ControlStrategyofSimultaneousNitrificationandDenitrificationinSBRSystem

1、control strategy of simultaneous nitrification and denitrification in sbr systemcontrol strategy of simultaneous nitrification and denitrification in sbr systemlou ju-qing, guo mao-xin, shen xiao-ming(department of environmental engineering, zhejiang gongshang university, hangzhou 310012, china)27 a

2、bstract: the influence of main process parameters on simultaneous nitrification and denitrification (snd) in a sequencing batch reactor (sbr) were investigated while treating actual municipal sewage. the influent average concentration of codcr and total nitrogen was 350mgl-1 and 35mgl-1. the experim

3、ent indicated the following four operation control strategies: (1) when operation cycle was 6 hours, oxidation of organic pollutants and simultaneous nitrification and denitrification could well completed in the sbr reactor; (2) tn removal rate could be increased significantly, 40% higher than tradi

4、tional sbr processes when idle period was set between influent and aeration; (3) the time of idle period could affect simultaneous nitrification and denitrification and the best time is 30 minutes; (4) increase of sludge organic load may improve tn removal efficiency, but nh3-n removal efficiency de

5、clines.key words: sbr; simultaneous nitrification and denitrification; idle; cycle; sludge loadlou ju-qing (1973- ), female, master, associate professor; main research field: water pollution control engineering. e-mail: ljq7393.guo mao-xin (1954- ), male, professor; main research field: water pollut

6、ion control engineering. e-mail: guo_mx.1. introductionthe classical theory of water consider that the nitrification and denitrification processes of biological nitrogen removal take place in independent or separate reactors respectively. nitrification is the self-transformation that from nitrite to

7、 nitrate by the ammonia, denitrification process is the heterotrophic transformation that from nitrates into nitrogen under anaerobic conditions1. however, in recent years, studies have shown that nitrification and denitrification could taken place in one bioreactor simultaneously, namely simultaneo

8、us nitrification and denitrification2. on the current domestic and international study of simultaneous nitrification and denitrification focused on the synthetic sewage of artificial preparation under specific reaction conditions, such as high temperature, high ph or low dissolved oxygen concentrati

9、on3, and also mainly research the impact of the do and c/n in simultaneous nitrification and denitrification4. now at home and abroad have no study which focus on sbr simultaneous nitrification and denitrification of real municipal sewage or wastewater under room temperature conditions. the water th

10、is article discussed was municipal sewage came from deqing sewage treatment plant, besides, this paper is focus on the influence and control conditions of the cycle, the order of idle in cycle, idle time and the load of sludge in simultaneous nitrification and denitrification process under the condi

11、tions that in normal temperature, not change the raw water quality, and not artificially adjust the ph and the temperature.2. materials and methods2.1 experimental equipment the sbr reactor we used was made of plexiglass, measuring 1555cm, the effective volume is 7.5l (fig. 1). the wastewater is tra

12、nsported by peristaltic pump. the system uses blast aeration and air is conveyed by air pump and microporous aeration into the reactor, besides, the do concentration is related to the amount of aeration, which controlled by rotameter. influent, aeration, sedimentation, drainage, idle time can be set

13、 based on the experimental needs, and controlled by time relay and solenoid valve.sbrreactorinfluent tankrotameterautomatic control panelagitation devicefig. 1 experimental equipment2.2 experimental water and sludge experimental water and vaccination sludge were taken from deqing sewage treatment pl

14、ant, the average chemical oxygen demand (codcr) and tn of the influent is 350mgl-1 and 35 mgl-1 respectively.2.3 analytical project and methodspotassium dichromate standards measured cod; cm-02n-ammonia detector test nh3-n; dianne ics-90-ion chromatography measured no2-n, no3-n and po43-p; toc-4100-

