Study On Partial Nitrification Process Using Zeolite Biological Aerated Filter

Compared with the traditional nitrification process,the partial nitrification process requires lower energy consumption when treating ammonia nitrogen wastewater.Generally,the partial nitrification process means that ammonium is oxidized to nitrite under aerobic conditions by ammonia-oxidizing bacteria（AOB）.Then the wastewater would be treated by the denitrification or the anaerobic ammonia oxidation process,which utlimatly realized the reduction of nitrite to N₂ and total nitrogen removal.Recently,the relative study about the partial nitrification process is becoming a hot issue in the field of nitrogen removal from wastewater.The partial nitrification process is affected by dissolved oxygen（DO）,temperature,free ammonia（FA）,free nitrous acid（FNA）and other influent parameters,which often lead to the unstable and low efficiency for the partial nitrification.Also,nitrogen loading rate（NLR）was reported as a key factor for the control of the partial nitrification process.Therefore,the zeolite with a high ammonium adsorption capacity is selected and filled in an upflow zeolite biological aeration filter（ZBAF）.The start-up and operation performance of the partial nitrification process was studied emphatically.Firstly,the zeolite was characterized via structure analysis and ammonium adsorption experiment.Then the ZBAF was inoculated with nitrifying sludge from the laboratory.During the operation,the hydraulic retention time（HRT）and the influent ammonium concentration were regluly changed in order to adjust NLR.The ZBAF system has been running for more than 180 days.The main results were concluded as the following:（1）At 283K and 298K,the saturated adsorption capacity of zeolite for ammonium were 5.79 mg/g and 8.11 mg/g,respectively.Increasing the temperature was beneficial to the adsorption of ammonium.Under the same conditions,p H=9 was the best adsorption environment for zeolite and the adsorption capacity of zeolite reaches the maximum（4.82 mg/g）.When the ammonium concentration was 50 mg/L,the adsorption reaction of zeolite（0.1 g）was completed within 90 min.The Langmuir,Freundlich,Koble-Corrigan,Temkin,Redlich-Peterson models were used to simulate the zeolite adsorption reaction.The results showed that the Langmuir model（R²=0.997）could be better for the description of the ammonium adsorption behavior of zeolite.The kinetic study showed that the pseudo-second-order kinetic model（R²=0.927）could be betterfor the description of the ammonium adsorption process of zeolite.The above-mentioned results showed that the adsorption of ammonium by zeolite is a single-layer chemical adsorption reaction.（2）When the influent ammonia nitrogen concentration was 300 mg/L and HRT was 3.09 h,the partial nitrification reaction was started.In the stable stage,the nitrite accumulation rate（NAR）of ZBAF effluent was higher than 80%.When HRT was changed to 4.17 h,the removal rate of ammonium increased from 70%to 80%while the NAR decreased from 75%to 60%.When influent ammonium incresed to 400mg/L,the ammonium removal rate decreased to 60%while NAR increased to 65%.When the influent ammonium and HRT were decreased to 200 mg/L and 2.15 h,the ammonium removal rate droped to 40%and the NAR increased to 90%with NLR of1.19 kg/（m³ d）.The results showed that increasing the ammonium concentration in the influent and shortening HRT would lead to a decrease of the ammonium removal rate and an increase of NAR.The research found that NLR has a greater influence on the nitritation operation of ZBAF.The analysis of ammonium,FA,nitrite and nitrate at different heights of the reactor showed that the start of the partial nitrification process could be achieved by controlling the FA concentration in the ZBAF reactor,and it was proved that the inhibition of NOB activity by FA was the key factor to achieve partial nitrification reaction.（3）In order to evaluate the activities of AOB and NOB in ZBAF,the kinetic study of samples at different heights of the ZBAF were carried out.The results showed that the highest AOB nitrification rate was 5.63 mg/（g VSS L h）at the height of 0.32 m-0.48 m,and the highest NOB nitrification rate was 2.83 mg/（g VSS L h）at the height of 0.16 m-0.32 m.The activities of AOB and NOB in the ZBAF system were determined jointly by the concentration of the substrate and FA.The analysis of the biological community structure showed that the dominant bacteria species in the ZBAF at the phylum level were Proteobacteria,Chloroflexi,and Bacteroidota.the abundances of Proteobacteria at the different heights（0.00-0.16 m,0.16-0.32 m,0.32-0.48 m,0.48-0.64 m,from the bottom to the upper）were 40.13%,42.99%,40.00%,and 34.14%,respectively;the abundances of Chloroflexi were 26.34%,27.30%,27.00%,30.11%;the abundances of Bacteroidota were 11.63%,13.01%,21.57%and 24.62%.At the genus level,the abundances of Nitrosomonas（one typical AOB）were 8.75%,10.21%,4.67%and 1.89%,which indicated that the microbial community structure was mainly inluenced by the FA concentration.