ReNu2Farm partners, located across North-Western Europe, have been working in recent years to develop innovative processes and technologies for the recovery of nutrients, particularly phosphate and nitrogen, from various sources, in order to create final end-products called recycling-derived fertilisers (RDF). These RDF include products such as composts, struvite, ashes, liquid concentrates, and other ammonium products recovered from sources including sewage sludge, animal manures and food wastes, among others. Due to the sources form which these products are derived, the possibility that they may contain potentially pathogenic (disease-causing) micro-organisms needed to be investigated. The current EU Fertilizing Products Regulation (FPR) (EU) 2019/1009, as set out by the European Parliament, outlines the standards for pathogens in fertilisers (including organic, organo-mineral and inorganic fertiliser products and soil improvers), in which it states that Salmonella spp. should be absent in every 25g of fertiliser product tested, and Escherichia coli concentrations should not exceed 1,000 colony forming units per 1g of product.
The ReNu2Farm partners at the Institute of Technology Carlow in Ireland have been conducting an evaluation of viable microorganisms in these RDF. Although producing RDF from such materials involves steps creating conditions under which pathogenic organisms cannot survive, the products were examined to ensure their microbiological safety. This work included assessing the microbial loads associated with the RDF, testing for the presence of coliforms, and subsequently pathogens based on coliform indicator results, and finally the presence of weeds. Most RDF contained a relatively low number of microorganisms, if any, while some contained high numbers, particularly composts and liquid concentrate. However, this is expected of such products due to their high organic matter content, but the critical question is if there are pathogens among these organisms. One way to test this is to search for coliform bacteria in the RDF. Coliforms are found in the digestive tracts and waste of animals, as well as in plant and soil material. Coliforms themselves are unlikely to cause illness, but they are used as indicator organisms for sanitary quality of foods and water. Their presence is indicative of faecal contamination, meaning that enteric pathogens, such as Salmonella, may remain in the product. RDF with coliform presence were further tested for the presence of the pathogens Salmonella spp., Listeria spp., E. coli and Campylobacter spp., by selectively enriching RDF samples for the growth of each specific pathogen. To our delight, the results revealed that Salmonella and Listeria were absent per 25g of tested RDF and less than 10 colony forming units of E. coli and Campylobacter were present per 1g of RDF. Additionally, a pot experiment ruled out the presence of viable weed seeds in RDF, also eliminating this concern for farmers.
Overall, we have concluded that all tested RDF products are in accordance with the EU Fertilizing Products Regulation 2019/1009 and are safe for land application as fertilisers from a microbiological perspective. Although the current pandemic has slowed our general project progress, the completion of this part of our work and the satisfactory associated findings constitute a further step in acheiving our overall ReNu2Farm project goals.
Figure. Some of the RDF tested – from left to right: Vallei en Veluwe struvite, Clarebout struvite, BMC ash and Outotec ash