Study On Nitrogen Removal Of Partial Nitrification-Anammox Combining With Sulfur-based Autotrophic Denitrification System And Organic Inhibition Mechanism

Anaerobic ammonia oxidation(Anammox)is the process by which Anammox bacteria metabolize NH4+-N and NO2--N,converting them into N2.The Anammox based partial nitrification-Anammox process can directly convert high concentration of NH4+-N to N2 without additional organic carbon source.The process could achieve high nitrogen removal efficiency using less oxygen,and its sludge yield is quiet low.It is of great significance for the treatment of high ammonia nitrogen wastewater and complex landfill leachate.However,the floating phenomenon of granular sludge,the secondary pollution caused by NO3--N products,and the inhibition of Anammox bacteria caused by organic wastewater have not been effectively solved in partial nitrification-Anammox process.Such problems limit the wider engineering application of this process.Focusing on the above problems,the innovative hybrid partial nitrification-Anammox(HPNA)reactor proposed was proposed in order to solve the floating problem of SNA granular sludge.The system of HPNA combining with sulfur autotrophic denitrification(SAD)was designed to solve the NO3--N secondary pollution and realize autotrophic nitrogen removal.Macroscopic experiments and microscopic simulations were used on typical organic matter present in landfill leachate,to discuss the inhibitory mechanism of organic matter on partial nitrification-Anammox process and the dominant bacteria.The specific research results are as follows:(1)The HPNA reactor contains the lower fluidized bed with mechanical stir the upper fixed bed with the biofilm filler,and aerates under the fixed bed for microbial enrichment.The reactor was successfully started in 28 days and the concentration of influent NH4+-N was always over 600 mg/L.After 211 days of operation,the HRT was shortened to 5.5 h.The average TN removal and NH4+-N removal reached 80%and 89%,respectively.Meanwhile,the NLR and NRR reached 3.7 kg-N/m3/d and 2.8 kg-N/m3/d respectively,which were 40%and 43%higher than the SNAP reactor operated at the same time.The HPNA reactor achieved stable operation and effective nitrogen removal under high NH4+-N concentration.The mechanical stir maintained the SNA granules,stimulated the EPS formation to enhance the cohesion and tightness of the granules,and facilitated the timely discharge of nitrogen,thus effectively avoided the granular floating.The dissolved oxygen in the reactor had a gradient distribution in the vertical direction,which separated the anaerobic zone(fluidized bed)from the aerobic zone(fixed bed),and achieved a farovable state in which the upper part preferentially enriches the AOB bacteria and the lower part mainly enriches the Anammox bacteria.By analyzing the sludge index,particle size and morphology,and community structure,the mechanism of granular sludge formation was discussed in detail.(2)The HPNA-SAD system could effectively remove the remaining NO2--N and accumulated NO3--N,and the concentration of NH4+-N was also slightly reduced.The TN removal increased from 88%by the HPNA reactor alone to 97%by the system.Microbial analysis showed that Thiobacillus denitrificans accounted for 72%of the total reads of the biological filter sample.In addition,denitrifying bacteria of Sulfurimonas and Simplicispira accounted for about 10%.The concentration of NH4+-N and TN in wastewater were reduced to 10 mg/L and 15 mg/L after the system treatment,which met the Class I emission standard for comprehensive wastewater discharge standard GB 8978-1996.The comparative BES system,which used less organic carbon sources(COD concentration of 100 mg/L),and enriched electrogenic bacteria at the anode and denitrifying bacteria at the cathode,could effectively remove NO2--N,NO3--N,and NH4+-N existing in HPNA effluent.However,in this study the BES system was operated in sequencing batch mode and the HRT was as long as 24 h,which was still in the laboratory scale.The denitrifying bacteria were domesticated in the HPNA reactor to realize its symbiosis with Anammox and AOB.Complete denitrification in HPNA could be achieved by this method in a short term,but later the Anammox bacteria gradually deactivated under the inhibition of organic,and the nitrogen removal performance of the reactor continued to decline.(3)The long time experiment and the short-term batch test were conducted simultaneously to further explore the mechanism of inhibition of bacteria by typical organic substances.Long time experiments showed that organic compounds such as NaAc,ethanol,and phenol had no significant effect on the activity of AOB bacteria,but had a strong inhibitory effect on the nitrogen metabolism of Anammox bacteria.The short-term inhibition test showed that the inhibition of Anammox bacteria by organic matter was rapidly produced at the beginning of the experiment,but the bacterial structure did not change significantly in a short time,suggesting that inhibition of Anammox bacteria during this period may not be caused by the large increase in denitrifying bacteria.The MOE molecular simulation results give a possible mechanism for the inhibition by organic compounds:the possibility that NaAc and phenol might connect to HZS competed with a large amount of haem in anammoxoxidation,resulting in partial inactivation of HZS due to incomplete binding of haem,thereby blocking the synthesis reaction of N2H4 and directly inhibiting the normal nitrogen metabolism of Anammox.The ethanol inhibition may be due to its inducing peroxidation within the Anammox bacteria,resulting in the destruction of the structure and function of the bacteria.