, the foam will freeze at the surface and our solids will collect in the freezing foam.”
And when that frozen top layer thaws, those solids (and by solids, remember we’re talking about raw sewage) drop back down and it’s “like a shock load to the system,” he said.

Wastewater Treatment 101
Solon operates an “extended aeration oxidation ditch activated sludge plant,” Kleppe said. It’s a basic, common method for treating wastewater.
The oxidation ditches (the City has three but operates two at a time) are open, oblong tanks in which wastewater circulates continuously as part of the treatment process.
If the city had a primary clarifier, it would help sift out non-organic material like sand and sediment, and the fats and greases would rise to the top where they could be skimmed off.
But the City doesn’t have a primary clarifier, so when sewage from the collection system (the bathroom and kitchen sinks of Solon) hits the treatment plant, it is pumped straight into the oxidation ditches.
That’s where a variety of microorganisms, which are already present in the waste stream, do their thing, Kleppe said.
The individual organisms break down the organic waste and use it as a food to grow and multiply, eventually clumping together around the suspended waste material and forming larger masses that settle out of the water, commonly referred to as “activated sludge.”
All the city provides is mechanical aeration, which adds air and keeps the contents in solution. The rest is a naturally-occurring, biological process, he said.
It takes about eight hours of constant aeration to achieve the desired results, and then the tanks’ contents are sent to a secondary clarifier– a big tank where sludge is allowed to settle.
A skimmer at the bottom of the clarifier pumps the sludge back into the oxidation ditch where the mass of microorganisms go back to work on a fresh batch.
The remaining contents of the clarifier, called the effluent, are discharged from the plant into Mill Creek.
From April to November, the public works staff hits the effluent with chlorine to kill off any remaining fecal matter; then de-chlorinate it to prevent chlorinated water from reaching the receiving stream.

Weird science
So now that we understand the system, we can understand what’s happening with FOG in the system.
When you pour the bacon grease from your skillet into a recycled can, it coagulates into a thick, waxy solid, right?
That’s what’s happening with the city’s sewer pipes and down in the treatment plant’s oxidation ditches.
FOG accumulates inside the pipes during cooler weather and can block the flow of sewage.
“It causes havoc at our lift stations,” Kleppe noted. The lift stations, which pump sewage uphill from lower elevations, become so clogged up with grease and oil they have to cleared four times a year with a chemical degreaser.
At the plant, the culprit is filamentous bacteria, specifically Nocardia, one of those organisms that occur naturally and can be useful for breaking down solid waste.
“They actually are beneficial,” Kleppe said. “Until they start over-running your plant.”
Nocardia loves grease and oil. They feed on it and grow.
On a microscopic level, filamentous bacteria are like little tree branches that filter out waste by grabbing solids to eat. The more solids it accumulates, the heavier it gets, and it makes its way to the bottom of the tank.
When there’s too much FOG in the system, the Nocardia multiply, but because of what they’re eating, they become more buoyant and rise to the top.
And where are all the fats, oils and greases coming from?
From your everyday residential and commercial customers.
It’s not a new problem, but it’s been getting worse.
The town keeps continuing to grow, and more food establishments are coming to town, Kleppe said. For the last several years, the city has been requiring new restaurants to install grease traps.
Implementing an inspection system and testing to identify the areas of town which are causing the most problems will be the next step, he said.

What you can do
The easiest way to help the city with the problem is to stop pouring oil down the drain.
Instead, Kleppe suggested, let liquid oil or grease cool to room temperature, put in a disposable container like a reusable storage bag, a used milk container or a glass jar, and put it in the garbage.
People think when they’re done frying food with vegetable oil, they can break the oil down by rinsing it with hot water, he said.
“It actually doesn’t,” Kleppe said. “The ground temperature where the sewer lines are is basically 50 degrees. That warm water that you think you’re flushing it down with is going to cool off before it even reaches the collection system.”
Kleppe also suggested scraping grease and food from plates into the garbage as well, but the very best way is to collect liquid oils for a period of time and dispose of them by setting them out with your recyclables at curbside in the original or a clearly marked container.
Any help would be appreciated, because during cold weather, those fat-eating Nocardia freeze on top of the oxidation ditch to a thickness not unlike a large chunk of ice.
It hasn’t caused major problems like an overflow of the tanks, but it is a big inconvenience causing a lot of extra work for city staff.
The discharge, however, is as clean as ever.
“We’re still below our permit limitations,” Kleppe said.
For example, one of the restrictions placed on effluent discharged from the plant is Biological Oxygen Demand (BOD). Solon’s state permit allow up to 25 milligrams per liter of BOD in the effluent, but the city is operating around 3 milligrams per liter.
“Our removal is very exceptional,” he said.
Total suspended solids and ammonia nitrogen concentrations are also well below permit requirement.
The treatment plant, located across the creek from Randall Park and down the hill from the Old Mill residential subdivision, was last updated in 2008, when the city added an oxidation ditch and two new clarifiers.
“We produce a very high-quality effluent,” Kleppe concluded.