Improving the understanding of concrete sewer corrosion through investigations of the gaseous hydrogen sulfide uptake and transformation processes in the corrosion layer

Abstract

Sulfide-induced corrosion of sewer infrastructure costs multi-billion dollars globally. Sewer maintenance and management largely depends on the estimation of the sewer corrosion rate, which currently can be very rough due to poor understanding of details of the process. Hence improved understanding of the corrosion processes has a major beneficial impact globally through increased service life and reduced repair/replacement costs. The overall aim of this thesis is to improve the understanding of sewer corrosion processes and develop strategies for corrosion control.To rapidly and non-destructively monitor the corrosion process, a methodology was developed based on measuring the H 2 S (sulfide) uptake rates (SUR) of concrete. The SUR of concrete coupons was determined by monitoring the temporal gaseous H 2 S concentrations in a temperature-and humidity-controlled gas-tight reactor. The results from repeated tests showed good reliability of the method. A severely corroded coupon exhibited higher SUR than a less corroded coupon, suggesting that the former having a higher sulfide oxidation activity than the latter. Additionally, temperature changes had a stronger effect on the SUR of the heavily corroded coupon compared to the less corroded coupon. The corrosion rates estimated from the SUR agreed well with those observed in real sewers under similar conditions. The effect high H 2 S concentrations on the SUR of coupon were investigated. During the high load situation, the SUR increased significantly but then decreased (compared to the baseline SUR) by about 7 -14% and 41 -50% immediately after short-and long-term high H 2 S load periods, respectively. For both conditions, the SUR gradually (over several hours) recovered to approximately 90% of the baseline SUR. Further tests suggest multiple factors may contribute to the observed decrease of SUR directly after the high H 2 S load. This includes the temporary storage of elemental sulfur in the corrosion layer and inhibition of sulfide oxidizing bacteria due to high H 2 S level and temporary acid surge. The sensitivity of the coupon SUR towards high H 2 S loads was largely dependent on its historical H 2 S exposure levels. IIThe deprivation of gaseous H 2 S for 1 h consistently caused temporary increase of the H 2 S uptake rate (SUR) immediately upon H 2 S re-supply whereas deprivation of both gaseous H 2 S and O 2 for 1 h posed little increase of the SUR after re-supply. The results suggest that the H 2 S uptake process could be limited by the oxidation of reduced sulfur species. Furthermore, the SUR decreased by 1.2% after deprivation of H 2 S for a relative long-term (i.e. 12 h), suggesting a reduced biological activity after the extended "starvation".The details of sulfide oxidation by comparing oxidation activity of a suspended solution of a corrosion layer with gaseous H 2 S uptake activity of a coupon were investigated. With sufficient dissolved oxygen (DO) and in the presence of sulfide, the mole ratio of consumed The potential of mitigating sewer cor...

The Sustainability of Concrete in Sewer Tunnel—A Narrative Review of Acid Corrosion in the City of Edmonton, Canada

“…However, the relationship between H 2 S concentration and the MIC rate remains unclear [19,20]. A wide range of H 2 S concentration-from 2 ppm to several hundred ppm-can trigger severe acid corrosion [21]. For example, severe corrosion was also reported in a low concentration environment (e.g., 4 ppm) [13].…”

“…First, moisture in the tunnel atmosphere condenses on the concrete wall, forming a moisture film. Then, due to carbonation, the surface pH of the concrete drops to around~9, and the SOB starts to colonize on the crown of the tunnel [21]. The H 2 S dissolved in the moisture film during the sulfide buildup is then oxidized by the SOB, which forms sulfuric acid.…”

“…High atmospheric temperature increase microbial activities [24,25], thereby raising the MIC rate. For example, the rates of sulfide oxidation at 25 • C were found 15% higher than those at 20 • C [21]. Temperature below 15.6 • C inhibits the bacteria's sulfide-oxidizing activity [26].…”

“…In addition, some chemicals dosed into the sewage can cause environmental problems. For example, unwanted chemicals may be generated as a result of the dosed chemical and the chemicals already in the sewage [21].…”

Corrosion and sulfur-related bacteria

“…Many types of microorganisms can trigger MIC, including bacteria, fungi, archaea and diatoms (Little & Lee, 2007;Sun, 2015;Usher et al, 2014). Among them, bacteria have been the subject of the majority of MIC research.…”