Application of dairy cattle wastewater as biofertilizer: quantitative microbial risk assessment of exposure to bioaerosols

Abstract

The reuse or recycling of wastewater provides environmental and economic benefits, representing a sustainable and circular alternative for the management of liquid waste. However, the application of effluents to agricultural crops via spraying creates a potentially dangerous situation for individuals exposed to airborne pathogens. This study used Quantitative Microbial Risk Assessment (QMRA) tools to quantitatively assess the microbial risks of occupational and public exposures to bioaerosols in fertigation scenarios by spraying untreated and treated wastewater. Analyses of Escherichia coli (EC) and Clostridium perfringens (CpSP) in raw and treated effluents as well as pathogen / indicator ratios from the literature were used to estimate the concentrations of Escherichia coli O157:H7 (EC-O157:H7) and Cryptospodirium spp. (Crypto) in the air, and the results were applied to an atmospheric microbiological dispersion model. From the concentrations of pathogens in the air, infectious risks for downwind receptors were calculated. The risks of infection by EC-O157:H7 to workers at 10 m and 50 m away from the emission source ranged between 8.30 x 10-1 and 3,35 x 10-3 pppy, whereas to residents at 100 m and 500 m ranged from 6.37 x 10-1 to 3.36 x 10-4 pppy. Peak values (95th percentile) of occupational and public risks associated with the exposure to Crypto were 3.29 x 10-3 and 1.5 x 10-3 pppy, respectively, and of risks regarding exposures to CpSP were lower than 1.41 x 10-6 pppy. Anaerobic digestion reduced risks by approximately one order of magnitude. The distance from the source was inversely proportional to the risk of exposure. It is recommended that wastewater is treated prior to its reuse and the adoption of application methods with low aerosolization potential. In addition, the need for workers to use personal protective equipment (PPE) is highlightedv.