15、online monitoring measured toc; wtw oxi170-dissolved oxygen meter measuring do; ma235 - ph meter test ph; xsp-3c biomicroscopy is used to observe biological phase; weight-method measured the mlss. analysis method refer to the document5. 3. results and discussion3.1 stable operation of system and sim

16、ultaneous nitrification and denitrificationas sewage and sludge were both collected from deqing sewage treatment plant, whose sludge has nitrification itself, we did not culture and domesticate vaccinated sludge and the main job was to debug the stable operation of devices. in the experiment, do con

17、centration was controlled about at 3mgl-1, and hrt was controlled in 8h and kept longer srt7. performing for 2 weeks, sludge concentration was 2500mgl-1. the sludge appeared to be a kind of light brown flocculus with better settlement performance and clean water, in which codcr average concentration

18、 was lower than 30mgl-1, ammonia concentration basically lower than 2mgl-1, and removal rate of codcr and ammonia reached above 90%. deducting the nitrogen consumed by bacteria proliferation, different levels of total nitrogen removal were detected in the reactor. this showed there went simultaneous

19、 nitrification and denitrification in the sbr reactor. the next step was to start the following research.3.2 control strategy about the order of idle processes in the cycle on simultaneous nitrification and denitrification so far, research processes of sbr simultaneous nitrification and denitrificat

20、ion has been operated in such order, which is influent, aeration, sedimentation, drainage and idle. there has not been a study on the effects of the order of idle processes in the cycle for simultaneous nitrification and denitrification. this experiment set the cycle within 8h, including influent an

21、d drainage for 30min, idle processes for 40 min, aeration for 370 min and sedimentation for 40 min. do concentration was controlled at 1.0-2.0 mgl-18 in the whole process by regulating aeration volume separately on the regular process a (influent, aeration, sedimentation, drainage and idleness) and

22、b (influent, idleness, aeration, sedimentation and drainage) that means put idle between aeration and influent. both processes having been performing for 10 days, we inspected respectively the changes of ammonia, nitrate and total nitrogen in those two processes. because of time constraints, we just

23、 identified daytime data of this cycle, which shows in the fig. 2.0510152025303512345678910time (d)concentration (mg.l-1)effluent tneffluent nh3-ninfluent nh3-ninfluent tn (1) concentration varying of nh3-n and tn in process aeffluent nh3-ninfluent nh3-ninfluent tneffluent tn05101520253012345678910t

24、ime (d)concentration (mg.l-1)(2) concentration varying of nh3-n and tn in process b02040608010012012345678910time (d)nh3-n in process btn in process atn in process bnh3-n in process aremoval rate (%)(3) removal of nh3-n and tn in process a and bfig. 2 changes of nh3-n, no3-n and tn in processes a an

25、d bas seen in the fig. 2(3), when influent concentration of ammonia were about at the same level, drainage ammonia concentration were kept at lower level (about 1 mgl-1) with higher removal rate of ammonia, which indicated that better nitration took place. the deduction of total nitrogen was detecte

26、d and this showed simultaneous nitrification and denitrification occurred in both processes. however, process b had a little higher ammonia removal rate and so much higher removal rate of total nitrogen than process a, which raise from 33.2% to 77.1% on average. from the (1) and (2) of fig. 2, the m

27、ain reason is that nitrate concentration in the fluent of process a was higher than process b, which caused an increase in total nitrogen of drainage, as well as showed in the fig. 2(1), drainage nitrate was more than influent counterpart, which illustrated denitrification degree in process a was fa

28、r less poor and that concentration of drainage nitrogen in the process b was more stable. this is because process a (influent, aeration, sedimentation, drainage and idle) lacked a hypoxia phase between influent and drainage, and that there went some denitrification in the sedimentation period and th

29、at there existed some hypoxia micro-environment inside activated sludge since do level was lower, but organic has been fully degraded in precipitation phase that can not meet the requirements of the carbon source in denitrification. on the contrary, in process b, idle was put before aeration corresp

