## 3 Results and Discussion
### Cultivation and Performance of ANAMMOX for Treating Partial Nitrification Effluents  
ANAMMOX was considered as a potentially useful technology for treating NO2\({}^{-}\)-N containing wastewater without an organic carbon source. In order to investigate the performance of NO2\({}^{-}\)-N reduction from the effluents of the partial nitrification reactor and the effects of non-biodegradable organic matter on the activity of ANAMMOX biomass, a UASB reactor experiment was conducted. Before introduction of IASBR effluents into the UASB, synthetic wastewater was fed to cultivate and enrich ANAMMOX bacteria. When the effluent NO2\({}^{-}\)-N concentration in the UASB was below 15 mg/L within 15 days, the concentration of influent synthetic wastewater increased as follows: 30 mg/L NH4\({}^{+}\)-N and 40 mg/L NO2\({}^{-}\)-N from Day 1 to Day 100 (Stage 1); 60 mg/L NH4\({}^{+}\)-N and 80 mg/L NO2\({}^{-}\)-N from Day 101 to Day 223 (Stage 2); and 90 mg/L NH4\({}^{+}\)-N and 120 mg/L NO2\({}^{-}\)-N from Day 223 to Day 289 (Stage 3). In the conventional ANAMMOX process, the theoretical ratio of consumed NO2\({}^{-}\)-N to consumed NH4\({}^{+}\)-N is 1.32, and the theoretical ratio of consumed NO3\({}^{-}\)-N to consumed NH4\({}^{+}\)-N is \(-\)0.26 [10]. In the cultivation period of ANAMMOX biomass, these ratios were  
Figure 6: Microbial population analysis of nitrification genus in two SBRs. calculated compared with the theoretical values in order to determine the ANAMMOX activity (Figure 7). In Stage 1, almost no NO2\({}^{-}\)-N was removed, and NH4\({}^{+}\)-N was partly consumed by microbial anabolism during the start-up periods. After operation for 38 days, the phenomenon of NO2\({}^{-}\)-N removal gradually appeared. However, it took 40-50 days for the profile of NO2\({}^{-}\)-N to reach a pseudo-steady state. In this period, 66.2% of NO2\({}^{-}\)-N removal was observed, and the ratio of consumed NO2\({}^{-}\)-N to consumed NH4\({}^{+}\)-N reached 0.95. In Stage 2, with the increase in influent synthetic wastewater concentrations, accumulated NO2\({}^{-}\)-N appeared again in the UASB. From Day 131, the concentration of NO2\({}^{-}\)-N began to decrease, and satisfactory ANAMMOX performance with an average ratio (consumed NO2\({}^{-}\)-N to consumed NH4\({}^{+}\)-N) of 1.24 was observed from Day 180 to Day 223. In Stage 3, no evident changes of ANAMMOX activity were obtained with higher nitrogen loading rates. This shows that a stable ANAMMOX reactor was established with an average NO2\({}^{-}\)-N removal rate of 81.5%. In order to investigate the effects of non-biodegradable organic matter on the activity of ANAMMOX biomass in livestock wastewater, the non-biodegradable organic matter was centrifuged from the effluent of IASBR after two days' continuous aeration in a flask with partial nitrification sludge. Influent synthetic wastewater in Stage 3 was fed into 100 mL flasks with different dosages of non-biodegradable organic matter (the initial COD concentrations were 50, 100, 150, 200, 250, 300, 350 and 400 mg/L in the flasks). Then, ANAMMOX biomass taken from the UASB was added into the flasks, and the biomass concentrations in the flasks were adjusted to close to those inside the UASB. Then, the flasks were continuously stirred with magnetic stirrers after stripping DO out for 3 min by using argon gas. Lastly, the effluents were withdrawn and influent synthetic wastewater with non-biodegradable COD was fed in again at a HRT of 8 h. After 1 day and 5 days, the effluent NH4\({}^{+}\)-N, NO2\({}^{-}\)-N and NO3\({}^{-}\)-N concentrations were measured to evaluate the effects of non-biodegradable organic matter on ANAMMOX (Figure 8). The results show that short-term exposure to non-biodegradable organic matter did not affect the activity of ANAMMOX biomass evidently. After 1 day's reaction, the NO2 -N removal rates were all kept at above 76% under the different non-biodegradable COD concentrations.