Study On Vibration-enhanced Anammox And Its Coupling Process For Nitrogen Removal Performance

Anaerobic ammonium oxidation(anammox)process was a popular process in recent years for biological nitrogen removal technology.In this process,ammonia and nitrite as the main substrate which converts to nitrogen under anaerobic conditions.No additional organic carbon or aeration was needed in the whole process.The process got a higher nitrogen removal efficiency and lower sludge yield rate.It plays great guidance for the practical application.Due to the long doubling time of the anammox bacteria(11-14 days),sensitive to environmental factors such as organic matter,dissolved oxygen and nitrite nitrogen,which makes the technology need a long start-up period and easily broke down.At the same time,due to the metabolic mechanism of anammox,a small amount of nitrate generated in this process.Thus,it was necessary to couple other denitrification processes to reduce the residual nitrate.Focusing on the above problems,this study proposed an anammox biofilm reactor which could add vibration.The gradient of concentration or temperature was effectively reduced when the vibration applied to the biofilm.Meanwhile,the shear rate of the biofilm was also increased.This paper explored the effects of vibration on the reactor start-up period,nitrogen removal rate and the morphology of biofilm.Based on the experimental results,the process parameters were optimized and the feasibility to cultivate granular sludge through this process was also discussed.Finally,based on vibration,the reactor which coupled partial nitrification,anammox and sulfur autotrophic denitrification was developed.The specific research results were obtained and shown as follows:(1)Due to vibration was applied to the biofilm frame,it could effectively transmit the vibration to the biofilm.During 180 days of operation,vibration effectively promoted the growth of anammox bacteria,increasing the amount of mixed liquid volatile solids suspended solids(MLVSS)in the reactor to 20.97 g/L.Meanwhile,the nitrogen removal rate(NRR)and specific anammox activity(SAA)increased to 20.279 kg-N/(m3·d)and 0.967 kg-N/(g-VSS·d),respectively,which was 2.79 and 1.65 times higher than the control reactor.The gradient concentration inside the reactor was effectively reduced and the reactor could operate stably when the influent nitrogen concentration increase to 2200-3000 mg/L.Simultaneously,the shear rate of the biofilm was effectively increased and promoted the amount of protein(PN)which secreted by the anammox bacteria increased more than 80%,reaching 268.1 ±9.50 mg/g-VSS.The average diameter of the single biofilm fiber also reached 17.13± 3.92 mm.The higher EPS secrete rate promoted the biofilm formatting a unique granular structure.The smaller granules alternate stacking on the surface of the biofilm which could greatly enhance the system's tolerance to nitrite.No inhibition was observed when the nitrite concentration reaches 500 mg/L(free nitrous acid FNA=0.0658 mg/L).The results of the microbial analysis showed that the affinity of anammox bacteria to the biofilm(fiber)was poor.In the biofilm formation phase,the relative abundance of the membrane was only 10%.However,the vibration could effectively promote the enrichment of anammox bacteria,the total proportion of anammox bacteria has increased to over 40%within six months.(2)The results of the sequencing batch experimental indicated that different vibration intensity,vibration period and internal reflux flow rate would affect the NRR.To ensure a better effluent(the total ammonia and nitrite were lower than 8 mg/L),high-intensity vibration(Lv7)could ensure a better nitrogen removal performance.The lower effluent nitrogen concentration the better performance by vibration could be achieved.Compare to the internal recycle mode(with a flow rate of 4000 L/h),the NRR in vibration mode(Lv7)increased nearly 300%under the same quality of effluent conditions.High-intensity vibration(Lv7)could release most of the nitrogen(about 552 mL)which accumulated in the biofilm within 5 seconds.It could significantly reduce the mass transfer resistance inside the biofilm and indirectly increases the activity of the bacteria located inside the biofilm.(3)Intermittent vibration could form a breathing effect inside the biofilm.This phenomenon obtained a higher NRR with lower energy consumption.Under the intermittent condition of 0-Lv7(5/60),the NRR of reactor R1 reached 10 kg-N/(m3·d),and the corresponding specific energy consumption was below 0.5(kW·h)/kg-N.It was only one tenth when the reactor applied continuous vibration which the same intensity.Since the vibration could directly be applied to the surface of the biofilm,the energy loss in the process was much than other processes(such as internal reflow).Meanwhile,the mass transfer efficiency of the biofilm could be more effectively improved.At low temperatures,the NRR could be also increased about 35%when the vibration stated.(4)During the initial start-up process,high-intensity vibration would cause some of the sludge to fall off from the biofilm.Applying a reasonable vibration to the biofilm could shorten the start-up time of the reactor.The reactor R6 was stated up under a lower intensity vibration,the biofilm was covered with granular sludge after 118 days operation.Continuous vibration to the reactor could be furtherly enlarge the granular structure.Finally,some of the granules would be fall off in the form of granular sludge.The average diameter of the granules is 2.38 mm,the sludge yield rate is 3.62×10-2 g-VSS/g-N,and the SAA is 0.621 g-N/(g-VSS·d).These granules could be effectively used to start-up other reactors.(5)The process of partial nitrification,anammox and sulfur autotrophic denitrification which coupling in a single reactor was successfully operated.The newly system could removal ammonia effectively.With a single ammonia influent(600 mg/L),the total nitrogen removal rate can be maintained above 98%after the start-up period.Vibration improved the mass transfer efficiency in the biofilm and promoted the species Candidatus Kueneniastuttgartiensis and Thiobacillus denitrificans could be symbiotic on the surface of the sulphur-based stone.Meanwhile,a unique reddish film was formed on the surface of the film.The EPS of this film could reach 328.4 mg/g-VSS(protein for 297.1 mg/g-VSS and polysaccharide for 31.3 mg/g-VSS),which greatly increases the number of microorganisms that could be carried on the surface of sulfur stone.Compared to the conventional system which connected the three in series,the integrated reactor promotes sulfur autotrophic denitrification only finished a short-cut denitrification process.Therefore,the sulfate production of the system was effectively reduced and only reached 41%of the theoretical stoichiometry.The experimental results shown that elemental sulfur does not inhibit the growth of anammox bacteria.In addition,based on the theoretical model of short-cut denitrification,the theoretical sulfate production of the reactor was 45%of the conventional theoretical value,and the sulfur to nitrogen ratio(S/N)ratio is about 3.393.