Quantification and Comparison of Risks Associated with Wastewater Use in Spray Irrigation

Jameson Mori, Sital Uprety, Yuqing Mao, Sotiria Koloutsou-Vakakis, Thanh H. Nguyen, Rebecca L. Smith

Research output: Contribution to journalArticlepeer-review


In the U.S., spray irrigation is the most common method used in agriculture and supplementing with animal wastewater has the potential to reduce water demands. However, this could expose individuals to respiratory pathogens such as Legionella pneumophila and nontuberculosis Mycobacteria (NTM). Disinfection with methods like anaerobic digestion is an option but can increase concentrations of cytotoxic ammonia (personal communication). Our study aimed to model the annual risks of infection from these bacterial pathogens and the air concentrations of ammonia and determine if anaerobically digesting this wastewater is a safe option. Air dispersion modeling, conducted in AERMOD, generated air concentrations of water during the irrigation season (May–September) for the years 2013–2018. These values fed into the quantitative microbial risk assessments for the bacteria and allowed calculation of ammonia air concentrations. The outputs of these models were compared to the safety thresholds of 10−4 infections/year and 0.5 mg/m3, respectively, to determine their potential for negative health outcomes. It was determined that infection from NTM was not a concern for individuals near active spray irrigators, but that infection with L. pneumophila could be a concern, with a maximum predicted annual risk of infection of 3.5 × 10−3 infections/year and 25.2% of parameter combinations exceeding the established threshold. Ammonia posed a minor risk, with 1.5% of parameter combinations surpassing the risk threshold of 0.5 mg/m3. These findings suggest that animal wastewater should be anaerobically digested prior to use in irrigation to remove harmful pathogens.

Original languageEnglish (US)
Pages (from-to)745-760
Number of pages16
JournalRisk Analysis
Issue number5
StatePublished - May 2021


  • anaerobic digestion
  • microbial risk assessment
  • wastewater irrigation

ASJC Scopus subject areas

  • Safety, Risk, Reliability and Quality
  • Physiology (medical)


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