Font Size: a A A

Enrichment Of Anaerobic Ammonium Oxidation Bacteria And Coupled With Denitrification Bacteria For Nitrogen Removal

Posted on:2017-03-27Degree:MasterType:Thesis
Country:ChinaCandidate:X P LiuFull Text:PDF
GTID:2271330503459946Subject:Environmental Science and Engineering
Abstract/Summary:PDF Full Text Request
For low C/N ratio sewage, aeration and external carbon sources are required in the traditional biological nitrification and denitrification process, which results in high energy consumption and high cost. The anaerobic ammonia oxidation(anammox) process can oxidize ammoia to nitrogen gas with nitrite as electron acceptor, which eliminates the requirements of external carbon sources. Thus, the anammox process is suitable for the treatment of low C/N ratio sewage. Generally, ammonium is the main nitrogen pollutant in the wastewater. In recent years, nitrite used in anaerobic ammonia oxidation is obtained through shortcut nitrification. However, it is difficult to control to realize the shortcut nitrification. Nitrate is the final product when shortcut nitrification is converted to complete nitrification. Moreover, anammox leaves about 10% of nitrogen as nitrate in the effluent. Thus, total nitrogen concentration could not meet the discharge standard.As nitrite is an intermediate of denitrification process, nitrite generated from nitrate could be used as electron acceptor in the anammox process. In this study, nitrite accumulation during denitrification process in low C/N ratio sewage was investigated by using sodium acetate as carbon source. The nitrifying sludge and denitrifying sludge were used as inocula to enrich anammox bacteria. And the effect of temperature on the anammox bacteria was studied. Finally, sodium acetate was added to the anammox system to enrich the denitrifying bacteria. The nitrogen removal performances by anammox bacteria and denitrifying bacteria were investigated in the sewage with different C/N ratios. The major conclusions were as follows:(1) The nitrite accumulation was observed in low C/N ratio sewage. The existence of nitrate could inhibit the reduction of nitrite to nitrogen gas. The maximum nitrite accumulation ratio(NAR) was affected by the temperature and C/N ratio of the influent. At the same temperature, the higher maximum NAR could be obtained when C/N ratio of the influent was increased. At the same C/N ratio, higher maximum NAR could be observed at higher temperature.(2) Aanaerobic ammonia oxidation reaction could be started up successfully by using nitrifying sludge and denitrifying sludge as inocula. The inoculation sludge in reactor R1 and R3 contained large amount of nitrifying bacteria. During the process of enrichment of anammox bacteria, the bacteria autolysis was not obviously observed in reactor R1 and R3. However, the inoculation sludge in reactor R2 contained large amount of denitrifying bacteria and the bacteria autolysis was observed obviously during the initial phase of cultivation. Then the lag phase, activity elevation stage and stationary stage appeared in three reactors. During the stationary stage, the ratios of NO2--N removal, NH4+-N removal and NO3--N production in reactor R1, R2 and R3 were 1.30:1:0. 23, 1.35:1:0. 10 and 1.23:1:0. 18, respectively.(3) The effect of temperature on the anammox activity was significant. When the temperature decreased from 35℃to 25℃, the maximum nitrite removal rate declined from 2.49mg/(g VSS·h) to 0.69 mg/(g VSS·h). At 20℃ and 15℃, the anammox activity was almost completely inhibited. Nitrification occurred in the system.(4) The existence of nitrite could inhibit the reduction of nitrite to nitrogen gas. Only after the nitrate was completely removed, nitrite could be reduced to N2 by the denitrifying bacteria in the anammox system. When the ratio of TOC/TN in the influent was 0.25, due to the lack of carbon source, NO2--N generated by the denitrifying bacteria was mainly removed by the anammox bacteria. Thus low concentration of NH4+-N and TN in the effluent were obtained. When the TOC/TN ratios were 1.0 and 1.5, nitrite was mainly removed by denitrifying bacteria after nitrate was completely removed. The anammox bacteria could not oxidize ammoia to nitrogen gas due to a deficiency in nitrite, which resulted in the increase of NH4+-N and TN concentration in the effluent.
Keywords/Search Tags:anammox, denitrification, nitrite, enrichment, low C/N ratio
PDF Full Text Request
Related items