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

Abstract In situ physico-chemical disinfectionof 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 disinfectionmethods is systematically compared and optimized must be based on reliable protocols. These protocol are currently not adequately addressing the neutralizationrelated issues: the neutralizationof the tested disinfectantafter specified conditions of concentration and contact time (CT) is necessary to prevent continued disinfectionafter the intended contact time; moreover such neutralizationis often necessary in practice and on a large scale to prevent adverse health and ecological impacts from remaining disinfectantafter the target CT is achieved. Few studies adequately assess the extent of neutralizationof the chemical disinfectantand are intended to optimize on-site disinfectionpractices for waste matrices posing high microbial risks. Hence, there is a need for effective and reproducible neutralizationprotocols in chemical disinfectiontrials and practice. Furthermore, for most of chemical disinfectantsused in healthcare settings there is no practical methodology to reliably and conveniently measure the residual disinfectantconcentration after its neutralizationand also determine the optimum concentration of the neutralizer. Because some neutralizingcompounds can themselves be toxic to the test microorganisms, it is necessary to optimize neutralizationprocedures in disinfectionexperiments 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 disinfectionand subsequent disinfectant neutralizationof any infectious faecal waste matrix. The example described is for the quaternary ammonium compound benzalkonium chlorideand its recommended chemical neutralizerin a high strength human faecal waste matrix.