| Partial Nitritation/Anammox(PN/A)had been widely recognized as a cost-effective biological nitrogen removal process for the treatment of wastewater with low carbon to nitrogen ratio(C/N).In PN/A process,nitrogen removal can be achieved with zero carbon demand and reduced aeration requirement due to its complete autotrophic nature.However,successful PN/A would require the limitation of Dissolved Oxygen(DO)concentration in the system to favor Ammonia Oxidation by Ammonia Oxidizing Bacteria(AOB).Currently,DO in most PN/A systems was supplied by mechanical aeration with undesirable oxygen transfer performance.To further imply the limitation of DO concentration,a precise but complex aeration control system would be required.And failure in the aeration control system could severely disrupt the stability of PN/A process.Nitrate produced by anaerobic ammonia oxidizing bacteria(An AOB)also reduces the total nitrogen removal rate(TNR)of PN/A process.Therefore,improvement in aeration control strategies,oxygen transfer rate,and TNR would promote the development and application of PN/A process.Algal-bacterium symbolic process had been applied in wastewater treatment for many years.In algal bacterium symbolic systems,microalgal could produce the DO required by aerobic bacteria through photosynthesis,which would lead to the reduction in aeration-related energy consumption and lower the operation cost.In this study,a novel Algae Enhanced Shortcut Nitrification/Anammox(AESN/A)MBR system was established by inoculating microalgae into the aerobic MBR of a stably operated two-stage PN/A MBR system.The nitrogen removal performance,energy consumption by aeration,biomass concentration of microorganisms in the Photo MBR were tested,and the diversity of the bacteria community during the operation was analyzed.The study went as follows:Synthetic wastewater was used in this study to simulate the secondary biochemical effluent from Ammonia Producing Plants.DO,p H control,and ammonia and nitrite dosing were implied to accelerate the start-up phase of the two-stage PN/A MBR system.At stable operation,a 7-day average ammonia removal efficiency and total nitrogen removal rate(TNR)reached92.23±0.96% and 81.57±1.74%,respectively,which showed the system was ready for further microalgae inoculation.After the inoculation of microalgae,the proposed AESN/A MBR was successfully started under the predetermined light intensity of 2000 lux and light-dark cycle of 8:16h.At stable operation,an average ammonia removal efficiency of 93.71±6.13% and total nitrogen removal rate(TNR)of 86.10±7.00% was achieved,indicating the system could effectively remove the ammonia nitrogen contained in the Synthetic secondary biochemical effluent from Ammonia Producing Plants.Meanwhile,microalgae in the Photo MBR produced DO for AOB,and reduced the energy consumption by aeration by 50%.Furthermore,while the biomass concentration of microorganisms in the Photo MBR slowly increased over time,the algae-tobacterium ratio remained steady throughout the operation.This indicated the proliferation speed of microalgae in the Photo MBR was close to that of the bacterium,and a balanced relationship was formed between newly inoculated microalgae and predominated bacterium.During the operation,flocs and granules in both reactors were sampled and highthroughput sequencing based on the V3-V4 region of the 16 S r RNA gene was conducted to reveal the shift in microbial community structure.The results of the alpha diversity index were as follows: The Chao1 estimator used to evaluate the diversity of the microbial community before and after the inoculation of microalgae was 531 and 431,respectively.This indicated the inoculated microalgae had a selective force on the local microbial community.The results of the principal component analysis showed that there was a major shift in microbial community structure before and after the inoculated microalgae.The results of species diversity analysis were as follows: The dominant phyla in the nitritation MBR and anammox MBR were Proteobacteria and Planctomycetes,respectively.After the successful start-up of the nitritation MBR,the relative abundance of the AOB genera Nitrosomonas reached 55.2% while the relative abundance of the NOB genera Nitrobacter dropped to 0.55%,indicating NOB was successfully washed out of the nitritation MBR during the start-up phase by controlling DO concentration and p H.After the inoculation of microalgae,the relative abundance of the AOB genera Nitrosomonas dropped to 35.55% while the relative abundance of other denitrifying bacteria genera such as Comamonas,Mizugakiibacer,Nakamurella,Taibaiella,and Thauera showed a small increase.This showed the inoculation of microalgae diversified the nitrogen metabolism pathway inside the reactor.In conclusion,the novel AESN/A MBR system could effectively remove the ammonia nitrogen contained in the Synthetic secondary biochemical effluent from Ammonia Producing Plants while consuming less power for aeration.Therefore,the construction of the AESN/A MBR system provided a certain degree of theoretical basis for achieving further ammonia polishing in the secondary biochemical effluent from Ammonia Producing Plants with high efficiency and low energy consumption,which is of great significance. |
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