The influence of sodium hypochlorite biocide on the corrosion of carbon steel in reclaimed water used as circulating cooling water

•The changes of polarisation curves and EIS over time were investigated.•Protective layers consist of microorganism metabolites and scale in the presence of microorganisms.•NaClO decreases the corrosion in circulating cooling water, whereas it promotes the corrosion in sterile water.•NaClO kills the microorganisms simultaneously along with the inhibition of corrosion and scaling in circulating cooling water. In this paper, we investigated the influence of sodium hypochlorite (NaClO) biocide on the corrosion of carbon steel in four different conditions during one dosing cycle. The results from the polarisation curve and electrochemical impedance spectroscopy (EIS) indicated that NaClO could affect the activity of microorganisms, leading to corrosion inhibition. The equivalent circuits had two time constants in the presence of biocide, which suggested that an oxide layer of NaClO was formed on the carbon steel surface. Environmental scanning electron microscopy (ESEM) and energy dispersive spectroscopy (EDS) were both employed to demonstrate that NaClO produced a good antibacterial activity, thereby indirectly retarding corrosion while simultaneously inhibiting scaling.