| Generally,ANAMMOX means that bacteria use ammonia and nitrite as electron donors and electron acceptors in an anaerobic environment,and directly convert the two into N2 and a small amount of NO3-.The concentration of NO2-contained in urban sewage is very small,and it is impossible to directly realize the anaerobic ammonia oxidation without NO2-.Municipal sewage（including industrial wastewater and domestic sewage）contains a certain amount of sulfate.If the sulfate can be used directly to remove ammonium nitrogen in Anammox,it will solve the problem of no NO2-.Sulfate-type anammox is reported difficult to be established.In the process of replacing of nitrite with SO42-,some studies have found that the conversion of NH4+and SO42-was not completely synchronized(that is,SO42-was not used as an electron acceptor to oxidize NH4+).In response to solve the problems above,research was launched.Firstly,two anaerobic ammonia oxidation systems was established,and then the supply of NO2-was directly stopped in influent,and SO42-was added instead.Changes in the nitrogen removal of the two reactors were compared and studied.The pathway of the nitrogen removal were explored from three aspects:the operation of the reactor,the change of the microbial flora structure and the qualitative material balance via batch experiments.The main results of the study are as follows:（1）The anammox UASB R1 was established within 40 days.The total nitrogen removal load in of the R1 was as high as 0.46 kg/（m3·d）.The sludge was dominated by Candidatus Kuenenia and Candidatus Brocadia,and the abundance of Anammox flora reached 24.41%.The results show that in the maximum influent concentration of the reactor R1 during the start-up phase,the maxium limit of ammonia nitrogen concentration was 258.29 mg/L,and that of nitrite nitrogen 297.23 mg/L.The reactor R1had a high resistance to load shock,the maximum recovery rate Rmax was 0.02 kg/（m3·d）,the recovery delay timeλwas 30.56 d,the maximum total nitrogen removal rate of the reactor reached 0.512 kg/（m3·d）.（2）The anammox sludge was used as the seeding sludge,and SO42-was used directly in the influent to replace NO2-as the electron acceptor to acclimate sludge and remove NH4+.After the reactor R2 had been running for 180 days,the change of ammonia nitrogen removal in the system was similar to that of Anammox bacteria.The overall ammonia nitrogen removal of the R2 was more than 40 mg/L,but sulfate was not removed.Therefore,the study believes that SO42-cannot be used as electron acceptor to oxidize NH4+.It is speculated that there may be other electron acceptors to remove NH4+.Adding 5 mmol/L of hydroxylamine to the reactor promoted the removal of ammonia nitrogen,indicating that the removal of ammonia nitrogen in the system was related to the activity of Anammox bacteria.The abundance of Candidatus Brocadia and Candidatus Jettenia detected in the reactor increased from 2.40%to 15.63%;Nitrosomonas increased from 0.03%to 6.32%;Nitrobacter abundance increased from0.12%to 1.54%.AOB bacteria activity was greater than NOB bacteria.The change in the number of bacteria indicates that the removal of ammonia nitrogen in the reactor was related to the activity of AOB,NOB and Anammox.In batch experiments,after a trace amount of oxygen was injected into the reaction flask,the removal of ammonia nitrogen in the system was significantly related to the nitrification of AOB and NOB bacteria and the activity of Anammox bacteria.It is speculated that the removal of ammonia nitrogen in the reactor was related to the amount of internal oxygen. |
