TRANSPORT OF AEROSOLIZED BACTERIA AND VIRUS FROM A SIMULATED CENTER-PIVOT IRRIGATION SYSTEM
Location: Northwest Irrigation and Soils Research
Project Number: 5368-63000-001-01
Start Date: Oct 01, 2010
End Date: Sep 30, 2012
The objective of this research project is to determine the downwind transport of bacteria and virus aerosolized during center-pivot irrigation events of dairy lagoon wastewater. We hypothesize that aerosolized bacteria and virus, associated with water droplets, will lose their ability to survive and/or decrease in concentration with distance from the source, minimizing an individual’s chance for exposure and possible infection.
Monitoring bioaerosols from a center pivot irrigation system in the field is difficult because sampling locations constantly change with wind direction and pivot location. Therefore, we will use an irrigation boom that is approximately 50 m long and with sprinklers spaced 3 m apart and 2 m above ground level (typical center pivotspan). The irrigation boom will be set up as a line source and oriented so that the prevailing wind is perpendicular to the line source. Lagoon wastewater will be pumped directly into a 1000-gallon tank and then transported to the field site at the USDA-ARS farm in Kimberly, ID. The wastewater will then be blended with irrigation water and pumped to the irrigation boom at the appropriate pressure for nozzle operation. A portable weather station will be located near the site to provide general meteorological data including wind speed, wind direction, air temperature, solar radiation, and relative humidity. Bioaerosol samples will be collected at 10, 50, 100, and 150 m downwind from the nozzles using all-glass impingers. The impingers will be placed on tripods at a height of 1.5 m, the average breathing height for humans. The impingers will be operated for 20 to 60 minutes to acquire a bioaerosol load sufficient for subsequent cultivation. Since pathogen concentrations (e.g. Salmonella spp., enterohemorrhagic Escherichia coli) tend to be relatively low in wastewaters, indicators of fecal contamination will be targeted for cultivation. The indicator organisms we have chosen for these studies are E. coli, total coliforms, enterococcus (subgroup of fecal streptococci), and coliphage. Prior to pumping, wastewater samples will be collected to determine the total culturable concentrations of the targeted microorganisms and other water quality parameters (e.g. pH, dissolved oxygen, salinity). While we will not quantify Salmonella spp. and enterohemorrhagic E. coli in the aerosol samples, we will determine the total concentration of these bacteria in the wastewaters. For the purposes of this project, we will acquire lagoon wastewater from either an open-lot or freestall dairy. Since droplet size is one of the most important factors affecting aerosol transport, the main effect that will be tested is droplet size. The lagoon wastewater will be blended 1:1 with clean irrigation water and pumped through sprinklers that generate either fine or large droplets. The experiments will be replicated three times with each sprinkler type. To take into account the affect of weather parameters on airborne microorganism transport and survival, the experiments will be performed in the spring and summer (both day and night). As a result, a total of 24 experiments will be conducted during this project’s lifecycle. Because wind is another important factor in aerosol transport, the experiments will only be conducted during sustained wind events that are 2 to 5 m/s. To ensure quality control, all aerosol samples will be stored on ice after collection and transported to our laboratory for immediate processing. Documents Trust with ID State. Log 40901. Formerly 5368-12630-002-04T (8/10).