In the minds of most people, human waste fits a common profile.

It’s nasty.

It’s smelly.

It’s swarming with bacteria.

But as farmers across North Carolina are finding out, sewage sludge can amount to quite a commodity.

For starters, it makes an excellent fertilizer.

But the material used on crops and livestock feed across the state is a long way from the raw waste found in septic tanks and sewers. Whether through stringent processing or heavy regulation, state officials take multiple steps to ensure the nutrients found in human waste make their way safely from the toilet to the table.

Convincing the public of this safety however, is not always easy.

Just ask Robert Rubin.

A professor emeritus in biological and agricultural engineering, he said it all boils down to a “psychological barrier” created in the early years.

“When you start talking about municipal waste — we all know where it comes from,” Rubin said. “We’re told from birth that you just don’t play in that stuff.”

Rubin however, never seemed to learn his lesson.

His interest in putting this material to good use began more than 30 years ago with a high school science project.

“I drove past the treatment plants every day on my way to school,” he said. “I wanted to find ways of using byproducts effectively.”

He was one of the key creators of a program in North Carolina to both train and certify operators to apply both classes of sewer sludge to farmland: the rigorously treated and pathogen-free class A material, as well as the lower quality class B material.

“Because of the professionalization, they do a better job,” Rubin said. “If they don’t do a good job, their certification is revoked. If they’re not certified they can’t do the work.”

Similar to commercial fertilizer, both classes of municipal waste are rich in nutrients like nitrogen and phosphorus, essential elements in which crops thrive.

But the balance of these nutrients can become a problem, especially if the soil can’t handle the nutrients provided by the fertilizer.

According to Mike Williams, associate professor of poultry science and director of the Animal and Poultry Waste Management Center, these problems are not limited to fertilizer from human waste.

The improper application of animal waste, commercial fertilizers and human waste can all lead to the migration of these additional elements into rivers and streams. This begins a process called eutrophication, in which naturally occurring algae flourish with the addition of nitrogen and phosphorous, deplete oxygen supplies in the water and throw entire ecosystems off balance.

“The primary challenge is the balance of the nutrient blend,” Williams said. “The problem is when you’re trying to grow a crop and you add more nutrients than the crop can process.”

That’s where the certified operators come in, Rubin said.

Specifically trained to apply treated sludge as well as animal waste to farms, they can evaluate special circumstances in the field, like varying topography or specific nutrient levels, to keep the environment safe in addition to pre-existing regulations.

“It depends on the characteristic of the community,” Rubin said.

Since farmers can purchase commercial fertilizers with specific needs in mind, like a low balance of nitrogen on a certain area of farmland, they often choose a type of fertilizer on a “cost-benefit” basis.

“Farmers make decisions like that every day,” Rubin said. “All [homeowners] care about is if their yard is green.”

But there is an extra incentive for farmers to use treated municipal waste: it’s free.

That’s one of the perks that first attracted Bill Bess to the concept around eight years ago.

The owner of a 150-acre beef cattle farm in Lincolnton, N.C., Bess uses the waste about every other year to fertilize the grass he uses as feed.

A company called Synagro even does the dirty work for him free of charge, spreading the sludge over the areas allowed according to regulations.

“We have this red clay land and it’s hard to grow organic material,” Bess said. “Sludge really helps the situation.”

In addition to the obvious benefits, Bess said the sludge even works better than some of the commercial-grade fertilizer he buys for parts of his farmland not applicable for sludge.

“They’ll apply it in the spring and it all appears the same,” Bess said. “But in July and August, the part the sludge was on is still green.”

What makes treated sewer sludge unique from commercial fertilizers and even animal wastes however, is the appearance of substances like drugs, preservatives and personal care products — all common household materials washed down the drain.

Even trace amounts of heavy metals like arsenic, cadmium or lead are sometimes present.

All of these materials however, are heavily monitored and regulated.

“Manure is reflective of the [animal’s] diet,” Williams said. “With municipal sludge, you’re not sure of the source. However, I do trust the guidelines.”

Bess said Synagro even submits documentation regarding the levels of these materials and the limits that may restrict the use of the waste.

He said he’s far from reaching these boundaries.

“I don’t see how I’ll ever reach the limits for trace materials,” he said.

He said the mere concept of applying treated sewer sludge to farmland is enough to skew public perception, but pointed out that recycling the material is a “win-win situation for everybody.”

“No farmer I know would purposely ruin their land — that’s his livelihood,” he said. “Farmers are the first, best and only stewards of the land.”

Rubin said he sees promise in the growth of sustainability in the research field, something he said wasn’t very prevalent in the academic field when he first began “playing” with waste.

“When I started, there was very little emphasis on resource recovery,” he said. “Now it’s driving research program.”

But despite working on a larger scale, he said he’s still pretty much working on that high school science project.

“Don’t tell my chemistry teacher though,” Rubin said. “He gave me an ‘A.'”