QMRA (quantitative microbial risk assessment) and HACCP (hazard analysis and critical control points) for management of pathogens in wastewater and sewage sludge treatment and reuse T. Westrell* , **, C. Schönning*, T.A. Stenström* and N.J. Ashbolt*** * Department of Parasitology, Mycology and Environmental Microbiology, Swedish Institute for Infectious Disease Control, SE-171 82 Solna, Sweden (E-mail: therese.westrell@smi.ki.se; caroline.schonning@smi.ki.se; thor-axel.stenstrom@smi.ki.se) ** Department of Water and Environmental Studies, University of Linköping, SE-581 83 Linköping, Sweden *** Centre for Water and Waste Technology, School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052, Australia (E-mail: n.ashbolt@unsw.edu.au) Abstract Hazard Analysis and Critical Control Points (HACCP) was applied for identifying and controlling exposure to pathogenic microorganisms encountered during normal sludge and wastewater handling at a 12,500 m 3 /d treatment plant utilising tertiary wastewater treatment and mesophilic sludge digestion. The hazardous scenarios considered were human exposure during treatment, handling, soil application and crop consumption, and exposure via water at the wetland-area and recreational swimming. A quantitative microbial risk assessment (QMRA), including rotavirus, adenovirus, haemorrhagic E. coli, Salmonella, Giardia and Cryptosporidium, was performed in order to prioritise pathogen hazards for control purposes. Human exposures were treated as individual risks but also related to the endemic situation in the general population. The highest individual health risk from a single exposure was via aerosols for workers at the belt press for sludge dewatering (virus infection risk = 1). The largest impact on the community would arise if children ingested sludge at the unprotected storage site, although in the worst-case situation the largest number of infections would arise through vegetables fertilised with sludge and eaten raw (not allowed in Sweden). Acceptable risk for various hazardous scenarios, treatment and/or reuse strategies could be tested in the model. Keywords HACCP; pathogens; quantitative microbial risk assessment; reuse; sewage sludge; wastewater Introduction The environmental goals of the Swedish Environmental Protection Agency are based on the concept of sustainable development. Conservation of natural resources, as a part of this, includes the reuse of nutrients from wastewater and sewage sludge (biosolids) to agricul- tural land. At the same time the demands from society on due diligence increase and more and more stringent norms and regulations are placed on producers. Despite limited defini- tive evidence for the association between human disease and current practices of sewage sludge and wastewater re-use (NRC, 2002), transmission of diseases through reuse prac- tices is possible and highly unwanted. Microbial risk assessment can function as a valuable tool to identify potential human health threats, yet to proceed from the theoretical assess- ment to practicalities it must be incorporated into a risk management framework. With the use of a risk management system possible health risks can be controlled and the public’s acceptability towards different recycling alternatives and products fertilised with human wastes could more easily be achieved. Within food and drinking water production the management system Hazard Analysis and Critical Control Points (HACCP) has been applied (FAO, 1997; WHO, 2003). HACCP offers a preventative management and quality assurance approach rather than random Water Science and Technology Vol 50 No 2 pp 23–30 © IWA Publishing 2004 23 Downloaded from https://iwaponline.com/wst/article-pdf/50/2/23/421552/23.pdf by guest on 19 November 2018