| The traditional nitrification-denitrification technology not only consumes a lot of energy,but also cannot meet the sewage discharge standard when treating domestic sewage with low C/N ratio.In the anaerobic ammonia oxidation（Anammox）process,anammox bacteria can use ammonium and nitrite as electron donors and electron acceptors respectively,to generate nitrogen under anaerobic conditions.Compared with the traditional denitrification process,this process does not require aeration and the addition of organic carbon sources,which can save 42-77%of the energy input and chemical dosing cost of the sewage treatment plant,so it is considered to be a more promising and environmentally friendly biological nitrogen removal process.Since the content of ammonium in urban sewage is much higher than that of nitrite,this will cause insufficient substrate to affect the reaction process of Anammox,so the reaction substrate nitrite will become the"barometer"of Anammox reaction.As a new type of nirtogen removal process,partial denitrification is favored because of its ability to stably produce nitrite for anammox processes,and its low demand for carbon sources,fast reaction rate,low greenhouse gas emissions,easy operation,it is considered to be the best process for coupling with Anammox.In addition,compared with traditional suspended sludge,granular sludge has the advantages of compact microbial structure,good sedimentation performance,higher biomass retention rate and shock load resistance.Therefore,this study used UASB reactor to study two different carbon sources（anhydrous sodium acetate and glucose）were used to cultivate partial denitrification granular sludge to investigate the nitrite accumulation and performance of the two systems.The gas self-circulation system is set up for optimization,and the effects of different C/N and high load shock are studied.The main conclusions are as follows:（1）The UASB reactor was used to start the partial denitrification system with anhydrous sodium acetate（S1）and glucose（S2）respectively,and the stable production of NO2--N was achieved after 120 days of operation.,the average NAR of S1 and S2are 65%and 53%.In the batch experiment on day 81,the NAR peak of S1 is 81%,which is higher than that of S2 76%,indicating that the NAR performance of S1 is better than that of S2.During the granulation process of PD sludge,the color of the sludge changed from gray to yellow,and the scanning electron microscope results showed that the sludge bacteria in the two systems were dominated by rod-shaped bacteria.When the two systems operated for 120 days,the average particle size of the granular sludge was 0.96 mm and 1.18 mm,respectively,and the particles in the range of 0.2-1.5 mm accounted for the largest proportion,accounting for 68.57%and 62.3%.In the S2 reactor,the proportion of particle size>3 mm is larger than that of S1,indicating that the granulation effect of S2 is slightly better than that of S1.On the 120th day,the population diversity of S1 and S2 sludge samples decreased,and Proteobacteria was the main bacterial phylum of S1 and S2 sludge,which increased from 24%of the seed sludge to 52.7%and 67.5%.In addition,the main bacterial genus of S1 and S2sludge samples was Thauera,which increased from 0%in seed sludge to 30.7%and25.31%,respectively.This difference in PD functional bacteria explained that the performance of S1 was better than S2.（2）In the gas circulation system,when the gas circulation flow was increased from0.4 L/h to 0.58 L/h,the NAR of S1 and S2 increased from 70%and 55%to 75%and57%,respectively,and the improvement effect of S2 was not as good as that of S1system.As the gas circulation flow increased from 0.58 L/h to 0.78 L/h,the performance of S1 and S2 degraded,and the NAR decreased from 75%and 58%to around 65%and 50%,respectively.This suggests that greater gas flow does not necessarily lead to better performance.By analyzing the EPS of granular sludge,it was found that the concentration of TB-EPS was always higher than that of LB-EPS in the two systems,and the content of PN was more important to the stability of granular sludge.By studying the influence of different influent C/N on the two systems,when the C/N is 3,the performance of S1 and S2 reaches the best state,and when the C/N gradually increases from 3 to 4.5,the NAR increases from 72%,60%to 60%and 47%respectively,and the accumulation of NO2--N decreased from 40mg/L,32mg/L to23mg/L and 18.3mg/L.Sufficient organic carbon source will make PD transition to complete denitrification.When C/N is 3,the activity of nitrate reductase of the two systems reaches the best state,and the inhibition degree of nitrite reductase is lower during the increase of C/N,so that the accumulated nitrite can continue to be reduced reaction,resulting in a decrease in accumulation.When C/N is 3,the abundance of nitrate reductase genes（nar G and nap A）reaches the highest,thus ensuring that the performances of S1 and S2 are both optimal.The abundances decreased from11.74×106,9.13×106 copies/g to 7.86×106and 6.8×106copies/g,respectively,and the changes of related functional genes corresponded to PD response performance.（3）PD granular sludge has a certain buffering effect on high-load shock.S1 and S2 showed good adaptability in stage I,with NAR of about 65%and 56%,respectively.As the load increased,both were affected to a certain extent,and the NAR dropped to48%and 40%respectively.In Phase III,the two systems gradually adapt to the impact of high load shocks,and the reduction in NAR narrows to the level of 5%and 3%.Through batch activity test of the system,it was found that the specific nitrate reduction rate of S1 and S2 decreased from 47.8,39.7 mg?（h?g）-1 to 32.1,27.7 mg?（h?g）-1,while the specific nitrate accumulation rate decreased from 30.3,27.6 mg?（h?g）-1 to 18.1,16.3 mg?（h?g）-1 respectively,and in Phase III the rate is reduced by 4%.With the increase of influent nitrate concentration,more PN secreted from EPS components of the two systems increased from 58.5,68.6 mg/gvss to 88.4,97.6 mg/gvss,respectively,and the PN/PS of EPS of the two systems increased from 7.53,8.03 to 10.6 and 11.8,respectively,PN was related to the hydrophobicity of the sludge surface.In addition,the proportion of C-C/H,the main hydrophobic component of EPS of S1 and S2,both increased from 45.31%and 52.41%to 61.78%and 68.66%,respectively,indicating that with the increase of water influent load,the two systems in EPS secreted more hydrophobic element components in the granular sludge to offset the impact of the influent load shock,and the hydrophobic component C-C/H content in S2 was higher,resulting in the inhibition effect of S2 on nitrite accumulation.lower than the S1 system.In the process of increasing influent load,Proteobacteria was the main bacterial phylum of S1 and S2 sludge,and the proportion dropped from 70.7%and 87.96%to 67.1%and73.5%,respectively.At the same time,Bacteroidota increased,indicating a strain mechanism for the two systems when faced with high-load shocks.In addition,the dominant genus in all samples was Thauera,whose proportion decreased from 35.3%and 30.7%to 32.6%and 23.76%,respectively.The dominant genus ensures the stability of the PD system,thus showing a certain ability to resist load shocks. |
