Like many towns and cities across the U.S., La Crosse recycles its solid waste by using it as farm fertilizer. Last year, the city applied about 12 million gallons of liquid biosolids, the specially processed sludge left over from treating wastewater, onto 8,000 acres of farm fields.
To meet federal regulations set by the Environmental Protection Agency, the La Crosse wastewater treatment plant samples its biosolids for phosphorus, nitrates, microbes and nine types of heavy metals before it is applied onto the fields.
However, the EPA doesn’t know whether these tests adequately determine the safety of these biosolids, according to a Nov. 15 report from the agency’s internal watchdog.
Although the agency has identified 352 pollutants found in biosolid waste, it lacks the human health and ecological toxicity data to complete risk assessments for these pollutants. According to the report, “more than 20 years after the Biosolids Rule was finalized, no new pollutants have been added to the list of nine metals regulated under the rule.”
While slow-releasing biosolid fertilizers provide nutrients, including nitrogen and phosphorus, and essential micronutrients, including nickel, zinc and copper, they also can contain emerging chemicals, such as pharmaceutical compounds, hormones, steroids, fire retardants and plasticizers. Once pumped onto fields, these compounds can wash away as run off into local water sources, ending up in the environment and in the food chain.
The La Crosse wastewater treatment plant processes waste from a mix of residential and industrial sources, including Trane and Chart Industries, said Jared Greeno, wastewater treatment plant superintendent. Trane and Chart are required to pre-treat their waste to remove heavy metals before it goes to the treatment plant.
Once treated, liquid biosolids — which resemble “a thick hot chocolate with very little odor” — are pumped onto the field with an applicator, Greeno said. The application site also can’t be on too steep a slope and must be at least 1,000 feet away from creeks and wellheads
“We also have to make sure the soil is the right consistency — that it’s not too sandy,” Greeno said. Sandier soil could allow the liquid to filtrate through the earth and reach the water table.
The city does not test its wastewater or waste solids for emerging contaminants, including those mentioned in the EPA audit report, though Greeno said that he gets a lot of questions related to pharmaceutical compounds in wastewater, which may become more of an issue in the future.
“At this time, we’re not required by DNR, so we haven’t done those tests,” Greeno said.
The Board of Public Works approved Monday an intent to apply for a Clean Water Fund loan in 2020 to help manage an increase in biosolid disposal, among other projects.