Manure and slurry typically contain a range of bacterial,viral and parasitic pathogens.These animal wastes are usually land-spread without treatment,which can pose a significant risk to human and animal health.Pathogens can be transferred as bioaerosols during landspreading,ingested directly from grass or vegetables,or be washed along runoff pathways to surrounding watercourses.Farm-based anaerobic digestion of animal wastes co-digested with food or food-production wastes offer benefits including energy recovery,increased farm income and noxious gas reduction.In this study,slurry was co-digested with FOG (fats,oils and grease) under conditions typical of Irish farm-based anaerobic digestion (AD),in miniature scale (50 mL) and laboratory scale (10 litre) mesophilic (37 ℃) continuously stirred tank reactors.Indicator bacteria-faecal coliforms,Escherichia coli and Enterococcus species-were monitored throughout the trials.The miniature-scale and laboratory-scale tests were comparable in terms of both physicochemical parameters and bacterial pathogen indicator die-off.These results suggest that miniature-scale assays can be used for initial testing to gauge the potential efficacy of system adjustments in terms of bacterial pathogen indicator survival.Despite optimal temperature for survival and growth,repeated tests have consistently shown faecal coliform die-off below the 1000 colony forming units/g minimum digestate standard,and 1-3 log reduction in enterococci numbers.Stored slurry showed significantly higher levels of bacterial survival than slurry processed in AD.Although farm-based AD shows potential as a means of mitigating pathogen spread to the environment,efforts to improve that mitigation,and the impact of underperforming systems must be assessed.
Anaerobic co-digestion Agricultural waste FOG Pathogen survival
Microbiology, School of Natural Sciences, National University of Ireland Galway, University Road, Ga Teagasc, Environmental Research Centre, Johnstown Castle, Wexford, Ireland University College Dublin, Veterinary Science Centre, Belfield, Dublin 4, Ireland Teagasc, Ashtown Food Research Centre, Ashtown, Dublin 15, Ireland University College Dublin, Biosystems and Food Engineering, Belfield, Dublin 4, Ireland