Environmental risk from digested manure in relation to their pathogen content and gaseous emissions

The primary objective of this study was to measure levels of ammonia and GHG emitted by pig and cattle manure samples before and after the anaerobic digestion process. Concurrently, to study the effect of anaerobic digestion on microorganisms’ survival in manure, emission measurements were performed together with microbiological essays to determine the microbial load (E. Coli O157 for bovine samples, Coliforms, Salmonella Species, Sulphite Reducing Anaerobes, Enterococci and Lactobacilli) in manure samples before and after treatment at different sampling times. Samples were taken before and after manure treatment: in the reception pit and after the digestion process. In the laboratory, 0.2 l of each sample was placed in a tank to measure gaseous emissions through the dynamic chamber method, using an infrared photo-acoustic detector IPD (Brüel & Kjaer, Multi-gas Monitor Type 1302), while collecting data every minute. These preliminary results highlight the efficacy of digestion treatment on bacteria abatement. Pathogens in cattle slurry were investigated, except for sulphite-reducing anaerobic bacteria (Clostridia) that, in some cases, were enhanced by anaerobic digestion (up to +41 %) and did not survive anaerobic digestion. Ammonia emission increased (up to +130 %) in cattle digested manure in comparison to fresh slurry. Carbon dioxide declined (-16 %) and, as expected, methane emission was considerably reduced (-82 %) by the anaerobic treatment. The current study is still in process, the expected results are to find a relation between ammonia, GHG emissions and microbial load before and after anaerobic digestion.