Study On Nitrogen Removal Performances And Kinetics Of Hybrid Anammox Reactor

The anaerobic ammonium oxidation (ANAMMOX) process, a novel biological nitrogen removal technology, can save at least 50% oxygen cost without additional organic carbon source and neutralizer compared to traditional nitrification-denitrification process, thus is significant to energy conservation and environmental protection. However, the extreme low growth rate of ANAMMOX bacteria was still the barrier of practical application of this process.From the point of view of microbial immobilization technical improvement, a hybrid reactor was proposed in this study which combined fixed bed for better microbial retention and fiuidized bed for better substrates transfer. And its nitrogen removal potential, sludge characteristic and microbial composition were investigated experimentally.On this basis, the ANAMMOX reaction rate equation, the mass tranfer dynamic of granular sludge and reactor were analyzed accordinglly. The main contents include:(1) A hybrid ANAMMOX reactor with recirculation was successfully set up. After 270 days operation, a higher NLR of 15.2 kg(N)·m-3·d-1 was got with relative NRR of 9.9 kg(N)·m-3·d-1. The total nitrogen removal efficiency and nitrite removal efficiency was kept above 82% and 95%.The dominant granular sludge size decreased from a range of 2 mm-5 mm to 1 mm～2 mm due to hydraulic shear enhanced by recirculation. The SAA was calculated to be 0.28 kg(N)·kg(MLSS)-1·d-1 and the average reactor activity was calculated to be 1.78 kg(N)·kg(MLSS)-1·d-1, suggesting better comprehensive nitrogen removal performances of hybrid reactor. The effluent SS concentration was mostly under 15 mg·L-without reactor clogging, suggeting better microbial retention and gas seperation condtion. By SEM observation and FISH analysis, a granular sludge structure that ANAMMOX was coated with AOB was confirmed and the ANAMMOX percentage was about 74%.(2) A hybrid ANAMMOX reactor with slow speed mechanical stirring was successfully set up.Only in 38 days, the NLR reached to 2.0 kg(N)·m-3·d-1 and then in about half a year, reached to 8.9 kg(N)·m-3·d-1, with the total nitrogen removal efficiency and nitrite removal efficiency kept above 78% and 92%. The SAA was calculated to be 0.32 kg(N)·kg(MLSS)-1·d-1, and the average reactor activity was calculated to be 0.70 kg(N)·kg(MLSS)-1·d-1, suggesting better comprehensive nitrogen removal performances of hybrid reactor. The effluent SS concentration was mostly under 10 mg·L-1 without granular sludge floatating, suggesting better microbial retention and gas seperation condtion. The SEM observation and FISH analysis revealed a specially compact structure of granular sluge that ANAMMOX and AOB mixed and distributed randomly. The ANAMMOX percentage was sbout 70%.(3) The form of ANAMMOX reaction rate equation was determined and the its parameters was obtained by nonlinear fitting method. A Haldane equation involving two substrates limiting and one substate inhibiting was chosen, and vmax, KS,NH4-N, KS,NO2-N and KI,N2-N were determined to be 1.59 g(N)·g(MLSS)-1·d-1,140.01 mg(N)·L-1,0.33 mg(N)·L-1 and 80007.60 mg(N)·L-1.(4) The effect of recirculation and mechanical stirring to the outer mass transfer of granular sludge was analyzed according to the result of ANAMMOX reaction rate equation and the standard diffusion-reaction model theory. It was found that fluidized factors affected much strongly to bigger grangule, and higher influent concentration led to higher enhancing rate to transfer coefficient under both of the recirculation and mechanical stirring condition. When the influent concentration was 500 mg(N)·L-1 with recirculation ratio of 500%, the enhancing rate to transfer coefficient under recirculation reached to a maximum of 4.5%, lower than that of 12.7% under mechanical stirring condition with the same influent concentration and a stiring speed of 40 rpm.(5) A effective diffusion coefficient of biofilm for ammonia and nitrite under recirculation condition were calculated to be 1.57×10-4 m2·d-1 and 1.48×10-4m2·d-1, while those under mechanical stirring condition were1.56×10-4 m2·d-1 and 1.47×10-4 m2·d-1.(6) Concerning about the convective mass transfer, a convection-diffussion-reaction coupled mass transfer equation was set up for the hybrid reactor with recirculation, and the substrate concentration along the reactor height was simulated and then compared to practical measurement results. The experiment data matched well with simulation results. The suitable recirculation ration was thought to be from 200% to 300% in this study.