*3.2. SEM*

Figure 3 displays the morphological characteristics of the biofilms grown on 304SS coupons after different immersion times in the *D. desulfuricans*-inoculated medium with and without BDMDAC addition. The surface morphologies of the 304SS coupons immersed in the culture medium without inoculation are shown for comparison. The SEM images reveal that the surfaces of the 304SS coupons were strongly influenced in the absence of *D. desulfuricans* and BDMDAC. First, Figure 3a,c show no visible corrosion products or biofilms formed on the 304SS coupons in the blank and BDMDAC solutions after 14 days of immersion, whereas Figure 3b displays corrosion products and biofilms on the 304SS coupon in the SRB solution. Some pitting is observable on the surface of the 304SS coupons in the blank and BDMDAC solutions, but this is only in a few locations. This observation is attributable to the presence of Cl− ions in the culture medium [50–52]. The EDS elemental analysis results (Table 1) reveal that, in addition to characteristic corrosion products (Fe and O), sulfur elements were detected after 14 days of immersion in the SRB solution. Sulfur elements mainly result from the metabolic activity of SRB (formation of FeS) [53]. Thus, the EDS results sugges<sup>t</sup> that the addition of BDMDAC in the SRB solution could decrease the activity of SRB and reduce the formation of biofilm. After extending the immersion time to 28 days, large areas of corrosion products and biofilms were observed on the coupons immersed in the SRB solution (Figure 3e), whereas the 304SS surface was largely intact in the blank and BDMDAC solutions (Figure 3d,f). Moreover, the EDS elemental analysis results revealed increased sulfur elements on the coupons immersed in the SRB solution. By contrast, sulfur elements were not observed on the 304SS coupons immersed in the blank and BDMDAC solutions. These results confirm the inhibition efficiency of 25 ppm BDMDAC.

**Figure 3.** SEM images of the 304SS coupons after different immersion times in various solutions: (**a**) blank for 14 days; (**b**) SRB for 14 days; (**c**) BDMDAC for 14 days; (**d**) blank for 28 days; (**e**) SRB for 28 days; and (**f**) BDMDAC for 28 days.


**Table 1.** EDS analysis results after 14 and 28 days of immersion.
