Sludge Happens —
But SAIC Is Turning It Green

Sludge Happens

The city of Ardmore, Okla., needed a new sewage treatment plant, but it also wanted a fresh way to deal with the inevitable byproduct of sewage treatment: sludge.

Enter SAIC engineering manager Tom Mansur, who came up with an award-winning solution that not only solved Ardmore’s problem, but saves them about 10 percent of their operating costs — and actually has the potential to make the town money.

The first time he visited the old sewage treatment plant, there had been a protracted wet spell that prevented the trucking of sludge. The day he visited, basins were brimming with millions of gallons of sludge.

A Novel, if Ancient, Solution

Sludge is essentially what’s left over after sewage is treated. All of the nonorganic matter — rubber and plastic products, and anything else that can be flushed or put down the garbage disposal — has been removed. What’s left is water and dead cells — protein and cell material. But it is neither odor free nor sanitary.

Mansur’s idea was to apply a practice common in many back yards — composting — on an industrial scale to turn the sludge into a more useful, less dangerous product. “When I presented that option to them, boy, their eyes lit up and they got all excited, and they said, ‘That’s what we want to do.’ ”

The town had been disposing of the sludge by spreading it on neighboring crop and pasture land, an expensive and arduous process that is eventually good for the land, but renders it off limits for crops or grazing for 18 months.

‘Cooking’ Out the Bad Stuff

Ardmore’s sewage plant is near the site of the city’s Operation Pride Program, where the city collects yard waste — leaves, tree trimmings, and so forth. Mansur designed a solution that would use both the yard waste and the sludge. The result of his design is a 24,000-square-foot facility that “dewaters” the sludge, then mixes it with ground-up yard waste (known as “wood amendment” in the technical jargon), aerates it, and deposits it in one of five composting bays, each of which measures 10 feet by 10 feet by 195 feet.

Composting is essentially what happens on the forest floor to tree and other plant litter as it decomposes, although composting vastly speeds the biodegradation of the material. That biodegradation is accomplished by aerobic microbes — microorganisms that breathe air — and so aeration of the mixture is essential to the composting process. The addition of the yard wastes helps there, particularly with the aeration.

“I tell you what,” Mansur said. “As soon as you mix that material with the wood amendment, and as soon as that stuff hits the air, it immediately starts cooking.” The cooking is the heat generated by microbes as they break down the nutrients in the mixture. “It starts steaming from the moment you put it in the bay.”

"I wouldn't have any problem putting it in my front yard and letting my grandkids play with it. It's better than dirt."

The compost stays in the bays for 21 days. For 10 of those days the temperature has to be at or above 45 degrees Celsius (113 degrees Fahrenheit), and for three of those days it must be at or above 55 degrees Celsius (131 degrees Fahrenheit). The prolonged high temperatures kill all of the harmful bacteria and viruses that might be present. “You get very good pathogen reduction,“ Mansur said. “In fact, the Ardmore plant, they’ll get pathogen results of ‘no pathogen detected’ “ after the composting process.

Better Than Dirt

When the batches of compost are finished, they’re thoroughly tested to make sure that they’re sanitary. Out of hundreds of piles of compost that have been generated since the project’s inception, Mansur said, only two have failed that testing and had to be recomposted.

“It is, in effect, sterilized,” Mansur said, “although that’s not the regulatory requirement. I wouldn’t have any problem putting it in my front yard and letting my grandkids play with it. It’s better than dirt.”

Water reclaimed in the production of the compost is cleaner than what goes into the system to make potable water, Mansur said. In discussions with the city, he’s been trying to make the case “for taking that water and pumping it back over to City Lake. Or, alternately, putting it in an impoundment and using it for irrigation.”

Also, the makeup of the compost, which packs readily and stays in place, makes it “particularly good for erosion control. Once you put it down or till it or just drive on it, it stays in place. It won’t prevent erosion, but it helps the soil become more absorptive,” he said. The compost can be applied to the same fields as the sludge was, but they can be used immediately, and it significantly reduces harmful runoff of nutrients into nearby streams.

An Award-Winning Effort

Mansur won the 2008 Grand Conceptor Award from the Oklahoma chapter of the American Council of Engineering Companies. The award is one of the most prestigious in the industry. “Getting the building designed and built took a lot of work,” Mansur said, “but without the enthusiasm and initiative of the city, the design would not have worked.”

The award was especially meaningful, Mansur said, because, as he understands the judging process, half of the judges aren’t engineers, “so it’s not just a bunch of engineers sitting around congratulating themselves.”

The plant manager, Carol Anderson, christened the plant’s compost “Okie Dirt” and trademarked the name for the city. Mansur speaks with her regularly, he said, and he’s been pushing the town to sell the compost. The way Mansur sees it, if the town sold Okie Dirt® for a good price, they could actually make money on the plant.