Worker exposure to bioaerosols from sludge dewatering facilities: risks and mitigations

Area of Science:

• Environmental microbiology
• Occupational health and safety

Background:

• Sludge dewatering in wastewater treatment plants (WWTPs) is a primary source of worker exposure to bioaerosols.
• Quantitative microbial risk assessment (QMRA) has limitations in providing immediate on-site risk data.
• Establishing critical concentration standards offers a practical approach to assess bioaerosol risks.

Purpose of the Study:

• To investigate Escherichia coli bioaerosol emissions from sludge dewatering.
• To estimate a ceiling-type exposure limit (EL) for acceptable risk levels.
• To analyze the impact of working postures, ventilation, and seasons on bioaerosol exposure.

Main Methods:

• Utilized Monte Carlo simulation and reverse QMRA to estimate exposure limits.
• Conducted sensitivity analysis to identify key risk parameters.
• Measured bioaerosol concentrations under varying environmental and operational conditions.

Main Results:

• Poor ventilation increased bioaerosol concentration by 1.6-1.7 times compared to natural ventilation.
• Respirable fractions (< 4.7 µm) constituted 78%-100% of emissions.
• Mask usage increased derived exposure limits by one to two orders of magnitude.

Conclusions:

• Masks significantly reduce inhaled bioaerosols, substantially increasing occupational exposure limits.
• Ventilation, working posture, and season influence bioaerosol exposure and derived ELs.
• This study provides crucial data for establishing occupational exposure limits in dewatering facilities.