A bioassay-based protocol for chemical neutralization of human faecal wastes treated by physico-chemical disinfection processes: A case study on benzalkonium chloride

Emanuele Sozzi*, Mahnoor Baloch, Joseph Strasser, Michael B. Fisher, Mats Leifels, Juan Camacho, Nadia Mishal, Sam F. Elmes, Grace Allen, Gregory Gadai, Lexi Valenti, Mark D. Sobsey

*Corresponding author for this work

Research output: Journal article (peer-reviewed)Journal article

9 Citations (Scopus)


In situ physico-chemical disinfection of high risk faecal waste is both effective and widely used as a sanitation management strategy for infection prevention and control. Systematic tests where the performance of alternative physico-chemical disinfection methods is systematically compared and optimized must be based on reliable protocols. These protocol are currently not adequately addressing the neutralization related issues: the neutralization of the tested disinfectant after specified conditions of concentration and contact time (CT) is necessary to prevent continued disinfection after the intended contact time; moreover such neutralization is often necessary in practice and on a large scale to prevent adverse health and ecological impacts from remaining disinfectant after the target CT is achieved. Few studies adequately assess the extent of neutralization of the chemical disinfectant and are intended to optimize on-site disinfection practices for waste matrices posing high microbial risks. Hence, there is a need for effective and reproducible neutralization protocols in chemical disinfection trials and practice. Furthermore, for most of chemical disinfectants used in healthcare settings there is no practical methodology to reliably and conveniently measure the residual disinfectant concentration after its neutralization and also determine the optimum concentration of the neutralizer. Because some neutralizing compounds can themselves be toxic to the test microorganisms, it is necessary to optimize neutralization procedures in disinfection experiments for the development of infection control practices using accepted positive control microbes. In the presented work, a stepwise bioassay-based protocol using representative faecal indicator microbes is described for optimizing chemical disinfection and subsequent disinfectant neutralization of any infectious faecal waste matrix. The example described is for the quaternary ammonium compound benzalkonium chloride and its recommended chemical neutralizer in a high strength human faecal waste matrix.

Original languageEnglish
Pages (from-to)155-167
Number of pages13
JournalInternational Journal of Hygiene and Environmental Health
Issue number2
Publication statusPublished - Mar 2019
Externally publishedYes


  • Benzalkonium chloride
  • Biocide
  • Chemical disinfection
  • Chemical neutralization
  • Chlorine
  • Cholera
  • Disaster medicine
  • Ebola
  • Faecal waste
  • Healthcare associated infections
  • Infectious hepatitis
  • Microbial bioassay
  • Pseudomonas syringae/virology
  • Bacteriophage phi 6
  • Humans
  • Polysorbates/chemistry
  • Waste Disposal, Fluid
  • Benzalkonium Compounds/chemistry
  • Lecithins/chemistry
  • Feces/microbiology
  • Disinfection/methods
  • Biological Assay
  • Disinfectants/chemistry
  • Escherichia coli/growth & development

ASJC Scopus subject areas

  • Public Health, Environmental and Occupational Health


Dive into the research topics of 'A bioassay-based protocol for chemical neutralization of human faecal wastes treated by physico-chemical disinfection processes: A case study on benzalkonium chloride'. Together they form a unique fingerprint.

Cite this