Even the most elite waste treatment systems currently available do not remove antibiotics from manure, according to a study which suggests that traces of the medicines leach into the environment, potentially contributing to the global rise of drug-resistant bacteria.
Researchers from University at Buffalo in the US studied two of the most elite waste treatment systems.
Both technologies - advanced anaerobic digestion and reverse osmosis filtration - leave behind concerning levels of antibiotic residues, which can include both the drugs themselves and molecules that the drugs break down into.
The research, published in the journals Chemosphere and Environmental Pollution, also uncovered new findings about solid excrement, which is often filtered out from raw, wet manure before the treatment technologies are implemented.
Researchers found that this solid matter may contain higher concentrations of antibiotics than unprocessed manure, a discovery that is particularly disturbing because this material is often released into the environment when it's used as animal bedding or sold as fertilizer.
"We were hoping that these advanced treatment technologies could remove antibiotics. As it turns out, they were not as effective as we thought they could be," said Diana Aga, who led the study.
"On the positive side, I think that a multistep process that also includes composting at the end of the system could significantly reduce the levels of antibiotics," said Aga.
"Our earlier studies on poultry litter demonstrated that up to 70 per cent reduction in antibiotics called ionophores can be achieved after 150 days of composting. Testing this hypothesis on dairy farm manure is the next phase of our project, and we are seeing some positive results," she said.
According to the US Food and Drug Administration (FDA), over 30 million pounds of antibiotics approved for use in food-producing livestock were sold or distributed in the US in 2016. These are just a fraction of the total antibiotics used annually around the world in humans and animals.
Though the new research focuses on dairy farms, the findings point to a larger problem.
"Neither of the treatment systems we studied was designed to remove antibiotics from waste as the primary goal," Aga said.
"Advanced anaerobic digestion is used to reduce odours and produce biogas, and reverse osmosis is used to recycle water. They were not meant to address removal of antibiotic compounds," she said.
"This problem is not limited to agriculture: Waste treatment systems today, including those designed to handle municipal wastewater, hospital wastes and even waste from antibiotic manufacturing industries, do not have treatment of antibiotics in mind," Aga said.
"This is an extremely important global issue because the rise of antibiotic resistance in the environment is unprecedented. We need to start thinking about this if we want to prevent the continued spread of resistance in the environment," she added.
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