30、onding to front anoxic phase. at this time, sludge organic load was higher, the organics in the influent could meet the needs of denitrifying bacteria on carbon sources and mixture that has not been drained played a role of refluxing mixture. this formed an integrated a/o system, having a significan

31、t effect on denitrification and completing synchronous nitrification and denitrification better in the same reactor.3.3 the control strategy of cycle on simultaneous nitrification and denitrificationin order to study the effect of simultaneous nitrification and denitrification as well as the mechani

32、sm of denitrification in sbr system, the mlss concentration was controlled about at 3000 mgl-1, and do concentration was controlled at 1.0-2.0 mgl-1, and the process b was taken for 10h, that in each cycle every 2h take a sample to analyze the concentration of codcr, nh3-n, , the changes in one cycl

33、e shows in fig. 3.020406080100120024681012time (h)removal rate (%)codcrnh3-nfig. 3 removal changes of codcr and nh3-n in one cyclein fig. 3 we find that codcr,nh3-n removal efficiency were significantly increased with the running time in one period of the sbr reactor, especially in the first 4h, rea

34、ch to 84.6% and 91.4% respectively. the codcr concentration decreased from 398 mgl-1 to below 100 mgl-1 in 4h, resulting in below 60 mgl-1 in the effluent water after 6h, which satisfied the first level standard for wastewater discharge of second-class town sewage treatment plants, and the removal e

35、fficiency maintained at over 90%, after that with the time goes the removal efficiency can hardly enhanced. nh3-n removal in the first 4h occurred quickly, after 6h of operation, the concentration decreased from 29.09 mgl-1 to 0.38 mgl-1, then remain basically unchanged. at the same time, the and co

36、ncentration were less than 1 mgl-1 and 10 mgl-1 respectively, and which havent increased with the decline of the nh3-n concentration. this indicate that the oxidation of organic matter, nitrification and denitrification can take place in the same sbr reactor at the same time. take all the things abo

37、ve into account we find that extend retention time can improve effluent water quality, but the reactor volume load will reduce, meanwhile the project cost and operation cost will increase. considered volume load, the removal efficiency and economic returns, the cycle time should be controlled at 6h

38、in the actual operation.3.4 the control strategy of idle time on simultaneous nitrification and denitrification in order to study the effect of idle time on the simultaneous nitrification and denitrification, the experimental conditions were controlled in the same with 3.3, performing 6h in every cy

39、cle. when the aeration meet to 4h, we detected the snd at the idle time of 20 min, 30 min and 45 min, the average experimental results of 10 times shows in table 1.table 1 removal of codcr, nh3-n and tn in different idle timeidle time(min)codcr (mgl-1)nh3-n (mgl-1)tn (mgl-1)influenteffluentinfluente

40、ffluentinfluenteffluent2037416.324.70.9032.210.43034317.823.70.4833.37.54536922.923.51.0732.97.7test results showed that when the aeration meet the demand of the degradation of organic matter and nh3-n nitrification reaction, idle time almost has no effect on codcr and nh3-n removal efficiency but h

41、as main influence on the denitrification. as seen in the table 1, tn removal efficiency increased from 20min to 30min, however, after 30 minutes, it maintained at the same level. this is because from the perspective of microbiology, nitrification and denitrification are two relatively independent bi

42、ochemical reactions, the former which needs the effective supply of oxygen oxidized ammonia to nitrate by nitrobacteria, while the latter is a facultative reaction only in anoxic and anaerobic conditions can reduce nitrate to nitrogen by denitrifying bacteria9. so there exists a balance between nitr

43、obacteria and denitrifying bacteria in the sbr system which can remove organic and nh3-n in the same time. usually, denitrifying bacteria has a low proportion in the activated sludge, besides, for the most part of them exist inside of the biological floccules, so that wastewater entered the hypoxic

