Effect of sodium bisulfite injection on the microbial community composition in a brackish-water-transporting pipeline

Abstract

Pipelines transporting brackish subsurface water, used in the production of bitumen by steam-assisted gravity drainage, are subject to frequent corrosion failures despite the addition of the oxygen scavenger sodium bisulfite (SBS). Pyrosequencing of 16S rRNA genes was used to determine the microbial community composition for planktonic samples of transported water and for sessile samples of pipe-associated solids (PAS) scraped from pipeline cutouts representing corrosion failures. These were obtained from upstream (PAS-616P) and downstream (PAS-821TP and PAS-821LP, collected under rapid-flow and stagnant conditions, respectively) of the SBS injection point. Most transported water samples had a large fraction (1.8% to 97% of pyrosequencing reads) of Pseudomonas not found in sessile pipe samples. The sessile population of PAS-616P had methanogens (Methanobacteriaceae) as the main (56%) community component, whereas Deltaproteobacteria of the genera Desulfomicrobium and Desulfocapsa were not detected. In contrast, PAS-821TP and PAS-821LP had lower fractions (41% and 0.6%) of Methanobacteriaceae archaea but increased fractions of sulfate-reducing Desulfomicrobium (18% and 48%) and of bisulfite-disproportionating Desulfocapsa (35% and 22%) bacteria. Hence, SBS injection strongly changed the sessile microbial community populations. X-ray diffraction analysis of pipeline scale indicated that iron carbonate was present both upstream and downstream, whereas iron sulfide and sulfur were found only downstream of the SBS injection point, suggesting a contribution of the bisulfite-disproportionating and sulfate-reducing bacteria in the scale to iron corrosion. Incubation of iron coupons with pipeline waters indicated iron corrosion coupled to the formation of methane. Hence, both methanogenic and sulfidogenic microbial communities contributed to corrosion of pipelines transporting these brackish waters.

Fig. 1.

Schematic of the brackish-water-gathering system. Water was collected through multiple pipelines, transporting 10³ m³/day each from the Grand Rapids formation (E1) and the McMurray formation (E2). The comingled water (E3; 10⁴ m³/day) was transported to a water treatment facility, where sodium bisulfite (SBS) was added to scavenge oxygen. Samples of pipe-associated solids (PAS) were obtained from sections of failed pipe collected either upstream (616P) or downstream (821TP of 821LP) from the SBS addition point. The main direction of flow is indicated by the arrows; the water in 821LP was often stagnant.

Fig. 2.

Pipe sections analyzed in this study. (A) Pipe section 616P (6 and 8 cm are the inner diameters [ID]). (B) Corrosion and scale on the inside pipe surface of 616P. (C) Closeup image of the pipe surface from a pipe section near 616P after removal of scale and cleaning. (D) Pipe section 821LP (22 cm is the outer diameter [OD]). (E) Corrosion and scale on the inside pipe surface of 821LP. (F) Corrosion and scale on the inside pipe surface of 821TP.

Fig. 3.

Amplicon library relational tree. The tree was generated using the UPGMA algorithm with the distance between communities calculated using the thetaYC coefficient in the Mothur software package. The tree was visualized with Dendroscope. Dendrogram subgroups a to i are indicated. Amplicon libraries from sessile PAS samples (a, c, and d) formed trees that were separate from those for planktonic samples of fast-flowing water (e to i). Amplicon libraries for PAW-821LP (c), the single sample of stagnant water, formed a tree with those for the PAS samples. Bar, 0.01 substitutions per nucleotide position.

Fig. 4.

NMDS ordination of amplicon libraries calculated using the majorization algorithm based on the thetaYC coefficient matrix. Each point in the plot represents a single amplicon library, as indicated with its amplicon library code (Table 1). The distances between points represent the differences between the amplicon libraries. The red and green points represent amplicon libraries from sessile samples (PAS) and planktonic samples (PAW), respectively, which were shipped together. There was no clear separation between the sessile and planktonic amplicon libraries. However, there was a significant community structure shift between amplicon libraries from samples collected before and after the point of SBS addition. The blue points represent amplicon libraries from planktonic water samples E1, E2, and E3 (Fig. 1), which were received at times T1 (28 October 2009), T2 (24 September 2009), and T3 (27 January 2010). Amplicon libraries from samples collected at T1 are more distant from the amplicon libraries from samples collected at T2 and T3 than those are from each other.

Fig. 5.

(A and B) Headspace methane (A) and ferrous iron formation by brackish waters incubated with iron coupons (B). (C) Corrosion rate of iron coupons as determined by metal weight loss. Data represent average results from two separate incubations with two coupons each. Brackish water samples E1-3, E2-3, and E3-3 (Table 2) were used for the experiment.