| The partial nitrification (PN) and anaerobic ammonium oxidation (ANAMMOX) processes are highly efficient, cost-effective and environmentally friendly biotechnology for nitrogen removal, which have attracted much attention to the environmentalists ever since their birth. Presently, the nitrogen and phosphorus have become the chief pollutants in the water body all over China, implying that the conventional biological nitrogen removal processes can not satisfy the needs of the society. Therefore, investigation of high-rate PN and ANAMMOX processes as an alternative is of great practical significance.However, since both functional bacteria, i.e. ammonia oxidation bacteria (AOB) and anaerobic ammonium oxidation bacteria (AAOB), have the disadvantages such as slow growth and sensitivity to the environmental conditions, it is rather difficult for the processes to start-up or operate stably. Hence, the application of PN and ANAMMOX processes has been retarded. In order to break the bottleneck, a systematical and profound study is carried out with respect mainly to bacterial cultivation, operation performance and process control. Major results are as follows:1) The high activity nitrifiers (HANs) were enriched and their metabolic characteristics were studied.①It was discovered that HANs could be successfully enriched by operating the PN system at high substrate concentrations. The free ammonia (FA) concentration was kept at 10-20 mg N·L-1, which was 10 times higher than the control one. The volumetric removal rate (VRR) and volumetric nitrite production rate (NPR) were 2.22±0.33 kg N·m-3·d-1 and 2.12±0.34 kg N·m-3·d-1, which were 3.2 and 3.6 times higher than the control ones, respectively,after 27 days’ running.②It was discovered that HANs had higher activity as well as higher tolerance to FA. The specific sludge activity (SSA) and half FA inhibition constant for HANs in batch cultivation were 2.87 g N·g-1VSS·d-1 and 613.9 mg NH3-N·L-1, which were 4.6 and 30.4 times higher than the control ones, respectively.③It was discovered that HANs had a lower net sludge production. The cell yield in continuous cultivation and decay rate in batch cultivation were 0.15 g VSS·g-1NH4+-N and 0.09 d-1, which were 45% and 1.2 times of the normal level, respectively. This low net sludge production was due to the fact that only 9% of the energy was allotted for cell synthesis by the HANs, which was 64% of the normal level.2) The performance of high-rate PN process was studied in an air-lift circulation reactor.①It was found that the PN process in air-lift circulation reactor was of high removal capacity. The maximal nitrogen loading rate (NLR), VRR and NPR were 16.7±1.5 kg N·m-3·d-1,13.0±1.3 kg N·m-3·d-1 and 12.3±1.4 kg N·m-3·d-1, respectively, with average nitrite accumulation of 94.6±3.9%.②It was found that the PN process in air-lift circulation reactor was of high stability. Under the conditions that influent ammonium concentration was 358.5-942.3 mg N·L-1, HRT was 0.86-2.00 h and pH was 8.00-8.43, the relative standard deviation of ammonium removal efficiency, effluent substrate concentration, and nitrite accumulation was 5.1%-19.4%,4.3%-26.5% and 4.4%-5.3%, respectively, indicating that the process was able to resist the fluctuation of influent substrate concentration, flow rate and pH.③It was found that the efficiency and stability of the PN process in air-lift circulation reactor could be attributed to the formation of nitrifying granules. The granules had higher settling velocity which led to a high sludge concentration of 7.9 g VSS·L-1, and optimized niche which led to a high SSA of 1.83 g N·g-1VSS·d-1.3) The process characteristics and control strategies of high-rate PN process were studied.①It was discovered that variation of alkalinity significantly influenced the PN performance by means of changing pH and FA concentration. When the alkalinity decreased from 2011.5 mg CaCO3·L-1 to 1711.0 mg CaCO3·L-1, the pH and FA concentration also decreased from 8.56 to 6.70 and from 4.8 mg NH3-N·L-1 to 0.3 mg NH3-N·L-1, respectively. As a result, the VRR firstly increased from 0.83 kg N·m-3·d-1 to 1.64 kg N·m-3·d-1, but then decreased to 0.53 kg N·m-3·d-1.②It was discovered that the control of alkalinity in PN system could be divided into three parts, i.e.a lowest required alkalinity content of 1660.0 mg CaCO3·L-1, an effective range of 1711.0-1840.0 mg CaCO3·L-1 and an optimal range of 1840.0-1853.0 mg CaCO3·L-1.