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

Abstract

A B S T R A C TIn 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.

Establishment of biocidal activity evaluation study protocol in healthcare facility for routine monitoring of antibacterial power of disinfectants

“…Each study involved its own control group as viability (microorganism) treatment for toxicity study and the toxicity (microorganism plus neutralizer) group for neutralizer efficacy. It should be noted that the microbial toxicity might originate from the neutralizer ingredients, disinfectant components (from its trace amounts, if complete neutralization was not ensured) and/or the byproduct of the chemical neutralization process due to neutralizer-biocide interaction (28,(30)(31)(32). The selected microbial count range for the serial dilution of > 40 to 100 CFU/plate was selected as an optimal bioburden range to minimize count error.…”

Didecyldimethylammonium Chloride- and Polyhexamethylene Guanidine-Resistant Bacteria Isolated from Fecal Sludge and Their Potential Use in Biological Products for the Detoxification of Biocide-Contaminated Wastewater Prior to Conventional Biological Treatment

“…The combined use of QAC and PHMG as biocides to prevent the biodegradation of human waste products by saprotrophic microorganisms and eliminate an unpleasant odor in fecal sludge (FS), for example, in environmentally safe toilet complexes (ESTC) of passenger railcars, has the task of preserving human waste products until their subsequent processing or disposal [ 42 , 43 ]. However, when disposed of in municipal wastewater treatment plants (WWTPs), such waste poses a potential threat, as it negatively affects activated sludge, inhibiting the processes of nitrification, denitrification, and biochemical oxygen demand (BOD) [ 44 , 45 ]. Therefore, before their disposal, preliminary neutralization of the toxic effect of biocides should be carried out.…”

Antimicrobial Properties of a Biocide Based on Quaternary Ammonium Compounds plus Polyhexamethylene Guanidine and Possible Methods for Its Deactivation

“…Biocides have found wide application as components of deodorants that prevent the biodegradation of fecal sludge (FS) and eliminate undesirable odor in dry closets, vacuum toilets in airplanes [9,10], and environmentally safe toilet complexes (ESTC) in passenger rail transport [11]. Most of these agents contain quaternary ammonium compounds (QACs) and guanidine derivatives (e.g., polyhexamethylene guanidine, PHMG), which inhibit the activity or cause the death of microorganisms and helminths [12,13].…”