Purpose: An experimental study was conducted in Beltsville, MD, to determine the emission and deposition of bioaerosols generated during feedstock mixing and windrow turning, common mechanical handling operations in composting processes.
Methods: Bioaerosols generated during mixing/turning of dairy manure solids (DMS, compost feedstock) and 2-week-old DMS-compost windrows were collected 3 m downwind of materials handling operations using 6-stage Anderson Impactors and SpinCon air samplers, operating at 28.3 l/min and 450 l/min, respectively; 30 samples from two experiments were analyzed. Samples (n = 14) of basil leaves from plants exposed to bioaerosol deposition at 3 m downwind were collected. Total aerobic bacteria (tAB), fecal coliform and E. coli concentrations were determined by conventional plating and MPN procedures.
Results: Populations of tAB, coliforms, and E. coli in for dairy solids and composts were not significantly different (P > 0.05). Airborne tAB concentrations were 4.29 and 6.39 log CFU/m3 and E. coli were 0.133 and 1.52 MPN/m3 during mixing and turning of DMS and compost, respectively. Particle-size distribution of tAB was not significantly different (P > 0.05) from that for composts. Both coliforms and E. coli were primarily associated with coarse particles (> 2.1 µm). Calculated deposition of E. coli on basil leaves at 3 m downwind = -3.48 and -4.31 log MPN cm-2·s-1, for DMS and compost, respectively.
Significance: These data will be useful in atmospheric dispersion modeling to predict, refine, and validate projected downwind concentrations of bacterial aerosols generated during dairy manure solids handling and composting operations under a variety of atmospheric conditions across various terrain.