ADDITION OF CATTLE MANURE TO FULL SCALE MUNICIPAL MESOPHILIC DIGESTION: DOES THIS COMPROMISE PATHOGEN REDUCTION?
Alan Senior1*, Lawrence Tring1, Maxine Mayhew1, Bryan Wallis, Donald MacBrayne2
1Scottish Water Solutions, 2Scottish Water
(free)
A full-scale, ten week trial was carried out to investigate the efficacy of standard mesophilic anaerobic digestion (MAD) in reducing the pathogen loads from cattle manure after mixing with sewage sludge. There is currently little experience of co-digestion of cattle manure and sewage sludge in the UK, either at bench or full scale. The Sludge Treatment Centre (STC) comprised screening, MAD, and dewatering to cake. The mean log reduction in pathogen count between digester feed and treated biosolids was 1.35 with respect to Escherichia coli, 2.77 with respect to faecal enterococci and 0.44 with respect to total coliforms. The average hydraulic residence time in the digesters during the trial was 31 days. The treated biosolids were found to be a valuable fertiliser. Despite operational challenges the trial successfully demonstrated at full scale that co-digestion of cattle manure with sewage sludge was practicable and that a reduction of pathogens comparable to standard digestion of sewage sludge was achieved.
KEY WORDS co-digestion, cattle manure, mesophilic anaerobic digestion, operational issues, pathogen reduction
