Corrosion inhibitors, which are commonly added into drinking water due to aging drinking water distribution system (DWDS) to reduce lead and copper level in drinking water, are usually phosphate-based and can provide nutrients to microorganisms grown inside premise plumbing systems. Biofilms can protect opportunistic pathogens from disinfectants, such as free chlorine and monochloramine. Understanding the effects of corrosion inhibitors on biofilms disinfectant consumption is important to access and control the microbial risk in DWDS. The biofilms were fed by groundwater amended with corrosion inhibitors (silicate, phosphate, and phosphate blends) over one year. Consumption of free chlorine or monochloramine in contact with biomass scrapped from these biofilms were measured from 0.5 to 48 hours. The free chlorine and monochloramine concentrations as functions of contact time were modeled as a pseudo-first order reaction between biomass and disinfectant (free chlorine or monochloramine). The reaction rate constants between disinfectants and biomass were not dependent on the biomass type (silicate, phosphate, and phosphate blends). However, the phosphate-based biofilms consumed more monochloramine after 24 hours stagnation than those grown without corrosion inhibitors. This observation can be contributed by the greater overall porosity found in the phosphate-based biofilms. The biofilms structure and chemical composition were characterized by optical coherence tomography (OCT) and Fourier-transform infrared spectroscopy (FTIR). Three-dimensional reconstruction and pore network modeling (PNM) were used to analyze the pore structure based on biofilms OCT images. The pore structure modeling results showed that more pores and larger throats were found in phosphate-based biofilms. These results showed that using phosphate-based corrosion inhibitors can promote biofilms with greater overall porosity compared to those grown without corrosion inhibitors. Since biomass grown with or without corrosion inhibitors had similar reaction rate constants with disinfectants, diffusive mass transport can play an important role in monochloramine consumption. These results suggested that using phosphate-based corrosion inhibitors can facilitate more porous biofilms and subsequently more monochloramine consumption, which is likely to increase the risk of exposing end-users to opportunistic pathogens in drinking water.

Effects of corrosion inhibitors on drinking water biofilms and their reactivity with free chlorine and monochloramine

ACS Spring Meeting 2021

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