Are Micropollutants A Threat To Biosolids?

Lately, biosolids have become more than just a byproduct of wastewater treatment. They are recognized as nutrient-rich sources of potential fuel, fertilizer, and profit. But just as potential profits may be buried below their deceiving appearance, they could harbor unwanted contaminants as well.

When pharmaceuticals and personal care products (PPCPs), things like shampoo, toothpaste, and old prescription medicines, are disposed of through household drains, they often pass through wastewater treatment plants. It’s relatively well known that PPCPs contaminate waterways and can have adverse environmental and health effects and that whatever is in wastewater could well end up in biosolids. As wastewater plants look to leverage biosolids as fertilizer, that may be a concern.

To shed light on the subject, the Water Environment Federation (WEF) hosted a webinar this month featuring four experts on contaminants of emerging concern like PPCPs and antibiotics who discussed their potential presence in biosolids.

“Emerging contaminants as a whole are a common topic brought up when discussing biosolids,” said Dr. Patrick Dube, WEF’s biosolids program manager. “The goal of this webinar was to provide an opportunity to allow prominent scientists working in this field to lend their expertise on the subject and address any concerns about emerging contaminants now and in the future.”

Contaminants like PPCPs and other micropollutants travel to wastewater facilities and resist treatment, persisting in biosolids once they are harvested. About 50 percent of all biosolids are recycled for land use as fertilizer, per the U.S. EPA, and the agency maintains strict regulations to keep contamination from reaching those who eat what is grown in the soil.

“The EPA has done work reviewing over 200 compounds and elements in biosolids from a list of thousands and after review, it identified 22 for a formal risk assessment,” Dube said. “This assessment determined that limits were needed to be in place for nine elements, which were implemented into federal guidelines that limit biosolids application to land.”

Biosolids can be treated to meet the standards of two classes to make them acceptable for land use: “Class A” and “Class B.” Class A biosolids have zero detectable levels of pathogens and can be used as compost for home gardens, lawns, and public spaces. Class B biosolids are also treated to a very high standard, but may retain some levels of pathogens. However, they can still be applied to farmland as fertilizer.

While getting biosolids to meet these standards requires extensive treatment efforts, PPCPs and other micropollutants do not, currently, pose any additional challenge.

“By employing best management practices and environmental management systems, [wastewater treatment plants] can ensure that the biosolids that come out of their facilities follow environmental and sustainable methods that aim to reduce worries about contaminants,” said Dube.

According to WEF’s Biosolids Resources guide, nanomaterials do not have a significant effect during land applications. Best efforts to combat PPCPs do not occur at the wastewater treatment plant, but rather through public awareness campaigns that seek to keep them from being disposed of down the drain in the first place.

“PPCPs were discussed in the webinar as an emerging contaminant,” Dube said. “Dr. Ed Topp, from Agriculture and Agri-Food Canada, discussed them and presented scientific studies that while PPCPs are present in biosolids, there is no uptake in crops being grown in biosolids-amended soils if proper application rates and management is used.”

A similar conclusion was shared by Dr. Jeffrey L. Ullman of the University of Utah on the issue of antibiotic presence in biosolids. With appropriate biosolids management, he said, antibiotic concentrations can be reduced and should be of little concern.

While much is still unknown about how PPCPs and other micropollutants in waterways affect the environment, and probably even less about how they can affect soil, WEF and its webinar presenters are confident that standard biosolid treatment procedures are safeguard enough for now.

“With proper application and use management, there is no threat for concern from emerging contaminants,” Dube said. “Scientists around the country are performing important research that aims to ensure that the land application of biosolids is a safe practice and continues to be so.”