A Study of Bacterial Aerosols at a Wastewater Irrigation Site

Although spray irrigation has become an important alternative to advanced wastewater treatment, its potential for disseminating aerosolized bacteria and viruses has also aroused interest. This study was designed to determine the amount of wastewater aerosolized and to determine the survival of selected bacteria in aerosols from chlorinated and unchlorinated effluent at an operating spray irrigation site. Bacterial aerosol levels significantly above background were demonstrated as far as 200 m from the spray; model predictions indicated detectable increases in airborne bacteria above background at 500 to 1,800 m for unchlorinated wastewater, depending on meterological conditions. When the wastewater was chlorinated, the reduction in aerosol bacterial levels was extensive; however, the reduction in bacterial levels in the aerosol was observed to be somewhat less than in the wastewater. Terminal disinfection, properly designed and operated to assure consistently good microbial reductions, is probably a more practical, cost effective measure than are buffer zones.