Recycling sludge as fertilizer?

Testing for environmental contaminants in wastewater biosolids

From: Ken Kingery, Duke University in ENN.com

Don Bousquet in URI Stormwater solutions

Every year waste treatment facilities in the United States process more than eight million tons of semi-solid sewage called biosolids -- about half of which is recycled into fertilizer and spread on crop land. The practice helps solve storage issues and produces revenue to support the treatment plants, but what else is being spread in that sludge?

As industry invents new materials and chemicals for modern products, many find their way to our skin and bloodstream and, subsequently, into our sinks and toilet bowls. More than 500 different organic chemicals have been identified in the biosolids used as fertilizer across the United States.

Federal law regulates remnant levels of heavy metals and pathogens in the biosolid fertilizer, but chemicals are not currently accounted for because it has been prohibitively expensive to even begin sorting out which ones might be ecologically unfriendly, says Claudia Gunsch, professor of civil and environmental engineering at Duke University.

In a recent study, Gunsch and colleagues from Duke's Pratt School of Engineering describe a new, cost-effective method for screening chemicals for potential environmental impact. 

They have used the test to show that triclosan, an antimicrobial agent currently under fire from environmentalists, has troubling concentrations in the environment, and they raise suspicions about three other commonly used antimicrobial products.

The team describes their new testing method and some of its early findings in the Feb. 4, 2014 Journal of Environmental Science & Technology.

"Because we're finding many emerging contaminants in biosolids, we wanted to develop a method where you could check them quickly and efficiently and flag the most potentially dangerous ones for more complex measurements," said Ryan Holzem, a graduate student in civil and environmental engineering at Duke and first author on the study.

An important benefit of fertilizing soil is replenishing nitrate levels, which are crucial to growing plants. One indicator of the soil's health is the rate at which native bacteria are breaking down those nitrates through a process called denitrification. If antimicrobials or other chemical agents are affecting the bacteria's ability to complete this process, the soil's quality is degraded.

The new screening technique involves growing a bacterium commonly found in soil that is important to the nitrogen cycle -- Paracoccus denitrificans -- in pure laboratory cultures.  Researchers then add various amounts of the chemicals in question to determine the minimum amount that affects the denitrification process.

Read more at Duke University.