| Description |
Studies were conducted to assess the magnitude, behavior and possible health hazard associated with microbiological aerosols created during the trickling filter process of sewage treatment. Experiments and field sampling trials were conducted using two types of biological air samplers. The samples taken in the field were analyzed for the numbers, sizes and types of microorganisms contained in the sewage generated aerosol. The research was conducted in three sections. The first experiments established the level of microorganisms in the liquid sewage at the point of aerosol generation. The level of naturally occurring bacteria in the air upwind was also determined to establish a control. This ambient background level of bacteria was established at 180 particles per cubic meter. Experiments were also conducted in the first section to determine the sensitivity of the isolation methods for the enteric pathogen Salmonella. The techniques of cold weather sampling, assay of the sampling fluid, effect of the sampling fluid on collected bacteria and field techniques were also evaluated. The second section of the study involved field air sampling trials at various distances downwind of the sewage treatment plant's trickling filter complex. Two plants of different sizes were studied. An average of 620 particles per cubic meter (p/m3) above the background level were recovered at 15 meters downwind. At 50 meters, this count declined to 240 p/m3 and at 100 meters 236 p/m3 were recovered. The coliform type bacterium recovered from actual aerosols averaged less particles per cubic meter than did the total bacterial aerosol. An average of 347 p/m^ were recovered at 15 meters, 106 p/m3 at 50 meters and 63 p/m3 at the 100 meter site. Because this was a natural aerosol created and existing under natural environmental conditions, the effects of the weather condition of solar radiation, wind speed, relative humidity and temperature as measured during each field trial were also evaluated. The final section of the investigation involved attempts to recover airborne enteric pathogens, fecal streptococci and coliphage. A species of Salmonella was recovered at 100 meters downwind in one of four trials. Other potential pathogenic enteric bacteria such as E. coli, Enterobacter, Proteus, and Klebsiella were tentatively identified by colony morphology but no quantative data was taken. Fecal streptococci were isolated in three of four trials with the high volume sampler. However, despite the fact the coliphage were isolated in the liquid sewage, no successful recoveries of airborne coliphage were made. The data from this study indicated that a continuous and sizeable aerosol containing the coliform indicators of fecal pollution and enteric pathogens as well as fecal streptococci was produced. It further indicated that these naturally produced aerosols are subject to the effects of the meteorological conditions under field conditions, Because of the aerosol, within 100 meters downwind of the treatment plant, an inhalation and aerosol contamination hazard exists. |
