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Ultrasound technology employs cavitation to generate high-pressure soundwaves to disrupt bacterial cells. This study reveals the effectiveness of a single frequency ultrasound device for bacterial cell inactivation. A low-cost ultrasound device having a single frequency, i.e. 22 kHz for lab-scale application, was developed first, and the prototype was mechanically designed and analyzed using the finite-element method to assure the targeted natural frequency could be achieved. The prototype was then tested inactivating bacterial cells, Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis), in a simple medium and a food system, and the results were then compared to a commercial system. A treatment time of up to 15 minutes was able to reduce E. coli and B. subtilis cells by 3.3 log and 2.8 log, respectively, and these results were similar to those of the commercial system. The effectiveness of bacterial cell inactivation using the developed single-frequency ultrasound device is then discussed. The findings are useful for designing low-cost ultrasound devices for application in the food industry.

The application of nitrate-mediated souring control has been proposed as a promising tool. However, the efficiency of this method remains controversial due to several unresolved issues, such as the determination of effective nitrate concentration, the optimal injection period, etc. In this study, we investigated the depletion of specific hydrocarbons as the electron donor for sulfate-reducing bacteria (SRB) and nitrate-reducing bacteria (NRB) by varying the nitrate concentration (1.5 mM and 4.5 mM) and injection timing (single, Ns; and multiple Nm) to control souring. Based on analysis of bacterial communities, genus Arcobacter was predominant, followed by NRB of family Rhodospirillaceae, which includes Thalassospira sp. By contrast, in the condition without nitrate addition (Nw/o), genus Desulfotignum was dominant. Both SRB and NRB share similar hydrocarbon preferences: toluene, ethylbenzene, and xylene. At the limiting nitrate concentration to suppress SRB activity, 1 mM, SRB could co-exist with NRB and promote a more diverse bacterial community.

Nitrate injection has been widely used to minimize the production of biological hydrogen sulfide in oil and gas field industry, by controlling the growth of sulfate-reducing bacteria (SRB) chemically and biologically. This study aimed to investigate the changes in the bacterial community in response to nitrate addition used to control biological souring. Specifically, we examined the effect of nitrate addition in an artificial souring experiment, using diluted crude oil as substrate and electron donor. Desulfotignum sp. was the predominant SRB under all conditions tested. Addition of nitrate at the beginning (N0) repressed the growth of SRB, as revealed by chemical and bacterial community analysis, concomitant with significant growth of the nitrate-reducing bacteria (NRB) Thalassospira sp. Nitrate addition after SRB growth (at day 28, N28) successfully remediated the sulfide produced by SRB, but no significant reduction in sulfate was observed subsequently; moreover, the bacterial communities before and after nitrate addition remained identical. Isolation of Desulfotignum YB01 (D. YB01) proved the resistance of this predominant SRB in high nitrate environment. Simultaneous reduction of sulfate and nitrate by D. YB01 was also observed in this study. Therefore, the phenomenon in the N28 experiment might be the result of the role of Arcobacter sp. which are nitrate-reducing sulfide-oxidizing bacteria, and/or the ability of Desulfotignum sp. to reduce nitrate and/or nitrite as a stress response. Thus, SRB might persist after nitrate addition, potentially causing subsequent SRB outbreaks.

Seawater injection to enhance oil recovery caused biological production of sulfide (souring) and microbiologically influenced corrosion (MIC). Nitrate injection is used as a common strategy to overcome the souring and MIC but still inefficient. This study aims to reveal the effect of nitrate injection on souring and MIC. This study showed that the addition of nitrate could be used to control souring but ineffective to control MIC in the environmental sample. In the real condition, which has a more complex bacterial community, nitrate injection caused severe pitting corrosion to compare with the condition without nitrate addition. Two isolates (Desulfotignum genuses) were identified as sulfate-reducing bacteria (SRB) with nitrate reducing ability.

Sludge oil contains 30%–50% hydrocarbon fractions that comprise saturated fractions, aromatics, resins, and asphaltene. Asphaltene fraction is the most persistent fraction. In this research, the indigenous bacteria that can degrade asphaltene fractions from a sludge oil sample from Balikpapan that was isolated using BHMS medium ( Bushnell-Hass Mineral Salt ) with 0.01% ( w /v) yeast extract, 2% ( w /v) asphaltene extract, and 2% ( w /v) sludge oil. The ability of the four isolates to degrade asphaltene fractions was conducted by the biodegradation asphaltene fractions test using liquid cultures in a BHMS medium with 0.01% (w/v) yeast extract and 2% (w/v) asphaltene extract as a carbon source. The parameters measured during the process of biodegradation of asphaltene fractions include the quantification of Total Petroleum Hydrocarbon (g), log total number of bacteria (CFU/ml), and pH. There are four bacteria (isolates 1, 2, 3, and 4) that ha ve been cha r acterized to degrade asphaltic fraction and have been identified as Bacillus sp. Lysinibacillus fusiformes, Acinetobacter sp., and Mycobacterium sp. , respectively. The results showed that the highest ability to degrade asphaltene fractions is that of Bacillus sp. (isolate 1) and Lysinibacillus fusiformes (Isolat e 2), with biodegradation percentages of asphaltene fractions being 50% and 55%, respectively, and growth rate at the exponential phase is 7.17x10 7 CFU/mL.days and 4.21x10 7 CFU/mL.days, respectively.

We have previously studied the effect of nitrate addition on the souring caused by sulfate-reducing bacteria (SRB). It revealed that the nitrate addition could suppress the growth of SRB and stimulate the growth of nitrate-reducing bacteria (NRB). It is not quite clear, however, whether NRB could lead to souring in oil fields and Microbiologically Influenced Corrosion (MIC). In this study, we isolated NRB and investigated the effect of isolated NRB on souring and MIC. Based on 16S ribosomal RNA identification, isolated NRB belongs to the genus Marinobacter and was named Marinobacter YB03. This bacterium is identified as NRB with sulfate reducing ability. Severe pitting corrosion was found on the carbon steel coupon associated with YB03. Therefore, YB03 promotes souring and corrosion.