Fate of Clostridia and other spore-forming Firmicute bacteria during feedstock anaerobic digestion and aerobic composting

Jessica Subirats; Hannah Sharpe; Edward Topp

doi:10.1016/j.jenvman.2022.114643

Fate of Clostridia and other spore-forming Firmicute bacteria during feedstock anaerobic digestion and aerobic composting

J Environ Manage. 2022 May 1:309:114643. doi: 10.1016/j.jenvman.2022.114643. Epub 2022 Feb 10.

Authors

Jessica Subirats¹, Hannah Sharpe², Edward Topp³

Affiliations

¹ Agriculture and Agri-Food Canada, London Research and Development Centre, London, Ontario, Canada; Department of Biology, University of Western Ontario, London, Ontario, Canada. Electronic address: jess.subi86@gmail.com.
² Agriculture and Agri-Food Canada, London Research and Development Centre, London, Ontario, Canada; Department of Biology, University of Western Ontario, London, Ontario, Canada.
³ Agriculture and Agri-Food Canada, London Research and Development Centre, London, Ontario, Canada; Department of Biology, University of Western Ontario, London, Ontario, Canada. Electronic address: ed.topp@agr.gc.ca.

PMID: 35151135
DOI: 10.1016/j.jenvman.2022.114643

Abstract

Pathogenic spore-forming Firmicutes are commonly present in animal and human wastes that are used as fertilizers in crop production. Pre-treatments of organic waste prior to land application offer the potential to abate enteric microorganisms, and therefore reduce the risk of contamination of crops or adjacent water resources with pathogens carried in these materials. The inactivation and reduction of gram-positive spore formers such as Clostridium spp., Clostridioides spp. and Bacillus spp. from animal and human waste can be challenging given the recalcitrance of the spores these bacteria produce. Given the significance of these organisms to human and animal health, information concerning spore-forming bacteria inactivation during anaerobic digestion (AD) and aerobic composting (AC) is required as the basis for recommending safe organic waste management practices. In this review, an assessment of the inactivation of spore-forming Firmicutes during AD and AC was conducted to provide guidance for practical management of organic matrices of animal or human origin. Temperature and pH may be the main factors contributing to the inactivation of spore-forming Firmicutes during batch lab-scale AD (log reduction <0.5-5 log). In continuous digesters, wet AD systems do not effectively inactivate spore-forming Firmicutes even under thermopholic conditions (log reduction -1.09 - 0.98), but dry AD systems could be a feasible management practice to inactivate spore-forming Firmicutes from organic materials with high solid content (log reduction 1.77-3.1). In contrast, composting is an effective treatment to abate spore-forming Firmicutes (log reduction 1.7-6.5) when thermophilic conditions last at least six consecutive days. Temperature, moisture content and composting scale are the key operating conditions influencing the inactivation of spore-forming Firmicutes during composting. Where possible, undertaking AD with subsequent composting to ensure the biosafety of digestate before its downstream processing and recycling is recommended to abate recalcitrant bacteria in digestate.

Keywords: Aerobic composting; Pathogen inactivation; Spore-forming firmicutes; anaerobic Digestion.

Publication types

Review

MeSH terms

Anaerobiosis
Clostridium*
Composting*
Spores, Bacterial