366 © IWA Publishing 2013 Water Science & Technoiogy | 67.2 | 2013 Fate of pathogen indicators in a domestic biend of food waste and wastewater through a two-stage anaerobic digestion system B. D. Rounsefell, C. A. O'Sullivan, N. Chinivasagam, D. Batstone and W. P. Clarke ABSTRACT Anaerobic digestion is a viabie on-site treatment technoiogy for rich organic waste streams such as food waste and biaci<water. In contrast to iarge-scale municipal wastewater treatment piants which are typicaiiy located away from the community, the effiuent from any type of on-site system is a potential pathogenic hazard because of the intimacy of the system to the community. The native concentrations of tiie pathogen indicators Escherichia coll, Closthdium perfringens and somatic coiiphage were traci<ed for 30 days under stable operation (organic loading rate (OLR) = 1.8 kgCOD m^^ day~\ methane yield = 52% on a chemicai oxygen demand (COD) basis) of a two-stage laboratory-scale digester treating a mixture of food waste and blaci<water. £ coli numbers were reduced by a factor of 10'^" in the thermophiiic stage, from ^o'•^^°3 to ^o^^'^*°'' cfu 100 mL~\ but regenerated by a factor of 10" in the mesophilic stage. Neither the thermophiiic nor mesophilic stages had any significant impact on C. perfringens concentrations. Coiiphage concentrations were reduced by a factor of lO''" across the two stages. The study shows that anaerobic digestion oniy reduces pathogen counts marginally but that counts in effiuent samples could be readiiy reduced to below detection iimits by filtration through a 0.22 Mm membrane, to investigate membrane filtration as a possible sanitation technique. Key words | anaerobic digestion, blackwater, food waste, pathogen B. D. Rounsefell C. A, O'Sullivan W. p. Clarke (corresponding author) Schools of Civil and Chemical Engineering, The University of Queensland, Brisbane, 4072, Qld. Australia E-mail: william.clarke@uq.ed.au N. Chinivasagam Animal Research Institute, Queensland Primary industries and Fisheries, Yeerongpilly, 4105, Qld, Australia D. Batstone Advanced Water Management Centre, The University of Queensland. Brisbane, 4072, Qld, Australia C. A. O'Sullivan Current address: Plant Industry, CSIRQ, Underwood Ave, Floreat, 6014, WA, Australia INTRODUCTION The putrescible waste produced by households is proble- matic as a source of odour and an attractant for vermin. While this material is often beneficially composted on prop- erties with gardens, on-site treatment is generally not considered for high density residences. However, waste dis- posal levies and the high demand for renewable energy provides incentive for households and residential clusters such as apartment blocks to consider on-site anaerobic digestion of rich organic waste streams such as food waste. Touet wastewater (blackwater) can also be digested although the organic content of blacl<water is low compared vwth solid organic waste at typical domestic production rates (Verstraete & Vandevivere 1999). However, the utility of an on-site anaerobic digestion system is enhanced if blacliwater can also be treated by the system, obviating the need for a dedicated on-site wastewater treatment system. The sanitation capacity of a digester under this circumstance is of interest. Anaerobic treatment has been shown to have the poten- tial to perform a degree of disinfection because the low pH and high temperature conditions that are suitable for hydro- lytic fermentative organisms are generally not viable for most pathogens (Olsen & Larsen 1987; Kunte et al. 1998). These conditions are readily achieved in the first stage of a two-stage digestion process where high temperatures can be maintained using only a portion of the produced biogas. In contrast, maintaining high temperatures in aerobic systems is reliant on imported energy where the heat energy demand would also be prohibitive due to the amount of agitation and sparging needed to maintain aerobic conditions. Olsen & Larsen (1987) found destruction times for Escherichia coli were of the order of hours at 53 C compared with days at 35 °C for animal slurry wastes being treated using anaerobic digestion. Nielsen & Petersen (2000) compared the effect that full-scale mesophilic and doi: 10.2166/wst.2012.573