Study On Optimization Of Anammox Process Conditions And Nitrogen Removal Characteristics

The present study is aimed to establish a high-efficiency anaerobic ammonia oxidation（anammox）process through enrichment of ANAMMOX bacteria and optimization of process conditions.The results of this research project are expected to be applied in the nitrogen removal from high-strength ammonium wastewater.Anammox bacteria were enriched in anaerobic sequencing biological reactors（ASBR）which were inoculated with activated sludge and fed with artificial wastewater containing 90 mg/L NH₄⁺-N and 120 mg/L.NO₂^--N.After 193 days’ of operation anammox bacteria were successfully enriched as indicated by a short feeding interval of 2 days and high removal rates of NH₄⁺-N and NO₂^--N of 99.91%and 88.07%,respectively.Steady-state operation was achieved at the end the enrichment period with a total nitrogen volumetric load of 140 mg/（L·d）.The effects of substrate,dissolved oxygen and NaCl on the anammox activity were investigated in steady-state anammox reactors.The results showed that anammox reaction was significantly influenced by both the type and the concentration of anammox substrate.Anammox activity was not inhibited by ammonium in the range of 90～540 mg/L.In stead,anaerobic oxidation of ammonium was significantly stimulated by higher ammonium concentration.However,an inhibitory effect on anaerobic oxidation of ammonium occurred when nitrite concentration was raised up to higher than 600 mg/L.And anaerobic reduction of nitrite could also be inhibited when nitrite concentration was further raised to 720 mg/L.Lower removal rates of ammonium and nitrite had been observed when TN was introduced at a concentration lower than 280 mg/L or at a concentration higher than 1050 mg/L.Maximum nitrogen removal efficiency[removal rates of ammonium and nitrite were 3.69 mg/（L·h）and 4.14 mg/（L·h）,respectively]could be achieved in the reactors fed with artificial wastewater at a TN concentration between 280 mg/L and 840 mg/L,an ideal feeding condition for anammox reactors.DO levels in the influent had significant effects on the anammox activity.The highest anammox activity was observed in the reactors where the DO concentration was≤3.0 mg/L and the average removal rates of ammonium and nitrite reached were 3.67 and 4.25 mg/（L·h）,respectively.DO concentration higher than 3.5 mg/L resulted in significant decreases in nitrogen removal rates due to a reversible inhibition effect.Therefore,the DO concentration in the anammox reactors should not exceed 3.0 mg/L.Influent NaCl concentration also showed a significant effect on anammox activity.In a single operation period designed for salinity shocking test,the highest anammox activity could be achieved in reactors where the influent NaCl concentration was between 5 and 15 g/L,and the average removal rates of ammonia and nitrite reached 3.71 and 4.34 mg/（L·h）,respectively.Whereas a reversible inhibition effect occurred once the NaCl concentration rose to the range of 20～50 g/L.However,in a consecutive operational period designed for multiple salinity shocking test,anammox bacteria thrived only at a lower salinity of 5 g/L NaCl while an irreversible inhibition occurred in the presence of NaCl in the range of 10～50 g/L.Therefore in order to maintain optimal anammox activity,the NaCl concentration in anammox reactor should not exceed 5 g/L.In order to minimize sludge loss and further improve TN volumetric load in the anammox reactors,the ASBR reactor filled with non-woven fabric was chosen and operated in the continuous mode.After 58 days of operation,the volumetric load of total nitrogen gradually increased to 0.465 kg/（m³.d）,and the system had maintained a highly efficient and steady-state all the time.In the newly established anammox denitrification system the average nitrogen removal rates reached 99.97%,91.13%and 83.78%for ammonia,nitrite and total nitrogen,respectively.