Ranking hazards pertaining to human health concerns from land application of anaerobic digestate

Ranking hazards pertaining to human health concerns from land
application of anaerobic digestate

Abstract

Anaerobic digestion (AD) has been identified as one of the cleanest producers of green energy. AD typically uses
organicmaterials as feedstock and, through a series of biological processes, producesmethane. Farmyardmanure
and slurry (FYM&S) are important AD feedstock and are typically mixed with agricultural waste, grass and/or
food wastes. The feedstock may contain many different pathogens which can survive the AD process and
hence also possibly be present in the final digestate. In this study, a semi-quantitative screening tool was developed
to rank pathogens of potential health concern emerging from AD digestate. A scoring system was used to
categorise likely inactivation during AD, hazard pathways and finally, severity as determined from reported
human mortality rates, number of global human-deaths and infections per 100,000 populations. Five different
conditions including mesophilic and thermophilic AD and three different pasteurisation conditions were
assessed in terms of specific pathogen inactivation. In addition, a number of scenarios were assessed to consider
foodborne incidence data fromIreland and Europe and to investigate the impact of rawFYM&S application (without
AD and pasteurisation). A sensitivity analysis revealed that the score for the mortality rate (S3)was themost
sensitive parameter (rank coefficient 0.49) to influence the final score S; followed by thermal inactivation score
(S1, 0.25) and potential contamination pathways (S2, 0.16). Across all the scenarios considered, the screening
tool prioritised Cryptosporidium parvum, Salmonella spp., norovirus, Streptococcus pyogenes, enteropathogenic
E. coli (EPEC), Mycobacterium spp., Salmonella typhi (followed by S. paratyphi), Clostridium spp., Listeria