③It was discovered that the variation of temperature also significantly influenced the PN performance by means of changing enzyme activity. When temperature was 16.8-22.4℃, the VRR and NPR were 0.54-1.70 kg N·m-3·d-1 and 0.53-1.65 kg N·m-3·d-1, respectively. There were two different activation energies corresponding to 65.6 kJ·mol-1 (at high temperature) and 584.9 kJ·mol-1 (at low temperature), with a boundary temperature at 17.4℃.④It was discovered that the control of temperature in PN system could be divided into two parts:if the temperature was lower than 17.4℃for a short-term period, no control was needed, while for a long-term period, the temperature was better to warm up to 17.4℃.4) The high activity ANAMMOX bacteria (HAAB) were enriched and their metabolic characteristics were studied.①It was discovered that HAAB could be successfully enriched in an up-flow biofilm filter (UBF). Under the conditions that HRT was 1.54 h, influent ammonium and nitrite were 947.8±17.4 mg N·L-1 and 1246.9±20.1 mg N·L-1, the volumetric ammonium removal rate (VARR), volumetric nitrite removal rate (VNRR) and volumetric removal rate (VRR) were 14.4±0.2 kg N·m-3·d-1,19.4±0.3 kg N·m-3·d-1 and 33.9±0.4 kg N·m-3·d-1. respectively, after 435 days’ cultivation.②It was discovered that HAAB had very good performances. The zone settling velocity (ZSV), SSA, doubling time and cell yield were 90-150 m·h-1,2.19 g N·g-1VSS·d-1,7.4 d and 0.48 gVSSg-1·NH4+-N respectively, which were superior compared to the reported values.③It was discovered that the cultivation of HAAB could be divided into three phases. At the initial phase, it was better to starve the culture to accelerate the decay of non-tagart bacteria. At the medial phase, it was better to increase the substrate concentration to enhance the growth of HAAB. At the final phase, it was better to recirculate the effluent to relieve the toxicity caused by substrates.5) The performance of high-rate ANAMMOX process in EGSB reactor was studied.①It was found that the ANAMMOX process in EGSB reactor was of high removal capacity. The HRT could be shortened to 0.237-0.267 h, resulting in a NLR up to 76.4 kg N·m-3·d-1 as well as a VRR up to 61.4 kg N·m-3·d-1, both of which were higher than the reported values.②It was found that the ANAMMOX process in EGSB reactor was of high stability. Under the conditions that influent nitrogen concentration was 3429.5-928.6 mg N·L-1, hydraulic loading rate was 90.0-101.5 L·L-1·d-1 and pH was 7.00-8.30, the relative standard deviation of nitrogen removal efficiency and effluent substrate concentration was 3.6%-6.9% and 14.4%-22.6%, respectively, indicating that the process was able to resist the fluctuation of influent substrate concentration, flow rate and pH.③It was found that the efficiency and stability of the ANAMMOX process in EGSB reactor was attributed to the retention of dense ANAMMOX granules. The granules led to a high sludge concentration of 24-28 g·L-1 inside the reactor, and exhibited a high SSA of 3.62 g N·g-1VSS·d-1.6) The process characteristics and control strategies of high-rate ANAMMOX process were studied.①It was discovered that the real substrates of ANAMMOX reaction were ammonium and nitrite salts. It was supported by the experimental facts:pH had little influence on the ammonium half saturation constant (4.16±0.49 mg N·L-1) at pH of 6.98-8.19, as well as on the nitrite half saturation constant (4.07±1.07 mg N·L-1)at pH of 6.95-8.30.②It was discovered that the low influent pH significantly influenced the ANAMMOX process performance by means of creating both low pH and free nitrite inhibition. This inhibition could be relieved with a recirculation rate of 4:1 when NLR was above 14.8 kg N·m-3·d-1. Three strategies were available in the case of severe inhibition, i.e. stopping operation, washing residual substrate with tap water or regulating pH by adding extra alkalinity.③It was discovered that high NLR could trigger the flotation of ANAMMOX granules. It resulted in a massive loss of sludge in the reactor, and in turn a decrease of system performance. The granule flotation was attributed to the formation of caves at the core of the granules, which held gas inside and caused the granular density less than that of water. "Collecting-breaking-returning" was an effective control strategy to solve granule floatation and recover system performance. |
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