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The effectiveness of the technologies installed in livestock waste treatment plants (slurry and manure) to remove or concentrate nutrients and to generate organic fertilizers of high agricultural value has been widely demonstrated. To date, however, the information available on the ability of these systems to reduce the concentration of other pollutants, such as drugs and antibiotics of veterinary origin, is very limited. In part, the lack of information is due to the fact that in the Spanish regulatory framework there is no measure that sets the maximum permitted amounts of these emerging pollutants.
In this matter, the European Union has proposed to take some measures, within the framework of the Zero Pollution Action Plan of the EU, such as the entry into force of the regulation of veterinary medicines and medicated feed. These regulations aim to reduce the use of veterinary antibiotics and restrict others to human consumption only. Thus, from January 28, 2022, the pharmacovigilance of veterinary antibiotics will be mandatory and the rules relating to the assessment of their risk to the environment will be revised.
In this context, the BETA Technology Center of the University of Vic – Universitat Central de Catalunya (UVic-UCC) and the Catalan Institute of Water Research (ICRA) have just presented a technical guide that includes the results of a study on the presence of drugs and antibiotics of veterinary use in livestock droppings and makes recommendations on how these pollutants can be reduced with the current technologies applied in the treatment of slurry. The manual aims to be a tool to guide companies in the livestock sector on which technologies are most effective and to propose mitigation strategies in order to prevent the use of slurry from posing a risk to the environment, animal health, and health public
The guide “Demonstration of the ability to reduce antibiotics in slurry treatment technologies: Technical advisory guide for the livestock sector” collects the results obtained in three real livestock manure treatment plants in Central Catalonia. According to Meritxell, Gros , ICRA researcher: ” the study confirms that, despite the improvements that have been made in the livestock sector in recent years to reduce the supply of drugs and antibiotics, the concentrations of drugs and antibiotics in pig slurries and cow manure detected are remarkable, up to mg/L in liquid fractions and mg/kg in solids ”. These concentrations are higher in pig slurry. “The most frequently detected compounds are antibiotics from the group of tetracyclines, fluoroquinolones, macrolides, lincosamides and tiamulin, which are used to treat gastrointestinal and respiratory diseases, together with flubendazole, a drug to treat intestinal parasites, and the anti-inflammatory flunixin”, adds Gros .
Four consolidated technologies
The study carried out by the consortium formed by the CT BETA and the ICRA has been carried out within the framework of the “Aids to Demonstration Activities” project of the 2014-2020 rural development program of the Department of Climate Action, Food and Rural Agenda of the Generalitat of Catalonia. The work focuses precisely on evaluating the effectiveness of four consolidated technologies to reduce the presence of drugs, antibiotics and antibiotic resistance genes in slurry of pig and bovine origin.
One of these technologies is phase separation, which consists of separating the liquid and solid fractions of slurries. Another technique is anaerobic digestion, to degrade organic matter, produce biogas to generate energy and a solid digestate that can be valued as bio-fertilizer. The third technology evaluated is nitrification-denitrification, which makes it possible to reduce the concentrations of nitrogen and organic matter in the liquid fractions of slurry. And, fourthly, composting has been studied, to reduce the biodegradable organic matter of the solid fraction and obtain a product with a high nutrient content that can be valued as a bio-fertilizer in agriculture.
An innovative treatment, reverse osmosis, has also been evaluated, which concentrates salts and nutrients and obtains a liquid stream, called permeate, with a low content of solids, colloidal matter, ions, drugs and antibiotics. Finally, this work also analyzes the need to implement additional treatment technologies to minimize the potential risk associated with the use of the products obtained as fertilizers in agriculture.
“The results of the case studies demonstrate that, although the technologies for the treatment of livestock excrement studied have been designed for the concentration or elimination of nutrients, these can also be useful for the reduction of the concentration of drugs and antibiotics of veterinary origin”, explains LÍdia Paredes , CT BETA researcher.
Recommendations for the livestock sector
The technical guide concludes with a series of recommendations for the livestock sector, regarding the management of livestock droppings and their valorization as agricultural fertilizers. First of all, it states that solid-liquid phase separation systems or those of reverse osmosis allow obtaining liquid effluents (concentrate in the case of osmosis) and solid fractions in the case of separation, with high contents of these compounds In addition, osmosis produces effluents with a low concentration of drugs and antibiotics. In the research it was found that, during the osmosis stage, the elimination of drugs and antibiotics was high (more than 90%); in composting, the removal percentages were moderate-high (more than 70%); during nitrification-denitrification they were moderate (between 40% and 80%) and with anaerobic digestion they were moderate-low (10-60% with some exceptions of compounds with high removals).
Second, the research determines that treatments based on the nitrification-denitrification (NDN) process, which are used to remove nitrogen from the liquid fractions of slurries, are also particularly efficient for the reduction of drugs and antibiotics in fractions liquids
A third conclusion points to the fact that anaerobic digestion (AD) systems present, in general, low drug and antibiotic removal yields and, therefore, the application of complementary post-treatment systems is recommended.
Finally, the study also concludes that composting is the preferred option to treat the solid fraction of slurry and manure and the dehydrated sludge of the NDN process, because this technology presents a high performance in reducing the concentration of drugs and antibiotics. This point is of particular interest, since most drugs and antibiotics are concentrated in this fraction.
“As the study points out, the applicability potential of these technologies is very high in Catalonia, where there are more than 20,000 livestock farms. In the design of new slurry treatment plants, it would be advisable to take into account the results of this research”, points out Paredes . New plants should include, in addition to nutrient removal, the reduction and removal of drugs, antibiotics, and antibiotic resistance genes.
