Reseach On Inactivation Of Bacteria In Subsea Oil-field Injection Water Using Multiple Wavelengths Ultraviolet Light-Emitting Diodes

The proper selection of efficient and environmental friendly disinfection technology for subsea injection water is significant to effective exploitation and stable operation of subsea oil field.Disinfection using ultraviolet light-emitting diodes(UV LEDs)can meet the requirements,therefore have a good prospect in the field of disinfection of subsea injection water.At present,there is no report on the application of UV LEDs in inactivation of bacteria in subsea injection water.The disinfection efficacy of UV LEDs is closely related to ultraviolet wavelength,wall-plug efficiency and bacterial species.UV-LEDs with peak wavelengths at 255 nm,280 nm,350 nm,and combinations of 255 nm and 350 nm,280 nm and 350 nm are investigated using a batch type reactor to determine their dose-based and time-based efficiency at disinfecting saprophytic bacteria,iron bacteria and sulfate reducing bacteria.The change of cell structure were also analyzed.A selection strategy of UV LEDs' wavelength is proposed.The results indicate that although 255 nm UV-LED obtains optimum germicidal effect,280 nm UV-LED approves to be practical owing to lowest electrical energy per order and the ability to cause irreversible damage to cell structure.Besides,the combination of 255 nm,280 nm and 350 nm UV LEDs induced no synergistic bactericidal effects.The disinfection efficiency of UV LEDs under different water quality conditions is also researched.Orthogonal test were utilized to examine the influence of ultraviolet wavelengths,irradiation time,turbidity,chromaticity and initial concentration of bacteria on the disinfection of saprophytic bacteria,iron bacteria and sulfate-reducing bacteria using UV LEDs.Effects of water quality factors on UV transmittance and disinfection efficiency of saprophytic bacteria are also studied.Results show that these factors,except chromaticity,exert a significant impact on disinfection efficiency.Water quality factors such as particles and iron ion mainly affect disinfection effect by changing UV transmittance,and the impact on disinfection efficiency is negligible when UV transmittance is higher than 80%.The bacterial load mainly affects the disinfection efficiency by changing the utilization rate of ultraviolet.Furthermore,the reactivation of bacteria and the repair of pyrimidine dimer after UV LED inactivation are investigated.The results show that UV dose is negatively correlated with the maximum survival ratio and the maximum reactivation rate and positively correlated with the number of pyrimidine dimers in DNA.280 nm LEDs could significantly repress reactivation of bacteria and the repair of pyrimidine dimer with the same energy consumption.The combination of UVC LED and UVA LED could also inhibit the reactivation of bacteria and the repair pyrimidine dimer.Besides,the DNA of iron bacteria is more resistant to UV damage than saprophytic bacteria.