The Field Water Samples

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3.3.1 Biofilm consortium, culture medium, and chemicals
The field water samples were collected from the oil and gas field. SRB were isolated from the samples using ATCC 1249 medium. The components are listed in Table 3-1. L-Cysteine (100 ppm) was added into the medium as oxygen scavenger to avoid possible oxygen leak. The original sample solution was frozen in 1.5 ml centrifugal tubes and stored in a −20 oC freezer. One tube of seed culture was used in the ATCC 1249 medium for testing for a month. After that, another tube of seed culture was used to prevent the culture to be too different from the original culture. The planktonic motile SRB cell concentrations in the ATCC 1249 medium was counted using a hemocytometer under a 400X
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Coupons were polished with 180, 400, and 600 # grid sand papers, sequentially. After polishing, coupons were washed with pure isopropanol and put under UV light for 20 minutes for the purpose of sterilization. Before incubation, medium, vials, pipettes, and tweezers were sterilized in an autoclave for 20 minutes at 121 oC and 15 psi. Medium and chemical solutions were sparged with the filtler-sterilized nitrogen for 45 minutes to remove the dissolved oxygen. The test matrix of the starvation test is showed in Table 3-3. The composition of the modified ATCC 1249 medium is listed in Table 3-4, in which carbon sources, such as sodium citrate, yeast extract, and sodium lactate, were removed from the original formula. When making 10% strength carbon source medium, a mixing method was used, which was mixing 10 ml full strength ATCC 1249 medium and 90 ml modified medium to make 100 ml culture medium for the starvation test. In operation, three duplicated coupons, 1 ml seed culture, and treatment chemicals were added into 125 ml anaerobic vials. It was done in a glove box, which was sparged with the filter-sterilized nitrogen for 45 minutes to achieve a strict anaerobic environment. Afterwards, vials were sealed with aluminum caps and incubated at 37 oC for 7 days. In this section, mediator was added in the modified medium, which carbon sources were completely reduced. The purpose of doing this is to investigate that if the electron promoters will
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