Pollution characteristics of full-scale butterfly valves: Risk assessment of heavy metal release behavior influenced by the bacterial communities and corrosion products

Abstract

Given that contamination of butterfly valves has not been well understood in drinking water distribution systems (DWDSs), this study aimed to investigate the synergistic adsorption/release effects of microorganisms and corrosives on heavy metals. Results showed that outer layer scales were relatively loose, while hard black inner scales were mainly composed of Fe3O4 and Fe2O3, allowing Ca, As, Cr, Tl, and Pb to accumulate with low-diverse bacteria, primarily Desulfovibrio. Loose black inner layer scales were mainly formed by Fe(OH)3 and Fe(OH)2, enabling Ca, Cr, and Pb to accumulate with high-diverse bacteria, notably Desulfovibrio, Xanthobacteraceae, and Gallionellaceae. Metals involved in the metabolic activity of bacteria showed a negative correlation with these bacteria. Metals complexed and precipitated extracellularly in bacteria exhibited a positive correlation with these bacteria. Individual Pollution Factor (ICF), Global Pollution Factor (GCF), and Risk Assessment Code (RAC) demonstrated high bio-availability risks for Cd, especially in loose deposits with significant mobility.