Energy forest irrigated with wastewater: a comparative microbial risk assessment

In this study, risks for human infection associated with irrigation of municipal wastewater on short rotation willow coppice (Salix) were evaluated in three countries. The aim was also to determine the reduction of indicator organisms and pathogens in the treatment plants. Two of the field sites were chosen for further evaluation by QMRA (quantitative microbial risk assessment) applied to three scenarios: accidental ingestions of wastewater, exposure to aerosols and ingestion of groundwater. The risks of infection for bacteria (Salmonella), virus (rotavirus) and protozoa (Giardia, Cryptosporidium) were characterised as probability of infections per exposure and number of infections per year. The highest risk for infection was associated with exposure to rotavirus in Culmore (Northern Ireland), by either accidental ingestion of wastewater or ingestion of groundwater (P(inf) 8 x 10(-1)). For Kvidinge (Sweden) the risk for virus infection by ingestion of wastewater were in the same range (P(inf) 7 x 10(-1)). The risk for Giardia infection differed between the two sites due to differences in concentration of this pathogen in the wastewater. The groundwater was found to have suffered faecal contamination due to the wastewater irrigation. Use of partially treated wastewater for irrigation of energy crops could be a sustainable option if site-specific recommendations are developed.