Modeling the Impact of Polychloramide Solution Properties on Bacterial Disinfection Kinetics

Anionic water-soluble polychloramide biocides are of interest because, compared to conventional cationic antimicrobial polymers, anionic biocides are less likely to be sequestered or deactivated by contact with non-microbial soil. Although electrostatics can prevent anionic polymers from adsorbing on microbes, water-soluble polychloramides appear to transfer oxidative chlorine during transient contacts between polymer chains and microbe surfaces. The Chick-Watson model of disinfection kinetics has been modified to account for the contributions of polychloramide molecular weight (MW) and the polychloramide configuration in solution estimated from the overlap concentration, C*, below which dilute polymer chains exist as discrete objects in solution. The key assumption in the modeling was that the transfer rate of oxidative chlorine from polychloramide chains to microbe surfaces impacts the disinfection kinetics. Because both C* and MW are measurable, the polymer-modified Chick-Watson (PCW) model has one less unknown parameter than the two-parameter Chick-Watson equation. The PCW model predicts that lower MW polymers are more effective biocides compared with high MW counterparts. Additionally, polymers with more compressed configurations in solution are more effective biocides. Experimental evidence supports these conclusions. Based on the estimated time scale of bacteria/polymer collisions compared with disinfection kinetics, arguments are made that bacteria surfaces must be contracted many times by polychloramide chains to achieve sufficient Cl transfer to deactivate bacteria.