[Pathogen distribution in waste water sprinkler irrigation].

The spray irrigation with pretreated wastewater was investigated on the sewage farm of the Braunschweig Sewage Utilization Association. The emission of airborne bacteria was measured by means of Andersen sampler (AS), Reuter centrifugal sampler (RCS), and sedimentation plates (SP). There was a good correlation of results obtained by parallel measurings of AS and RCS. The RCS was more effective by the factor 11.5 than the AS sampling airborne microorganisms. However, the AS gaves the distribution curve of differently big airborne particulates (Table 1). The medium decrease of bacteria from the sprinkler determined by AS and SP was similar (Fig. 1). With low wind velocity, an aerosol containing enterobacteria was yet detectable at a distance of 60-160 m down-wind from the spray sprinkler. The transport of bacteria as a function of the wind velocity is given in Fig. 2 increasing about 25 m for an increase of the wind velocity of 1 m/sec. During the spray irrigation, the composition of bacteria in the airborne particles is varying continuously. The following order of succession of die-away rates was found: Aeromonas, Plesiomonas, Vibrio greater than Acinetobacter, Pseudomonas greater than Enterobacter greater than Citrobacter greater than E. coli greater than Klebsiella greater than gram-positive bacteria (Table 3). Only seldom and under extreme conditions, gram-negative bacteria were detected in a range between 200-300 m beyond of concentrations as they were found also in controls without irrigation. This result substantiates a minimum protective distance of 300 m between sprinkler and human settlements.