Biogas digestate from food waste had nearly as many pharmaceutical residues as digestate from sewage sludge, new study shows
Photo for representation: iStock Norwegian Institute of Bioeconomy Research (NIBIO) has completed research indicating that recycled food waste may contain pharmaceutical residues. Astrid Solvåg Nesse, a researcher at NIBIO, examined biogas digestate from food waste to identify pollutants and was surprised by the relatively high levels of pharmaceutical residues discovered.
The study, published on February 8, 2024 on the NIBIO website, revealed that biogas digestate from food waste had nearly as many pharmaceutical residues as digestate from sewage sludge.
Nesse suggested a potential cause for this phenomenon, stating, "One theory is that it may be related to poor source sorting. For example, people who have mistakenly disposed of pharmaceutical residues along with their food waste."
The research also brought forth positive news, indicating that fungi cultivated in biogas digestate showed minimal absorption of contaminants. Nesse said, “Recycled organic material in the form of biogas digestate can be effectively used as fertiliser, as long as it does not contain substances we prefer not to have in the soil.”
The study highlighted the process involved, explaining that when food waste or sewage sludge undergoes biogas plant processing, it produces energy-rich biogas and a byproduct known as biogas digestate or slurry.
While this digestate contains nutrients and can be utilised as fertiliser, it may also contain substances like pharmaceutical residues that can pose risks to soil health and organisms living in and off the soil.
Notably, the research underscored the challenge of using biogas digestate as fertiliser, stating that it may contain pollutants harmful to plants and the environment.
The findings pointed out that various medications, including diclofenac commonly found in pain-relieving and anti-inflammatory products, were discovered in recycled food waste. The report drew attention to the decline in vulture populations in India and Pakistan in 2004, linking it to vultures consuming cattle treated with diclofenac.
In addition to pharmaceutical residues, the study analysed the presence of per- and polyfluoroalkyl substances (PFAS) in biogas digestate. Higher concentrations of PFAS were found in biogas digestate from sewage sludge compared to that from food waste. PFAS are man-made chemicals used in products such as Teflon pans and water-repellent textiles.
Nesse conducted growth experiments with fungi cultivated in digestate, aiming to explore whether mushroom cultivation could effectively utilise contaminated recycled organic waste.
The results showed minimal absorption of pharmaceuticals and perfluorinated substances by the fungi, with these substances remaining in the growth medium. However, over time, the study observed a significant decrease in the amount of contaminants in the growth medium.
In conclusion, Nesse stated that it is possible to produce edible mushrooms on contaminated digestate while simultaneously reducing contamination in the digestate. She will defend her dissertation at the Norwegian University of Life Sciences on February 16, 2024.
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