Impact of background water quality on disinfection performance and silver release of immobilized silver nanoparticles: Modeling disinfection kinetics, bactericidal mechanism and aggregation behavior

An aminosilane-based surface functionalization strategy was adopted to immobilize silver nanoparticles (AgNPs) on to silica materials to minimize leaching of silver into the aqueous environment. The disinfection potential and silver release of immobilized-AgNPs and chloridized silver surfaces were investigated for simulated lake water under varying water chemistry conditions. While the presence of both hardness and natural organic matter (NOM) adversely affected the disinfection kinetics and silver release from immobilized-AgNPs, alkalinity had only minor impact on disinfection performance over the concentration range 30-600 mg L-1. The higher disinfection efficacy of immobilized-AgNPs was ascribed to their contact-killing mechanism of action. In contrast, chloridized Ag that caused disinfection through the release of silver ions showed lower disinfection efficacy. Divalent cations and NOM greatly influenced the surface characteristics and morphology of the immobilized-AgNPs. However, immobilized AgNPs were more shielded than colloidal AgNPs when exposed to similar harsh conditions characterized by high hardness and NOM concentration. Under all the tested conditions, where 100% disinfection was achieved, the amount of silver release from immobilized AgNPs was less than 22 mu g L-1, which is well below the USEPA permissible limit. The disinfection kinetics of immobilized-AgNPs was best fitted by the Hom model (R-2 = 0.974), where its lumped parameters k(h) and m were found to vary with variation in background water quality. Sensitivity analyses indicated that for 'm' value higher than 1.9, complete disinfection could not be achieved regardless of many fold increase in 'k(h)' value.