Bacterial aerosol emission from wastewater treatment plants: Culture methods and bio-molecular tools

In this report we describe the results of a study conducted in order to better estimate airborne microorganisms. A method based on a bio-molecular technique, Polymerase Chain Reaction (PCR) was compared with the culture methods based on the viable counts of total and fecal bacteria. Microbial aerosol emission from the surfaces of aeration tanks of an industrial and municipal wastewater treatment plant (Como, Italy), at different seasons, was determined. This study was accomplished by conducting test runs in which SAS (Surface Air Systems, PBI) viable sampler, Sartorius MD8 with membrane gelatine filter and gravity method with Petri dishes were used to collect bacterial aerosol samples in situ. Total aerobic heterothropic bacteria, Mycetes, total and fecal coliforms were determined. The preliminary results show that: no correlation was found between the two different passive and active culture techniques, due to the different mechanisms of capture of bioaerosol agents on the media; optimal values for the recovery of E. coli viable bacteria by MD8 sampler with gelatine membrane, time and temperature of storage, were recognised. For the PCR technique, a couple of primers (URL 301-URR 432) to detect E. coli, on definite air samples, was used, operative conditions were defined, and then, applied in monitoring on in situ bioaerosol samples. At the wastewater plant, the highest total aerobic bacteria emission rate during the preliminary mechanical treatments and in correspondence of the enclosed activated sludge phase, as a consequence of the remarkable aeration of the tanks, were registered. The sensitivity (82 CFU/m3) and rapidity (less than 8 hours) of the biomolecular methods to determine the presence and the fecal coliforms (E. coli) rate in bioaerosols was considered satisfactory.