Basic Research Of Mixotrophic Anammox

Anaerobic ammonia oxidation (Anammox) is a new pathway for nitrogen removal. It has many advantages when compared with traditional nitrification-denitrification process. Anammox is considered as the most cost-effective nitrogen removal process. Domestic and foreign scholars have acquired a lot of important results. Anammox bacteria was considered as a strictly autotrophic bacterium with doubling time of 10.4d. The start-up time of Anammox reactor is 110d which limits the application of this process. In this study, the metabolism of anammox bacteria with organic carbon source was studied through continuous cultivation experiment and batch tests based on the previous results. The mixotrophic anammox bacterias which can oxidize acetate was successfully cultivated. Its activity as well as the effected factors, such as pH and concentration of organic matters were analyzed. The main results are as follows:(1) During the cultivation of mixotrophic anammox bacteria, the concentration of NH4+-N, NO2--N, NO3--N and sodium acetate were 70 mg/L,70 mg/L,20 mg/L and 95 mg/L, respectively. The influent pH value and HRT were kept at 8.0 and 1d, respectively. Ammonium, nitrite, nitrate and acetate were removed stably after 145 days.(2) During the process of cultivation, the effluent pH value was 8.7. Acetate has no effect on the removal of ammonium and nitrite but promoted the anammox reaction, the removal efficiencies stayed at 98.48% and 100%. The removal efficiency of acetate kept around 70%-80% and the nitrate changed into net consumption from net production, which showed the removal of organic matter and nitrate are synchronous.(3) The color of biofilm changed gradually during the cultivation. The color was red in the initial stage. With the heterotrophic activity of anammox bacteria incresed, biofilm color changed into yellow.(4) 0.1g/L penicillin has little effect on the activity of anammox bacteria under inorganic influent condition. After 46h cultivation at O.lg/L penicillin addition, the concentration of ammonium and nitrite were 5.54mgN/L and 0.16mgN/L with removal efficiencies of 92.61% and 99.75%, respectively. As for test without penicillin addition, the concentration of ammonium and nitrite were 1.28mgN/L and 2.79mgN/L with removal efficiencies of 98.29% and 95.61%, respectively.(5) Under organic influent condition,0.1g/L penicillin addition has little effect on removal efficiencies of nitrite and ammonia but led to removal efficiencies of nitrate and COD synchronously increase. The removal efficiencies of nitrate with penicillin addition and without penicillin addition were 1.57 mg/(L·h) and 1.38 mg/(L·h), while those of organic matter were 29.45 mg/(L·h) and 23.92 mg/(L·h), respectively. Anammox bacteria have metabolic diversity. It has the abilities of autotrophic metabolism and heterotrophic denitrification metabolism. Under organic influent condition, anammox bacteria can change its metabolism pathway and oxidize acetate through denitrification.(6) pH value has obvious effect on anammox. The anammox was inhibited at influent pH of 6 and 9, the suitable pH range was 7-8. When influent pH were controlled at 6,7,8 and 9, effluent pH of 8.43,8.70,8.59,9.27 were obtained respectively.(7) When the concentrations of sodium acetate were increased(0.128g/L, 0.160g/L,0.225g/L,0.290g/L), the removal efficiencies of ammonia and nitrite decreased. The decrease of nitrite removal efficiency is less obvious than that of ammonium because part of the nitrite were removed through denitrification. The average removal efficiencies of organic matter showed little difference at different influent sodium acetate concentrations. It was supposed that, organic matter while mianly removed by anammox bacteria at low concentration of organic matter while mainly by denitrifying bacteria at high concentration of organic matter. With the increase of organic matter concentration, the effluent nitrate concentration gradually decreased because of the decrease of nitrate production resulting from anammox and the nitrate consumption through denitrification.