Effects of iron-oxidizing bacteria and humic acid of various molecular weights on iron corrosion in drinking water distribution systems

Iron corrosion in drinking water distribution systems (DWDSs) is the root cause of the deterioration of drinking water quality. Humic acid (HA) is a critical component of dissolved organic matter in drinking water. However, the influences of HA on iron pipe corrosion in DWDSs have not been fully understood, especially the combined effects of corrosive microorganisms and HA with different molecular weights (MWs). This study used bench-scale reactors to explore the impacts of iron-oxidizing bacteria (IOB) (Microbacterium oxydans ZT-1, a common iron-oxidizing bacterium) and HA with different MWs on iron pipe corrosion. Before 6 d, loose and porous goethite (α-FeOOH) was the most prevalent compound in the corrosion products. The addition of ZT-1 and HA promoted iron corrosion and release. Under the condition of ZT-1 + > 100-kDa HA, the maximum values of corrosion rate and total iron concentrations were 0.23 mm/a and 9.94 mg/L, respectively. As corrosion proceeded, magnetite (Fe₃O₄) formed from FeOOH, and Fe-HA complexes accumulated, resulting in deceleration of iron corrosion. After 54 d, the corrosion rate and total iron concentration had decreased by ZT-1, and HA with different MWs.