An assessment of pathogen removal during composting of the separated solid fraction of pig manure

The aim was to investigate pathogen survival during composting of pig manure solids with and without bulking agents in two trials of 56 days duration, each with four treatments. Salmonella was detected in the sawdust and straw bulking agents but was undetectable in the compost, except in one treatment at day 0. Enteric indicator organisms were reduced by day 7 (P < 0.001) and were undetectable in the final compost, except for coliform which were present at 3.66–4.43log10 CFU/g. Yeasts and moulds were reduced and aerobic spore-formers remained stable in one trial but both increased in the other (P < 0.001). Bacillus licheniformis and Clostridium sporogenes were the predominant culturable spore-forming bacteria recovered. Microbial counts were influenced by the bulking agent but only at particular time points (P < 0.05). Overall, the pig manure-derived compost complied with EU regulations for processed manure products, as E. coli and Enterococcus were below limits and it was Salmonella-free.