## 3 Results and Discussion
### Cultivation and Performance of ANAMMOX for Treating Partial Nitrification Effluents
However, according to the results after 5 days' reaction, high concentrations of COD could further inhibit ANAMMOX activity with the extension of exposure reaction time. When the non-biodegradable COD concentration was more than 200 mg/L, the NO2 -N removal rate decreased rapidly from 71.2% to 49.8%. It was found that non-biodegradable organic matter in the livestock wastewater had potential inhibition ability against ANAMMOX activity under high concentrations and long-term exposure conditions. The reason might be that the non-biodegradable organic matter, including cellulose and hemicelluloses in livestock wastewater, could disrupt the structure of the biofacies and lead to changes in extracellular polymeric substances (EPS) contents and granulation of ANAMMOX biomass [27]. The long-term performance of the treatment efficiency of the livestock wastewater after partial nitrification by using ANAMMOX technology were investigated at the different non-biodegradable COD concentration gradients. The effluents of IASBR with NH4 Cl adjustment (containing 1240 \(\pm\) 45 mg/L of COD, 26 \(\pm\) 3 mg/L of BOD5, 420 \(\pm\) 7 mg/L of NH4 -N and 552 \(\pm\) 28 mg/L of NO2 -N) were fed into the UASB after diluting 10 times from Day 1 to Day 17 (118 \(\pm\) 13 mg COD/L), diluting 7.5-times from Day 18 to Day 35 (168 \(\pm\) 9 mg COD/L) and diluting 5 times from Day 36 to Day 50 (242 \(\pm\) 17 mg COD/L), respectively (Figure 9). Figure 8: Influence of non-biodegradable organic matter on ANAMMOX activity (\(\blacklozenge\): nitrite removal rate after 1 day; \(\blacksquare\): nitrite removal rate after 5 days). In the condition of 10-times dilution, 80.1% of NO\({}_{2}\)\({}^{-}\)-N was removed immediately after 3 days. It shows that the treatment efficiency of cultured ANAMMOX bacteria was stable under the low concentration of non-biodegradable organic matter condition. In the condition of 7.5-times dilution, with the increases in influent COD and NO\({}_{2}\)\({}^{-}\)-N concentrations, the performance of effluent NO\({}_{2}\)\({}^{-}\)-N in UASB became worse from Day 18. However, the resumption of ANAMMOX activity was confirmed after 4 days and an average NO\({}_{2}\)\({}^{-}\)-N removal rate of 87.4% was achieved in this period. At this COD loading rate, non-biodegradable organic matter did not severely affect the activity of ANAMMOX. In the third stage, effluent NO\({}_{2}\)\({}^{-}\)-N and NH\({}_{4}\)\({}^{+}\)-N gradually increased and the NO\({}_{2}\)\({}^{-}\)-N removal rate decreased to 60.5%. Potential inhibition of ANAMMOX biomass appeared with the increase in COD concentrations. One of the reasons was that ANAMMOX activity became worse under high concentrations of non-biodegradable organic matter according to Figure 8; another reason might be that heterotrophic denitrifiers existed in the effluents of IASBR which could compete with ANAMMOX bacteria at a high loading rate [28]. The long-term experimental results demonstrate that when the concentration of non-biodegradable organic matter was lower than 168 \(\pm\) 9 mg COD/L, the application of ANAMMOX technology on nitrogen removal from the effluents of partial nitrification treating livestock wastewater was feasible.