Research On The Denitrification Performance Of Marine Anammox Bacteria Under The Action Of Ultraviolet And Electron Mediators

Anaerobic ammonium oxidation?anammox?is a novel and promising biological nitrogen removal process.In particular,marine anammox bacteria?MAB?show excellent adaptability to saline environments.However,the application of anammox is restricted by the sensitivity to environmental conditions and long doubling time.The objective of this study was to explore whether ultraviolet?UV?irradiation and electron shuttles were beneficial to promote MAB enrichment and electron transfer,and finally strengthened nitrogen removal.The results indicated that MAB exhibited a high tolerance to UV-C irradiation,up to12000 mJ/cm² which was the optimal dose to promote the enrichment of MAB.Compared with the control group,the relative abundance of Candidatus Scalindua was selectively enhanced by 1.19 folds under this dose.When the dose was higher than 12000mJ/cm²,the inhibition was aggravated.The recovery of inhibited ammonium removal rate was negatively correlated with UV dose.The relative abundance of symbiotic heterotrophs?e.g.Reinekea,Marinobacter and Halomonas?with high adaptation was increased.Assimilatory nitrate/nitrite reduction and denitrification were strengthened,and great?NO₂^--N/?NH₄⁺-N and?NO₃^--N/?NH₄⁺-N deviation from the theoretical values were led.Excessive extracellular polymeric substances and the special structure of MAB acted as a primary and secondary defense line to cope with UV irradiation,respectively.Based on the PICRUSt analysis,marine anammox bacterial community possessed diversified tolerance mechanisms to UV irradiation,such as dark repair,signal transduction,osmoregulation,interspecific competition/cooperation,reinforced extracellular structures and cell motility.In the presence of 9,10-Anthraquinone-2-sulfaonate?AQS?and riboflavin?RF?,the substrate conversion rate in the first hour could be enhanced by 2.19 and 1.48 folds with 0.02 mM AQS and 0.05 mM RF,respectively.Meanwhile,the concentration of NO₃^--N was decreased due to the enhanced denitrification.When the concentration of AQS and RF was higher than 0.05 mM,the nitrogen removal performance was inhibited.By contrast,the tolerance of MAB to AQS was higher than RF.The half inhibitory concentrations of AQS and RF were 0.3 and 0.1 mM,respectively.AQS and RF played a positive role in in the respiratory electron-transport chain of MAB.However,the inhibited nitrogen removal was mainly ascribed to the sensitivity of MAB to organics,cytotoxicity of AQS and bioconversion of RF.Therefore,AQS and RF were not excellent electron shuttles for MAB.The remodified Logisitic model and modified Boltzmann model were suitable for describing the nitrogen removal process of MAB with addition of AQS and RF??0.3 mM?.