The Study Of The Start Of UAFB-anammox Reactor And Nitrogen Removal When Treating Ammonium At Low Concentration From Sewage

Compared with the conventional biological nitrogen removal technology,the anaerobic ammonium oxidation?anammox?process is more energy efficient and has lower operating cost without the addition of the external organic carbon resource.Thus,the novel biological nitrogen removal technology based on anaerobic ammonium oxidation reaction has rapidly become a research hotspot in the field of nitrogen removal.In general,ammonium and nitrite were utilized as an electron donor and an electron acceptor by anammox bacteria in the strict anaerobic conditions,and the nitrogen gas?N₂?was formed through the conversion of ammonium and nitrite during the anaerobic ammonium oxidation process.The influencing factors include dissolved oxygen?DO?,the nitrogen?ammonium and nitrite?concentrations,pH,temperature,organic matter concentrations,substrate concentration and light conditions.When the municipal sewage treatment was tried to adopt the mainstream anaerobic ammonia oxidation process to remove nitrogen,the ammonium at the low concentration in wastewater may be the crucial limiting factor which influence the growth of anammox bacteria and thus the performance of mainstream anaerobic ammonium oxidation process.In this study,an up-flow anaerobic fixed-bed reactor?UAFB?was used to carry out the start-up and performance test of the anammox process at low concentrations?the initial concentrations of ammonium and nitrite were both controlled at 28 mg N/L?.The polyurethane sponge and the elastic fiber with a certain volume ratio were filled in the UAFB reactor which was inoculated with the anaerobic granular sludge from the UASB reactor in the local starch wastewater treatment plant.The UAFB system has been operated for more than 160days.During the whole experience,the total nitrogen loading rate?NLR?increased by shortening the hydraulic retention time?HRT?.The main results include as following:?1?The HRT of the UAFB reactor controlled at a temperature of 30±1°C was gradually reduced from 17.5 h to 3.0 h and thus the total nitrogen loading rate NLR increased from 0.056 to 0.320 kg N/m³/d.The ammonium and nitrite concentrations in the effluent were both lower than 5 mg N/L during the stable period of each stage.In the stable phase of the final stage?HRT=3.0 h?,the removal rates of ammonium and nitrite were both over 98%and the removal rate of total nitrogen?TN?was about80%.The start-up and long-term stable operation for the anammox process was successfully realized under low nitrogen concentration.?2?In the final stage,two kinds of carriers were taken out from the UAFB,and the nitrogen removal performance test was carried out by the ex-situ kinetics analysis.The experimental results showed that the polyurethane sponge has stable and high-efficiency anammox performance.The ratio of consumed nitrite and ammonia with produced nitrate?calculated with unit mg N/L?was:?[NH₄⁺]:?[NO₂^-]:?[NO₃^-]=1:1.01:0.55.In contrast,elastic fibers fluctuated during the treatment of various initial concentrations?28 mg N/L and 56 mg N/L?,and the ratios of consumed nitrite and ammonia with produced nitrate?calculated with unit mg N/L?were:?[NH₄⁺]:?[NO₂^-]:?[NO₃^-]=1:1.82:0.36 and?[NH₄⁺]:?[NO₂^-]:?[NO₃^-]=1:1.47:0.71.Further,the ex-situ anammox activity values of the two carriers are:5.63mg N-NH₄/L/h/L _PSS and 3.90 mg N-NH₄/L/h/L _FB,respectively.The above-mentioned results indicated that the microorganisms per unit volume of the polyurethane sponge carrier have a relatively higher anammox activity than that of the elastic fibers in a single UAFB system.Compared with the elastic fiber carrier,the polyurethane sponge was much more microporous?which is benefited for the growth of the microorganism?and was also better resistant under the hydraulic shear force.?3?Scanning electron microscopy?SEM?and energy spectrum?EDS?analysis showed that the biomass was rich in the polyurethane sponge.Its pore structure was complex and comfortable for the growth of microorganisms in the polyurethane sponge.The surface of the elastic fiber carrier is relatively smooth.When the HRT is reduced,the hydraulic shearing force is enhanced and the microorganisms was easily detached from the surface of the fibrous carrier.However,it should be pointed out that the filamentous structure of the surface of the elastic fiber ball tends to retain and enrich a large amount of microorganisms in the initial stage of the anammox reaction?under low hydraulic shear force?in the UAFB system.Further analysis of the main components of the microbial extracellular polymer?EPS?on the two carriers,the main components of EPS of sludge attached on the polyurethane sponge,including protein?50%?,polysaccharides?36.21%?and humic acid?13.79%?;the main content of microbial EPS on elastic fibers was comprising:humic acid?54.34%?,protein?31.96%?and polysaccharide?13.70%?.It can be concluded from the literature that high protein content in EPS is beneficial to the granulation of microorganisms.?4?The 16S rRNA high-throughput gene sequencing method was firstly used to analyze the microbial diversity of suspended microorganisms in different stages of the UAFB system in different stages of the experiment.Then the microbial diversity of biofilm on the two carriers in the stable period of the final stage was compared.The results showed that the microbial population diversity in the UAFB showed a downward trend with the operation of the experiment.In the stable phase of the final stage,the main anammox species in the UAFB reactor was Candidatus Brocadia?14.15%?.The microbial structure of biofilm on the two carriers is similar and the proportion of anammox bacteria on the polyurethane sponge carrier was slightly higher than that of the fibrous carrier.