Fecal Indicator and Pathogen Reduction in Vegetation Microcosms

Abstract

Municipal wastewater has been applied as a fertilizer to coniferous forest in northern Sweden with the additional aims to purify the wastewater and reduce the treatment costs. This practice has the potential to introduce pathogenic microorganisms from the applied wastewater or sludge to the environment, with a subsequent risk of transmission to exposed humans or animals. Seasonality and climatological conditions, in particular low temperature, humidity and low sun intensity will furthermore affect the persistence of pathogens in the forest in northern Scandinavia and may therefore enhance the survival and thereby the exposure risk. The survival of two pathogens (Salmonella senftenberg and Campylobacter coli) and four fecal indicator organisms; bacteria strains (E. coli and E. fecalis) and bacteriophages (S. typhimurium phage 28 B and ϕx174), used here as viral models, was evaluated in microcosms (60 Litre terrariums) with two vegetation regimes (characterized as moss and lichen) at selected temperatures (+3 • C to +27 • C) and artificial light exposure (light and dark). Salmonella persisted in high numbers after 35 days in the vegetation, indicating a potential risk for further transmission. Neither the vegetation regime nor temperature or light exposure as independent factors governed the reduction of the indicator bacteria and the bacteriophages. The persistence of the indicator organisms was generally best supported in the moss vegetation at low temperature in the dark, where the time for a 90% reduction (T 90 ) was in the range from 8 days (E. coli) to 31 days (Salmonella phage). The die-off characteristics found in this study provide baseline values for further validations in the field and verify that the purification and reuse of municipal wastewater in coniferous forest could potentially be responsible for transmission of fecal pathogens to humans and animals.

Long‐term Hygienic Barrier Efficiency of a Compact On‐site Wastewater Treatment System

“…The S.t. 28 B has been used in several challenge tests (Åström et al, 2006; Carlander et al, 2000) and has proven to be a rather persistent and conservative model virus in transport and inactivation studies. The somatic coliphage φX174 is well characterized and widely used in transport and inactivation studies (Chu et al, 2001; Chu et al, 2003; Deborde et al, 1999; Collins et al, 2006; Leclerc et al, 2000).…”

Preharvest Transmission Routes of Fresh Produce Associated Bacterial Pathogens with Outbreak Potentials: A Review

“…One of the strategies required to minimize the preharvest dissemination of infectious bacteria to fresh produce is the stoppage of all forms of soil amendment and to some extent irrigation for some time prior to harvesting of farm produce, since the occurrence of foodborne pathogens on fresh produce via these routes is almost inevitable [285,286,287]. This formed the “90 to 120 days rule” of not harvesting farm produce 90 days (for farm produce whose edible parts touch the soil) or 120 days (for farm produce whose edible parts do not touch the soil) after the application of manure [288,289].…”

Sewage sludge fertilization of conifer forests in the Nordic countries and North America

“…Pre-application moss surface concentrations of faecal coliforms, faecal enterococci Clostridium and colifages were close to zero in the experiment in Movattnet, where septic sludge was applied through PVC pipes with drilled outlet holes and with centrifugal sprinklers (Åström and Sahlén 2003). In contrast, total coliforms showed a count of 10 3 CFU/g.…”

“…Total coliforms and Clostridium has shown the highest survival. However, since these may also occur naturally in the forest ecosystem, even without sludge application, results are more difficult to interpret and their value as indicators has been questioned (Stenström 1996;Åström and Sahlén 2003). The forest organic layer and the mineral soil are very effective in retaining micro organisms, and the risk for ground water contamination of sewage pathogens seems to be very small.…”