Periodic deprivation of gaseous hydrogen sulfide affects the activity ofthe concrete corrosion layer in sewers
Sulfide induced concrete corrosion significantly reduces the service life of the sewer systems. Gaseoushydrogen sulfide (H2S) levels are a key factor affecting the corrosion rate and thesefluctuate due to thediurnalflow pattern of sewers. Currently, there is little known about how suchfluctuations, in particularthe periodic deprivation of H2S, may affect the corrosion activity. This study investigated the impact ofthe deprivation of H2S on the sulfide uptake rate (SUR) of concrete coupons incubated in laboratorycorrosion chambers. After systematic evaluation of the gaseous H2S concentration profiles of two sewersystems, two types of profiles, i.e. short- (1 h) and long- (12 h) term deprivation of H2S, were applied tothe concrete coupons. In comparison to the baseline SUR, exposing the concrete coupon to 0 ppm of H2Sfor 1 h consistently caused a temporary increase of the SUR (i.e. 3.2%e12.5%) following re-supply of H2Sat baseline levels. With the continuous re-supply of H2S, there was gradual and steady decrease of SUR tothe level close to the baseline SUR. However, for the case after deprivation of H2S for 12 h, the SUR was5.1% lower than baseline SUR and gradually increased to a level similar to the baseline SUR during the 20e30 min of continuous re-supply of H2S. In addition, the simultaneous deprivation of H2S and O2for 1 hhad negligible impact on the SUR. Further analysis suggests that the historically accumulated in-termediates of sulfide oxidation could act as electron donors for sulfide oxidizing bacteria (SOB). Thereplenishment of the intermediates upon the re-supply of H2S could play a key role in the increase of SURafter short-term deprivation of H2S. However, the activity of SOB could be diminished after long-termdeprivation of H2S, although the sulfur intermediates still could be available. Estimating the sulfideuptake by concrete using the SUR of the average H2S concentration could lead to overestimation of thesulfide uptake. There could be more significant overestimation for the case with longer deprivation ofH2S.