AltEn group explores bringing thermal treatment units for on-site cleanup at Mead plant site

Source: By Chris Dunker, Lincoln Journal Star • Posted: Monday, January 2, 2023

More than a year has passed since a coalition of seed companies submitted a plan for cleaning up pesticide-laden solid and liquid waste products at AltEn, a now-closed ethanol plant near Mead.

Submitted to the Nebraska Department of Environment and Energy on Nov. 1, 2021, the 111-page document detailed the steps taken by the so-called AltEn Facility Response Group to stabilize the site, while also outlining several proposals for disposing of the toxic material.

Unlike other ethanol plants, AltEn used seed coated with pesticides to produce ethanol, leaving behind byproducts heavily contaminated by neonicotinoid pesticides that are highly mobile and persistent in the environment, as well as toxic to insects and aquatic wildlife.

The state of Nebraska sued the company for some 18 violations of state environmental regulations, as the seed companies that formerly supplied AltEn — Bayer, Corteva, Syngenta, AgReliant, Beck’s Superior Hybrids and Winfield Solutions — took the lead in cleaning up the site.

At the seed companies’ direction, nearly 99,000 tons of solid byproduct known as wet cake and contaminated soil was entombed under a combination of clay, polyester fiber and Portland cement earlier this year after six months of work.

As much as 100,000 tons in additional solid waste, including sludge from the lagoon systems also saturated with pesticides, still needs remediation, according to state documents.

The response group described the Posi-Shell cover as a stopgap measure until a permanent solution for disposing of or destroying the material was identified, but in the months since, has been quietly exploring permanent options, including hauling the material to an incinerator or a landfill.

Both of those options have been deemed unworkable by the AltEn Facility Response Group, landfill companies and the residents of Mead.

Documents posted to the state environmental agency’s website last month indicate the AltEn Facility Response Group and regulators may be leaning toward using mobile thermal treatment units — an option proposed in the November 2021 remedial action plan.

“Thermal treatment is the most complete destructive technology for the wet cake,” the plan states. “Both off-site thermal treatment at an industrial facility and on-site options would be considered as part of the overall strategy for the wet cake.”

In an Oct. 25 email to the Environmental Protection Agency, Tom Buell, administrator of the Department of Environment and Energy’s Monitoring and Remediation Division, said the state was “interested to know if there are any mobile incinerators available,” particularly those that could reach temperatures in excess of 1,100 degrees Fahrenheit, an extreme heat needed to destroy the pesticides.

The answer from EPA officials seemed to be no. Or, at least, that there were other options that would be more easily accessible like “thermal desorption.”

Rather than incineration, which would reduce all the contaminated material to ash — and create potential air emission problems — thermal desorption uses a lower level of heat to separate the contaminants from the soil or other solid byproducts.

It also differs from the process used to create biochar, the result of heating organic material to a few thousand degrees in the absence of oxygen to create a charcoal-like substance that can be added as a soil amendment.

AltEn had previously tried to turn its wet cake into biochar, which it planned to sell to area farmers in Saunders County, but the system was prone to breaking down and was not effective in removing the pesticides.

Thermal desorption, on the other hand, heats the material in a rotating kiln until any chemicals are vaporized to the point they can be removed.

Think of thermal desorption like using a clothes dryer, explained John Gierke, a professor of geological and mining engineering sciences at Michigan Technical University.

Clothes dry more quickly if there is also heat applied to the tumbling, because the combination of the two causes the water to evaporate faster, he said.

“That’s what thermal desorption does, it heats up the soil and most organic contaminants become more physically and chemically active as they get hotter and are more likely to volatilize,” Gierke said.

Once the contaminants have been volatilized — in AltEn’s case, neonicotinoids that have been measured in solid byproducts at high concentrations reaching tens and hundreds of thousands of parts per billion — they can be separated from the solids and captured.

“The challenge is to capture all the vapors and treat those,” Gierke said, adding that an additional incineration process could be used to accomplish that task.

It’s a remediation strategy that has been widely used for decades, including at Superfund environmental cleanup sites like the McKin Co. in Maine, where chemicals used to clean tanks leached into the soil and groundwater in the 1960s and early 1970s.

About 11,500 cubic yards of contaminated material at McKin was run through a heated dryer at temperatures of a few hundred degrees over the course of about 18 months in the mid-1980s, which successfully removed both organic and petroleum compounds from the soil.

The total cost of cleaning up the site was reported as $2.9 million.

Gierke said on-site pilot testing would likely be able to determine what level of heat was needed to ensure the pesticides separate from the solid waste at AltEn, but said the science behind the method was sound enough that soil or other byproducts could likely be reused after being treated.

Clean Earth Mobile Services, one of a handful of companies specializing in the remediation method, eliminated an estimated 450,000 tons of soil contaminated with chlorinated organic compounds — including polychlorinated biphenyls, or PCB — in Florida using the method.

The cleanup of the soil allowed it to be reused in residential areas, according to the Florida Department of Environmental Protections.

Gierke described thermal desorption as a “proactive, almost an aggressive approach.” Although it isn’t as energy-intense as incineration, thermal desorption still comes with a potentially prohibitive cost.

A spokesman for Clean Earth, one of two companies that operate mobile thermal desorption units along with Nelson Environmental Technologies of Edmonton, Canada, declined to provide an estimate for what a project the size and scope of AltEn would cost.

“Several factors need to be evaluated to determine what type and size thermal treatment is ideal for each project, including the property layout and location, available utilities, quantity of material to be treated, material characteristics and time frame for treatment,” the company’s website states.

The remedial action plan submitted to the state by the seed companies indicates “energy content” would be a potential constraint on the method ultimately selected to dispose of the wet cake from AltEn.

“Information on the energy content is necessary to determine the constraints on thermal treatment, beneficial reuse and cement kiln blending,” the report states.

The plan also said any remediation action would also need to consider how quickly the material could be processed on-site and transported to an off-site treatment facility, as well as the final disposal location.

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