Experimental study on microorganism ecological distribution and contamination mechanism in supply air ducts

Abstract To investigate the microorganism ecological distribution and contamination mechanism in supply air ducts, a series of experiments for testing microbial counts and identifying the microorganism species were conducted under different cases. The results showed that Gram-positive accounted for 56% while Gram-negative for 44% for all bacteria which were made up of Cocci and Bacillus . The detective fungi contained Penicillium , Aspergillus , Cladosporium , Alternaria , Mucor , and Trichoderma , which accounts for 30.1%, 17.2%, 41.8%. 5.6%, 2.8%, 0.5%, respectively and the predominant fungi were Penicillium , Aspergillus and Cladosporium . The supply air velocity had a great influence on the dust distribution in whole test facility. The microorganism counts and deposition dust were positively correlated, when deposition dust increased 1 times, the microorganism counts could maximally increase 1–2 times, and the bacteria correlation coefficient was more significant than fungi ( R bacteria  >  R fungi ). The microorganism counts declined with relative humidity and temperature increasing, and the bacteria were more susceptible to the relative humidity and temperature than fungi ( R bacteria  >  R fungi ). Orthogonal experiment design indicated the main factor of the microbial growth was temperature; but at supply air velocity of 3.0 m/s, the relative humidity was the main influence factor to the fungal growth.