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Title: Source of aersolized bacteria during land application of biosolids

Author
item Brooks, John
item GERBA, C - UNIVERSITY OF ARIZONA
item PEPPER, I - UNIVERSITY OF ARIZONA

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2007
Publication Date: 11/1/2007
Citation: Brooks, J.P., Gerba, C.P., Pepper, I.L. 2007. Diversity of of aersolized bacteria during land application of biosolids. Journal of Applied Microbiology. 103:1779-1790.

Interpretive Summary: Wastewater treatment processes generate sewage sludge as a large by-product of the process. Sewage sludge is then treated to produce Class B biosolids, which can have large numbers of bacteria, both good and bad. These biosolids can then be used as a beneficial fertilizer on agricultural lands. During the process of Class B biosolids land application, a large amount of bacteria can be aerosolized. Particularly in the desert southwest, the amount of aerosolized soil that can be liberated into the air is enough to compete with particulate matter of biosolids origin. All these particles can have both good and bad bacteria. The purpose of this study was to determine the source and diversity of bacteria aerosolized during these land application events. Class B biosolids were land applied to an agricultural site located within the south central area of Arizona. Air samples were collected downwind of the biosolids operations and DNA was collected from these samples to determine bacterial source and diversity. A specific gene associated with bacteria was analyzed to determine the type of bacteria. These types were then grouped by large familial groupings and analyzed to determine their source. Bacteria collected downwind of biosolids land application appeared to be mainly from soil associated with the site. Bacteria collected downwind of soil aerosolization without biosolids produced similar profiles, demonstrating that a large amount of aerosolized bacteria during biosolids land application in the desert southwest may be of soil origin.

Technical Abstract: Land application of biosolids can lead to the generation of bioaerosols downwind of the operation, however bioaerosols can also potentially be associated with a number of other onsite sources including soil. The purpose of this study was to determine the diversity of bacterial communities associated with bioaerosols generated during land application of biosolids using non-cultural methods. Anaerobically digested Class B biosolids were land applied to an agricultural site located within the south central area of Arizona. Aerosol samples were collected downwind of the biosolids operations. Aerosol samples were collected via the use of SKC Biosamplers and were subsequently extracted for the presence of bacterial community DNA. All DNA was amplified using polymerase chain reaction with 16s rDNA primers and subsequently cloned to select for significant clone sequences. Following DNA sequencing, all sequences were aligned and phylogenetic trees were developed to generate community profiles. The majority of aerosolized bacterial clone sequences belonged to the Actinobacteridae, Alpha, and Beta Proteobacterial groups of bacteria. These profiles differed from upwind, background samples. Aerosol samples collected downwind of soil aerosolization produced similar profiles. No one clone sequence isolated from the aerosol samples could be solely attributed to biosolids, and on the contrary the majority appeared to be arisen from soil. This study demonstrates that in dry arid climates the majority of aerosols associated with biosolids land application are associated with the onsite soil.