Reduction of Lead Oxide (PbO2) and Release of Pb(II) in Mixtures of Natural Organic Matter, Free Chlorine and Monochloramine

Abstract

The primary focus of this paper is to elucidate the influence of mixtures of natural organic matter (NOM) and free chlorine and NOM and monochloramine on the reduction of PbO2 in drinking water. Parallel experiments using PbO2 particles of two different sizes (approximately 20 and approximately 200 nm) were conducted to explore the effects of particle size on this process. In the absence of NOM, reduction of PbO2 was observed in monochloramine solutions but not in free chlorine solutions. In the presence of NOM, significant Pb(II) formation was observed in disinfectant-free solutions. The release of Pb(II) was suppressed by the additional presence of free chlorine until the point in time when free chlorine was exhausted. Monochloramine also repressed Pb(II) formation in the presence of NOM but not as significantly as free chlorine. The presence of NOM and monochloramine does not necessarily act additively or synergistically due to complex interactions including reduction of PbO2 by NOM, monochloramine mediated reduction of PbO2, and oxidation of NOM by monochloramine. Higher surface area-normalized Pb(ll) formation was found in experiments using larger PbO2 particles. The high reactivity generally associated with nanoparticles was not observed in our study.