Giardia and its implications for sludge disposal

The beneficial use of wastewater sludge is to some extent restricted by the presence of human pathogens. Following a risk assessment and monitoring programme it was found that the pathogen which posed the highest potential risk of infection in treated sludge was Giardia. Giardia cyst concentrations were found to be approximately 900/g wet weight of sludge following anaerobic digestion, although not all of the cysts may have been infective. In further studies three methods of wastewater sludge disposal or treatment were investigated. Anaerobically digested and mechanically dewatered sludge was stored for up to 60 weeks, incorporated into sandy soil and composted on a laboratory scale. Giardia cysts remained at levels which could be considered a public health concern after storage of sludge for over one year and after composting. However, cysts appeared to be destroyed within 12 weeks following soil amendment. The implications of the presence of Giardia for sludge disposal are discussed. Copyright (C) 1996 IAWQ.