44、zone through the aerobic of the activated sludge and completed denitrification need some time. at the influent concentration of this experiment it needs 30 min to complete denitrification, and then extend the time the has no effect for the amount of denitrifying bacteria were limited. nitrification

45、and denitrification time was not only related to idle time, but also related to the influent concentration, so we should identify idle time according to the concentration in actual project.3.5 the control strategy of organic sludge load on simultaneous nitrification and denitrificationthe effect of

46、c/n on simultaneous nitrification and denitrification has reported in many documents that they compound the water in laboratory10. however, it is more meaningful to study the impact of organic sludge load on simultaneous nitrification and denitrification for that the concentration and c/n ratio of a

47、 real city sewage influent remained at one level. in experiment or actual operation we can control organic sludge load by controlling the concentration of mlss, this experiment performing as 3.4.the concentration of codcr, nh3-n, tn under different organic sludge load at 30 min of idle time show in

48、the fig. 4.6070809010000.10.20.30.4sludge load (kgbod5/kgmlss.d)removal rate (%)codcrnh3-ntnfig. 4 removal of codcr, nh3-n and tn in different sludge loadas seen in the fig. 4, when the organic sludge in the lower load (less than 0.2kgbod5/kgmlssd), the organic degradation basically would not be aff

49、ected, codcr removal efficiency was more than 95%, then with sludge organic load increased codcr removal efficiency declined. in order to achieve simultaneous nitrification and denitrification, we controlled dissolved oxygen at a relatively low level. with organic sludge load increased, do seemed no

50、t sufficient, which lead to the decline of organic removal efficiency. nh3-n removal efficiency declined with the increase of organic load, because the nitrification process of nitrifying bacteria which belongs to self-nurturing type of aerobic bacteria does not need organic carbon, on the contrary

51、when organic load is high, other heterotrophic bacteria multiplied quickly restrained the activity of nitrobacteria by competing do with them. however, the increased load of organic sludge can raise the tn removal efficiency, because on one hand when the organic sludge load is low, organic matter is

52、 consumed quickly in the aerobic district of sludge floc and only a small amount of organic sludge spread into anoxic zone of sludge flock, which unable to meet the demand of denitrifying bacteria on the carbon source that result in declining of tn removal efficiency. on the other hand when sludge o

53、rganic load is high, although the concentration of nh3-n increased with the removal efficiency of nh3-n decreased, the concentration of caused by nh3-n nitrogen declined. according to the total nitrification reaction11, 1 mgl-1 nh3-n can produce 3.38 mgl-1 means that nh3-n increased by 1 mgl-1, decr

54、eased by 3.38 mgl-1 in effluent. at the same time, with the effects of denitrification enhanced more was reduced, so the tn removal efficiency increased, which shows that the organic sludge load affect simultaneous nitrification and denitrification results directly.4. conclusions(1) when operation c

55、ycle is 6 hours and dissolved oxygen concentration is 1.0-2.0 mgl-1, sbr reactor can well complete oxidation of sewage organics and simultaneous removal of nitrification and denitrification.(2) sbr process is adjusted to be influent, idle, aeration, sedimentation, drain, in other words is put idle p

56、eriod between influent and aeration. this step can increase significantly tn removal rate, 40% higher than traditional sbr processes, also can increase nh3-n removal rate slightly and make the nitrogen concentration in effluent more stable.(3) the time of idle period can affect simultaneous nitrific

57、ation and denitrification, when the chemical oxygen demand (cod) is 350mgl-1 and the average tn is 35mgl-1, the best time is 30 minutes; nitrification and denitrification time was not only related to idle time, but also related to the influent concentration, so we should identify idle time according

58、 to the concentration in actual project.(4) increase of sludge organic load may improve tn removal rate, but nh3-n removal rate declines. in practical engineering, should combine the concentration of influent and requirement of the effluent to determine the appropriate load of organic sludge.(5) this experiment only study the simultaneous nitrification and denitrification process of sbr syst