Key Technologies And Mechanisms Of Autotrophic Nitrogen Removal From Wastewater

The massive discharge of nitrogen containing wastewater has caused a series of problems to environment and human health. Nitrogen pollution has become an important environment issue around the world. The partial nitrification (PN) process and anaerobic ammonium oxidation (Anammox) process are two autotrophic nitrogen removal processes. Due to their cost effectiveness and high efficiency, they show a wide prospect to fight the nitrogenous pollution.However, the acidification of PN process needs pH control by the addition of external alkalinity, which will increase the cost and difficulty of operation. Nitrite is a toxicant, while PN process needs its accumulation. The conversion rate of PN process is slow relative to Anammox process and the regulation of NH4+-N/NO2-N ratio in PN process is difficult to meet the reqirement of Anammox process. In order to break the bottlenecks, an acid-tolerant partial nitrification (APN) process and an autotrophic nitrogen removal process in a granular sludge bed reactor (GSB-ANR) were developed and their mechanisms were investigated. The major results are as follows:1. The realization technology of PN process and the control technology of NH4+-N/NO2--N ratio in PN process were studied.①The "co-culture &screening" technology was developed to realize PN process. The "co-culture &screening" technology included two steps, firstly the nitrification process was started-up by enriching aerobic ammonia-oxidizing microbes and nitrite-oxidizing microbes, and then it was transited into the PN process by washing out nitrite-oxidizing microbes. The PN process could be successfully started-up by using this technology at a fixed pH of7.5. Its nitrogen loading rate and ammonium conversion rate were as high as9.42kg-N m-3d-1and4.74kg-N m-3d-1, respectively. And to our knowledge, it was up to the top level reported in literatures.②The"DO-HRT"(dissolved oxygen concentration-hydraulic retention time) control technology was developed to regulate NH4+/-N/NO2--N ratio of PN process. When DO and HRT satisfied the relationship0.66-0.5-DO<HRT<0.97-0.53-DO(0.5mg L-1<DO<0.7mg L-1,0.45h<HRT<0.53h), NH4+/NO2-ratio was in the range of1:1.04to1:1.47and the performance of PN process was excellent. 2. The realization technology and acid-tolerant mechanisms of acid-tolerant nitrification process, and the realization barrier of acid-tolerant PN process were studied.①An acid-tolerant nitrification process was started-up using the "co-culture&screening" technology at a fixed pH of6.0. Its nitrogen loading rate and ammonium conversion rate were as high as1.26kg-N m-3d-1and1.13kg-N m-3d-1, respectively. Compared with normal PN process (pH=7.5), the acid-tolerant PN process could decrease the consumption of alkalinity by1.7g-CaCO3g-1NH4+-N.②It was discovered that the enrichment of acid-tolerant microorganisms, Nitrosospira and ammonia-oxidizing archaea (AOA) was the acid-tolerant mechanism of acid-tolerant nitrification process. The results of DGGE (denaturing gradient gel electrophoresis) and FISH (fluorescent in situ hybridization) showed that acid-tolerant Nitrosospira and AOA were enriched in the acid-tolerant nitrification sludge (pH=6.0), but they were not distected in the normal nitrification sludge (pH=7.5). And in acid-tolerant nitrification sludge the abudance of AOA and ammonia-oxidizing bacteria (AOB) was similar.③It was discovered that the difficult regulation of NH4+-N/NO2--N ratio was the main barriers for the realization of acid-tolerant PN process. The NO2-accumulation efficiency of acid-tolerant PN sludge was low and the regulation of NH4+-N/NO2--N ratio was difficult due to the low sludge concentration caused by the poor settlement and the small activity advantage of aerobic ammonia-oxidizing microbes over nitrite-oxidizing microbes caused by low ammonia-oxidizing microbes concentration.3. An autotrophic nitrogen removal process in a granular sludge bed reactor (GSB-ANR) was developed and its working mechanisms were inverstigated.①The GSB-ANR process was successful developed and its performance was studied. The aerobic ammonium oxidation and Anammox were carried out in single air-lift reactor. Since the nitrite was consumed once it was produced in the GSB-ANR process, the acidification and the nitrite toxicity were satisfactorily avoided and the NH4+-N/NO2--N ratio was easily regulated. Its volumetric nitrogen loading rate and total nitrogen removal rate reached5.44kg-N m-3day-1and2.57kg-N m-3day-1, respectively. And to our knowledge, it was up to the top level reported in literatures. ②The working mechanisms of GSB-ANR prcess were investigated. It was discovered that the high level of sludge granulation (98.54%), the good settling properties and the excellent autonomous nitrogen removal capability of granule sludge together contributed to the high-rate performance of GSB-ANR process. The limited oxygen penetration depths resulted in the separation of aerobic and anaerobic zone in granuler sludge. AOB would enrich in the aerobic zone (exterior layer), and Anammox bacteria would enrich in the anaerobic zone (inside layer). The separation of aerobic and anaerobic zone laid a solid foundation for the capability of simultaneous nitrogen removal in GSB-ANR process.