Assessment of emissions and potential occupational exposure to carbon monoxide during biowaste composting

Authors: SOBIERAJ, KAROLINA - Wroclaw University Of Environmental And Life Sciences; GIEZ, KAROLINA - Wroclaw University Of Environmental And Life Sciences; Koziel, Jacek; BIALOWIEC, ANDRZEJ - Wroclaw University Of Environmental And Life Sciences

Submitted to: bioRxiv
Publication Type: Pre-print Publication
Publication Acceptance Date: 8/7/2023
Publication Date: 8/7/2023
Citation: Sobieraj, K., Giez, K., Koziel, J.A., Bialowiec, A. 2023. Assessment of emissions and potential occupational exposure to carbon monoxide during biowaste composting. bioRxiv. Available: https://doi.org/10.1101/2023.08.06.552181.
DOI: https://doi.org/10.1101/2023.08.06.552181

Interpretive Summary: Carbon monoxide (CO) is a toxic air pollutant, commonly associated with CO poisoning. CO is typically released when there is no sufficient oxygen present to efficiently convert fuels into energy and carbon dioxide. Much lesser known CO source is composting, a common practice of treating agricultural biowaste. Scientists from ARS-Bushland and Wroclaw University of Environmental and Life Sciences (Poland) collaborated to address this gap in knowledge. In this research, CO emissions from industrial-scale compost plants in Poland were measured to assess the occupational risk of CO inhalation for workers. Indoor plants are being phased-in as preferred technology because they improve the management of compost and the quality of final product. The maximum CO emissions occurred at an enclosed (indoor) plant after compost piles were turned, ranging from several to over 100 times higher compared to before turning. Compost plant operators involved in turning can be exposed to thresholds of CO that exceed daily lawful limits. It is recommended that occupational air quality monitoring, work safety protocols, personal protective equipment, and appropriate ventilation be considered to reduce the risk of CO inhalation, especially to personnel routinely working with compost turning.

Technical Abstract: Biowaste composting is considered a sustainable management practice. However, not much is known about the occupational exposure to the release of toxic process gases in large composting plants. This research aimed to bridge this gap by assessing the potential of carbon monoxide (CO) releases from compost and means to mitigate the occupational risks. CO emissions from biowaste composting were measured at two plants processing green waste, sewage sludge, and/or undersize fraction of municipal solid waste. Effects of the compost age, location of composting piles (indoor of closed hall vs. outdoor), and seasons (autumn vs. winter) were studied. Higher CO emission rates were observed for 4-wk-old piles compared to 8-wk-old, located in a closed composting hall, isolated from ambient conditions (wind and temperature <10 °C). The maximum CO emissions occurred after the material was turned, ranging from several to >100 times higher compared to the baseline before turning. The top sections of piles released greater CO concentrations compared with the sides. Results were used to model occupational exposures during typical daily management operations. The 1-h concentration can reach 2.8 mg CO·m-3 (2 ppm) before turning, and as much as nearly 10 mg CO·m-3 (9 ppm) and near the WHO threshold for an 8-h human exposure. Turning outdoor piles did not result in measurable CO concentration spikes. Occupational exposure inside the enclosed composting hall should not exceed 8 h, assuming moderate physical effort. The risk of excessive exposure to CO could be reduced by implementing work safety protocols and monitoring, personal protective equipment, and ensuring appropriate ventilation aiming to dilute emissions during and shortly after turning operations.