Composting has the potential to turn horse waste into fertilizer for agricultural use, but how hygienic is the end product? Does the composting process reduce the number of potentially pathogenic bacteria and kill parasite eggs?
Paula Fernanda Alves Ferreira and her fellow researchers conducted an experiment to determine the effects of composting on the microbiological and parasitic load in three types of animal production waste. Their study in Brazil involved horse bedding, organic poultry litter, and conventional poultry litter – each composted separately.
The researchers, with the Federal Rural University of Rio de Janeiro, analyzed the materials before and after composting for the presence and quantities of Salmonella species, helminth eggs and heat-tolerant coliforms.
The composting process, carried out in wire mesh cylinders 1.2 meters in diamater and 1 meter high, greatly reduced coliform levels in all three materials, with the reduction in these bacteria at the end of the composting process reaching close to 100%.
However, despite the big reductions seen during composting, the remaining levels of coliforms remained above levels accepted under Brazilian legislation for use in organic agriculture.
Further processing would therefore have been necessary to render it useable, although they said that the use of much bigger composting piles, which would have generated more heat, would likely have increased the sanitizing efficiency of the composting process.
All the fresh residues had contained helminth eggs before composting, with the horse bedding exhibiting the highest amount compared to the others. No helminth eggs were detected at the end of the composting process.
Salmonella species were absent in both the raw materials and the final compost.
“Composting was effective in eliminating helminth eggs and reducing thermotolerant coliform levels,” the study team reported in the International Journal of Recycling of Organic Waste in Agriculture. However, the final composts, produced indoors over a 125-day period in a hot and humid climate, and involving turning and irrigating, retained a higher pathogenic microbial load than that allowed under law for use in agriculture.
Discussing their findings, the researchers said all three materials behaved similarly during the composting process. The maximum temperature in the poultry wastes crept above 65 degrees Celsius. The highest temperature detected in the horse bedding was 63 degrees.
They said the higher temperature in the poultry waste was probably related to its higher nitrogen content and its finer texture. In contrast, the coarser horse bedding provided better aeration, but would be more prone to heat loss.
After 68 days, all three materials registered temperatures below 45 degrees and, at the end of the composting experiment temperatures were between 29 and 34 degrees – close to room temperature.
“Although animal waste is a sustainable alternative in agriculture, it needs to be environmentally safe. Therefore, it is necessary to use methods that guarantee its sanitation.
“Thus, more studies are needed to evaluate the use of additional techniques that guarantee the reduction of thermotolerant coliforms up to the maximum limit established for organic agriculture, such as solarization.”
The study team comprised Ferreira, Júlia Ferreira Xavier, Danielli Monsores Bertholoto, Dayanne Araújo de Melo, Thaís Ribeiro Correia, Shana de Mattos de Oliveira Coelho, Miliane Moreira Soares de Souza, Marco Antônio de Almeida Leal, Ednaldo da Silva Araújo and Irene da Silva Coelho.
Effect of composting on the microbiological and parasitic load in animal production wastes in Brazil
Paula Fernanda Alves Ferreira, Júlia Ferreira Xavier, Danielli Monsores Bertholoto, Dayanne Araújo de Melo, Thaís Ribeiro Correia, Shana de Mattos de Oliveira Coelho, Miliane Moreira Soares de Souza, Marco Antônio de Almeida Leal, Ednaldo da Silva Araújo and Irene da Silva Coelho.
International Journal of Recycling of Organic Waste in Agriculture, September 21, Vol. 10, no. 3, pp. 265–273, https://doi.org/10.30486/ijrowa.2021.1909128.1132